Demystifying dehumidifiers
A dehumidifier is a great idea for keeping the boat, caravan or car dry and free from mildew while it's laid up for the winter, but most just don't work at low temperature.
The perfect boat dehumidifier?
Refrigerant dehumidifiers
Most domestic dehumidifiers work on the refrigeration principle. Moist air is drawn over a refrigerated element where water vapour condenses and is drained away. That's great in a warm climate or in the home for laundry drying etc, but as the ambient temperature falls below about 15 degrees, the water on the cold element begins to freeze rather than condense.
To overcome the freezing problem, some dehumidifiers have an automatic defrost capability that reheats the element periodically to remove the ice. While this does enable them to operate as slightly lower temperatures, it takes more energy and reduces their efficiency further in cold conditions.
Winter temperature seldom rises to 15 degrees, so just when you need them, refrigerant dehumidifiers become ineffective, or at best very inefficient!
Check the spec!
If you look at the specification of most dehumidifiers, the extraction rate is quoted at 60%RH and 30°C. This gives a good indication of how it will perform in keeping a room comfortable in a hot, sticky climate. To keep your boat free from damp during a typical British winter, you need to know what it will do at around 10°C or less. You won't find that information for a refrigerant dehumidifier - you need a completely different technology!
Adsorption dehumidifiers
Adsorption dehumidifiers are different. They work like this:
- Moisture from the air is attracted to a desiccant carried on a rotor.
- Moist desiccant is carried around to a drying sector, where gentle heat drives the water off and into a reservoir.
- Warm dry desiccant moves around ready to take more water from the air.
This technology works well at all temperatures and because it doesn’t have to cool the air to precipitate moisture, the process is significantly more energy-efficient than a refrigerant device.
Even more importantly, there is little loss in efficiency throughout the operating range, including the crucial 1 to 15 degree range. (At zero, moisture freezes out of the air anyway).
There's no cooling effect and no compressor, so practically all the energy consumed by the unit is converted into heat that warms the air while it is working.
The adsorption system has previously only been cost-effective for large commercial applications, but the principle has been developed into a brilliant new dehumidifier that we think is pretty well perfect for keeping a boat dry through a typical British winter.
|
Desiccant types |
Refrigerant types |
|---|---|---|
Operating principle |
Operates by water adsorption on a desiccant, which is automatically regenerated by warming. |
Works by condensing moisture on a refrigerated element approx 15 degrees below ambient. |
Effective operating temperature range |
1to 40°C Remains effective in UK winter temperature range 1 to 15°C. No issues with freezing up however cold |
15 to 40°C Operation ceases or is impaired below 15°C ambient. Some models have hot gas defrosting. |
Outlet air temperature |
Outlet air is 10-12C warmer than inlet |
Outlet air is colder than inlet air. |
Noise levels |
Practically silent in operation on low fan speed |
Refrigerating compressor may be noisy in addition to fan |
The perfect boat dehumidifier?
Follow this link for information on the perfect boat dehumidifier.