Can You Install a Dehumidifer on an HVAC Roof Top Unit?

Dehumidifiers

• Dehumidifiers remove moisture from the air through condensation or with a drying medium. Most home air conditioners use condensation to remove the moisture from the air with cooling coils. This occurs naturally when air is pulled into the HVAC system and passed over cooling coils filled with refrigerant. The coils lower the air temperature to the dew point so the moisture in the air condenses and collects on the coils. This means of cooling occurs naturally every time you run the air conditioner, but in some locations, you might need a separate dehumidifier to remove water vapor without cooling the air.

Desiccant Dehumidifiers

• Desiccant dehumidifiers are used more often with commercial HVAC units in exceptionally humid areas where running a standard air conditioner does not drop the humidity levels enough. These units pass the air over a drum filled with a dry or liquid drying agent. Moisture from the air sticks to the drum, drying the air without cooling it. These are also useful for humid, but cool climates where you do not want to lower the temperature, just get rid of the dampness in the air.

HVAC Units

• Home HVAC units are typically installed in the attic of a home, but large homes and multi-family housing might use a rooftop HVAC system to supply the heating and cooling needs for the building. These pull outside air through the unit, passing it over cooling coils and into the house through the duct system. To dry outside air before it enters the HVAC system, a separate desiccant dehumidifier can be installed on the roof with the HVAC system. This
  dries outside air before it enters the building through the HVAC system's ducts.

Placement for Dehumidifiers

• When installing a separate dehumidifier, if you choose to add a supplementary unit, the best place for it will be in a central location. This draws air from around the space to dry it. If you have a supplementary dehumidifier installed on the roof, you do not have the option to recirculate air through the room because the rooftop dehumidifier only uses outside air. Choosing a separate condensing dehumidifier that recirculates air will operate more efficiently over time. Once it drys the air in a room, recirculating the air creates less condensation, reducing the number of times you need to drain the condensation pan.