Choosing a Shed or Garage dehumidifier - How To Banish Rust And Mildew From Your Shed

Some products are naturally sexy and attract attention. Take the ipad 2 for example. When it was released it was just a slightly better version of the original. Slightly thinner, slightly faster and with an extra camera and better graphics. Hardly earth shattering.

But it was front page news and hundreds of pages of copy were devoted to it.

This is quite a contrast to the humble garage dehumidifier

In the last few years there have been three significant innovations to the basic mechanical refrigerative dehumidifier that have enabled them to perform significantly better, a lot more efficiently and in a wider range of conditions than ever before.

These innovations are great news for protecting the contents of your shed from the effects of a damp atmosphere and they seem to have passed without any major fanfare.

So lets put the situation to rights and discuss them right here

However before we start on the innovations lets just recap on the problem of damp and condensation in sheds and garages. In the absence of more serious problems, such as a leaking roof or damp coming up from the ground due to lack of a decent damp barrier, the cause of damp in sheds and garages is due to lack of heating and ventilation. In an unheated closed secure store the air temperature rises and falls, sometimes the dew point is reached and dampness precipitates out of the air on to the items stored, making them damp. The temperature often does not rise enough again in the winter months to dry out this dampness.

It is this dampness that causes steel tools to go rusty and encourages mildew and fungal growth on fabrics. Many sheds and garages are left unheated overnight and any paper or books will become damp over time too. The damp environment is also helpful to moths, fleas and other undesirable insect life.

The first part of the solution is to make the space as airtight as possible. If you are going to install a garage dehumidifier then you do need to make sure that you are not sucking in air and dampness from the whole neighbourhood.

Once you have your space ready, leak free and reasonably airtight it is time to go about researching your dehumidifier options.

There are three categories of garage dehumidifier

The three types of dehumidifiers are;

  • The traditional mechanical refrigerative dehumidifier (with hot gas defrost)
  • The desiccant type dehumidifier
  • The solar powered dehumidifier

Lets start with the traditional mechanical refrigerative dehumidifier

The hot gas defrost innovation

The mechanical refrigerative dehumidifier has a compressor like in your fridge. It uses the compressor to cool some internal coils of pipes and then blows the damp air from the room over these cold pipes and the moisture from the air condenses on the pipes and is then collected for disposal.

The problem with this traditional type of dehumidifier was that it did not work well at lower temperatures. In a normal house that was heated to a comfortable 20C but needed lower humidity in the winter months because of drying clothes etc indoors then this was fine. But in an unheated garage where the day time temperature might struggle to reach 10C then the coils just became iced up and the dehumidifier ceased to work.

The innovation here was the hot gas defrost. As the temperature dropped below the comfortable operating temperature of 15C the dehumidifier would automatically reverse its action and the cold pipes would heat up melting the frozen water.

The heating up of the cold pipes removes the problem of the coils freezing up but it does reduce the efficiency of the garage dehumidifier.

The desiccant type dehumidifier overcame the problem of iced coils

The desiccant dehumidifier has only recently been reduced to a size suitable for domestic use. Before this it was widely used in industry for removing hundreds of litres of waters from damp buildings and in industrial processes.

The latest domestic desiccant dehumidifiers remove about 8 litres or so of water per day. They use a different process than the traditional dehumidifier. The air from the room is blown over discs that contain material that naturally absorbs moisture. The moisture is then collected and the discs heated to restore their moisture absorbing capability.

This new type of low temperature garage dehumidifier works at temperatures down to 1C and will reduce humidity to below 40% relative humidity.

Both the mechanical refrigerative dehumidifier and the dessicant dehumidifier need an electrical power supply to operate.

The solar dehumidifier does not even need a power supply

The solar dehumidifier is mounted on a side of the shed that has a good exposure to sunlight. The dehumidifier has a black plate that heats up the air inside the unit. The unit also has a solar electric cell that power some control circuitry and an electric fan.

The unit is constantly taking cold air that has naturally less moisture in it from outside, warming it up and then blowing it into the shed where it displace the stale colder air that has a higher moisture content.

The solar dehumidifier sounds magical but it works. Not as ruthlessly efficient as the desiccant dehumidifier but if you have a shed that needs a drier atmosphere and a bit of air circulation then this unit will help to revive an otherwise stale atmosphere.

There are of course other types of dehumidifier

If you do some research you will come across other types of desiccant dehumidifier and of course the Peltier dehumidifier. These types of dehumidifier are really only suitable for small spaces such as storage cupboards or boxes due to their small capacity.

There are three main options when choosing a garage dehumidifier

The three types of dehumidifier that are suitable for reducing humidity in a shed;

  • Mechanical refrigerant
  • Desiccant
  • Solar
For reducing the humidity in a garage or shed I would recommend the desiccant dehumidifier if you need to keep the atmosphere really dry. If you need to just freshen up the atmosphere and keep the humidity down then the solar dehumidifier is a good option especially if you do not have an electrical supply.

I still reckon that the release of the next generation ipad will have more publicity than the next dehumidifier innovation. But the garage dehumidifier will do a lot better job of keeping the inside of your storage space free from damp.

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