Air Handling Unit Control: Energy Recovery Wheel

Energy recovery wheels with bypass dampers are commonly installed as part of your dedicated outdoor air handling unit. The effectiveness of energy transfer has improved as energy wheel technology has improved. When and when not to use the energy wheel continues to be a source of confusion we see on our jobs.

To get the most energy savings out of your energy wheel you want to use it only when the outgoing exhaust air mixing with the incoming outdoor air is beneficial. With that in mind here are a few quick guidelines and tips on energy wheels to maximize your return:

• Specify bypass dampers with your energy wheels. This saves fan energy and lengthens the life of the energy wheel material.

• Include energy wheel status in required controls points list. This can be accomplished using a wheel rotation sensor or current switch on the wheel motor.

Basic operating conditions:

• When unit is heating: If outdoor air enthalpy is less than exhaust air enthalpy the energy wheel should be enabled, and the energy wheel bypass damper closed. This will allow the incoming outdoor air to be heated and less humid prior to being mechanically heated. The greater the difference between the enthalpy, the more heat transfer!

• When unit is heating: If outdoor air enthalpy is greater than exhaust air enthalpy the energy wheel should be disabled, and the energy wheel bypass damper opened. The outdoor air is more beneficial for heating without mixing. This rarely occurs because typically if a space requires heating it means that the outdoor air enthalpy is low.

• When unit is cooling: If outdoor air enthalpy is greater than exhaust air enthalpy the energy wheel should be enabled, and the energy wheel bypass damper closed. This will allow the incoming outdoor air to be cooled and less humid prior to being mechanically cooled. The greater the difference between the enthalpy, the more heat transfer!

• When unit is cooling: If outdoor air enthalpy is less than exhaust air enthalpy the energy wheel should be disabled, and the energy wheel bypass damper opened. The outdoor air is more beneficial for cooling without mixing. This situation allows for free economizer cooling. This occurs most often in the shoulder seasons of spring and fall and is ultimately the most energy saving operation for your outdoor air handling unit.

• When unit is in neither heating nor cooling: The energy wheel should be disabled, and the energy wheel bypass dampers opened.

If you would like help determining your energy recovery wheel operation strategy, contact Elevate Building Commissioning today! We strive to provide helpful, long-lasting solutions for your building system operation and energy use strategies.