Linked article claims that heat-pump clothes dryers increase interior air temperature significantly
calum_wilde
| Posted in Mechanicals on
Linked article claims that heat-pump clothes dryers (HPCDs) increase interior air temperature significantly. How is that possible?
https://aceee.org/files/proceedings/2016/data/papers/1_160.pdf
Page 10 of that study claims that the homeowners complained of excess heat from the heat pump clothes dryers. If the heat pump is taking heat from the room and putting it in the dryer drum, only to be radiated back into the room again, then the only increase in heat should be from the motor/compressor’s losses. Would that be enough to cause 100 F temperatures?
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Replies
Calum,
These dryers are unvented, I think. They use electricity. Anytime that you use an electric appliance indoors, the appliance converts electric energy to heat. The heat stays in the room where the appliance is located.
My heat pump dryer creates quite a bit of waste heat. This situation can be a plus in the winter but is less desirable if forced to dry clothes during summertime daylight hours.
Here in Maine, any heat produced by our heat pump dryer is welcome in heating season.
We don't use the dryer much in summer, when we don't need to shovel a path to the clothesline.
Stephen,
I'm in Halifax, Nova Scotia. I get it. LOL
Steve,
Are you using any electric resistance heat along with the heat pump?
Martin,
The dryer is using a motor and compressor to move heat via the refrigerant cycle. If used in full heat pump mode, wouldn't it create similar levels of heat to a deep freezer or fridge?
All, thanks for the replies!
Calum,
A refrigerator definitely heats up the room in which it is located.
It's not exactly like a refrigerator or freezer, which by design take heat from inside the appliance and dump it into the room air.
Heat pump dryers are both adding heat to the air inside the dryer with one coil to vaporize the water, and removing heat from the air to re-condense and collect that moisture with the other coil. Neither process is 100% efficient and there's a fair amount of energy used by the compressor motor and blower motor. It's mostly the cooling air of the motors that is heating up the room.
Think of it at a 300-500 watt space heater in heat-pump-only mode, a 1500-2000 watt space heater if the heating element is engaged (which most models have as an option for shorter drying times when you're in a hurry).
By contrast a standard electric dryer is running ~4000 watts, but dumping all the heat and moisture outside, not in the room.
.
Calum,
My dryer does not have a resistance heat mode.
It does heat the room, can't escape that, mine uses 2-2.5kWh a load of electricity, hence adds that much heat to the room over its 1.5ish hours of operation per load.
Dana, I didn't realize they still use that much power, now it's making sense.
Steve and Alan, thanks.
Reminds me of the classic thermodynamics question from college. A perfectly insulated room has a refrigerator inside, plugged in and running. The fridge door is wide open. Does the room get cooler, heat up, or stay the same temp?
Markm3,
The room heats up. The difference between that theoretical question and mine is, well first and foremost, I didn't realize how much power the heat pump would be using. I was thinking it would be closer to the power and heat dissipated by a residential fridge, not an order of magnitude or two more than that. And second, my house is still far from perfectly insulated.
I was envisioning an extra 50-100 watts which even in the summer my basement could deal with just fine. But 300-1200 watts, depending on the mode, would heat the area up dramatically. As the highest temperature I've ever seen in my basement was 23C, maybe the extra heat would be a good thing though.
(I really need to get on insulating my slab, I just need a spare ~$5000or so...)
I use mine in summer, its no big deal and your uninsulated slab can handle the extra heat without blinking.
The thermodynamics question is answered easily, cold removed is identical to heat ejected but the energy used to make the heat move (pointlessly in this case) is added to the room hence it gets warmer.
I should have mentioned the heat is easily measurable, 2500W/hr is about 8500 BTU, this is the amount of heat your adding. You can compare this to the removal capacity of your central air or avoided furnace use. Assume your central air has a COP of 3 so it would take 2800btu of its capacity for 1 hour to remove the heat generated.
That said my unit is in the basement and i try not to use the central air in summer (its old and rather inefficient) but have not noticed the upstairs being significantly warmer even with no central air use all day. The basement is cooler (house is century old 2x4 with loose fill cellulose, no basement wall/floor insulation) typically and the basement gets a bit warmer (not stifling) when the dryer is used. It does not seem to translate into noticeable upstairs extra warmth (though theoretically it has to to some degree).
Alan,
Thanks for the replies. I'm fairly sure I'd like to get one. Now I just need to pick one...