Dehumidifiers remove moisture from the air and help to control the level of relative humidity. There are two main types of dehumidifier technology that do this: Desiccant and refrigerator coil technology.

Refrigerant Dehumidifier

These work by condensing moisture out of the air. Damp air from within the building is drawn into the dehumidifier and passed over a cold evaporator coil which cools the air below its dewpoint temperature. This results in condensation that can be collected from the cold coils. This water is collected in a pan and either removed manually or some dehumidifiers have a hose through which the water is automatically purged.

The dry air in the machine is then passed over warm condensing coils, heating the again before exiting the machine. This dry air is in many machines pushed out at pressure so can be directed at specific damp affected areas to accelerate drying.

Desiccant Dehumidifier

These operate by way of passing air through a rotor which contains moisture adsorbent desiccant material. Once water is removed from the air, dry air can be blown back into the building, thereby encouraging drying. Water collected within the desiccant wheel is removed by adding heat so the vaporised moisture can then be ducted out of the building.

The desiccant material is typically silica gel, which is not of the usual ‘gel’ texture but is a porous form of granular silica, the internal structure of which comprises a network of microscopic interconnected pores. These can adsorb moisture by attracting it within each granule. It is by the addition of heat that this moisture can then be released from the desiccant by evaporation and pushed out of the building, leaving the desiccant wheel ready again to collect further moisture.

Comparing Performance

1. Extraction Rates:

The main benefit of refrigerator coil dehumidifiers over desiccant is that they can remove a larger volume of moisture per day. They are therefore particularly useful at the early stage of flood restoration when saturated materials require drying rapidly.

However, extraction rates do depend on the make and model of dehumidifier and we suggest researching the manufacturers’ guidelines of extraction rates of the equipment you are considering.

2. Operating Temperature:

Importantly, the two technologies perform differently in the lower temperature range. Desiccant dehumidifiers are capable of operating in cold temperature conditions, as the silica gel desiccant still adsorbs moisture regardless of temperature.

Conversely, refrigerant dehumidifiers suffer a fall in water extraction at colder temperatures, as the dew point is harder to reach and condensation of moisture out of the cold air is more difficult to achieve.

2. Dehumidifier Running Costs:

Generally, refrigerator coil dehumidifiers consume less electricity so they are cheaper to run. If you provide us with the cost of your electricity in pence per kilowatt hour (KWH) then we can indicate the cost of running equipment for the duration of the drying program.

3. Noise:

Refrigerant technology uses compressors which generally make these dehumidifiers slightly louder than desiccant.Size / weight / manoeuvrability:

4. Size / Weight / Manoeuvrability:

Refrigerated coil dehumidifiers usually are heavier as they contain weightier components, and they are often larger in size. However, the ones we use come with wheels so although larger then the desiccants are in some ways easier to manoeuvre around. When hiring a dehumidifier we can give guidance on the use of each machine and which option best suits your needs.

• Causes of Residential Water Damage
• Condensation – Why have I got it & What can I do?