Before buying a whole building-dehumidifier, make sure that the existing HVAC equipment is optimized to remove both sensible and latent heat. As with any HVAC upgrade, improve the building enclosure with cost-effective retrofits. If this HVAC-and-enclosure optimization is successful, you may not need a dehumidifier.
This type of dehumidifier works well in humid climates where the building needs more heating than cooling. In addition to dehumidifying, this most-common type of whole-house dehumidifier heats the air flowing through it. It’s COP as a heater is between 1.5 and 2.0 and the heating capacity of available products is between 3000 and 8500 BTU/hr (1 to 2.5 kW).
Whole-house dehumidifiers are specialty products that require careful research, installation, and commissioning. The three products we discuss here are for single-family buildings or small multifamily buildings.
- Split-system whole-house dehumidifiers
- Ducted whole-house dehumidifiers
- Ventilating whole-house dehumidifiers
Ducted whole-building dehumidifiers
This type of dehumidifier works well in humid climates where the building needs more heating than cooling. In addition to dehumidifying, this most-common type of whole-house dehumidifier heats the air flowing through it. It’s COP as a heater is between 1.5 and 2.0 and the heating capacity of available products is between 3000 and 8500 BTU/hr (1 to 2.5 kW).
Desiccant whole-building dehumidifiers
Desiccant dehumidifiers dehumidify air with a desiccant rather than an evaporator coil. A desiccant is a liquid that removes water vapor from the air passing through it, because it is so very dry. After the desiccant absorbs the water vapor, it needs heat to dry and to again be capable of removing more water vapor. A desiccant dehumidifier’s efficiency is only about 25% of a refrigerated dehumidifier. However, desiccant dehumidifier’s maintain their efficiency in extreme temperatures, while refrigerated dehumidifiers’ efficiency drops quickly above 80°F or 26°C.
Split-system whole-building dehumidifiers
This type of dehumidifier works well in a humid climate where a building needs more cooling than heating. The evaporator condenses water vapor on its coldsurface. The split-system dehumidifier has an outdoor condenser to reject the heat collected by the evaporator. Thus, this dehumidifier functions as an air conditioner. Its air-conditioning capacity is small, but may be enough for small airtight homes and homes in mild but humid cooling climates. The air conditioning capacity of available products is between 3000 and 5000 BTU/hr (0.9 to 1.5 kW).
Ventilating whole-building dehumidifiers
The ventilating dehumidifier combines an outdoor air inlet to one of the three whole-house dehumidifier types described above. This dehumidifier brings fresh air into a home like a supply only ventilation system discussed previously. Make-up air comes through air leaks in the building enclosure similar to a supply-only ventilation system.
For more information on whole-building dehumidifiers, see Residential Energy, Chapter 11