AHU - Cooling Operation

AHU - Cooling Operation

Testing Procedure

Pre-Conditions Check

Before testing is started, it must be verified that the AHU is running and that return temperature is not so high that heating would not be detectable.
  • Verify that device is “Occupied”.
  • Verify fan is running by checking that duct pressure is more than 0.4psi [Pressure Min Threshold]
  • Verify that return temperature is less than 60°F [RAT Cooling Threshold] in order to be able to provide heating.
If any of these conditions are not met, STOP the workflow and ARCHIVE.

Setup Testing Conditions

In order to ensure that testing is accurate, outside sources of heating and cooling need to be eliminated or minimized and the mixed damper needs to be open. If any of these conditions are applicable and not verified, then the testing will be aborted.
Stop Active Heating
  • Verify that discharge temperature is within 10△°F [Heating - Delta] above mixed temperature
Stop Active Cooling
  • Verify that discharge temperature is within 10△°F [Cooling - Delta] below mixed temperature
Open Mixed Damper
  • Verify that mixed temperature is within 5△°F [Ventilation - Delta] below return temperature

Test Heating

Start Cooling Operation      
  • Command Heating to “ON”
  • Pass if Discharge Air is 10△°F [Cooling - Delta] more than mixed temperature.
Or, if mixed temperature is not available,
  • Pass if Discharge Air is greater than 45°F [DAT Arb Cooling Threshold] 

Parameters

​
DisplayHint
Pressure Min Threshold [0.4psi] How much should the duct pressure be minimally.
RAT Cooling Threshold [60°F] How much should the RAT minimally be for our loop to be able to provide cooling.
Loop Diff Pressure Min Threshold [3△°F] How much should the loopsystem differential pressure be minimally.
Ventilation - Delta [5△°F] The temperature threshold tolerance for fully open mixed damper. Delta below RAT for fully open mixed damper.
Cooling - Delta [10△°F] The threshold tolerance for cooling. Delta between MAT and DAT.
Heating - Delta [10△°F] The threshold tolerance for heating. The threshold tolerance for cooling. Delta between MAT and DAT.
DAT Arb Cooling Threshold [45°F] The DAT below which there would be indication of cooling.
Reaction Time [300sec] How long to wait for the actuators to fully do their job.
Stabilization Time [60sec] How long to wait for the system to come to stability after we have given it an actuator command and the conditions have been fullfiled.
Measure After [60sec] How long to wait in seconds to start checking the feedback readings.

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