3.7.2.2 Cooling Control | COMNET

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 below the space setpoint

Cooling Supply Air Temperature Control
Applicability	Any cooling system
Definition	The method of controlling the supply air temperature. Choices are: No control – for this scheme the cooling coils are energized whenever there is a call for cooling Fixed (constant) Reset by warmest zone, airflow first Reset by warmest zone, temperature first Reset by outside air dry-bulb temperature Scheduled setpoint Staged setpoint (for single zone VAV and DX with multiple stages)
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	For baseline building systems 1 through 4, the SAT control is fixed. For systems 5 through 8, the air temperature for coolingshall be reset higher by 5°F under the minimum cooling load conditions using a reset by warmest zone, flow first strategy This strategy sets the cooling coil temperature each hour to adequately cool the zone with the highest temperature. find the lowest supply air flow rate that will satisfy all the zone cooling loads at the maximum setpoint temperature. If this flow is greater than the maximum, the flow is set to the maximum and the setpoint temperature is reduced to satisfy the cooling loads. The airflow first strategy minimizes zone reheat coil energy (or overcooling) and central chiller energy consumption at the cost of possible increased fan energy. This SAT reset may driven back to the design SAT if a maximum humidity setpoint is not met. For system 9 and 10 (heating and ventilation) this input is not applicable.

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 figures below: 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 3.7.2-1: SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT)
Units	Data structure (two matched pairs of SAT and OAT, see above)
Input Restrictions	As designed.
Baseline Rules	The schedule defaults to: Supply Air High = Supply Air Low + 5 Supply Low = (greater of SAT or 50F) Outside High = 80°F Outside Low = 60°F

Cooling Supply Air Temperature
Applicability	Applicable to all systems
Definition	The SAT setpoint at design cooling conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	20°F below the zone temperature setpoint, except in laboratories, where it is to be set at 17°F below the zone temperature

Cooling Supply Air Temperature Control
Applicability	Any cooling system
Definition	The method of controlling the SAT. Choices are: No control – for this scheme the cooling coils are energized whenever there is a call for cooling Fixed (constant) Reset by warmest zone, airflow first This control strategy resets the cooling SAT of a central forced air HVAC system according to the cooling demand of the warmest zone. The airflow first control approach tries to find the lowest supply airflow rate that will satisfy all the zone cooling loads at the maximum setpoint temperature. If this flow is greater than the maximum, the flow is set to the maximum and the setpoint temperature is reduced to satisfy the cooling loads. The airflow first strategy minimizes zone reheat coil energy (or overcooling) and central chiller energy consumption at the cost of possible increased fan energy. Reset by warmest zone, temperature first This control strategy resets the cooling SAT of a central forced air HVAC system according to the cooling demand of the warmest zone. The temperature first control approach tries to find the highest setpoint temperature that will satisfy all the zone cooling loads at the minimum supply airflow rate. If this setpoint temperature is less than the minimum, the setpoint temperature is set to the minimum, and the supply airflow rate is increased to meet the loads. The temperature first strategy minimizes fan energy consumption at the cost of possible increased zone reheat coil energy (or overcooling) and central chiller energy consumption. Reset by outside air dry-bulb temperature Scheduled setpoint Staged setpoint (for single zone VAV and DX with multiple stages)
Units	List (see above)
Input Restrictions	As designed
Baseline Building	For baseline building systems 1 through 4, there is no SAT control. The cooling coil modulates based on the zone thermostat setpoint. For systems 5 through 8, the air temperature for cooling shall be reset higher by 5°F under the minimum cooling load conditions using a reset by warmest zone, airflow first strategy. For system 11, the supply air temperature setpoint shall be reset from minimum supply air temperature at 50% cooling load to space temperature at 0% cooling load. For systems 9, 10, 12, and 13 (heating and ventilation and single zone systems), this input is not applicable.

Cooling Reset Schedule by Outside Air Temperature
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 9): The coldest cooling SAT The corresponding (hot) outdoor air dry-bulb setpoint The warmest cooling SAT The corresponding (cool) outdoor air dry-bulb setpoint Figure 9. SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT)
Units	Data structure (two matched pairs of SAT and OAT, see above)
Input Restrictions	As designed
Baseline Building	Not applicable

Cooling Supply Air Temperature
Applicability	Applicable to all systems
Definition	The SAT setpoint at design cooling conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations 20°F below the zone temperature setpoint, except in laboratories, where it is to be set at 17°F below the zone temperature. G3.3 Minor Alterations Same as proposed.

Cooling Supply Air Temperature Control
Applicability	Any cooling system
Definition	The method of controlling the SAT. Choices are: No control – for this scheme the cooling coils are energized whenever there is a call for cooling Fixed (constant) Reset by warmest zone, airflow first This control strategy resets the cooling SAT of a central forced air HVAC system according to the cooling demand of the warmest zone. The airflow first control approach tries to find the lowest supply airflow rate that will satisfy all the zone cooling loads at the maximum setpoint temperature. If this flow is greater than the maximum, the flow is set to the maximum and the setpoint temperature is reduced to satisfy the cooling loads. The airflow first strategy minimizes zone reheat coil energy (or overcooling) and central chiller energy consumption at the cost of possible increased fan energy. Reset by warmest zone, temperature first This control strategy resets the cooling SAT of a central forced air HVAC system according to the cooling demand of the warmest zone. The temperature first control approach tries to find the highest setpoint temperature that will satisfy all the zone cooling loads at the minimum supply airflow rate. If this setpoint temperature is less than the minimum, the setpoint temperature is set to the minimum, and the supply airflow rate is increased to meet the loads. The temperature first strategy minimizes fan energy consumption at the cost of possible increased zone reheat coil energy (or overcooling) and central chiller energy consumption. Reset by outside air dry-bulb temperature Scheduled setpoint Staged setpoint (for single zone VAV and DX with multiple stages)
Units	List (see above)
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations For baseline building systems 1 through 4, there is no SAT control. The cooling coil modulates based on the zone thermostat setpoint. For systems 5 through 8, the air temperature for cooling shall be reset higher by 5°F under the minimum cooling load conditions using a reset by warmest zone, airflow first strategy. For system 11, the supply air temperature setpoint shall be reset from minimum supply air temperature at 50% cooling load to space temperature at 0% cooling load. For systems 9, 10, 12, and 13 (heating and ventilation and single zone systems), this input is not applicable. 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 cooling 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.

Cooling Reset Schedule by Outside Air Temperature
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 9): The coldest cooling SAT The corresponding (hot) outdoor air dry-bulb setpoint The warmest cooling SAT The corresponding (cool) outdoor air dry-bulb setpoint Figure 9. SAT Cooling Setpoint Reset based on Outdoor Air Temperature (OAT)
Units	Data structure (two matched pairs of SAT and OAT, see above)
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations Not applicable G3.3 Minor Alterations See the Cooling Supply Air Temperature Control descriptor for baseline requirements.