NA7.5.1 Variable Air Volume Systems Outdoor Air Acceptance

Use Form NRCA-MCH-02-A

Purpose of the Test

This test ensures that adequate outdoor air ventilation is provided through the variable air volume air handling unit at two representative operating conditions. The test consists of measuring outdoor air values at maximum flow and at or near minimum flow. The test verifies that the minimum volume of outdoor air, as required per §120.1(b)2, is introduced to the air handling unit and is within 10% of the required volume when the system is in occupied mode at these two conditions of supply airflow.

Note that this test should be performed in conjunction with NA7.5.6 (NRCA-MCH-07-A) Supply Fan Variable Flow Controls Acceptance test procedures to reduce the overall system testing time as both tests use the same two conditions of airflow for their measurements. Related acceptance tests for these systems include the following:

•      NA7.5.4 Air Economizer Controls

•      NA7.5.5 Demand Control Ventilation (DCV) Systems (if applicable)

•      NA7.5.6 Supply Fan Variable Flow Controls

Instrumentation

Performance of this test will require measuring outdoor air flow. The instrumentation needed to perform the task may include, but is not limited to:

•      An airflow measurement probe (e.g. hot-wire anemometer or velocity pressure probe), or

•      If the system was installed with an airflow monitoring station (AFMS) on the outdoor air, it can be used for the measurements if it has a calibration certificate or is field calibrated.

•      A watch or some equivalent instrument to measure time in minutes

Test Conditions

To perform the test, it will be necessary to override the normal operation of the controls. The control system of the air handling unit and zone controls must be complete, including:

•      Supply fan capacity control (typically a variable speed drive )

•      Air Economizer control

•      Minimum outdoor air damper control

•      Zone airflow control (including zone thermostats and VAV boxes)

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

•      Duct work

•      VAV boxes

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

•      Electrical power to air handling unit and control system components

•      Completion of air handling unit start-up procedures, per manufacturer’s recommendations

Document the initial conditions before executing system overrides or manipulation of the setpoints and schedules.  All systems must be returned to normal at the end of the test.

It will be necessary to reference NRCC-MCH-03-E (Column M) or the mechanical equipment schedules to determine the total required outdoor airflow for the system.

Estimated Time to Complete

Construction inspection: 0.5 hours to 2 hours (depending on complexity and difficulty in calibrating the “system” controlling outdoor air flow)

Functional testing: 1 to 3 hours (depending on the type of zone control and the number of zones)

Acceptance Criteria

Sensor used to control outdoor air flow was calibrated in the field or at the factory, with documentation attached.

Measured outdoor airflow reading is within 10 percent of the total value found on the Standards Mechanical Plan Check document NRCC-MCH-03-E, Column M under the following conditions:

•      Minimum system airflow or 30 percent of total design flow

•      Design supply airflow

Potential Issues and Cautions

Use caution when performing test during winter months in cold climates. Since outdoor airflow must remain constant as supply fan flow is reduced, total supply flow can approach 100 percent outdoor air. Be sure that all freeze protection and heating coil controls are functioning before performing test.

Coordinate test procedures with the controls contractor since they may be needed to assist with manipulation of the BAS to achieve the desired operating conditions.

Ensure economizer and demand controlled ventilation controls are disabled before performing the test.