I have been asked to explain what the difference is between AIR CONDITIONING and DEHUMIDIFYING. So in two words …..NOT MUCH! The principles of the two systems are very similar. Both —

  • cool air
  • discharge heat
  • dispose of condensed moisture, and
  • have independent controls.

Dehumidifier

In your average home dehumidifier, warm moist air is drawn across a cool coil in the front of a small self-contained unit. As the warm, moist air has its temperature rapidly changed (dropped), this moisture condenses. This moisture drains to the base of the coil and is collected in the drain pan or condensate tub.

Since this process generates heat (at the compressor), the air that has been cooled and consequently dried somewhat, is diverted through the back of the unit where the heat generated by the compressor is transferred to the cool dry air. It is then blown back into the area being dehumidified. Hence the discharge of warm air out the back.

I am told that the other reason for this discharge is to insure that the ambient air temperature is increased, thereby allowing it to absorb more moisture (relative humidity – remember?). The warm dry air now has a greater affinity for moisture retention so it absorbs additional amounts of moisture. As it “recycles” and returns to the inlet of the dehumidifier, it holds more moisture than it originally did.

The one main draw back to a dehumidifier as opposed to an AC unit is the primary function of the dehumidifier — to remove moisture so the production of heat and the ensuing discomfort it may create is not an issue in the manufacturers eyes.

If a dehumidifier unit is undersized, it will not be able to overcome the humidity levels completely. It will create a warm damp, environment in the area in which it is placed. If it is oversized, it will produce more heat than anticipated, and the temperature in the “dehumidified zone” will rise dramatically.

The Almighty Air Conditioner

This unit really doesn’t “condition” the air. It cools it. It takes some moisture out. It makes life more bearable. It helps you with not perspiring while sleeping. It pulls some solid particles out of the air. (???really?) t…is…just ….GREAT!

Seriously though, what occurs with the “Central Air Unit” is the rapid cooling (and dehumidification) of the air being moved across the coil in the plenum of your heating system. That “A” coil, that was added years ago, is the reason you are cool (not your flowered shirt).

The Freon gas is pumped from the outdoor (condensing) unit into the coil (evaporator) inside. As it cools the evaporator coil ( +/- 56F), the air moving across the cold coil drops its humidity and the ensuing “condensate” runs out from the tube that comes from the corner of the coil. At the same time, in the outdoor unit, the compressor is drawing Freon back outside in the suction line and as the Freon is compressed, heat is generated. Simultaneously the outdoor fan draws cooler ambient air across the coil outside and the heat is dispelled into the atmosphere (not into your basement).

The Freon is then returned to the indoor coil & the cycle starts all over again – that’s it. – “sort of”. As with the “DH” unit, size is important. An undersized AC will never keep up to the load and an oversized unit will leave the occupants in a cold damp environment because it does not run long enough to remove adequate amounts of moisture from the air. As you can see, in both cases —

  • cooling & the generation of heat is involved,
  • condensation is collected and disposed of.
  • proper sizing of the equipment is of paramount importance.

One other point, when a central air unit first starts its cycles, the majority of its energy is used to dehumidify rather than cool. If you practice night set back for heating, DO NOT APPLY THOSE PRINCIPLES TO COOLING. All you will do is make your AC unit work harder to dry the air each morning and the ensuing extended load just uses more energy. Choose a comfortable temperature & leave it there! I hope that helped you.