NA7.5.8 Supply Water Temperature Reset Controls Acceptance

Use Form NRCA-MCH-09-A

Purpose of the Test

The intent of the test is to ensure that both the chilled water and hot water supply temperatures are automatically reset based on either building loads or outdoor air temperature, as indicated in the control sequences. Many HVAC systems are served by central chilled and heating hot water plants. The supply water operating temperatures must meet peak loads when the system is operating at design conditions. As the loads vary, the supply water temperatures can be adjusted to satisfy the new operating conditions. Typically the chilled water supply temperature can be raised as the cooling load decreases, and heating hot water supply temperature can be lowered as the heating load decreases.

This requirement only applies to chilled and hot water systems that are not designed for variable flow and that have a design capacity greater than or equal to 500 kBtuh (thousand BTU’s per hour) , according to Standards Section 140.4(k)4.

Instrumentation

Performance of this test will require measuring water temperatures as well as possibly air temperatures. The instrumentation needed to perform the task may include, but is not limited to:

•      Hand-held temperature probe, ice water, or drywell bath. Must be calibrated within the last year.

Test Conditions

To perform the test, it may be necessary to use the building automation system (BAS) to manipulate system operation to achieve the desired control. BAS programming for the operation of the chillers, boilers, air handling units, and pumps must be complete, including but not limited to:

•      Supply water temperature control

•      Equipment start-stop control

•      All control sensors installed and calibrated

•      Control loops are tuned

All systems must be installed and ready for system operation, including:

•      Chillers, boilers, pumps, air handling units, valves, piping, etc.

•      All piping is pressure tested, flushed, cleaned, and filled with water

•      Control sensors (temperature, humidity, flow, pressure, etc.)

•      Electrical power to all equipment

Start-up procedures for all pieces of equipment are complete, per manufacturer’s recommendations

Document the initial conditions before overrides or manipulation of the BAS.All systems must be returned to normal at the end of the test.

Estimated Time to Complete

Construction inspection: 0.5 to 1 hours (depending on availability of construction documentation (i.e. plumbing drawings, material cut sheets, specifications, etc ) as well as sensor calibration.)

Functional testing: 1 to 2 hours (depending on familiarity with BAS, method employed to vary operating parameters, and time interval between control command and system response)

Acceptance Criteria

Supply water temperature sensors are field calibrated, to within one percent of calibrated reference sensor, with supporting documentation attached to MECH-09A form.

Sensor performance complies with specifications.

Supply water reset works according to control schedule, and actual water temperature is within 2% of control setpoint.

Potential Problems and Cautions

If the heating hot water temperature reset is tested when there is minimal heating load, make sure to test the low end of the reset first (coldest hot water supply temperature).If the hottest supply water temperature is tested first, it could be difficult to dissipate the heat in the hot water loop without artificially creating a heating load. Waiting for a small heating load to dissipate the heat in the loop could add significant time to the test procedure.

Where humidity control is required, chilled water supply water reset is not recommended.