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Is the heat pump worth it?

  1. Aug 24, 2015 #1

    sophiecentaur

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    The old tumble drier is past its use-by date and it is time to get a new one. The old one vents through a pipe to the outside and the new one will be a condensing type.
    I really can't think that they are efficient devices (efficiency in the loose sense, of course) as they seem to use the incoming, room temperature, air to cool the outgoing air in a heat exchanger and the condensate is collected in a tank.
    There are now 'heat pump' versions available, which I guess, use a refrigeration unit to increase the temperature difference, and drying the inlet air etc. etc.
    Does anyone have experience of the new types and are they worth the extra £100+? The refrigeration unit is just one more thing to go wrong, of course but they do tend to run and run in other devices.
     
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  3. Aug 24, 2015 #2

    anorlunda

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    Do you have spec sheets for the old and new types of dryers? They should be easy to Google.

    Edit: Here in the USA, they offer energy guide stickers on appilances that estimate the total energy cost per year.
     
  4. Aug 24, 2015 #3

    sophiecentaur

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    Thanks for the response.
    I was intending to look at the 'facts' after getting some general opinions. Things like reliability and whether they make excessive noise (yes, I know there's a dB rating on the label). The ABCD 'efficiency' rating on the label could be relevant but they all just heat up the environment one way or another. We tend to use the good old washing line most of the time!!
    I will, at this juncture, open a few more tabs and look at the specs, as suggested.
     
  5. Aug 24, 2015 #4

    DrClaude

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    I'm annoyed that here in Sweden, it is very difficult to get a dryer that is not of the condenser type. I understand that throwing out warm air is a waste of energy, but my experience is that a condenser type is much worse at doing its job of drying clothes (I am comparing to my experience with dryers in Canada, which are all of the kind where the warm, moist air is evacuated outside).

    The dryer we have now has a heat pump, and I guess that it is more economical than the traditional condenser when you use it a lot. But when it is time to change, I will look hard to find a dryer that throws out the warm air instead of recycling it.
     
  6. Aug 24, 2015 #5

    anorlunda

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    Swedes are never satisfied. :wink: When I lived there, the only type available was the torkskåp. It was terrible.

    ets_1900_e.jpg
     
  7. Aug 24, 2015 #6

    sophiecentaur

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    There is another important factor and that is the humidity of the ambient air. If the air, drawn in, is sopping wet already then its relative humidity when it's been warmed up could still not be low. Room air that has come from a cold, dry outside would do some drying by just tumbling the clothes and any added heat is a real bonus. With a good refrigeration unit ("heat pump") and effective re-cycling of the heat, you could be somewhere the energy used approaching the mass X latent heat limit.
    I have looked at a number of specs and advertising blurb but they seem shy of giving drying time information or even power rating, even though they tell you (as the EU demand) the kWh needed for a standard load of damp washing.
    there are so many decisions to make when moving into a new place.
     
  8. Aug 24, 2015 #7

    anorlunda

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    So what is the answer? It would be interesing to compare that number for all the types of electric clothes dryers.
     
  9. Aug 25, 2015 #8

    sophiecentaur

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    Yes indeed. I read a review of a certain tumbler in which the guy said he was not surprised that his new heat pump tumbler was not drying the clothes well when he saw it was only a 900W load, compared with his old dryer that was 2.5kW. That's heat pumps for you - and also demonstrates public ignorance about heat pumps.
    There must be a lot of potential for a heat pump system but it still would need to be designed right. It is actually working in quite a benign circumstance, compared with a pump used for heating and cooling buildings because the temperature difference between the two heat exchangers need not be extreme.
    The coefficient of performance is discussed here (Hyperphysics) and, although it is presented a bit back to front for this application, it shows that , for a given COP, more heat is transferred for a smaller temperature difference. (Obvious really)
    The only thing that worries me - and which probably accounts for the range of energy use figures for the different tumblers I've looked at - is that it's fairly new to the market and so some of the designs may not be optimal or reliable. Fridge cooling units are fantastically reliable (ime) so that may not be a problem but operating termperatures and air flow rates may still need to be tiffled before the whole benefit of a heat pump is realised. As it's a 'sealed system' it would be easier to assess performance than the venting and condenser types, where ambient temperature and humidity would talk louder.
    It's still a pretty sexy idea, though. I think we really have to buy one!
     
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