ASHRAE-90.1-2022- - Page 105
Extracted Content
| Table 6.5.9 Hot-Gas Bypass Limitation | Col2 |
|---|---|
| Rated Capacity | Maximum Hot-Gas Bypass, % of Total Capacity |
| 240,000 Btu/h | 15% |
| >240,000 Btu/h | 10% |
exhaust systems . Where demand ventilation systems are used to meet Section 6.5.7.2.3, additional performance testing shall be required to demonstrate proper capture and containment at minimum airflow.
6.5.7.3 Laboratory Exhaust Systems. Buildings with laboratory exhaust systems having a total exhaust rate greater than 5000 cfm shall include at least one of the following features:
a. VAV laboratory exhaust and room supply system capable of and configured to reduce exhaust and
makeup airflow rates and/or incorporate a heat recovery system to precondition makeup air from laboratory exhaust that shall meet the following:
A + B × ( E / M ) 50% where A = percentage that the exhaust and makeup airflow rates can be reduced from design conditions B = sensible energy recovery ratio E = exhaust airflow rate through the heat recovery device at design conditions M = makeup airflow rate of the system at design conditions b. VAV laboratory exhaust and room supply systems that are required to have minimum circulation rates to
comply with code or accreditation standards shall be capable of and configured to reduce zone exhaust and makeup airflow rates to the regulated minimum circulation values or the minimum required to maintain pressurization relationship requirements. Systems serving nonregulated zones shall be capable of and configured to reduce exhaust and makeup airflow rates to 50% of the zone design values or the minimum required to maintain pressurization relationship requirements. c. Direct makeup (auxiliary) air supply equal to at least 75% of the exhaust airflow rate, heated no warmer
than 2°F below room set point, cooled to no cooler than 3°F above room set point, no humidification added, and no simultaneous heating and cooling used for dehumidification control.
6.5.8 Radiant Heating Systems 6.5.8.1 Heating Unenclosed Spaces. Radiant heating shall be used when heating is required for unen- closed spaces .
Exception to 6.5.8.1: Loading docks equipped with air curtains. 6.5.8.2 Heating Enclosed Spaces. Radiant heating systems that are used as primary or supplemental heating for enclosed spaces must be in conformance with the governing provisions of the standard, including but not limited to the following:
a. Radiant hydronic ceiling or floor panels (used for heating or cooling) b. Combination or hybrid systems incorporating radiant heating (or cooling) panels c. Radiant heating (or cooling) panels used in conjunction with other systems such as VAV or thermal stor age systems
6.5.9 Hot-Gas Bypass Limitation. Cooling systems shall not use hot-gas bypass or other evaporator pressure control systems unless the system is designed with multiple steps of unloading or continuous capacity modulation. The capacity of the hot-gas bypass shall be limited as indicated in Table 6.5.9 for VAV units. Hot-gas bypass shall not be used on constant-volume units.
6.5.10 Door Switches. Any conditioned space with a door, including doors with more than one-half glass, opening to the outdoors shall be provided with controls that, when any such door is open,
a. disable mechanical heating or reset the heating set point to 55°F or lower within five minutes of the door
opening and b. disable mechanical cooling or reset the cooling set point to 90°F or greater within five minutes of the
door opening. Mechanical cooling may remain enabled if outdoor air temperature is below space temperature.
Exceptions to 6.5.10:
- Building entries with automatic closing devices.
- Any space without a thermostat .
ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 103