NA7.5.9 Hydronic System Variable Flow Control Acceptance

Use Form NRCA-MCH-10-A

Purpose of the Test

All hydronic variable flow chilled water and water-loop heat pump systems with total circulating pump power larger than 5 hp shall vary system flow rate by modulating pump speed using a variable frequency drive (VFD) or equivalent according to Standards Section 140.4(k)6. Pump speed and flow must be controlled as a function of differential pressure, and pump motor demand must be no more than thirty percent design wattage at fifty percent design flow.

As the loads within the building fluctuate, control valves should modulate the amount of water passing through each coil and add or remove the desired amount of energy from the air stream to satisfy the load. In the case of water-loop heat pumps, each two-way control valve associated with a heat pump will be closed when that unit is not operating The purpose of the test is to ensure that, as each control valve modulates, the pump variable frequency drive (VFD) responds accordingly to meet system water flow requirements.

Note, this is not required on heating hot water systems with variable flow designs or for condensing water serving only water cooled chillers.

Related acceptance tests for these systems include the following:

•      NA7.5.7 Valve Leakage Test (if applicable)

Instrumentation

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

•      Differential pressure gauge (hydronic manometer)

Test Conditions

To perform the test, it will be necessary to use the control system to manipulate system operation to achieve the desired control. At a minimum, control system programming for the operation of the central equipment, control valves, and pumps must be complete, including, but not limited to:

•      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:

•      Heat pumps, cooling towers, boilers, pumps, control valves, piping, etc.

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

•      Control sensors (temperature, 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 hour (depending on availability of construction documentation – i.e. plumbing drawings, material cut sheets, specifications, etc. – as well as sensor calibration)

Functional testing: 2 to 4 hours (depending on familiarity with BAS, method employed to vary operating parameters, verification method for system flow and VFD power)

Acceptance Criteria

Differential pressure sensor(s) are field calibrated.

For systems without DDC to individual coils, pressure sensor(s) are located at or near the most remote HX or control valve, or the HX requiring the greatest differential pressure.

For systems with DDC to individual coils, the pressure sensor(s) may be located anywhere, but are reset according to the valve requiring the greatest pressure and shall be no less than 80 percent open.

System controls to the setpoint stably.

Potential Problems and Cautions

Difficulties could be encountered with manipulating the control system if not familiar with the programming language. Therefore, a controls contractor should be on-site to assist with adjusting system operation and overriding controls.