3.7.2 System Controls

Schedules

Cooling Schedule
Applicability All cooling systems
Definition A schedule that represents the availability of cooling
Units Data structure: schedule, on/off
Input Restrictions For tax deduction calculations, the fan schedules from Tables 12 through 16 of Appendix C shall be used for cooling availability. For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C shall be used as a default. The cooling availability schedule shall be consistent with the supply fan schedule and thermostat schedules to reduce the likelihood of unmet load hours.
Baseline Rules Same as the proposed design
Heating Schedule
Applicability All systems
Definition A schedule that represents the availability of heating
Units Data structure: schedule, on/off
Input Restrictions For tax deduction calculations, the schedules from Tables 12 through 16 of Appendix C shall be used. For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C shall be used as a default. The heating availability schedule shall be consistent with the supply fan schedule.
Baseline Rules Same as the proposed design
Air-Handler Schedule
Applicability All systems that do not cycle with loads
Definition A schedule that indicates when the air handler operates continuously
Units Data structure: schedule, on/off
Input Restrictions For the purpose of tax deduction calculations, the fan schedule is prescribed. One of the schedules from Appendix C, Tables 12-16 shall be used.

For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C are defaults, but other schedules may be used when detailed information is known about the proposed design.

When a fan system serves several occupancies, the fan schedule must remain ON to serve the operating hours of each occupancy.
Baseline Rules Same as the proposed design
Air Handler Fan Cycling
Applicability All fan systems
Definition This building descriptor indicates whether the system supply fan operates continuously or cycles with building loads. The fan systems in most commercial buildings operate continuously.
Units List: continuous or cycles with loads
Input Restrictions Continuous fan operation during occupied periods is a prescribed input, except for hotel guest rooms and high-rise residential. For these building types, continuous operation is the default, however, the option to let the fan cycle with loads may be used when the following conditions are met and documented:
  • The spaces served by the system are located within 25 ft of an operable window.
  • The openable window area is at least 4% of the floor space.
  • Other requirements for natural ventilation specified in ASHRAE Standard 62.1-2007, Section 5.1 are satisfied.
For natural ventilation systems, an air conditioner is modeled in the proposed design even though one is not specified for the proposed design. This fan in the simulated air conditioner is allowed to cycle with loads since the simulated air conditioner is assumed to operate only when natural ventilation is unable to satisfy thermal comfort.
Baseline Rules Same as proposed design, except for natural ventilation, in which case the fans in the baseline building are assumed to operate continuously
Optimum Start Control
Applicability Systems with the control capability for flexible scheduling of system start time based on building loads.
Definition Optimum start control adjusts the start time of the HVAC unit such that the space is brought to setpoint just prior to occupancy. This control strategy modifies the heating, cooling, and fan schedules.
Units Boolean (Yes/No)
Input Restrictions As designed
Baseline Rules The baseline building shall have optimum start controls when the baseline building design supply airflow is greater than 10,000 cfm.
Night-Cycle HVAC Fan Control
Applicability All systems
Definition The control of an HVAC system that is triggered by the heating or cooling temperature setpoint for thermal blocks during periods when the heating, cooling and fan systems are scheduled to be off. The choices are:
  • Cycle on call from any zone
  • Cycle on call from the primary control zone
  • Stay off
  • Cycle zone fans only (for systems with fan-powered boxes) Restart fans below given ambient temperature.
Units None
Input Restrictions As designed. However, night-cycle control shall be cycled on call from any zone for heating in climate zones 2 through 8, and for cooling in climate zones 1b, 2b, and 3b.
Baseline Rules Cycle on call from any zone

Cooling Control

Cooling Supply Air Temperature
Applicability Applicable to all systems
Definition The supply air temperature setpoint at design cooling conditions
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules 20°F lower than the design room air temperature
Cooling Supply Air Temperature Control
Applicability Any system with multiple cooling stages or unloading
Definition The method of controlling the supply air temperature. Choices are:
  • Fixed (constant)
  • Reset by warmest zone
  • Reset by outside air dry-bulb temperature
  • Scheduled setpoint
Units List (see above)
Input Restrictions As designed
Baseline Rules For baseline building systems 1 through 4, the SAT control is not applicable. For systems 5 through 8, the SAT control shall be reset by outside dry-bulb temperature.
Cooling Reset Schedule by OSA
Applicability When the proposed design resets SAT by outside air dry-bulb temperature
Definition A linear reset schedule that represents the SAT setpoint as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see [bookref id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-oat-for-dry-b-and-marine-c-climates"]):
  • The coldest cooling supply air temperature
  • The corresponding (hot) outdoor air dry-bulb setpoint
  • The warmest cooling supply air temperature
  • The corresponding (cool) outdoor air dry-bulb setpoint

[figure title="SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT) for Dry (B) and Marine (C) Climates" id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-oat-for-dry-b-and-marine-c-climates"]SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT) for Dry (B) and Marine (C) Climates[/figure]

[figure title="SAT cooling setpoint reset based on outdoor air temperature for humid 'A' climates" id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-for-humid-a-climates"]SAT cooling setpoint reset based on outdoor air temperature for humid “A” climates[/figure]

Units Data structure (two matched pairs of SAT and OAT, see above)
Input Restrictions As designed
Baseline Rules Applicable for baseline building systems 5 through 8. For these systems, the minimum SAT shall be equal to the design conditions SAT when OAT is equal to or greater than 80 F. The maximum SAT shall be 5 F greater than the minimum when the OAT is 60 F or less.

Heating Control

Preheat Setpoint
Applicability Systems with a preheat coil located in the outside air stream
Definition The control temperature leaving the preheat coil
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules Same as the proposed design
Heating Supply Air Temperature
Applicability All systems
Definition The supply air temperature leaving the air handler when the system is in a heating mode (not the air temperature leaving the reheat coils in VAV boxes)
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules 110°F for system types 1-4; 70°F for system types 5-8
Heating Supply Air Temperature Control
Applicability Systems with the capability to vary heating SAT
Definition The method of controlling heating SAT. Choices are:
  • Fixed (constant)
  • Reset by coldest zone
  • Reset by outside air dry-bulb temperature
  • Scheduled setpoint
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules Fixed (constant)
Heating Reset Schedule by OSA
Applicability Systems that reset the heating SAT by outside dry-bulb temperature (this typically applies to dual-duct systems or to single zone systems with hydronic heating coils)
Definition A linear reset schedule that represents the heating supply air temperature or hot deck supply air temperature (for dual duct systems) as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see [bookref id="example-of-sat-heating-setpoint-reset-based-on-outdoor-air-temperature-oat"]):
  • The hottest heating supply air temperature
  • The corresponding (cold) outdoor air dry-bulb threshold
  • The coolest heating supply air temperature
  • The corresponding (mild) outdoor air dry-bulb threshold

[figure title="Example of SAT heating setpoint reset based on outdoor air temperature (OAT)." id="example-of-sat-heating-setpoint-reset-based-on-outdoor-air-temperature-oat"]Example of SAT heating setpoint reset based on outdoor air temperature (OAT)[/figure]

Units Data structure (°F)
Input Restrictions As designed
Baseline Rules Not applicable

Night Purge

The baseline building does not have night purge controls. If the software supports it and the proposed design has the features, the following keywords may be used to model night purge. Note that night purge is coupled with thermal mass in the building, which is specified by other building descriptors.

Night Purge Availability Schedule
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition A schedule which represents the availability of night purge controls.
Units Data structure: schedule, on/off
Input Restrictions As designed. The default is no night purge control.
Baseline Rules Not applicable
Night Purge Control
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition The control strategy for operation of nighttime purge. The control strategy may take account of indoor temperature, season, indoor temperature and other factors.
Units Data structure
Input Restrictions As designed
Baseline Rules Not applicable
Night Purge Fan Ratio
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition The ratio of fan speed for a night purge cycle.
Units Ratio
Input Restrictions As designed. The default is 100% (or fans available at full speed).
Baseline Rules Not applicable
90.1-2007

Schedules

Cooling Schedule
Applicability All cooling systems
Definition A schedule that represents the availability of cooling
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C shall be used as a default. The cooling availability schedule shall be consistent with the supply fan schedule and thermostat schedules to reduce the likelihood of unmet load hours.
Baseline Rules Same as the proposed design
Heating Schedule
Applicability All systems
Definition A schedule that represents the availability of heating
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C shall be used as a default. The heating availability schedule shall be consistent with the supply fan schedule.
Baseline Rules Same as the proposed design
Air-Handler Schedule
Applicability All systems that do not cycle with loads
Definition A schedule that indicates when the air handler operates continuously
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C are defaults, but other schedules may be used when detailed information is known about the proposed design.

When a fan system serves several occupancies, the fan schedule must remain ON to serve the operating hours of each occupancy.
Baseline Rules Same as the proposed design
Air Handler Fan Cycling
Applicability All fan systems
Definition This building descriptor indicates whether the system supply fan operates continuously or cycles with building loads. The fan systems in most commercial buildings operate continuously.
Units List: continuous or cycles with loads
Input Restrictions Continuous fan operation during occupied periods is a prescribed input, except for hotel guest rooms and high-rise residential. For these building types, continuous operation is the default, however, the option to let the fan cycle with loads may be used when the following conditions are met and documented:
  • The spaces served by the system are located within 25 ft of an operable window.
  • The openable window area is at least 4% of the floor space.
  • Other requirements for natural ventilation specified in ASHRAE Standard 62.1-2007, Section 5.1 are satisfied.
For natural ventilation systems, an air conditioner is modeled in the proposed design even though one is not specified for the proposed design. This fan in the simulated air conditioner is allowed to cycle with loads since the simulated air conditioner is assumed to operate only when natural ventilation is unable to satisfy thermal comfort.
Baseline Rules Same as proposed design, except for natural ventilation, in which case the fans in the baseline building are assumed to operate continuously
Optimum Start Control
Applicability Systems with the control capability for flexible scheduling of system start time based on building loads.
Definition Optimum start control adjusts the start time of the HVAC unit such that the space is brought to setpoint just prior to occupancy. This control strategy modifies the heating, cooling, and fan schedules.
Units Boolean (Yes/No)
Input Restrictions As designed
Baseline Rules The baseline building shall have optimum start controls when the baseline building design supply airflow is greater than 10,000 cfm.
Night-Cycle HVAC Fan Control
Applicability All systems
Definition The control of an HVAC system that is triggered by the heating or cooling temperature setpoint for thermal blocks during periods when the heating, cooling and fan systems are scheduled to be off. The choices are:
  • Cycle on call from any zone
  • Cycle on call from the primary control zone
  • Stay off
  • Cycle zone fans only (for systems with fan-powered boxes) Restart fans below given ambient temperature.
Units None
Input Restrictions As designed. However, night-cycle control shall be cycled on call from any zone for heating in climate zones 2 through 8, and for cooling in climate zones 1b, 2b, and 3b.
Baseline Rules Cycle on call from any zone

Cooling Control

Cooling Supply Air Temperature
Applicability Applicable to all systems
Definition The supply air temperature setpoint at design cooling conditions
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules 20°F lower than the design room air temperature
Cooling Supply Air Temperature Control
Applicability Any system with multiple cooling stages or unloading
Definition The method of controlling the supply air temperature. Choices are:
  • Fixed (constant)
  • Reset by warmest zone
  • Reset by outside air dry-bulb temperature
  • Scheduled setpoint
Units List (see above)
Input Restrictions As designed
Baseline Rules For baseline building systems 1 through 4, the SAT control is not applicable. For systems 5 through 8, the SAT control shall be reset by outside dry-bulb temperature.
Cooling Reset Schedule by OSA
Applicability When the proposed design resets SAT by outside air dry-bulb temperature
Definition A linear reset schedule that represents the SAT setpoint as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see [bookref id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-oat-for-dry-b-and-marine-c-climates"]):
  • The coldest cooling supply air temperature
  • The corresponding (hot) outdoor air dry-bulb setpoint
  • The warmest cooling supply air temperature
  • The corresponding (cool) outdoor air dry-bulb setpoint

[figure title="SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT) for Dry (B) and Marine (C) Climates" id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-oat-for-dry-b-and-marine-c-climates"]SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT) for Dry (B) and Marine (C) Climates[/figure]

[figure title="SAT cooling setpoint reset based on outdoor air temperature for humid 'A' climates" id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-for-humid-a-climates"]SAT cooling setpoint reset based on outdoor air temperature for humid “A” climates[/figure]

Units Data structure (two matched pairs of SAT and OAT, see above)
Input Restrictions As designed
Baseline Rules Applicable for baseline building systems 5 through 8. For these systems, the minimum SAT shall be equal to the design conditions SAT when OAT is equal to or greater than 80 F. The maximum SAT shall be 5 F greater than the minimum when the OAT is 60 F or less.

Heating Control

Preheat Setpoint
Applicability Systems with a preheat coil located in the outside air stream
Definition The control temperature leaving the preheat coil
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules Same as the proposed design
Heating Supply Air Temperature
Applicability All systems
Definition The supply air temperature leaving the air handler when the system is in a heating mode (not the air temperature leaving the reheat coils in VAV boxes)
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules 110°F for system types 1-4; 70°F for system types 5-8
Heating Supply Air Temperature Control
Applicability Systems with the capability to vary heating SAT
Definition The method of controlling heating SAT. Choices are:
  • Fixed (constant)
  • Reset by coldest zone
  • Reset by outside air dry-bulb temperature
  • Scheduled setpoint
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules Fixed (constant)
Heating Reset Schedule by OSA
Applicability Systems that reset the heating SAT by outside dry-bulb temperature (this typically applies to dual-duct systems or to single zone systems with hydronic heating coils)
Definition A linear reset schedule that represents the heating supply air temperature or hot deck supply air temperature (for dual duct systems) as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see [bookref id="example-of-sat-heating-setpoint-reset-based-on-outdoor-air-temperature-oat"]):
  • The hottest heating supply air temperature
  • The corresponding (cold) outdoor air dry-bulb threshold
  • The coolest heating supply air temperature
  • The corresponding (mild) outdoor air dry-bulb threshold

[figure title="Example of SAT heating setpoint reset based on outdoor air temperature (OAT)." id="example-of-sat-heating-setpoint-reset-based-on-outdoor-air-temperature-oat"]Example of SAT heating setpoint reset based on outdoor air temperature (OAT)[/figure]

Units Data structure (°F)
Input Restrictions As designed
Baseline Rules Not applicable

Night Purge

The baseline building does not have night purge controls. If the software supports it and the proposed design has the features, the following keywords may be used to model night purge. Note that night purge is coupled with thermal mass in the building, which is specified by other building descriptors.

Night Purge Availability Schedule
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition A schedule which represents the availability of night purge controls.
Units Data structure: schedule, on/off
Input Restrictions As designed. The default is no night purge control.
Baseline Rules Not applicable
Night Purge Control
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition The control strategy for operation of nighttime purge. The control strategy may take account of indoor temperature, season, indoor temperature and other factors.
Units Data structure
Input Restrictions As designed
Baseline Rules Not applicable
Night Purge Fan Ratio
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition The ratio of fan speed for a night purge cycle.
Units Ratio
Input Restrictions As designed. The default is 100% (or fans available at full speed).
Baseline Rules Not applicable
90.1-2010

Schedules

Cooling Schedule
Applicability All cooling systems
Definition A schedule that represents the availability of cooling
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C shall be used as a default. The cooling availability schedule shall be consistent with the supply fan schedule and thermostat schedules to reduce the likelihood of unmet load hours.
Baseline Rules Same as the proposed design
Heating Schedule
Applicability All systems
Definition A schedule that represents the availability of heating
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C shall be used as a default. The heating availability schedule shall be consistent with the supply fan schedule.
Baseline Rules Same as the proposed design
Air-Handler Schedule
Applicability All systems that do not cycle with loads
Definition A schedule that indicates when the air handler operates continuously
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C are defaults, but other schedules may be used when detailed information is known about the proposed design.

When a fan system serves several occupancies, the fan schedule must remain ON to serve the operating hours of each occupancy.
Baseline Rules Same as the proposed design
Air Handler Fan Cycling
Applicability All fan systems
Definition This building descriptor indicates whether the system supply fan operates continuously or cycles with building loads. The fan systems in most commercial buildings operate continuously.
Units List: continuous or cycles with loads
Input Restrictions Continuous fan operation during occupied periods is a prescribed input, except for hotel guest rooms and high-rise residential. For these building types, continuous operation is the default, however, the option to let the fan cycle with loads may be used when the following conditions are met and documented:
  • The spaces served by the system are located within 25 ft of an operable window.
  • The openable window area is at least 4% of the floor space.
  • Other requirements for natural ventilation specified in ASHRAE Standard 62.1-2007, Section 5.1 are satisfied.
For natural ventilation systems, an air conditioner is modeled in the proposed design even though one is not specified for the proposed design. This fan in the simulated air conditioner is allowed to cycle with loads since the simulated air conditioner is assumed to operate only when natural ventilation is unable to satisfy thermal comfort.
Baseline Rules Same as proposed design, except for natural ventilation, in which case the fans in the baseline building are assumed to operate continuously
Optimum Start Control
Applicability Systems with the control capability for flexible scheduling of system start time based on building loads.
Definition Optimum start control adjusts the start time of the HVAC unit such that the space is brought to setpoint just prior to occupancy. This control strategy modifies the heating, cooling, and fan schedules.
Units Boolean (Yes/No)
Input Restrictions As designed
Baseline Rules The baseline building shall have optimum start controls when the baseline building design supply airflow is greater than 10,000 cfm.
Night-Cycle HVAC Fan Control
Applicability All systems
Definition The control of an HVAC system that is triggered by the heating or cooling temperature setpoint for thermal blocks during periods when the heating, cooling and fan systems are scheduled to be off. The choices are:
  • Cycle on call from any zone
  • Cycle on call from the primary control zone
  • Stay off
  • Cycle zone fans only (for systems with fan-powered boxes) Restart fans below given ambient temperature.
Units None
Input Restrictions As designed. However, night-cycle control shall be cycled on call from any zone for heating in climate zones 2 through 8, and for cooling in climate zones 1b, 2b, and 3b.
Baseline Rules Cycle on call from any zone

Cooling Control

Cooling Supply Air Temperature
Applicability Applicable to all systems
Definition The supply air temperature setpoint at design cooling conditions
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules 20°F lower than the design room air temperature
Cooling Supply Air Temperature Control
Applicability Any system with multiple cooling stages or unloading
Definition The method of controlling the supply air temperature. Choices are:
  • Fixed (constant)
  • Reset by warmest zone
  • Reset by outside air dry-bulb temperature
  • Scheduled setpoint
Units List (see above)
Input Restrictions As designed
Baseline Rules For baseline building systems 1 through 4, the SAT control is not applicable. For systems 5 through 8, the SAT control shall be reset by outside dry-bulb temperature.
Cooling Reset Schedule by OSA
Applicability When the proposed design resets SAT by outside air dry-bulb temperature
Definition A linear reset schedule that represents the SAT setpoint as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see Figure 6.7.2-1 and Figure 6.7.2-2):
  • The coldest cooling supply air temperature
  • The corresponding (hot) outdoor air dry-bulb setpoint
  • The warmest cooling supply air temperature
  • The corresponding (cool) outdoor air dry-bulb setpoint

SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT) for Dry (B) and Marine (C) Climates

 

Figure 6.7.2-1: SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT) for Dry (B) and Marine (C) Climates

 

SAT cooling setpoint reset based on outdoor air temperature for humid “A” climates

 

Figure 6.7.2-2: SAT cooling setpoint reset based on outdoor air temperature for humid 'A' climates

Units Data structure (two matched pairs of SAT and OAT, see above)
Input Restrictions As designed
Baseline Rules Applicable for baseline building systems 5 through 8. For these systems, the minimum SAT shall be equal to the design conditions SAT when OAT is equal to or greater than 80 F. The maximum SAT shall be 5 F greater than the minimum when the OAT is 60 F or less.

Heating Control

Preheat Setpoint
Applicability Systems with a preheat coil located in the outside air stream
Definition The control temperature leaving the preheat coil
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules Same as the proposed design
Heating Supply Air Temperature
Applicability All systems
Definition The supply air temperature leaving the air handler when the system is in a heating mode (not the air temperature leaving the reheat coils in VAV boxes)
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules 110°F for system types 1-4; 70°F for system types 5-8
Heating Supply Air Temperature Control
Applicability Systems with the capability to vary heating SAT
Definition The method of controlling heating SAT. Choices are:
  • Fixed (constant)
  • Reset by coldest zone
  • Reset by outside air dry-bulb temperature
  • Scheduled setpoint
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Baseline Rules Fixed (constant)
Heating Reset Schedule by OSA
Applicability Systems that reset the heating SAT by outside dry-bulb temperature (this typically applies to dual-duct systems or to single zone systems with hydronic heating coils)
Definition A linear reset schedule that represents the heating supply air temperature or hot deck supply air temperature (for dual duct systems) as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see Figure 6.7.2-3):
  • The hottest heating supply air temperature
  • The corresponding (cold) outdoor air dry-bulb threshold
  • The coolest heating supply air temperature
  • The corresponding (mild) outdoor air dry-bulb threshold

Example of SAT heating setpoint reset based on outdoor air temperature (OAT)

 

Figure 6.7.2-3: Example of SAT heating setpoint reset based on outdoor air temperature (OAT)

Units Data structure (°F)
Input Restrictions As designed
Baseline Rules Not applicable

Night Purge

The baseline building does not have night purge controls. If the software supports it and the proposed design has the features, the following keywords may be used to model night purge. Note that night purge is coupled with thermal mass in the building, which is specified by other building descriptors.

Night Purge Availability Schedule
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition A schedule which represents the availability of night purge controls.
Units Data structure: schedule, on/off
Input Restrictions As designed. The default is no night purge control.
Baseline Rules Not applicable
Night Purge Control
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition The control strategy for operation of nighttime purge. The control strategy may take account of indoor temperature, season, indoor temperature and other factors.
Units Data structure
Input Restrictions As designed
Baseline Rules Not applicable
Night Purge Fan Ratio
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition The ratio of fan speed for a night purge cycle.
Units Ratio
Input Restrictions As designed. The default is 100% (or fans available at full speed).
Baseline Rules Not applicable
90.1-2016 BM

This section addresses the following control topics:

Building EQ

Schedules

Cooling Schedule
Applicability All cooling systems
Definition A schedule that represents the availability of cooling
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C shall be used as a default. The cooling availability schedule shall be consistent with the supply fan schedule and thermostat schedules to reduce the likelihood of unmet load hours.
Heating Schedule
Applicability All systems
Definition A schedule that represents the availability of heating
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C shall be used as a default. The heating availability schedule shall be consistent with the supply fan schedule.
Air-Handler Schedule
Applicability All systems that do not cycle with loads
Definition A schedule that indicates when the air handler operates continuously
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C are defaults, but other schedules may be used when detailed information is known about the proposed design.

When a fan system serves several occupancies, the fan schedule must remain ON to serve the operating hours of each occupancy.
Air Handler Fan Cycling
Applicability All fan systems
Definition This building descriptor indicates whether the system supply fan operates continuously or cycles with building loads. The fan systems in most commercial buildings operate continuously.
Units List: continuous or cycles with loads
Input Restrictions Continuous fan operation during occupied periods is a prescribed input, except for hotel guest rooms and high-rise residential. For these building types, continuous operation is the default, however, the option to let the fan cycle with loads may be used when the following conditions are met and documented:
  • The spaces served by the system are located within 25 ft of an operable window.
  • The openable window area is at least 4% of the floor space.
  • Other requirements for natural ventilation specified in ASHRAE Standard 62.1-2007, Section 5.1 are satisfied.
For natural ventilation systems, an air conditioner is modeled in the proposed design even though one is not specified for the proposed design. This fan in the simulated air conditioner is allowed to cycle with loads since the simulated air conditioner is assumed to operate only when natural ventilation is unable to satisfy thermal comfort.
Optimum Start Control
Applicability Systems with the control capability for flexible scheduling of system start time based on building loads.
Definition Optimum start control adjusts the start time of the HVAC unit such that the space is brought to setpoint just prior to occupancy. This control strategy modifies the heating, cooling, and fan schedules.
Units Boolean (Yes/No)
Input Restrictions As designed
Night-Cycle HVAC Fan Control
Applicability All systems
Definition The control of an HVAC system that is triggered by the heating or cooling temperature setpoint for thermal blocks during periods when the heating, cooling and fan systems are scheduled to be off. The choices are:
  • Cycle on call from any zone
  • Cycle on call from the primary control zone
  • Stay off
  • Cycle zone fans only (for systems with fan-powered boxes) Restart fans below given ambient temperature.
Units None
Input Restrictions As designed.

Cooling Control

Cooling Supply Air Temperature
Applicability Applicable to all systems
Definition The supply air temperature setpoint at design cooling conditions
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Cooling Supply Air Temperature Control
Applicability Any system with multiple cooling stages or unloading
Definition The method of controlling the supply air temperature. Choices are:
  • Fixed (constant)
  • Reset by warmest zone
  • Reset by outside air dry-bulb temperature
  • Scheduled setpoint
Units List (see above)
Input Restrictions As designed
Cooling Reset Schedule by OSA
Applicability When the proposed design resets SAT by outside air dry-bulb temperature
Definition A linear reset schedule that represents the SAT setpoint as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see [bookref id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-oat-for-dry-b-and-marine-c-climates"]):
  • The coldest cooling supply air temperature
  • The corresponding (hot) outdoor air dry-bulb setpoint
  • The warmest cooling supply air temperature
  • The corresponding (cool) outdoor air dry-bulb setpoint

[figure title="SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT) for Dry (B) and Marine (C) Climates" id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-oat-for-dry-b-and-marine-c-climates"]SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT) for Dry (B) and Marine (C) Climates[/figure]

[figure title="SAT cooling setpoint reset based on outdoor air temperature for humid 'A' climates" id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-for-humid-a-climates"]SAT cooling setpoint reset based on outdoor air temperature for humid “A” climates[/figure]

Units Data structure (two matched pairs of SAT and OAT, see above)
Input Restrictions As designed

Heating Control

Preheat Setpoint
Applicability Systems with a preheat coil located in the outside air stream
Definition The control temperature leaving the preheat coil
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Heating Supply Air Temperature
Applicability All systems
Definition The supply air temperature leaving the air handler when the system is in a heating mode (not the air temperature leaving the reheat coils in VAV boxes)
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Heating Supply Air Temperature Control
Applicability Systems with the capability to vary heating SAT
Definition The method of controlling heating SAT. Choices are:
  • Fixed (constant)
  • Reset by coldest zone
  • Reset by outside air dry-bulb temperature
  • Scheduled setpoint
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Heating Reset Schedule by OSA
Applicability Systems that reset the heating SAT by outside dry-bulb temperature (this typically applies to dual-duct systems or to single zone systems with hydronic heating coils)
Definition A linear reset schedule that represents the heating supply air temperature or hot deck supply air temperature (for dual duct systems) as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see [bookref id="example-of-sat-heating-setpoint-reset-based-on-outdoor-air-temperature-oat"]):
  • The hottest heating supply air temperature
  • The corresponding (cold) outdoor air dry-bulb threshold
  • The coolest heating supply air temperature
  • The corresponding (mild) outdoor air dry-bulb threshold

[figure title="Example of SAT heating setpoint reset based on outdoor air temperature (OAT)." id="example-of-sat-heating-setpoint-reset-based-on-outdoor-air-temperature-oat"]Example of SAT heating setpoint reset based on outdoor air temperature (OAT)[/figure]

Units Data structure (°F)
Input Restrictions As designed

Night Purge

The baseline building does not have night purge controls. If the software supports it and the proposed design has the features, the following keywords may be used to model night purge. Note that night purge is coupled with thermal mass in the building, which is specified by other building descriptors.

Night Purge Availability Schedule
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition A schedule which represents the availability of night purge controls.
Units Data structure: schedule, on/off
Input Restrictions As designed. The default is no night purge control.
Night Purge Control
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition The control strategy for operation of nighttime purge. The control strategy may take account of indoor temperature, season, indoor temperature and other factors.
Units Data structure
Input Restrictions As designed
Night Purge Fan Ratio
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition The ratio of fan speed for a night purge cycle.
Units Ratio
Input Restrictions As designed. The default is 100% (or fans available at full speed).
Energy Star

Schedules

Cooling Schedule
Applicability All cooling systems
Definition A schedule that represents the availability of cooling
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C shall be used as a default. The cooling availability schedule shall be consistent with the supply fan schedule and thermostat schedules to reduce the likelihood of unmet load hours.
Heating Schedule
Applicability All systems
Definition A schedule that represents the availability of heating
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C shall be used as a default. The heating availability schedule shall be consistent with the supply fan schedule.
Air-Handler Schedule
Applicability All systems that do not cycle with loads
Definition A schedule that indicates when the air handler operates continuously
Units Data structure: schedule, on/off
Input Restrictions For green building ratings and Design to Earn ENERGY STAR, the schedules in Appendix C are defaults, but other schedules may be used when detailed information is known about the proposed design.

When a fan system serves several occupancies, the fan schedule must remain ON to serve the operating hours of each occupancy.
Air Handler Fan Cycling
Applicability All fan systems
Definition This building descriptor indicates whether the system supply fan operates continuously or cycles with building loads. The fan systems in most commercial buildings operate continuously.
Units List: continuous or cycles with loads
Input Restrictions Continuous fan operation during occupied periods is a prescribed input, except for hotel guest rooms and high-rise residential. For these building types, continuous operation is the default, however, the option to let the fan cycle with loads may be used when the following conditions are met and documented:
  • The spaces served by the system are located within 25 ft of an operable window.
  • The openable window area is at least 4% of the floor space.
  • Other requirements for natural ventilation specified in ASHRAE Standard 62.1-2007, Section 5.1 are satisfied.
For natural ventilation systems, an air conditioner is modeled in the proposed design even though one is not specified for the proposed design. This fan in the simulated air conditioner is allowed to cycle with loads since the simulated air conditioner is assumed to operate only when natural ventilation is unable to satisfy thermal comfort.
Optimum Start Control
Applicability Systems with the control capability for flexible scheduling of system start time based on building loads.
Definition Optimum start control adjusts the start time of the HVAC unit such that the space is brought to setpoint just prior to occupancy. This control strategy modifies the heating, cooling, and fan schedules.
Units Boolean (Yes/No)
Input Restrictions As designed
Night-Cycle HVAC Fan Control
Applicability All systems
Definition The control of an HVAC system that is triggered by the heating or cooling temperature setpoint for thermal blocks during periods when the heating, cooling and fan systems are scheduled to be off. The choices are:
  • Cycle on call from any zone
  • Cycle on call from the primary control zone
  • Stay off
  • Cycle zone fans only (for systems with fan-powered boxes) Restart fans below given ambient temperature.
Units None
Input Restrictions As designed.

Cooling Control

Cooling Supply Air Temperature
Applicability Applicable to all systems
Definition The supply air temperature setpoint at design cooling conditions
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Cooling Supply Air Temperature Control
Applicability Any system with multiple cooling stages or unloading
Definition The method of controlling the supply air temperature. Choices are:
  • Fixed (constant)
  • Reset by warmest zone
  • Reset by outside air dry-bulb temperature
  • Scheduled setpoint
Units List (see above)
Input Restrictions As designed
Cooling Reset Schedule by OSA
Applicability When the proposed design resets SAT by outside air dry-bulb temperature
Definition A linear reset schedule that represents the SAT setpoint as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see [bookref id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-oat-for-dry-b-and-marine-c-climates"]):
  • The coldest cooling supply air temperature
  • The corresponding (hot) outdoor air dry-bulb setpoint
  • The warmest cooling supply air temperature
  • The corresponding (cool) outdoor air dry-bulb setpoint

[figure title="SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT) for Dry (B) and Marine (C) Climates" id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-oat-for-dry-b-and-marine-c-climates"]SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT) for Dry (B) and Marine (C) Climates[/figure]

[figure title="SAT cooling setpoint reset based on outdoor air temperature for humid 'A' climates" id="sat-cooling-setpoint-reset-based-on-outdoor-air-temperature-for-humid-a-climates"]SAT cooling setpoint reset based on outdoor air temperature for humid “A” climates[/figure]

Units Data structure (two matched pairs of SAT and OAT, see above)
Input Restrictions As designed

Heating Control

Preheat Setpoint
Applicability Systems with a preheat coil located in the outside air stream
Definition The control temperature leaving the preheat coil
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Heating Supply Air Temperature
Applicability All systems
Definition The supply air temperature leaving the air handler when the system is in a heating mode (not the air temperature leaving the reheat coils in VAV boxes)
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Heating Supply Air Temperature Control
Applicability Systems with the capability to vary heating SAT
Definition The method of controlling heating SAT. Choices are:
  • Fixed (constant)
  • Reset by coldest zone
  • Reset by outside air dry-bulb temperature
  • Scheduled setpoint
Units Degrees Fahrenheit (°F)
Input Restrictions As designed
Heating Reset Schedule by OSA
Applicability Systems that reset the heating SAT by outside dry-bulb temperature (this typically applies to dual-duct systems or to single zone systems with hydronic heating coils)
Definition A linear reset schedule that represents the heating supply air temperature or hot deck supply air temperature (for dual duct systems) as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see [bookref id="example-of-sat-heating-setpoint-reset-based-on-outdoor-air-temperature-oat"]):
  • The hottest heating supply air temperature
  • The corresponding (cold) outdoor air dry-bulb threshold
  • The coolest heating supply air temperature
  • The corresponding (mild) outdoor air dry-bulb threshold

[figure title="Example of SAT heating setpoint reset based on outdoor air temperature (OAT)." id="example-of-sat-heating-setpoint-reset-based-on-outdoor-air-temperature-oat"]Example of SAT heating setpoint reset based on outdoor air temperature (OAT)[/figure]

Units Data structure (°F)
Input Restrictions As designed

Night Purge

The baseline building does not have night purge controls. If the software supports it and the proposed design has the features, the following keywords may be used to model night purge. Note that night purge is coupled with thermal mass in the building, which is specified by other building descriptors.

Night Purge Availability Schedule
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition A schedule which represents the availability of night purge controls.
Units Data structure: schedule, on/off
Input Restrictions As designed. The default is no night purge control.
Night Purge Control
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition The control strategy for operation of nighttime purge. The control strategy may take account of indoor temperature, season, indoor temperature and other factors.
Units Data structure
Input Restrictions As designed
Night Purge Fan Ratio
Applicability Systems that operate the fans for nighttime purge of heat gains
Definition The ratio of fan speed for a night purge cycle.
Units Ratio
Input Restrictions As designed. The default is 100% (or fans available at full speed).