ASHRAE-90.1-2022- - Page 320
Extracted Content
- Cooling systems in Climate Zones 3C, 4C, 5B, 5C, 6B, 7, and 8.
- Where the largest exhaust source is less than 75% of the design outdoor airflow . This exception shall only be used if exhaust air energy recovery is not used in the proposed design .
- Systems requiring dehumidification that employ energy recovery in series with the cooling coil. This exception shall only be used if exhaust air energy recovery and series-style energy recovery coils are not used in the proposed design .
- Systems serving laboratory HVAC zones with a total laboratory exhaust volume greater than 15,000 cfm.
G3.2.3 System-Specific Baseline HVAC System Requirements. Baseline HVAC systems shall conform with provisions in this section, where applicable, to the specified baseline system types, as indicated in section headings.
G3.2.3.1 Heat Pumps (Systems 2 and 4). Electric air source heat pumps shall be modeled with electric auxiliary heat and an outdoor air thermostat . The systems shall be controlled to energize auxiliary heat only when the outdoor air temperature is less than 40°F. The air source heat pump shall be modeled to continue to operate while auxiliary heat is energized.
G3.2.3.2 Type and Number of Boilers (Systems 1, 5, 7, 11, and 12). The boiler plant shall be natural draft, except as noted in Section G3.2.1.4. The baseline building design boiler plant shall be modeled as having a single boiler if the baseline building design plant serves a gross conditioned floor area of 15,000 ft [2] or less, and as having two equally sized boilers for plants serving more than 15,000 ft [2] . Boilers shall be staged as required by the load.
G3.2.3.3 Hot-Water Supply Temperature (Systems 1, 5, 7, 11, and 12). Hot-water design supply temperature shall be modeled as 180°F and design return temperature as 130°F.
G3.2.3.4 Hot-Water Supply Temperature Reset (Systems 1, 5, 7, 11, and 12). Hot-water supply temperature shall be reset based on outdoor dry-bulb temperature using the following schedule: 180°F at 20°F and below, 150°F at 50°F and above, and ramped linearly between 180°F and 150°F at temperatures between 20°F and 50°F.
Exception to G3.2.3.4: Systems served by purchased heat.
G3.2.3.5 Hot-Water Pumps (Systems 1, 5, 7, 11, and 12). The baseline building design hot-water pump power shall be 19 W/gpm. The pumping system shall be modeled as primary-only with continuous variable flow and a minimum of 25% of the design flow rate. Hot-water pumps shall only be enabled when a load exists on the associated hot-water loop . Hot-water systems serving 120,000 ft [2] or more shall be modeled with variable-speed drives, and systems serving less than 120,000 ft [2] shall be modeled as riding the pump curve.
Exception to G3.2.3.5: The pump power for systems using purchased heat shall be 14 W/gpm.
G3.2.3.6 Piping Losses (Systems 1, 5, 7, 8, 11, 12, and 13). Piping losses shall not be modeled in either the proposed design or baseline building design for hot-water, chilled-water, or steam piping .
G3.2.3.7 Type and Number of Chillers (Systems 7, 8, 11, 12, and 13). Electric chillers shall be used in the baseline building design regardless of the cooling energy source, e.g. direct-fired absorption or absorption from purchased steam. The baseline building design ’s chiller plant shall be modeled with chillers having the number and type as indicated in Table G3.2.3.7 based on the peak coincident cooling load of baseline HVAC systems using chilled water.
Exception to G3.2.3.7: Systems using purchased chilled water shall be modeled in accordance with
Section G3.2.1.6.
G3.2.3.8 Chilled-Water Design Supply Temperature (Systems 7, 8, 11, 12, and 13). Chilled-water design supply temperature shall be modeled at 44°F and return water temperature at 56°F.
G3.2.3.9 Chilled-Water Supply Temperature Reset (Systems 7, 8, 11, 12, and 13). Chilled-water supply temperature shall be reset based on outdoor dry-bulb temperature using the following schedule: 44°F at 80°F and above, 54°F at 60°F and below, and ramped linearly between 44°F and 54°F at temperatures between 80°F and 60°F.
Exception to G3.2.3.9:
- If the baseline chilled-water system serves a computer room HVAC system, the supply chilledwater temperature shall be reset higher based on the HVAC system requiring the most cooling; i.e., the chilled-water set point is reset higher until one cooling-coil valve is nearly wide open. The maximum reset chilled-water supply temperature shall be 54°F.
- Systems served by purchased chilled water.
318 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)