How to dry your clothes – a comparison of tumble drying methods.

I’ve been investigating tumble dryers to see which is most environmentally friendly. Surprisingly, I’ve not found a good comparison of the basic types, so here’s mine.

There are three main types of tumble dryer: vented, condensing and heat pump. And then there are washer dryers, which combine a washing machine and a condensing dryer.

Rather than looking at brands, colours and gadgetry, let’s look at some basics.

  • Heat is needed to dry the clothes.  This generate humid air that contains that heat energy.
  • Condensing and heat pump dryers both use cool air from outside the tumble dryer to condense the water from the humid air. The heat in the humid air is transferred into the air from outside the dryer, and so heats up the house.
  • Heat pumps are more efficient than heating elements for generating the temperatures to evaporate the water on your clothes and so will use less electricity than condensing driers.  But it will also heat up the house less.
  • Vented dryers and washer dryers (which are an inefficient form of condensing drier) both discard the heat from the humid air outside the house. That’s OK in summer, but in winter that is wasted energy that could be heating your home and saving on heating fuel bills.
    • The vented dryer throws it away via the vent pipe.
    • The washer dryer is worse, it takes in fresh cold water, heats it up with the humid air from drying the clothes and then throws it away down the drain. i.e. it throws the heat away and it wastes lots of water.
  • Vented dryers also suffer from the high likelihood of the vent pipe coming loose and flooding the room with very humid air, often causing mould growth when undetected.

So:

If you heat your house in winter, both vented dryers and washer driers are throwing away heat that you then have to provide with your heating system.  i.e. they are wasteful.

Washer dryers not only waste heat, but they waste water too.

If you heat your house with electricity there is no benefit in winter from a heat pump dryer, as the energy saved in the dryer must be added by your electrical heater.  But it will save you energy in the summer (but why not dry your clothes outside in the summer?)

So, my conclusion is that although heat pump dryers will be marginally better from a total energy usage point of view, the extra complexity is probably not worth it and a condensing dryer is probably the best choice.

And in the summer, use a washing line or internal drying rack.  The internal drying rack has the advantage that the drying of the clothes will actually cool the surrounding air like a primitive air conditioning system.

Image from http://worldartsme.com/

About Minimalist Christian

Phil Hemsley is a graduate of the University of Cambridge, and a Fellow of the Institution of Mechanical Engineers in the UK. He works for a multinational company in the power industry, has presented technical papers at international conferences and holds many patents. He has published two books, the most recent is "The Big Picture, an Honest Examination of God Science and Purpose". He has lived on both sides of the faith fence. He is married, with two daughters.
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2 Responses to How to dry your clothes – a comparison of tumble drying methods.

  1. Anonymous says:

    Perhaps you coul consider a CD design (Compact Drum) during your well earned impending retirement.
    Same heat input across a smaller volume should reduce drying time.
    A better balance of U/C0 (underwear vs pure cottons) may yield better cycle efficiency.
    Perhaps you could also investigate a conical drum where the usable exhaust annulus could be different in summer vs winter operation- thus allowing flexible part load and base load operation.
    Just some thoughts.
    Rgds
    Gary Holloway
    Mininalist Engineer.
    🙂

    Like

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