General > General Technical Chat
The US electrical system
tom66:
--- Quote from: cliffyk on June 27, 2020, 04:11:17 am ---Do heat pump based clothes dryers exist? Interesting concept--our "new" (2 years old) R-410a based central HVAC system with heat pump (common here in Florida) can, in heat pump mode, produce a good flow (1600+ cfm) of 85° F air with an outdoor ambient of 40° F--below that 13.2 kW of coiled nichrome kicks in for "emergency" heat. We see the latter for usually < 100 hours/year...
--- End quote ---
Yes, we have those in Europe. They are relatively expensive because you need the equivalent of a 9000 BTU/hr A/C unit (~800W input power, 2600W output power) in the bottom of your dryer, plus all the associated complexities of a heatpump system, but they are considerably more energy efficient provided they are operating in a warm room. And no, they aren't the only models available. We have heat pump, condenser and vented dryers all available for sale.
The dryer we have is a condenser dryer, which is slightly more efficient than a straight vented arrangement as heat is recycled through the system and no heat is deliberately exhausted to atmosphere. Cold metal coils (by shear thermal mass) condense the water in the hot humid air, which is then recycled through the machine. A small pump moves that water into a disposal tank. Humidity sensors detect when the humid air has become dry enough for the clothes to be considered "done".
Since my dryer is often operating in a cold garage (in summer clothes are hang-dried) I don't know if a heat pump would be much better. It would depend on how efficient it is at extracting heat from a 5C room.
tooki:
Relatively expensive? I’ve seen no-name heat pump dryers on sale here for $300.
(And it’s not like 9000BTU AC is that big. Those are routinely used as window AC units in USA, and don’t cost very much.)
Non-heat-pump condenser dryers use more energy than vented, not less: https://www.cda.eu/laundry/condenser-vs-vented/
They only made sense when you couldn’t have a vent. With the advent of heat pump dryers, are plain condenser dryers don’t make sense at all.
tom66:
Are you sure? The EU standards (Annex IV):
https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32012R0932
state that the 'standard' of each dryer should consume (@8kg capacity):
Vented - 4.1 kWh/cycle
Condenser - 2.30 kWh/cycle
The ratings get better at lower capacities, with the energy consumption of a 5kg vented dryer and 5kg condenser dryer only differing by about 20% or so, although the condenser still wins. I'd be curious why there isn't a linear relationship, it might relate to the extra energy required by the condenser system, pushing the hot air through the internal condensation system might consume extra energy and give more opportunity for heat loss inside the machine perhaps. The energy consumption of the tumble motor shouldn't be that high (100W or so.)
I have not seen a heatpump dryer for under £400 (~$500USD) here but then again, my current tumble dryer was a road-side find (it had a blown fuse...) I suspect that it may be more expensive to buy these types of dryers here as regulations for refrigerants may be more strict. I would be surprised if propane is an acceptable refrigerant in such a device, which is common in cheap A/C units and refrigerators here.
There's probably the other factor that as you mention, condenser dryers are preferred as there is limited ventilation requirement, with no exhaust to atmosphere, especially important for flat dwellers.
NiHaoMike:
--- Quote from: tooki on June 28, 2020, 08:40:07 am ---Non-heat-pump condenser dryers use more energy than vented, not less: https://www.cda.eu/laundry/condenser-vs-vented/
--- End quote ---
In cold climates, vented dryers are the least efficient after accounting for heat lost from the building.
duak:
I set up a little drying cabinet for delicates in the furnace closet. The excess heat from the house's original furnace and hot water heater would dry laundry and remove the humid air by combusting it and firing it up the B-vent. After replacing both units with closed combustion units, the furnace closet was cooler and had no natural venting. I now had room for a dehumidifier that keeps the closet and most of the lower floor less humid than before, especially in the summer. The dehumidifier doesn't run all the time even when drying laundry. Three or four pairs of jeans or a few terry cloth towels will dry overnight as long as the circulating fan moves air around in the closet.
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