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goodguy
06-04-2007, 02:58 AM
Hi all,
I'm just throwing ideas around in my own simple mind but I've been wondering about maybe building a heat pump that can produce hot water enough for radiant heat. I know there is another thread that is discussing similar ideas.
Suppose I used a compressor that is rated to provide @ 40f evap and 110f condensing. Perhaps using 134A.

I would use ground water as the heat source @ 48f through a coaxial heat exchanger and using a second coaxial coil for a condenser

I think by using a 40-60 gallon storage tank hooked to a circulator that would pump water through the condenser would do the trick. ( depending on heat load of course)

As the temperature of the water rises,( lets say to 150f? or sooner) it could activate a small air cooled condenser to expel excess heat that would stay within the room(house.)
and if the compressor discharge temp got too high, maybe incorporating a quench valve to cool the compressor.


I think in theory this could work but am I wasting energy and money in such a way that I should just hook up a electric water heater? What water temp should I try to achieve?
What should the flow rate of my circulator be?
What refrigerant would be best
Any thoughts would be appreciated Thanks in advance.

Goodguy

taz24
06-04-2007, 12:04 PM
Hi all,

Any thoughts would be appreciated Thanks in advance.

Goodguy

The heat pump princeple is a very good cost effective way of generating heat.
You can get between 3 and 5 times the heat energy out for the cost of the electrical energy in.

You just need to be aware of maximum heat output. A good, well designed system can generate about 65degC to 75degC water temp but the higher the out put temp, the lower the efficency of the system.

In principle the idea is fine but a lot of thought needs to be put into it to get the best out of it.

Cheers taz.

The MG Pony
07-04-2007, 12:40 AM
Taz is right, I have hit a few road blocks I'm trying to solve, your idea is exactly what I was planning then I decided air source for the evaporator and yet my again change. For radiant heat I have figured all one needs is water to at least 40C and have it flowing all the time.

If you want to make it a revers cycle that is where it gets real tricky, thats my road block is how to make mine revers cycle capable.

If you all ready looked at my project R-134a seems to be a good choice, R-22 has hotter discharge though, set it up so the compressor has nice low temp suction gas and that should ensure it doesn't over heat.

BTY Where in Canada? I'm in BC.

Pooh
07-04-2007, 12:49 AM
Guys
the main problem I have encountered when talking to people about heat pumps is the fact that most people want flow temperatures of 50 deg plus for heating, my question to them is why so hot, if you do not turn the heating off during the day and night and just maintain the temperature flow temps of 40 deg are more than adequate even with standard radiators. It is an education process with the user as to the fact that the room temperature stays constant even though the radiator is only just warm.

Ian

goodguy
07-04-2007, 03:19 AM
Pony, Pooh,
With water flowing all the time how could you control the space and not over or under heat it?
A variable speed pump?

Is there a maximum water temperature where efficiency "peaks"? (Depending on the system of course. Generally?)

Pony,
134a or 401a seems to be the better choice looking at a pt chart. Lower boiling temperatures, and it would probably give better compression ratios for the compressor. I am on the other side of the country, PEI. Ever been? Heat is my only concern at the moment, the summer is too short. LOL

goodguy

The MG Pony
07-04-2007, 10:16 PM
Too cold you ice up your evap, the trick is balance, higher the suction pressure better compressor efficiency (Lower power usage) R-22 has a very high SP for a given evap temp.

Water at 40C the deltas will be small and heat transfer will modulate it's self mostly, what you do is use a three way temp modulated valve. So as the set point is reached inside the valve slowly shifts the water to a by pass loop back to the tank, compressor only comes on to keep the tank at 40C.

for a jerkier system you could use two solenoids, one shuts off when set temp reached and the other opens, no where as grace full as a 3 way modulated valve though, ebay is where one can usually score one of them cheap, I just got a 300 dollar valve for 60 bucks cad :D

No unfortunately I've never been out of BC.

Look at my project, you'll get some good info from there

The MG Pony
07-04-2007, 10:17 PM
http://www.refrigeration-engineer.com/forums/showthread.php?t=6808 < Here is the link.

And a schematic to go with my tops post discription.

Ooops! Got the FD on the gas discharge where it should be on the liquid lol!

And if you want to get real fancy you can use a V48AB-1 to divert flow to an auxilery water cooler, so say the tank is hot and the living area isn't calling for any heat as head pressur risses the V48AB-1 will divert the water to say a drive way heating loop or a snow melting loop to drop head pressurs :)

Added a nw corrected pic that may help you in deciding how to do it

AYIBIBIO
08-03-2008, 05:14 PM
I,m happy to read abuot your plan. Now, I also have same plans. I will like to remind you that you can use an air source unit, and use that extra heat for defrosting the outdoor unit when the need comes. I am planing to do just that. Remember that the hot water at the top (upper part) of the tank can get very hot due to stratification, and that is good news. Please don,t waste it, use the room termostart to controll the circulation pump, and the tank termostart to controll the compressor. This will let you have controll over the tank temperature.I will like to hear from you, because, I,m also trying to build same thing, but air sourcs. Hope to hear from you.