CONDENSATION = MOIST.
IT IS THE CHANGE FROM A VAPOUR (GAS)
TO A CONDENSED STATE (LIQUID)
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This change is caused by a combination of two factors:
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The difference in temperature between the air and a surface.
It's not a matter of any particular temperature but of a difference between two.
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The relative humidity in the air. When air is cooled, relative humidity
increases, until at a particular temperature, called the dew point, the air
becomes saturated and forms water droplets on the surface.
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Warm and dry climates don't suffer so badly from this problem, which is why e.g. Californian classics are usually better preserved than European ones. But in our North West European climate, condensation occurs both indoors and outdoors. It's most common in winter, due to sudden changes in temperature, but it can occur whenever water vapour in the air comes in contact with a lower surface temperature.
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In an unheated room, even if completely closed and insulated, the air is still influenced by the temperature and humidity outside. On top of that the air stands still. These are the perfect conditions for condensation to occur. Anyone who ever experimented with storing a car in an old container will confirm he/she learned the hard way. Don't let this happen to you!
We see this happening when we take a cold bottle out of the fridge: the sudden temperature difference makes the vapour turn into droplets immediately.
Evaporation is the opposite - the change of a liquid into a gas.
When either air humidity or temperature difference change sufficiently,
the droplets turn back into vapour.
This, too, is something we see
happening every day.
Condensation means moist, too much moist, which means damage to any car that isn't driven for a longer period of time. It causes corrosion not only on the paint, but also on all metal parts inside the vehicle. The moist also triggers mildew which can ruin the upholstery and give the interior a bad smell.
HOW TO PREVENT CONDENSATION
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There are two ways to prevent condensation:
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AVOID TEMPERATURE DIFFERENCES between air and surface, which can be achieved by either
- heating the air
or by
- strong air circulation
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TAKE THE MOIST OUT of the air
A CAR COVER CAN DO NEITHER, THEREFORE A CAR COVER CANNOT PREVENT CONDENSATION !
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A car cover must be made of breathable material to allow the vapour to escape from under the cover, once the droplets evaporate. But the evaporation process depends on the balance between temperature and air humidity:
if the temperature remains too low the droplets won't evaporate, meaning that the car will remain wet under the cover. Even if the cover absorbs the droplets the car will still be wet, and so will all its interior parts.
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This can occur on cold winter days, and is even worse indoors than outdoors, because outdoors the wind causes some air circulation which helps reduce the difference in temperature between the air and the surface (your car). During cold weather periods it's therefore vital to check your car on condensation. If it's really bad and ongoing you need to take other measures than simply putting a cover over it.
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Apart from installing heating in your storage room, you have the following options:
USE A DEHUMIDIFIER TO TAKE THE MOIST
out of the air. There are plenty of products on the market that do a great job. However, they need maintenance - they must be emptied or replaced regularly, which in many cases means often.
Some electric dehumidifiers use a hose or a pump to get rid of the water captured. The energy consumption is generally less than that of a heater but still considerable at average 500W for a mid size electric dehumidifier.
HEAT THE ROOM WITH A MOBILE HEATER
To make this work the space must be well insulated, and have electricity. The average energy consumption of mobile heaters lies around 1500W, which will make your energy bill explode.
USE A STORAGE SYSTEM
There are various concepts, some use strong air circulation, others concentrate on dehumidifying. They are described here.