220.127.116.11.3 High-Limit Shutoff
All air economizers shall be capable of and configured to automatically reduce outdoor air intake to the design minimum outdoor air quantity when outdoor air intake will no longer reduce cooling energy use. High-limit shutoff control types and associated set points for specific climate zones shall be chosen from Table 18.104.22.168.3.
Table 22.214.171.124.3 High-Limit Shutoff Control Settings for Air Economizerb
|Control Type||Allowed Only in Climate Zone at Listed Set Point||Required High-Limit Set Points (Economizer Off when):|
|Fixed dry-bulb temperature||0B, 1B, 2B, 3B, 3C, 4B, 4C, 5B, 5C, 6B, 7, 8||TOA > 75°F||Outdoor air temperature exceeds 75°F|
|5A, 6A||TOA > 70°F||Outdoor air temperature exceeds 70°F|
|0A, 1A, 2A, 3A, 4A,||TOA > 65°F||Outdoor air temperature exceeds 65°F|
|Differential dry-bulb temperature||0B, 1B, 2B, 3B, 3C, 4B, 4C, 5A, 5B, 5C, 6A, 6B, 7, 8||TOA > TRA||Outdoor air temperature exceeds return air temperature|
|Fixed enthalpy with fixed dry-bulb temperature||All||hOA > 28 Btu/lba
or TOA > 75°F
|Outdoor air enthalpy exceeds 28 Btu/lba of dry aira or outdoor air temperature exceeds 75°F|
|Differential enthalpy with fixed dry-bulb temperature||All||hOA > hRA
or TOA> 75°F
|Outdoor air enthalpy exceeds return air enthalpy or outdoor air temperature exceeds 75°F|
- At altitudes substantially different than sea level, the fixed enthalpy limit shall be set to the enthalpy value at 75°F and 50% rh. As an example, at approximately 6000 ft elevation, the fixed enthalpy limit is approximately 30.7 Btu/lb.
- Devices with selectable rather than adjustable set points shall be capable of being set to within 2°F and 2 Btu/lb of the set point listed.