We (in Michigan) are looking at the new GE Hybrid (heat pump/electric back up) hot water heater. Currently we have propane. We would be placing the hot water heater in the conditioned walkout basement, in the utility room, which is next to the woodstove area which mostly heats our home. We figure the woodstove puts out enough heat that the small amount of heat the hwh would draw from the room would be minimal. The GE expells air that is 15 degrees cooler than it came in.( In our case 75-80 degrees in would be 60-65 degrees out. ) There are only two adults here most of the time, with minimal hot water usage. Our current old tank usually only runs once or twice an evening. I think perhaps the late spring and early fall might be the only times that the cooling might be an issue (when the stove is not burning). In the summer, of course, it would be nice to have the cooling. Compared to purchasing a new regular propane hwh, and with federal tax credits figured in, we figure we easily pay back any difference in cost within 5 years. There are no dealers in our area yet that carry the GE Hybrid, so we would have to special order it. Installation is very similar to installing a regular electric tank. I would like anyone to respond to this who might have something to add that perhaps we might not have considered, or if someone out there has experience with the GE Hybrid; we would like to know things like...How often does it run, and for how many people in your house? Fan/air pull strength? Noise level? Technical problems? I have compared it to other heat pump hybrids, and the GE seems slightly superior to me, at least on paper. Thank you for any info.

I looked at it, but seemed to me it was better using the heating system to direclt provide hot water through a heat exchanger than a heat pump, we have a long heating season however.

During the heating season, it will be no less energy efficient than an electric heater. Other times, it would be considerably more efficient than electric or propane hot water heaters.

we looked at them briefly, but ruled them out.   We are on natural gas, so that is different than your situation.  What we found was that the upfront cost was significantly higher, and the cost to use was actually more expensive than a direct vent natural gas.  The heat pump water heater was cheaper than a "normal" electric water heater, but not cheaper than nat. gas.

 

Because you heat with wood, you might burn a bit more wood to heat up your hot water but it should be cheaper for you in the long run. If you don't mind wasting some water in summer if it is really hot you can run your hot water to get the unit to start and cool your house down. Maybe wash your car with hot water or fill a pool for kids or grand kids or neighbor kids

In heating dominated climates it's hard to make them pay. During the heating season you're paying for the heat with the heating system at whatever price/system efficiency you get with that PLUS the electricity to drive the heat pump. During the active cooling season you're lowering the cooling load represented by the HW heater by about half, not more.

Recovery time on any of them are atrocious compared to propane tank heaters. (Look up the first-hour gallons numbers!)

For two people with minimal HW needs in a heating dominated climate, a direct vented sealed-combustion propane fired tank would likely be cheaper to run overall. Wood isn't free, and is burned at ~70% efficiency (on a good day). Propane may be more expensive per delivered BTU than wood, but the bulk of standby loss of the tank still accrues to the conditioned space, offsetting heating fuel use, and there's minimal electrical power use. If you insulate all of the near-tank plumbing and as much of the distribution plumbing you can to at least R4 (5/8"wall or larger closed cell pipe insulation) your standby losses drop considerably.

To tell where the operational cost crossover point is would require a sharp pencil and more data on your water use patterns & volume, electricity, propane, and wood prices. It's not a no-brainer the way it is in cooling dominated climates in areas without natural gas service. (NG fired tanks can still be cheaper to run in cooling dominated climates- it's a matter of relative electricity & NG fuel rates.) If wood IS free for you, then it can work if you can handle the poor first-hour gallons performance.

The "PLUS" is canceled out by the minus of the electricity used by the heat pump being released into the air or reducing the btu extracted from the surrounding air - ie, the cost of electric water heat is an upper bound on the energy costs of a heat pump water heater, even if it didn't have a heating element (assuming you would never heat with something more expensive than electricity, you don't keep your water heater in unconditioned space and your house is cooler than your hot water).

Agreed, purchase and maintenance costs are important considerations and if you have natural gas - use it.

I have had great luck with heat pump water heaters.I bought 12 of these two years and sold all but three . everybody loves them.... I have a Nyle unit in my own house ..... It is tied into a 40 gallon electric water heater.....

The only down side to heat pump water heaters is in the spring and fall when you aren't using the wood stove.The area the HPWH is drawing the BTUs from will get cool . These things are a 7,000 BTU air conditioner so there fantastic in the summer and the will dehimidfy your basement..... ( People aren't having to run dehumidifers in the summer . Another savings )

I put a KWH meter on my unit so I know what my hot water cost are ... I use 3 KWH a day for Hot water .
In NH that cost me $15.00 a month for hot water for two people .

It cuts the cost of electricty to make hot water in half and dehumidifies ...... 
And as long as you understand it will cool in the area it is drawing the BTUs from and plan on compensating
for that with the wood stove you will be very happy with a HPWH...

I have been happy with mine  and so have my customers..

Dave in NH

Should be pretty well suited for my Louisiana climate. But Dana, you mentioned the recovery time being atrocious - should it be a problem if the capacity is large enough?

Back in Michigan ; Yes, our wood is free and plentiful (thanks to the emerald ash borer!), and yes we do have low hot water needs. The first hour rating on the hybrid hwh is 63 gallons in energy efficient mode. The electric back- up speeds it up any time you request it to, however. The manufacturer says that in the act of heating 10 new gallons of water, the GE will pull 700 cubic foot of air (slowly) and reduce the air temp of that air by 2 degrees. Parked in the basement by the furnace, the woodstove, and the laundry, we think that should be a pretty small heat loss. The manufacturer says that the cooling air from it in the summer is insignificant to home temperatures. This particular design only came out late last year, I believe. Dave, I agree with your estimates on monthly cost to run it. I figured it would cost us $20 mo maximum, compared to a standard propane which uses $40 -$50 cost per month. We figure, compared to purchasing a new standard propane heater, we would recoup our costs and be ahead in 2 years time. We don't have a gas option, only propane. The cost of the SUPER efficient propane hwh was very high compared to the benefit of energy savings. We ordered our new GE hybrid yesterday, from Sears, and expect it to come next week. Installation should be easy. I'll let you guys know how it works out. I'm excited to experiment with this newcomer! Dave, you didn't say anything about noise. I know they make a fan noise... is it very loud? Angie

The noise is about the same as a small window AC unit running on low.

Dave in NH

Posted By Jelly on 17 Feb 2010 09:16 PM
Should be pretty well suited for my Louisiana climate. But Dana, you mentioned the recovery time being atrocious - should it be a problem if the capacity is large enough?

With enough storage capacity, the recovery time become irrelevant.

These units are by nowhere near as efficient as running a desuperheater off your AC or heat pump though. (Maybe half, on a good day.)

> nowhere near as efficient as running a desuperheater off your AC

What is your support for this?

Also consider that quite often the AC isn't being used, so then it doesn't heat water at all.

Posted By jonr on 22 Feb 2010 06:14 PM
> nowhere near as efficient as running a desuperheater off your AC

What is your support for this?

Also consider that quite often the AC isn't being used, so then it doesn't heat water at all.

What, you need supporting evidence for the sky being blue now too?

Desuperheaters are running on systems with average COPs twice that of tank-top compressors, and the compressor is outside of conditions, not adding to the cooling load the way a tank-top compressor does.  During the cooling season the cooling effect of the desuperheater increases the net COP of the cooling system- the water heating during cooling mode really is operating cost-negative- it's not an additional load to the system, it's a load reduction/efficiency enhancement.  The heat pump hot water heater still represents a net load (albeit a half the size of an electric tank.)

Even if the cooling system is only operating in cooling mode on half the days of the year and a separate system is used for space-heating, and the rest of the water load is done with electric resistance heating, it's already broken even with a heat-pump water heater.

Or the sky being green - let's see - the GE heat pump water heater claims an energy factor of 2.35. Then add something for the fact that energy factor includes tank standby losses, but COP for an AC doesn't. Then add something substantial for the cooling that the heat pump water heater provides. This puts us over COP = 3,  much better than 1/2.

Heat pump water heaters are also operating cost negative during the cooling season. Every btu extracted from the inside air is that much heat that the AC doesn't have to extract. Since you might pay to run the water heater heat pump for cooling anyway, the water heat is "free" - depends how you want to think of it (but be consistent).

The only real difference between a water heater heat pump and an AC (aka heat pump) is that the water heater heat pump compressor is inside - the effect of this depends on how well the design moves this heat directly into the water and doesn't allow it to effect the surrounding air. Geo systems have this same minor issue (the compressor is inside).   Other than that, COPs for both AC and water heater heat pumps should be about the same.

Mayhaps I've been too wordy, or not enough of the right words.

A condensed form is:

The heat pump on the water heating being inside of conditioned sapce is EVERYTHING, since it simply can't deliver all of the compressor's heat to the water, and is thus a real net cooling load to the AC system.

It's the difference between being a net cooling load in one case vs. a net lowering of the cooling load in the other, which from an ascribed efficiency point of view, is HUGE. The net increase in energy used heating water with a desuperheater is negative- dumping heat to water at DHW temps takes less compressor energy than dumping it to air at summertime air temps.

Either that, or the sky really IS green.

Posted By Dana1 on 25 Feb 2010 03:36 PM
Mayhaps I've been too wordy, or not enough of the right words.

A condensed form is:

The heat pump on the water heating being inside of conditioned sapce is EVERYTHING, since it simply can't deliver all of the compressor's heat to the water, and is thus a real net cooling load to the AC system.

It's the difference between being a net cooling load in one case vs. a net lowering of the cooling load in the other, which from an ascribed efficiency point of view, is HUGE. The net increase in energy used heating water with a desuperheater is negative- dumping heat to water at DHW temps takes less compressor energy than dumping it to air at summertime air temps.

Either that, or the sky really IS green.

First I have to say I agree that overall the efficiency of a geo unit would be better heating water than an air source heat pump on a water heater.

What I don't understand is why you keep mentioning since the water to air heat pump is inside the conditioned space the heat from the unit adds to the cooling load. At the same time aren't most geo units also in the conditioned space (ours is) and while cooling the house they are in the same situation as the air source unit on a water heater? I am just trying to understand, is it because the geo unit can reject more heat to the ground or out of the conditioned space rather then it leaking in to the conditioned space as would be the case with the water heater unit?

Wouldn't efficiency wise a geo unit would be the best, but I would think in a cooling dominated climate an air source heat pump on the water heater would be the next best thing for heating water and cooling the house. I know in Hawaii in a house we were in that didn't have AC my wife would let hot water run down the drain to get the air source heat pump to kick on and cool the house. I can assure you it did cool and dehumidify the house, not like central AC or even a window unit, but it was certainly better than nothing and definitely didn't warm the space up.

As Brock experienced, a heat pump water heater certainly does not add net cooling load (aka heat) to the interior space - quite the opposite. It's doing the same thing as a geo heat pump in cooling mode - except that the heat is going into a hot water tank instead of your yard (or some combination of your yard and your hot water tank if you use a desuperheater).

I guess the upshot for me down here in the swamps is that adding a desuperheater on my air source heat pump/AC unit and buying a Marathon electric tank, will still beat buying an air source water heater and leaving my air source heat pump/AC alone?

That is, unless our winters get longer due to climate change, and if this winter is an indication then that may be a possibility! Of course it would only be temporary, before the seas rise and swallow us all and Arkansas becomes the new gulf coast...

Posted By jonr on 25 Feb 2010 07:04 PM
As Brock experienced, a heat pump water heater certainly does not add net cooling load (aka heat) to the interior space - quite the opposite. It's doing the same thing as a geo heat pump in cooling mode - except that the heat is going into a hot water tank instead of your yard (or some combination of your yard and your hot water tank if you use a desuperheater).

 Unless it adds 100% of it's compressor heat to the water (which it can't), it DOES add heat to the interior space. This load is much less than the heat it's extracting from the room and pumping into the water, but the heat pump would have to remain below room temp to not put some heat into conditioned space.

But it's a small load, to be sure-could even be less than the heating up of the wires to the tank from the current.  But a small net positive is radically different from a small net-negative, eh?