airsource heatpump HOT WATER
Last Post 12 May 2009 08:47 PM by Jelly. 21 Replies.
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JellyUser is Offline
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03 Apr 2009 09:27 AM
At the energystar website I read about new air-source heat-pump water-heaters at this link:

energy star heat pump water heaters

The problem is it doesn't look like any have been brought to market yet. Has anybody seen or heard about any manufacturers? The energy star site says they're coming in 09, but I can only find adapters. You have to pay for a tank unit, plus an expensive adapter like this one:

airtap

What if my heating and air conditioning is supplied by an air source heat pump? Could I get hot water from the same unit?
newbiejohnUser is Offline
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03 Apr 2009 09:30 AM
Check out GotoHallowell.com they are coming out with a unit if they havnt already.

I owned the 'Acadia' in my last home, a cold climate heat pump and it worked great....
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04 Apr 2009 09:36 AM
Jelly, Here is a manufacturer in Maine: http://www.nyletherm.com/waterheating.htm#3
And here is retailer selling the Airtap, and claiming tax credits that cut its price by 42 percent: http://shop.energysmartcompany.com/water-heating-176/airtap-137/airtap-a7-heat-pump-water-heater-574.html
Another manufacturer in Ga.: http://www.aers.com/index.html
And a maker of commercial systems in Washington state: http://www.colmaccoil.com/heatpumps/
These are perfect for me, and I have a year to wait so there should be more choice then.
JellyUser is Offline
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04 Apr 2009 08:09 PM
toddm, thank you for those links.

Since they are all intended to be mounted on to an existing electric water heater, I suppose I could just install the regular storage unit and wait a bit until there are more on the market to choose from.

I read something on one of the sites about needing 1000 cubic feet of space to draw air from. Guess I'd better not install my water heater in a closet!
lrakowskUser is Offline
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04 Apr 2009 09:10 PM
People are going crazy about them in Mass.

Here, check this link out.

http://www.residential.carrier.com/knowledge/guides/hybridheat.shtml

Hybrid Heat is the Carrier version.  Acadia is another version.  I recommend Carrier because their controllers are better.


lrakowskUser is Offline
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04 Apr 2009 09:11 PM
water heaters come with a flat plate heat exchanger...if you have a quality contractor...you will be able to find savings.

toddmUser is Offline
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05 Apr 2009 06:51 AM
Jelly,
It fits a passive solar house like a glove: store heat while the sun shines. It could dry out the house too much in the winter, though. We'll see.
I'm building a 4x5 "chimney" that serves as a plenum to move air at low speeds between floors. So I can put it in a closet and bring the heat to it.
Owner/builders should be looking at add-ons. After you move in, you can claim as many tax credits as the next guy. Even I should be done by 2016. :)
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05 Apr 2009 02:59 PM
toddm, I'm missing something - storing heat while the sun shines? These units draw heat from the interior air don't they?

About the space to draw air from - I suppose I could make a louver from the WH closet to the utility room, or even just open up the closet and connect the two rooms together. That should give me plenty of air.
BrockUser is Offline
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05 Apr 2009 06:20 PM
It's funny I saw these in the 80's in military housing. I remember visiting my in laws in Florida, California and Hawaii. All three locations used heat pumps on top of the water heater. The bad thing was they were connected to 40-gallon tanks. Fine for the two people who are suppose to live in the housing, but when 4 or 6 of us were visiting the unit's couldn't keep up. If I recall correctly they were about 1 ton each or 12,000 BTU. On the plus side the housing didn't have AC, so I convinced them to close up the house and eventually it cooled off inside, when it got warmer in the evening I just ran some hot water down the drain and the place cooled off, they were amazed. Oh the units were in the same room as the only air intake for the small furnace that was ducted around the house. So I also switched on their circulation fan which pulled that cold air from the utility closet and moved it around the house. It also made hot water faster this way even though the utility closet had a 24x24 vent in the door.

I think some of them now will kick in the traditional electric element once you hit like 100F and the heat pumps run up to 120F.

Jelly I think Todd is saying if he can heat up the house with solar he can move that heat in to the water to be used later for radiant or whatever.
Green Bay, WI. - 4 ton horizontal goethermal, 16k gallon indoor pool, 3kw solar PV setup, 2 ton air to air HP, 3400 sq ft
JellyUser is Offline
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05 Apr 2009 11:31 PM
Brock, so do you think if it had been a 60 gallon tank it could have kept up with demand? What I hear you saying is the limitation was due to tank size, not the heat pump. I wonder if they heat faster or slower than electric resistance?

Air source heat pumps are pretty common around here for AC and forced air heat (and swimming pool heaters too). It seems like you could just use the same unit for your domestic hot water. Every time you used your AC you could be charging your hot water tank. Or maybe that's too many tasks for one unit? AC plus hot water in the summer, and forced air heat plus hot water in the winter?
BrockUser is Offline
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06 Apr 2009 08:33 AM
If an electric has dual 4000w elements that would be 8000x3.41 or about 27,000 BTU or 13,500 if running a single 4000w element. So it is probably a bit less than traditional electric? I would think just sizing the tank for the number of people would be the way to go.

If I lived in the south I would get an 80 gallon tank and put one of these on it.

I would also agree that in any cooling dominated climate they should first run the refrigerant through a pre heater tank and then outside in a simple series connection. Then any time your cooling your recapturing that heat to pre heat water and once the water was too hot to absorb more heat the outside unit would pick up the load. Maybe it’s a lot more complicated than I am thinking?

My guess is because to really take advantage of this setup you would need a pre-tank with some sort of heat exchanger and the plumbing would be more complicated for a standard HVAC who isn’t familiar with heat pumps.
Green Bay, WI. - 4 ton horizontal goethermal, 16k gallon indoor pool, 3kw solar PV setup, 2 ton air to air HP, 3400 sq ft
JellyUser is Offline
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06 Apr 2009 10:06 AM
Brock, is this energy recovery unit along the lines of what you're thinking?
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06 Apr 2009 10:12 AM
Very neat! Yes for a standard AC unit this would help out a lot. Of course it would help more with a preheat tank or shutting off or turning way down the setting on existing water heater.
Green Bay, WI. - 4 ton horizontal goethermal, 16k gallon indoor pool, 3kw solar PV setup, 2 ton air to air HP, 3400 sq ft
toddmUser is Offline
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06 Apr 2009 10:35 AM
Jelly, passive solar is feast or famine, so anything you can do to capture heat during the day and hold it is money in the bank. I'd want the heat pump on a timer or a thermostat so it didn't add to the chill at night. Used this way the average efficiency could be near 300 percent.
But it wouldn't be large enough to heat the accumulator tank I have in mind. (120 to 200 gallons.) The Airtap is 7000 btu/hr. The Nyle is 8000. I'd look at it as incremental gain at times when the my wood stove boiler is likely to be cold and the house warm. Now, heat pump and solar hot water together may be enough. They would also be complementary if the heat pump can efficiently add the last 30 or 40 degrees that are hard to get with solar collectors.
Jelly, if you google "desuperheater" you'll find heat exchangers designed to heat domestic water with the waste heat from regular air-source heat pumps or air conditioners. Here is one on ebay for $430: http://cgi.ebay.com/WASTE-HEAT-RECOVERY-SAVE-ENERGY-ELECTRICITY-POWER-MONEY_W0QQitemZ360110324614QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item360110324614&_trksid=p3286.c0.m14&_trkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A1|293%3A1|294%3A50
Note that it will only work on the chilling cycle of a heat pump.
Finally, I don't know why you couldn't buy a mini split system heat pump and connect the refrigerant lines to your water heater tank instead of the air handler. You'd need a tank built for the purpose -- and more than one reason for doing so -- but custom tanks exist: www.stsscoinc.com and www.heatweb.com. The former is a Pa co. specializing in heat storage tanks. The latter is a British company that specializes in integrating solar, wood heat and conventional boilers. Dunno why they couldn't add a refrigerant HX, too.
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06 Apr 2009 12:33 PM
If you have a whole house heating/cooling heat pump, a desuperheater (like the ECU HR06 energy recovery unit Jelly pointed to) in combination with either a standard tank heater or a storage tank + on-demand will likely outperform any of the tank-top units by quite a bit.

a: When the heat pump is in air-conditioning mode using the desuperheater will increase the effective coefficient of peformance (COP) since it'll be partially water-coupled to the thermal mass of the HW storage tank, not just air-coupled.

b: With the household heat pump in space-heating mode, any heat that is extracted from the room air by a tank-top unit would then to be pumped back into the space by the heat pump, with no advantage over having the desuperheater pumping it into the water directly.

It's probably cheaper overall to go with an oversized tank HW heater + desuperheater with a circulation pump that runs whenever the heat pump is running. With a tempering valve on the output of the HW heater you can set up the tank thermostat to kick on the elements to maintain ~115-120F in the tank, but allow the desuperheater to take it up to as high as 150F (or whatever the peak coil temp ends up being) with a recirculation pump whenever the heat pump is otherwise running for heating or cooling (rather than making tank-temp -maintenance cycles, which may be inefficiency short-cycles for a whole-house heat pump.) Standby losses on 80- 120 gallon tanks aren't dramatically more than 40 gallon tanks (surface area grows less quickly than volume), and with more thermal mass to work with the lower the peak temp, and greater the improvement on overall heating/AC/HW-heating system efficiency. With a big enough storage tank one might consider heating the tank solely with the desupeheater it as a separate zone-call to the heat pump whenever the tank needs to come up to temp, but it requires a system-specific detailed efficiency analysis to figure out whether that buys you anything efficiency-wise. In many cases it would, but with very large heat pumps, probably not.
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06 Apr 2009 12:58 PM
Wow, Dana1, I think you're going to have to post a diagram, because I cannot wrap my head around that! And I can just about guarantee there is no HVAC contractor around my neck of the woods that could either.
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06 Apr 2009 01:40 PM
Dana, a desuperheater won't help if there is no air conditioning load, as is the case in the woods in Pa. I am hoping a heat pump and solar collectors will keep my accumulator tank warm, if not hot, through the summer, and knock the edge off humidity besides. Granted, the payback in this use would be piddling, except for passive solar and regular episodes of overheating through the winter. Comfort then becomes an argument for heat pump hot water. Beats opening windows at 6 p.m. when you arrive home in a stifling house -- and hearing the furnace kick on two hours later.
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07 Apr 2009 09:16 AM
Posted By toddm on 04/06/2009 1:40 PM
Dana, a desuperheater won't help if there is no air conditioning load, as is the case in the woods in Pa. I am hoping a heat pump and solar collectors will keep my accumulator tank warm, if not hot, through the summer, and knock the edge off humidity besides. Granted, the payback in this use would be piddling, except for passive solar and regular episodes of overheating through the winter. Comfort then becomes an argument for heat pump hot water. Beats opening windows at 6 p.m. when you arrive home in a stifling house -- and hearing the furnace kick on two hours later.

Yabbut, Jelly lives in swampy semi-tropical Louisiana, not the cool & dry hills of PA- you can bet that for a large fraction of the year there's a significant AC load.

And if you have a large enough tank you can efficiently heat it by running the heat pump even when there ISN'T an air conditioning load.  But it's relative to the size of the heat pump- using it just for raising the temp of 100gallons hot water buffer by 10F at a time (from say 115F to 125F which is ~8300BTUs) won't be very efficient for a 5 ton unit- it'll be an efficiency-robbing short-cycle.  For a 2 ton unit it could be quite reasonable though.  The heat pump controls would treat it as a separate "zone", not running the air-handler blower for hot-water-only calls,  instead running the circulation pump between the desuperheater and the storage tank during those cycles.  The heat transfer of the desuperheater and the flow rate of the water pump need to be designed to provide an adequate load in such a configuration- don't just hack it, let a pro do the math.
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07 Apr 2009 09:43 AM
Better yet, I am going to live in the house for a year or so first. With passive solar, you get what you get, even after the pros run the numbers. A couple weeks back I drove from my building site to Blue Ridge Summit, six miles west and a thousand feet higher. Fog at the bottom. Bright sun at the top.
JellyUser is Offline
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07 Apr 2009 10:12 AM
Yeah, the AC is needed for the majority of the year in these parts. But there are about 4 months of the year on the other hand, when the heat pump would be on call for forced air heat. During those months would it make more sense to just switch the hot water heater tank back over to resistance? Or would letting the heat pump do double duty actually increase the efficiency?

Finding a pro to do the math is what I'm worried about.
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