Step 1. Disable demand controlled ventilation (DCV) system modes, if applicable.
For DDC systems, this may include overriding the readings from the CO2 sensor(s) or temporarily disabling the sensor(s).
Step 2. Simulate a cooling load and enable the economizer.
Simulating a cooling load and enabling the economizer can be accomplished by:
•Commanding the discharge air temperature setpoint to be lower than current discharge conditions.
•For a fixed dry-bulb or enthalpy control strategy, raising the economizer lockout setpoint to be above current outdoor air conditions (if this is not the case already) to enable the economizer.
•For a differential dry-bulb control strategy, raise the return air conditions to be above current outdoor air conditions (if this is not the case already) to enable the economizer.
•Verify and Document
•Outdoor air damper modulates open to a maximum position.
•Return air damper modulates closed and is 100 percent closed when the outdoor air dampers are 100 percent open. Return dampers should close tight to minimize leakage.
•Outdoor air damper is 100 percent open before mechanical cooling is enabled. This implies that cooling coil valves in chilled water systems should not modulate or compressors in DX systems should not start until the unit is in 100 percent economizer mode. Depending on the speed of the PID loop, it is possible that mechanical cooling could be commanded on before the outdoor air dampers actually stroke fully open. If this occurs, it does not mean the system has failed the test. One option is to watch the output of the PID loop and verify that the COMMAND sent to the outdoor air damper reaches 100 percent before a command is sent to the mechanical cooling devices.
•Although space pressurization requirements are not part of the current Standards, most systems employ some form of control strategy to maintain space pressure during economizer mode. Control strategies can include, but are not limited to: 1) return fan speed control; 2) dedicated relief fans; or 3) relief damper controls. Observe that the space served by the air handling unit being tested does not appear to experience any pressurization problems (i.e., perimeter doors pushed open or excessive airflow between zones served by different units).
Step 3 Simulate a cooling load and disable the economizer.
Continuing from the procedures outlined in Step 2:
•Keep the discharge air temperature setpoint lower than current discharge conditions.
•For a fixed dry-bulb or enthalpy control strategy, lower the economizer lockout setpoint to be below current outdoor air conditions (if this is not the case already) to disable the economizer.
•For a differential dry-bulb or enthalpy control strategy; lower the return air conditions to be below current outdoor air conditions (if this is not the case already) to disable the economizer.
Verify and Document
•Outdoor air damper closes to a minimum position.
•Return air damper opens to normal operating position when the system is not in economizer mode.
•Mechanical cooling remains enabled to satisfy discharge air temperature setpoint.
Step 4. If the system has heating, simulate a heating demand and enable the economizer.
Continuing from the procedures outlined in Step 3:
•Command the discharge air temperature setpoint to be higher than current discharge conditions.
•For a fixed dry-bulb or enthalpy control strategy, raise the economizer lockout setpoint to be above current outdoor air conditions (if this is not the case already) to keep the economizer enabled.
•For a differential dry-bulb control strategy, raise the return air conditions to be above current outdoor air conditions (if this is not the case already) to keep the economizer enabled.
Verify and Document
•Outdoor air dampers remain at a minimum position.
•Return air dampers remain open.
•Heating is enabled to satisfy discharge air temperature setpoint.
•Mechanical cooling is disabled.
Step 5. Turn off all systems.
Switch the system into unoccupied mode.
Verify and Document
•Outdoor air dampers close completely.
•Heating and cooling do not operate.
Step 6: Return system back to normal operating condition.
•Ensure all schedules, setpoints, operating conditions, and control parameters are placed back at their initial conditions.