Understanding Dehu Specs

1/10/2018 (Permalink)

When checking out the specs on a dehumidifier you’ll usually find listed under the section “Water Removal” two numbers. One is noted as AHAM (Association of Home Appliance Manufacturers) and one is “Capacity at Saturation”. But what do these numbers represent and how are they calculated?

AHAM certifies that the PPD (Pints per day) a manu-facturer claims their product will remove is accurate. All dehu’s are tested in a controlled environment where the temperature is 80° F with a relative humidity of 60%. The units are run for 24 hours and the measured amount of extracted water becomes the official AHAM rating.

But even though each dehu is tested the same, the problem is that real world conditions are many times quite different. There have also been questions about whether the ratings that are being applied to “Home” appliances should have any bearing on the type of commercial units that you employ. And that’s where the “saturation” number becomes important.

Saturation can best be described as any extreme condition where the amount of moisture that is in the air is so high that a dehu is forced to run continually over a 24 hour period (100% RH). Situations like this might arise with flooded basements or natural disasters like hurricanes. So the saturation PPD rating will be at the top end of your dehu’s capability.

There exist a sizable number of temperature/humidity combinations that occur naturally or are due to the use of heat drying that causes faster evaporation. These all affect a dehumidifiers performance. Having more than two test conditions listed in the unit’s specs could give you a better idea of its overall performance, but that’s not likely to happen. But having some understanding of its performance capacity will help to ensure you’ve got the right sized unit on the job.