Should I get a heat pump clothes dryer?
May 9, 2021 7:01 AM Subscribe
I am about to buy a new washer and dryer (stackables). I was assuming I would get a gas dryer, because that's the type I have now, but I now see there is something called a "heat pump" dryer that's supposed to be more energy-efficient. I'm reading about them, but I just can't picture what this pump is all about. What kind of heat is it? Is it separate from the dryer itself? Does it use electricity or gas or ... what? I'm in New York City, if that makes a difference.
Heat pumps use electricity to draw heat out of the air and convert it to heat you can use to heat clothes in your dryer (or in your house). They’re more energy efficient than the alternatives, and as the electric grid in NYC converts from half-natural gas to more renewable energy sources in the next 10-20 years, that means your dryer will be running on that cleaner energy mix.
I don’t have one, but it looks like the biggest downside is that they can take a little longer to dry your clothes and the upside is that it’s better for the environment, cheaper to run over the long term, and don’t require a vent to the outside because they recirculate the heated air.
posted by A Blue Moon at 7:48 AM on May 9, 2021 [1 favorite]
I don’t have one, but it looks like the biggest downside is that they can take a little longer to dry your clothes and the upside is that it’s better for the environment, cheaper to run over the long term, and don’t require a vent to the outside because they recirculate the heated air.
posted by A Blue Moon at 7:48 AM on May 9, 2021 [1 favorite]
Response by poster: One more sub-question: condenser dryers leave clothes a little damp, on purpose. You're supposed to take them out and hang them up and in a few minutes they'll be dry. Is the same true for heat pump dryers? I'm wondering since rustcrumb's post reminded me of this fact about condenser dryers (I know someone with an LG all-in-one washer/condenser dryer and they have to do this second drying step).
posted by DMelanogaster at 7:53 AM on May 9, 2021
posted by DMelanogaster at 7:53 AM on May 9, 2021
A heat pump is a device, usually powered by electricity, that uses most of the electricity it consumes to move heat energy rather than simply converting it to heat directly.
So a heat pump will always have a cold side where heat energy goes into it, and a hot side where the heat energy it's moving (plus any waste heat it generates internally) comes out. There's one in your refrigerator, with the cold side inside the insulated interior and the hot side in those black radiator coils on the back. An air conditioner is a heat pump with room air being pushed through fins on the cold side to cool it, and outside air being pushed through fins on the hot side outside the building to remove the heat being pumped through from the cold side. A reverse cycle air conditioner lets you switch the hot and cold sides, and extract the heat energy it uses to warm the room from the cold air outside by making it even colder.
A heat pump clothes dryer has a blower fan that pushes air through fins on the cold side of the heat pump, then through fins on the hot side, then through the drum, then back around to the cold side fins again. This sounds kind of strange - it seems pointless to burn electricity on cooling and then immediately re-heating the same air - but there's method in the madness.
The key thing to understand is that when the air goes past the damp clothes in the drum, two things happen: the air picks up some moisture from the clothes, and the clothes get cooled as moisture evaporates from them. When that moisture-laden air goes through the cold-side fins, water condenses out of it just like it would on the side of a cold can of beer. That condensation process warms the cold side up a little, then trickles out the dryer's drain tube.
The heat pump transfers all the heat energy picked up by condensing the water, plus a bit of its own waste heat, to the hot side. So after the circulating air has been through both the cold side and the hot side, it ends up a little bit warmer and a whole lot dryer than it was when it came out of the drum.
That warmth then slightly overcompensates for the heat the clothes lost by evaporation, so the interior of the drum ends up a little bit warmer than room temperature, promoting more evaporation. But the main thing that gets the clothes dry is the fairly extreme dryness of the air that's being pushed through the drum. Basically, any moisture that's in the circulating air is going to get condensed out on the cold side of the heat pump and drained out of the machine.
These units are much more energy-efficient than gas dryers or old-style electric dryers because what they're not doing is heating up a whole lot of air only to vent it straight into the great outdoors. Such heat as they do generate is pretty well contained inside the machine for the entire drying cycle.
If you're in any doubt about how effective relatively cool though extremely dry air can be at soaking up moisture, try running your car's air conditioner and its windscreen demister at the same time. You end up with a fairly similar thing: air goes through the chiller fins first, becoming very cold and very dry, with the water that condenses out of it draining under the car; then it gets warmed back up by the heater core before being blown over your windscreen. You will find that this de-fogs your screen way faster than just running the heater by itself.
On preview: a condenser dryer is a heat pump dryer.
posted by flabdablet at 7:59 AM on May 9, 2021
So a heat pump will always have a cold side where heat energy goes into it, and a hot side where the heat energy it's moving (plus any waste heat it generates internally) comes out. There's one in your refrigerator, with the cold side inside the insulated interior and the hot side in those black radiator coils on the back. An air conditioner is a heat pump with room air being pushed through fins on the cold side to cool it, and outside air being pushed through fins on the hot side outside the building to remove the heat being pumped through from the cold side. A reverse cycle air conditioner lets you switch the hot and cold sides, and extract the heat energy it uses to warm the room from the cold air outside by making it even colder.
A heat pump clothes dryer has a blower fan that pushes air through fins on the cold side of the heat pump, then through fins on the hot side, then through the drum, then back around to the cold side fins again. This sounds kind of strange - it seems pointless to burn electricity on cooling and then immediately re-heating the same air - but there's method in the madness.
The key thing to understand is that when the air goes past the damp clothes in the drum, two things happen: the air picks up some moisture from the clothes, and the clothes get cooled as moisture evaporates from them. When that moisture-laden air goes through the cold-side fins, water condenses out of it just like it would on the side of a cold can of beer. That condensation process warms the cold side up a little, then trickles out the dryer's drain tube.
The heat pump transfers all the heat energy picked up by condensing the water, plus a bit of its own waste heat, to the hot side. So after the circulating air has been through both the cold side and the hot side, it ends up a little bit warmer and a whole lot dryer than it was when it came out of the drum.
That warmth then slightly overcompensates for the heat the clothes lost by evaporation, so the interior of the drum ends up a little bit warmer than room temperature, promoting more evaporation. But the main thing that gets the clothes dry is the fairly extreme dryness of the air that's being pushed through the drum. Basically, any moisture that's in the circulating air is going to get condensed out on the cold side of the heat pump and drained out of the machine.
These units are much more energy-efficient than gas dryers or old-style electric dryers because what they're not doing is heating up a whole lot of air only to vent it straight into the great outdoors. Such heat as they do generate is pretty well contained inside the machine for the entire drying cycle.
If you're in any doubt about how effective relatively cool though extremely dry air can be at soaking up moisture, try running your car's air conditioner and its windscreen demister at the same time. You end up with a fairly similar thing: air goes through the chiller fins first, becoming very cold and very dry, with the water that condenses out of it draining under the car; then it gets warmed back up by the heater core before being blown over your windscreen. You will find that this de-fogs your screen way faster than just running the heater by itself.
On preview: a condenser dryer is a heat pump dryer.
posted by flabdablet at 7:59 AM on May 9, 2021
Should I get a heat pump clothes dryer?
If outdoor line drying isn't going to work for you: yes.
posted by flabdablet at 8:07 AM on May 9, 2021 [1 favorite]
If outdoor line drying isn't going to work for you: yes.
posted by flabdablet at 8:07 AM on May 9, 2021 [1 favorite]
a condenser dryer is a heat pump dryer.
No, they are different. A condenser dryer uses a heating element just like a conventional vented dryer, but the heating element is smaller because most of the heat is recovered by a heat exchanger/condenser before recycling. There is no heat pump. Just a passive heat exchanger.
A heat pump dryer, well, has a heat pump, so is going to be considerably more expensive to purchase than a condensing dryer which has a passive condenser.
As far as operating efficiency, a condensing dryer is midway between a vented dryer and a heat pump dryer. A vented dryer just vents out all of its heat. The condensing dryer recycles some of its heat. A heat pump dryer multiplies the input energy to produce heat.
posted by JackFlash at 8:18 AM on May 9, 2021 [1 favorite]
No, they are different. A condenser dryer uses a heating element just like a conventional vented dryer, but the heating element is smaller because most of the heat is recovered by a heat exchanger/condenser before recycling. There is no heat pump. Just a passive heat exchanger.
A heat pump dryer, well, has a heat pump, so is going to be considerably more expensive to purchase than a condensing dryer which has a passive condenser.
As far as operating efficiency, a condensing dryer is midway between a vented dryer and a heat pump dryer. A vented dryer just vents out all of its heat. The condensing dryer recycles some of its heat. A heat pump dryer multiplies the input energy to produce heat.
posted by JackFlash at 8:18 AM on May 9, 2021 [1 favorite]
condenser dryers leave clothes a little damp, on purpose. You're supposed to take them out and hang them up and in a few minutes they'll be dry. Is the same true for heat pump dryers?
Our heat pump dryer has a "cupboard dry" setting that can get our clothes bone dry.
posted by EndsOfInvention at 8:40 AM on May 9, 2021 [2 favorites]
Our heat pump dryer has a "cupboard dry" setting that can get our clothes bone dry.
posted by EndsOfInvention at 8:40 AM on May 9, 2021 [2 favorites]
I have a newish bosch heat pump dryer, it's pretty efficient judging by the way it doesn't release any heat into the room (the clothes are still toasty when it's done).
The default settings sometimes leave things very slightly damp, but there's a setting for increasing the threshold when it decides things are dry.
The model I have only needs electricity, and can optionally have a drain hose (without a drain hose, the water drains into a removeable drawer that needs to be emptied after every run). There's a filter that catches lint that needs emptying after every run too, some of the more expensive ones have self cleaning filters.
posted by samj at 8:45 AM on May 9, 2021 [3 favorites]
The default settings sometimes leave things very slightly damp, but there's a setting for increasing the threshold when it decides things are dry.
The model I have only needs electricity, and can optionally have a drain hose (without a drain hose, the water drains into a removeable drawer that needs to be emptied after every run). There's a filter that catches lint that needs emptying after every run too, some of the more expensive ones have self cleaning filters.
posted by samj at 8:45 AM on May 9, 2021 [3 favorites]
There is no heat pump. Just a passive heat exchanger.
Fair enough. Didn't realize anybody bothered.
A heat pump dryer multiplies the input energy to produce heat.
Not so much to produce heat as to produce dryness (which is, after all, the desired end result).
The cold side is air-coupled back to the hot side as the air flows in a closed loop; also, most of the heat recovered from water vapour being condensed on the cold plates was got from inside the drum as evaporative cooling in the first place. So such heat as the machine does make is pretty much just waste heat from the losses in the heat pump, rather than the kind of coefficient-of-performance-boosted output you'd see from a heat pump with hot and cold sides in separate environments.
The increased efficiency of a heat pump dryer over a hot air dryer is due to the extremely dry air you get by running it through the chiller fins and then warming it up again being much better at pulling water out of fabrics than typical room air would be, plus the fact there isn't a stream of warm air removing heat from the evaporation zone.
The typically lower drum temperature is kinder on clothes, too, especially elastics.
posted by flabdablet at 8:45 AM on May 9, 2021
Fair enough. Didn't realize anybody bothered.
A heat pump dryer multiplies the input energy to produce heat.
Not so much to produce heat as to produce dryness (which is, after all, the desired end result).
The cold side is air-coupled back to the hot side as the air flows in a closed loop; also, most of the heat recovered from water vapour being condensed on the cold plates was got from inside the drum as evaporative cooling in the first place. So such heat as the machine does make is pretty much just waste heat from the losses in the heat pump, rather than the kind of coefficient-of-performance-boosted output you'd see from a heat pump with hot and cold sides in separate environments.
The increased efficiency of a heat pump dryer over a hot air dryer is due to the extremely dry air you get by running it through the chiller fins and then warming it up again being much better at pulling water out of fabrics than typical room air would be, plus the fact there isn't a stream of warm air removing heat from the evaporation zone.
The typically lower drum temperature is kinder on clothes, too, especially elastics.
posted by flabdablet at 8:45 AM on May 9, 2021
Let me argue against a gas dryer. An important facet of reducing global climate change is decarbonization, moving from energy sources that emit carbon to (hopefully sustainable) energy sources that are carbon neutral.
If you get an electric dryer (whether a standard resistive dryer or a heat pump model) then if your local electrical utility moves to a carbon-neutral energy source, badabing badaboom, your dryer is now carbon neutral.
If you get a natural gas dryer, it will always emit carbon. Further, you will always be natural gas customer, justifying the ongoing burning of natural gas by your fellow customers and incrementally slowing the extinction of your region's natural gas utility company.
(Full disclosure: I am motivated by my feelings of guilt at having purchasing a natural gas furnace to replace our borked natural gas furnace a few years ago, and accepting a gift of a natural gas dryer no longer needed by a family member last year, before I had really gotten the message about decarbonization. As flabdablet suggests, it's all the more motivation to line dry whenever possible.)
posted by BrashTech at 8:51 AM on May 9, 2021 [2 favorites]
If you get an electric dryer (whether a standard resistive dryer or a heat pump model) then if your local electrical utility moves to a carbon-neutral energy source, badabing badaboom, your dryer is now carbon neutral.
If you get a natural gas dryer, it will always emit carbon. Further, you will always be natural gas customer, justifying the ongoing burning of natural gas by your fellow customers and incrementally slowing the extinction of your region's natural gas utility company.
(Full disclosure: I am motivated by my feelings of guilt at having purchasing a natural gas furnace to replace our borked natural gas furnace a few years ago, and accepting a gift of a natural gas dryer no longer needed by a family member last year, before I had really gotten the message about decarbonization. As flabdablet suggests, it's all the more motivation to line dry whenever possible.)
posted by BrashTech at 8:51 AM on May 9, 2021 [2 favorites]
Fair enough. Didn't realize anybody bothered.
Condenser dryers have been the standard in Europe for years. Heat pump dryers are relatively new, have fewer models to choose from and are twice as expensive to purchase as heat pump dryers.
posted by JackFlash at 8:55 AM on May 9, 2021
Condenser dryers have been the standard in Europe for years. Heat pump dryers are relatively new, have fewer models to choose from and are twice as expensive to purchase as heat pump dryers.
posted by JackFlash at 8:55 AM on May 9, 2021
If Canstar (Australia) is to be believed (and it generally is), then that price differential probably varies a fair bit from market to market. However, I would expect the energy consumption difference, with the heat pump units eating about half of what a comparable condenser-only unit would, to be fairly consistent.
Drying a load of clothes is such an inherently energy-intensive process that I would also expect any reasonably well-made heat pump unit to last long enough to pay back its increased purchase price easily in reduced energy bills, even if gas is currently very cheap where you live.
posted by flabdablet at 9:04 AM on May 9, 2021 [1 favorite]
Drying a load of clothes is such an inherently energy-intensive process that I would also expect any reasonably well-made heat pump unit to last long enough to pay back its increased purchase price easily in reduced energy bills, even if gas is currently very cheap where you live.
posted by flabdablet at 9:04 AM on May 9, 2021 [1 favorite]
→
I am someone with an LG all-in-one washer/condenser dryer and I've never had to do this. Clothes come out perfectly dry.
posted by scruss at 10:37 AM on May 9, 2021
(I know someone with an LG all-in-one washer/condenser dryer and they have to do this second drying step)
I am someone with an LG all-in-one washer/condenser dryer and I've never had to do this. Clothes come out perfectly dry.
posted by scruss at 10:37 AM on May 9, 2021
I have one of those LG units too, it’s great and your clothes come out dry if you do the whole cycle, including the ‘cool down’ which lasts approximately 4 hours. That’s the trade off.
(It gets my clothes almost-dry after an hour or so)
posted by Admiral Viceroy at 2:00 PM on May 9, 2021
(It gets my clothes almost-dry after an hour or so)
posted by Admiral Viceroy at 2:00 PM on May 9, 2021
I have a heat pump dryer partly because we couldn't do vented in my building, and it's slower than a traditional dryer but otherwise gets clothes plenty dry. So far I do not regret the purchase.
posted by ch1x0r at 3:36 PM on May 9, 2021
posted by ch1x0r at 3:36 PM on May 9, 2021
I used to have a condenser dryer, now I have a heat pump one and I think it’s great. Doesn’t heat up the room as much. Quite energy efficient. Only downside is it takes aaaaaaages. But things come out fully dry and it seems almost free to operate which makes up for the higher price.
posted by kitten magic at 6:41 PM on May 9, 2021
posted by kitten magic at 6:41 PM on May 9, 2021
Here’s the Technology Connections on Heat Pumps
posted by snuffleupagus at 9:00 PM on May 9, 2021 [2 favorites]
posted by snuffleupagus at 9:00 PM on May 9, 2021 [2 favorites]
(Sorry to hijack this thread) I'm looking for a heat pump dryer as well, and I've read some things about heat pump dryers needing to use more water; something like that they use water to transfer to heat or something. Is there any truth to this?
posted by destrius at 10:56 PM on May 9, 2021
posted by destrius at 10:56 PM on May 9, 2021
No.
posted by flabdablet at 12:24 AM on May 10, 2021
posted by flabdablet at 12:24 AM on May 10, 2021
Longer answer: No dryer "uses water" in the sense of needing a water supply connected. If you have an appliance that can dry clothes and does have a water supply connected, that's because it's a combo washer/dryer and it needs the water for the wash part.
something like that they use water to transfer to heat or something
The way heat energy gets moved around inside a heat pump dryer is a little more intricate than what happens in the old fashioned blast-everything-with-hot-air type.
Water evaporates from the clothes inside the drum as the dryer blows air through them, thereby turning into water vapour dissolved in the air. That evaporation tends to lower the temperature inside the drum (exactly the same way that evaporating sweat lowers the temperature of your skin), and when the vapour-laden air leaves the drum it carries the associated heat energy out with it.
That moist air stream then passes through a set of fins connected to the cold side of the heat pump, upon which most of the water vapour in it condenses back into liquid water that dribbles off down the drain. The process of condensation gives back the same amount of heat energy that the water vapour picked up while evaporating from the clothes in the first place, dumping that energy into the cold side of the heat pump and tending to raise its temperature (i.e. make it slightly less cold; it will never get warm enough for a human being to describe it as other than "very cold", so it will always be plenty cold enough to condense most of the water vapour that blows through it).
That is the process by which a heat pump dryer "uses water to transfer heat". It evaporates that water from the clothes, moves it to the cold-side fins as water vapour, then condenses it back to liquid, transferring the heat of evaporation that it pulled out of the drum into the cold fins on the way. Note that no external water supply is involved in that transfer, only the water that was making the clothes wet, which is exactly what a dryer is designed to remove.
To complete the cycle, the heat pump pumps the heat energy collected from its cold side, plus a bit more heat generated by its own internal losses, over to its hot side. The now-dried cold air stream that's been blown through the cold-side fins is then directed over another set of fins on the hot side, and exits as a warm air stream that's still every bit as dry. That then gets blown back into the drum to pick up more water vapour from the clothes inside.
Because there always will be some losses (i.e. energy directly converted to heat) in any mechanical contrivance, heat pumps included, the air that's blown back into the drum will always tend to be a little warmer than it was the first time around the loop, so the temperature of the air circulating inside the dryer will rise a little over time.
And because the air inside the dryer does get fully recirculated inside it, the only thing that actually comes out of a heat pump clothes dryer is the water that started off making the clothes wet, plus a relatively small amount of heat energy that leaks out through the entire body of the appliance as radiant heat, plus whatever excess warmth ends up in the dried clothes.
Heat pump driers don't use more anything except initial build materials. They're more complex machines than simple heater dryers, which is why they cost more to buy. But they cost way less to operate.
posted by flabdablet at 12:59 AM on May 10, 2021 [3 favorites]
something like that they use water to transfer to heat or something
The way heat energy gets moved around inside a heat pump dryer is a little more intricate than what happens in the old fashioned blast-everything-with-hot-air type.
Water evaporates from the clothes inside the drum as the dryer blows air through them, thereby turning into water vapour dissolved in the air. That evaporation tends to lower the temperature inside the drum (exactly the same way that evaporating sweat lowers the temperature of your skin), and when the vapour-laden air leaves the drum it carries the associated heat energy out with it.
That moist air stream then passes through a set of fins connected to the cold side of the heat pump, upon which most of the water vapour in it condenses back into liquid water that dribbles off down the drain. The process of condensation gives back the same amount of heat energy that the water vapour picked up while evaporating from the clothes in the first place, dumping that energy into the cold side of the heat pump and tending to raise its temperature (i.e. make it slightly less cold; it will never get warm enough for a human being to describe it as other than "very cold", so it will always be plenty cold enough to condense most of the water vapour that blows through it).
That is the process by which a heat pump dryer "uses water to transfer heat". It evaporates that water from the clothes, moves it to the cold-side fins as water vapour, then condenses it back to liquid, transferring the heat of evaporation that it pulled out of the drum into the cold fins on the way. Note that no external water supply is involved in that transfer, only the water that was making the clothes wet, which is exactly what a dryer is designed to remove.
To complete the cycle, the heat pump pumps the heat energy collected from its cold side, plus a bit more heat generated by its own internal losses, over to its hot side. The now-dried cold air stream that's been blown through the cold-side fins is then directed over another set of fins on the hot side, and exits as a warm air stream that's still every bit as dry. That then gets blown back into the drum to pick up more water vapour from the clothes inside.
Because there always will be some losses (i.e. energy directly converted to heat) in any mechanical contrivance, heat pumps included, the air that's blown back into the drum will always tend to be a little warmer than it was the first time around the loop, so the temperature of the air circulating inside the dryer will rise a little over time.
And because the air inside the dryer does get fully recirculated inside it, the only thing that actually comes out of a heat pump clothes dryer is the water that started off making the clothes wet, plus a relatively small amount of heat energy that leaks out through the entire body of the appliance as radiant heat, plus whatever excess warmth ends up in the dried clothes.
Heat pump driers don't use more anything except initial build materials. They're more complex machines than simple heater dryers, which is why they cost more to buy. But they cost way less to operate.
posted by flabdablet at 12:59 AM on May 10, 2021 [3 favorites]
Also by the way: A dehumidifier, i.e. a machine designed to lower the humidity of room air without changing its temperature much, uses essentially the same design pattern: a heat pump where a single air stream gets chilled on the cold side and then re-warmed on the hot side, and the cold side has a drain to remove the water that condenses on it.
You can think of a heat pump clothes dryer as a tumbling drum and a dehumidifier connected to each other in a closed air loop.
posted by flabdablet at 1:11 AM on May 10, 2021 [1 favorite]
You can think of a heat pump clothes dryer as a tumbling drum and a dehumidifier connected to each other in a closed air loop.
posted by flabdablet at 1:11 AM on May 10, 2021 [1 favorite]
In NYC, if you live in an apartment, I would check whether the rules allow you to have a gas dryer now. My co-op does not permit gas dryers in individual units. Your existing one may have been grandfathered in under prior rules and you might not be able to put in a new one even if you have an existing one.
posted by bedhead at 7:23 AM on May 10, 2021
posted by bedhead at 7:23 AM on May 10, 2021
Longer answer: No dryer "uses water" in the sense of needing a water supply connected. If you have an appliance that can dry clothes and does have a water supply connected, that's because it's a combo washer/dryer and it needs the water for the wash part.
Not true. Most modern dryers have a steam function that requires a water hook up. They sell little double things you put on your washer water line to run a second water line to your dryer. No drain though, because it uses really small amounts of water and turns it into steam. Is the steam feature worth it in my opinion? No.
posted by The_Vegetables at 7:24 AM on May 10, 2021
Not true. Most modern dryers have a steam function that requires a water hook up. They sell little double things you put on your washer water line to run a second water line to your dryer. No drain though, because it uses really small amounts of water and turns it into steam. Is the steam feature worth it in my opinion? No.
posted by The_Vegetables at 7:24 AM on May 10, 2021
Best answer: Most modern dryers have a steam function that requires a water hook up
Condensers without heat pumps to make them cold, dryers designed to get things wet, dogs and cats living together... mass hysteria!
I hate living in the End Times.
posted by flabdablet at 10:42 AM on May 10, 2021 [1 favorite]
Condensers without heat pumps to make them cold, dryers designed to get things wet, dogs and cats living together... mass hysteria!
I hate living in the End Times.
posted by flabdablet at 10:42 AM on May 10, 2021 [1 favorite]
Response by poster: Thank you for all this information!
notes: we already have a gas furnace and we're old and don't expect this to change in our lifetimes. We own the (small) brownstone so no rules against gas dryers. Still have to check about sizes of condenser/heat pump dryers -- if they're always small - too small for a quilt? Will do more research. All in all, I'm hearing the negatives about gas.
thanks again!
posted by DMelanogaster at 6:01 AM on May 11, 2021
notes: we already have a gas furnace and we're old and don't expect this to change in our lifetimes. We own the (small) brownstone so no rules against gas dryers. Still have to check about sizes of condenser/heat pump dryers -- if they're always small - too small for a quilt? Will do more research. All in all, I'm hearing the negatives about gas.
thanks again!
posted by DMelanogaster at 6:01 AM on May 11, 2021
This thread is closed to new comments.
Heat pumps are electric and tend to be a more efficient heating mechanism than creating heat from electricity directly. With electrical resistors (like in a toaster), one unit of energy of electricity turns directly into the same amount of heat energy. This sounds good, but in fact a heat pump can actually move 2-4 units of thermal energy for each unit of electrical energy. That is, with electrical resistive heating, 1 joule of electrical energy gets you 1 joule of thermal energy, but a heat pump can use 1 joule of electrical energy to move 2-4 units of thermal energy. This is possible because the pump is moving thermal energy in the environment, it is not transforming or creating energy.
Looking at the energy star website, a heat pump dryer can be more efficient, and also has different requirements for air venting. Typical electric dryers use electricity to heat air, which is then circulated with damp clothes to adsorb moisture, then the hot air and moisture are vented outside via ducts. A heat pump dryer uses a heat pump to heat air, mixes that hot + dry air with clothes to adsorb moisture. Then, the that hot + wet air travels through through the heat pump's cold-side heat exchanger to condense the moisture out of the air and recapture the thermal energy, leaving cold + dry air. Then the cold+dry air repeats the cycle. So, it doesn't vent hot air out of the unit, but instead needs to drain the liquid water out of the unit occasionally.
I have limited experience with these dryers. I used one on a vacation once, and I found that it left my clothes ever so slightly damp. I'm not sure if that is simply a fact of how these dryers work, or if different settings or better maintenance could have achieved perfect dryness from dryer, or what.
posted by rustcrumb at 7:42 AM on May 9, 2021 [5 favorites]