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Anybody here using a heat pump water heater they like? If so please tell me what kind, how long you have been using it, and other such pertinent info. I am in the process of building a very efficient(net zero in the future) home, and in researching the options for domestic hot water, the heat pump water heater seems to be a good fit. Unfortunately, I am seeing mixed reviews on several models, so am looking for real world users with some time with one for data on which, if any, models are reliable long term and user-pleasing. Thanks in advance for any light you can shed....
My experience when shopping for ductless heat pumps was that the sale rep wasn't interested in selling me a heat pump water heater. Where I'm at, we heat the house 8 months a year, and since they draw heat from the interior, you're basically cooling your house to heat your water. That only seems to make sense in areas where you use AC or rarely use heat.
What puzzles me is why you can't just run them as a loop off of the main exterior unit, at least not that I've found.
Yeah, it is in development in Europe, using the exterior GSHP for heating/cooling, hot water, and I believe even refrigeration. Still a new deal, though, and America seems slow to follow all things European when it comes to building science.
I heat with wood, and only about four months a year, so the cooling effect is actually a plus to me, as is the reduced electrical load for eventual net zero reasons. With the wood stove, a bit of heat robbing in a very efficient and semi-passive solar 1100 sf house is not a concern. The energy use claims of these units tell me I should save ~400 dollars annually over using a normal resistance water heater. Plenty of reason to use a HPWH if I can find one I can live with.
Are you asking about a hybrid that uses a heat pump as well as an electric element, or HP exclusively? I would think that recovery time on an exclusively heat-pump water heater would be very slow. One person takes a shower, next person has to wait 6 hours?
One option is to install an on-demand water heater, and plumb an exclusive HPWH on the incoming cold-water feed into the on-demand unit. This gives you some of the cost savings of the heat pump.
I am talking about a hybrid, actually, although our home probably will not use much hot water. We wash clothes in cold water, and it is just my wife and I, so we generally shower together of an evening, since I have plumbed dual shower heads into the shower for that purpose. We use low-flow shower heads, also, and often use our outdoor solar shower in the summer months. We are generally very conservative with our energy use, we average less than 1200kw per month right now, and we are living in an older house trailer that was on the farm when we bought it. Other than the wood stove, it is total electric, and on a well. Older fridge, electric dryer, yada yada. This winter with the temps and wind, the furnace has come on at night to help out the wood stove, too. The soup can is LEAKY...
New house will be an air sealed envelope with double stud walls insulated to R-40, energy star windows placed and sized for passive solar and natural ventilation, R-60 attic, cool roof design, well shaded, acid stained concrete slab floors for thermal mass, propane cookstove and dryer, with extensive use of outdoor and indoor(winter) clotheslines. A wood stove for heat, with a mini split heat pump added later if necessary for air conditioning. As far as that goes, I will install some earth tubing for a certain amount of dehumidification and cooling of incoming fresh air. The tubes will be 9' underground, on the heavily shaded north slope of the homesite. Awning windows at the peak of the gable should create a stack ventilation condition, drawing fresh air in through the tubes without use of fans. With the slab floors, earth tubes, cool roof, and shade, we should need very little active cooling, and a heat pump water heater may well provide the additional cooling needed, if any, although I do not expect it to be running very much, so maybe not. The summer kitchen we have in a nearby pavilion will allow us to cook outside the house as desired, mitigating that heat source. Heating is not a problem, as we heat with wood, and I have a lifetime supply of that on the property. As well, the solar gain from the south facing glazing should warm the slab sufficiently that the stove may only be needed on cloudy days. All the lighting will use LED bulbs, and appliances will be chosen with energy efficiency as a major criteria. With all these measures, we hope to get the electricity usage down below 400kw/month or lower. We plan on adding a grid-tied solar array later, to cancel out the utility bill. A HPWH seems to fit into this scenario like a glove, if reliability is not an issue.
The most efficient way to heat during the colder weather in your case would be directly with the wood because then you eliminate inefficiencies and the electric consumption altogether. If it's just a small wood stove you can use thermosiphon loop, it's just a very small coil that runs through the stove. It doesn't give you instant hot water but will heat a tank of water overnight. This one is in a small coal stoker, as the water in the coil heats it will naturally circulate into the tank.
The way you would set this up is something like this. Some things to note here. If you aren't using a lot of water you can get way with just one storage tank, if you carefully schedule water usage you can turn the electric off. Another alternative is to use a timer so it's not using electric to heat water after you leave for work. The two tank system works best if you use a lot of hot water becsue you can maximize the amount of hot water being generated by the stove. There is no cold water going into the electric powered hot water tank.
The tank you re using for the loop needs to be above the stove as depicted here on the blocks. Last thing to note is there is two relief valves indicated here, you only need one.
As for air sourced heat pumps on the hot water tanks they make sense in a warmer climate where removing heat from the home is a desirable side affect , not so in colder climate. Those could actually drive up your energy bills, it's always going to be cheaper and more efficient to heat the water directly with your primary heating fuel. If you don't mind the extra work for the wood so be it, it's not cheaper becsue of efficiency. It's cheaper becsue the cost per BTU for the wood is less.
Quote:
Originally Posted by countryboy73
The energy use claims of these units tell me I should save ~400 dollars annually over using a normal resistance water heater. Plenty of reason to use a HPWH if I can find one I can live with.
They would probably use a 1/3 what your normal electric hot water tanks uses but you have to keep in mind that's only becsue it's using the heat in the air for fuel. To put this into perspective if you were using electric for your primary heat all of the electric being consumed by the heat pump is not needed.
Last edited by thecoalman; 02-26-2015 at 09:06 AM..
I have considered the use of the wood stove as a thermosiphon heater, but that does not take care of the other 8 months of the year. I may still do it, however, to cut electric usage even more on an annual basis. My main interest in the HPWH is the reduced electrical load(500 watts vs. 9000) it requires to operate. This is important to the ability to achieve net zero or off grid capability at some measure of cost effectiveness. with our water use schedule and frequency the heating delay is of little importance, as is the cooling effect. In the summer, the cooling effect is a plus, in the winter, unnoticeable. My main concern, and the Achilles' heel that is likely to drop the HPWH system from consideration, is the reliability issue. The complexity of the current systems and reports of refrigerant leaks in even the best models give me pause.
I am also looking at a floor plan redesign to place all plumbing in close proximity to the water heater, insulating supply lines, and simply going to one of the more efficient resistance models, augmenting it in winter with the wood stove and a solar collector.
Personally, I would go with propane for hot water, just because it's a cheaper way to make heat than electricity. Alternately, if you oversize your solar production, you can use a water heater element as a dump load.
Quote:
Originally Posted by countryboy73
My main concern, and the Achilles' heel that is likely to drop the HPWH system from consideration, is the reliability issue. The complexity of the current systems and reports of refrigerant leaks in even the best models give me pause.
There is at least one company making a air source HPWH add-on unit which connects to a regular tank-type water heater. This way, even if the heat pump portion is not reliable, you still have a working water heater. And if your tank fails, you can move the heat pump over to the new tank.
I moved into a tiny micro apartment of about 200 square feet. They recently remodeled all of the apartments in this old building (a converted hotel built in 1920's). They put heat pumps in the closets.
What happens in this situation, is that it puts out freezing cold air, causing really uncomfortable drafts and of course, creating condensation and nearly freezing my things in the closet.
I started a thread here about why my electric water heater was putting out freezing cold air. Changed the setting to electric only, and problem solved.
But, I just wanted to chime in to let you know it's also noisy, and the transfer of the cold air is a freezing draft. So, just keep in mind where you will put it. It was obviously a bad idea to put my heat pump in a 48" wide by 25" deep closet. It takes up half of my closet. Definitely not designed for that. But, they aren't quiet, and the draft created is fairly severe, from my experience in my situation here.
I do, however, intend to use it as an air conditioner this summer, if it gets too warm in here without a/c.
o noisy, and the transfer of the cold air is a freezing draft. So, just keep in mind where you will put it. It was obviously a bad idea to put my heat pump in a 48" wide by 25" deep closet. It takes up half of my closet. Definitely not designed for that. But, they aren't quiet, and the draft created is fairly severe, from my experience in my situation here.
I do, however, intend to use it as an air conditioner this summer, if it gets too warm in here without a/c.
It doesn't sound as though the install was done anywhere close to code. IIRC, when I looked into it a HPWH required something on the order of 1000 cubic feet of free airspace in the install location. You have what, maybe 70 cubic feet?
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Heat Pump add-on for traditional water heater
