ASHP with thermal storage?

[Daox]

Is anyone aware of ASHP setups that have thermal storage?

The idea I was thinking of is having an ASHP heating water for in floor heating use. I'm not sure if ASHPs are being used to do this vs just heat air, but I think it would make great sense to add thermal storage to the system. The reason being is the ASHP could run during the day when its warmer than it is at at night collecting heat at a more efficient rate. Then, at night it could just draw off the warmed tank of water instead of trying to draw heat out of colder air.

I don't know how much the day/night temperature gains you, but I'd imagine it has to be significant. Around these parts there is easily a 20F temperature differential between night and day. From what I've read this seems to be a quite sizable boost in efficiency.

Sorry if this is a repost of some other idea or system. I don't read all the heat pump stuff, but the idea popped into my head and I thought I'd share it.

[nexsuperne]

I do this, and it works well. I have a 300litre store which charges up on solar and ashp and then runs the underfloor heating and hot water. I can top it up using my wood burner.

[Xringer]

On a day like today, my Sanyos are off, due to the solar gain..

I have consider the idea of cranking up the house temperature to 24 (75.2) during the warm part of winter days.
That would give us a summer-like Tee-shirt environment during the day. (I would love that)!
Which will heat up the 'mass' of material inside the house (and the walls etc).

In the evening, when the outdoor air temp started to drop, I would return our setpoint to 21C.
(And down to 20C at bedtime).

Depending on the outside temp, it could take many hours before the Sanyo remotes issued a call for heat..

The only problem: My wife isn't from Texas, and likes to keep the master
bedroom around 19c (66.2F) during the winter.

[S-F]

This sounds like a reasonable idea. You would need to find a way to make sure it didn't run at night, or at least ran less. Couple this idea with those solar panel, evaporators? From the other recent thread and you'd probably be way ahead.

[Xringer]

Since we use our Sanyos so much during the winter and summer, I've been wondering
about the idea of inserting a small HX into the output of the compressor.

When the HX was hot, water/glycol could be pumped through the HX,
or the circulator pump could left turned off when the hot water storage tank was at setpoint,
or when heating (or cooling the house) demand was high.
During the warm part of the day, stealing a few BTUh for heating water isn't
going to boost up the power usage a lot.

http://i46.photobucket.com/albums/f1.../referFlow.jpg

During the summer, stealing some heat off the compressor output to heat my hot water,
would make the cooling mode use less power..

[AC_Hacker]

Originally Posted by Daox

Is anyone aware of ASHP setups that have thermal storage?

The idea I was thinking of is having an ASHP heating water for in floor heating use.

Yes,this is really a great idea.

There is a high-ticket product called Daikin Altherma , which presently has an entry price of $18k or so.

There are heat pump water heaters, but their output is pretty low. Might work for a small or extremely well insulated place.

In your neck of the woods, the air is pretty cold so it might be a really big challenge for the current crop of ASHPs unless you wanted to use them for the shoulder seasons.

CO2 as a refrigerant is coming on strong... that could well be your answer.

So regarding DIY ASHP with storage, there's nexsuperne... maybe we can get him to post some photos of his setup. Also Acuario is heating his pool and home with a DIY ASHP that is heating water. He has photos.

Also Xringer has a thread (actually two threads) describing his progress in making a heat pump water heater.

This winter I bought a vintage 2-Ton ASHP for $50 for the very purpose that you suggest. Right now I'm waiting for the rain to stop so I can get started on the project.

I've been looking into using an inverter technology mini-split outdoor unit to heat water. It seems that there is some serial communication going on between the IDU and the ODU, to make the ODU turn on and also to control the compressor speed. So just replacing the IDU with a big brazed plate HX is not going to cut it. There will need to be some logic and some temp sensors, etc. Hacking at this level may be above my pay grade. I wish we has some monster tech types here on ER who could help out. There's a guy who is selling an inverter type mini-split this weekend. He wants $400... too much. If I can get him down to $50, it might be a go... I wasted more than $50 on college classes, and learned nothing.

So, knowing what the HDD is for your area can give you a clue if ASHP will work for you. I'm at about 4,500 for the heating season here. Air source works great virtually all the time. Xringer's HDD is higher... he has problem days from time to time. So what is your HDD?

The water part is very nice but the heat has to come from the ASHP.

A solar assisted heat pump would be a great setup for you, with some fossil fuel for the cold snaps... while you're waiting for CO2 heat pumps to come on line.

Warm floors are the way to go. Having a high-efficiency radiant floor is good for a fossil fuel boiler, but makes an even bigger difference when you use a heat pump.

-AC

[Daox]

I wasn't really talking about me specifically. I just don't recall this being talked about so I wanted to start a thread on it to get some info and idea floating about. Mainly, what would this gain you? Are we talking 5% less energy use (due to ~20F warmer air) or are we talking 20%? Is this a great idea or only an ok idea? Obviously one of the drawbacks is that you have to heat the water to a higher temperature which would lessen the efficiency somewhat too.

As for the HDD, I'm around 7000 annual I believe.

[AC_Hacker]

Originally Posted by Daox

Mainly, what would this gain you? Are we talking 5% less energy use (due to ~20F warmer air) or are we talking 20%? Is this a great idea or only an ok idea? Obviously one of the drawbacks is that you have to heat the water to a higher temperature which would lessen the efficiency somewhat too.

OK... this is something I have thought about a great deal, as part of the 'manifesto' project and also since I have come to realize that in my neck of the woods (HDD = 4500) with winters being mild, even mostly frost free, ASHP are a great fit. There is quite a bit of relevant discussion in the DIY radiant floor thread, too.

If you're bringing up the issue of a heat pump with water out and it's advantages, you also have to consider at the same time the final radiating surface, because it is all so tightly coupled.

Quick answer, yes, it would be a meaningful gain in efficiency and for the average Joe, it would be too much trouble and expense to pursue... but then we are not average Joes are we?

So here are the gain parts:

• Using air to distribute heat means that a coil (condenser) must be able to get its temperature up to about 120F or so to transfer the heat into the air. On the other hand, if a very large radiant surface (very large radiators, or a radiant floor) is used, then the temperature required of the working fluid can be lowered. This will result in greater efficiency because the 'temperature lift' is less. I have done some modeling of my situation using WattsRadiant software (which I think is very good) and I can get by in design conditions with feed water temps of about 85F.
  
• Additionally, if a radiant floor is used, the radiant mode tends to reduce temperature stratification in a room. Temperature stratification for heated air usually has a delta-T of around 10F or even higher. Since humans tend to sit or lie down when they relax, this usually brings them closer to the floor... at a height of about 2 feet or so. When they are in relax mode, they aren't self-generating as much heat and so higher temperatures are required to maintain comfort. So people tend to adjust their heating systems so that the temp for relax mode is in the neighborhood of 67F at a height of 2' from the floor. Temp stratification means that the temp at ceiling height will be around 77F (or more)... which increases heat loss through the ceiling. If a radiant floor is used, relax mode brings the person closer to the heat source when more heat is needed... all very natural... and air temps of around 65F at 2' above the floor will feel comfortable. There will be temp stratification with radiant floor heating but it will be less.

So there is actually a multiple win, from advantages of using water as a medium of heat exchange, and also from advantages inherent in radiant floors.

I have said before, but it is worth repeating that the gains to a fossil fuel system from using water as a heat transfer medium AND radiant floors are admittedly modest, but the gains to a heat pump system, using the very same strategy, are large because heat pump efficiency is so sensitive to 'temperature lift'.

I have tried various scenarios using the WattsRadiant program, and looking at various tube spacing to see what feed temps are required, and what difference exists between tubing under-floor, tubing-in-slab, and top of floor hydronic installations, and the differences are huge. Also, what goes on top of the radiant surface makes a huge difference. Putting a wood floor over the radiant surface and then a padded carpet over that really strangles the efficiency. When I modeled close-spaced tube + concrete board overlay + linoleum or ceramic or rubber tile... things really started to pop! I realized it was possible to get by with feed temps down in the mid 80s.

Gary came pretty close with his radiant floor project, using homemade spreader plates. I think he should have tightened up his spacings, and also used thicker aluminum, and topped it with thin concrete board.

I have found commercial products that will give me the efficiency I'm looking for (WarmBoard & Roth Radiant Panel & RAUPANEL. They're all top of floor, low mass, high efficiency and very expensive.

Just think of them as 'Serious Floors'.


-AC

[Acuario]

Sounds a similar idea to what I did with my boiler water preheater.. an update is probably in order after being absent for a while..

Well, to say it worked well is an understatement. I didn't need to turn on the oil boiler until the 2nd week in January and then only for about 6 weeks in total. Oil consumption dropped from 1500 Litres in a winter to 200 Litres, and this with both more house (170M2 instead of 100M2) and a constantly warm house instead of just morning/evening. I did change the windows and have cavity wall insulation installed so it wasn't all down to the heatpump.

I couldn't find the photos I put up before so I'll post the schematic and a couple of the project..

..just re-discovered the pages http://www.tortosaforum.com/boiler.html

Nigel

p.s. just today got given a Daikin inverter about 6-7Kw heating so looking for a project....