Q. How much cross contamination occurs with the use of an Energy Recovery Wheel? Does exhaust air get mixed back into the supply air stream?
A. Cross contamination refers to the amount of air that is leaked from one side of the wheel to the other. Leakage rates are significantly reduced by using higher quality wheels. Higher quality wheels use better seals, minimizing leakage.
Cross contamination can also be reduced significantly by fan configuration. If the Supply Fan is in a blow thru and the Exhaust Fan is in a draw thru configuration then any leakage will go from the supply to the exhaust side of the wheel.
Carryover is a different type of concern when using an Energy Recovery Wheel. Carryover occurs when a contaminant is transferred from the exhaust side to the supply side of the airstream through the rotation of the wheel. Research has shown that the potential for contaminants carryover varies as a function of the contaminant properties, the construction of the total energy wheel (quality of the wheel) and the desiccant utilized.
To minimize carryover, a Purge Section can be used. The purge section uses outdoor air to clean or purge the wheel matrix before it rotates from the exhaust air stream to the supply air stream.
How much cross contamination and carryover occurs is completely dependent on the quality of Energy Recovery Wheel, the type of desiccant used and the Air Handling Unit design.