NA7.10.3.1 Evaporative Condensers and Condenser Fan Motor Variable Speed Controls

Use Form NRCA-PRC-05-A

Purpose of the Test

Instrumentation

Performance of this test will require measuring the ambient wet bulb temperature, relative humidity, and condenser operating pressure. The instrumentation needed to perform the task may include, but is not limited to:

•      A temperature sensor calibrated to +/- 0.7°F between -30°F and 200°F

•      A relative humidity (RH) sensor calibrated to +/- 1% between 5% and 90% RH

•      A pressure sensor shall be calibrated to +/- 2.5 psi between 0 and 500 psig

Test Conditions

The test will be performed by varying the control parameters used by the condenser control system.  Therefore, the condenser control system must be installed and operating, including completion of all start-up procedures per manufacturer’s or designer’s recommendations, to perform the test.

Document the value of the initial control parameters before starting the test.

Estimated Time to Complete

Construction inspection: 1 hour (for one evaporative condenser)

Functional testing: 3 hour (for one evaporative condenser)

Acceptance Criteria

•      The evaporative condenser minimum condensing temperature control setpoint is 70°F or lower.

•      The target condensing temperature is reset in response to ambient wet bulb temperature, by using a temperature difference (TD) between the condensing temperature and the ambient wet bulb temperature.

•      The condenser fan speed is continuously variable and the condenser fans are controlled in unison – varying the speed of all fans serving a common high-side at the same time.

Potential Issues and Cautions

Coordinate test procedures with the refrigeration or controls contractor, or the facility supervisor since they may be needed to assist with the manipulation of the control system.

To ensure proper overall system operation, make sure that the system pressure is not held at excessively low or high values for an extended period of time when varying the saturated condensing temperature (SCT) control setpoint.  Avoid abrupt changes in pressure.  Coordinate with facility operator or refrigeration contractor.