NA7.5.15 Supply Air Temperature Reset Controls Acceptance

Use Form NRCA-MCH-16-A

Purpose of the Test

The purpose of the test is to ensure that the supply air temperature in a constant or variable air volume application serving multiple zones, according to Section 140.4(f), modulates to meet system heating and cooling loads.

Space conditioning systems must have zone level controls to avoid reheat, recool, and simultaneous cooling and heating (§ 140.4(d)); or, must have controls to reset supply air temperature (SAT) by at least 25 percent of the difference between the design supply-air temperature and the design room air temperature (§ 140.4(f)(2).

Air distribution systems serving zones with constant loads shall be designed for the air flows resulting from the fully reset (e.g. lowest/highest) supply air temperature.

The requirements for SAT reset apply to both CAV and VAV systems. Exceptions include:

• Systems with specific humidity needs for exempt process loads (computer rooms or spaces serving only IT equipment are not exempt)

• Zones served by space-conditioning systems in which at least 75 percent of the energy for reheating, or providing warm air in mixing systems, is provided from a site-recovered or site-solar energy source

• Systems in which supply air temperature reset would increase overall building energy use.

• Systems with controls to prevent reheat, recool, and/or simultaneous cooling and heating

Supply air temperature may be reset in response to building loads, zone temperature, outside air temperature, or any other appropriate variable.

Instrumentation

The instrumentation needed to perform the task may include, but is not limited to:

•  Hand-held temperature probe or temperature data logger. Must be calibrated within the last year, with date of calibration noted on the Acceptance Form MECH 16-A.

Test Conditions

Confirm all systems and components are installed and ready for system operation, including:

•  Duct work

•  Terminal boxes

•  Heating and/or cooling coils

•  Outside air dampers and controls

•  Supply air temperature sensor(s)

•  Electrical power to air handling unit

Air handling unit start-up procedures should be complete, per manufacturer’s recommendations. If applicable, BAS programming for the operation of the air handling unit and terminal boxes should be complete, including but not limited to:

•      Heating and cooling coil temperature control

•      Terminal box control (including zone temperature sensors and reheat coils)

•      Discharge air temperature sensor

Controls for economizer or outside air damper should be disabled during testing to prevent any unwanted interaction.

Before testing, ensure all schedules, set points, operating conditions, and control parameters are documented. All systems must be returned to normal at the end of the test.

Document current supply air temperature.

Estimated Time to Complete

Construction inspection: 0.5 to 1 hours (depending on sensor calibration)

Functional testing: 0.5 to 1 hours (depending on system control stability)

Acceptance Criteria

Construction Inspection Criteria: The temperature sensor(s) must be factory calibrated, field calibrated by TAB technician or other, or field checked by test technician with a calibrated standard. Calibration certificate or other supporting documentation must be provided.

Functional Testing: For each system, the test criteria include:

•      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. Supply air temperature and temperature setpoint must be documented in the acceptance form.

Potential Issues and Conditions

Coordinate test procedures with the controls contractor and building staff, if possible, since they may be needed to assist with manipulation of the BAS to achieve the desired operating conditions.

Check to make sure that chilled / hot water coils, if used, are not already fully open and calling for maximum cooling / heating. If this is the case, reverse Steps 1 and 2 and change the set point range as necessary to allow system to operate within acceptable bounds during the test and not be forced to meet an impossible set point.

In general, take care to avoid demand peaks exceeding what would be encountered during the normal operation of the building.

Ensure that all disabled reset sequences are enabled upon completion of this test.