3.7 HVAC Secondary Systems

This group of building descriptors relate to the secondary HVAC systems. There is not a one-to-one relationship between secondary HVAC system components in the proposed design and the baseline building since the baseline building system is determined from building type, size and heating source. Appendix A shows the applicability of each building descriptor for the eight baseline building systems. Depending on the nature of the proposed design, any of the building descriptors could apply.

This group of building descriptors relate to the secondary HVAC systems. There is not a one-to-one relationship between secondary HVAC system components in the proposed design and the baseline building since the baseline building system is determined from building type, size and heating source. See Table 3.1-1, 3.1-2 and 3.1-3. Additional detail on the baseline building systems is provided in the tables below. Depending on the nature of the proposed design, any of the building descriptors could apply.

Table 3.7-1: Baseline Building System Type

Baseline Building System	System Type
System 1 – PTAC	Single Zone Heating and Cooling
System 2 – PTHP	Single Zone Heating and Cooling
System 3 – PSZ-AC	Single Zone Heating and Cooling
System 4 – PSZ-HP	Single Zone Heating and Cooling
System 5 – Packaged VAV with Reheat	Single Duct VAV
System 6 – Packaged VAV with PFP boxes	Single Duct VAV
System 7 – VAV with Reheat	Single Duct VAV
System 8 – VAV with PFP boxes	Single Duct VAV
System 9 – Heating and Ventilation	Constant Volume Heat/Vent (no cooling)
System 10 – Heating and Ventilation	Constant Volume Heat/Vent (no cooling)
System 11. SZ–VAV	Single-zone VAV
System 12. SZ-CV-HW	Single zone with hot water heat
System 13. SZ-CV-ER	Single zone with electric resistance heat

Table 3.7-2: Summary of Baseline Building Secondary HVAC System Properties

System	Fan Control	Economizer	Cooling Type	Cooling Efficiency.	Minimum Supply T.	Heating Type	Heating Efficiency	Maximum Supply T.
1 PTAC	Constant volume	Not required	Direct Expansion	Minimum SEER or EER based on equipment type and output capacity of proposed unit(s). Adjusted EER is calculated to account for supply fan energy.	20 °F below occupied space cooling setpoint	Hot-water fossil fuel boiler	Minimum AFUE, Thermal Efficiency, COP or HSPF based on equipment type and output capacity of baseline unit(s).	20 °F above occupied space heating setpoint
2 PTHP						Electric heat pump
3 PSZ-AC		Integrated economizer with dry-bulb high limit by climate zone. See 6.7.4 ‘Outside Air Controls and Economizer’ for details and exceptions.				Fossil fuel furnace
4 PSZ-HP						Electric heat pump
5 PVAV	Variable volume					Hot-water fossil fuel boiler
6 PVAV / PFP						Electric resistance
7 VAV			Chilled water	See 6.8 Primary Systems		Hot-water fossil fuel boiler
8 VAV / PFP						Electric resistance
9 HV Furnace	Constant volume	Not required	None	None		Fossil fuel furnace
10 HV Electric						Electric resistance
11 SZ-VAV	Variable volume	Integrated economizer with dry-bulb high limit by climate zone. See 6.7.4 for details.	Chilled water	See 6.8 Primary Systems		See note.
12 SZ-CV-HW	Constant Volume					Hot-water fossil fuel boiler
13 SZ-CV-ER						Electric resistance

Table 3.7-3: Summary of Baseline Building Variable Volume Fan Control and Reheat

Code	Supply Fan Control	PFP Fan	Reheat Terminal Flow
5 PVAV	Variable speed controlled by variable speed drives. The part load performance of VAV fans is required to be modeled in accordance to section ‘Fan Part Load Curve’ in ‘Fan Systems’.		Minimum volume setpoint for reheat is highest of 30% of zone peak flow, minimum outdoor air flow rate or airflow rate required by applicable rating authority. See Section 3.6.5 for details
6 PVAV / PFP		PIU fan would be constant volume. AHU fan should cycle on only for cooling. Zone fans should provide unoccupied heating.		Fans for PIU units are sized for 50% of peak design primary air
7 VAV
8 VAV / PFP		PIU fan would be constant volume. AHU fan should cycle on only for cooling. Zone fans should provide unoccupied heating.		Fans for PIU units are sized for 50% of peak design primary air

90.1-2019

This group of building descriptors relate to the secondary HVAC systems. There is not a one-to-one relationship between secondary HVAC system components in the proposed design and the baseline building since the baseline building system is determined from building type, size, and heating source. Depending on the nature of the proposed design, any of the building descriptors could apply. The HVAC baseline systems are described in the summary tables below for reference. The details of individual building descriptor definitions can be found in Sections 3.7 and 3.8.

Table 41. System 1 and System 2 Descriptions


System Description	Packaged terminal air conditioner (#1) or packaged terminal heat pump (#2)
Supply Fan Control	Constant volume
Min Supply Temp	20°F below occupied space cooling setpoint
Cooling System	DX
Cooling Efficiency	Minimum seasonal energy efficiency ratio (SEER) or EER based on equipment type and output capacity of proposed unit(s). Adjusted EER is calculated to account for supply fan energy.
Maximum Supply Temp	20°F above occupied space heating setpoint
Heating System	Hot water boiler (#1) or heat pump (#2)
Heating Efficiency	Minimum annual fuel utilization efficiency (AFUE), thermal efficiency, COP, or heating seasonal performance factor (HSPF) based on equipment type and output capacity of baseline unit(s)
Economizer	None
Ducts	N/A (not ducted)

This group of building descriptors relate to the secondary HVAC systems.