ASHRAE-90.1-2022- - Page 092

Extracted Content

6.5.2.2.3 Hydronic (Water Loop) Heat Pump Systems. Hydronic heat pumps connected to a common heat-pump water loop with central devices for heat rejection (e.g., cooling tower) and heat addition (e.g., boiler ) shall have the following:

a. Controls that are capable of and configured to provide 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 (e.g., tower and boiler ). b. For Climate Zones 3 through 8, if a closed-circuit cooling tower (fluid cooler) is used, either an auto-

matic valve shall be installed to bypass all but a minimal flow of water around the tower (for freeze protection) or low-leakage positive closure dampers shall be provided. If an open-circuit cooling tower is used directly in the heat-pump loop, an automatic valve shall be installed to bypass all heat-pump water flow around the tower. If an open-circuit cooling tower is used in conjunction with a separate heat exchanger to isolate the tower from the heat-pump loop, then heat loss shall be controlled by shutting down the circulation pump on the cooling tower loop.

Exception to 6.5.2.2.3: 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.

6.5.2.3 Dehumidification. Where humidity controls are provided, such controls shall prevent reheating, mixing of hot and cold airstreams, or other means of simultaneous heating and cooling of the same airstream.

Exceptions to 6.5.2.3:

1. The system is capable of and configured to reduce supply air volume to 50% or less of the design airflow rate or the minimum outdoor air ventilation rate specified in ASHRAE Standard 62.1 or other applicable federal, state, or local code or recognized standard, whichever is larger, before simultaneous heating and cooling takes place.
2. The individual fan cooling unit has a design cooling capacity of 65,000 Btu/h or less and is capable of and configured to unload to 50% capacity before simultaneous heating and cooling takes place.
3. The individual mechanical cooling unit has a design cooling capacity of 40,000 Btu/h or less. An individual mechanical cooling unit is a single system comprising a fan or fans and a cooling coil capable of providing mechanical cooling .
4. Systems serving spaces where specific humidity levels are required to satisfy process application needs, such as vivariums; museums; surgical suites; pharmacies; and buildings with refrigerating systems, such as supermarkets, refrigerated warehouses, and ice arenas, and where the building includes site-recovered energy or on-site renewable energy that provides energy equal to at least 75% of the annual energy for reheating or for providing warm air in mixing systems . This exception does not apply to computer rooms .
5. At least 90% of the annual energy for reheating or for providing warm air in mixing systems is provided from site-recovered energy (including condenser heat) or on-site renewable energy .
6. Systems where the heat added to the airstream is the result of the use of a desiccant system, and 75% of the heat added by the desiccant system is removed by a heat exchanger, either before or after the desiccant system, with energy recovery.

6.5.2.4 Humidification 6.5.2.4.1 Humidifiers with preheating jackets mounted in the airstream shall be provided with an auto- matic valve to shut off preheat when humidification is not required.

6.5.2.4.2 Humidification system dispersion-tube hot surfaces in the airstreams of ducts or air-handling units shall be insulated with a product with an insulating value of at least R-0.5.

Exception to 6.5.2.4.2: Systems where mechanical cooling, including economizer operation, does not

occur simultaneously with humidification.

6.5.2.5 Preheat Coils. Preheat coils shall have controls that stop their heat output whenever mechanical cooling, including economizer operation, is occurring.

6.5.2.6 Ventilation Air Heating Control. Units that provide ventilation air to multiple zones and operate in conjunction with zone heating and cooling systems shall not use heating or heat recovery to warm supply air above 60°F when representative building loads or outdoor air temperature indicate that the majority of zones require cooling.

Exception to 6.5.2.6: Units that heat the airstream using only series energy recovery when representative

building loads or outdoor air temperature indicate that the majority of zones require cooling in Climate Zones 0A, 1A, 2A, 3A, and 4A.

90 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)