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Forum Index : Other Stuff : DIY heat pump designs

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Haxby

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Joined: 07/07/2008
Location: Australia
Posts: 397
Posted: 03:47am 12 Jun 2022
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Has anyone here built any DIY style heat pumps? If so, would you care to share your findings?

I hear LPG gas works well for the purpose, as long as there are no leaks.

I have a design in my head where a hydronic heating/cooling system for a house could be centred around an insulated 5000L poly water tank.

The poly tank stores thermal energy (instead of a battery) and is heated or cooled with a DIY heat pump that uses PV solar panels during the day.
 
Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1523
Posted: 01:17pm 12 Jun 2022
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I have had the idea for some time as well but still on the TO DO list.

I use LPG in all my cars Air con.  it works BLOODY well!
The new refrigeration gas , forget the name is supposedly  highly filtered LPG.
The charge weight is different to 134a So I just go by the pressures when I charge a system.  I run a bit high on the high side which still can be a little low on the low side but works fine.

The thing about leaking LPG is hysteria.  There has never been a case of the LPG in vehicle Crashes ( already used for many years in some countries) causing a fire or injury.  It's not like there is a 9 KG bottle's worth in a system, it's less than one of those little camping cartridges.

I am going to use a car system. They are equal in output to a mid size  domestic split unit so not exactly weak.  That said, the thermal capacity of 5Kl of water is huge!
If you heated water from 10o to 60o, that's 290 Kwh of thermal energy.
Even if you have a 3:1 efficiency on the pump side, still going to need 100KWH to get it there PLUS any mechanical/ conversion losses being DIY. If you can't do that in a day then the system will be limited to what you can. I would wonder if it would be better to run a smaller reserve at a higher temperature differential just so the tank is smaller and would have less area for thermal heat loss/ gain and easier/ cheaper to insulate?

For cooling, you are going to be trying to cool in the wrong part of the day using solar but there are workarounds to that too.

On real hot days I have a micro sprayer system set up on the condenser unit of my AC.
It uses about 4 L of water an hour and sprays a mist onto the condenser fins. This I have measured to drop the output temp over 20 o and can easily bring the compressor back into it's operating range where as being 45o can be outside of it and having it struggle.  Water is good for absorbing or storing a huge amount of energy and a bit of misting does wonders in this case.

Not sure what the evaporator would have to be like, may be able to just use one from an AC system and put it in the tank?

My idea was to use a small Diesel engine to drive the compressor as then I have the waste heat from the engine to feed back in the system for heating and gain efficiency there. I would just add a RX valve into the system so it could be used winter or summer being a car system is cooling only but not hard to do either way.

One thing I know, Hydronic takes a LOT of energy.
Best heating out there I know of, I spose cooling would be just as nice.

The the fall off insolation in winter you are going to need a LOT of panels.
Summer, not so bad as you production factor is 5-6 on the kw of panels you have installed so manageable. when it's down to 2-3 In winter.... Going to need your own solar farm I think.

A hybrid system with an engine and an electric drive would probably be the best of both both seasonal Applications.
 
johnmc
Senior Member

Joined: 21/01/2011
Location: Australia
Posts: 272
Posted: 12:20am 14 Jun 2022
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Dave, with Hydronics, the heat from the floor rises does that mean, if you piped cold liquid in the hydronics  system the cold would be lost to the ground.   ,
Cheers john
johnmc
 
Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1523
Posted: 12:34am 14 Jun 2022
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  johnmc said  Dave, with Hydronics, the heat from the floor rises does that mean, if you piped cold liquid in the hydronics ¬†system the cold would be lost to the ground. ¬† ,
Cheers john


Errrr, well..... Could be!  :0)

Hopefully it would still radiate into the house.

last night was pretty cold here. standing next to the windows they replaced wall with in this place, you can feel the cold falling  down creating a draft.
It was so evident, I taped one window up to make sure it was not a draft from poor sealing.
It wasn't unfortunately.

last winter I fitted some bubble wrap to the fly screens on the frosted En suite glass. Mrs threw a hissy fit and tore it all off.  Couldn't even really see it but she wasn't having it.

Really has no sense of how this sort of things work and is happy not to have, just pay the bills that I try to keep down.

I was looking again last night wondering where I could get cheap sheets of perspex from to fit them to the windows.  I don't think there is any remotely economical way or making this in any way efficient without spending more than it's worth to do so.
 
Haxby

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Joined: 07/07/2008
Location: Australia
Posts: 397
Posted: 02:17am 18 Jun 2022
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Good to hear from someone that has used LPG successfully Davo99.

I was thinking of using LPG with domestic air conditioning pumps, with all parts being housed outside the house. The heat exchanger inside the water tank would be just a 1/2 inch copper pipe. Nothing fancy.
 
Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1523
Posted: 12:54am 19 Jun 2022
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I cant see why it wouldn't work. The new gas is just LPG that is filtered finer supposedly and dried better.  You would have to make sure there was still oil in the compressors or add some.

As for the line in the tank, not sure about that. 1/2" is pretty big on the high side and you would be bound by what the TX vale was anyway. I think 1/4 or 3/8 would do it but then again may  depend on how long the run is and 1/2 may allow less due to the greater pressure drop and surface area of the tube.

OTOH, if you are heating water then that may reduce the expansion as well.
Not something I have looked into but you would need to find out about them I think.
 
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