3.7.6 Heating Systems

General

Heating Source
Applicability All systems that provide heating
Definition The source of heating for the heating and preheat coils. The choices are:
  • Hot water
  • Steam
  • Electric resistance
  • Electric heat pump
  • Gas furnace
  • Gas heat pump (optional feature)
  • Oil furnace
  • Heat recovery (for preheat coils in proposed designs)
Units List (see above)
Input Restrictions As designed
Baseline Rules Based on the prescribed system type. Refer to the HVAC System Map in [bookref id="hvac-mapping"].

[table title="Heating Source for Baseline Building" id="heating-source-for-baseline-building"]

Baseline Building System Heating Source
System 1 – PTAC Gas Furnace
System 2 – PTHP Heat pump
System 3 – PSZ-AC Gas or Oil Furnace
System 4 – PSZ-HP Heat pump
System 5 – Packaged VAV with Reheat Hot water
System 6 – Packaged VAV with PFP boxes Electric Resistance
System 7 – VAV with Reheat Hot water
System 8 – VAV with PFP boxes Electric Resistance

Preheat Coil

Preheat Coil Capacity
Applicability Systems with a preheat coil located in the outside air stream
Definition The heating capacity of a preheating coil at design conditions.
Units Btu/h
Input Restrictions As designed
Baseline Rules If the proposed design has a preheat coil and it can be modeled in the baseline building system, then the baseline building also has a preheat coil sized to meet the preheat coil temperature specified for the proposed design. Autosize to maintain the preheat coil temperature of the proposed design.

Heating Coils

Systems with boilers have heating coils, including baseline building systems 1, 5 and 7.

Heating Coil Capacity
Applicability All systems with a heating coil
Definition The heating capacity of a heating coil at ARI conditions
Units Btu/h
Input Restrictions As designed. Adjust the capacity if the number of unmet load hours exceeds 300.
Baseline Rules Autosize with a heating oversizing factor of 25%. If the number of unmet load hours for the proposed design exceeds the number of unmet load hours for the baseline building by more than 50, reduce the heating coil capacity as indicated in [bookref id="procedure-for-adjusting-equipment-hvac-sizes-in-the-baseline-building"].

Furnace

Furnace Capacity
Applicability Systems with a furnace
Definition The full load heating capacity of the unit
Units Btu/h
Input Restrictions As designed. Adjust the capacity if the number of unmet load hours exceeds 300.
Baseline Rules Autosize with an oversizing factor of 25% (let the software determine heating capacity based on the building loads). If the number of unmet load hours for the proposed design exceeds the number of unmet load hours for the baseline building by more than 50, reduce the furnace capacity as indicated 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"].
Furnace Fuel Heating Efficiency
Applicability Systems with a furnace
Definition The full load thermal efficiency of either a gas or oil furnace at design conditions. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:

(6.7.6-1)

$ 1) All\ Single\ Package\ Equipment$
$ E_t = 0.005163 \times AFUE + 0.4033 $
$ 2) Split\ Systems, AFUE \leq 83.5$
$ E_t = 0.002907 \times AFUE + 0.5787$
$ 3) Split\ Systems, AFUE \textgreater 83.5 $
$ E_t = 0.011116 \times AFUE - 0.098185$

where

AFUE The annual fuel utilization efficiency (%)
Et The thermal efficiency (fraction)
Units Fraction
Input Restrictions As designed
Baseline Rules Look up the requirement from the equipment efficiency tables in Table 6.8.1E of Standard 90.1-2007 Table 6.2.1E of Standard 90.1-2001. Use the heating input of the proposed design system to determine the size category.
Furnace Fuel Heating Part Load Efficiency Curve
Applicability Systems with furnaces
Definition An adjustment factor that represents the percentage of full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:

(6.7.6-2)

$$ Fuel_{partload} = Fuel_{rated} \times F\!HeatP\!LC$$

(6.7.6-3)

$$ F\!HeatP\!LC = \left ( a + b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left( \frac{Q_{partload}}{Q_{rated}} \right )^2 \right )$$

where

FHeatPLC The Fuel Heating Part Load Efficiency Curve
Fuelpartload The fuel consumption at part load conditions (Btu/h)
Fuelrated The fuel consumption at full load (Btu/h)
Qpartload The capacity at part load conditions (Btu/h)
Qrated The capacity at rated conditions (Btu/h)

[table title="Furnace Efficiency Curve Coefficients" id="furnace-efficiency-curve-coefficients"]

Coefficient Furnace
a 0.0186100
b 1.0942090
c -0.1128190
Units Data structure
Input Restrictions As designed when data is available, otherwise use the default values are provided above.
Baseline Rules Use defaults
Furnace Fuel Heating Pilot
Applicability Systems that use a furnace for heating
Definition The fuel input for a pilot light on a furnace
Units Btu/h
Input Restrictions As designed
Baseline Rules Zero (pilotless ignition)
Furnace Fuel Heating Fan/Auxiliary
Applicability Systems that use a furnace for heating
Definition The fan energy in forced draft furnaces and the auxiliary (pumps and outdoor fan) energy in fuel-fired heat pumps
Units Kilowatts (kW)
Input Restrictions As designed
Baseline Rules Not applicable

Electric Heat Pump

Electric Heat Pump Heating Capacity
Applicability All heat pumps
Definition The full load heating capacity of the unit, excluding supplemental heating capacity at ARI rated conditions
Units Btu/h
Input Restrictions As designed
Baseline Rules Autosize and use an oversizing factor of 25% (let the software determine heating capacity based on the building loads). The autosized equipment may need to be downsized to achieve a maximum difference in unmet load hours between the proposed design and the baseline building of 50.
Electric Heat Pump Supplemental Heating Source
Applicability All heat pumps
Definition The auxiliary heating source for a heat pump heating system. The common control sequence is to lock out the heat pump compressor when the supplemental heat is activated. Other building descriptors may be needed if this is not the case. Choices for supplemental heat include:
  • Electric resistance
  • Gas furnace
  • Oil furnace
  • Hot water
  • Other
Units List (see above)
Input Restrictions As designed
Baseline Rules Electric resistance
Electric Heat Pump Heating Efficiency
Applicability All heat pumps
Definition

The heating efficiency of a heat pump at ARI rated conditions as a dimensionless ratio of output over input. The software must accommodate user input in terms of either the Coefficient of Performance (COP) or the Heating Season Performance Factor (HSPF). Where HSPF is provided, COP shall be calculated as follows:

(6.7.6-4)

$ 1) All\ Single\ Package\ Equipment$
$ C\!O\!P = 0.2778 \times H\!S\!P\!F + 0.9667 $
$ 2) All\ Split\ Systems$
$ C\!O\!P = 0.4813 \times H\!S\!P\!F - 0.2606$

For all unitary and applied equipment where the fan energy is part of the equipment efficiency rating, the COP shall be adjusted as follows to remove the fan energy:

(6.7.6-5)

$$ C\!O\!P_{adj} = \frac{\frac{H\!C\!A\!P_{rated}}{3.413} - B\!H\!P_{supply} \times 0.7457}{\frac{H\!C\!A\!P_{rated}}{C\!O\!P \times 3.413} - B\!H\!P_{supply} \times 0.7457}$$

where

COPadj The adjusted coefficient of performance for simulation purposes
COP The ARI rated coefficient of performance
HCAPrated The ARI rated heating capacity of a packaged unit (kBtu/h)
BHPsupply The supply fan brake horsepower (bhp).

Refer to building descriptor Supply Fan BHP.

Units Unitless
Input Restrictions As designed
Baseline Rules For the purpose of green building ratings, look up the requirement from the equipment efficiency Table 6.8.1B and Table 6.8.1D in ASHRAE Standard 90.1-2007. For the purpose of tax deduction calculations, find the equipment efficiency from Table 6.2.1B and 6.2.1D in ASHRAE Standard 90.1-2001. Use the heating capacity of the proposed design to determine the size category.
Electric Heat Pump Heating Capacity Adjustment Curve(s)
Applicability All heat pumps
Definition

A curve or group of curves that represent the available heat-pump heating capacity as a function of evaporator and condenser conditions. The default curves are given as follows:

(6.7.6-6)

$$ Q_{available} = C\!A\!P\_FT \times Q_{rated}$$For air-cooled heat pumps:

(6.7.6-7)

$$ C\!A\!P\_FT = a + b \times t_{odb} + c \times \left. t_{odb}\right. ^2 + d \times \left. t_{odb}\right. ^3 $$

For water-cooled heat pumps:

(6.7.6-8)

$$ C\!A\!P\_FT = a + b \times t_{db} + d \times t_{wt}$$

where

Qavailable Available heating capacity at present evaporator and condenser conditions (kBtu/h)
tdb The entering coil dry-bulb temperature (°F)
twt The water supply temperature (°F)
todb The outside-air dry-bulb temperature (°F)
Qrated Rated capacity at ARI conditions (in kBtu/h

[table title="Heat Pump Capacity Adjustment Curves (CAP-FT)" id="heat-pump-capacity-adjustment-curves-(CAP-FT)"]

Coefficient Water-Source Air-Source
a 0.4886534 0.2536714
b -0.0067774 0.0104351
c N/A 0.0001861
d 0.0140823 -0.0000015
Units Data structure
Input Restrictions User may input curves or use default curves. If defaults are overridden, supporting documentation shall be provided.
Baseline Rules Use default curves.
Electric Heat Pump Heating Efficiency Adjustment Curve(s)
Applicability All heat pumps
Definition

A curve or group of curves that varies the heat-pump heating efficiency as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(6.7.6-9)

$$ P\!LR = \frac{Q_{operating}}{Q_{available}\left ( t_{db},t_{odb/wt}\right )}$$

(6.7.6-10)

$$ E\!I\!R\_F\!P\!LR = a + b \times P\!LR + c \times P\!LR^2 + d \times P\!LR^3 $$

Air Source Heat Pumps:

(6.7.6-11)

$$ E\!I\!R\_FT = a + b \times \left ( \frac{t_{odb}}{t_{db}} \right ) + c \times \left ( \frac{t_{odb}}{t_{db}} \right ) ^2 + d \times \left ( \frac{t_{odb}}{t_{db}} \right )^3$$Water Source Heat Pumps:

(6.7.6-12)

$$ E\!I\!R\_FT = a + b \times t_{wt} + d \times t_{db}$$

(6.7.6-13)

$$ P_{operating} = P_{rated} \times E\!I\!R\_F\!P\!LR \times E\!I\!R\_FT \times C\!AP\_FT $$

where

PLR Part load ratio based on available capacity (not rated capacity)
EIR-FPLR A multiplier on the EIR of the heat pump as a function of part load ratio
EIR-FT A multiplier on the EIR of the heat pump as a function of the wet-bulb temperature entering the coil and the outdoor dry-bulb temperature
Qoperating Present load on heat pump (Btu/h)
Qavailable Heat pump available capacity at present evaporator and condenser conditions (Btu/h).
tdb The entering coil dry-bulb temperature (°F)
twt The water supply temperature (°F)
todb The outside air dry-bulb temperature (°F)
Prated Rated power draw at ARI conditions (kW)
Poperating Power draw at specified operating conditions (kW)

[table title="Heat Pump Heating Efficiency Adjustment (Curves)" id="heat-pump-heating-efficiency-adjustment-curves"]

Coefficient Air-and Water-Source
EIR-FPLR
Water-Source
EIR-FT
Air-Source
EIR-FT
a 0.0856522 1.3876102 2.4600298
b 0.9388137 0.0060479 -0.0622539
c -0.1834361 N/A 0.0008800
d 0.1589702 -0.0115852 -0.0000046
Units None
Input Restrictions User may input curves or use default curves. If defaults are overridden, documentation shall be provided.
Baseline Rules Use default curves
Electric Heat Pump Supplemental Heating Capacity
Applicability All heat pumps
Definition The design heating capacity of a heat pump supplemental heating coil at ARI conditions
Units Btu/h
Input Restrictions As designed
Baseline Rules Autosize
Electric Supplemental Heating Control Temp
Applicability All heat pumps
Definition The outside dry-bulb temperature below which the heat pump supplemental heating is allowed to operate
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Default to 40°F
Baseline Rules 40°F
Coil Defrost
Applicability Air-cooled electric heat pump
Definition The defrost control mechanism for an air-cooled heat pump. The choices are:
  • Hot-gas defrost, on-demand
  • Hot-gas defrost, timed 3.5 minute cycle
  • Electric resistance defrost, on-demand
  • Electric resistance defrost, timed 3.5 minute cycle
Defrost shall be enabled whenever the outside air dry-bulb temperature drops below 40°F.
Units List (see above)
Input Restrictions Default to use hot-gas defrost, timed 3.5 minute cycle. User may select any of the above.
Baseline Rules The baseline building uses the default.
Coil Defrost kW
Applicability Heat pumps with electric resistance defrost
Definition The capacity of the electric resistance defrost heater
Units Kilowatts (kW)
Input Restrictions As designed. This descriptor defaults to 0 if nothing is entered.
Baseline Rules Not applicable. Baseline building systems 2 and 4 use hot-gas, timed 3.5 minute cycle.
Crank Case Heater kW
Applicability All heat pumps
Definition The capacity of the electric resistance heater in the crank case of a direct expansion (DX) compressor. The crank case heater operates only when the compressor is off.
Units Kilowatts (kW)
Input Restrictions As designed. This descriptor defaults to 0 if nothing is entered.
Baseline Rules Zero (0)
Crank Case Heater Shutoff Temperature
Applicability All heat pumps
Definition The outdoor air dry-bulb temperature above which the crank case heater is not permitted to operate.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. This descriptor defaults to 50°F.
Baseline Rules 50°F

Heat Recovery

Exhaust to Outside Heat Recovery Effectiveness
Applicability Any system with outside air heat recovery
Definition

The effectiveness of an air-to-air heat exchanger between the building exhaust and entering outside air streams. Effectiveness is defined as follows:

(6.7.6-14)

$$ H\!R\!E\!F\!F = \frac{\left ( E\!E\!A_{db} - E\!L\!A_{db}\right )}{\left ( E\!E\!A_{db} - O\!S\!A_{db}\right )}$$where

HREFF The air-to-air heat exchanger effectiveness
EEAdb The exhaust air dry-bulb temperature entering the heat exchanger
ELAdb The exhaust air dry-bulb temperature leaving the heat exchanger
OSAdb The outside air dry-bulb temperature
Units Ratio
Input Restrictions As designed
Baseline Rules Required for fan systems with a design supply air flow rate of 5,000 cfm or greater if the minimum outside air quantity is 70% of the design air flow rate. If required, the energy recovery system should have at least 50% effectiveness. Energy recovery is not required for heating systems in climate zones 1 through 3 or for cooling systems in climate zones 3c, 4c, 5b, 5c, 6b, 7 and 8.
Condenser Heat Recovery Effectiveness
Applicability Systems that use recover heat from a condenser
Definition The percentage of heat rejection at design conditions from a DX or heat pump unit in cooling mode that is available for space or water heating.
Units Percent (%)
Input Restrictions As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.
Baseline Rules Not applicable for most conditions. Condenser heat recovery is required for 24-hour facilities when the heat rejection exceeds 6,000,000 Btu/h and the design service water heating load exceeds 1,000,000 Btu/h. When required, the effectiveness will be 60%.
Heat Recovery Use
Applicability Systems that use heat recovery
Definition The end use of the heat recovered from a DX or heat pump unit. The choices are:
  • Reheat coils
  • Water heating
Units List (see above)
Input Restrictions As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.
Baseline Rules Not applicable for most conditions. The end use will be water heating if required for 24-hour facility operation.
90.1-2007

/3765-electric-heat-pumpGeneral

Heating Source
Applicability All systems that provide heating
Definition The source of heating for the heating and preheat coils. The choices are:
  • Hot water
  • Steam
  • Electric resistance
  • Electric heat pump
  • Gas furnace
  • Gas heat pump (optional feature)
  • Oil furnace
  • Heat recovery (for preheat coils in proposed designs)
Units List (see above)
Input Restrictions As designed
Baseline Rules Based on the prescribed system type. Refer to the HVAC System Map in [bookref id="hvac-mapping"].

[table title="Heating Source for Baseline Building" id="heating-source-for-baseline-building"]

Baseline Building System Heating Source
System 1 – PTAC Gas Furnace
System 2 – PTHP Heat pump
System 3 – PSZ-AC Gas or Oil Furnace
System 4 – PSZ-HP Heat pump
System 5 – Packaged VAV with Reheat Hot water
System 6 – Packaged VAV with PFP boxes Electric Resistance
System 7 – VAV with Reheat Hot water
System 8 – VAV with PFP boxes Electric Resistance

Preheat Coil

Preheat Coil Capacity
Applicability Systems with a preheat coil located in the outside air stream
Definition The heating capacity of a preheating coil at design conditions.
Units Btu/h
Input Restrictions As designed
Baseline Rules If the proposed design has a preheat coil and it can be modeled in the baseline building system, then the baseline building also has a preheat coil sized to meet the preheat coil temperature specified for the proposed design. Autosize to maintain the preheat coil temperature of the proposed design.

Heating Coils

Systems with boilers have heating coils, including baseline building systems 1, 5 and 7.

Heating Coil Capacity
Applicability All systems with a heating coil
Definition The heating capacity of a heating coil at ARI conditions
Units Btu/h
Input Restrictions As designed. Adjust the capacity if the number of unmet load hours exceeds 300.
Baseline Rules Autosize with a heating oversizing factor of 25%. If the number of unmet load hours for the proposed design exceeds the number of unmet load hours for the baseline building by more than 50, reduce the heating coil capacity as indicated in [bookref id="procedure-for-adjusting-equipment-hvac-sizes-in-the-baseline-building"].

Furnace

Furnace Capacity
Applicability Systems with a furnace
Definition The full load heating capacity of the unit
Units Btu/h
Input Restrictions As designed. Adjust the capacity if the number of unmet load hours exceeds 300.
Baseline Rules Autosize with an oversizing factor of 25% (let the software determine heating capacity based on the building loads). If the number of unmet load hours for the proposed design exceeds the number of unmet load hours for the baseline building by more than 50, reduce the furnace capacity as indicated 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"].
Furnace Fuel Heating Efficiency
Applicability Systems with a furnace
Definition The full load thermal efficiency of either a gas or oil furnace at design conditions. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:

(6.7.6-1)

$ 1) All\ Single\ Package\ Equipment$
$ E_t = 0.005163 \times AFUE + 0.4033 $
$ 2) Split\ Systems, AFUE \leq 83.5$
$ E_t = 0.002907 \times AFUE + 0.5787$
$ 3) Split\ Systems, AFUE \textgreater 83.5 $
$ E_t = 0.011116 \times AFUE - 0.098185$

where

AFUE The annual fuel utilization efficiency (%)
Et The thermal efficiency (fraction)
Units Fraction
Input Restrictions As designed
Baseline Rules Look up the requirement from the equipment efficiency tables in Table 6.8.1E of Standard 90.1-2007. Use the heating input of the proposed design system to determine the size category.
Furnace Fuel Heating Part Load Efficiency Curve
Applicability Systems with furnaces
Definition An adjustment factor that represents the percentage of full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:

(6.7.6-2)

$$ Fuel_{partload} = Fuel_{rated} \times F\!HeatP\!LC$$

(6.7.6-3)

$$ F\!HeatP\!LC = \left ( a + b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left( \frac{Q_{partload}}{Q_{rated}} \right )^2 \right )$$

where

FHeatPLC The Fuel Heating Part Load Efficiency Curve
Fuelpartload The fuel consumption at part load conditions (Btu/h)
Fuelrated The fuel consumption at full load (Btu/h)
Qpartload The capacity at part load conditions (Btu/h)
Qrated The capacity at rated conditions (Btu/h)

[table title="Furnace Efficiency Curve Coefficients" id="furnace-efficiency-curve-coefficients"]

Coefficient Furnace
a 0.0186100
b 1.0942090
c -0.1128190
Units Data structure
Input Restrictions As designed when data is available, otherwise use the default values are provided above.
Baseline Rules Use defaults
Furnace Fuel Heating Pilot
Applicability Systems that use a furnace for heating
Definition The fuel input for a pilot light on a furnace
Units Btu/h
Input Restrictions As designed
Baseline Rules Zero (pilotless ignition)
Furnace Fuel Heating Fan/Auxiliary
Applicability Systems that use a furnace for heating
Definition The fan energy in forced draft furnaces and the auxiliary (pumps and outdoor fan) energy in fuel-fired heat pumps
Units Kilowatts (kW)
Input Restrictions As designed
Baseline Rules Not applicable

Electric Heat Pump

Electric Heat Pump Heating Capacity
Applicability All heat pumps
Definition The full load heating capacity of the unit, excluding supplemental heating capacity at ARI rated conditions
Units Btu/h
Input Restrictions As designed
Baseline Rules Autosize and use an oversizing factor of 25% (let the software determine heating capacity based on the building loads). The autosized equipment may need to be downsized to achieve a maximum difference in unmet load hours between the proposed design and the baseline building of 50.
Electric Heat Pump Supplemental Heating Source
Applicability All heat pumps
Definition The auxiliary heating source for a heat pump heating system. The common control sequence is to lock out the heat pump compressor when the supplemental heat is activated. Other building descriptors may be needed if this is not the case. Choices for supplemental heat include:
  • Electric resistance
  • Gas furnace
  • Oil furnace
  • Hot water
  • Other
Units List (see above)
Input Restrictions As designed
Baseline Rules Electric resistance
Electric Heat Pump Heating Efficiency
Applicability All heat pumps
Definition

The heating efficiency of a heat pump at ARI rated conditions as a dimensionless ratio of output over input. The software must accommodate user input in terms of either the Coefficient of Performance (COP) or the Heating Season Performance Factor (HSPF). Where HSPF is provided, COP shall be calculated as follows:

(6.7.6-4)

$ 1) All\ Single\ Package\ Equipment$
$ C\!O\!P = 0.2778 \times H\!S\!P\!F + 0.9667 $
$ 2) All\ Split\ Systems$
$ C\!O\!P = 0.4813 \times H\!S\!P\!F - 0.2606$

For all unitary and applied equipment where the fan energy is part of the equipment efficiency rating, the COP shall be adjusted as follows to remove the fan energy:

(6.7.6-5)

$$ C\!O\!P_{adj} = \frac{\frac{H\!C\!A\!P_{rated}}{3.413} - B\!H\!P_{supply} \times 0.7457}{\frac{H\!C\!A\!P_{rated}}{C\!O\!P \times 3.413} - B\!H\!P_{supply} \times 0.7457}$$

where

COPadj The adjusted coefficient of performance for simulation purposes
COP The ARI rated coefficient of performance
HCAPrated The ARI rated heating capacity of a packaged unit (kBtu/h)
BHPsupply The supply fan brake horsepower (bhp).

Refer to building descriptor Supply Fan BHP.

Units Unitless
Input Restrictions As designed
Baseline Rules For the purpose of green building ratings, look up the requirement from the equipment efficiency Table 6.8.1B and Table 6.8.1D in ASHRAE Standard 90.1-2007. Use the heating capacity of the proposed design to determine the size category.
Electric Heat Pump Heating Capacity Adjustment Curve(s)
Applicability All heat pumps
Definition

A curve or group of curves that represent the available heat-pump heating capacity as a function of evaporator and condenser conditions. The default curves are given as follows:

(6.7.6-6)

$$ Q_{available} = C\!A\!P\_FT \times Q_{rated}$$For air-cooled heat pumps:

(6.7.6-7)

$$ C\!A\!P\_FT = a + b \times t_{odb} + c \times \left. t_{odb}\right. ^2 + d \times \left. t_{odb}\right. ^3 $$

For water-cooled heat pumps:

(6.7.6-8)

$$ C\!A\!P\_FT = a + b \times t_{db} + d \times t_{wt}$$

where

Qavailable Available heating capacity at present evaporator and condenser conditions (kBtu/h)
tdb The entering coil dry-bulb temperature (°F)
twt The water supply temperature (°F)
todb The outside-air dry-bulb temperature (°F)
Qrated Rated capacity at ARI conditions (in kBtu/h

[table title="Heat Pump Capacity Adjustment Curves (CAP-FT)" id="heat-pump-capacity-adjustment-curves-(CAP-FT)"]

Coefficient Water-Source Air-Source
a 0.4886534 0.2536714
b -0.0067774 0.0104351
c N/A 0.0001861
d 0.0140823 -0.0000015
Units Data structure
Input Restrictions User may input curves or use default curves. If defaults are overridden, supporting documentation shall be provided.
Baseline Rules Use default curves.
Electric Heat Pump Heating Efficiency Adjustment Curve(s)
Applicability All heat pumps
Definition

A curve or group of curves that varies the heat-pump heating efficiency as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(6.7.6-9)

$$ P\!LR = \frac{Q_{operating}}{Q_{available}\left ( t_{db},t_{odb/wt}\right )}$$

(6.7.6-10)

$$ E\!I\!R\_F\!P\!LR = a + b \times P\!LR + c \times P\!LR^2 + d \times P\!LR^3 $$

Air Source Heat Pumps:

(6.7.6-11)

$$ E\!I\!R\_FT = a + b \times \left ( \frac{t_{odb}}{t_{db}} \right ) + c \times \left ( \frac{t_{odb}}{t_{db}} \right ) ^2 + d \times \left ( \frac{t_{odb}}{t_{db}} \right )^3$$Water Source Heat Pumps:

(6.7.6-12)

$$ E\!I\!R\_FT = a + b \times t_{wt} + d \times t_{db}$$

(6.7.6-13)

$$ P_{operating} = P_{rated} \times E\!I\!R\_F\!P\!LR \times E\!I\!R\_FT \times C\!AP\_FT $$

where

PLR Part load ratio based on available capacity (not rated capacity)
EIR-FPLR A multiplier on the EIR of the heat pump as a function of part load ratio
EIR-FT A multiplier on the EIR of the heat pump as a function of the wet-bulb temperature entering the coil and the outdoor dry-bulb temperature
Qoperating Present load on heat pump (Btu/h)
Qavailable Heat pump available capacity at present evaporator and condenser conditions (Btu/h).
tdb The entering coil dry-bulb temperature (°F)
twt The water supply temperature (°F)
todb The outside air dry-bulb temperature (°F)
Prated Rated power draw at ARI conditions (kW)
Poperating Power draw at specified operating conditions (kW)

[table title="Heat Pump Heating Efficiency Adjustment (Curves)" id="heat-pump-heating-efficiency-adjustment-curves"]

Coefficient Air-and Water-Source
EIR-FPLR
Water-Source
EIR-FT
Air-Source
EIR-FT
a 0.0856522 1.3876102 2.4600298
b 0.9388137 0.0060479 -0.0622539
c -0.1834361 N/A 0.0008800
d 0.1589702 -0.0115852 -0.0000046
Units None
Input Restrictions User may input curves or use default curves. If defaults are overridden, documentation shall be provided.
Baseline Rules Use default curves
Electric Heat Pump Supplemental Heating Capacity
Applicability All heat pumps
Definition The design heating capacity of a heat pump supplemental heating coil at ARI conditions
Units Btu/h
Input Restrictions As designed
Baseline Rules Autosize
Electric Supplemental Heating Control Temp
Applicability All heat pumps
Definition The outside dry-bulb temperature below which the heat pump supplemental heating is allowed to operate
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Default to 40°F
Baseline Rules 40°F
Coil Defrost
Applicability Air-cooled electric heat pump
Definition The defrost control mechanism for an air-cooled heat pump. The choices are:
  • Hot-gas defrost, on-demand
  • Hot-gas defrost, timed 3.5 minute cycle
  • Electric resistance defrost, on-demand
  • Electric resistance defrost, timed 3.5 minute cycle
Defrost shall be enabled whenever the outside air dry-bulb temperature drops below 40°F.
Units List (see above)
Input Restrictions Default to use hot-gas defrost, timed 3.5 minute cycle. User may select any of the above.
Baseline Rules The baseline building uses the default.
Coil Defrost kW
Applicability Heat pumps with electric resistance defrost
Definition The capacity of the electric resistance defrost heater
Units Kilowatts (kW)
Input Restrictions As designed. This descriptor defaults to 0 if nothing is entered.
Baseline Rules Not applicable. Baseline building systems 2 and 4 use hot-gas, timed 3.5 minute cycle.
Crank Case Heater kW
Applicability All heat pumps
Definition The capacity of the electric resistance heater in the crank case of a direct expansion (DX) compressor. The crank case heater operates only when the compressor is off.
Units Kilowatts (kW)
Input Restrictions As designed. This descriptor defaults to 0 if nothing is entered.
Baseline Rules Zero (0)
Crank Case Heater Shutoff Temperature
Applicability All heat pumps
Definition The outdoor air dry-bulb temperature above which the crank case heater is not permitted to operate.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. This descriptor defaults to 50°F.
Baseline Rules 50°F

Heat Recovery

Exhaust to Outside Heat Recovery Effectiveness
Applicability Any system with outside air heat recovery
Definition

The effectiveness of an air-to-air heat exchanger between the building exhaust and entering outside air streams. Effectiveness is defined as follows:

(6.7.6-14)

$$ H\!R\!E\!F\!F = \frac{\left ( E\!E\!A_{db} - E\!L\!A_{db}\right )}{\left ( E\!E\!A_{db} - O\!S\!A_{db}\right )}$$where

HREFF The air-to-air heat exchanger effectiveness
EEAdb The exhaust air dry-bulb temperature entering the heat exchanger
ELAdb The exhaust air dry-bulb temperature leaving the heat exchanger
OSAdb The outside air dry-bulb temperature
Units Ratio
Input Restrictions As designed
Baseline Rules Required for fan systems with a design supply air flow rate of 5,000 cfm or greater if the minimum outside air quantity is 70% of the design air flow rate. If required, the energy recovery system should have at least 50% effectiveness. Energy recovery is not required for heating systems in climate zones 1 through 3 or for cooling systems in climate zones 3c, 4c, 5b, 5c, 6b, 7 and 8.
Condenser Heat Recovery Effectiveness
Applicability Systems that use recover heat from a condenser
Definition The percentage of heat rejection at design conditions from a DX or heat pump unit in cooling mode that is available for space or water heating.
Units Percent (%)
Input Restrictions As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.
Baseline Rules Not applicable for most conditions. Condenser heat recovery is required for 24-hour facilities when the heat rejection exceeds 6,000,000 Btu/h and the design service water heating load exceeds 1,000,000 Btu/h. When required, the effectiveness will be 60%.
Heat Recovery Use
Applicability Systems that use heat recovery
Definition The end use of the heat recovered from a DX or heat pump unit. The choices are:
  • Reheat coils
  • Water heating
Units List (see above)
Input Restrictions As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.
Baseline Rules Not applicable for most conditions. The end use will be water heating if required for 24-hour facility operation.
90.1-2010

General

Heating Source
Applicability All systems that provide heating
Definition The source of heating for the heating and preheat coils. The choices are:
  • Hot water
  • Steam
  • Electric resistance
  • Electric heat pump
  • Gas furnace
  • Gas heat pump (optional feature)
  • Oil furnace
  • Heat recovery (for preheat coils in proposed designs)
Units List (see above)
Input Restrictions As designed
Baseline Rules Based on the prescribed system type. Refer to the HVAC System Map in Figure 6.1.2-1.

Table 6.7.6-1: Heating Source for Baseline Building

Baseline Building System Heating Source
System 1 – PTAC Gas Furnace
System 2 – PTHP Heat pump
System 3 – PSZ-AC Gas or Oil Furnace
System 4 – PSZ-HP Heat pump
System 5 – Packaged VAV with Reheat Hot water
System 6 – Packaged VAV with PFP boxes Electric Resistance
System 7 – VAV with Reheat Hot water
System 8 – VAV with PFP boxes Electric Resistance
System 9 – Heating and Ventilation Electric Resistance
System 10 – Heating and Ventilation Gas Furnace

Preheat Coil

Preheat Coil Capacity
Applicability Systems with a preheat coil located in the outside air stream
Definition The heating capacity of a preheating coil at design conditions.
Units Btu/h
Input Restrictions As designed
Baseline Rules If the proposed design has a preheat coil and it can be modeled in the baseline building system, then the baseline building also has a preheat coil sized to meet the preheat coil temperature specified for the proposed design. Autosize to maintain the preheat coil temperature of the proposed design.

Heating Coils

Systems with boilers have heating coils, including baseline building systems 1, 5 and 7.

Heating Coil Capacity
Applicability All systems with a heating coil
Definition The heating capacity of a heating coil at ARI conditions
Units Btu/h
Input Restrictions As designed. Adjust the capacity if the number of unmet load hours exceeds 300.
Baseline Rules Autosize with a heating oversizing factor of 25%. 

Furnace

Furnace Capacity
Applicability Systems with a furnace
Definition The full load heating capacity of the unit
Units Btu/h
Input Restrictions As designed. Adjust the capacity if the number of unmet load hours exceeds 300.
Baseline Rules Autosize with an oversizing factor of 25% (let the software determine heating capacity based on the building loads). 
Furnace Fuel Heating Efficiency
Applicability Systems with a furnace
Definition The full load thermal efficiency of either a gas or oil furnace at design conditions. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:

(6.7.6-1)

$ 1) All\ Single\ Package\ Equipment$
$ E_t = 0.005163 \times AFUE + 0.4033 $
$ 2) Split\ Systems, AFUE \leq 83.5$
$ E_t = 0.002907 \times AFUE + 0.5787$
$ 3) Split\ Systems, AFUE \textgreater 83.5 $
$ E_t = 0.011116 \times AFUE - 0.098185$

where

AFUE The annual fuel utilization efficiency (%)
Et The thermal efficiency (fraction)
Units Fraction
Input Restrictions As designed
Baseline Rules Look up the requirement from the equipment efficiency tables in Table 6.8.1E of Standard 90.1-2007. Use the heating input of the proposed design system to determine the size category.
Furnace Fuel Heating Part Load Efficiency Curve
Applicability Systems with furnaces
Definition An adjustment factor that represents the percentage of full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:

(6.7.6-2)

$$ Fuel_{partload} = Fuel_{rated} \times F\!HeatP\!LC$$

(6.7.6-3)

$$ F\!HeatP\!LC = \left ( a + b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left( \frac{Q_{partload}}{Q_{rated}} \right )^2 \right )$$

where

FHeatPLC The Fuel Heating Part Load Efficiency Curve
Fuelpartload The fuel consumption at part load conditions (Btu/h)
Fuelrated The fuel consumption at full load (Btu/h)
Qpartload The capacity at part load conditions (Btu/h)
Qrated The capacity at rated conditions (Btu/h)

Table 6.7.6-2: Furnace Efficiency Curve Coefficients

Coefficient Furnace
a 0.0186100
b 1.0942090
c -0.1128190
Units Data structure
Input Restrictions As designed when data is available, otherwise use the default values are provided above.
Baseline Rules Use defaults
Furnace Fuel Heating Pilot
Applicability Systems that use a furnace for heating
Definition The fuel input for a pilot light on a furnace
Units Btu/h
Input Restrictions As designed
Baseline Rules Zero (pilotless ignition)
Furnace Fuel Heating Fan/Auxiliary
Applicability Systems that use a furnace for heating
Definition The fan energy in forced draft furnaces and the auxiliary (pumps and outdoor fan) energy in fuel-fired heat pumps
Units Kilowatts (kW)
Input Restrictions As designed
Baseline Rules Not applicable

Electric Heat Pump

Electric Heat Pump Heating Capacity
Applicability All heat pumps
Definition The full load heating capacity of the unit, excluding supplemental heating capacity at ARI rated conditions
Units Btu/h
Input Restrictions As designed
Baseline Rules Autosize and use an oversizing factor of 25% (let the software determine heating capacity based on the building loads). The autosized equipment may need to be downsized to achieve a maximum difference in unmet load hours between the proposed design and the baseline building of 50.
Electric Heat Pump Supplemental Heating Source
Applicability All heat pumps
Definition The auxiliary heating source for a heat pump heating system. The common control sequence is to lock out the heat pump compressor when the supplemental heat is activated. Other building descriptors may be needed if this is not the case. Choices for supplemental heat include:
  • Electric resistance
  • Gas furnace
  • Oil furnace
  • Hot water
  • Other
Units List (see above)
Input Restrictions As designed
Baseline Rules Electric resistance
Electric Heat Pump Heating Efficiency
Applicability All heat pumps
Definition

The heating efficiency of a heat pump at ARI rated conditions as a dimensionless ratio of output over input. The software must accommodate user input in terms of either the Coefficient of Performance (COP) or the Heating Season Performance Factor (HSPF). Where HSPF is provided, COP shall be calculated as follows:

(6.7.6-4)

$ 1) All\ Single\ Package\ Equipment$
$ C\!O\!P = 0.2778 \times H\!S\!P\!F + 0.9667 $
$ 2) All\ Split\ Systems$
$ C\!O\!P = 0.4813 \times H\!S\!P\!F - 0.2606$

For all unitary and applied equipment where the fan energy is part of the equipment efficiency rating, the COP shall be adjusted as follows to remove the fan energy:

(6.7.6-5)

$$ C\!O\!P_{adj} = \frac{\frac{H\!C\!A\!P_{rated}}{3.413} - B\!H\!P_{supply} \times 0.7457}{\frac{H\!C\!A\!P_{rated}}{C\!O\!P \times 3.413} - B\!H\!P_{supply} \times 0.7457}$$

where

COPadj The adjusted coefficient of performance for simulation purposes
COP The ARI rated coefficient of performance
HCAPrated The ARI rated heating capacity of a packaged unit (kBtu/h)
BHPsupply The supply fan brake horsepower (bhp).

Refer to building descriptor Supply Fan BHP.

Units Unitless
Input Restrictions As designed
Baseline Rules For the purpose of green building ratings, look up the requirement from the equipment efficiency Table 6.8.1B and Table 6.8.1D in ASHRAE Standard 90.1-2007. Use the heating capacity of the proposed design to determine the size category.
Electric Heat Pump Heating Capacity Adjustment Curve(s)
Applicability All heat pumps
Definition

A curve or group of curves that represent the available heat-pump heating capacity as a function of evaporator and condenser conditions. The default curves are given as follows:

(6.7.6-6)

$$ Q_{available} = C\!A\!P\_FT \times Q_{rated}$$For air-cooled heat pumps:

(6.7.6-7)

$$ C\!A\!P\_FT = a + b \times t_{odb} + c \times \left. t_{odb}\right. ^2 + d \times \left. t_{odb}\right. ^3 $$

For water-cooled heat pumps:

(6.7.6-8)

$$ C\!A\!P\_FT = a + b \times t_{db} + d \times t_{wt}$$

where

Qavailable Available heating capacity at present evaporator and condenser conditions (kBtu/h)
tdb The entering coil dry-bulb temperature (°F)
twt The water supply temperature (°F)
todb The outside-air dry-bulb temperature (°F)
Qrated Rated capacity at ARI conditions (in kBtu/h

Table 6.7.6-3: Heat Pump Capacity Adjustment Curves (CAP-FT)

Coefficient Water-Source Air-Source
a 0.4886534 0.2536714
b -0.0067774 0.0104351
c N/A 0.0001861
d 0.0140823 -0.0000015
Units Data structure
Input Restrictions User may input curves or use default curves. If defaults are overridden, supporting documentation shall be provided.
Baseline Rules Use default curves.
Electric Heat Pump Heating Efficiency Adjustment Curve(s)
Applicability All heat pumps
Definition

A curve or group of curves that varies the heat-pump heating efficiency as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(6.7.6-9)

$$ P\!LR = \frac{Q_{operating}}{Q_{available}\left ( t_{db},t_{odb/wt}\right )}$$

(6.7.6-10)

$$ E\!I\!R\_F\!P\!LR = a + b \times P\!LR + c \times P\!LR^2 + d \times P\!LR^3 $$

Air Source Heat Pumps:

(6.7.6-11)

$$ E\!I\!R\_FT = a + b \times \left ( \frac{t_{odb}}{t_{db}} \right ) + c \times \left ( \frac{t_{odb}}{t_{db}} \right ) ^2 + d \times \left ( \frac{t_{odb}}{t_{db}} \right )^3$$Water Source Heat Pumps:

(6.7.6-12)

$$ E\!I\!R\_FT = a + b \times t_{wt} + d \times t_{db}$$

(6.7.6-13)

$$ P_{operating} = P_{rated} \times E\!I\!R\_F\!P\!LR \times E\!I\!R\_FT \times C\!AP\_FT $$

where

PLR Part load ratio based on available capacity (not rated capacity)
EIR-FPLR A multiplier on the EIR of the heat pump as a function of part load ratio
EIR-FT A multiplier on the EIR of the heat pump as a function of the wet-bulb temperature entering the coil and the outdoor dry-bulb temperature
Qoperating Present load on heat pump (Btu/h)
Qavailable Heat pump available capacity at present evaporator and condenser conditions (Btu/h).
tdb The entering coil dry-bulb temperature (°F)
twt The water supply temperature (°F)
todb The outside air dry-bulb temperature (°F)
Prated Rated power draw at ARI conditions (kW)
Poperating Power draw at specified operating conditions (kW)

Table 6.7.6-4: Heat Pump Heating Efficiency Adjustment (Curves)

Coefficient Air-and Water-Source
EIR-FPLR
Water-Source
EIR-FT
Air-Source
EIR-FT
a 0.0856522 1.3876102 2.4600298
b 0.9388137 0.0060479 -0.0622539
c -0.1834361 N/A 0.0008800
d 0.1589702 -0.0115852 -0.0000046
Units None
Input Restrictions User may input curves or use default curves. If defaults are overridden, documentation shall be provided.
Baseline Rules Use default curves
Electric Heat Pump Supplemental Heating Capacity
Applicability All heat pumps
Definition The design heating capacity of a heat pump supplemental heating coil at ARI conditions
Units Btu/h
Input Restrictions As designed
Baseline Rules Autosize
Electric Supplemental Heating Control Temp
Applicability All heat pumps
Definition The outside dry-bulb temperature below which the heat pump supplemental heating is allowed to operate
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Default to 40°F
Baseline Rules 40°F
Coil Defrost
Applicability Air-cooled electric heat pump
Definition The defrost control mechanism for an air-cooled heat pump. The choices are:
  • Hot-gas defrost, on-demand
  • Hot-gas defrost, timed 3.5 minute cycle
  • Electric resistance defrost, on-demand
  • Electric resistance defrost, timed 3.5 minute cycle
Defrost shall be enabled whenever the outside air dry-bulb temperature drops below 40°F.
Units List (see above)
Input Restrictions Default to use hot-gas defrost, timed 3.5 minute cycle. User may select any of the above.
Baseline Rules The baseline building uses the default.
Coil Defrost kW
Applicability Heat pumps with electric resistance defrost
Definition The capacity of the electric resistance defrost heater
Units Kilowatts (kW)
Input Restrictions As designed. This descriptor defaults to 0 if nothing is entered.
Baseline Rules Not applicable. Baseline building systems 2 and 4 use hot-gas, timed 3.5 minute cycle.
Crank Case Heater kW
Applicability All heat pumps
Definition The capacity of the electric resistance heater in the crank case of a direct expansion (DX) compressor. The crank case heater operates only when the compressor is off.
Units Kilowatts (kW)
Input Restrictions As designed. This descriptor defaults to 0 if nothing is entered.
Baseline Rules Zero (0)
Crank Case Heater Shutoff Temperature
Applicability All heat pumps
Definition The outdoor air dry-bulb temperature above which the crank case heater is not permitted to operate.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. This descriptor defaults to 50°F.
Baseline Rules 50°F

Heat Recovery

Exhaust to Outside Heat Recovery Effectiveness
Applicability Any system with outside air heat recovery
Definition

The effectiveness of an air-to-air heat exchanger between the building exhaust and entering outside air streams. Effectiveness is defined as follows:

(6.7.6-14)

$$ H\!R\!E\!F\!F = \frac{\left ( E\!E\!A_{db} - E\!L\!A_{db}\right )}{\left ( E\!E\!A_{db} - O\!S\!A_{db}\right )}$$where

HREFF The air-to-air heat exchanger effectiveness
EEAdb The exhaust air dry-bulb temperature entering the heat exchanger
ELAdb The exhaust air dry-bulb temperature leaving the heat exchanger
OSAdb The outside air dry-bulb temperature
Units Ratio
Input Restrictions As designed
Baseline Rules Required for fan systems with a design supply air flow rate of 5,000 cfm or greater if the minimum outside air quantity is 70% of the design air flow rate. If required, the energy recovery system should have at least 50% effectiveness. Energy recovery is not required for heating systems in climate zones 1 through 3 or for cooling systems in climate zones 3c, 4c, 5b, 5c, 6b, 7 and 8.
Condenser Heat Recovery Effectiveness
Applicability Systems that use recover heat from a condenser
Definition The percentage of heat rejection at design conditions from a DX or heat pump unit in cooling mode that is available for space or water heating.
Units Percent (%)
Input Restrictions As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.
Baseline Rules Not applicable for most conditions. Condenser heat recovery is required for 24-hour facilities when the heat rejection exceeds 6,000,000 Btu/h and the design service water heating load exceeds 1,000,000 Btu/h. When required, the effectiveness will be 60%.
Heat Recovery Use
Applicability Systems that use heat recovery
Definition The end use of the heat recovered from a DX or heat pump unit. The choices are:
  • Reheat coils
  • Water heating
Units List (see above)
Input Restrictions As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.
Baseline Rules Not applicable for most conditions. The end use will be water heating if required for 24-hour facility operation.
90.1-2016 BM
Building EQ

General

Heating Source
Applicability All systems that provide heating
Definition The source of heating for the heating and preheat coils. The choices are:
  • Hot water
  • Steam
  • Electric resistance
  • Electric heat pump
  • Gas furnace
  • Gas heat pump (optional feature)
  • Oil furnace
  • Heat recovery (for preheat coils in proposed designs)
Units List (see above)
Input Restrictions As designed

Preheat Coil

Preheat Coil Capacity
Applicability Systems with a preheat coil located in the outside air stream
Definition The heating capacity of a preheating coil at design conditions.
Units Btu/h
Input Restrictions As designed

Heating Coils

Heating Coil Capacity
Applicability All systems with a heating coil
Definition The heating capacity of a heating coil at ARI conditions
Units Btu/h
Input Restrictions As designed. Adjust the capacity if the number of unmet load hours exceeds 300.

Furnace

Furnace Capacity
Applicability Systems with a furnace
Definition The full load heating capacity of the unit
Units Btu/h
Input Restrictions As designed. Adjust the capacity if the number of unmet load hours exceeds 300.
Furnace Fuel Heating Efficiency
Applicability Systems with a furnace
Definition The full load thermal efficiency of either a gas or oil furnace at design conditions. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:

(6.7.6-1)

$ 1) All\ Single\ Package\ Equipment$
$ E_t = 0.005163 \times AFUE + 0.4033 $
$ 2) Split\ Systems, AFUE \leq 83.5$
$ E_t = 0.002907 \times AFUE + 0.5787$
$ 3) Split\ Systems, AFUE \textgreater 83.5 $
$ E_t = 0.011116 \times AFUE - 0.098185$

where

AFUE The annual fuel utilization efficiency (%)
Et The thermal efficiency (fraction)
Units Fraction
Input Restrictions As designed
Furnace Fuel Heating Part Load Efficiency Curve
Applicability Systems with furnaces
Definition An adjustment factor that represents the percentage of full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:

(6.7.6-2)

$$ Fuel_{partload} = Fuel_{rated} \times F\!HeatP\!LC$$

(6.7.6-3)

$$ F\!HeatP\!LC = \left ( a + b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left( \frac{Q_{partload}}{Q_{rated}} \right )^2 \right )$$

where

FHeatPLC The Fuel Heating Part Load Efficiency Curve
Fuelpartload The fuel consumption at part load conditions (Btu/h)
Fuelrated The fuel consumption at full load (Btu/h)
Qpartload The capacity at part load conditions (Btu/h)
Qrated The capacity at rated conditions (Btu/h)

[table title="Furnace Efficiency Curve Coefficients" id="furnace-efficiency-curve-coefficients"]

Coefficient Furnace
a 0.0186100
b 1.0942090
c -0.1128190
Units Data structure
Input Restrictions As designed when data is available, otherwise use the default values are provided above.
Furnace Fuel Heating Pilot
Applicability Systems that use a furnace for heating
Definition The fuel input for a pilot light on a furnace
Units Btu/h
Input Restrictions As designed
Furnace Fuel Heating Fan/Auxiliary
Applicability Systems that use a furnace for heating
Definition The fan energy in forced draft furnaces and the auxiliary (pumps and outdoor fan) energy in fuel-fired heat pumps
Units Kilowatts (kW)
Input Restrictions As designed

Electric Heat Pump

Electric Heat Pump Heating Capacity
Applicability All heat pumps
Definition The full load heating capacity of the unit, excluding supplemental heating capacity at ARI rated conditions
Units Btu/h
Input Restrictions As designed
Electric Heat Pump Supplemental Heating Source
Applicability All heat pumps
Definition The auxiliary heating source for a heat pump heating system. The common control sequence is to lock out the heat pump compressor when the supplemental heat is activated. Other building descriptors may be needed if this is not the case. Choices for supplemental heat include:
  • Electric resistance
  • Gas furnace
  • Oil furnace
  • Hot water
  • Other
Units List (see above)
Input Restrictions As designed
Electric Heat Pump Heating Efficiency
Applicability All heat pumps
Definition

The heating efficiency of a heat pump at ARI rated conditions as a dimensionless ratio of output over input. The software must accommodate user input in terms of either the Coefficient of Performance (COP) or the Heating Season Performance Factor (HSPF). Where HSPF is provided, COP shall be calculated as follows:

(6.7.6-4)

$ 1) All\ Single\ Package\ Equipment$
$ C\!O\!P = 0.2778 \times H\!S\!P\!F + 0.9667 $
$ 2) All\ Split\ Systems$
$ C\!O\!P = 0.4813 \times H\!S\!P\!F - 0.2606$

For all unitary and applied equipment where the fan energy is part of the equipment efficiency rating, the COP shall be adjusted as follows to remove the fan energy:

(6.7.6-5)

$$ C\!O\!P_{adj} = \frac{\frac{H\!C\!A\!P_{rated}}{3.413} - B\!H\!P_{supply} \times 0.7457}{\frac{H\!C\!A\!P_{rated}}{C\!O\!P \times 3.413} - B\!H\!P_{supply} \times 0.7457}$$

where

COPadj The adjusted coefficient of performance for simulation purposes
COP The ARI rated coefficient of performance
HCAPrated The ARI rated heating capacity of a packaged unit (kBtu/h)
BHPsupply The supply fan brake horsepower (bhp).

Refer to building descriptor Supply Fan BHP.

Units Unitless
Input Restrictions As designed
Electric Heat Pump Heating Capacity Adjustment Curve(s)
Applicability All heat pumps
Definition

A curve or group of curves that represent the available heat-pump heating capacity as a function of evaporator and condenser conditions. The default curves are given as follows:

(6.7.6-6)

$$ Q_{available} = C\!A\!P\_FT \times Q_{rated}$$For air-cooled heat pumps:

(6.7.6-7)

$$ C\!A\!P\_FT = a + b \times t_{odb} + c \times \left. t_{odb}\right. ^2 + d \times \left. t_{odb}\right. ^3 $$

For water-cooled heat pumps:

(6.7.6-8)

$$ C\!A\!P\_FT = a + b \times t_{db} + d \times t_{wt}$$

where

Qavailable Available heating capacity at present evaporator and condenser conditions (kBtu/h)
tdb The entering coil dry-bulb temperature (°F)
twt The water supply temperature (°F)
todb The outside-air dry-bulb temperature (°F)
Qrated Rated capacity at ARI conditions (in kBtu/h

[table title="Heat Pump Capacity Adjustment Curves (CAP-FT)" id="heat-pump-capacity-adjustment-curves-(CAP-FT)"]

Coefficient Water-Source Air-Source
a 0.4886534 0.2536714
b -0.0067774 0.0104351
c N/A 0.0001861
d 0.0140823 -0.0000015
Units Data structure
Input Restrictions User may input curves or use default curves. If defaults are overridden, supporting documentation shall be provided.
Electric Heat Pump Heating Efficiency Adjustment Curve(s)
Applicability All heat pumps
Definition

A curve or group of curves that varies the heat-pump heating efficiency as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(6.7.6-9)

$$ P\!LR = \frac{Q_{operating}}{Q_{available}\left ( t_{db},t_{odb/wt}\right )}$$

(6.7.6-10)

$$ E\!I\!R\_F\!P\!LR = a + b \times P\!LR + c \times P\!LR^2 + d \times P\!LR^3 $$

Air Source Heat Pumps:

(6.7.6-11)

$$ E\!I\!R\_FT = a + b \times \left ( \frac{t_{odb}}{t_{db}} \right ) + c \times \left ( \frac{t_{odb}}{t_{db}} \right ) ^2 + d \times \left ( \frac{t_{odb}}{t_{db}} \right )^3$$Water Source Heat Pumps:

(6.7.6-12)

$$ E\!I\!R\_FT = a + b \times t_{wt} + d \times t_{db}$$

(6.7.6-13)

$$ P_{operating} = P_{rated} \times E\!I\!R\_F\!P\!LR \times E\!I\!R\_FT \times C\!AP\_FT $$

where

PLR Part load ratio based on available capacity (not rated capacity)
EIR-FPLR A multiplier on the EIR of the heat pump as a function of part load ratio
EIR-FT A multiplier on the EIR of the heat pump as a function of the wet-bulb temperature entering the coil and the outdoor dry-bulb temperature
Qoperating Present load on heat pump (Btu/h)
Qavailable Heat pump available capacity at present evaporator and condenser conditions (Btu/h).
tdb The entering coil dry-bulb temperature (°F)
twt The water supply temperature (°F)
todb The outside air dry-bulb temperature (°F)
Prated Rated power draw at ARI conditions (kW)
Poperating Power draw at specified operating conditions (kW)

[table title="Heat Pump Heating Efficiency Adjustment (Curves)" id="heat-pump-heating-efficiency-adjustment-curves"]

Coefficient Air-and Water-Source
EIR-FPLR
Water-Source
EIR-FT
Air-Source
EIR-FT
a 0.0856522 1.3876102 2.4600298
b 0.9388137 0.0060479 -0.0622539
c -0.1834361 N/A 0.0008800
d 0.1589702 -0.0115852 -0.0000046
Units None
Input Restrictions User may input curves or use default curves. If defaults are overridden, documentation shall be provided.
Electric Heat Pump Supplemental Heating Capacity
Applicability All heat pumps
Definition The design heating capacity of a heat pump supplemental heating coil at ARI conditions
Units Btu/h
Input Restrictions As designed
Electric Supplemental Heating Control Temp
Applicability All heat pumps
Definition The outside dry-bulb temperature below which the heat pump supplemental heating is allowed to operate
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Default to 40°F
Coil Defrost
Applicability Air-cooled electric heat pump
Definition The defrost control mechanism for an air-cooled heat pump. The choices are:
  • Hot-gas defrost, on-demand
  • Hot-gas defrost, timed 3.5 minute cycle
  • Electric resistance defrost, on-demand
  • Electric resistance defrost, timed 3.5 minute cycle
Defrost shall be enabled whenever the outside air dry-bulb temperature drops below 40°F.
Units List (see above)
Input Restrictions Default to use hot-gas defrost, timed 3.5 minute cycle. User may select any of the above.
Coil Defrost kW
Applicability Heat pumps with electric resistance defrost
Definition The capacity of the electric resistance defrost heater
Units Kilowatts (kW)
Input Restrictions As designed. This descriptor defaults to 0 if nothing is entered.
Crank Case Heater kW
Applicability All heat pumps
Definition The capacity of the electric resistance heater in the crank case of a direct expansion (DX) compressor. The crank case heater operates only when the compressor is off.
Units Kilowatts (kW)
Input Restrictions As designed. This descriptor defaults to 0 if nothing is entered.
Crank Case Heater Shutoff Temperature
Applicability All heat pumps
Definition The outdoor air dry-bulb temperature above which the crank case heater is not permitted to operate.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. This descriptor defaults to 50°F.

Heat Recovery

Exhaust to Outside Heat Recovery Effectiveness
Applicability Any system with outside air heat recovery
Definition

The effectiveness of an air-to-air heat exchanger between the building exhaust and entering outside air streams. Effectiveness is defined as follows:

(6.7.6-14)

$$ H\!R\!E\!F\!F = \frac{\left ( E\!E\!A_{db} - E\!L\!A_{db}\right )}{\left ( E\!E\!A_{db} - O\!S\!A_{db}\right )}$$where

HREFF The air-to-air heat exchanger effectiveness
EEAdb The exhaust air dry-bulb temperature entering the heat exchanger
ELAdb The exhaust air dry-bulb temperature leaving the heat exchanger
OSAdb The outside air dry-bulb temperature
Units Ratio
Input Restrictions As designed
Condenser Heat Recovery Effectiveness
Applicability Systems that use recover heat from a condenser
Definition The percentage of heat rejection at design conditions from a DX or heat pump unit in cooling mode that is available for space or water heating.
Units Percent (%)
Input Restrictions As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.
Heat Recovery Use
Applicability Systems that use heat recovery
Definition The end use of the heat recovered from a DX or heat pump unit. The choices are:
  • Reheat coils
  • Water heating
Units List (see above)
Input Restrictions As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.
Energy Star

General

Heating Source
Applicability All systems that provide heating
Definition The source of heating for the heating and preheat coils. The choices are:
  • Hot water
  • Steam
  • Electric resistance
  • Electric heat pump
  • Gas furnace
  • Gas heat pump (optional feature)
  • Oil furnace
  • Heat recovery (for preheat coils in proposed designs)
Units List (see above)
Input Restrictions As designed

Preheat Coil

Preheat Coil Capacity
Applicability Systems with a preheat coil located in the outside air stream
Definition The heating capacity of a preheating coil at design conditions.
Units Btu/h
Input Restrictions As designed

Heating Coils

Heating Coil Capacity
Applicability All systems with a heating coil
Definition The heating capacity of a heating coil at ARI conditions
Units Btu/h
Input Restrictions As designed. Adjust the capacity if the number of unmet load hours exceeds 300.

Furnace

Furnace Capacity
Applicability Systems with a furnace
Definition The full load heating capacity of the unit
Units Btu/h
Input Restrictions As designed. Adjust the capacity if the number of unmet load hours exceeds 300.
Furnace Fuel Heating Efficiency
Applicability Systems with a furnace
Definition The full load thermal efficiency of either a gas or oil furnace at design conditions. The software must accommodate input in either Thermal Efficiency (Et) or Annual Fuel Utilization Efficiency (AFUE). Where AFUE is provided, Et shall be calculated as follows:

(6.7.6-1)

$ 1) All\ Single\ Package\ Equipment$
$ E_t = 0.005163 \times AFUE + 0.4033 $
$ 2) Split\ Systems, AFUE \leq 83.5$
$ E_t = 0.002907 \times AFUE + 0.5787$
$ 3) Split\ Systems, AFUE \textgreater 83.5 $
$ E_t = 0.011116 \times AFUE - 0.098185$

where

AFUE The annual fuel utilization efficiency (%)
Et The thermal efficiency (fraction)
Units Fraction
Input Restrictions As designed
Furnace Fuel Heating Part Load Efficiency Curve
Applicability Systems with furnaces
Definition An adjustment factor that represents the percentage of full load fuel consumption as a function of the percentage full load capacity. This curve shall take the form of a quadratic equation as follows:

(6.7.6-2)

$$ Fuel_{partload} = Fuel_{rated} \times F\!HeatP\!LC$$

(6.7.6-3)

$$ F\!HeatP\!LC = \left ( a + b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left( \frac{Q_{partload}}{Q_{rated}} \right )^2 \right )$$

where

FHeatPLC The Fuel Heating Part Load Efficiency Curve
Fuelpartload The fuel consumption at part load conditions (Btu/h)
Fuelrated The fuel consumption at full load (Btu/h)
Qpartload The capacity at part load conditions (Btu/h)
Qrated The capacity at rated conditions (Btu/h)

[table title="Furnace Efficiency Curve Coefficients" id="furnace-efficiency-curve-coefficients"]

Coefficient Furnace
a 0.0186100
b 1.0942090
c -0.1128190
Units Data structure
Input Restrictions As designed when data is available, otherwise use the default values are provided above.
Furnace Fuel Heating Pilot
Applicability Systems that use a furnace for heating
Definition The fuel input for a pilot light on a furnace
Units Btu/h
Input Restrictions As designed
Furnace Fuel Heating Fan/Auxiliary
Applicability Systems that use a furnace for heating
Definition The fan energy in forced draft furnaces and the auxiliary (pumps and outdoor fan) energy in fuel-fired heat pumps
Units Kilowatts (kW)
Input Restrictions As designed

Electric Heat Pump

Electric Heat Pump Heating Capacity
Applicability All heat pumps
Definition The full load heating capacity of the unit, excluding supplemental heating capacity at ARI rated conditions
Units Btu/h
Input Restrictions As designed
Electric Heat Pump Supplemental Heating Source
Applicability All heat pumps
Definition The auxiliary heating source for a heat pump heating system. The common control sequence is to lock out the heat pump compressor when the supplemental heat is activated. Other building descriptors may be needed if this is not the case. Choices for supplemental heat include:
  • Electric resistance
  • Gas furnace
  • Oil furnace
  • Hot water
  • Other
Units List (see above)
Input Restrictions As designed
Electric Heat Pump Heating Efficiency
Applicability All heat pumps
Definition

The heating efficiency of a heat pump at ARI rated conditions as a dimensionless ratio of output over input. The software must accommodate user input in terms of either the Coefficient of Performance (COP) or the Heating Season Performance Factor (HSPF). Where HSPF is provided, COP shall be calculated as follows:

(6.7.6-4)

$ 1) All\ Single\ Package\ Equipment$
$ C\!O\!P = 0.2778 \times H\!S\!P\!F + 0.9667 $
$ 2) All\ Split\ Systems$
$ C\!O\!P = 0.4813 \times H\!S\!P\!F - 0.2606$

For all unitary and applied equipment where the fan energy is part of the equipment efficiency rating, the COP shall be adjusted as follows to remove the fan energy:

(6.7.6-5)

$$ C\!O\!P_{adj} = \frac{\frac{H\!C\!A\!P_{rated}}{3.413} - B\!H\!P_{supply} \times 0.7457}{\frac{H\!C\!A\!P_{rated}}{C\!O\!P \times 3.413} - B\!H\!P_{supply} \times 0.7457}$$

where

COPadj The adjusted coefficient of performance for simulation purposes
COP The ARI rated coefficient of performance
HCAPrated The ARI rated heating capacity of a packaged unit (kBtu/h)
BHPsupply The supply fan brake horsepower (bhp).

Refer to building descriptor Supply Fan BHP.

Units Unitless
Input Restrictions As designed
Electric Heat Pump Heating Capacity Adjustment Curve(s)
Applicability All heat pumps
Definition

A curve or group of curves that represent the available heat-pump heating capacity as a function of evaporator and condenser conditions. The default curves are given as follows:

(6.7.6-6)

$$ Q_{available} = C\!A\!P\_FT \times Q_{rated}$$For air-cooled heat pumps:

(6.7.6-7)

$$ C\!A\!P\_FT = a + b \times t_{odb} + c \times \left. t_{odb}\right. ^2 + d \times \left. t_{odb}\right. ^3 $$

For water-cooled heat pumps:

(6.7.6-8)

$$ C\!A\!P\_FT = a + b \times t_{db} + d \times t_{wt}$$

where

Qavailable Available heating capacity at present evaporator and condenser conditions (kBtu/h)
tdb The entering coil dry-bulb temperature (°F)
twt The water supply temperature (°F)
todb The outside-air dry-bulb temperature (°F)
Qrated Rated capacity at ARI conditions (in kBtu/h

[table title="Heat Pump Capacity Adjustment Curves (CAP-FT)" id="heat-pump-capacity-adjustment-curves-(CAP-FT)"]

Coefficient Water-Source Air-Source
a 0.4886534 0.2536714
b -0.0067774 0.0104351
c N/A 0.0001861
d 0.0140823 -0.0000015
Units Data structure
Input Restrictions User may input curves or use default curves. If defaults are overridden, supporting documentation shall be provided.
Electric Heat Pump Heating Efficiency Adjustment Curve(s)
Applicability All heat pumps
Definition

A curve or group of curves that varies the heat-pump heating efficiency as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(6.7.6-9)

$$ P\!LR = \frac{Q_{operating}}{Q_{available}\left ( t_{db},t_{odb/wt}\right )}$$

(6.7.6-10)

$$ E\!I\!R\_F\!P\!LR = a + b \times P\!LR + c \times P\!LR^2 + d \times P\!LR^3 $$

Air Source Heat Pumps:

(6.7.6-11)

$$ E\!I\!R\_FT = a + b \times \left ( \frac{t_{odb}}{t_{db}} \right ) + c \times \left ( \frac{t_{odb}}{t_{db}} \right ) ^2 + d \times \left ( \frac{t_{odb}}{t_{db}} \right )^3$$Water Source Heat Pumps:

(6.7.6-12)

$$ E\!I\!R\_FT = a + b \times t_{wt} + d \times t_{db}$$

(6.7.6-13)

$$ P_{operating} = P_{rated} \times E\!I\!R\_F\!P\!LR \times E\!I\!R\_FT \times C\!AP\_FT $$

where

PLR Part load ratio based on available capacity (not rated capacity)
EIR-FPLR A multiplier on the EIR of the heat pump as a function of part load ratio
EIR-FT A multiplier on the EIR of the heat pump as a function of the wet-bulb temperature entering the coil and the outdoor dry-bulb temperature
Qoperating Present load on heat pump (Btu/h)
Qavailable Heat pump available capacity at present evaporator and condenser conditions (Btu/h).
tdb The entering coil dry-bulb temperature (°F)
twt The water supply temperature (°F)
todb The outside air dry-bulb temperature (°F)
Prated Rated power draw at ARI conditions (kW)
Poperating Power draw at specified operating conditions (kW)

[table title="Heat Pump Heating Efficiency Adjustment (Curves)" id="heat-pump-heating-efficiency-adjustment-curves"]

Coefficient Air-and Water-Source
EIR-FPLR
Water-Source
EIR-FT
Air-Source
EIR-FT
a 0.0856522 1.3876102 2.4600298
b 0.9388137 0.0060479 -0.0622539
c -0.1834361 N/A 0.0008800
d 0.1589702 -0.0115852 -0.0000046
Units None
Input Restrictions User may input curves or use default curves. If defaults are overridden, documentation shall be provided.
Electric Heat Pump Supplemental Heating Capacity
Applicability All heat pumps
Definition The design heating capacity of a heat pump supplemental heating coil at ARI conditions
Units Btu/h
Input Restrictions As designed
Electric Supplemental Heating Control Temp
Applicability All heat pumps
Definition The outside dry-bulb temperature below which the heat pump supplemental heating is allowed to operate
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Default to 40°F
Coil Defrost
Applicability Air-cooled electric heat pump
Definition The defrost control mechanism for an air-cooled heat pump. The choices are:
  • Hot-gas defrost, on-demand
  • Hot-gas defrost, timed 3.5 minute cycle
  • Electric resistance defrost, on-demand
  • Electric resistance defrost, timed 3.5 minute cycle
Defrost shall be enabled whenever the outside air dry-bulb temperature drops below 40°F.
Units List (see above)
Input Restrictions Default to use hot-gas defrost, timed 3.5 minute cycle. User may select any of the above.
Coil Defrost kW
Applicability Heat pumps with electric resistance defrost
Definition The capacity of the electric resistance defrost heater
Units Kilowatts (kW)
Input Restrictions As designed. This descriptor defaults to 0 if nothing is entered.
Crank Case Heater kW
Applicability All heat pumps
Definition The capacity of the electric resistance heater in the crank case of a direct expansion (DX) compressor. The crank case heater operates only when the compressor is off.
Units Kilowatts (kW)
Input Restrictions As designed. This descriptor defaults to 0 if nothing is entered.
Crank Case Heater Shutoff Temperature
Applicability All heat pumps
Definition The outdoor air dry-bulb temperature above which the crank case heater is not permitted to operate.
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. This descriptor defaults to 50°F.

Heat Recovery

Exhaust to Outside Heat Recovery Effectiveness
Applicability Any system with outside air heat recovery
Definition

The effectiveness of an air-to-air heat exchanger between the building exhaust and entering outside air streams. Effectiveness is defined as follows:

(6.7.6-14)

$$ H\!R\!E\!F\!F = \frac{\left ( E\!E\!A_{db} - E\!L\!A_{db}\right )}{\left ( E\!E\!A_{db} - O\!S\!A_{db}\right )}$$where

HREFF The air-to-air heat exchanger effectiveness
EEAdb The exhaust air dry-bulb temperature entering the heat exchanger
ELAdb The exhaust air dry-bulb temperature leaving the heat exchanger
OSAdb The outside air dry-bulb temperature
Units Ratio
Input Restrictions As designed
Condenser Heat Recovery Effectiveness
Applicability Systems that use recover heat from a condenser
Definition The percentage of heat rejection at design conditions from a DX or heat pump unit in cooling mode that is available for space or water heating.
Units Percent (%)
Input Restrictions As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.
Heat Recovery Use
Applicability Systems that use heat recovery
Definition The end use of the heat recovered from a DX or heat pump unit. The choices are:
  • Reheat coils
  • Water heating
Units List (see above)
Input Restrictions As designed. The software must indicate that supporting documentation is required on the output forms if heat recovery is specified.