They claim a 3-4 year payback on these electric water heater heat pump systems. I am thinking of going this route instead of solar hot water because it’s a much longer payback time and a much higher installation cost with solar hot water.

Rheem Hybrid Heater

What do you guys think?

The payback is def better than Solar Thermal, and a properly installed HPWH will use less kWh than a badly installed solar system.

Third party tests liked the Rheem less than the GE, and liked the AOSmith best of all. On the basis of COP.

Their report is too big to post....Google "HPWH_Lab_Evaluation_Final_Report_20111109.pdf"

My only problem with HPWHs is that they basically use the same systems as a fridge and they don't last as long as they used to. They are still new (at least GE is) on the market, just a few years so I wonder what the lifespan really is, considering how long a fridge will last these days.

That said, what is your definition of green? A solar water heater is a green product and a HPWH is, hopefully, an energy efficient product( which could be green if powered by PV). Different thing from my perspective. Payback muddies the waters.

I would also look at the Steibel Eltron if it is available in your area.

I see that the GE ones are $1000 now. They are taking heat from the interior, so the numbers get better in hot climates (with AC) and worse in cold climates. Now if they would just combine it with the refrigerator.....

With a nod to jonr's idea about combining the water heater and the refrigerator, I did think about putting one in a walk-in cooler, but unless you have the proper airflows, you can end up taking heat from the interior just the same. I had a hard time figuring out how to use one here in Washington state, but in a hot climate they would be pretty interesting.

Posted By jonr on 20 Aug 2012 09:19 AM
I see that the GE ones are $1000 now. They are taking heat from the interior, so the numbers get better in hot climates (with AC) and worse in cold climates. Now if they would just combine it with the refrigerator.....

The AirGenerate AirTap has ducted outdoor air as one possible installation configuration, which would work OK in temperate-cool climates. It's ability to make hot water with the heat pump falls off a cliff below ~20F source-air, so it's usefulness in climates cooler US climate zones 1-4 is pretty limited.

[edited to add]

In a more careful read of the installation manual, the ducted air is exhaust-only (and 400cfm!), which means it sucking in that much outdoor air somewhere else in the house. That's only more efficient than some other heat pump unit if the exhaust air is cooler on average than the outdoor air it's sucking in, which might work for climate zone 4, but maybe only the warmer edge.

Just have a thought about these types of water heaters in mixed northern climates.

There's probably at least 6 months of the year where running one of these heat pump water heaters have beneficial cooling/dehumidifying aspects. The GE model and I presume all of the others have the ability to switch entirely to the electric resistance heat mode. Why not just switch to the all electric mode during the months where the cooling/dehumidifying benefits aren't there? I bet that the unit's operating cost is still better than heating water with propane.

Now, if you have natural gas service, it's probably significantly cheaper just to go that route.

Sure in the winter, switch it to electric mode if electricity is lower cost than propane. But if that's the case, you should heat your whole house with electricity.

Here again the USA lags FAR behind the rest of the world. There are literally hundreds of "split" DHW heaters made in China these use an outdoor section that usually looks like that of a "minisplit" and an indoor section with refrigerant lines between. Typically the indoor section is basically the DHW tank. Some advertise operation down to -20c, (-4f) before they drop to a COP of 1 and revert to resistance heating. Above 40 f the COP typically exceeds 3. What that means is they use less electricity than an ordinary electric DHW heater whenever it's warmer than -4f and over a year less than half as much in any US climate.

I thought the mini-split type water heater was a Japanese invention (but yes, they're not new.)  The Japanese also have combo refrigerator/HW-heaters sized about right for typical Japanese-kitchen hot water use.  Both make more total net efficiency sense than the tank-top versions in cooler US climate zones.

I keep getting hints that the mini-split water heaters will be coming to our shores "soon", but keep hearing the same rumors about CO2-refrigerant air source heat pumps too- I'll believe it when I see it.  As I understand it most of the mini-split type water heaters are CO2 refrigerant (to be able to deliver the higher output temps of DHW efficiently) not R410A like most mini-splits sold in the US. 

The Nippondenso "Eco Cute" water heater is a CO2 type, and has more than a decade of real-world use behind it now.   I'm not sure of the relationship between Sanyo & Nippondenso (aka Denso), but they're selling what appears to be same line of water heaters under the same "Eco Cute" name. It was apparently a consortium that came up with the first versions.  (I'm sure there are many imitators in Asia using a variety of refrigerant & compressor types.)  It could be that whatever regulatory hurdles slowing the import to the US of hydronic output CO2 heat pumps for the space heating market are the same for the Eco Cute.   Both  Sanyo and Denso space-heating hydronic heat pumps are well suited to many homes with radiant heat in US zones 5 & 6, but there is no telling when they will arrive.

The Daikin Altherma air-to-hydronic heat pump (R410A) has DHW heating capabilities though, and is available in the US, but it's bigger deal than the DHW-only heat pumps.

Before you by an air-source heat pump water heater, call a few hundred plumbers and see if any will come out to service the one you are interested in.

It never pays to get too far ahead of the curve, particularly when the return on investment is 10 -20 dollars a month.

I'd be more interested in (and more likely to become an early adopter) if the heat-pump was a CO2 refrigerant unit with a 9kw+ output rating (big enough to more than handle my average mid-winter heat load, and natural gas was $2/therm, eh? ;-)

The tank-top units might make financial sense in 25cent/kwh cooling dominated places like HI (where the ROI would be over $50/month) but approximately never in 7cent/kwh parts of the heating dominated upper midwest.

For some hard-to-fathom reason they're heavily subsidized in MA- enough to cover the cost of the unit (the costs are essentially just the installation after rebate, for the smaller GEs at box store pricing.) The only rationale I can think of for the subsidy here is that by combining HW heating and the air conditioning benefit reduces peak-power loads/costs to the utility during the cooling season enough to for them to kick in something, but for the fixed-rate residential customer there's very little advantage if any. The wholesale price of peak-power to the utilities during the air conditioning peaks are several times the fixed-rate residential rate that they can charge.

The way the utilities are regulated in MA they make more money by reducing load than by building new generating capacity, so there's probably some analysis to show that 500,000 GeoSprings = 1 gas fired peaker that they don't have to build, or something like that. Beats me.

Our rural coop (Minneapolis Metro) offers a "interruptable" power plan, and shuts off power to A.C., DHW and space heating during peak hours. All the same game. Gov't. getting in the way of building new crucial power plants and regular folks getting by. In Japan, where all power is imported, extraordinary machinery makes sense. It might even help N. Americans when we run out of buck-a-therm natural gas in another couple of generations.

Posted By BadgerBoilerMN on 23 Aug 2012 05:40 PM
Before you by an air-source heat pump water heater, call a few hundred plumbers and see if any will come out to service the one you are interested in.

It never pays to get too far ahead of the curve, particularly when the return on investment is 10 -20 dollars a month.

Supposedly it comes with a 10 year warranty and Rheem assists in finding a qualified company.

Posted By Liebler on 23 Aug 2012 02:53 PM
Here again the USA lags FAR behind the rest of the world. There are literally hundreds of "split" DHW heaters made in China these use an outdoor section that usually looks like that of a "minisplit" and an indoor section with refrigerant lines between. Typically the indoor section is basically the DHW tank. Some advertise operation down to -20c, (-4f) before they drop to a COP of 1 and revert to resistance heating. Above 40 f the COP typically exceeds 3. What that means is they use less electricity than an ordinary electric DHW heater whenever it's warmer than -4f and over a year less than half as much in any US climate.

You can say that again. The main thought and practice of builders here is that homes must "breathe" and they build them leaky because it helps the home to breathe.

Have any of you cold climate guys considered the gas absorption heat pump? Natural Gas COPs are 1.4 to 1.7, some electricity is required.

Posted By BadgerBoilerMN on 23 Aug 2012 06:24 PM
Our rural coop (Minneapolis Metro) offers a "interruptable" power plan, and shuts off power to A.C., DHW and space heating during peak hours. All the same game. Gov't. getting in the way of building new crucial power plants and regular folks getting by. In Japan, where all power is imported, extraordinary machinery makes sense. It might even help N. Americans when we run out of buck-a-therm natural gas in another couple of generations.

Now that we're straying off topic...

The interuptible power is often referred to in the power industry as "demand response" capacity, putting some control of the grid-load in the hands of the grid operator to avoid the steep capitalization & operating costs of peak power generation.  The capital costs of peakers are very expensive, far in excess of the fuel costs since their capacity factor (the average output over a year divided by the max output capability) is typically in very low double-digits- under 20% and in some places it's in single-digits. (Compare this to the "unreliable" power of large scale wind, that comes in with capacity factors of about 30%.)  Building and maintaining a powerplant that's use at 10-20% capacity is expensive no matter what the fuel costs are, and they HAVE to charge a premium for their power to have a business. Buying the same grid capacity in "nega-watts" with demand-response control is much cheaper to the grid operator and ultimately the ratepayer, while grid reliability goes up:  Brown-outs (or worse) become less likely.

As grids get smarter more demand response can be built in, which is just one method of "grid hardening" variable output renewable sources such as wind & solar.  It's unlikely that signing up for demand-response on bigger loads would be required of residential customers, but by giving customers who sign up for the variable rates with some demand-response on heavy loads like central air conditioners, electric clothes dryers, and water-heater, then giving them acces t real-time grid pricing information via smart meters it residential customers can (voluntarily or automatically, or a combination thereof) make a huge dent in their power bills.  It's not for everyone, but where these schemes have been tried out almost nobody who signs up for demand response opts out later.

Demand response is under intense development in Japan- critically necessary due to both their bizarre split-grid and the shut down of a large fraction of their baseload capacity after the tsunami/Fukushima disaster.  Half the country if 50Hz 220V, Euro-style, half is 60Hz, 110V, N-American style, with only limited capacity to share power between the two.  It's simply not possible to build new generation capacity (of any type) quickly, but implementing demand response to put upper bounds on the grid load is both (relatively) cheap and quick.  But it's far more than a band-aid- it's putting Japan in the forefront of the technology to implement & manage smart-grids.  Japan WILL build more generating capacity going forward, but a smarter grid allows them to minimize capitalization costs by maximizing capacity factors on all of their grid sources.

Taking it even further off-topic...

As much as the detractors of wind-power make an issue out of it's variable output & comparatively low capacity factor, the levelized cost of energy for wind at at the current ~30% capacity factor (including all capitalization & maintenance costs) isn't dramatically higher than cheap-gas burned in state of the art combined-cycle gas plants, and is CHEAPER than power burned in simpler gas-thermal plants (at any capacity factor, not just low CF peakers).  That cost has also been coming down at a rapid rate as wind technology matures and manufacturing rates increase. Even without subsidy there is an economic argument for grid operators to continue wind development even in the face of cheap gas.  With wind the vast majority of the cost is in the capitalization, and once the it is built the marginal cost per kwh is near zero, and the levelized cost per kwh is a fixed, very stable number that can be counted on.  In parts of the US where wind has been more heavily developed (notably TX & IA) the low marginal cost/kwh of wind has had the effect of depressing the price of power to both the grid operator and the ratepayer, since in the day-ahead market (how most wholesale power is bought & sold in the US) wind, like (hydro & nukes) is a $0 bidder- they accept whatever the rest of the market will charge, and when the wind blow hard it displaces powerplants with fuel costs, and the excess wind is purchased at whatever the next-cheapest generators bid was, even when it's below the overall levelized cost for wind. This puts the operators of marginal thermal plants with real fuel costs that cannot be discounted at a disadvantage, eating into THEIR capacity factor.  But it puts a damper on the overall average cost & prices from which ratepayer rates are derived.

Even with cheap gas there is cost-volatility related to the non-stable price of the fuel, and while they are at historical lows now, there's no room for them to fall further- at ~$2/MMBTU gas operaters start capping off shale-gas wells that don't have sufficient liquids that can be sold a higher price- they're too unprofitable to even pump.   At $4/MMBTU gas the levelized cost off wind power is cheaper even at 2010 wind costs, and the cost of large scale wind has come down since then.  It is in grid operators' longer term interest to continue to build up a wind portfolio even in the face of cheap gas as a hedge against fuel price volatility and against potential future carbon taxes.  With the development of smarter grids and greater demand response capacity cheap-wind may come to dominate some local markets LONG before the cheap gas runs out.  Given that on a levelized cost basis it's below grid-parity in some markets RIGHT NOW now, wind has a future.  Whether wind continues to get the benefit of a Federal subsidy only affects the rate of implementation, but not the eventual grid-share.  A rapid shut down of Federal support (as may very well happen) will be disruptive to the industry and may scale back or halt some recently developed or planned manufacturing capacity, but it's not necessarily a death knell, as some wind advocates have suggested.

> gas absorption heat pump

Are there readily available systems out there for residential use? They aren't very efficient for cooling, but for heating, 1.4 is better than .95. http://www.ornl.gov/adm/partnerships/factsheets/10-G01078_ID2389.pdf

No offense, but the heat stealing on these units is a widely misunderstood topic. A number of frankly incorrect screeds on the intertubes are dedicated to the topic.  Folks think they are paying twice for a given BTU, once with a furnace to put the BTU in the space, and then a second time to pump it, so it has to be more expensive than just paying once (like a conventional tank).

Looking more carefully, if the unit runs at a given COP, then it only pumps (COP-1)/COP, about 50% from the space, and the remainder (also about 50%) comes from the compressor work running the pump (that, like most work, ends up as heat BTUs).  So, by this math, a HPWH still saves you money, per DHW BTU, relative to a conventional tank in a cold climate during winter, provided your space heat BTUs are cheaper than electric resistance BTUs (which is almost always the case).  It just saves you less than it does in the summer.

In summary, half the heat comes from your grid, at a cost/BTU the same as a conventional tank.  The remaining BTUs from your space have to be made up, but only at the cost/BTU of your central furnace (and then only during the heating season).

In summary, half the heat comes from your grid, at a cost/BTU the same as a conventional tank.

You are adding to the confusion. For example, the above is not true when comparing a HPWH to a conventional nat gas water heater (a common case).

Back when, I kicked around the idea of using a HP hot water heater to temper passive solar in a lower-mass, well insulated house. You mount it in a chimney chase or similar ducted location and put it on a thermostat so it runs at temps above 75. A heat dump loop connecting a water/glycol heat exchanger in the tank with an air/glycol HX outside would keep it running. You'd oversize HP and tank. You could add 55-gal drum-type tanks in series until you got storage right. The same dump loop could provide heat overnight with a second glycol/air HX in your chimney chase. In the summer the heat dump would allow the HP to operate as on-demand air conditioning.

On the minus side, it's hard to find residential stand-alone HPs of decent size. E-Tech still had these 1-ton units a couple years back. http://www.etechbyaosmith.com/res_waterheating.html AO Smith apparently wanted E-Tech for commercial stand alones, so larger units should be available.