3.7.2.3 Heating Control | COMNET

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	Not applicable

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	20 °F above space temperature setpoint for systems 1-4. Same as maximum reset cooling supply air temperature for systems 5-8 and 105 °F for systems 9 and 10.

Heating Supply Air Temperature Control
Applicability	Systems with the capability to vary heating SAT
Definition	The method of controlling heating SAT. Choices are: No control – the heating coil is energized on a call for heating, but the supply air temperature is not directly controlled, but instead is dependent on the entering air temperature, the heating capacity and the airflow rate. Fixed (constant) Reset by coldest zone, temperature first Reset by outside air dry-bulb temperature Staged setpoint 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 below): 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 3.7.2-2: Example of SAT heating setpoint reset based on outdoor air temperature (OAT)
Units	Data structure (°F)
Input Restrictions	As designed
Baseline Rules	Not applicable

This section addresses building descriptors related to heating and preheating control. Section 3.7.6 addresses all other details related to heating systems.

Preheat Setpoint
Applicability	Systems 5 though 8
Definition	The control temperature leaving the preheat coil
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	The baseline will be modeled with preheat coil in the mixed air stream controlled to a fixed setpoint 20°F less than the design room heating temperature setpoint

Heating Supply Air Temperature
Applicability	All systems
Definition	The SAT leaving the air handler when the system is in design heating mode (not the air temperature leaving the reheat coils in VAV boxes)
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	20°F above zone temperature setpoint for systems 1 through 4 and 12 through 13. Same as maximum reset cooling SAT for systems 5 through 8 and 105°F for systems 9 and 10. For baseline system 11, the heating supply air temperature shall be modulated to maintain space temperature and fan volume shall be fixed at minimum airflow.

Heating Supply Air Temperature Controls
Applicability	Systems with the capability to vary heating SAT setpoint
Definition	The method of controlling heating SAT. Choices are: No control – the heating coil is energized on a call for heating, and the SAT is not directly controlled, but instead is dependent on the entering air temperature, the heating capacity and the airflow rate Fixed (constant) Reset by coldest zone, airflow first Reset by coldest zone, temperature first Reset by outside air dry-bulb temperature Staged setpoint Scheduled setpoint
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	No control is specified for heating SAT for systems 1 through 4, 9, 10, and 11 through 13. For systems 5 through 8, the heating SAT is fixed to the maximum reset cooling SAT.

Heating Reset Schedule by Outside Air
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 SAT or hot deck SAT (for dual duct systems) as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see Figure 10): The hottest heating SAT The corresponding (cold) outdoor air dry-bulb threshold The coolest heating SAT The corresponding (mild) outdoor air dry-bulb threshold Figure 10. Example of SAT Heating Setpoint Reset based on Outdoor Air Temperature.
Units	Data structure (°F)
Input Restrictions	As designed
Baseline Building	Not applicable

This section addresses building descriptors related to heating and preheating control. Section 3.7.6 addresses all other details related to heating systems.

Preheat Setpoint
Applicability	Systems 5 though 8
Definition	The control temperature leaving the preheat coil
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations The baseline will be modeled with preheat coil in the mixed air stream controlled to a fixed setpoint 20°F less than the design room heating temperature setpoint. G3.3 Minor Alterations Baseline shall be modeled such that the preheat coils have controls that stop their heat output whenever mechanical cooling, including economizer operation, is occurring. Exception: the preheat setpoint should be modeled the same in the baseline and proposed if, based on the requirements of 90.1-2022 Section 6.1.4 and the scope of the alteration, 90.1-2022 Section 6.5.2.5 requirements are inapplicable.

Heating Supply Air Temperature
Applicability	All systems
Definition	The SAT leaving the air handler when the system is in design heating mode (not the air temperature leaving the reheat coils in VAV boxes)
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations 20°F above zone temperature setpoint for systems 1 through 4 and 12 through 13. Same as maximum reset cooling SAT for systems 5 through 8 and 105°F for systems 9 and 10. For baseline system 11, the heating supply air temperature shall be modulated to maintain space temperature and fan volume shall be fixed at minimum airflow. G3.3 Minor Alterations Same as proposed.

Heating Supply Air Temperature Controls
Applicability	Systems with the capability to vary heating SAT setpoint
Definition	The method of controlling heating SAT. Choices are: No control – the heating coil is energized on a call for heating, and the SAT is not directly controlled, but instead is dependent on the entering air temperature, the heating capacity and the airflow rate Fixed (constant) Reset by coldest zone, airflow first Reset by coldest zone, temperature first Reset by outside air dry-bulb temperature Staged setpoint Scheduled setpoint
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations No control is specified for heating SAT for systems 1 through 4, 9, 10, and 11 through 13. For systems 5 through 8, the heating SAT is fixed to the maximum reset cooling SAT. G3.3 Minor Alterations Baseline shall be modeled as minimally compliant with Standard 90.1-2022 Section 6.5.3.5. Standard 90.1-2022 Section 6.5.3.5 requires that multiple zone HVAC systems be modeled to automatically reset the supply air temperature in response to representative building loads or outdoor air temperature. The controls should be modeled to reset the supply air temperature at least 25% of the difference between the design supply air temperature and the design room air temperature. Controls that adjust the reset based on zone humidity are allowed to be modeled in Climate Zones 0B, 1B, 2B, 3B, 3C, and 4 through 8. HVAC zones that are expected to experience relatively constant loads should be modeled to have a maximum air-flow to accommodate the fully reset supply air temperature. Exceptions to 6.5.3.5: Systems in Climate Zones 0A, 1A, and 3A with less than 3000 cfm of design outdoor air. Systems in Climate Zone 2A with less than 10,000 cfm of design outdoor air. Systems in Climate Zones 0A, 1A, 2A, and 3A with at least 80% outdoor air and employing exhaust air energy recovery complying with Section 6.5.6.1. Systems that prevent reheating, recooling, or mixing of heated and cooled supply air. Systems in which at least 75% of the energy for reheating (on an annual basis) is from site recovered energy or on-site renewable energy Exception: the heating supply air temperature control should be modeled the same in the baseline and proposed if, based on the requirements of 90.1-2022 Section 6.1.4 and the scope of the alteration, 90.1-2022 Section 6.5.3.5 requirements are inapplicable.

Heating Reset Schedule by Outside Air
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 SAT or hot deck SAT (for dual duct systems) as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points (see Figure 10): The hottest heating SAT The corresponding (cold) outdoor air dry-bulb threshold The coolest heating SAT The corresponding (mild) outdoor air dry-bulb threshold Figure 10. Example of SAT Heating Setpoint Reset based on Outdoor Air Temperature.
Units	Data structure (°F)
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations Not applicable G3.3 Minor Alterations See the Heating Supply Air Temperature Controls descriptor for baseline requirements.