Test Comments
Some of the most common control variables used to reset supply air temperature set point include, but are not limited to: outdoor air temperature; zone or return air temperature; zone box damper position; or number of zone boxes calling for heating or cooling. Examples of each control strategy are provided below.
•Outdoor air temperature. One control strategy is to reset supply air temperature based on outdoor air temperature. For example, cold deck or cooling mode temperature may reset linearly between 55°F and 65°F while the outdoor air temperature is between 80°F and 50°F, respectively.
•Zone or return air temperature. Another control strategy is to reset supply air temperature based on zone temperature or return air temperature. For example, supply air temperature may modulate to maintain a zone temperature dead band between 70°F and 76°F.
•Zones calling for cooling or heating. In a VAV system, the building automation system may reset the supply air temperature based on the needs of the zone with the highest heating or cooling loads, or based on a certain percent response from the zone boxes for cooling or heating. For example, in a “trim and response” sequence, the air handler supply temperature may reset downwards by 0.5°F when the maximum system demand is above 100%, or reset upwards by 0.5°F when the maximum system demand is below 80%.
Construction Inspection
Reference supporting documentation if needed.
Verify that supply air temperature reset controls are installed per the requirements of the 2013 Building Energy Efficiency Standards section 140.4(f): Multi-zone systems 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.
If an exception is taken to these requirements, note the exception, in which case the test is not needed.
Document that all system air temperature sensor(s) are factory or field calibrated or reads accurately against a calibrated temperature standard. Attach a copy of the calibration certificate, TAB verification results, or field verification results including results from system air sensors and calibrated reference standard. Calibration certificates from the manufacturer are acceptable.
Document the current supply air temperature.
Functional Testing
Economizer controls and/or outside air damper should be disabled during testing to prevent any unwanted interaction or effect on air temperature.
Check to make sure that chilled and hot water coils, if used, are not already fully open and calling for maximum cooling or heating. If this is the case, reverse Steps 1 and 2 in the test and/or change the set point range as necessary to conduct this test.
Document the reset control parameter (e.g. zone air temperature).
Step 1. During occupied mode, adjust the reset control parameter to decrease the supply air temperature (to the lower supply temperature limit).
Override reset control variable to decrease supply air temperature.
For example, temporarily replace outside temperature signal with a high fixed temperature value for outside air temperature, or temporarily override zone damper signals to imitate all zones calling for maximum cooling. For example, if the supply air is currently 65°F, and the control strategy calls for 60°F cool supply air when outdoor air temperature is above 70°F, override the sensor reading to 75°F.
If the reset control variable input cannot be modified, then change the limit of the variable around the currently occurring value. For example, modify the reset schedule to set the outside air set point high limit below the current outside air temperature, or shift the entire set point range. If the control strategy calls for 55°F cool supply air when outdoor air temperature is above 80°F, and the current outdoor air temperature is 75°F, adjust the maximum limit from 80°F to 70°F.
Verify and Document
•Supply air temperature controls modulate as intended.
•Actual supply air temperature decreases to meet the new set point within +/- 2°F.
•Supply air temperature stabilizes within 15 minutes.
Document both supply air temperature setpoint and actual supply air temperature.
Step 2. During occupied mode, adjust the reset control parameter to increase the supply air temperature (to the upper supply temperature limit).
Override reset control variable to increase supply temperature.
If the reset control variable input cannot be modified, then change the limit of the variable around the currently occurring value. For example, modify the reset schedule to create an outside air set point low limit above the current outside air temperature, or shift the entire set point range.
Verify and Document
•Supply air temperature controls modulate as intended.
•Actual supply air temperature decreases to meet the new set point within +/- 2°F.
•Supply air temperature stabilizes within 15 minutes.
Document both supply air temperature setpoint and actual supply air temperature.
Step 3. Restore reset control parameter to automatic control.
Ensure all set points, operating conditions, and control parameters are placed back at their initial conditions. Remove any system overrides initiated during the test.
Verify
•Supply air temperature controls modulate as intended.
•Actual supply air temperature decreases to meet the new set point within +/- 2°F. Document both supply air temperature setpoint and actual supply air temperature.
•Supply air temperature stabilizes.