Q&A - Testing Dehumidifiers - Short #206

HVAC School - For Techs, By Techs

In this short podcast episode of the Q&A series, Bryan answers a question about testing dehumidifiers (submitted by Steven via Speakpipe).

Dehumidifiers run air over a cold evaporator coil (to pull moisture out of the air and drain it out) and then reheat it over a condenser coil. The air leaving a dehumidifier is of a higher sensible temperature than the air going in, but there are fewer overall grains of moisture.

To see how well a dehumidifier is working, you will need to know the dehumidifier's rating and have the manufacturer's charts at your disposal. You'll also need to be mindful of barometric pressure and know the basics of using a psychrometric chart or app.

You'll want to monitor the dew point delta (the difference between the dew point of the air going in and the air going out) to determine how well a dehumidifier is doing its job. Entering air conditions will heavily impact a dehumidifier's performance, and power consumption is another important measure of dehumidifier efficiency.

To collect data, you must place one psychrometer at the dehumidifier inlet and one at the outlet; you'll get the dry-bulb and wet-bulb temperatures needed to make a comparative measurement and plot points on the psychrometric chart. You can also measure the condensate output and do the math to determine how much moisture is being removed per hour, but that would hinge on constant operation and consistent entering air conditions.

"Dehumidifier Facts and Troubleshooting" tech tip by Genry Garcia: https://hvacrschool.com/dehumidifier-facts-troubleshooting/

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