3.7.3 Fan Systems

Baseline Building Fan System Summary

The baseline building fan system is summarized in this section. See [bookref id="hvac-mapping"] for the HVAC baseline building system mapping.

Total baseline building fan system power for the baseline building fan systems is given in [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] for ASHRAE Standard 90.1-2007 and [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2001"] for ASHRAE Standard 90.1-2001. In these tables, "cfms" is the supply fan air flow at peak design conditions. This is calculated for the baseline building with the sizing procedure described in [bookref id="calculation-process-for-tax-deductions-and-green-building-ratings"] and [bookref id="procedure-for-adjusting-equipment-hvac-sizes-in-the-baseline-building"]. This brake horsepower includes the supply fan, the return fan, and exhaust fans. Exhaust fans include kitchen hoods, toilets, fume hoods, and other miscellaneous fans that operate at design conditions.

[table title="Baseline Building Fan System – ASHRAE Standard 90.1-2007" id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"]

  System Types 1-2 System Types 3-4 System Types 5-8
Brake Horsepower (bhp) Not applicable 0.00094 x cfms + A 0.0013 x cfms + A
Fan Motor Efficiency (hm) Not applicable ASHRAE Standard 90.1-2007, Table 10.8 ASHRAE Standard 90.1-2007, Table 10.8
Fan Power (W) 0.3 x cfm (bhp x 746)/$\eta$m (bhp x 746)/$\eta$m
The term “A” for system types 3-8, is calculated based on equipment in the proposed design using the procedure in Table 6.5.3.1.1B of ASHRAE Standard 90.1-2007. This accounts for various additional fan pressure drops associated with special conditions.

[table title="Baseline Building Fan System – ASHRAE Standard 90.1-2001" id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2001"]

  Fan Size System Types 1-4 System Types 5-8
Nameplate Horsepower (nhp) < 20,000 cfm 0.0012 x cfms + Pfilter + Pprocess + Prelief 0.0017 x cfms + Pfilter + Pprocess + Prelief
  => 20,000 cfm  0.0011 x cfms + Pfilter + Pprocess + Prelief 0.0015 x cfms + Pfilter + Pprocess + Prelief
Fan Motor Efficiency (hm)   ASHRAE Standard 90.1-2001, Table 10.2 ASHRAE Standard 90.1-2001, Table 10.2
Brake Horsepower (bhp)   nhp x $\eta$m nhp x $\eta$m
Fan Power (W)   (bhp x 746)/ $\eta$m (bhp x 746)/ $\eta$m
The terms Pfilter, Pprocess, and Prelief account for additional pressure drop. These are based on features in the proposed design such as special filtration, process fans, and relief or return fans. See Section 6.3.3.1 of ASHRAE Standard 90.1-2001 and the associated User's Manual for details on how to calculate these adders.

When the proposed design has exhaust fans (toilets or kitchens), return fans, or fume hood exhaust systems, the baseline building has the same systems. The brake horsepower determined from [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] and [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2001"] is allocated to these baseline building fan systems proportionally to the allocation in the proposed design. The allocation of brake horsepower to the supply fan, the return and any exhaust or fume hood fans is based on the ratios described below.

Supply Fan Ratio
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust or return fans
Definition The ratio of supply fan brake horsepower in the proposed design to total fan system brake horsepower for the proposed design at design conditions
Units Unitless ratio
Input Restrictions Derived from other building descriptors
Baseline Rules Same as proposed design
Return Fan Ratio
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust or return fans
Definition The ratio of return fan brake horsepower in the proposed design to total fan system brake horsepower for the proposed design at design conditions
Units Unitless ratio
Input Restrictions Derived from other building descriptors
Baseline Rules Same as proposed design
Exhaust Fan Ratio
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust or return fans
Definition The ratio of exhaust fan brake horsepower in the proposed design to total fan system brake hp for the proposed design at design conditions. Exhaust fans include toilet exhaust, kitchen hoods and other miscellaneous exhaust. Fume hood exhaust is treated separately.
Units Unitless ratio
Input Restrictions Derived from other building descriptors. In the event that a common exhaust system serves thermal blocks that are served by different HVAC systems, the brake horsepower shall be divided in proportion to design cfm.
Baseline Rules Same as proposed design

Supply Fans

Fan System Modeling Method
Applicability All fan systems
Definition

Software commonly models fans in three ways.

  • Power-per-unit-flow. The simple method is for the user to enter the electric power per unit of flow (W/cfm). This method is commonly used for unitary equipment and other small fan systems.
  • Static pressure. A more detailed method is to model the fan as a system whereby the static pressure, fan efficiency, part-load curve, and motor efficiency are specified at design conditions.
  • Break horsepower. A third method is to specify brake horsepower at design conditions instead of fan efficiency and static pressure. This is a variation of the second method whereby brake horsepower is specified in lieu of static pressure and fan efficiency. The latter two methods are commonly used for VAV and other larger fan systems.
Units List: power-per-unit-flow, static pressure or brake horsepower
Input Restrictions As designed. The power-per-unit-flow method shall be used when no fan performance data is available for the proposed design cooling system, e.g. only EER or SEER are available.
Baseline Rules If the proposed design uses the power-per-unit-flow method, the baseline building shall also use this method, otherwise the baseline building shall use the brake horsepower method.
Supply Fan Design Air Rated Capacity
Applicability All fan systems
Definition The design air flow rate of the supply fan(s) at design conditions. This building descriptor sets the 100% point for the fan part-load curve.
Units cfm
Input Restrictions As designed. This input should be at least as great as the sum of the design air flow specified for each of the thermal blocks that are served by the fan system. For multiple deck systems, a separate entry should be made for each deck.
Baseline Rules The program shall automatically size the air flow at each thermal block to meet the loads. The design air flow rate calculation shall be based on a 20 degree temperature differential between supply air and the room air. The supply fan design air flow rate shall be the sum of the calculated design air flow for the thermal blocks served by the fan system.
Fan Control Method
Applicability All fan systems
Definition A description of how the supply (and return/relief) fan(s) are controlled. The options include:
  • Constant volume
  • Variable-flow, inlet or discharge dampers
  • Variable-flow, inlet guide vanes
  • Variable-flow, variable speed drive (VSD)
  • Variable-flow, variable pitch blades
  • Variable-flow, other
  • Two-speed
  • Constant volume, cycling (fan cycles with heating and cooling)
Units List (see above)
Input Restrictions As designed
Baseline Rules Applicable to variable air volume systems
Based on the prescribed system type. Refer to the HVAC System Map in [bookref id="hvac-mapping"].

[table title="Baseline Building Fan Control Method" id="baseline -bilding-fan-control-method"]

Baseline building System Fan Control Method
System 1 – PTAC Constant volume
System 2 – PTHP Constant volume
System 3 – PSZ-AC Constant volume
System 4 – PSZ-HP Constant volume
System 5 – Packaged VAV with Reheat Variable-flow, variable speed drive (VSD)
System 6 – Packaged VAV with PFP boxes Variable-flow, variable speed drive (VSD)
System 7 – VAV with Reheat Variable-flow, variable speed drive (VSD)
System 8 – VAV with PFP boxes Variable-flow, variable speed drive (VSD)
Supply Fan Brake Horsepower
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design shaft brake horsepower of the supply fan(s). This input does not need to be supplied if the Supply Fan kW is supplied.
Units Horsepower (hp)
Input Restrictions As designed. If this building descriptor is specified for the proposed design, then the Static Pressure and Fan Efficiency are not.
Baseline Rules See [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] for ASHRAE Standard 90.1-2007 and [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2001"] for ASHRAE Standard 90.1-2001. These tables give the baseline building fan system brake horsepower. The brake horsepower for the supply fan is this value times the Supply Fan Ratio (see above).
Supply Fan Static Pressure
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design static pressure for the supply fan. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the supply fan does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Supply Fan Efficiency
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The efficiency of the fan at design conditions
Units Unitless
Input Restrictions As designed. The supply fan efficiency does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Supply Motor Efficiency
Applicability All supply fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Baseline Rules From Table 10.8 of ASHRAE Standard 90.1-2007 or Table 10.2 of ASHRAE Standard 90.1-2001
Fan Position
Applicability All supply fans
Definition The position of the supply fan relative to the cooling coil. The configuration is either draw through (fan is downstream of the coil) or blow through (fan is upstream of the coil).
Units List (see above)
Input Restrictions As designed.
Baseline Rules Draw through
Motor Position
Applicability All supply fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed.
Baseline Rules In the air stream
Fan Part-Flow Power Curve
Applicability All variable flow fan systems
Definition A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow. The curve is typically represented as a quadratic equation with an absolute minimum power draw specified.
Units Unitless ratio
Input Restrictions

As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.

(6.7.3-1)

$Greater \;of$

$PLR = a + b \cdot FanRatio + c \cdot FanRatio^2 + d \cdot FanRatio^3$

$PLR = PowerMin $

where

PLR Ratio of fan power at part load conditions to full load fan power
PowerMin Minimum fan power
FanRatio Ratio of cfm at part-load to full-load cfm
a, b, c and d Constants from [bookref id="fan-curve-default-values"] below

[table title="Fan Curve Default Values" id="fan-curve-default-values"]

 

Fan Type - Control Type a b c d %PowerMin
AF or BI riding the curvea 0.1631 1.5901 -0.8817 0.1281 70%
AF or BI with inlet vanesa 0.9977 -0.659 0.9547 -0.2936 50%
FC riding the curvea 0.1224 0.612 0.5983 -0.3334 30%
FC with inlet vanesa 0.3038 -0.7608 2.2729 -0.8169 30%
Vane-axial with variable pitch bladesa 0.1639 -0.4016 1.9909 -0.7541 20%
Any fan with VSD (use for baseline building)b 0.0013 0.1470 0.9506 -0.0998 20%
VSD with static pressure resetc -0.0031 0.0991 1.0268 -0.1128 20%
Data Sources: 
a.     ECB Compliance Supplement, public review draft, Version 1.2, March 1996, but adjusted to be relatively consistent with the curve specified in the PRM.   
b.     The fan curve for VSD is specified in Table G3.1.3.15
c.     Advanced VAV System Design Guide, California Energy Commission, CEC Publication 500,-03-082 A-11, April 2005, but adjusted to be relatively consistent with the curve specified in the PRM..
Baseline Rules Not applicable for baseline building systems 1-4. The curve for VSD fans shall be used for baseline building systems 5-8 with no adjustment for static pressure setpoint reset.
Supply Fan kW
Applicability Fan systems that use the power-per-unit-flow method
Definition The supply fan power per unit of flow.
Units kW/cfm
Input Restrictions

As designed or specified in the manufacturers’ literature. For units with rated total cooling capacities less than 120,000 Btu/h, the user may default to a value calculated as follows:

(6.7.3-2)

$$ Fan_{kw} = 0.365 \times \frac{Q_{rated}}{30,000} $$

where

Fankw The supply fan power (kW)
Qrated The rated total cooling capacity (Btu/h)
Baseline Rules Applicable when the baseline building uses the power-per-unit-flow method. Fan power is determined using [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] for ASHRAE Standard 90.1-2007 and [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2001"] for ASHRAE Standard 90.1-2001. This power is then multiplied by the supply fan ratio.

Relief Fans

The baseline building has a return fan when the baseline building system is type 3 through 8 and the proposed design has a return fan.

Plenum Zone
Applicability Any system with return ducts or return air plenum
Definition A reference to the thermal block that serves as return plenum or where the return ducts are located
Units Text, unique
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. Same as the proposed design when the proposed design has a plenum, otherwise, the return air ducts are assumed to be located in the space.
Return Air Path
Applicability Any system with return ducts or return air plenum
Definition Describes the return path for air. This can be one of the following: ducted return; plenum return; or direct-to-unit.
Units List (see above)
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. For baseline building systems 1 and 2, the return air path shall be direct-to-unit. For baseline building systems 3 through 8 and when the proposed design is direct-to-unit, the baseline building shall be ducted return, otherwise the baseline building return air path shall be same as proposed design.
Return/Relief Air Rated Capacity
Applicability All systems with a return or relief fan
Definition The design air flow fan capacity of the return or relief fan(s). This sets the 100% fan flow point for the part-load curve (see below).
Units cfm
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. The return fan air Rated Capacity shall be equal to the baseline building supply fan capacity less exhaust air flow.
Return/Relief Fan Brake Horsepower
Applicability Any system with return or relief fans that uses the brake horsepower method
Definition The design shaft brake horsepower of the return/relief fan(s)
Units Brake horsepower (bhp)
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. The bhp of the return fan shall be the fan system brake horsepower (see [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] and [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2001"]) times the return fan ratio. In other words, brake horsepower is allocated in proportion to the proposed design.
Return/Relief Design Static Pressure
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for return fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the return fan does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Return/Relief Fan Efficiency
Applicability Any system with return or relief fans that uses the static pressure method
Definition The efficiency of the fan at design conditions
Units Unitless
Input Restrictions As designed. The return/relief fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Return/Relief Motor Efficiency
Applicability All return fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Baseline Rules From Table 10.8 of ASHRAE Standard 90.1-2007 or Table 10.2 of ASHRAE Standard 90.1-2001
Motor Position
Applicability All return fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed.
Baseline Rules In the air stream
Fan Part-Flow Power Curve
Applicability All return fans for variable flow fan systems.
Definition A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow.
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.
Baseline Rules Not applicable for baseline building systems 1-4. The curve for VSD fans shall be used for baseline building systems 5-8 that have a return/relief fan.
Return/Relief Fan kW
Applicability Any system with a return fan
Definition The supply fan power per unit of flow
Units kW/cfm
Input Restrictions As specified in the manufacturers’ literature
Baseline Rules Applicable when the baseline building uses the power-per-unit-flow method. Fan power is determined using [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] for ASHRAE Standard 90.1-2007 and [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2001"] for ASHRAE Standard 90.1-2001. This power is then multiplied by the return fan ratio.

Exhaust Fan Systems

Exhaust fans include toilet exhaust, kitchen exhaust, as well as fume hoods in laboratories and other spaces. Some systems typically operate at constant flow, while flow varies for other systems depending on, for instance, the position of the sash for fume hoods. Exhaust fan flow is specified and scheduled for each thermal block. An exhaust fan system may serve multiple thermal blocks. The baseline building has exhaust fans when the proposed design has exhaust fans. The exhaust air flow is the same for the baseline building and the proposed design.

Exhaust Fan Name
Applicability All exhaust systems serving multiple thermal blocks
Definition A unique descriptor for each exhaust fan. This should be keyed to the construction documents, if possible, to facilitate plan checking. Exhaust rates and schedules at the thermal block level refer to this name.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans.
Baseline Rules The baseline building will have an exhaust system that corresponds to the proposed design. The name can be identical to that used for the proposed design or some other appropriate name may be used.
Exhaust Fan System Modeling Method
Applicability All exhaust fan systems
Definition Software commonly models fans in three ways. See definition for supply system modeling method.
Units List: power-per-unit-flow, static pressure or brake horsepower
Input Restrictions As designed
Baseline Rules If the proposed design uses the power-per-unit-flow method, the baseline building shall also use this method, otherwise the baseline building shall use the brake horsepower method.
Exhaust Fan Rated Capacity
Applicability All exhaust systems
Definition The rated design air flow rate of the exhaust fan system. This building descriptor defines the 100% flow case for the part-flow curve. Actual air flow is the sum of the flow specified for each thermal block, as modified by the schedule for each thermal block.
Units cfm
Input Restrictions As designed
Baseline Rules Same as proposed design
Fan Control Method
Applicability All exhaust fan systems
Definition A description of how the exhaust fan(s) are controlled. The options include:
  • Constant volume
  • Two-speed
  • Variable-flow, inlet or discharge dampers
  • Variable-flow, inlet guide vanes
  • Variable-flow, variable speed drive (VSD)
  • Variable-flow, variable pitch blades
Units List (see above)
Input Restrictions As designed, however, when exhaust fan flow at the thermal block level is varied through a schedule, one of the variable-flow options shall be specified.
Baseline Rules The baseline building exhaust fan control shall generally be the same as the proposed design. For laboratories that have exhaust flow of 5,000 cfm or more, the baseline building exhaust flow shall vary in response to scheduled fume hood exhaust and lab zone airflow schedules. Fume hood exhaust flow control shall be the same as design, and general exhaust (relief) shall be VSD.
Exhaust Fan Schedule
Applicability All exhaust fan systems
Definition A schedule that indicates when the exhaust fan system is available for operation. Exhaust fan flow is specified at the thermal block level.
Units Data structure: schedule, on/off
Input Restrictions The exhaust fan system shall be available during all periods when one or more thermal blocks served by the system are scheduling exhaust.
Baseline Rules Same as the proposed design
Exhaust Fan Brake Horsepower
Applicability All exhaust fan systems
Definition The design shaft brake horsepower of the exhaust fan(s).
Units Brake horsepower (bhp)
Input Restrictions As designed
Baseline Rules The bhp for the baseline building is the total system fan horsepower from [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] or [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2001"] times the exhaust fan ratio.
Exhaust Fan Design Static Pressure
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for exhaust fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the exhaust fan does not need to be specified if the exhaust fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When static pressure and fan efficiency are entered for the proposed design, the baseline building shall use brake horsepower.
Exhaust Fan Efficiency
Applicability Any exhaust fan system that uses the static pressure method
Definition The efficiency of the exhaust fan at rated capacity
Units Unitless
Input Restrictions As designed. The exhaust fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When static pressure and fan efficiency are entered for the proposed design, the baseline building shall use brake horsepower.
Exhaust Fan Motor Efficiency
Applicability All exhaust fan systems
Definition The full-load efficiency of the motor serving the exhaust fan
Units Unitless
Input Restrictions As designed
Baseline Rules From Table 10.8 of ASHRAE Standard 90.1-2007 or Table 10.2 of ASHRAE Standard 90.1-2001
Fan Part-Flow Power Curve
Applicability All variable flow exhaust fan systems
Definition A part-load power curve which represents the ratio full-load power draw of the exhaust fan as a function of the ratio full-load air flow.
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.
Baseline Rules The baseline building fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.
Exhaust Fan KW
Applicability All exhaust systems
Definition The fan power of the exhaust fan per unit of flow. This building descriptor is applicable only with the power-per-unit-flow method.
Units W/cfm
Input Restrictions As designed.
Baseline Rules The fan system power from [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] or [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2001"]
90.1-2007

Baseline Building Fan System Summary

The baseline building fan system is summarized in this section. See [bookref id="hvac-mapping"] for the HVAC baseline building system mapping.

Total baseline building fan system power for the baseline building fan systems is given in [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"]. In this table, "cfms" is the supply fan air flow at peak design conditions. This is calculated for the baseline building with the sizing procedure described in [bookref id="calculation-process-for-tax-deductions-and-green-building-ratings"] and [bookref id="procedure-for-adjusting-equipment-hvac-sizes-in-the-baseline-building"]. This brake horsepower includes the supply fan, the return fan, and exhaust fans. Exhaust fans include kitchen hoods, toilets, fume hoods, and other miscellaneous fans that operate at design conditions.

[table title="Baseline Building Fan System – ASHRAE Standard 90.1-2007" id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"]

  System Types 1-2 System Types 3-4 System Types 5-8
Brake Horsepower (bhp) Not applicable 0.00094 x cfms + A 0.0013 x cfms + A
Fan Motor Efficiency (hm) Not applicable ASHRAE Standard 90.1-2007, Table 10.8 ASHRAE Standard 90.1-2007, Table 10.8
Fan Power (W) 0.3 x cfm (bhp x 746)/$\eta$m (bhp x 746)/$\eta$m
The term “A” for system types 3-8, is calculated based on equipment in the proposed design using the procedure in Table 6.5.3.1.1B of ASHRAE Standard 90.1-2007. This accounts for various additional fan pressure drops associated with special conditions.

When the proposed design has exhaust fans (toilets or kitchens), return fans, or fume hood exhaust systems, the baseline building has the same systems. The brake horsepower determined from [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] is allocated to these baseline building fan systems proportionally to the allocation in the proposed design. The allocation of brake horsepower to the supply fan, the return and any exhaust or fume hood fans is based on the ratios described below.

Supply Fan Ratio
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust or return fans
Definition The ratio of supply fan brake horsepower in the proposed design to total fan system brake horsepower for the proposed design at design conditions
Units Unitless ratio
Input Restrictions Derived from other building descriptors
Baseline Rules Same as proposed design
Return Fan Ratio
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust or return fans
Definition The ratio of return fan brake horsepower in the proposed design to total fan system brake horsepower for the proposed design at design conditions
Units Unitless ratio
Input Restrictions Derived from other building descriptors
Baseline Rules Same as proposed design
Exhaust Fan Ratio
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust or return fans
Definition The ratio of exhaust fan brake horsepower in the proposed design to total fan system brake hp for the proposed design at design conditions. Exhaust fans include toilet exhaust, kitchen hoods and other miscellaneous exhaust. Fume hood exhaust is treated separately.
Units Unitless ratio
Input Restrictions Derived from other building descriptors. In the event that a common exhaust system serves thermal blocks that are served by different HVAC systems, the brake horsepower shall be divided in proportion to design cfm.
Baseline Rules Same as proposed design

Supply Fans

Fan System Modeling Method
Applicability All fan systems
Definition

Software commonly models fans in three ways.

  • Power-per-unit-flow. The simple method is for the user to enter the electric power per unit of flow (W/cfm). This method is commonly used for unitary equipment and other small fan systems.
  • Static pressure. A more detailed method is to model the fan as a system whereby the static pressure, fan efficiency, part-load curve, and motor efficiency are specified at design conditions.
  • Break horsepower. A third method is to specify brake horsepower at design conditions instead of fan efficiency and static pressure. This is a variation of the second method whereby brake horsepower is specified in lieu of static pressure and fan efficiency. The latter two methods are commonly used for VAV and other larger fan systems.
Units List: power-per-unit-flow, static pressure or brake horsepower
Input Restrictions As designed. The power-per-unit-flow method shall be used when no fan performance data is available for the proposed design cooling system, e.g. only EER or SEER are available.
Baseline Rules If the proposed design uses the power-per-unit-flow method, the baseline building shall also use this method, otherwise the baseline building shall use the brake horsepower method.
Supply Fan Design Air Rated Capacity
Applicability All fan systems
Definition The design air flow rate of the supply fan(s) at design conditions. This building descriptor sets the 100% point for the fan part-load curve.
Units cfm
Input Restrictions As designed. This input should be at least as great as the sum of the design air flow specified for each of the thermal blocks that are served by the fan system. For multiple deck systems, a separate entry should be made for each deck.
Baseline Rules The program shall automatically size the air flow at each thermal block to meet the loads. The design air flow rate calculation shall be based on a 20 degree temperature differential between supply air and the room air. The supply fan design air flow rate shall be the sum of the calculated design air flow for the thermal blocks served by the fan system.
Fan Control Method
Applicability All fan systems
Definition A description of how the supply (and return/relief) fan(s) are controlled. The options include:
  • Constant volume
  • Variable-flow, inlet or discharge dampers
  • Variable-flow, inlet guide vanes
  • Variable-flow, variable speed drive (VSD)
  • Variable-flow, variable pitch blades
  • Variable-flow, other
  • Two-speed
  • Constant volume, cycling (fan cycles with heating and cooling)
Units List (see above)
Input Restrictions As designed
Baseline Rules Applicable to variable air volume systems
Based on the prescribed system type. Refer to the HVAC System Map in [bookref id="hvac-mapping"].

[table title="Baseline Building Fan Control Method" id="baseline -bilding-fan-control-method"]

Baseline building System Fan Control Method
System 1 – PTAC Constant volume
System 2 – PTHP Constant volume
System 3 – PSZ-AC Constant volume
System 4 – PSZ-HP Constant volume
System 5 – Packaged VAV with Reheat Variable-flow, variable speed drive (VSD)
System 6 – Packaged VAV with PFP boxes Variable-flow, variable speed drive (VSD)
System 7 – VAV with Reheat Variable-flow, variable speed drive (VSD)
System 8 – VAV with PFP boxes Variable-flow, variable speed drive (VSD)
Supply Fan Brake Horsepower
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design shaft brake horsepower of the supply fan(s). This input does not need to be supplied if the Supply Fan kW is supplied.
Units Horsepower (hp)
Input Restrictions As designed. If this building descriptor is specified for the proposed design, then the Static Pressure and Fan Efficiency are not.
Baseline Rules See [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] for ASHRAE Standard 90.1-2007. These tables give the baseline building fan system brake horsepower. The brake horsepower for the supply fan is this value times the Supply Fan Ratio (see above).
Supply Fan Static Pressure
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design static pressure for the supply fan. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the supply fan does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Supply Fan Efficiency
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The efficiency of the fan at design conditions
Units Unitless
Input Restrictions As designed. The supply fan efficiency does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Supply Motor Efficiency
Applicability All supply fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Baseline Rules From Table 10.8 of ASHRAE Standard 90.1-2007
Fan Position
Applicability All supply fans
Definition The position of the supply fan relative to the cooling coil. The configuration is either draw through (fan is downstream of the coil) or blow through (fan is upstream of the coil).
Units List (see above)
Input Restrictions As designed.
Baseline Rules Draw through
Motor Position
Applicability All supply fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed.
Baseline Rules In the air stream
Fan Part-Flow Power Curve
Applicability All variable flow fan systems
Definition A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow. The curve is typically represented as a quadratic equation with an absolute minimum power draw specified.
Units Unitless ratio
Input Restrictions

As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.

(6.7.3-1)

$Greater \;of$

$PLR = a + b \cdot FanRatio + c \cdot FanRatio^2 + d \cdot FanRatio^3$

$PLR = PowerMin $

where

PLR Ratio of fan power at part load conditions to full load fan power
PowerMin Minimum fan power
FanRatio Ratio of cfm at part-load to full-load cfm
a, b, c and d Constants from [bookref id="fan-curve-default-values"] below

[table title="Fan Curve Default Values" id="fan-curve-default-values"]

 

Fan Type - Control Type a b c d %PowerMin
AF or BI riding the curvea 0.1631 1.5901 -0.8817 0.1281 70%
AF or BI with inlet vanesa 0.9977 -0.659 0.9547 -0.2936 50%
FC riding the curvea 0.1224 0.612 0.5983 -0.3334 30%
FC with inlet vanesa 0.3038 -0.7608 2.2729 -0.8169 30%
Vane-axial with variable pitch bladesa 0.1639 -0.4016 1.9909 -0.7541 20%
Any fan with VSD (use for baseline building)b 0.0013 0.1470 0.9506 -0.0998 20%
VSD with static pressure resetc -0.0031 0.0991 1.0268 -0.1128 20%
Data Sources: 
a.     ECB Compliance Supplement, public review draft, Version 1.2, March 1996, but adjusted to be relatively consistent with the curve specified in the PRM.   
b.     The fan curve for VSD is specified in Table G3.1.3.15
c.     Advanced VAV System Design Guide, California Energy Commission, CEC Publication 500,-03-082 A-11, April 2005, but adjusted to be relatively consistent with the curve specified in the PRM..
Baseline Rules Not applicable for baseline building systems 1-4. The curve for VSD fans shall be used for baseline building systems 5-8 with no adjustment for static pressure setpoint reset.
Supply Fan kW
Applicability Fan systems that use the power-per-unit-flow method
Definition The supply fan power per unit of flow.
Units kW/cfm
Input Restrictions

As designed or specified in the manufacturers’ literature. For units with rated total cooling capacities less than 120,000 Btu/h, the user may default to a value calculated as follows:

(6.7.3-2)

$$ Fan_{kw} = 0.365 \times \frac{Q_{rated}}{30,000} $$

where

Fankw The supply fan power (kW)
Qrated The rated total cooling capacity (Btu/h)
Baseline Rules Applicable when the baseline building uses the power-per-unit-flow method. Fan power is determined using [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] for ASHRAE Standard 90.1-2007. This power is then multiplied by the supply fan ratio.

Relief Fans

The baseline building has a return fan when the baseline building system is type 3 through 8 and the proposed design has a return fan.

Plenum Zone
Applicability Any system with return ducts or return air plenum
Definition A reference to the thermal block that serves as return plenum or where the return ducts are located
Units Text, unique
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. Same as the proposed design when the proposed design has a plenum, otherwise, the return air ducts are assumed to be located in the space.
Return Air Path
Applicability Any system with return ducts or return air plenum
Definition Describes the return path for air. This can be one of the following: ducted return; plenum return; or direct-to-unit.
Units List (see above)
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. For baseline building systems 1 and 2, the return air path shall be direct-to-unit. For baseline building systems 3 through 8 and when the proposed design is direct-to-unit, the baseline building shall be ducted return, otherwise the baseline building return air path shall be same as proposed design.
Return/Relief Air Rated Capacity
Applicability All systems with a return or relief fan
Definition The design air flow fan capacity of the return or relief fan(s). This sets the 100% fan flow point for the part-load curve (see below).
Units cfm
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. The return fan air Rated Capacity shall be equal to the baseline building supply fan capacity less exhaust air flow.
Return/Relief Fan Brake Horsepower
Applicability Any system with return or relief fans that uses the brake horsepower method
Definition The design shaft brake horsepower of the return/relief fan(s)
Units Brake horsepower (bhp)
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. The bhp of the return fan shall be the fan system brake horsepower (see [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"]) times the return fan ratio. In other words, brake horsepower is allocated in proportion to the proposed design.
Return/Relief Design Static Pressure
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for return fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the return fan does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Return/Relief Fan Efficiency
Applicability Any system with return or relief fans that uses the static pressure method
Definition The efficiency of the fan at design conditions
Units Unitless
Input Restrictions As designed. The return/relief fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Return/Relief Motor Efficiency
Applicability All return fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Baseline Rules From Table 10.8 of ASHRAE Standard 90.1-2007
Motor Position
Applicability All return fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed.
Baseline Rules In the air stream
Fan Part-Flow Power Curve
Applicability All return fans for variable flow fan systems.
Definition A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow.
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.
Baseline Rules Not applicable for baseline building systems 1-4. The curve for VSD fans shall be used for baseline building systems 5-8 that have a return/relief fan.
Return/Relief Fan kW
Applicability Any system with a return fan
Definition The supply fan power per unit of flow
Units kW/cfm
Input Restrictions As specified in the manufacturers’ literature
Baseline Rules Applicable when the baseline building uses the power-per-unit-flow method. Fan power is determined using [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] for ASHRAE Standard 90.1-2007. This power is then multiplied by the return fan ratio.

Exhaust Fan Systems

Exhaust fans include toilet exhaust, kitchen exhaust, as well as fume hoods in laboratories and other spaces. Some systems typically operate at constant flow, while flow varies for other systems depending on, for instance, the position of the sash for fume hoods. Exhaust fan flow is specified and scheduled for each thermal block. An exhaust fan system may serve multiple thermal blocks. The baseline building has exhaust fans when the proposed design has exhaust fans. The exhaust air flow is the same for the baseline building and the proposed design.

Exhaust Fan Name
Applicability All exhaust systems serving multiple thermal blocks
Definition A unique descriptor for each exhaust fan. This should be keyed to the construction documents, if possible, to facilitate plan checking. Exhaust rates and schedules at the thermal block level refer to this name.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans.
Baseline Rules The baseline building will have an exhaust system that corresponds to the proposed design. The name can be identical to that used for the proposed design or some other appropriate name may be used.
Exhaust Fan System Modeling Method
Applicability All exhaust fan systems
Definition Software commonly models fans in three ways. See definition for supply system modeling method.
Units List: power-per-unit-flow, static pressure or brake horsepower
Input Restrictions As designed
Baseline Rules If the proposed design uses the power-per-unit-flow method, the baseline building shall also use this method, otherwise the baseline building shall use the brake horsepower method.
Exhaust Fan Rated Capacity
Applicability All exhaust systems
Definition The rated design air flow rate of the exhaust fan system. This building descriptor defines the 100% flow case for the part-flow curve. Actual air flow is the sum of the flow specified for each thermal block, as modified by the schedule for each thermal block.
Units cfm
Input Restrictions As designed
Baseline Rules Same as proposed design
Fan Control Method
Applicability All exhaust fan systems
Definition A description of how the exhaust fan(s) are controlled. The options include:
  • Constant volume
  • Two-speed
  • Variable-flow, inlet or discharge dampers
  • Variable-flow, inlet guide vanes
  • Variable-flow, variable speed drive (VSD)
  • Variable-flow, variable pitch blades
Units List (see above)
Input Restrictions As designed, however, when exhaust fan flow at the thermal block level is varied through a schedule, one of the variable-flow options shall be specified.
Baseline Rules The baseline building exhaust fan control shall generally be the same as the proposed design. For laboratories that have exhaust flow of 5,000 cfm or more, the baseline building exhaust flow shall vary in response to scheduled fume hood exhaust and lab zone airflow schedules. Fume hood exhaust flow control shall be the same as design, and general exhaust (relief) shall be VSD.
Exhaust Fan Schedule
Applicability All exhaust fan systems
Definition A schedule that indicates when the exhaust fan system is available for operation. Exhaust fan flow is specified at the thermal block level.
Units Data structure: schedule, on/off
Input Restrictions The exhaust fan system shall be available during all periods when one or more thermal blocks served by the system are scheduling exhaust.
Baseline Rules Same as the proposed design
Exhaust Fan Brake Horsepower
Applicability All exhaust fan systems
Definition The design shaft brake horsepower of the exhaust fan(s).
Units Brake horsepower (bhp)
Input Restrictions As designed
Baseline Rules The bhp for the baseline building is the total system fan horsepower from [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"] times the exhaust fan ratio.
Exhaust Fan Design Static Pressure
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for exhaust fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the exhaust fan does not need to be specified if the exhaust fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When static pressure and fan efficiency are entered for the proposed design, the baseline building shall use brake horsepower.
Exhaust Fan Efficiency
Applicability Any exhaust fan system that uses the static pressure method
Definition The efficiency of the exhaust fan at rated capacity
Units Unitless
Input Restrictions As designed. The exhaust fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When static pressure and fan efficiency are entered for the proposed design, the baseline building shall use brake horsepower.
Exhaust Fan Motor Efficiency
Applicability All exhaust fan systems
Definition The full-load efficiency of the motor serving the exhaust fan
Units Unitless
Input Restrictions As designed
Baseline Rules From Table 10.8 of ASHRAE Standard 90.1-2007
Fan Part-Flow Power Curve
Applicability All variable flow exhaust fan systems
Definition A part-load power curve which represents the ratio full-load power draw of the exhaust fan as a function of the ratio full-load air flow.
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.
Baseline Rules The baseline building fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.
Exhaust Fan KW
Applicability All exhaust systems
Definition The fan power of the exhaust fan per unit of flow. This building descriptor is applicable only with the power-per-unit-flow method.
Units W/cfm
Input Restrictions As designed.
Baseline Rules The fan system power from [bookref id="baseline-building-fan-system-–-ASHRAE-standard-90.1-2007"]
90.1-2010

Baseline Building Fan System Summary

The baseline building fan system is summarized in this section. See Figure 6.1.2-1 for the HVAC baseline building system mapping.

Total baseline building fan system power for the baseline building fan systems is given in Table 6.7.3-1. In this table, "cfms" is the supply fan air flow at peak design conditions. This is calculated for the baseline building with the sizing procedure described in Figure 2.4-1. This brake horsepower includes the supply fan, the return fan, and exhaust fans. Exhaust fans include kitchen hoods, toilets, fume hoods, and other miscellaneous fans that operate at design conditions.

Table 6.7.3-1: Baseline Building Fan System – ASHRAE Standard 90.1 2010

  System Types 1-2 System Types 3-4 System Types 5-8 System Types 9-10
Brake Horsepower (bhp) Not applicable 0.00094 x cfms + A 0.0013 x cfms + A Not Applicable
Fan Motor Efficiency (hm) Not applicable ASHRAE Standard 90.1-2007, Table 10.8 ASHRAE Standard 90.1-2007, Table 10.8 Not Applicable
Fan Power (W) 0.3 x cfm (bhp x 746)/$\eta$m (bhp x 746)/$\eta$m 0.3 x cfms OR
0.054 x CFMnmc
The term “A” for system types 3-8, is calculated based on equipment in the proposed design using the procedure in Table 6.5.3.1.1B of ASHRAE Standard 90.1-2010. This accounts for various additional fan pressure drops associated with special conditions. *CFMnmc is the baseline non-mechanical cooling fan airflow in cfm.  This alternate equation is only used if there is a non-mechanical cooling system in place.

When the proposed design has exhaust fans (toilets or kitchens), return fans, or fume hood exhaust systems, the baseline building has the same systems. The brake horsepower determined from Table 6.7.3-1 is allocated to these baseline building fan systems proportionally to the allocation in the proposed design. The allocation of brake horsepower to the supply fan, the return and any exhaust or fume hood fans is based on the ratios described below.

Supply Fan Ratio
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust or return fans
Definition The ratio of supply fan brake horsepower in the proposed design to total fan system brake horsepower for the proposed design at design conditions
Units Unitless ratio
Input Restrictions Derived from other building descriptors
Baseline Rules Same as proposed design
Return Fan Ratio
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust or return fans
Definition The ratio of return fan brake horsepower in the proposed design to total fan system brake horsepower for the proposed design at design conditions
Units Unitless ratio
Input Restrictions Derived from other building descriptors
Baseline Rules Same as proposed design
Exhaust Fan Ratio
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust or return fans
Definition The ratio of exhaust fan brake horsepower in the proposed design to total fan system brake hp for the proposed design at design conditions. Exhaust fans include toilet exhaust, kitchen hoods and other miscellaneous exhaust. Fume hood exhaust is treated separately.
Units Unitless ratio
Input Restrictions Derived from other building descriptors. In the event that a common exhaust system serves thermal blocks that are served by different HVAC systems, the brake horsepower shall be divided in proportion to design cfm.
Baseline Rules Same as proposed design

Supply Fans

Fan System Modeling Method
Applicability All fan systems
Definition

Software commonly models fans in three ways.

  • Power-per-unit-flow. The simple method is for the user to enter the electric power per unit of flow (W/cfm). This method is commonly used for unitary equipment and other small fan systems.
  • Static pressure. A more detailed method is to model the fan as a system whereby the static pressure, fan efficiency, part-load curve, and motor efficiency are specified at design conditions.
  • Break horsepower. A third method is to specify brake horsepower at design conditions instead of fan efficiency and static pressure. This is a variation of the second method whereby brake horsepower is specified in lieu of static pressure and fan efficiency. The latter two methods are commonly used for VAV and other larger fan systems.
Units List: power-per-unit-flow, static pressure or brake horsepower
Input Restrictions As designed. The power-per-unit-flow method shall be used when no fan performance data is available for the proposed design cooling system, e.g. only EER or SEER are available.
Baseline Rules If the proposed design uses the power-per-unit-flow method, the baseline building shall also use this method, otherwise the baseline building shall use the brake horsepower method.
Supply Fan Design Air Rated Capacity
Applicability All fan systems
Definition The design air flow rate of the supply fan(s) at design conditions. This building descriptor sets the 100% point for the fan part-load curve.
Units cfm
Input Restrictions As designed. This input should be at least as great as the sum of the design air flow specified for each of the thermal blocks that are served by the fan system. For multiple deck systems, a separate entry should be made for each deck.
Baseline Rules

The program shall automatically size the air flow at each thermal block to meet the loads. The design air flow rate calculation shall be based on a 20 degree temperature differential between supply air and the room air. The supply fan design air flow rate shall be the sum of the calculated design air flow for the thermal blocks served by the fan system.


For laboratory spaces, the design air flow rate calculation shall be based on a 17 degree temperature differential rather than 20.  For baseline systems 9 and 10, the design air flow rate calculation shall be based on a supply air temperature setpoint of 105 degrees.

Fan Control Method
Applicability All fan systems
Definition A description of how the supply (and return/relief) fan(s) are controlled. The options include:
  • Constant volume
  • Variable-flow, inlet or discharge dampers
  • Variable-flow, inlet guide vanes
  • Variable-flow, variable speed drive (VSD)
  • Variable-flow, variable pitch blades
  • Variable-flow, other
  • Two-speed
  • Constant volume, cycling (fan cycles with heating and cooling)
Units List (see above)
Input Restrictions As designed
Baseline Rules Applicable to variable air volume systems
Based on the prescribed system type. Refer to the HVAC System Map in Figure 6.1.2-1.

Table 6.7.3-2: Baseline Building Fan Control Method

Baseline building System Fan Control Method
System 1 – PTAC Constant volume
System 2 – PTHP Constant volume
System 3 – PSZ-AC Constant volume
System 4 – PSZ-HP Constant volume
System 5 – Packaged VAV with Reheat Variable-flow, variable speed drive (VSD)
System 6 – Packaged VAV with PFP boxes Variable-flow, variable speed drive (VSD)
System 7 – VAV with Reheat Variable-flow, variable speed drive (VSD)
System 8 – VAV with PFP boxes Variable-flow, variable speed drive (VSD)
System 9 – Heating and Ventilation Constant Volume
System 10 – Heating and Ventilation Constant Volume
*Effective 1/1/2012, all air-conditioning equipment and air-handling units with dx cooling and a cooling capacity greater than or equal to 110,000 Btu/h that serve single zones shall have supply fans controlled by two-speed motors or variable speed drives.  At cooling demands less than or equal to 50% , the supply fan controls shall reduce the airflow to no greater than the larger of the following: 1)1/2 of the full fan speed or 2)the minimum outdoor air.
Supply Fan Brake Horsepower
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design shaft brake horsepower of the supply fan(s). This input does not need to be supplied if the Supply Fan kW is supplied.
Units Horsepower (hp)
Input Restrictions As designed. If this building descriptor is specified for the proposed design, then the Static Pressure and Fan Efficiency are not.
Baseline Rules See Table 6.7.2-1 for ASHRAE Standard 90.1-2007. These tables give the baseline building fan system brake horsepower. The brake horsepower for the supply fan is this value times the Supply Fan Ratio (see above).
Supply Fan Static Pressure
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design static pressure for the supply fan. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the supply fan does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Supply Fan Efficiency
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The efficiency of the fan at design conditions
Units Unitless
Input Restrictions As designed. The supply fan efficiency does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Supply Motor Efficiency
Applicability All supply fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Baseline Rules From Table 10.8 of ASHRAE Standard 90.1-2007
Fan Position
Applicability All supply fans
Definition The position of the supply fan relative to the cooling coil. The configuration is either draw through (fan is downstream of the coil) or blow through (fan is upstream of the coil).
Units List (see above)
Input Restrictions As designed.
Baseline Rules Draw through
Motor Position
Applicability All supply fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed.
Baseline Rules In the air stream
Fan Part-Flow Power Curve
Applicability All variable flow fan systems
Definition A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow. The curve is typically represented as a quadratic equation with an absolute minimum power draw specified.
Units Unitless ratio
Input Restrictions

As designed. The default fan curve shall be selected from Equation (6.7.3-1) and Table 6.7.3-3 for the type of fan specified in the proposed design.

(6.7.3-1)

$Greater \;of$

$PLR = a + b \cdot FanRatio + c \cdot FanRatio^2 + d \cdot FanRatio^3$

$PLR = PowerMin $

where

PLR Ratio of fan power at part load conditions to full load fan power
PowerMin Minimum fan power
FanRatio Ratio of cfm at part-load to full-load cfm
a, b, c and d Constants from Table 7.7.3-3 below

Table 6.7.3-3:Fan Curve Default Values

 

Fan Type - Control Type a b c d %PowerMin
AF or BI riding the curvea 0.1631 1.5901 -0.8817 0.1281 70%
AF or BI with inlet vanesa 0.9977 -0.659 0.9547 -0.2936 50%
FC riding the curvea 0.1224 0.612 0.5983 -0.3334 30%
FC with inlet vanesa 0.3038 -0.7608 2.2729 -0.8169 30%
Vane-axial with variable pitch bladesa 0.1639 -0.4016 1.9909 -0.7541 20%
Any fan with VSD (use for baseline building)b 0.0013 0.1470 0.9506 -0.0998 20%
VSD with static pressure resetc -0.0031 0.0991 1.0268 -0.1128 20%
Data Sources: 
a.     ECB Compliance Supplement, public review draft, Version 1.2, March 1996, but adjusted to be relatively consistent with the curve specified in the PRM.   
b.     The fan curve for VSD is specified in Table G3.1.3.15
c.     Advanced VAV System Design Guide, California Energy Commission, CEC Publication 500,-03-082 A-11, April 2005, but adjusted to be relatively consistent with the curve specified in the PRM..
Baseline Rules Not applicable for baseline building systems 1-4. The curve for VSD fans shall be used for baseline building systems 5-8 with no adjustment for static pressure setpoint reset.
Supply Fan kW
Applicability Fan systems that use the power-per-unit-flow method
Definition The supply fan power per unit of flow.
Units kW/cfm
Input Restrictions

As designed or specified in the manufacturers’ literature. For units with rated total cooling capacities less than 120,000 Btu/h, the user may default to a value calculated as follows:

(6.7.3-2)

$$ Fan_{kw} = 0.365 \times \frac{Q_{rated}}{30,000} $$

where

Fankw The supply fan power (kW)
Qrated The rated total cooling capacity (Btu/h)
Baseline Rules Applicable when the baseline building uses the power-per-unit-flow method. Fan power is determined using Table 6.7.3-1 for ASHRAE Standard 90.1-2007. This power is then multiplied by the supply fan ratio.

Relief Fans

The baseline building has a return fan when the baseline building system is type 3 through 8 and the proposed design has a return fan.

Plenum Zone
Applicability Any system with return ducts or return air plenum
Definition A reference to the thermal block that serves as return plenum or where the return ducts are located
Units Text, unique
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. Same as the proposed design when the proposed design has a plenum, otherwise, the return air ducts are assumed to be located in the space.
Return Air Path
Applicability Any system with return ducts or return air plenum
Definition Describes the return path for air. This can be one of the following: ducted return; plenum return; or direct-to-unit.
Units List (see above)
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. For baseline building systems 1 and 2, the return air path shall be direct-to-unit. For baseline building systems 3 through 8 and when the proposed design is direct-to-unit, the baseline building shall be ducted return, otherwise the baseline building return air path shall be same as proposed design.
Return/Relief Air Rated Capacity
Applicability All systems with a return or relief fan
Definition The design air flow fan capacity of the return or relief fan(s). This sets the 100% fan flow point for the part-load curve (see below).
Units cfm
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. The return fan air Rated Capacity shall be equal to the baseline building supply fan capacity less exhaust air flow.
Return/Relief Fan Brake Horsepower
Applicability Any system with return or relief fans that uses the brake horsepower method
Definition The design shaft brake horsepower of the return/relief fan(s)
Units Brake horsepower (bhp)
Input Restrictions As designed
Baseline Rules Applicable when the baseline building has a return fan. The bhp of the return fan shall be the fan system brake horsepower (see Table 6.7.3-1) times the return fan ratio. In other words, brake horsepower is allocated in proportion to the proposed design.
Return/Relief Design Static Pressure
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for return fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the return fan does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Return/Relief Fan Efficiency
Applicability Any system with return or relief fans that uses the static pressure method
Definition The efficiency of the fan at design conditions
Units Unitless
Input Restrictions As designed. The return/relief fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When Static Pressure and Fan Efficiency are entered for the proposed design, the baseline building shall use Brake Horsepower.
Return/Relief Motor Efficiency
Applicability All return fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Baseline Rules From Table 10.8 of ASHRAE Standard 90.1-2007
Motor Position
Applicability All return fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed.
Baseline Rules In the air stream
Fan Part-Flow Power Curve
Applicability All return fans for variable flow fan systems.
Definition A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow.
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (6.7.3-1) and Table 6.7.3-3 for the type of fan specified in the proposed design.
Baseline Rules Not applicable for baseline building systems 1-4. The curve for VSD fans shall be used for baseline building systems 5-8 that have a return/relief fan.
Return/Relief Fan kW
Applicability Any system with a return fan
Definition The supply fan power per unit of flow
Units kW/cfm
Input Restrictions As specified in the manufacturers’ literature
Baseline Rules Applicable when the baseline building uses the power-per-unit-flow method. Fan power is determined using Table 6.7.3-1 for ASHRAE Standard 90.1-2007. This power is then multiplied by the return fan ratio.

Exhaust Fan Systems

Exhaust fans include toilet exhaust, kitchen exhaust, as well as fume hoods in laboratories and other spaces. Some systems typically operate at constant flow, while flow varies for other systems depending on, for instance, the position of the sash for fume hoods. Exhaust fan flow is specified and scheduled for each thermal block. An exhaust fan system may serve multiple thermal blocks. The baseline building has exhaust fans when the proposed design has exhaust fans. The exhaust air flow is the same for the baseline building and the proposed design.

Exhaust Fan Name
Applicability All exhaust systems serving multiple thermal blocks
Definition A unique descriptor for each exhaust fan. This should be keyed to the construction documents, if possible, to facilitate plan checking. Exhaust rates and schedules at the thermal block level refer to this name.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans.
Baseline Rules The baseline building will have an exhaust system that corresponds to the proposed design. The name can be identical to that used for the proposed design or some other appropriate name may be used.
Exhaust Fan System Modeling Method
Applicability All exhaust fan systems
Definition Software commonly models fans in three ways. See definition for supply system modeling method.
Units List: power-per-unit-flow, static pressure or brake horsepower
Input Restrictions As designed
Baseline Rules If the proposed design uses the power-per-unit-flow method, the baseline building shall also use this method, otherwise the baseline building shall use the brake horsepower method.
Exhaust Fan Rated Capacity
Applicability All exhaust systems
Definition The rated design air flow rate of the exhaust fan system. This building descriptor defines the 100% flow case for the part-flow curve. Actual air flow is the sum of the flow specified for each thermal block, as modified by the schedule for each thermal block.
Units cfm
Input Restrictions As designed
Baseline Rules

Same as the proposed design except that baseline building kitchen exhaust rate may not exceed the maximum levels defined by ASHRAE 90.1-2010, Table 6.5.7.1.3.

 

Fan Control Method
Applicability All exhaust fan systems
Definition A description of how the exhaust fan(s) are controlled. The options include:
  • Constant volume
  • Two-speed
  • Variable-flow, inlet or discharge dampers
  • Variable-flow, inlet guide vanes
  • Variable-flow, variable speed drive (VSD)
  • Variable-flow, variable pitch blades
Units List (see above)
Input Restrictions As designed, however, when exhaust fan flow at the thermal block level is varied through a schedule, one of the variable-flow options shall be specified.
Baseline Rules

The baseline building exhaust fan control shall generally be the same as the proposed design. For laboratories that have exhaust flow of 5,000 cfm or more, the baseline building exhaust flow shall vary in response to scheduled fume hood exhaust and lab zone airflow schedules. Fume hood exhaust flow control shall be the same as design, and general exhaust (relief) shall be VSD.

 

If a kitchen zone design exhaust rate is greater than 5,000 cfm, the baseline building system serving the kitchen shall be system type 5 or 7 with a demand ventilation system on 75% of the exhaust air. The system shall reduce exhaust and replacement air system airflow rates by 50% for one half of the kitchen occupied hours.

Exhaust Fan Schedule
Applicability All exhaust fan systems
Definition A schedule that indicates when the exhaust fan system is available for operation. Exhaust fan flow is specified at the thermal block level.
Units Data structure: schedule, on/off
Input Restrictions The exhaust fan system shall be available during all periods when one or more thermal blocks served by the system are scheduling exhaust.
Baseline Rules Same as the proposed design
Exhaust Fan Brake Horsepower
Applicability All exhaust fan systems
Definition The design shaft brake horsepower of the exhaust fan(s).
Units Brake horsepower (bhp)
Input Restrictions As designed
Baseline Rules The bhp for the baseline building is the total system fan horsepower from Table 6.7.3-1 times the exhaust fan ratio.
Exhaust Fan Design Static Pressure
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for exhaust fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the exhaust fan does not need to be specified if the exhaust fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When static pressure and fan efficiency are entered for the proposed design, the baseline building shall use brake horsepower.
Exhaust Fan Efficiency
Applicability Any exhaust fan system that uses the static pressure method
Definition The efficiency of the exhaust fan at rated capacity
Units Unitless
Input Restrictions As designed. The exhaust fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Rules Not applicable. When static pressure and fan efficiency are entered for the proposed design, the baseline building shall use brake horsepower.
Exhaust Fan Motor Efficiency
Applicability All exhaust fan systems
Definition The full-load efficiency of the motor serving the exhaust fan
Units Unitless
Input Restrictions As designed
Baseline Rules From Table 10.8 of ASHRAE Standard 90.1-2007
Fan Part-Flow Power Curve
Applicability All variable flow exhaust fan systems
Definition A part-load power curve which represents the ratio full-load power draw of the exhaust fan as a function of the ratio full-load air flow.
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (6.7.3-1) and Table 6.7.3-3  for the type of fan specified in the proposed design.
Baseline Rules The baseline building fan curve shall be selected from Equation (6.7.3-1) and Table 6.7.3-3  for the type of fan specified in the proposed design.
Exhaust Fan KW
Applicability All exhaust systems
Definition The fan power of the exhaust fan per unit of flow. This building descriptor is applicable only with the power-per-unit-flow method.
Units W/cfm
Input Restrictions As designed.
Baseline Rules The fan system power from Table 6.7.3-1.
90.1-2019

Baseline Building Fan System Summary

The baseline building fan system is summarized in this section. See Table 3 for the HVAC baseline building system mapping.

Total baseline building fan system power for the baseline building fan systems is given in the following sections as well as Table 53 and Table 54. Table 52 summarizes all descriptors for fan systems and their applicability to supply, return/relief, and exhaust fans.

Table 4 summarizes inputs for each of the three approaches for imputing system fan power (fan power method, brake horsepower method, and design pressure drop method).

· In these tables, CFMs is the baseline fan supply fan airflow at peak design conditions.

· The fan system power includes the supply fan, the return fan, and exhaust fans.

· Exhaust fans include kitchen hoods, toilets, fume hoods, and other miscellaneous fans that operate at design conditions.

When the proposed design has return fans, exhaust fans (toilets or kitchens), or fume hood exhaust systems, the baseline building has the same systems. Fan power will be allocated to the baseline supply, return, and exhaust fans based on the Fan System Power described below and the ratio of each fans power in the proposed design to the proposed design fan system power.

Table 52. Building Descriptor Applicability for Fan Systems

Inputs Supply Fan Return/ Relief Fan Exhaust Fans (Hoods)
Modeling Method yes Same as supply yes
Air Rated Capacity yes yes yes
Plenum Zone no yes no
Return Air Path no yes no
Fan Control Method no Same as supply yes
Brake Horsepower yes yes yes
Static Pressure yes yes yes
Fan Efficiency yes yes yes
Motor Efficiency yes yes yes
Fan Position yes no no
Motor Position yes yes  no
Part-Load Power Curve yes yes yes
Fan KW yes yes yes

Table 53. Baseline Fan System Details for Fan System Power

System Fan Power Method (W/cfm) Brake Horsepower Method (bhp/cfm) Design Pressure Drop (DPD) Method Fan Motor Efficiency ŋm Fan Mech Efficiency DPD (If no additional pressure drop credits) (a)
1 & 2 0.3 W/cfm x ŋm x 0.00134 bhp/cfm x fan mech efficiency x 6356 80% 65% 1.33 in. w.g

3, 4, 12. &

13

(bhp x 746)/ŋm 0.00094 x CFMs + A bhp/cfm x fan mech efficiency x 6356 Standard 90.1-2019, Table G3.9.1(a) 65% 3.88 in. w.g.

5 through

8

(bhp x 746)/ŋm 0.0013 x CFMs + A bhp/cfm x fan mech efficiency x 6356 Standard 90.1-2019, Table G3.9.1(a) 65% 5.37 in. w.g.

9 & 10

supply fan

0.3 W/cfm x ŋm x 0.00134 bhp/cfm x fan mech efficiency x 6356 Standard 90.1-2019, Table G3.9.1(a) 65% 1.33 in. w.g.

9 & 10

non-

mechanical

cooling

fan(b)

0.054 W/cfm x ŋm x 0.00134 bhp/cfm x fan mech efficiency x 6356 80% 65% 0.24 in. w.g.
11 (bhp x 746)/ŋm 0.00062 x CFMs + A bhp/cfm x fan mech efficiency x 6356 Standard 90.1-2019, Table G3.9.1(a) 65% 2.56 in. w.g.

The term “A” for system types 3 through 8 is calculated based on equipment included in the proposed design

using the procedure in Table 6.5.3.1.1 of ASHRAE Standard 90.1-2019 and the airflows from the baseline

design. This accounts for various additional fan pressure drops associated with special conditions.

(a) Fan motor efficiency is the efficiency from Table G3.9.1 of Standard 90.1-2019 for the next motor size

greater than the bhp.

(b) This alternate equation is only used if there is a non-mechanical cooling fan in place in the proposed design.

(c) If system qualified for additional pressure drop credits DPD should be calculated based on adjusted bhp.

Pressure Drop Adjustment  
Applicability Any system serving zones served by systems in the proposed design which qualify for pressure drop adjustments in Table 54
Definition Adjustments to fan power limitations related to application-specific requirements as allowed by Standard 90.1-2019 Table 6.5.3.1-1
Units List
Input Restrictions As designed
Baseline Building Calculated from Section 6.5.3.1-1 of Standard 90.1-2019 for baseline system fans. Pressure drop adjustment is based on the device from Table 54 being present in the proposed design.

Table 54. Baseline Building: Fan Power Limitation Pressure Drop Adjustment

Device Adjustment
Credits  

Return or exhaust systems required by code or

accreditation standards to be fully ducted, or systems

required to maintain air pressure differentials between

adjacent rooms.

0.5 in. w.c. (2.15 in. w.c. for laboratory and vivarium systems)
Return and/or exhaust airflow control devices 0.5 in. w.c.
Exhaust filters, scrubbers, or other exhaust treatment The pressure drop of device calculated at fan system design condition
Particulate filtration credit: MERV 9 through 12 0.5 in. w.c.
Particulate filtration credit: MERV 13 through 15 0.9 in. w.c.

Particulate filtration credit: MERV 16 and greater and

electronically enhanced filters

Pressure drop calculated at 2x clean filter pressure drop at fan system design condition
Carbon and other gas-phase air cleaners Clean filter pressure drop at fan system design condition
Biosafety cabinet Pressure drop of device at fan system design condition
Energy recovery device and other coil runaround loop (2.2 × Energy Recovery Effectiveness)—0.5 in w.c. for each airstream
Coil runaround loop 0.6 in. w.c. for each airstream

Evaporative humidifier/cooler in series with another

cooling coil

Pressure drop of device at fan system design condition
Sound attenuation section 0.15 in. w.c.
Exhaust systems serving fume hoods 0.35 in. w.c.

Laboratory and vivarium exhaust systems in high-rise

buildings

0.25 in. w.c./100 ft of vertical duct exceeding 75 ft.
Deductions  
Systems without central cooling device –0.6 in. w.c.
Systems without central heating device –0.3 in. w.c.
Systems with central electric resistance heat –0.2 in. w.c.

 

Fan Power Adjustment   
Applicability All fan systems qualifying for pressure drop adjustments as described above.
Definition Standard 90.1-2019 specifies a “pressure drop adjustment” for fan systems with requirements for filtration or other process requirements.
Units List
Input Restrictions Derived from other building descriptors
Baseline Building

Pressure drop adjustment is calculated separately for each applicable device. Credit for each device is specified in the section above.

A = sum of zones (PD_sum ´ CFMd_baseline/4131)

Where:

PD = Each applicable pressure drop adjustment from the proposed design

CFMd = The design airflow through each applicable device in cfm from the baseline building

Note: In scenarios where the proposed and baseline building have varying zone to system assignment, the pressure drop credit ‘A’ shall be calculated for each thermal zone in the proposed building, using the design flow rates in the proposed building design. For multi-zone systems in the proposed building, the pressure drop adjustment will be split for each zone based on the zone to system airflow ratio. The pressure drop adjustment for the baseline building will then be calculated by adjusting the calculated PDA by the ratio of baseline building design airflow rate to proposed building design air flow rate for each zone. The baseline system pressure drop adjustment will be a sum of the individual pressure drop adjustments of the applicable zones.

 

Supply Fan Ratio  
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust, or return fans
Definition The ratio of supply fan brake horsepower in the proposed design to total fan system brake horsepower for the proposed design at design conditions.
Units Unitless fraction (0 to 1)
Input Restrictions As designed
Baseline Building Same as proposed

 

Return Fan Ratio  
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust, or return fans
Definition The ratio of return fan brake horsepower in the proposed design to total fan system brake horsepower for the proposed design at design conditions
Units Unitless fraction (0 to 1)
Input Restrictions Derived from other building descriptors
Baseline Building Same as proposed

 

Exhaust Fan Ratio  
Applicability Systems that serve thermal blocks that have exhaust, fume hoods, kitchen exhaust, or return fans
Definition

The ratio of exhaust fan brake horsepower in the proposed design to total fan system brake hp for the proposed design at design conditions. Exhaust fans include toilet exhaust, kitchen hoods, and other miscellaneous exhaust.

For fan systems with multiple exhaust fans, the exhaust fan ratios shall be calculated separately for each exhaust fan.

Units Unitless ratio
Input Restrictions Derived from other building descriptors. In the event that a common exhaust system serves thermal blocks that are served by different HVAC systems, the brake horsepower shall be divided in proportion to design cfm.
Baseline Building Same as proposed

 

Supply Fans 

Fan System Modeling Method  
Applicability All fan systems
Definition Software commonly models fans in three ways. The simple method is for the user to enter the electric power per unit of flow (W/cfm). This method is commonly used for unitary equipment and other small fan systems. A more detailed method is to model the fan as a system whereby the static pressure, fan efficiency, and motor efficiency are specified at design conditions. A third method is to specify brake horsepower at design conditions instead of fan efficiency and static pressure. This is a variation of the second method whereby brake horsepower is specified in lieu of static pressure and fan efficiency.
Units List: Power-Per-Unit-Flow, Design Pressure Drop, or Brake Horsepower
Input Restrictions As designed
Baseline Building Systems 1, 2, 9, and 10 should use power per unit flow if allowed by the software. If not allowed used one of the other methods as described in Table 54. All other baseline system shall use the brake horsepower method. If that method is not available, static pressure method should be used.

 

Supply Fan Design Air Rated Capacity  
Applicability All fan systems
Definition The design airflow rate of the supply fan(s) at design conditions. This building descriptor sets the 100% point for the fan part-load curve.
Units cfm
Input Restrictions As designed
Baseline Building

The software shall automatically size the system airflow to meet the baseline building loads based on

· a supply-air-to-room-air temperature difference of 20°F,

· or the minimum outdoor airflow rate,

· or the airflow rate required to comply with the applicable codes or accreditation standards, whichever is greater.

The baseline system airflow is determined by the load to be met by the airflow and the 20°F (11°C) temperature difference. The loads to be used would be the design load as determined by the sizing runs specified in Section G3.1.2.2, not the cooling or heating capacity of the system as determined using the sizing factors, also specified in G3.1.2.2. Using the system cooling and heating capacity will result in oversized baseline system airflows and energy cost because of the oversizing factors used in G3.1.2.2.

See additional discussion in Section 3.5.5.1 for VAV systems. spaces with special process requirements.) The supply fan design airflow rate shall be the sum of the calculated design airflow for the thermal zones served by the fan system.

For laboratory spaces, the design airflow rate calculation shall be based on a 17°F temperature differential rather than 20°F.

For baseline systems 9 and 10, the design supply airflow rates shall be based on the temperature difference between a SAT setpoint of 105°F and the design space heating temperature setpoint, the minimum outdoor airflow rate or the airflow rate required to comply with applicable codes, whichever is greater.

If the proposed design HVAC system airflow rate based on latent loads greater than the same based on sensible loads, then the same supply-air-to-room humidity ratio difference (gr/lb) used to calculate the proposed design airflow should be used to calculate the design airflow rates for the baseline building.

 

Fan Control Method  
Applicability All fan systems
Definition

A description of how the supply (and return/relief) fan(s) is controlled. The options include:

· Constant volume

· Variable-flow, inlet or discharge dampers

· Variable-flow, inlet guide vanes

· Variable-flow, variable speed drive (VSD)

· Variable-flow, variable pitch blades

· Variable-flow, other

· Two-speed

· Constant volume, cycling (fan cycles with heating and cooling)

Units List (see above)
Input Restrictions As designed
Baseline Building Based on the baseline system type, summarized in Table 55

 

Table 55. Baseline Building Fan Control Method

System No. System Type Fan Control
System 1 Package terminal air conditioner Constant volume
System 2 Packaged terminal heat pump Constant volume
System 3 Packaged roof top air conditioner Constant volume
System 4 Packaged roof top heat pump Constant volume
System 5 Packaged rooftop VAV with reheat Variable volume, variable speed drive (VSD)
System 6 Packaged rooftop VAV with PFP boxes and reheat Variable volume, VSD
System 7 Packaged rooftop VAV with reheat Variable volume, VS
System 8 VAV with parallel fan-powered boxes and reheat Variable volume, VSD
System 9 Warm air furnace, gas fired Constant volume
System 10 Warm air furnace, electric Constant volume
System 11 Single zone VAV Variable volume, VSD
System 12 Single zone system (CHW and HW boiler) Constant volume
System 13 Single zone system (CHW and electric resistance) Constant volume

 

Supply Fan Brake Horsepower  
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design shaft brake horsepower of the supply fan(s). This input does not need to be supplied if the supply fan kW is supplied.
Units Horsepower (hp)
Input Restrictions As designed. If this building descriptor is specified for the proposed design, then the static pressure and fan efficiency are not required.
Baseline Building

Fans for parallel fan-powered boxes are not included in fan power calculations.

Table 53 of this document gives the baseline building fan system brake horsepower. The brake horsepower for the supply fan is this value times the supply fan ratio (see above).

 

Supply Fan Static Pressure   
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design static pressure for the supply fan. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H2O)
Input Restrictions As designed. The design static pressure for the supply fan does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Baseline Building The baseline building is defined by Table 53. This approach only works if the system has only a supply fan. If return/exhaust fans are also present in the system, then the supply fan bhp needs to be calculated and divided amongst the supply, return, and exhaust fans.

 

Supply Fan Efficiency   
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The efficiency of the fan at design conditions; this is the static efficiency and does not include motor losses
Units Unitless
Input Restrictions As designed. The supply fan efficiency does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Baseline Building The baseline supply fan efficiency shall be 65%.

 

Supply Motor Efficiency   
Applicability All supply fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Baseline Building For systems 1, 2, 9, and 10, motor efficiency is assumed to be 80%. The motor efficiency for systems 3 through 8 is determined from Table G3.9.1 of ASHRAE Standard 90.1-2019 (Table 56 below).

 

Table 56. Minimum Nominal Efficiency for Electric Motors (%)

Shaft Input Power Full-Load Motor Efficiency, %
1

82.5

1.5 84
2 84
3 87.5
5 87.5
7.5 89.5
10 89.5
15 91
20 91
25 92.4
30 92.4
40 93
50 93
60 93.6
75 94.1
100 94.5
125 94.5
150 95
200 95

 

Fan Position  
Applicability All supply fans
Definition The position of the supply fan relative to the cooling coil. The configuration is either draw through (fan is downstream of the coil) or blow through (fan is upstream of the coil).
Units List (see above)
Input Restrictions As designed
Baseline Building Draw through

 

Motor Position  
Applicability All supply fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed
Baseline Building In the air stream

 

Fan Part-Flow Power Curve  
Applicability All variable flow fan systems
Definition A part-load power curve that represents the percentage full-load power draw of the supply fan as a function of the percentage full-load airflow. The curve is typically represented as a cubic equation with an absolute minimum power draw specified.
Units Unitless ratio
Input Restrictions

The fan curve shall be selected from Equation (11) and Table 57 for the type of fan specified in the proposed design. 

??????? ?? ???=?+?⋅????????+?⋅????????2+?⋅????????3 ???=????????

Where:

PLR = Ratio of fan power at part load conditions to full load fan power

PowerMin = Minimum fan power ratio

FanRatio = Ratio of cfm at part-load to full-load cfm

a, b, c and d = Constants from Table 57

 

Table 57. Fan Curve Default Values

Fan Type- Control Type A B c d %PowerMin
Multi Zone VAV with Airfoil (AF) or Backward Incline (BI) riding the curve(a) 0.1631 1.5901 -0.8817 0.1281 70%
Multi Zone VAV with AF or BI with inlet vanes(a) 0.9977 -0.659 0.9547 -0.2936 50%
Multi Zone VAV with Forward Curved (FC) fans riding the curve(a) 0.1224 0.612 0.5983 -0.3334 30%
Multi Zone VAV with FC with inlet vanes(a) 0.3038 -0.7608 2.2729 -0.8169 30%
Multi Zone VAV with vane-axial with variable pitch blades(a) 0.1639 -0.4016 1.9909 -0.7541 20%
Multi Zone VAV with VSD and fixed SP setpoint(b) 0.0013 0.1470 0.9506 -0.0998 20%
Multi zone VAV with static pressure reset(c) 0.04076 0.0881 -0.0729 0.9437 10%
Single zone VAV fan(d) 0.027828 0.026583 -0.087069 1.030920 10%

Data Sources:

(a) ECB Compliance Supplement, public review draft, Version 1.2, March 1996, but adjusted to be relatively consistent with the curve specified in the PRM.

(b) The fan curve for VSD is specified in Table G3.1.3.15.

(c) This is the good SP reset VSD fan curve from the advanced VAV design guide used for MZVAV systems.

(d) This is the perfect SP reset VSD fan curve from the advanced VAV design guide used for SZVAV systems.

http://www.energy.ca.gov/2003publications/CEC-500-2003-082/CEC-500-2003-082-A-11.PDF 

 

Baseline Building Not applicable for baseline building systems 1 through 4. Baseline systems 5 through 8 will use the curve for “Multi zone VAV with fixed static pressure setpoint” curve. System 11 shall use the “Single zone VAV fan” curve. Constant volume fans are used for systems 9, 10, 12, and 13 and hence the descriptor is not applicable.

 

Supply Fan Power Index (kW/cfm)  
Applicability Fan systems that use the power-per-unit-flow method
Definition The supply fan power per unit of flow
Units kW/cfm
Input Restrictions As designed or specified in the manufacturers’ literature
Baseline Building Applicable when the baseline building uses the power-per-unit-flow method. Fan power is determined using Table 53 of this document. This power is then multiplied by the supply fan ratio.

 

Static Pressure Reset Controls   
Applicability All VAV fan systems. Baseline systems 5 through 8.
Definition Static pressure reset controls, reset the fan static pressure for VAV systems-based zone damper position. For systems with DDC of individual zone boxes reporting to the central control panel, static pressure setpoint shall be reset based on the zone requiring the most pressure.
Units Unitless
Input Restrictions As designed. If static pressure reset is implemented in the proposed system, the curve for “Multi zone VAV with static pressure reset curve” shall be used.
Baseline Building Not applicable for baseline building systems 1 through 4 or 9, 10, 11, 12, and 13. The curve for “Multi Zone VAV with VSD and fixed SP setpoint”’ shall be used for baseline building systems 5 through 8.

 

Return/ Relief Fans 

System design supply airflow rates for the baseline building design shall be based on a supply-air-to room-air temperature difference of 20°F or the minimum outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards, whichever is greater. For systems 3, 4, and 11 through 13, if return or relief fans are specified for systems serving the corresponding zones in the proposed design, the baseline building design shall also be modeled with fans serving the same functions. For systems 5 through 8, if return or relief fans are specified in the proposed building, then the baseline systems serving the corresponding zones will be modeled with a return/relief fan.

Plenum Zone  
Applicability Any system with return ducts or return air plenum
Definition A reference to the thermal zone that serves as return plenum or where the return ducts are located
Units Text, unique
Input Restrictions As designed
Baseline Building Applicable when the baseline building has a return fan. Same as the proposed design when the proposed design has a plenum; otherwise, the return air ducts are assumed to be located in the space.

 

Return Air Path  
Applicability Any system with return ducts or return air plenum
Definition Describes the return path for air. This can be one of the following: ducted return; plenum return; or direct-to-unit.
Units List (see above)
Input Restrictions As designed
Baseline Building For baseline building systems 1 and 2, the return air path shall be direct-to-unit. For baseline building systems 3 through 8 and 11 through 13 and when the proposed design is direct-to-unit, the baseline building shall be ducted return, otherwise the baseline building return air path shall be the same as proposed design.

 

Return/ Relief Air Rated Capacity  
Applicability All systems with a return or relief fan
Definition The design airflow fan capacity of the return or relief fan(s). This sets the 100% fan flow point for the part-load curve (see below).
Units cfm
Input Restrictions As designed
Baseline Building Applicable when the baseline building has a return fan. Return or relief fans shall be sized for the baseline system supply fan air quantity less the minimum outdoor air, or 90% of the supply fan air quantity, whichever is larger.

 

Return/ Relief Fan Brake Horsepower  
Applicability Any system with return or relief fans that uses the brake horsepower method
Definition The design shaft brake horsepower of the return/relief fan(s)
Units Brake horsepower (bhp)
Input Restrictions As designed
Baseline Building Applicable when the baseline building has a return fan. The bhp of the return fan shall be the system fan brake horsepower multiplied by the return fan ratio. In other words, brake horsepower is allocated in proportion to the proposed design.

 

Return/ Relief Design Static Pressure  
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for return fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H2O gauge)
Input Restrictions As designed. The design static pressure for the return fan does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Building Return fan static pressure = (Return fan BHP ´ 6356 ´ 0.65)/cfm return

 

Return/ Relief Fan Efficiency  
Applicability Any system with return or relief fans that uses the static pressure method
Definition The efficiency of the fan at design conditions; this is the static efficiency and does not include the efficiency loss of the motor
Units Unitless
Input Restrictions As designed. The return/relief fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Baseline Building 65%

 

Return/ Relief Motor Efficiency  
Applicability All return fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Baseline Building For baseline systems 1, 2, 9, 10, 12, and 13 is 80%. For baseline systems 3 through 8 and 11, fan motor efficiency is determined from Table G3.9.1 of Standard 90.1-2019 for the next motor size greater than the bhp calculated, through the process described above, using a totally enclosed fan motor at 1800 rpm.

 

Motor Position  
Applicability All return fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed
Baseline Building In the air stream

 

Fan Part-Flow Power Curve  
Applicability All return fans for variable flow fan systems
Definition A part-load power curve that represents the percentage full-load power draw of the return fan as a function of the percentage full-load airflow
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (11) and Table 57 for the type of fan specified in the proposed design.
Baseline Building Not applicable for baseline building systems 1 through 4. The curve for “Multi zone VAV with static pressure reset curve” shall be used for baseline building systems 5 through 8 and system 11.

 

Return/ Relief Fan Power Index  
Applicability Any system with a return fan
Definition The return fan power per unit of flow
Units kW/cfm
Input Restrictions As specified in the manufacturers’ literature
Baseline Building Applicable when the baseline building uses the power-per-unit-flow method. Fan power is determined using Table 53. This power is then multiplied by the return fan ratio.

 

Exhaust Fan Systems 

Exhaust fans include toilet, kitchen and laboratory exhaust. Some systems typically operate at constant flow, while flow varies for other systems depending on, for instance, the position of the sash for fume hoods. Exhaust fan flow is specified and scheduled for each thermal zone. An exhaust fan system may serve multiple thermal zones. The baseline building has exhaust fans when the proposed design has exhaust fans. The design exhaust airflow is the same for the baseline building and the proposed building.

Exhaust Fan Name  
Applicability All exhaust systems serving multiple thermal zones
Definition A unique descriptor for each exhaust fan. This should be keyed to the construction documents, if possible, to facilitate plan checking. Exhaust rates and schedules at the thermal zone level refer to this name.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans
Baseline Building The baseline building will have an exhaust system that corresponds to the proposed design. The name can be identical to that used for the proposed design or some other appropriate name may be used.

 

Exhaust Fan System Modeling Guide  
Applicability All exhaust fan systems
Definition Software commonly models fans in three ways. See definition for supply system modeling method.
Units List: Power-Per-Unit-Flow, Static Pressure, or Brake Horsepower
Input Restrictions As designed
Baseline Building If the proposed design uses the power-per-unit-flow method, the baseline building shall also use this method, otherwise the baseline building shall use the static pressure method

 

Exhaust Fan Rated Capacity   
Applicability All exhaust systems
Definition The rated design airflow rate of the exhaust fan system. This building descriptor defines the 100% flow case for the part-flow curve. Actual airflow is the sum of the flow specified for each thermal zone, as modified by the schedule for each thermal zone.
Units cfm
Input Restrictions As designed
Baseline Building Same as the proposed design except that baseline building kitchen exhaust rate may not exceed the maximum levels defined by Section 3.5.5.3 of this document

 

Fan Control Method   
Applicability All exhaust fan systems
Definition

A description of how the exhaust fan(s) are controlled. The options include:

· Constant volume

· Two-speed

· Variable-flow, inlet or discharge dampers

· Variable-flow, inlet guide vanes

· Variable-flow, VSD

· Variable-flow, variable pitch blades

Units List (see above)
Input Restrictions As designed, however, when exhaust fan flow at the thermal zone level is varied through a schedule, one of the variable-flow options shall be specified
Baseline Building The baseline building exhaust fan control shall generally be the same as the proposed design. Exceptions: Exhaust fans s serving laboratory spaces shall reduce the exhaust air volume during unoccupied periods to the largest of 50% of zone peak airflow, the minimum outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards as described in Section 3.5.5.3 under descriptor Laboratory: Exhaust Minimum Airflow Rate.

 

Exhaust Fan Schedule    
Applicability All exhaust fan systems
Definition A schedule that indicates when the exhaust fan system is available for operation. Exhaust fan flow is specified at the thermal zone level.
Units Data structure: schedule, on/off
Input Restrictions As designed
Baseline Building Same as the proposed design for exhaust fans not serving kitchen or laboratory spaces For kitchen and laboratory zone exhaust, refer to Section 3.5.5.3 of this document

 

Exhaust Fan Brake Horsepower  
Applicability All exhaust fan systems
Definition The design shaft brake horsepower of the exhaust fan(s)
Units Brake horsepower (bhp)
Input Restrictions As designed
Baseline Building The bhp for the baseline building is the total system fan horsepower from Table 53 of this document multiplied by the exhaust fan ratio

 

Exhaust Fan Design Static Pressure  
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for exhaust fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H2O)
Input Restrictions As designed for exhaust fans not serving kitchens. The design static pressure for the exhaust fan does not need to be specified if the exhaust fan bhp is specified.
Baseline Building

The exhaust fan static pressure for the baseline building would be equal to the total fan system static pressure (specified in section Supply Fan Static Pressure) multiplied by the exhaust fan ratio

Exhaust Fan Static Pressure = (Exhaust Fan BHP ´ 6356 ´ 0.65)/cfm exhaust

 

Exhaust Fan Efficiency   
Applicability Any exhaust fan system that uses the static pressure method
Definition The efficiency of the exhaust fan at rated capacity; this is the static efficiency and does not include losses through the motor
Units Unitless
Input Restrictions As designed. The exhaust fan efficiency does not need to be specified if the return fan bhp is specified.
Baseline Building

For baseline system, fan efficiency is 65%

 

Exhaust Fan Motor Efficiency   
Applicability All exhaust fan systems
Definition The full-load efficiency of the motor serving the exhaust fan
Units Unitless
Input Restrictions As designed
Baseline Building

From Table G3.9.1 of Standard 90.1-2019 for the next motor size greater than the bhp calculated, through the process described above, using a totally enclosed fan motor at 1800 rpm

 

Fan Part-Flow Power Curve  
Applicability All variable flow exhaust fan systems
Definition A part-load power curve that represents the power draw of the exhaust fan as a function of the airflow
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (11) and Table 57 for the type of fan specified in the proposed design.
Baseline Building

Same as proposed

 

Exhaust Fan Power Index   
Applicability All exhaust systems
Definition The fan power of the exhaust fan per unit of flow. This building descriptor is applicable only with the power-per-unit-flow method.
Units kW/cfm
Input Restrictions As designed
Baseline Building

The fan system power from Table 53 multiplied by the exhaust fan ratio

 

Building EQ

Supply Fans

Fan System Modeling Method
Applicability All fan systems
Definition

Software commonly models fans in three ways.

  • Power-per-unit-flow. The simple method is for the user to enter the electric power per unit of flow (W/cfm). This method is commonly used for unitary equipment and other small fan systems.
  • Static pressure. A more detailed method is to model the fan as a system whereby the static pressure, fan efficiency, part-load curve, and motor efficiency are specified at design conditions.
  • Break horsepower. A third method is to specify brake horsepower at design conditions instead of fan efficiency and static pressure. This is a variation of the second method whereby brake horsepower is specified in lieu of static pressure and fan efficiency. The latter two methods are commonly used for VAV and other larger fan systems.
Units List: power-per-unit-flow, static pressure or brake horsepower
Input Restrictions As designed. The power-per-unit-flow method shall be used when no fan performance data is available for the proposed design cooling system, e.g. only EER or SEER are available.
Baseline Rules If the proposed design uses the power-per-unit-flow method, the baseline building shall also use this method, otherwise the baseline building shall use the brake horsepower method.
Supply Fan Design Air Rated Capacity
Applicability All fan systems
Definition The design air flow rate of the supply fan(s) at design conditions. This building descriptor sets the 100% point for the fan part-load curve.
Units cfm
Input Restrictions As designed. This input should be at least as great as the sum of the design air flow specified for each of the thermal blocks that are served by the fan system. For multiple deck systems, a separate entry should be made for each deck.
Baseline Rules The program shall automatically size the air flow at each thermal block to meet the loads. The design air flow rate calculation shall be based on a 20 degree temperature differential between supply air and the room air. The supply fan design air flow rate shall be the sum of the calculated design air flow for the thermal blocks served by the fan system.
Fan Control Method
Applicability All fan systems
Definition A description of how the supply (and return/relief) fan(s) are controlled. The options include:
  • Constant volume
  • Variable-flow, inlet or discharge dampers
  • Variable-flow, inlet guide vanes
  • Variable-flow, variable speed drive (VSD)
  • Variable-flow, variable pitch blades
  • Variable-flow, other
  • Two-speed
  • Constant volume, cycling (fan cycles with heating and cooling)
Units List (see above)
Input Restrictions As designed

 

Supply Fan Brake Horsepower
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design shaft brake horsepower of the supply fan(s). This input does not need to be supplied if the Supply Fan kW is supplied.
Units Horsepower (hp)
Input Restrictions As designed. If this building descriptor is specified for the proposed design, then the Static Pressure and Fan Efficiency are not.
Supply Fan Static Pressure
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design static pressure for the supply fan. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the supply fan does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Supply Fan Efficiency
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The efficiency of the fan at design conditions
Units Unitless
Input Restrictions As designed. The supply fan efficiency does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Supply Motor Efficiency
Applicability All supply fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Fan Position
Applicability All supply fans
Definition The position of the supply fan relative to the cooling coil. The configuration is either draw through (fan is downstream of the coil) or blow through (fan is upstream of the coil).
Units List (see above)
Input Restrictions As designed.
Motor Position
Applicability All supply fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed.
Fan Part-Flow Power Curve
Applicability All variable flow fan systems
Definition A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow. The curve is typically represented as a quadratic equation with an absolute minimum power draw specified.
Units Unitless ratio
Input Restrictions

As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.

(6.7.3-1)

$Greater \;of$

$PLR = a + b \cdot FanRatio + c \cdot FanRatio^2 + d \cdot FanRatio^3$

$PLR = PowerMin $

where

PLR Ratio of fan power at part load conditions to full load fan power
PowerMin Minimum fan power
FanRatio Ratio of cfm at part-load to full-load cfm
a, b, c and d Constants from [bookref id="fan-curve-default-values"] below

[table title="Fan Curve Default Values" id="fan-curve-default-values"]

 

Fan Type - Control Type a b c d %PowerMin
AF or BI riding the curvea 0.1631 1.5901 -0.8817 0.1281 70%
AF or BI with inlet vanesa 0.9977 -0.659 0.9547 -0.2936 50%
FC riding the curvea 0.1224 0.612 0.5983 -0.3334 30%
FC with inlet vanesa 0.3038 -0.7608 2.2729 -0.8169 30%
Vane-axial with variable pitch bladesa 0.1639 -0.4016 1.9909 -0.7541 20%
Any fan with VSD (use for baseline building)b 0.0013 0.1470 0.9506 -0.0998 20%
VSD with static pressure resetc -0.0031 0.0991 1.0268 -0.1128 20%
Data Sources: 
a.     ECB Compliance Supplement, public review draft, Version 1.2, March 1996, but adjusted to be relatively consistent with the curve specified in the PRM.   
b.     The fan curve for VSD is specified in Table G3.1.3.15
c.     Advanced VAV System Design Guide, California Energy Commission, CEC Publication 500,-03-082 A-11, April 2005, but adjusted to be relatively consistent with the curve specified in the PRM..
Supply Fan kW
Applicability Fan systems that use the power-per-unit-flow method
Definition The supply fan power per unit of flow.
Units kW/cfm
Input Restrictions

As designed or specified in the manufacturers’ literature. For units with rated total cooling capacities less than 120,000 Btu/h, the user may default to a value calculated as follows:

(6.7.3-2)

$$ Fan_{kw} = 0.365 \times \frac{Q_{rated}}{30,000} $$

where

Fankw The supply fan power (kW)
Qrated The rated total cooling capacity (Btu/h)

Relief Fans

The baseline building has a return fan when the baseline building system is type 3 through 8 and the proposed design has a return fan.

Plenum Zone
Applicability Any system with return ducts or return air plenum
Definition A reference to the thermal block that serves as return plenum or where the return ducts are located
Units Text, unique
Input Restrictions As designed
Return Air Path
Applicability Any system with return ducts or return air plenum
Definition Describes the return path for air. This can be one of the following: ducted return; plenum return; or direct-to-unit.
Units List (see above)
Input Restrictions As designed
Return/Relief Air Rated Capacity
Applicability All systems with a return or relief fan
Definition The design air flow fan capacity of the return or relief fan(s). This sets the 100% fan flow point for the part-load curve (see below).
Units cfm
Input Restrictions As designed
Return/Relief Fan Brake Horsepower
Applicability Any system with return or relief fans that uses the brake horsepower method
Definition The design shaft brake horsepower of the return/relief fan(s)
Units Brake horsepower (bhp)
Input Restrictions As designed
Return/Relief Design Static Pressure
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for return fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the return fan does not need to be specified if the return fan brake horsepower (bhp) is specified.
Return/Relief Fan Efficiency
Applicability Any system with return or relief fans that uses the static pressure method
Definition The efficiency of the fan at design conditions
Units Unitless
Input Restrictions As designed. The return/relief fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Return/Relief Motor Efficiency
Applicability All return fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Motor Position
Applicability All return fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed.
Fan Part-Flow Power Curve
Applicability All return fans for variable flow fan systems.
Definition A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow.
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.
Return/Relief Fan kW
Applicability Any system with a return fan
Definition The supply fan power per unit of flow
Units kW/cfm
Input Restrictions As specified in the manufacturers’ literature

Exhaust Fan Systems

Exhaust fans include toilet exhaust, kitchen exhaust, as well as fume hoods in laboratories and other spaces. Some systems typically operate at constant flow, while flow varies for other systems depending on, for instance, the position of the sash for fume hoods. Exhaust fan flow is specified and scheduled for each thermal block. An exhaust fan system may serve multiple thermal blocks.

Exhaust Fan Name
Applicability All exhaust systems serving multiple thermal blocks
Definition A unique descriptor for each exhaust fan. This should be keyed to the construction documents, if possible, to facilitate plan checking. Exhaust rates and schedules at the thermal block level refer to this name.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans.
Exhaust Fan System Modeling Method
Applicability All exhaust fan systems
Definition Software commonly models fans in three ways. See definition for supply system modeling method.
Units List: power-per-unit-flow, static pressure or brake horsepower
Input Restrictions As designed
Exhaust Fan Rated Capacity
Applicability All exhaust systems
Definition The rated design air flow rate of the exhaust fan system. This building descriptor defines the 100% flow case for the part-flow curve. Actual air flow is the sum of the flow specified for each thermal block, as modified by the schedule for each thermal block.
Units cfm
Input Restrictions As designed
Fan Control Method
Applicability All exhaust fan systems
Definition A description of how the exhaust fan(s) are controlled. The options include:
  • Constant volume
  • Two-speed
  • Variable-flow, inlet or discharge dampers
  • Variable-flow, inlet guide vanes
  • Variable-flow, variable speed drive (VSD)
  • Variable-flow, variable pitch blades
Units List (see above)
Input Restrictions As designed, however, when exhaust fan flow at the thermal block level is varied through a schedule, one of the variable-flow options shall be specified.
Exhaust Fan Schedule
Applicability All exhaust fan systems
Definition A schedule that indicates when the exhaust fan system is available for operation. Exhaust fan flow is specified at the thermal block level.
Units Data structure: schedule, on/off
Input Restrictions The exhaust fan system shall be available during all periods when one or more thermal blocks served by the system are scheduling exhaust.
Exhaust Fan Brake Horsepower
Applicability All exhaust fan systems
Definition The design shaft brake horsepower of the exhaust fan(s).
Units Brake horsepower (bhp)
Input Restrictions As designed
Exhaust Fan Design Static Pressure
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for exhaust fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the exhaust fan does not need to be specified if the exhaust fan brake horsepower (bhp) is specified.
Exhaust Fan Efficiency
Applicability Any exhaust fan system that uses the static pressure method
Definition The efficiency of the exhaust fan at rated capacity
Units Unitless
Input Restrictions As designed. The exhaust fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Exhaust Fan Motor Efficiency
Applicability All exhaust fan systems
Definition The full-load efficiency of the motor serving the exhaust fan
Units Unitless
Input Restrictions As designed
Fan Part-Flow Power Curve
Applicability All variable flow exhaust fan systems
Definition A part-load power curve which represents the ratio full-load power draw of the exhaust fan as a function of the ratio full-load air flow.
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.
Exhaust Fan KW
Applicability All exhaust systems
Definition The fan power of the exhaust fan per unit of flow. This building descriptor is applicable only with the power-per-unit-flow method.
Units W/cfm
Input Restrictions As designed.
Energy Star

Supply Fans

Fan System Modeling Method
Applicability All fan systems
Definition

Software commonly models fans in three ways.

  • Power-per-unit-flow. The simple method is for the user to enter the electric power per unit of flow (W/cfm). This method is commonly used for unitary equipment and other small fan systems.
  • Static pressure. A more detailed method is to model the fan as a system whereby the static pressure, fan efficiency, part-load curve, and motor efficiency are specified at design conditions.
  • Break horsepower. A third method is to specify brake horsepower at design conditions instead of fan efficiency and static pressure. This is a variation of the second method whereby brake horsepower is specified in lieu of static pressure and fan efficiency. The latter two methods are commonly used for VAV and other larger fan systems.
Units List: power-per-unit-flow, static pressure or brake horsepower
Input Restrictions As designed. The power-per-unit-flow method shall be used when no fan performance data is available for the proposed design cooling system, e.g. only EER or SEER are available.
Baseline Rules If the proposed design uses the power-per-unit-flow method, the baseline building shall also use this method, otherwise the baseline building shall use the brake horsepower method.
Supply Fan Design Air Rated Capacity
Applicability All fan systems
Definition The design air flow rate of the supply fan(s) at design conditions. This building descriptor sets the 100% point for the fan part-load curve.
Units cfm
Input Restrictions As designed. This input should be at least as great as the sum of the design air flow specified for each of the thermal blocks that are served by the fan system. For multiple deck systems, a separate entry should be made for each deck.
Baseline Rules The program shall automatically size the air flow at each thermal block to meet the loads. The design air flow rate calculation shall be based on a 20 degree temperature differential between supply air and the room air. The supply fan design air flow rate shall be the sum of the calculated design air flow for the thermal blocks served by the fan system.
Fan Control Method
Applicability All fan systems
Definition A description of how the supply (and return/relief) fan(s) are controlled. The options include:
  • Constant volume
  • Variable-flow, inlet or discharge dampers
  • Variable-flow, inlet guide vanes
  • Variable-flow, variable speed drive (VSD)
  • Variable-flow, variable pitch blades
  • Variable-flow, other
  • Two-speed
  • Constant volume, cycling (fan cycles with heating and cooling)
Units List (see above)
Input Restrictions As designed

 

Supply Fan Brake Horsepower
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design shaft brake horsepower of the supply fan(s). This input does not need to be supplied if the Supply Fan kW is supplied.
Units Horsepower (hp)
Input Restrictions As designed. If this building descriptor is specified for the proposed design, then the Static Pressure and Fan Efficiency are not.
Supply Fan Static Pressure
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The design static pressure for the supply fan. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the supply fan does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Supply Fan Efficiency
Applicability All fan systems, except those specified using the power-per-unit-flow method
Definition The efficiency of the fan at design conditions
Units Unitless
Input Restrictions As designed. The supply fan efficiency does not need to be specified if the supply fan brake horsepower (bhp) is specified.
Supply Motor Efficiency
Applicability All supply fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Fan Position
Applicability All supply fans
Definition The position of the supply fan relative to the cooling coil. The configuration is either draw through (fan is downstream of the coil) or blow through (fan is upstream of the coil).
Units List (see above)
Input Restrictions As designed.
Motor Position
Applicability All supply fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed.
Fan Part-Flow Power Curve
Applicability All variable flow fan systems
Definition A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow. The curve is typically represented as a quadratic equation with an absolute minimum power draw specified.
Units Unitless ratio
Input Restrictions

As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.

(6.7.3-1)

$Greater \;of$

$PLR = a + b \cdot FanRatio + c \cdot FanRatio^2 + d \cdot FanRatio^3$

$PLR = PowerMin $

where

PLR Ratio of fan power at part load conditions to full load fan power
PowerMin Minimum fan power
FanRatio Ratio of cfm at part-load to full-load cfm
a, b, c and d Constants from [bookref id="fan-curve-default-values"] below

[table title="Fan Curve Default Values" id="fan-curve-default-values"]

 

Fan Type - Control Type a b c d %PowerMin
AF or BI riding the curvea 0.1631 1.5901 -0.8817 0.1281 70%
AF or BI with inlet vanesa 0.9977 -0.659 0.9547 -0.2936 50%
FC riding the curvea 0.1224 0.612 0.5983 -0.3334 30%
FC with inlet vanesa 0.3038 -0.7608 2.2729 -0.8169 30%
Vane-axial with variable pitch bladesa 0.1639 -0.4016 1.9909 -0.7541 20%
Any fan with VSD (use for baseline building)b 0.0013 0.1470 0.9506 -0.0998 20%
VSD with static pressure resetc -0.0031 0.0991 1.0268 -0.1128 20%
Data Sources: 
a.     ECB Compliance Supplement, public review draft, Version 1.2, March 1996, but adjusted to be relatively consistent with the curve specified in the PRM.   
b.     The fan curve for VSD is specified in Table G3.1.3.15
c.     Advanced VAV System Design Guide, California Energy Commission, CEC Publication 500,-03-082 A-11, April 2005, but adjusted to be relatively consistent with the curve specified in the PRM..
Supply Fan kW
Applicability Fan systems that use the power-per-unit-flow method
Definition The supply fan power per unit of flow.
Units kW/cfm
Input Restrictions

As designed or specified in the manufacturers’ literature. For units with rated total cooling capacities less than 120,000 Btu/h, the user may default to a value calculated as follows:

(6.7.3-2)

$$ Fan_{kw} = 0.365 \times \frac{Q_{rated}}{30,000} $$

where

Fankw The supply fan power (kW)
Qrated The rated total cooling capacity (Btu/h)

Relief Fans

The baseline building has a return fan when the baseline building system is type 3 through 8 and the proposed design has a return fan.

Plenum Zone
Applicability Any system with return ducts or return air plenum
Definition A reference to the thermal block that serves as return plenum or where the return ducts are located
Units Text, unique
Input Restrictions As designed
Return Air Path
Applicability Any system with return ducts or return air plenum
Definition Describes the return path for air. This can be one of the following: ducted return; plenum return; or direct-to-unit.
Units List (see above)
Input Restrictions As designed
Return/Relief Air Rated Capacity
Applicability All systems with a return or relief fan
Definition The design air flow fan capacity of the return or relief fan(s). This sets the 100% fan flow point for the part-load curve (see below).
Units cfm
Input Restrictions As designed
Return/Relief Fan Brake Horsepower
Applicability Any system with return or relief fans that uses the brake horsepower method
Definition The design shaft brake horsepower of the return/relief fan(s)
Units Brake horsepower (bhp)
Input Restrictions As designed
Return/Relief Design Static Pressure
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for return fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the return fan does not need to be specified if the return fan brake horsepower (bhp) is specified.
Return/Relief Fan Efficiency
Applicability Any system with return or relief fans that uses the static pressure method
Definition The efficiency of the fan at design conditions
Units Unitless
Input Restrictions As designed. The return/relief fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Return/Relief Motor Efficiency
Applicability All return fans, except those specified using the power-per-unit-flow method
Definition The full-load efficiency of the motor serving the supply fan
Units Unitless
Input Restrictions As designed. Not applicable when the power-per-unit-flow method is used.
Motor Position
Applicability All return fans
Definition The position of the supply fan motor relative to the cooling air stream. The choices are: in the air stream or out of the air stream.
Units List (see above)
Input Restrictions As designed.
Fan Part-Flow Power Curve
Applicability All return fans for variable flow fan systems.
Definition A part-load power curve which represents the percentage full-load power draw of the supply fan as a function of the percentage full-load air flow.
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.
Return/Relief Fan kW
Applicability Any system with a return fan
Definition The supply fan power per unit of flow
Units kW/cfm
Input Restrictions As specified in the manufacturers’ literature

Exhaust Fan Systems

Exhaust fans include toilet exhaust, kitchen exhaust, as well as fume hoods in laboratories and other spaces. Some systems typically operate at constant flow, while flow varies for other systems depending on, for instance, the position of the sash for fume hoods. Exhaust fan flow is specified and scheduled for each thermal block. An exhaust fan system may serve multiple thermal blocks.

Exhaust Fan Name
Applicability All exhaust systems serving multiple thermal blocks
Definition A unique descriptor for each exhaust fan. This should be keyed to the construction documents, if possible, to facilitate plan checking. Exhaust rates and schedules at the thermal block level refer to this name.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans.
Exhaust Fan System Modeling Method
Applicability All exhaust fan systems
Definition Software commonly models fans in three ways. See definition for supply system modeling method.
Units List: power-per-unit-flow, static pressure or brake horsepower
Input Restrictions As designed
Exhaust Fan Rated Capacity
Applicability All exhaust systems
Definition The rated design air flow rate of the exhaust fan system. This building descriptor defines the 100% flow case for the part-flow curve. Actual air flow is the sum of the flow specified for each thermal block, as modified by the schedule for each thermal block.
Units cfm
Input Restrictions As designed
Fan Control Method
Applicability All exhaust fan systems
Definition A description of how the exhaust fan(s) are controlled. The options include:
  • Constant volume
  • Two-speed
  • Variable-flow, inlet or discharge dampers
  • Variable-flow, inlet guide vanes
  • Variable-flow, variable speed drive (VSD)
  • Variable-flow, variable pitch blades
Units List (see above)
Input Restrictions As designed, however, when exhaust fan flow at the thermal block level is varied through a schedule, one of the variable-flow options shall be specified.
Exhaust Fan Schedule
Applicability All exhaust fan systems
Definition A schedule that indicates when the exhaust fan system is available for operation. Exhaust fan flow is specified at the thermal block level.
Units Data structure: schedule, on/off
Input Restrictions The exhaust fan system shall be available during all periods when one or more thermal blocks served by the system are scheduling exhaust.
Exhaust Fan Brake Horsepower
Applicability All exhaust fan systems
Definition The design shaft brake horsepower of the exhaust fan(s).
Units Brake horsepower (bhp)
Input Restrictions As designed
Exhaust Fan Design Static Pressure
Applicability Any system with return or relief fans that uses the static pressure method
Definition The design static pressure for exhaust fan system. This is important for both fan electric energy usage and duct heat gain calculations.
Units Inches of water column (in. H20)
Input Restrictions As designed. The design static pressure for the exhaust fan does not need to be specified if the exhaust fan brake horsepower (bhp) is specified.
Exhaust Fan Efficiency
Applicability Any exhaust fan system that uses the static pressure method
Definition The efficiency of the exhaust fan at rated capacity
Units Unitless
Input Restrictions As designed. The exhaust fan efficiency does not need to be specified if the return fan brake horsepower (bhp) is specified.
Exhaust Fan Motor Efficiency
Applicability All exhaust fan systems
Definition The full-load efficiency of the motor serving the exhaust fan
Units Unitless
Input Restrictions As designed
Fan Part-Flow Power Curve
Applicability All variable flow exhaust fan systems
Definition A part-load power curve which represents the ratio full-load power draw of the exhaust fan as a function of the ratio full-load air flow.
Units Unitless ratio
Input Restrictions As designed. The default fan curve shall be selected from Equation (6.7.3-1) and [bookref id="fan-curve-default-values"] for the type of fan specified in the proposed design.
Exhaust Fan KW
Applicability All exhaust systems
Definition The fan power of the exhaust fan per unit of flow. This building descriptor is applicable only with the power-per-unit-flow method.
Units W/cfm
Input Restrictions As designed.