3.9.1 Water Heating

Water heating systems shall always be modeled for both the proposed design and baseline building when the proposed building is expected to have a water heating load, even if no water heating is shown on the plans or specifications for the proposed design. In such instances, an electric resistance system shall be modeled for both the proposed design and baseline building, meeting the efficiency requirements of the baseline standard.

When the construction documents show a water heating system, the layout and configuration of the baseline building system shall be the same as the proposed design, e.g. the baseline building shall have the same number of water heaters and the same distribution system.

System Loads and Configuration

Water Heating System Name
Applicability All water heating systems
Definition A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules The naming convention for the baseline building system shall be similar to the proposed design.
Water Heating Peak Use
Applicability All water heating systems, required
Definition

An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances, etc.). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation.

Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc.

It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.

Units Btu/h or gallons/h
Input Restrictions For the purpose of federal tax deductions, peak use shall be specified as a thermal load using the California 2005 ACM values from Appendix B, Table 5. For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B are default values, but other values may be used with justification.
Baseline Rules Hot water consumption or load in the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption. Examples of such measures include: low-flow terminal devices or controls, alternative sanitizing technologies, or heat recovery laundry or showers drains.
Water Heating Schedule
Applicability All water heating systems, required
Definition A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units Data structure: schedule, fractional
Input Restrictions For the purpose of federal tax deductions, the schedules for the California 2005 ACM from Appendix B, Table 7 shall be used. For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B, Table 7 are default values, but other values may be used with justification.
Baseline Rules Hot water schedules for the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption and the impact of the measure can be best approximated through an adjustment to the schedule. In general, such measures would be addressed through an adjustment to the water heating, peak use (see above).
Water Heating System Configuration
Applicability All water heating systems, required
Definition The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units Data structure
Input Restrictions None
Baseline Rules The baseline building shall have the same configuration and layout as the proposed design.

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability All water heaters
Definition A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules The naming convention for the baseline building system shall be similar to the proposed design.
Water Heater Type and Size
Applicability All water heaters
Definition

This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below. See Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007 for more detail.

  • Electric water heaters (storage and instantaneous)
    • Small (≤ 12 kW)
    • Large (> 12 kW)
  • Heat pump
  • Gas storage water heaters
    • Small (≤ 75,000 Btu/h)
    • Medium (> 75,000 and ≤ 155,000 Btu/h)
    • Large (> 155,000 Btu/h)
  • Gas instantaneous water heaters
    • Small (> 50,000 and < 200,000 Btu/h)
    • Large (≥ 200,000 Btu/h)
  • Oil storage water heaters
    • Small (≤ 105,000 Btu/h)
    • Medium (> 105,000 and ≤ 155,000 Btu/h)
    • Large (> 155,000 Btu/h)
  • Oil instantaneous water heaters
    • Small (≤ 210,000 Btu/h)
    • Large (> 210,000 Btu/h)
  • Gas hot water supply boiler
  • Oil hot water supply boiler
Units List (see above)
Input Restrictions The water heater type shall agree with equipment specified in the construction documents.
Baseline Rules Water heaters in the baseline system shall be the same as those in the proposed design, except when the proposed design has a heat pump water heater, in which case the baseline building system shall have an electric storage water heater.
Rated Capacity
Applicability All water heaters
Definition The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007 or Table 7.2.2 of ASHRAE Standard 90.1-2001
Units Thousands of British Thermal Units per hour (MBH)
Input Restrictions As designed. If the loads are not met, autosize.
Baseline Rules Autosize
Energy Factor
Applicability Equipment covered by NAECA, which includes small storage and instantaneous water heaters
Definition The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units Unitless ratio
Input Restrictions Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules The EF for the baseline building system shall be determined from Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.
Thermal Efficiency
Applicability Oil and gas fired water heaters not covered by NAECA
Definition The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units Unitless ratio
Input Restrictions Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules The thermal efficiency for the baseline building system shall be determined from Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.
Tank Standby Loss
Applicability Water heaters not covered by NAECA
Definition The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units Btu/h for the entire tank
Input Restrictions As specified in manufacturer data and documented on the construction documents
Baseline Rules The tank standby loss for the baseline building system shall be determined from Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007.
Fuel Water Heater Part Load Efficiency Curve
Applicability Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified
Definition A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.
Units Percent (%)
Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(6.9.1-1)

$$ Fuel_{partload} = Fuel_{design} \times F\!HeatP\!L\!C$$ $$F\!HeatP\!L\!C = \left ( a+ b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \right )$$where

FHeatPLC The fuel heating part load efficiency curve
Fuelpartload The fuel consumption at part load conditions (Btu/h)
Fueldesign The fuel consumption at design conditions (Btu/h)
Qpartload The water heater capacity at part load conditions (Btu/h)
Qrated The water heater capacity at design conditions (Btu/h)
a Constant, 0.021826
b Constant, 0.977630
c Constant, 0.000543
Baseline Rules The baseline building equipment shall use the default curve

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability All recirculation systems
Definition A unique descriptor for each water heating recirculation system
Units Text, unique
Input Restrictions Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules The naming convention for the baseline building system shall be similar to the proposed design.
Pumping Power
Applicability All recirculation systems
Definition The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units Watts (W)
Input Restrictions Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Baseline Rules Pumping power in the baseline building shall be the same as the proposed design unless specific measures are included in the proposed design to reduce the pumping power. Example measures could include reducing pumping head by oversizing distribution piping or specifying premium efficiency motors or pumps.
Schedule
Applicability All recirculation systems
Definition An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units Data structure: schedule, on/off or fraction
Input Restrictions The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.
Baseline Rules Recirculation schedules for the baseline building shall be the same as the proposed design.
Piping
Applicability All recirculation systems
Definition The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions All piping in the recirculation system should be included. Heat loss for each of the three conditions should be consistent with piping runs, sizes, and insulation as shown on the construction documents.
Baseline Rules The length and size of piping in the baseline building shall be the same as the proposed design. Insulation in the baseline building shall be as prescribed in Table 6.8.3 for ASHRAE Standard 90.1-2007 and Table 6.2.4.1.3 of ASHRAE Standard 90.1-2001.

Water Healing Auxiliaries

External Storage Tanks
Applicability All water heating systems that have an external storage tank
Definition Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units Btu/h for the entire tank
Input Restrictions As specified in manufacturer data and documented on the construction documents
Baseline Rules Heat loss associated with the storage tank in the baseline building shall meet the requirements for an unfired storage tank in the baseline standards which is an insulation R-value of 12.5. The surface area and location of the storage tank shall be the same as the proposed design.
Heat Recovery
Applicability Water heating systems that are coupled to heat recovery equipment
Definition Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units Data structure: depends on the equipment producing the heat
Input Restrictions There are no restrictions, other than agreement with the construction documents.
Baseline Rules

The baseline building has heat recovery when the baseline standard is ASHRAE Standard 90.1-2007 and the conditions of Section 6.5.6.2 of that standard are satisfied. The baseline building is modeled with heat recovery when all of the following conditions are true:

The building operates 24 hours per day.

The building has water cooled chillers with a heat rejection capacity greater than 6 million Btu/h. This equates to about 400 tons of electric chiller capacity.

The water heating peak use is greater than 1,000,000 Btu/h.

See the User's Manual for ASHRAE Standard 90.1-2007, page 6-82 for details on the requirements for the heat recovery system and exceptions to the requirement.

Solar Thermal
Applicability Water heating systems with a solar thermal system
Definition

A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal.

Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design.
Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to account for the temporal mismatch in some manner.

Units Data structure: will vary with the software and system details
Input Restrictions There are no restrictions, other than agreement with the construction documents.
Baseline Rules The baseline building has no solar auxiliary system.
Combined Space Heating and Water Heating
Applicability Projects that use a boiler to provide both space heat and water heating
Definition A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units Data structure
Input Restrictions The proposed design may have a combined space and water heating system.
Baseline Rules The baseline building shall be modeled with separate space heating and water heating systems, meeting the prescriptive requirements for each. The water heating system shall use the same fuel as the combined boiler.
90.1-2007

Water heating systems shall always be modeled for both the proposed design and baseline building when the proposed building is expected to have a water heating load, even if no water heating is shown on the plans or specifications for the proposed design. In such instances, an electric resistance system shall be modeled for both the proposed design and baseline building, meeting the efficiency requirements of the baseline standard.

When the construction documents show a water heating system, the layout and configuration of the baseline building system shall be the same as the proposed design, e.g. the baseline building shall have the same number of water heaters and the same distribution system.

System Loads and Configuration

Water Heating System Name
Applicability All water heating systems
Definition A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules The naming convention for the baseline building system shall be similar to the proposed design.
Water Heating Peak Use
Applicability All water heating systems, required
Definition

An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances, etc.). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation.

Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc.

It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.

Units Btu/h or gallons/h
Input Restrictions For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B are default values, but other values may be used with justification.
Baseline Rules Hot water consumption or load in the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption. Examples of such measures include: low-flow terminal devices or controls, alternative sanitizing technologies, or heat recovery laundry or showers drains.
Water Heating Schedule
Applicability All water heating systems, required
Definition A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units Data structure: schedule, fractional
Input Restrictions For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B, Table 7 are default values, but other values may be used with justification.
Baseline Rules Hot water schedules for the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption and the impact of the measure can be best approximated through an adjustment to the schedule. In general, such measures would be addressed through an adjustment to the water heating, peak use (see above).
Water Heating System Configuration
Applicability All water heating systems, required
Definition The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units Data structure
Input Restrictions None
Baseline Rules The baseline building shall have the same configuration and layout as the proposed design.

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability All water heaters
Definition A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules The naming convention for the baseline building system shall be similar to the proposed design.
Water Heater Type and Size
Applicability All water heaters
Definition

This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below. See Table 7.8 of ASHRAE Standard 90.1-2007 for more detail.

  • Electric water heaters (storage and instantaneous)
    • Small (≤ 12 kW)
    • Large (> 12 kW)
  • Heat pump
  • Gas storage water heaters
    • Small (≤ 75,000 Btu/h)
    • Medium (> 75,000 and ≤ 155,000 Btu/h)
    • Large (> 155,000 Btu/h)
  • Gas instantaneous water heaters
    • Small (> 50,000 and < 200,000 Btu/h)
    • Large (≥ 200,000 Btu/h)
  • Oil storage water heaters
    • Small (≤ 105,000 Btu/h)
    • Medium (> 105,000 and ≤ 155,000 Btu/h)
    • Large (> 155,000 Btu/h)
  • Oil instantaneous water heaters
    • Small (≤ 210,000 Btu/h)
    • Large (> 210,000 Btu/h)
  • Gas hot water supply boiler
  • Oil hot water supply boiler
Units List (see above)
Input Restrictions The water heater type shall agree with equipment specified in the construction documents.
Baseline Rules Water heaters in the baseline system shall be the same as those in the proposed design, except when the proposed design has a heat pump water heater, in which case the baseline building system shall have an electric storage water heater.
Rated Capacity
Applicability All water heaters
Definition The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007.
Units Thousands of British Thermal Units per hour (MBH)
Input Restrictions As designed. If the loads are not met, autosize.
Baseline Rules Autosize
Energy Factor
Applicability Equipment covered by NAECA, which includes small storage and instantaneous water heaters
Definition The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units Unitless ratio
Input Restrictions Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules The EF for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.
Thermal Efficiency
Applicability Oil and gas fired water heaters not covered by NAECA
Definition The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units Unitless ratio
Input Restrictions Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules The thermal efficiency for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.
Tank Standby Loss
Applicability Water heaters not covered by NAECA
Definition The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units Btu/h for the entire tank
Input Restrictions As specified in manufacturer data and documented on the construction documents
Baseline Rules The tank standby loss for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007.
Fuel Water Heater Part Load Efficiency Curve
Applicability Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified
Definition A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.
Units Percent (%)
Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(6.9.1-1)

$$ Fuel_{partload} = Fuel_{design} \times F\!HeatP\!L\!C$$ $$F\!HeatP\!L\!C = \left ( a+ b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \right )$$where

FHeatPLC The fuel heating part load efficiency curve
Fuelpartload The fuel consumption at part load conditions (Btu/h)
Fueldesign The fuel consumption at design conditions (Btu/h)
Qpartload The water heater capacity at part load conditions (Btu/h)
Qrated The water heater capacity at design conditions (Btu/h)
a Constant, 0.021826
b Constant, 0.977630
c Constant, 0.000543
Baseline Rules The baseline building equipment shall use the default curve

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability All recirculation systems
Definition A unique descriptor for each water heating recirculation system
Units Text, unique
Input Restrictions Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules The naming convention for the baseline building system shall be similar to the proposed design.
Pumping Power
Applicability All recirculation systems
Definition The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units Watts (W)
Input Restrictions Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Baseline Rules Pumping power in the baseline building shall be the same as the proposed design unless specific measures are included in the proposed design to reduce the pumping power. Example measures could include reducing pumping head by oversizing distribution piping or specifying premium efficiency motors or pumps.
Schedule
Applicability All recirculation systems
Definition An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units Data structure: schedule, on/off or fraction
Input Restrictions The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.
Baseline Rules Recirculation schedules for the baseline building shall be the same as the proposed design.
Piping
Applicability All recirculation systems
Definition The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions All piping in the recirculation system should be included. Heat loss for each of the three conditions should be consistent with piping runs, sizes, and insulation as shown on the construction documents.
Baseline Rules The length and size of piping in the baseline building shall be the same as the proposed design. Insulation in the baseline building shall be as prescribed in Table 6.8.3 for ASHRAE Standard 90.1-2007.

Water Healing Auxiliaries

External Storage Tanks
Applicability All water heating systems that have an external storage tank
Definition Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units Btu/h for the entire tank
Input Restrictions As specified in manufacturer data and documented on the construction documents
Baseline Rules Heat loss associated with the storage tank in the baseline building shall meet the requirements for an unfired storage tank in the baseline standards which is an insulation R-value of 12.5. The surface area and location of the storage tank shall be the same as the proposed design.
Heat Recovery
Applicability Water heating systems that are coupled to heat recovery equipment
Definition Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units Data structure: depends on the equipment producing the heat
Input Restrictions There are no restrictions, other than agreement with the construction documents.
Baseline Rules

The baseline building has heat recovery when the baseline standard is ASHRAE Standard 90.1-2007 and the conditions of Section 6.5.6.2 of that standard are satisfied. The baseline building is modeled with heat recovery when all of the following conditions are true:

  • The building operates 24 hours per day.
  • The building has water cooled chillers with a heat rejection capacity greater than 6 million Btu/h. This equates to about 400 tons of electric chiller capacity.
  • The water heating peak use is greater than 1,000,000 Btu/h.

See the User's Manual for ASHRAE Standard 90.1-2007, page 6-82 for details on the requirements for the heat recovery system and exceptions to the requirement.

Solar Thermal
Applicability Water heating systems with a solar thermal system
Definition

A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal.

Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design.
Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to account for the temporal mismatch in some manner.

Units Data structure: will vary with the software and system details
Input Restrictions There are no restrictions, other than agreement with the construction documents.
Baseline Rules The baseline building has no solar auxiliary system.
Combined Space Heating and Water Heating
Applicability Projects that use a boiler to provide both space heat and water heating
Definition A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units Data structure
Input Restrictions The proposed design may have a combined space and water heating system.
Baseline Rules The baseline building shall be modeled with separate space heating and water heating systems, meeting the prescriptive requirements for each. The water heating system shall use the same fuel as the combined boiler.
90.1-2010

Water heating systems shall always be modeled for both the proposed design and baseline building when the proposed building is expected to have a water heating load, even if no water heating is shown on the plans or specifications for the proposed design. In such instances, an electric resistance system shall be modeled for both the proposed design and baseline building, meeting the efficiency requirements of the baseline standard.

When the construction documents show a water heating system, the layout and configuration of the baseline building system shall be the same as the proposed design, e.g. the baseline building shall have the same number of water heaters and the same distribution system.

System Loads and Configuration

Water Heating System Name
Applicability All water heating systems
Definition A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules The naming convention for the baseline building system shall be similar to the proposed design.
Water Heating Peak Use
Applicability All water heating systems, required
Definition

An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances, etc.). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation.

Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc.

It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.

Units Btu/h or gallons/h
Input Restrictions For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B are default values, but other values may be used with justification.
Baseline Rules Hot water consumption or load in the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption. Examples of such measures include: low-flow terminal devices or controls, alternative sanitizing technologies, or heat recovery laundry or showers drains.
Water Heating Schedule
Applicability All water heating systems, required
Definition A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units Data structure: schedule, fractional
Input Restrictions For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B, Table 7 are default values, but other values may be used with justification.
Baseline Rules Hot water schedules for the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption and the impact of the measure can be best approximated through an adjustment to the schedule. In general, such measures would be addressed through an adjustment to the water heating, peak use (see above).
Water Heating System Configuration
Applicability All water heating systems, required
Definition The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units Data structure
Input Restrictions None
Baseline Rules The baseline building shall have the same configuration and layout as the proposed design.

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability All water heaters
Definition A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules The naming convention for the baseline building system shall be similar to the proposed design.
Water Heater Type and Size
Applicability All water heaters
Definition

This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below. See Table 7.8 of ASHRAE Standard 90.1-2007 for more detail.

  • Electric water heaters (storage and instantaneous)
    • Small (≤ 12 kW)
    • Large (> 12 kW)
  • Heat pump
  • Gas storage water heaters
    • Small (≤ 75,000 Btu/h)
    • Medium (> 75,000 and ≤ 155,000 Btu/h)
    • Large (> 155,000 Btu/h)
  • Gas instantaneous water heaters
    • Small (> 50,000 and < 200,000 Btu/h)
    • Large (≥ 200,000 Btu/h)
  • Oil storage water heaters
    • Small (≤ 105,000 Btu/h)
    • Medium (> 105,000 and ≤ 155,000 Btu/h)
    • Large (> 155,000 Btu/h)
  • Oil instantaneous water heaters
    • Small (≤ 210,000 Btu/h)
    • Large (> 210,000 Btu/h)
  • Gas hot water supply boiler
  • Oil hot water supply boiler
Units List (see above)
Input Restrictions The water heater type shall agree with equipment specified in the construction documents.
Baseline Rules Water heaters in the baseline system shall be the same as those in the proposed design, except when the proposed design has a heat pump water heater, in which case the baseline building system shall have an electric storage water heater.
Rated Capacity
Applicability All water heaters
Definition The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007.
Units Thousands of British Thermal Units per hour (MBH)
Input Restrictions As designed. If the loads are not met, autosize.
Baseline Rules Autosize
Energy Factor
Applicability Equipment covered by NAECA, which includes small storage and instantaneous water heaters
Definition The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units Unitless ratio
Input Restrictions Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules The EF for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.
Thermal Efficiency
Applicability Oil and gas fired water heaters not covered by NAECA
Definition The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units Unitless ratio
Input Restrictions Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Baseline Rules The thermal efficiency for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.
Tank Standby Loss
Applicability Water heaters not covered by NAECA
Definition The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units Btu/h for the entire tank
Input Restrictions As specified in manufacturer data and documented on the construction documents
Baseline Rules The tank standby loss for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007.
Fuel Water Heater Part Load Efficiency Curve
Applicability Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified
Definition A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.
Units Percent (%)
Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(6.9.1-1)

$$ Fuel_{partload} = Fuel_{design} \times F\!HeatP\!L\!C$$ $$F\!HeatP\!L\!C = \left ( a+ b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \right )$$where

FHeatPLC The fuel heating part load efficiency curve
Fuelpartload The fuel consumption at part load conditions (Btu/h)
Fueldesign The fuel consumption at design conditions (Btu/h)
Qpartload The water heater capacity at part load conditions (Btu/h)
Qrated The water heater capacity at design conditions (Btu/h)
a Constant, 0.021826
b Constant, 0.977630
c Constant, 0.000543
Baseline Rules The baseline building equipment shall use the default curve

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability All recirculation systems
Definition A unique descriptor for each water heating recirculation system
Units Text, unique
Input Restrictions Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Baseline Rules The naming convention for the baseline building system shall be similar to the proposed design.
Pumping Power
Applicability All recirculation systems
Definition The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units Watts (W)
Input Restrictions Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Baseline Rules Pumping power in the baseline building shall be the same as the proposed design unless specific measures are included in the proposed design to reduce the pumping power. Example measures could include reducing pumping head by oversizing distribution piping or specifying premium efficiency motors or pumps.
Schedule
Applicability All recirculation systems
Definition An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units Data structure: schedule, on/off or fraction
Input Restrictions The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.
Baseline Rules Recirculation schedules for the baseline building shall be the same as the proposed design.
Piping
Applicability All recirculation systems
Definition The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions All piping in the recirculation system should be included. Heat loss for each of the three conditions should be consistent with piping runs, sizes, and insulation as shown on the construction documents.
Baseline Rules The length and size of piping in the baseline building shall be the same as the proposed design. Insulation in the baseline building shall be as prescribed in Table 6.8.3 for ASHRAE Standard 90.1-2007.

Water Healing Auxiliaries

External Storage Tanks
Applicability All water heating systems that have an external storage tank
Definition Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units Btu/h for the entire tank
Input Restrictions As specified in manufacturer data and documented on the construction documents
Baseline Rules Heat loss associated with the storage tank in the baseline building shall meet the requirements for an unfired storage tank in the baseline standards which is an insulation R-value of 12.5. The surface area and location of the storage tank shall be the same as the proposed design.
Heat Recovery
Applicability Water heating systems that are coupled to heat recovery equipment
Definition Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units Data structure: depends on the equipment producing the heat
Input Restrictions There are no restrictions, other than agreement with the construction documents.
Baseline Rules

The baseline building has heat recovery when the baseline standard is ASHRAE Standard 90.1-2007 and the conditions of Section 6.5.6.2 of that standard are satisfied. The baseline building is modeled with heat recovery when all of the following conditions are true:

  • The building operates 24 hours per day.
  • The building has water cooled chillers with a heat rejection capacity greater than 6 million Btu/h. This equates to about 400 tons of electric chiller capacity.
  • The water heating peak use is greater than 1,000,000 Btu/h.

See the User's Manual for ASHRAE Standard 90.1-2007, page 6-82 for details on the requirements for the heat recovery system and exceptions to the requirement.

Solar Thermal
Applicability Water heating systems with a solar thermal system
Definition

A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal.

Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design.
Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to account for the temporal mismatch in some manner.

Units Data structure: will vary with the software and system details
Input Restrictions There are no restrictions, other than agreement with the construction documents.
Baseline Rules The baseline building has no solar auxiliary system.
Combined Space Heating and Water Heating
Applicability Projects that use a boiler to provide both space heat and water heating
Definition A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units Data structure
Input Restrictions The proposed design may have a combined space and water heating system.
Baseline Rules The baseline building shall be modeled with separate space heating and water heating systems, meeting the prescriptive requirements for each. The water heating system shall use the same fuel as the combined boiler.
90.1-2016 BM

Water heating systems shall always be modeled for both the proposed design and baseline building when the proposed building is expected to have a water heating load, even if no water heating is shown on the plans or specifications for the proposed design. In such instances, an electric resistance system shall be modeled for both the proposed design and baseline building, meeting the efficiency requirements of the baseline standard.

When the construction documents show a water heating system, the layout and configuration of the baseline building system shall be the same as the proposed design, e.g. the baseline building shall have the same number of water heaters and the same distribution system.

System Loads and Configuration

Water Heating System Name

Applicability

All water heating systems

Definition

A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.

Units

Text, unique

Input Restrictions

Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.

Baseline Rules

The naming convention for the baseline building system shall be similar to the proposed design.

 

Water Heating Peak Use

Applicability

All water heating systems, required

Definition

An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation.

Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc.

It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.

Units

Btu/h or gallons/h

Input Restrictions

As designed. If data is unavailable, the defaults in Appendix B may be used.

Baseline Rules

Hot water consumption or load in the baseline building shall be the same as the proposed design, except in cases where:

  • A specific measure is specified for the proposed design that will reduce water consumption. Examples of such measures include low-flow terminal devices or controls.
  • SHW energy consumption can be demonstrated to be reduced by increasing makeup water temperature or reducing SHW temperature (e.g., alternative sanitizing technologies for dishwashing and heat recovery to entering makeup water).
  • SHW energy consumption can be demonstrated to be reduced by reducing the hot fraction of mixed water. Examples include heat recovery laundry or showers drains.

NOTE: Calculations need to be provided to support the difference in service hot water loads between the proposed and baseline model.

 

Water Heating Schedule

Applicability

All water heating systems

Definition

A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.

Units

Data structure: schedule, fractional

Input Restrictions

As designed. If information is unkown, use the defaults from Appendix B and C.

Baseline Rules

Hot water schedules for the baseline building shall be the same as the proposed design, except in cases where a specific measure is specified for the proposed design that will reduce water consumption and the impact of the measure can be best approximated through an adjustment to the schedule. In general, such measures would be addressed through an adjustment to the water heating, peak use (see above).

 

Water Heating System Configuration

Applicability

All water heating systems

Definition

The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.

Units

Data structure

Input Restrictions

None

Baseline Rules

The baseline building shall have the same configuration and layout as the proposed design, except that a separate system shall be provided for each building area classification.

 

Water Main Temperature Schedule

Applicability

All water heating systems

Definition

A monthly temperature schedule indicating the water mains temperature. This temperature and the setpoint temperature are used to convert the load into a water flow rate.

Units

Data structure: schedule, °F

Input Restrictions

Entering water temperature can be defaulted to the values in Table 3.9.1-1 or provided by the user.

Baseline Rules

Same as proposed

Table 3.9.1-1: Monthly Average Water Main Temperatures (°F)

 

Climate Zone

Month

1A

1B

2A

2B

3A

3B

3C

4A

4B

4C

5A

5B

5C

6A

6B

7

8

January

76.5

70.2

64.6

65.8

56.5

59.4

59.7

50.8

52.3

52.9

45.5

48.0

50.6

43.1

43.1

37.6

32.0

February

77.1

72.2

65.0

67.3

56.4

59.5

59.5

50.0

51.7

52.3

44.1

47.0

49.9

41.6

41.6

35.6

32.0

March

79.0

77.6

67.9

72.2

59.5

62.4

60.1

52.2

53.8

53.4

45.8

48.7

50.7

42.7

42.5

36.1

32.0

April

81.7

85.1

72.7

79.5

65.0

67.4

61.5

57.0

58.3

56.1

50.1

53.1

52.7

46.4

45.6

39.0

32.0

May

84.6

92.6

77.9

87.2

71.6

73.3

63.2

63.1

64.0

59.5

56.0

58.8

55.5

51.6

50.2

43.5

32.9

June

86.8

98.1

82.3

93.1

77.4

78.4

64.8

68.9

69.3

62.9

61.9

64.3

58.3

57.0

54.9

48.5

36.9

July

87.7

100.2

84.6

95.8

80.8

81.3

65.9

72.7

72.8

65.2

66.2

68.2

60.4

61.1

58.6

52.6

40.7

August

87.1

98.1

84.2

94.3

80.9

81.3

66.1

73.6

73.5

65.9

67.6

69.4

61.1

62.8

60.2

54.7

43.1

September

85.1

92.6

81.2

89.2

77.8

78.3

65.4

71.3

71.3

64.7

65.9

67.6

60.3

61.6

59.2

54.2

43.4

October

82.4

85.1

76.4

81.8

72.2

73.2

64.0

66.4

66.7

62.0

61.5

63.2

58.2

57.9

56.0

51.3

41.5

November

79.5

77.6

71.1

74.2

65.6

67.3

62.3

60.3

61.0

58.5

55.6

57.5

55.4

52.6

51.4

46.7

38.0

December

77.4

72.2

66.8

68.3

59.9

62.3

60.7

54.6

55.8

55.2

49.7

51.9

52.6

47.2

46.7

41.7

33.8

 

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name

Applicability

All water heaters

Definition

A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.

Units

Text, unique

Input Restrictions

Where applicable (This should match the tags that are used on the plans such that a plan reviewer can make a connection.)

Baseline Rules

The naming convention for the baseline building system shall be similar to the proposed design.

 

Water Heater Type and Size

Applicability

All water heaters

Definition

This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below.

  • Electric water heaters (storage and instantaneous)
    • Small (≤ 12 kW)
    • Large (> 12 kW)
    • Heat pump
  • Gas storage water heaters
    • Small (≤ 75,000 Btu/h)
    • Large (> 75,000 Btu/h)
  • Gas instantaneous water heaters
    • Small (> 50,000 and < 200,000 Btu/h)
    • Large (≥ 200,000 Btu/h) and < 10 gal
    • Large (≥ 200,000 Btu/h) and ≥ 10 gal
  • Oil storage water heaters
    • Small (≤ 105,000 Btu/h)
    • Large (> 105,000 Btu/h)
  • Oil instantaneous water heaters
    • Small (≤ 210,000 Btu/h)
    • Large (> 210,000 Btu/h) and < 10 gal
    • Large (> 210,000 Btu/h) and ≥ 10 gal
  • Gas hot water supply boiler
  • Oil hot water supply boiler
  • Heat exchanger from steam or district hot water

Units

List (see above)

Input Restrictions

The water heater type shall agree with equipment specified in the construction documents.

If no service hot water system exists or has been specified, but the building will have service hot water loads, a service water system using electric resistance heat shall be assumed.

For buildings that will have no service hot water load, no service water heating system shall be modeled.

Baseline Rules

Water heaters in the baseline system shall be based on the building classification. See Table 3.9.1-2 below.

Table 3.9.1-2: Baseline Building Water Heater Type (Table G3.1.1-2)

Gas Storage

Electric Resistance Storage

Automotive facility

Dining: Bar lounge/leisure

Dining: Cafeteria/fast food

Dining: Family

Dormitory

Exercise center

Fire station

Gymnasium

Health-care clinic

Hospital

Hotel

Manufacturing facility

Motel

Multifamily

Penitentiary

Performing arts theater

School/university

Sports arena

Workshop

All Others

Convention center

Courthouse

Library

Motion picture theater

Museum

Office

Parking garage

Police station

Post office

Religious building

Retail

Town hall

Transportation

Warehouse

 

Rated Capacity

Applicability

All water heaters

Definition

The heating capacity of a water heater at the rated conditions specified in DOE 10 CFR Part 430 or ANSI Z21.10.

Units

kBtu/h

Input Restrictions

As designed.

Baseline Rules

Autosize

 

Storage Volume

Applicability

All water heaters

Definition

The storage volume of a gas-fired water heater. This is used in the standby loss calculations and baseline calculations of energy factor (EF).

Units

gallons

Input Restrictions

As designed.

Baseline Rules

Autosize

 

Energy Factor

Applicability

Equipment covered by National Appliance Energy Conservation Act (NAECA), which includes small storage and instantaneous water heaters

Definition

The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.

Units

Unitless ratio

Input Restrictions

Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.

Baseline Rules

The EF for the baseline building system shall be determined from Table 7.8 of ASHRAE Standard 90.1-2007, depending on the purpose of the simulations.

Table 3.9.1-3: Baseline Water Heater Efficiency

 

Size Category (Input)

Performance Required

Electric Storage

≤ 12 kW

EF= 0.97 - 0.00035 V

 

> 12 kW

%h = 0.3 + 27/Vm

Gas Storage

≤ 75,000 Btu/h

EF = 0.67 -0.0005V

 

> 75,000 Btu/h

Et = 80%, SL = Q/799 + 16.6 √V

SL = Standby loss in percent per hour; V = Rated tank volume (gallons; Vm = Measured volume in the tank; Q = nameplate input rate (Btu/h); Et = thermal efficiency; %h = tank loss per hour expressed as a percentage

 

Thermal Efficiency

Applicability

Oil and gas fired water heaters not covered by NAECA energy factor requirements

Definition

The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input

Units

Unitless ratio between 0 and 1.0

Input Restrictions

Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.

Baseline Rules

Thermal efficiency is only used when the baseline system is a gas storage water heater > 75,000 Btu/h. In this case, the thermal efficiency (Et) is 80%.

 

Tank Standby Loss

Applicability

Water heaters not covered by NAECA energy factor requirements

Definition

The tank standby loss for storage tanks, which includes the effect of recovery efficiency.

Units

Btu/h for the entire tank or percent standby loss (%h)

Input Restrictions

As specified in manufacturer data and documented on the construction documents

Baseline Rules

See Table 9.1.3-3.

 

Tank Off-Cycle Loss Coefficient

Applicability

Water heaters

Definition

The tank standby loss coefficient (UA) for the water heater. For small water heaters covered by NAECA, the loss coefficient is a derived parameter, a function of the energy factor and recovery efficiency.

Units

Btu/h-°F

Input Restrictions

For NAECA covered water heaters, the loss coefficient is calculated by the following:

(Equation 3.9.1-1)

$$UA = \frac{1/EF = 1/RE}{67.4 \cdot (\frac{24}{41094}-\frac{1}{RE \cdot P_{on}})}$$

Where:

EF = The energy factor of the rated water heater (unitless)

RE = The recovery efficiency of the rated water heater. If this data is not available, the default shall be 0.78 for gas water heaters and 0.93 for electric water heaters.

Pon = The input power to the water heater, in Btu/h

Baseline Rules

The baseline loss coefficient for NAECA water heaters shall be 10 Btu/h-°F for gas-fired water heaters

 

Off-Cycle Parasitic Losses

Applicability

Water heaters

Definition

The rate of parasitic losses, such as a pilot light or controls, when the water heater is not heating. If modeled explicitly, pilot lights should contribute to off-cycle heating.

Units

Watts

Input Restrictions

As designed

Baseline Rules

0

 

Off-Cycle Fuel Type

Applicability

Water heaters

Definition

The type of fuel that serves energy using parasitic equipment, such as a pilot light or controls, when the water heater is not heating

Units

List: electricity, gas, oil, propane

Input Restrictions

As designed

Baseline Rules

Not applicable

 

On-Cycle Parasitic Losses

Applicability

Water heaters

Definition

The rate of parasitic losses, such as a pilot light or draft fan controls, when the water heater is heating. This may be different than off cycle losses if the flue energy is considered.

Units

Watts

Input Restrictions

As designed

Baseline Rules

0

 

On-Cycle Fuel Type

Applicability

Water heaters

Definition

The type of fuel that serves energy using parasitic equipment, such as a pilot light or controls, when the water heater is not heating

Units

List: electricity, gas, oil, propane

Input Restrictions

As designed

Baseline Rules

Not applicable

 

Water Heater Ambient Temperature  Indicator

Applicability

Water heaters

Definition

The location of the water heater for determining losses and energy interaction with the surroundings

Units

List: Schedule, Zone, Outdoors

Input Restrictions

As designed. When “Schedule” is used, a time of day schedule needs to be specified with temperature schedule for each hour.

Baseline Rules

Same as proposed

 

Fuel Water Heater Part Load Efficiency Curve

Applicability

Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified

Definition

A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.

Units

Percent (%)

Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(Equation 3.9.1-2)

$$Fuel_{PartLoad} = Fuel_{Design} \times FHeatPLC$$

$$FHeatPLC = a + b \cdot \frac{Q_{PartLoad}}{Q_{Rated}} + c \cdot \left ( \frac{Q_{PartLoad}}{Q_{Rated}} \right ) ^{2}$$

where

FHeatPLC

The fuel heating part load efficiency curve

Fuelpartload

The fuel consumption at part load conditions (Btu/h)

Fueldesign

The fuel consumption at design conditions (Btu/h)

Qpartload

The water heater capacity at part load conditions (Btu/h)

Qrated

The water heater capacity at design conditions (Btu/h)

a

Constant, 0.021826

b

Constant, 0.977630

c

Constant, 0.000543 

 

Baseline Rules

The baseline building equipment shall use the default curve

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name

Applicability

All recirculation systems

Definition

A unique descriptor for each water heating recirculation system

Units

Text, unique

Input Restrictions

Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.

Baseline Rules

The naming convention for the baseline building system shall be similar to the proposed design.

 

Pumping Power

Applicability

All recirculation systems

Definition

The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.

Units

Watts (W)

Input Restrictions

Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.

Baseline Rules

Pumping power in the baseline building shall be the same as the proposed design unless specific measures are included in the proposed design to reduce the pumping power. Example measures could include reducing pumping head by oversizing distribution piping or specifying premium efficiency motors or pumps.

 

Schedule

Applicability

All recirculation systems

Definition

An on/off or fraction schedule that indicates when the recirculation system is expected to be operated

Units

Data structure: schedule, on/off or fraction

Input Restrictions

The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.

Baseline Rules

Recirculation schedules for the baseline building shall be the same as the proposed design.

 

Piping

Applicability

All recirculation systems

Definition

The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).

Units

Btu/h-°F specified separately for outdoor, indoor, or buried locations

Input Restrictions

In accordance with Standard 90.1-2016, Section G3.1.3.6, piping heat losses are not modeled for the proposed building

Baseline Rules

Same as proposed design.

Water Healing Auxiliaries

External Storage Tank Insulation

Applicability

All water heating systems that have an external storage tank

Definition

Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.

Units

R-value (h-ft2-°F/Btu)

Input Restrictions

As specified in manufacturer data and documented on the construction documents

Baseline Rules

The baseline building does not have an external storage tank.

 

External Storage Tank Area

Applicability

All water heating systems that have an external storage tank

Definition

Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This documents the entire exterior surface area of the tank.

Units

ft²

Input Restrictions

As specified in manufacturer specifications

Baseline Rules

The baseline building does not have an external storage tank.

 

Heat Recovery

Applicability

Water heating systems that are coupled to heat recovery equipment

Definition

Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.

Units

Data structure: depends on the equipment producing the heat

Input Restrictions

There are no restrictions, other than agreement with the construction documents.

Baseline Rules

The baseline building has heat recovery when the when all of the following conditions are true:

  • The building operates 24 hours per day.
  • The building has water cooled chillers with a heat rejection capacity greater than 6 million Btu/h. This equates to about 400 tons of electric chiller capacity.
  • The water heating peak use is greater than 1,000,000 Btu/h.

 

Solar Thermal

Applicability

Water heating systems with a solar thermal system

Definition

A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal.

Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design.

Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to provide storage to account for the temporal mismatch.

Units

Data structure: will vary with the software and system details

Input Restrictions

There are no restrictions, other than agreement with the construction documents.

Baseline Rules

The baseline building has no solar auxiliary system.

 

Combined Space Heating and Water Heating

Applicability

Projects that use a boiler to provide both space heat and water heating

Definition

A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.

Units

Data structure

Input Restrictions

The proposed design may have a combined space and water heating system.

Baseline Rules

The baseline building shall be modeled with separate space heating and water heating systems, meeting the prescriptive requirements for each. The water heating system shall use the same fuel as the combined boiler.

Building EQ

System Loads and Configuration

Water Heating System Name
Applicability All water heating systems
Definition A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Water Heating Peak Use
Applicability All water heating systems, required
Definition

An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances, etc.). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation.

Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc.

It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.

Units Btu/h or gallons/h
Input Restrictions For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B are default values, but other values may be used with justification.
Water Heating Schedule
Applicability All water heating systems, required
Definition A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units Data structure: schedule, fractional
Input Restrictions For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B, Table 7 are default values, but other values may be used with justification.
Water Heating System Configuration
Applicability All water heating systems, required
Definition The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units Data structure
Input Restrictions None

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability All water heaters
Definition A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Water Heater Type and Size
Applicability All water heaters
Definition

This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below. See Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007 for more detail.

  • Electric water heaters (storage and instantaneous)
    • Small (≤ 12 kW)
    • Large (> 12 kW)
  • Heat pump
  • Gas storage water heaters
    • Small (≤ 75,000 Btu/h)
    • Medium (> 75,000 and ≤ 155,000 Btu/h)
    • Large (> 155,000 Btu/h)
  • Gas instantaneous water heaters
    • Small (> 50,000 and < 200,000 Btu/h)
    • Large (≥ 200,000 Btu/h)
  • Oil storage water heaters
    • Small (≤ 105,000 Btu/h)
    • Medium (> 105,000 and ≤ 155,000 Btu/h)
    • Large (> 155,000 Btu/h)
  • Oil instantaneous water heaters
    • Small (≤ 210,000 Btu/h)
    • Large (> 210,000 Btu/h)
  • Gas hot water supply boiler
  • Oil hot water supply boiler
Units List (see above)
Input Restrictions The water heater type shall agree with equipment specified in the construction documents.
Rated Capacity
Applicability All water heaters
Definition The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007 or Table 7.2.2 of ASHRAE Standard 90.1-2001
Units Thousands of British Thermal Units per hour (MBH)
Input Restrictions As designed. If the loads are not met, autosize.
Energy Factor
Applicability Equipment covered by NAECA, which includes small storage and instantaneous water heaters
Definition The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units Unitless ratio
Input Restrictions Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Thermal Efficiency
Applicability Oil and gas fired water heaters not covered by NAECA
Definition The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units Unitless ratio
Input Restrictions Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Tank Standby Loss
Applicability Water heaters not covered by NAECA
Definition The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units Btu/h for the entire tank
Input Restrictions As specified in manufacturer data and documented on the construction documents
Fuel Water Heater Part Load Efficiency Curve
Applicability Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified
Definition A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.
Units Percent (%)
Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(6.9.1-1)

$$ Fuel_{partload} = Fuel_{design} \times F\!HeatP\!L\!C$$ $$F\!HeatP\!L\!C = \left ( a+ b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \right )$$where

FHeatPLC The fuel heating part load efficiency curve
Fuelpartload The fuel consumption at part load conditions (Btu/h)
Fueldesign The fuel consumption at design conditions (Btu/h)
Qpartload The water heater capacity at part load conditions (Btu/h)
Qrated The water heater capacity at design conditions (Btu/h)
a Constant, 0.021826
b Constant, 0.977630
c Constant, 0.000543

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability All recirculation systems
Definition A unique descriptor for each water heating recirculation system
Units Text, unique
Input Restrictions Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Pumping Power
Applicability All recirculation systems
Definition The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units Watts (W)
Input Restrictions Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Schedule
Applicability All recirculation systems
Definition An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units Data structure: schedule, on/off or fraction
Input Restrictions The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.
Piping
Applicability All recirculation systems
Definition The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions All piping in the recirculation system should be included. Heat loss for each of the three conditions should be consistent with piping runs, sizes, and insulation as shown on the construction documents.

Water Healing Auxiliaries

External Storage Tanks
Applicability All water heating systems that have an external storage tank
Definition Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units Btu/h for the entire tank
Input Restrictions As specified in manufacturer data and documented on the construction documents
Heat Recovery
Applicability Water heating systems that are coupled to heat recovery equipment
Definition Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units Data structure: depends on the equipment producing the heat
Input Restrictions There are no restrictions, other than agreement with the construction documents.
Solar Thermal
Applicability Water heating systems with a solar thermal system
Definition

A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal.

Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design.
Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to account for the temporal mismatch in some manner.

Units Data structure: will vary with the software and system details
Input Restrictions There are no restrictions, other than agreement with the construction documents.
Combined Space Heating and Water Heating
Applicability Projects that use a boiler to provide both space heat and water heating
Definition A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units Data structure
Input Restrictions The proposed design may have a combined space and water heating system.
Energy Star

System Loads and Configuration

Water Heating System Name
Applicability All water heating systems
Definition A unique descriptor for each water heating system. A system consists of one or more water heaters, a distribution system, an estimate of hot water use, and a schedule for that use. Nonresidential buildings will typically have multiple systems, perhaps a separate electric water heater for each office break room, etc. Other building types such as hotels and hospitals may have a single system serving the entire building.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Water Heating Peak Use
Applicability All water heating systems, required
Definition

An indication of the peak hot water usage (e.g. service to sinks, showers, and kitchen appliances, etc.). When specified per occupant, this value is multiplied by design occupancy density values and modified by service water heating schedules to obtain hourly load values which are used in the simulation.

Peak consumption is commonly specified as gallons per hour per occupant, dwelling unit, hotel room, patient room, or floor area. If consumption is specified in gallons per hour, then additional inputs would be needed such as supply temperature, cold water inlet temperature, etc.

It is also common to specify peak use as a thermal load in Btu/h. In the latter case, there is an implied assumption for the cold water inlet temperature, supply temperature, distribution losses, and other factors. The thermal load does not include conversion efficiencies of water heating equipment.

Units Btu/h or gallons/h
Input Restrictions For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B are default values, but other values may be used with justification.
Water Heating Schedule
Applicability All water heating systems, required
Definition A fractional schedule reflecting the time pattern of water heating use. This input modifies the water heating peak use, described above.
Units Data structure: schedule, fractional
Input Restrictions For the purpose of green building ratings and Design to Earn ENERGY STAR, the inputs from Appendix B, Table 7 are default values, but other values may be used with justification.
Water Heating System Configuration
Applicability All water heating systems, required
Definition The configuration and layout of the water heating system, including the number of water heaters; the size, location, length and insulation of distribution pipes; recirculation systems and pumps; and any other details about the system that would affect the energy model.
Units Data structure
Input Restrictions None

Water Heaters

This section describes the building descriptors for water heaters. Typically, a building will have multiple water heating systems and each system can have multiple water heaters, so these building descriptors may need to be specified more than once.

Water Heater Name
Applicability All water heaters
Definition A unique descriptor for each water heater in the system. Some systems will have multiple pieces of equipment, for instance a series of water heaters plumbed in parallel or a boiler with a separate storage tank.
Units Text, unique
Input Restrictions Where applicable, this should match the tags that are used on the plans such that a plan reviewer can make a connection.
Water Heater Type and Size
Applicability All water heaters
Definition

This building descriptor includes information needed to determine the criteria from baseline standards. The choices are listed below. See Table 7.2.2 of ASHRAE Standard 90.1-2001 or Table 7.8 of ASHRAE Standard 90.1-2007 for more detail.

  • Electric water heaters (storage and instantaneous)
    • Small (≤ 12 kW)
    • Large (> 12 kW)
  • Heat pump
  • Gas storage water heaters
    • Small (≤ 75,000 Btu/h)
    • Medium (> 75,000 and ≤ 155,000 Btu/h)
    • Large (> 155,000 Btu/h)
  • Gas instantaneous water heaters
    • Small (> 50,000 and < 200,000 Btu/h)
    • Large (≥ 200,000 Btu/h)
  • Oil storage water heaters
    • Small (≤ 105,000 Btu/h)
    • Medium (> 105,000 and ≤ 155,000 Btu/h)
    • Large (> 155,000 Btu/h)
  • Oil instantaneous water heaters
    • Small (≤ 210,000 Btu/h)
    • Large (> 210,000 Btu/h)
  • Gas hot water supply boiler
  • Oil hot water supply boiler
Units List (see above)
Input Restrictions The water heater type shall agree with equipment specified in the construction documents.
Rated Capacity
Applicability All water heaters
Definition The heating capacity of a water heater at the rated conditions specified in Table 7.8 of ASHRAE Standard 90.1-2007 or Table 7.2.2 of ASHRAE Standard 90.1-2001
Units Thousands of British Thermal Units per hour (MBH)
Input Restrictions As designed. If the loads are not met, autosize.
Energy Factor
Applicability Equipment covered by NAECA, which includes small storage and instantaneous water heaters
Definition The energy factor (EF) is the ratio of the energy delivered by the water heater divided by the energy used, in the same units. EF is calculated according to the DOE 10 CFR Part 430 test procedure, which specifies a 24-hour pattern of draws, a storage temperature, inlet water temperature, and other test conditions. These conditions result in the energy delivered for the test period. Energy inputs are measured for the same test period and the EF ratio is calculated.
Units Unitless ratio
Input Restrictions Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Thermal Efficiency
Applicability Oil and gas fired water heaters not covered by NAECA
Definition The full load efficiency of a water heater at rated conditions expressed as a dimensionless ratio of output over input
Units Unitless ratio
Input Restrictions Building descriptors for the proposed design should be consistent with equipment specified on the construction documents or observed in the candidate building.
Tank Standby Loss
Applicability Water heaters not covered by NAECA
Definition The tank standby loss for storage tanks, which includes the effect of recovery efficiency.
Units Btu/h for the entire tank
Input Restrictions As specified in manufacturer data and documented on the construction documents
Fuel Water Heater Part Load Efficiency Curve
Applicability Equipment not covered by NAECA for which a thermal efficiency, as opposed to an EF is specified
Definition A set of factors that adjust the full-load thermal efficiency for part load conditions. Typically, the factor is set as a curve.
Units Percent (%)
Input Restrictions

The following default curve shall be used unless detailed information is provided to justify alternative values. The default curve shall take the form of a quadratic equation as follows:

(6.9.1-1)

$$ Fuel_{partload} = Fuel_{design} \times F\!HeatP\!L\!C$$ $$F\!HeatP\!L\!C = \left ( a+ b \times \frac{Q_{partload}}{Q_{rated}} + c \times \left ( \frac{Q_{partload}}{Q_{rated}}\right )^2 \right )$$where

FHeatPLC The fuel heating part load efficiency curve
Fuelpartload The fuel consumption at part load conditions (Btu/h)
Fueldesign The fuel consumption at design conditions (Btu/h)
Qpartload The water heater capacity at part load conditions (Btu/h)
Qrated The water heater capacity at design conditions (Btu/h)
a Constant, 0.021826
b Constant, 0.977630
c Constant, 0.000543

Recirculation Systems

This section describes the building descriptors for hot water recirculation systems. The baseline building has a recirculation system when the proposed design does. This is one aspect of the water heating system configuration (see above).

Recirculation System Name
Applicability All recirculation systems
Definition A unique descriptor for each water heating recirculation system
Units Text, unique
Input Restrictions Where applicable, this should match the tags or descriptions that are used on the plans such that a plan reviewer can make a connection.
Pumping Power
Applicability All recirculation systems
Definition The electric demand of the pumps when the recirculation system is operating. This input is a function of the flow rate, the pumping head, the motor efficiency, and the pump efficiency. Some software may allow each of these factors to be separately entered.
Units Watts (W)
Input Restrictions Pumping power shall be consistent with the piping configuration, flow rate, and equipment specified on the construction documents.
Schedule
Applicability All recirculation systems
Definition An on/off or fraction schedule that indicates when the recirculation system is expected to be operated
Units Data structure: schedule, on/off or fraction
Input Restrictions The schedule for operation of the recirculation system shall be consistent with the design intent of the system. Hotels, hospitals, and other 24x7 institutional buildings will typically have a system that runs continuously. The schedule should be consistent with the controls called for on the construction documents: no control (runs constantly), timer control, temperature control, timer/temperature control, or demand control.
Piping
Applicability All recirculation systems
Definition The heat loss rate of piping for recirculating systems. This may be defined separately for pipe that is exposed to outdoor conditions, indoor or semi-heated conditions, or buried underground conditions. These losses may be modeled as additional loads on the water heater(s).
Units Btu/h-°F specified separately for outdoor, indoor, or buried locations
Input Restrictions All piping in the recirculation system should be included. Heat loss for each of the three conditions should be consistent with piping runs, sizes, and insulation as shown on the construction documents.

Water Healing Auxiliaries

External Storage Tanks
Applicability All water heating systems that have an external storage tank
Definition Some water heating systems have a storage tank that is separate from the water heater(s) that provides additional storage capacity. This building descriptor addresses the heat loss related to the external tank, which is an additional load that must be satisfied by the water heater(s). The heat loss shall account for the surface area and U-factor tank, as well as the average temperature conditions where the tank is located. Some software may allow these factors to be separately specified.
Units Btu/h for the entire tank
Input Restrictions As specified in manufacturer data and documented on the construction documents
Heat Recovery
Applicability Water heating systems that are coupled to heat recovery equipment
Definition Building equipment such as air conditioners, chillers, gas fired generators, etc. produce thermal energy that may be recovered and used to heat water. The heat producing characteristics are generally defined for the equipment that is producing the heat, not the equipment that is receiving the heat (water heaters in this case). The building descriptors will vary depending on the equipment. The models for heat producing equipment need to produce output on an hourly basis so that the schedule of heat production and heating needs can be aligned and evaluated in the water heating model.
Units Data structure: depends on the equipment producing the heat
Input Restrictions There are no restrictions, other than agreement with the construction documents.
Solar Thermal
Applicability Water heating systems with a solar thermal system
Definition

A solar thermal water heating system consists of one or more collectors. Water is passed through these collectors and is heated under the right conditions. There are two general types of solar water heaters: integrated collector storage (ICS) systems and active systems. Active systems include pumps to circulate the water, storage tanks, piping, and controls. ICS systems generally have no pumps and piping is minimal.

Solar systems may be tested and rated as a complete system or the collectors may be separately tested and rated. SRCC OG-300 is the test procedure for whole systems and SRCC OG-100 is the test procedure for collectors. The building descriptors used to define the solar thermal system may vary with each software application and with the details of system design.
Heat produced by solar thermal systems will generally not align perfectly with the need for heating, so the model needs to account for the temporal mismatch in some manner.

Units Data structure: will vary with the software and system details
Input Restrictions There are no restrictions, other than agreement with the construction documents.
Combined Space Heating and Water Heating
Applicability Projects that use a boiler to provide both space heat and water heating
Definition A system that provides both space heating and water heating from the same equipment, generally the space heating boiler. Such systems are restricted by the baseline standards, but may be modeled in the candidate building. The restrictions are due to the misalignment of the space heating load and the water heating load. The first is highly intermittent and weather dependent, while the latter is more constant and not generally related to the weather.
Units Data structure
Input Restrictions The proposed design may have a combined space and water heating system.