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| Image public domain via Wikimedia Commons |
If
you had clothes on the line yesterday or over the last week or so,
you'll have noticed there was "great drying". That's because winds were
coming from a generally eastern direction and east winds are usually dry
with low humidity. Unlike the prevailing winds that come from a SW
direction, carrying moisture from the Atlantic, easterlies come overland
from continental Europe and moisture content isn't as high. So clothes
dry faster and you'll have noticed the ground and fallen leaves dried up
too.
I bought a dehumidifier recently, mostly to deal with condensation problems in a utility room that isn't heated. Ideally insulating walls would help solve the problem, but this is a stopgap solution. The dehumidifier also comes in handy for drying clothes, but first some science. Skip it if you just want to know about clothes drying.
I bought a dehumidifier recently, mostly to deal with condensation problems in a utility room that isn't heated. Ideally insulating walls would help solve the problem, but this is a stopgap solution. The dehumidifier also comes in handy for drying clothes, but first some science. Skip it if you just want to know about clothes drying.
Relative humidity
Relative
humidity (RH) is defined as the ratio of moisture in air to the maximum
amount of water that air can contain, expressed as a percentage. So
100% is saturated and 0% is completely dry air. In the winter in
Ireland, humidity is typically over 80% and often near 99% on warm, damp
days. Air can only hold a certain amount of moisture per unit volume.
Once it becomes saturated, i.e a relative humidity of 100%, water starts
to condense out. Now the amount of water air can hold depends on
temperature. As temperature drops, it can hold less. That's what causes
fog after a sunny day in autumn when temperature plummets and also why
water condenses on window panes and cold walls because they're cooler
than the ambient temperature in a room. So the RH of the air increases
as it hits such surfaces and possibly reaches the dew point. (Not always
though, because the RH may have been low to start with) The dew point
temperature is the temperature that air with a certain RH and a certain
temperature must be cooled to for it to reach an RH of 100% and
condensation to occur.
How does a dehumidifier work?
A
dehumidifier works more or less the same as a fridge. Coils in the
appliance containing a refrigerant are cooled and a fan circulates air
from a room over them. Air is cooled to below the dew point and water
condenses out to be collected in a container. Usually a desired RH can
be set on the appliance and it will cut in and out to maintain that set
point.
Drying clothes with a dehumidifier
If
you can't dry clothes outside, you can put them in a tumble drier. That
typically uses two units per hour. The alternative is to put them on a
clothes horse or radiators, but that can cause condensation problems
because the water has to go somewhere. Ventilation might be an issue if
you're limited to where you can dry your clothes and opening windows
isn't an option. An alternative is to use a dehumidifier to regulate RH
so that clothes hung indoors dry faster. It isn't as quick as using a
drier, but if you have a day to spare, it speeds things up by reducing
the humidity, allowing water to evaporate faster. Dehumidifiers are
cheaper to run than a drier, typically the power use is about 150 W,
compared to the 2000 W or so of a tumble drier.