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Old 09-30-11, 08:03 AM   #1
Acuario
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Default Types of heat pump

Hi,

I've been looking at various designs of heat pumps and they fit into two main categories;
1. Air source
2. Ground source

Air source tend to be 'monoblock' with the compressor etc. fitted in the same box as the evaporator; the heat exchanger either being in the same box or elsewhere.

Ground source generally have both the evaporator and condensor in the same box and use brine as a heat transport.

I came across a third variation that has me interested; the only manufacturer I can find is Danfoss - I guess they know a thing or two about refrigeration!

The design seems to be a sort of hybrid; they circulate brine to an external evaporator that has air as its heat source, and the internal unit then has (as per a ground source heat pump) 2 heat exchangers for the condensor and evaporator.

Any thoughts on this design? It has me intrigued as one of the problems I've suffered with is icing of my evaporator on cold days (yes I need to build a control system to stop it but it's more fun to experiment).

Using brine then it would be possible to construct a large air source heat 'collector' that would operate at very low temperatures and hopefully wouldn't freeze up..

Search Google for Danfoss DHP-A (note it's not the DHP-AX) to see what I'm on about.

Nigel


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Old 09-30-11, 03:35 PM   #2
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Originally Posted by Acuario View Post
Any thoughts on this design? It has me intrigued as one of the problems I've suffered with is icing of my evaporator on cold days (yes I need to build a control system to stop it but it's more fun to experiment).l
Hi Nigel,

I looked through the sales literature, but I don't quite get the whole layout.

As far as I understand, there is a remote outside unit that is an ASHP, and it uses brine to transfer heat to the inside unit which seems to be the water tank. Am I getting the scheme?

At any rate, there is wording in the literature that says, "Defrosting is done automatically only on demand which further boosts efficiency", so apparently, just having brine does not eliminate the frost, the unit just has an intelligent way to handle the frost as it forms, rather than having a repeating defrost cycle, whether there is frost or not.

Otherwise, if my understanding is correct, this unit is not so very different from the Daikin Altherma. This system uses a monobloc to extract heat from the air, and then to send water into the house where it could be used for domestic hot water. The heated water coming into the house is then used for space heating via air convection (probably less efficient) or hydronic radiant floor heating (probably more efficient). Their system can also allow for solar thermal input, when it is available.

So, how do you plan on hacking a system together as you have envisioned it? I'd like to know more of your thoughts.

I am actually thinking along related lines myself, especially when I realized that there were days last winter when the air temp was actually higher than the ground source loop temp where I live.

I'm thinking along the lines of a hybrid ground-source/air-source system. I already have a small loop field in place, and it would be to my advantage to utilize the heat in the air when conditions are favorable for that.

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Old 09-30-11, 08:56 PM   #3
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Default Interesting..

If I went with a HX on the spare Sanyo, it would be configured like the Daikin Altherma Bi-Valent setup..



Which is almost what I'm doing right now. Turning off the Sanyo below 5deg F
and turning on the oil heat (forced baseboard hot-water).
I just call it the Hybrid Mode.

Having the HydroBox outdoors might be a good idea, just in case the
government gets really crazy and outlaws R410A, and forces us to use R290..
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Old 10-01-11, 12:45 AM   #4
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Which is almost what I'm doing right now. Turning off the Sanyo below 5deg Fand turning on the oil heat (forced baseboard hot-water). I just call it the Hybrid Mode.
You'll need a lot more radiant area if you expect to successfully drive your hydronic heaters with your Sanyo. It just won't produce the same high feed temps as your oil burner.

Quote:
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Having the HydroBox outdoors might be a good idea, just in case the
government gets really crazy and outlaws R410A, and forces us to use R290.
Well, R-410a was meant to solve the problem of destroying the ozone layer, which it did. In fact, G.H.W.Bush couldn't be concerned with ozone depletion until a hole in the ozone opened up over Kinnebunkport, ME, which is where the Bush family vacation home is located. Then he took it serious.

Problem is that R-410a is a very serious global warming gas, and it takes a very long time to break down.

Propane and Butane are both good refrigerant gases, but there is the no harm to either the ozone or global warming.

Carbon Dioxide is a great refrigerant gas, no ozone problem and eventually it gets taken up by plants. But no corporation has a patent on it, so revenues will suffer.

Too bad that these problems can't be wished away. It would be so much easier that way.

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Old 10-01-11, 03:12 AM   #5
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The difference/benefit is that there is no restriction on the size of the 'heat collector' - as is the case with ground source, put in as many loops as you want.

Ok, in the case of the Daikin they provide a pre-built external box, presumably with the typical heat matrix, fan etc. but it's the idea of being able to effectively use the ground source principle of 2 'water' circuits + the closed loop refrigerent circuit that has me interested..

The size limit of the heat collector (evaporator) goes away for air-source, which is the limiting factor when hacking, so, logic says, if it's big enough it isn't all going to frost up. Where I live there is no possibility of ground source due to the amount of rock so air source is the only option; fortunately I have quite a lot of roof area that I can experiment with. On one website I did see mention of a 'fence' collector - same sort of thing I guess.

Nigel
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Old 10-01-11, 10:34 AM   #6
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Nigel, you got me thinking about a cold-weather add-on..

Assuming that I had a small geothermal 60F (15.5C) heat source..
I could dip into that geo-source during extremely cold weather.
(When there was very little heat in the air to be harvested).

Here's the first revision.


The Geo-source: Perhaps a few hundred gallons of solar boosted water in storage.?.
Or maybe a pair of small wells in the back yard?
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Old 10-01-11, 12:11 PM   #7
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Originally Posted by Acuario View Post
Ok, in the case of the Daikin they provide a pre-built external box, presumably with the typical heat matrix, fan etc. but it's the idea of being able to effectively use the ground source principle of 2 'water' circuits + the closed loop refrigerent circuit that has me interested..
OK, I understand where you're going here...

Too bad about the soil (rock) conditions there. It would be truly useful to have an earth reservoir, not only for heat harvesting, but also for heat storage. But if the rock conditions are as bad as you say, then that's not an option. (However, you might want to monitor what Geo NR Gee is doing, on the 'manifesto' thread, with regard to drilling through rock. He has acquired a tricone bit and is about to do some rock drilling, himself)

So, you're considering using multiple ASHP heads, each feeding into a brine circuit, and an evaporator HX for extracting the heat from the brine circuit. Correct me if I got that part wrong.

Since you're making your own HXs, you may not have any performance data, so this is gonna have to be a pretty intuitive endeavor. Either that, or you can build slowly, do performance testing as you go, and adjust as measurements dictate.

Some thoughts I have about this project:
  • Brine is corrosive. you won't be able to use inexpensive iron pumps or valving.
  • You'll want to insulate the brine loop to keep the heat in.
  • You'll want to size your brine loop flow rate to accommodate your maximum load situation. There will be times when you won't need to run the maximum number of ASHP heads.
  • Controlling the various heads, pumps and fans will be a creative challenge in itself.
  • You'll want to size the brine loop, so as to reduce friction, so that you don't need a large circulation pump. This involves factors such as: fluid viscosity, fluid flow rate, pipe diameter, heat exchanger head loss, check-valve head losses, and pipe length.
  • Since you'll likely have a varying number of ASHP heads coming on and off, you'll probably want a 'smart' circulation pump like the Grundfos Alpha or similar.
  • I would think that having your ASHP heads in parallel, with a check valve on each parallel branch would be the best approach.
  • There is an 'inefficiency penalty' of about 10% per heat exchanger, so you'd pay the penalty at the ASHP/brine heat exchanger, and also at the brine/inside heat exchanger.
  • If you had some kind of heat storage tank, like a big water tank that was well-insulated, it would open up other possibilities, such as solar heat storage, when available, bio-mass heat storage, propane or oil or gas heat storage, if there were favorable market fluctuations, storage of 'waste heat' from refrigerators, generators, etc.

As a source of helpful information, here is a link to some information that could prove useful to designing and implementing this project. For starters, I would reccomend issue 9, from 2011, titled: "Geo-Hydronic Systems". I recommend this one for it's treatment of heat transport and fluid mechanics. Others may be equally valuable, and since you are a clever maker, you can probably fabricate many of the items they are trying to sell you.

All in all, I think this would be a great project. No one else on EcoRenovator has seriously proposed a project that has so much potential. From what I have seen of your clever and persistent approach to solving problems, I think you will surely succeed.

If I or anyone else on this forum can be of help, please ask. Let us know about on-going ideas, problems, progress.

Good of luck on this project. Don't forget, lots of pictures!

Best Regards,

-AC_Hacker
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Old 10-13-11, 01:42 AM   #8
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Default Types of heat pump

Hi,
I will suggest you to visit GeoPro Design: A full Geothermal System Design and GSHP Installation Services here you will get full knowledge of Ground Source Heat Pump design and its installation procedure in full detail.
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Old 10-13-11, 12:37 PM   #9
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Hi,
I will suggest you to visit GeoPro Design: A full Geothermal System Design and GSHP Installation Services here you will get full knowledge of Ground Source Heat Pump design and its installation procedure in full detail.
I am puzzled by your post.

Are you aware that EcoRenovator is a DIY forum?

In what way do you think that the web site you suggest will be useful to the DIY community?

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Old 10-13-11, 02:30 PM   #10
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Hes probably just a spammer. He just hasn't been banned... yet.

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