I am getting down to design of my system which will start in earnest when I close on the house next week. Repalcing a couple heat pumps and an oil boiler with either 1 or 2 GHP and DSH. I see lots of folks who've run numbers on different options for finishing tanks. What are some thoughts out there on the Heat Pump Water heaters (GE Geospring, Whirlpool, etc). The way I am figuring it is such. In summer, when the DSH doesn't fully meet water load, I am basically getting additional cooling and dehumidification of my basement at maybe a 2.5 COP. In my shoulder months where I am not running much either way, i am getting free dehumidification. In the worst case while heating and still running my air source heat pump water heater i figure 1 unit of heat to water at COP of 2.5 costs me 0.4 units electric. Now I need to move another unit of heat from my loop to the basement air at a COp of 4.0 so costs me another 0.25 units of electric. It seems effectively that i just moved 1.0 unit of heat to my water at the expense of 0.65 units of electricity, or net COP of 1.5. Seems to me this could balance out on costs with enough data. SOme of the intangibles are the fact that current homeowner had an electric dehumidifier plugged up and running when I did home inspection, so i assume i need to do something to dehumidify at any rate. Would appreciate any thoughts or any data someone has to bear out the theory..............Trent

Just my anecdotal observations as a homeowner...I have a 4 ton geo unit with a buffer and a finishing tank. The finishing tank has an AirTap Air-Source heat pump water heater. Everything is located in an unfinished, unheated basement. Pipes in the basement are insulated.

My experience is that in the spring, summer, and fall, the AirTap does a nice job on the 40 gallon finishing tank. We're only 2 people at home and we don't need a ton of continuous hot water. It will take a heat pump water heater longer to heat the finishing tank (assuming it was cold water coming in) than electric elements or a gas/oil-fired water heater. But it does so by removing heat from the basement (in my case).

In the winter, I found that it reduced the temperature of an already cool basement (we have laundry down there) so I switch it off in the winter, and put the electric elements on (breaker-control). In the spring, summer, and fall, the electric elements are off and it's all heat-pump water heater (and geo buffer) doing the hot water for the home.

I love the dehumidification of the basement as a 'byproduct'. I keep meaning to duct the cold air output of the AirTap into the first floor somehow, but once a/c season really begins, the geo buffer tank takes care of most of the load, and the AirTap runs only a few times a day to maintain hot water at 135F (the max mine goes).

I do turn it off in winter because it is cooling the basement even further (gets down to 55 in the dead of winter and the AirTap running, brrr), and the heat being taken is coming from somewhere...probably upstairs! as the floor/ceiling between basement and first floor is uninsulated.

I know my situation isn't ideal, but I think I've found a good balance in my case. I love the Heat Pump Water Heater, and it's on 9 or 10 months of the year.
WEL0487

Stuart

I'm not a fan of AirTap products that immerse a single wall copper tube with high pressure refrigerant in direct contact with domestic water. A tube failure injects refrigerant, oil, and goodness knows what else into the potable water system. This view is supported by building codes.

You can connect one or more geo DSH coils to a single preheat tank. If more than one, add swing check valves to prevent backflow through inactive geo unit DSH coils.

Heat pump water heaters are highly effective in mild to warm climates but should be deployed with caution anywhere north of Climate Zone 3.

Operating cost of heating and cooling systems, and thus payback / ROI for various alternatives depends mostly on the home's envelope...size and quality of insulation, windows, etc

Operating cost of water heating depends mostly on number and behavior of occupants. A 1-2 person household is most economically served by a basic gas or electric water heater. OTOH a household of 6 likely uses enough hot water to justify both the DSH option and preheat tank AND a heat pump water heater finishing tank.

"Full size DeSuperheating and as is no more a hybrid than any desuperheater asjust named: On-Demand by temperature control, Priority HW has proven a little longer ROI but substantially more returned in dollars over 10 years from the 4-to-7 year ROI alone as a difference to little HW generation by desuperheating alone. Fam of 3-4 benefitting can be accounted."

Ok, I gotta throw a yellow flag on this one.
1) on demand temp control is not the same as employing a DSH. More compressor starts, more operating hours, you are taking them off the end of the heat pump life.
2) I don't know how much you charge for this feature, but in my kneck of the woods a family of 2 would pay about $150/yr for DSH and an electric finish tank. (2 is what the OP had to generate hot water for). So if it is a $1,500 extra you will need to make the hot water for free for 10 years to pay for it.

There might be more I disagreed with, but ........ to quote a Looby classic: "English-much?"

One follow up @joe.ami OP is actually looking to provide DHW for a family of 7, not 2. That will tweak my payback some. My designer (Mark Custis) is meeting me on site next week, after I close, to nail down a design. i am just throwing thoughts out there now to hear some thoughts from others to tickle my and his brains.

Apologies. I somehow started reading in the middle and quoted the wrong poster.
With a family of 7 you may find the recovery of the unit unsatisfactory. At the very least you would be looking at a second tank or significant electric element contribution (shrinking COP or ROI).
We have had other extensive calculations on this topic and have decided in my AO They might be a little better than a wash over electric finish tanks and nearly upside down by the time you factor in purchase price.

Mark is a "cheapest energy for the job guy". Though we have worked together I don't know that we ever discussed this product specifically, but I know he is comfort (vs economy) driven which means deliver what you want when you want it. The ASHP water heaters do not necessarily perform along those lines.

If you are getting radiant and a water to water system you have other choices but at the end of the day don't be afraid of a nice cheap storage tank.

mt,
We have a very similar setup to Stuarts, with a few changes. Out set-up: Single 4T geo with DSH, a 50 gallon buffer (used Elec heater turned off), and a 50 Gallon GE heat Pump water heater. We run the GE unit on "E" heat mode all year, so it only uses the heat pump and no electric elements. I have it set to 125 deg. F. Our basement has a finished space with some heating and cooling via supply and return ducting and also utility/storage room space with no heating. The utility space has all the mechanicals. We have two adults and two kids.

In the spring and the fall, when the Geo is not running much, the buffer will be cold and the HPWH does all the work. It does chill the utiltiy room some, but not horribly so. The finished side stays comfy with the ducting tempering that space. Good for the kids. In the mid summer, I turn on a dehumidifier as well to keep the finished side RH below 55 or 60%. It runs considerably less since I added the GE HPWH, but it still runs as the GE run time is down during the summer.

Once in a blue moon, in the spring and fall seasons (buffer cold), when we all shower one after another, we can run low on the hot water. When the Geo is running, we never run out, since the buffer is there and really boosts the HW storage capacity. During the winter and hot parts of the summer, the GE HPWH runs a lot less. You can change mode to "hybrid" if you want more hot water at times, but I never put it there.

I like your thinking on the transfer of energy and the costs associated with that. You line of thinking makes sense and seems to fit what I see in my home. If you go Geo and HPWH you will still likely need to run a dehumidifier in mid summer, though less that without the HPWH.

With local and federal incentives, getting the HPWH made sense to me in our situation, even though it steals heat from the envelope in the swing seasons. This stolen heat is somewhat offset by the extra cooling and reduced need for dehumidification in the summer. How much, I am not sure...

FWIW, As a whole, I am very satisfied with our set-up. Our 100% electric home annual consumption went from 21000 KWH/year to 13000 KWH/year after the GEO and HPWH went in. We had a SEER 12 air source HP and a regualr hot water heater prior. We also inceased attic to R50 from R30ish at the same time. No other changes to affect consumption. With our 10KW solar, we are just about net zero for last year.

Good luck with your choices.
Chris

A lot is still up in the air. One cursory review of the house leaves much to the imagination on design. Current layout has oil boiler with brazed plate indirect DHW to an 80 gallon storage. That 80 gal tank is notionally my buffer. Current system also handles all heating through hot water coils in the supply plenum. The main parts are still up in the air though. Possibly one package unit one split, or Mark is thinking we may go with hydronic with a thermal storage tank and pumped chilled/hot water to fan-coils. Options for dedicated hot water come into play. I'd imagine by Friday next we will have a rough plan which I'll share after we see the guts of the house and it develops.

With 7 hot water users you might want to think about 2 choices.
1) you install a dedicated heat pump for domestic hot water
2) you can run your tank as a priority zone off you w-w heat pump

You need a large tank with an oversized inside heat exchanger which can transfer the amount of heat at the temperature the heat pumps makes it. A 108 gallon Stiebel Elton tank with the 2 inside heat exchangers piped in series couple with 3 way high Cv motorized valves works very well. You need to add the DHW load to the total system load. In my opinion it is the best and most elegant way. It requires know how from the installer or designer. Here is an example, more on our website.

http://welserver.com/WEL0383/

doc....how are the operating costs around $10.50/day but the monthly is less than $200?

Perhaps
a single unit
with a fullsize water heating coil that acts as, and does 100% desperheating as well as heat-exchange
while in cooling
loop pumps off, then... RECLAIM mode of heat-recovery
while in heating
desuperheats to HW too
and the circulation is DRIVEN by programming, then

then temps are set from the same ONE control board that supply air is set to variably control blower to say 97 degrees, no matter what stage of Dual compressor Three staging
Will it fit, knowing compressors can last over thirty years in GeoThermal?

A smaller GT with other things , Mini's etc, is fine when that fits.

Mark is a self professed wet head who prefers WTW vs WTA in design. As I said, he will offer a good design for the project.
He prefers Comfortaire products which I wholeheartedly endorse.

John's continued reference to a little known company has probably trebled it's inter net foot print in just a few weeks.

Posted By robinnc on 27 Apr 2012 11:27 PM
doc....how are the operating costs around $10.50/day but the monthly is less than $200?

Since on a cold day he heatpump runs more and longer, but during the month there are warm days where it does not. The daily cost is not an average, but the current day.

Do you mean the daily cost if it had to stay running for 24 hours? What size would that be close to?

Posted By knotET on 01 May 2012 12:34 PM
Do you mean the daily cost if it had to stay running for 24 hours? What size would that be close to?

No, we measure power consumption, updated every minute. The daily costs are accumulated costs for electricity the geosystem has used today so far, and resets every day at midnight.

Thanks Doc!

Posted By knotET on 01 May 2012 12:34 PM
Do you mean the daily cost if it had to stay running for 24 hours? What size would that be close to?

As you can see in the graphs, this is a 6 ton dual stage W-W heatpump and it uses between 5KW and 7KW when running, including the circulation pumps, depending on the source and load temperatures. There are some cold days where the system runs 24 hours due to an old, in concrete radiant system when it has to heat up the slab when the outside temperature drops. They were close to $6000 for oil 3 years ago, the geo now does the heat and 24/7 domestic hot water for about $1800/year. Hope this helps.

I think my system is similar to Chris above.  3 TON TTV DSH piped to unpowered electric buffer tank, and GE HPWH finishing tank, I run it in Hybrid mode in the shoulder seasons as  I don't get enough help from the DSH to carry the GE unit through on Eheat mode (7 people in the house).  We run it at 125.  We have very predictable peak hot water loads, so it would be a huge benefit if I could program the unit to raise the tank setpoint at those specific times, but I suspect that isn't something that will be available anytime soon.

Before the DSH was connected I was straigtt electric storage, so I needed an additional tank either way, with fed /state rebates or credits, 10% off card, sale at Lowes, etc. the difference between a standard tank and the GE HPWH was less than $500 ($275-$740),  including 10 year parts/labor warranty.  Since we use a fair bit of water the simple payback period was just over 3 years, and a potential for more volume right away.   Of course as electricity costs go up the ROI gets better.   

To boost capacity during shoulder months, I plan to install a circulator between the tanks to allow the GE unit to heat the buffer tank at night, in the eHeat mode.  Depending on how I control the circulator pump I could have 120 gallons of hot water available each morning.  The T's and check valve are installed and I have the pump, but haven't installed it yet.     :(  

By the way, in case it is of interest, below I've inserted a past post of mine on this forum from almost 2 years ago on an efficiency calculation for an airsource heat pump water heater pulling heat from a heated space.  NOTE:  Some things have changed since the posting, including some self-education! :)  This calculation and the savings impact shown are more of a worst case scenario, and only relevant for periods of time when your space heating is operating reguarly.   Any time you are not close to needing heating and the amount of space temperature depression due to the GE HPWH operation is not enough require space heating,  the efficiency increases dramatically.   Hot water then is created between 2.3 and 2.75 times cheaper than a standard elec. tank (depending on ambient temperature, tank setpoint, and operating mode).  Any time it's hot and you have your A/C on the GE HPWH is essentially making free hot water.

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Over the past year or so I’ve read a bit about new heat pump water heaters (GE, Rheem, Whirlpool, and several others offer these). These units pull heat out of the air and put it in your domestic hot water. Problem is the manufacturer and government rating for energy star and tax credit (COP) ignores the heat taken from the space. It seems like the only case where you could possibly ignore the heat taken from the space is if you happen to have an application where the average annual space heating load is equal to the average annual space cooling load. And even then you have to assume steady space and domestic hot water loads whereas in reality they will have lots of peaks and spikes that will not line-up. I searched around a bit and couldn’t find any explanation on how to account for this in a cost/benefit (payback) analysis.

Since we are heating dominated, I came up with the following for effective “heating season” COP for a HP water heater……

Effective Overall HPWH COP = HPWH Rated COP / (1 + (HPWH Rated COP / Space Heat COP) )

Example… Hot Water: GE Model HPWH COP 2.35 has one of the highest published/rated COP.

Space: ClimateMaster Heat Pump has rated heating COP of 3.5 (adjusted to include pumping penalty)
Effective HPWH COP = 2.35 / (1+ (2.35 / 3.5 ) ) = ~ 1.4

If the above is correct, assuming a heating dominated climate and ignoring cooling side benefit and tank loses… savings over a standard electric water heater is less than 30% (1 - ( 1 / Effective HPWH COP ) ). 
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Jokin,

Thanks for the input. I really like the idea of the nightime circulator during the shoulder months. Expecting my installation to start in 3 weeks. I'll definitely have my installer consider same. I already have an 80 gallon storage tank which was used with the oil boiler and plan to add the 80 gallon HPWH. Luckily we do spread load a bit. the wife and I are up and out of the showers by 5 AM. Dishes, babies and parents usually get cleaned on a staggered schedule from 5-8 PM. It would be nice to pipe it in to add a circulator if we do find a future need for 160 gallons of hot.

Posted By jokin on 16 May 2012 01:22 PM
We have very predictable peak hot water loads, so it would be a huge benefit if I could program the unit to raise the tank setpoint at those specific times, but I suspect that isn't something that will be available anytime soon.

We have predictable peak hot water loads too.  Have you considered a water heater timer?  We have an Intermatic EH40 (about $64 on amazon right now.)