Heat pump clothes dryer
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SpaceBus
Minister of Fire
They aren't too popular here, but I really want one. We are a two person household, so a small dryer would work for us. My wife and I really like the LG all-in-one that uses a heat pump to dry, but the whole unit is ungodly expensive.
semipro
Minister of Fire
They've been around for a while now.
We have the LG ThinQ model and are happy with it thus far.
It replaced a series of 3 Bosch condensing ventless units that we had bad luck with.
Our experience is that the technical challenge is removing the lint so that it doesn't clog the heat exchanger. Maintenance with the Bosch units was recurring and challenging. and they seemed to have a critical flaw in the way the drum was constructed.
The LG unit seems to have a better design with two easily accessible lint filters but time will tell.
The smaller size is not an issue for us as we hang larger items out on a clothesline.
We have the LG ThinQ model and are happy with it thus far.
It replaced a series of 3 Bosch condensing ventless units that we had bad luck with.
Our experience is that the technical challenge is removing the lint so that it doesn't clog the heat exchanger. Maintenance with the Bosch units was recurring and challenging. and they seemed to have a critical flaw in the way the drum was constructed.
The LG unit seems to have a better design with two easily accessible lint filters but time will tell.
The smaller size is not an issue for us as we hang larger items out on a clothesline.
brenndatomu
Minister of Fire
After installing a HPWH it occurred to me that a HP fridge/water heater combo would compliment each other nicely...and in my case the WH sits very close to being right under the fridge, so the line set (or however they tied together) wouldn't even be very long
SpaceBus
Minister of Fire
I love heat pump appliances, so awesome, especially in the summer when the extra cooling in the room is a bonus. As long as your heat source that is providing the energy in the house is cheaper than the electricity or fuel to run a normal DHW or dryer it's good in the winter too. Not more efficient energy-wise in the winter than a normal electric DHWH or dryer, but potentially cheaper at least! Very cool stuff. Right now I don't have any HP applicances since my mine are electric and I heat with electric mini splits, so it's a wash and we don't really have much benefit from the cooling bonus at this latitude. When I switch to wood, if wood comes out cheaper per BTU/hr than I will get the HP water heater and maybe one of these fancy dryers as well!
My understanding from a few years ago was that a typical dryer user will require a learning curve. Maybe you can update?. The drying cycle was claimed to take far longer and the capacity was claimed much lower so more loads. It was recomended that it only be paired with high efficiency washer that could take out as much water as possible (always a good idea but horizonal washers got a bad rep early on).
Heat pump dryers are pretty common in Europe, Switzerland even banned the sale of vented dryers back in 2012.
Keep in mind a heat pump dryer is not like a heat pump hot water heater, they don't remove heat from the house, they actually add it due to their ventless nature. The power input to the compressor (about 1000watts) ends up in the room, which would add to the cooling load in hot climates.
Keep in mind a heat pump dryer is not like a heat pump hot water heater, they don't remove heat from the house, they actually add it due to their ventless nature. The power input to the compressor (about 1000watts) ends up in the room, which would add to the cooling load in hot climates.
semipro
Minister of Fire
Our HP clothes dryer is located in the same room as our HP water heater so we're hopefully capturing that 1000w for water heating.
WRT a summer cooling load increase when using an HP dryer, I'd imagine that the warm make-up air sucked into the house from outdoors when a vented dryer is running would create a similar increase in cooling load.
brenndatomu
Minister of Fire
I wonder, do all the HP type appliance transfer heat/cooling to the air of the house...none of them connect to another appliance with a lineset?
Ah I had no idea these were all ventless with no option for vented, but I guess it makes sense. Here is a study meta analysis that actually goes into some minor detail about the process. The main advantage is capturing some of the heat out of the waste stream and recycling it in the process. Hybrid heat pump dryers with standard electric heating elements along with the heat pump came out to be the most efficient. The median payback period on the energy savings from one study mentioned was 22.1 years. The one trick they seem to miss as far as I can see - they did not compare them to unvented operation of standard electric dryers where the process heat is also recaptured at basically 100%. The bonus over a standard dryer in that case would be very low, most likely zero. Since most people only operate dryers that way in the winter, it would at least have a part-year efficiency bonus in most installations.
Heat pumps in unvented space/appliances don't make heat more efficiently than a simple heating element in an unvented appliance of course, and that's always the rub... Your just stealing exact same quantity of lower quality heat out of the room, increasing the energy quality temporarily for a constrained high entropy process, where the entropy of the compressor is also useful to the process. It takes the exact same amount of energy to evaporate the water out of the clothes, no matter how you spin it (heh heh) - all that matters is how much energy is wasted to the exterior of the process/building/etc. The energy state in any unvented appliance install where heat/energy does not exit the main containment vessel (home/reservoir) will always be at equilibrium.
The Bosch, Samsung, and Miele machines are all 4 cu ft. The only full size, 7 cu ft, is Whirlpool. The cost isn't too far off other standard dryers. The basic dryer is $600 with a timer and an element. Standard machine is $1k and the next price point is the $1200-1400 range. The Whirlpool is $1300
EbS-P
Minister of Fire
If you can hang laundry out I don’t see these as really a good financial investment. I see the ventless aspect as the biggest selling feature. I want to see average cost of owner ship for 10-15 years.
semipro
Minister of Fire
thecoalman
Member
Depends on how you want to look at it. Let's suppose your primary heat is gas. You are first going to put 3000 BTU's into the heating space and then use about 1000 BTU's of electric to move it into the heater. That's 4000 BTU's of energy when you could of directly heated the water with the gas using only 3000... In the winter time you will never beat the cost or efficiency of directly using the same fuel source as your primary heat to heat your hot water.
On the other hand since the cost per BTU for natural gas, coal or wood is really low this will be cheaper than regular electric heater since the cost per BTU for electric is so high. There is always an efficiency loss strictly looking at the BTU's though.
In the summer since the cooling effect and de-humidification are desirable if you wanted to factor in the energy savings for less energy AC/Dehumidifier the efficiency goes off the charts over just the normal efficiency.
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This is not completely correct but I see where you're coming from. If you want to heat with a gas hot water heater, it's going to be vented and not 100% efficient. When you heat your house with gas and use a heat pump water heater, and if you need 3000 BTU to heat a certain quantity of water to a certain temperature, you will use the heat from the room at the coefficient of performance + heat generated in the compressor cycle = 3000 BTU, no energy is created or lost in the process, it either goes into the water or back into the room, which goes into the water, 100% of the energy used and moved stays in the house, nearly completely contained in the water. In your example, which was COP 2:1, 1000 BTU of electric heat ending up being used would only scavenge 2000 BTU from the home to do the same work of 3000 BTU of heated water... When you compare it to a vented appliance, you lose some % of the energy needed to the exterior of the building, whatever the efficiency of that appliance is rated, and you will always lose at least some energy to the vent. So in the vented appliance, you use 3000 BTU + losses in the water heating process.
You could make the case that using the primary gas heat in the water heater directly is more efficient in the total circuit than the ventless heat pump if the gas hot water heater it would be replacing is > efficiency of your gas air space heater. This is not really the fault of the heat pump though, just that you lost energy before it got to the hot water heater stage of the overall efficiency gradient. If you have a boiler that does both DHW and heats the home, a heat pump tank really wouldn't ever make sense to operate in the winter there - you'd just be trading part of the boiler's output for the fraction of electric that heats the water.
The BIG factor that needs considering in any winter efficiency margin comparison is that the house is a variable, lossy medium - you would need to take into account the fraction of heat that is lost from the initial air heating before it makes it to the heat pump as well. So an example would be a 98% furnace feeding a 4:1 COP HPWH, and say it takes 1 hour to put the 3000 BTU of final energy in the water, 600 BTU from the electric and 2400 BTU from the heated room. But, say you lost 30% of your initial heat from the furnace to the outdoors over that 1 hour period, so the 2400 BTU from the room was not 98% efficient gas heat, but rather .98 * .70 = 68.6% efficient gas heat by the time it is entering the water heater gradient... Our example here compares poorly then to a normal non condensing gas storage water heater which would be about 80%, and the fancier condensing models are close to what a condensing furnace can do, at ~95%.
Cost is a different and separate factor on top of it all, and if the electric cost of running the compressor + extra room air efficiency losses is > cost of the direct heat losses on the replaced vented appliance, then you lose money in the difference during operation.
The summer is definitely a better use case overall for most users, the cooling+de-humidification is usually a benefit, removing unwanted excess energy from the home and discharging it underground into the septic tank or sewer system in the long run, like an open loop ground source heat pump in "cooling mode"
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Last time I calculated electricity and gas cost per BTU, electricity was 6x more expensive. It motivated me to run gas lines to the kitchen stove and dryer.
And that is how the spark spread was born https://www.google.com/search?client=firefox-b-1-d&q=spark+spread
To make it more interesting, use a water cooled generator and upstream of the radiator install a heat exchanger to heat a building while generating power. And that is what a combined heat and power plant does. Of course it only works if there is a simultaneous demand for power and heat (like a hospital or a papermill. On one of my projects the ratio of useful heat in, versus electrical (converted to btus) plus thermal was around 71%. A typical boiler based power plant was lucky to get to 40% . The best combined cycle natural gas fired power plants are in the mid fifties.
Sure. Its the same as an incandescent light bulb in a cold room. If you turn it on for heat, the light is a happy bonus.
thecoalman
Member
What you are forgetting is neither is the boiler or furnace producing your primary heat. Whether you are directly heating the water with gas or you are using a heat pump utilizing it from the primary heat there is an efficiency loss in the heat produced by gas.
The bottom line is if you are robbing heat from a primary heat source with a heat pump it can never beat the effciency/cost of directly heating the water with that fuel.
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I've not forgotten, it's just not the most relevant factor. Usually most homes will only have one water heater. A heat pump tank installed in place of an 80% efficient gas storage hot water tank can easily beat that delivered efficiency in any well designed tight home that loses less than ~20% in the air circuit. The overall weighted efficiency would be (WeightedRoomUse * PrimaryHeat% * HouseLoss%) * (100% * WeightedElectricUse) Most gas homes today use storage water heaters that have abysmal efficiency, but have furnaces with very high efficiency, which is why it can conceivably come out ahead. Since we usually can't control nor care about the efficiency of the gas or the electricity produced at the primary generation or mining sites, this is as far as we care about here - optimizing efficiency and cost in the local setup we control.
You could install a 95% water heater in place of the common 80% unit for more expense, in which case a heat pump on site could not realistically beat that during the winter, but this is not the entire consideration. People should consider HPWH on the basis of both annual operating efficiency and cost.
But, the original post I made I wasn't really thinking of fossil heat sources at all since I usually ignore them completely - I was only thinking of wood heat where a HPWH let's you scavenge cheap locally sourced wood fuel inexpensively during winter to replace either an electric or bottled gas hot water heater. If you have a wood stove or a wood furnace, a heat pump is the cheapest, easiest way to scavenge that cheap wood heat for domestic hot water, as changing to a boiler is the only other semi-feasible option - which would be many multiples the cost without ever achieving a realistic payback period. Plus, you get the bonus efficiency in the summer, making it more attractive still.
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EbS-P
Minister of Fire
I have thought about this some. My reasoning is this. HVAC heatpump has a COP of 4 as does the heatpump appliance. So every four units of heat the appliance utilizes it costs two units. Or COP of 2.
If you are installing a HP dryer I’m guessing either A you can’t vent it so gas is out and or B you are trying to be as green as possible and gas is out. At the bare minimum HP dryer is twice as efficient as an electric dryer.
Using wood heat during the winter makes it a maximum of what ever the cop appliance is times more efficient. There is no summer benefit to to running a HP dryer unlike a HPWH. All the electricity consumed is transformed into heat inside the home.
If you are installing a HP dryer I’m guessing either A you can’t vent it so gas is out and or B you are trying to be as green as possible and gas is out. At the bare minimum HP dryer is twice as efficient as an electric dryer.
Using wood heat during the winter makes it a maximum of what ever the cop appliance is times more efficient. There is no summer benefit to to running a HP dryer unlike a HPWH. All the electricity consumed is transformed into heat inside the home.
I admit I am having a harder time justifying a HP dryer from most energy/efficiency standpoints. I think in places like Sweden it is also common to have delivered hot water to the home from a central citywide heating system, this could come into play on the large scale to prioritize the heat pump dryers. Plus, they have a long winter season, so the summer heat penalty is not such a problem in very cold climates...
thecoalman
Member
I'd agree, if you have coal or wood regardless of other factors the cost per BTU is so low does it matter? There is also other things to consider with coal or wood, you might have the unit in the basement and aren't necessarily interested in keeping it heated to the temp it's at anyway.
That said if you want to maximize the cost/efficiency you can heat water using a coal or wood stove with a thermosiphon loop to heat the water in a tank. The only issue is it's a slow process and if you run out of hot water it's going to be a long time before you have anymore unless it's connected to working water heater.
It's actually better suited for wood because even with the best SS pipe they tend to corrode in time with the coal. Basically you only need to install small loop of SS pipe over the fire, typically one end goes to drain on the water tank and the other to where the pressure release valve is. Just to be perfectly clear you are not elimating the pressure release valve but you'll need plumb in a nipple and T to accomodate both. Ideally you raise the tank as high as you can. Hot water will slowly but surely circulate into the tank.
You'll also need to make sure the tank can handle some pretty high temps. A mixing valve for the outlet supply is an absolute must because this can raise water temps pretty high to the point it's instant trip to the emergency room.
You don't necessarily need to hook it to tank that is independently heated. Instead you can feed it to plain insulated tank that in turn feeds your heated tank. This is proabaly the best method as far as being the most efficient.
Well cost is one consideration, and an important one of course, while efficiency is another, competing but independent consideration. Usually we are buying these appliances for a period of time/service life, so we have to do an annual cost basis calculation and a service life calculation, as well as how the appliance fits into our long term planning for sourcing our fuels and electricity. Anyone who is on fossil fuels is considering that the prices are likely going to explode globally over the next few decades, likewise we each have a different target for the most desirable fuels, how self sufficient we want to be, etc. So we are discussing a lot of general heat pump math that may or may not apply directly to the dryer situation, but the math is always the same so it's at least good to become practiced with thinking it all the way through. Let's look at this example from the post above yours:
Then, we have the summer time case where the heat pump dryer adds heat into the room instead of putting it outside. So we have to compare that to the electric dryer, where it is venting outside which is desirable in the summer, but also it's often pulling in warm make up air from outside the building in the process, which normally would add some additional heat load to the AC as well...
Probably the most ideal case for electric drying appliance would be a vented *hybrid heat pump dryer that decides when to vent based on outdoor air temp, and either operates in a vented mode (where it could also have a outdoor air intake making it even better) or to operate ventless when it's cold outside and the heat is a bonus to the home.
This is pretty much true in all cases where the standard electric dryer is vented. In a winter time unvented electric dryer comparison, it is not more efficient, but it uses less electricity directly. The overall efficiency of the heat pump dryer here is dependent on that same math we did for the heat pump hot water heater, but the circumstances are changed slightly. If you are heating the house with electricity as well, the efficiency is at best the same in both cases. If you are heating with an electric heat pump/mini split and not straight resistance heat, you are adding BTU load to that system, and added BTU load pushes those systems into a lower COP region, which increases the cost/BTU proportionally. Then you have to add back in the house energy losses between the heater and the dryer just like we did for the heat pump hot water heater. If you are heating with another fuel source, the efficiency metric is the same as we did before for the hot water heater, to come to a final efficiency % of the clothes dryer cycle.
Then, we have the summer time case where the heat pump dryer adds heat into the room instead of putting it outside. So we have to compare that to the electric dryer, where it is venting outside which is desirable in the summer, but also it's often pulling in warm make up air from outside the building in the process, which normally would add some additional heat load to the AC as well...
Probably the most ideal case for electric drying appliance would be a vented *hybrid heat pump dryer that decides when to vent based on outdoor air temp, and either operates in a vented mode (where it could also have a outdoor air intake making it even better) or to operate ventless when it's cold outside and the heat is a bonus to the home.
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