A5.207.2 Space Conditioning Systems
Mechanical space-conditioning systems supplying heated or cooled air to multiple zones shall include controls that automatically reset supply-air temperatures:
- In response to representative building loads or to outdoor air temperature; and
- By at least 25 percent of the difference between the design supply-air temperature and the design room air temperature.
Air distribution systems serving zones that are likely to have constant loads, such as interior zones, shall be designed for the air flows resulting from the fully reset supply-air temperature.
Electric resistance heating systems shall not be used for space heating.
- Where an electric-resistance heating system supplements a heating system in which at least 60 percent of the annual energy requirement is supplied by site-solar or recovered energy.
- Where the total capacity of all electric-resistance heating systems serving the entire building is less than 10 percent of the total design output capacity of all heating equipment serving the entire building.
- Where an electric resistance heating system serves an entire building that is not a high-rise residential or hotel/motel building; and has a conditioned floor area no greater than 5,000 square feet; and has no mechanical cooling; and is in an area where natural gas is not currently available and an extension of a natural gas system is impractical, as determined by the natural gas utility.
Each fan powered by a motor of 7.5 hp (5.6 kW) or larger shall have the capability to operate that fan at 2/3 of full speed or less and shall have controls that automatically change the fan speed to control the leaving fluid temperature or condensing temperature/pressure of the heat rejection device.
- Heat rejection devices included as an integral part of the equipment listed in Tables A5.207.1-A through A5.207.1-E.
- Condenser fans serving multiple refrigerant circuits.
- Condenser fans serving flooded condensers.
- Up to 1/3 of the fans on a condenser or tower with multiple fans where the lead fans comply with the speed control requirement.
Open cooling towers configured with multiple condenser water pumps shall be designed so that all cells can be run in parallel with the larger of:
- The flow that's produced by the smallest pump or
- 33 percent of the design flow for the cell.
Open cooling towers with a combined rated capacity of 900 gpm and greater at 95°F condenser water return, 85°F condenser water supply and 75°F outdoor wet-bulb temperature shall use propeller fans and shall not use centrifugal fans.
HVAC chilled and hot water pumping shall be designed for variable fluid flow and shall be capable of reducing pump flow rates to no more than the larger of: a) 50 percent or less of the design flow rate; or b) the minimum flow required by the equipment manufacturer for the proper operation of equipment served by the system.
- Systems that include no more than three control valves.
- Systems having a total pump system power less than or equal to 11/2 HP.
Chilled and hot water systems with a design capacity exceeding 500,000 Btu/hr supplying chilled or heated water (or both) shall include controls that automatically reset supply water temperatures as a function of representative building loads or outside air temperature.
Exception: Hydronic systems that use variable flow to reduce pumping energy in accordance with Section A220.127.116.11.1.
- For systems without direct digital control of individual coils reporting to the central control panel, differential pressure shall be measured at or near the most remote heat exchanger or the heat exchanger requiring the greatest differential pressure.
- For systems with direct digital control of individual coils with central control panel, the static pressure set point shall be reset based on the valve requiring the most pressure and the set- point shall be no less than 80 percent open. The pressure sensor(s) may be mounted anywhere.
- Heating hot water systems.
- Condenser water systems serving only water-cooled chillers.
Hydronic heat pumps connected to a common heat pump water loop with central devices for heat rejection and heat addition shall have controls that are capable of providing a heat pump water supply temperature dead band of at least 20°F between initiation of heat rejection and heat addition by the central devices.
Exception: Where a system loop temperature optimization controller is used to determine the most efficient operating temperature based on real-time conditions of demand and capacity, dead bands of less than 20°F shall be allowed.
Has more than 25 percent duct surface area located in one or more of the following spaces:
- Outdoors; or
- In a space directly under a roof with fixed vents or openings to the outside or unconditioned spaces; or
- In an unconditioned crawlspace; or
- In other unconditioned spaces.
The leakage rate shall be confirmed through field verification and diagnostic testing, in accordance with procedures set forth in the Reference Nonresidential Appendix NA1 of the California Energy Commission 2008 Building Energy Efficiency Standards for Residential and Nonresidential Buildings.