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Old 01-31-21, 09:29 AM   #4
IamIan
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The DIY heat pump approach I've been experimenting with is converting a used mass produced window air conditioning air to air style heat pump unit.

The mass produced effect means they are inexpensive , and even good condition used ones are available for even less $ (craigs list and such).

The power use scale is good for my current direction .. It takes about ~5kw of heat to heat my house (~800SqFt living ~600SqFt Basement work shop) on those cold single digit F winter nights .. A Heat pump with a COP of about ~3 means it should be able to do that for about ~1.7kw of electrical input .. of course that's isn't the common outside temp .. Soo the vast majority of the time 95%+ far less than they will be needed .. and future planed insulation upgrades will also further reduce the amount of kw needed.

My 1st experiments have been with the smaller ~500w (5-6k BTU) versions.

There are lots of videos and such out on the web of people doing similar for gaming CPUs , Brewing (Wine / Beer) , pet enclosures (aquarium , reptile).

Although the air / air style system works .. and I could blow the cold air where I want to take heat .. and the hot air where I want to give heat .. after only a little testing I decided I wanted to modify it to run as a liquid / liquid style system instead of air/air.

Air/Air is easier , and has the benefit of not needing to worry about frozen water breaking something .. but frost can build up and stop it from working effectively.

Water/water has some attractive benefits .. because of the higher specific heat and material density of liquids like water .. more wh of heat can be moved for a given dT .. that is good because the larger the dT the more it tries to leach out into places I don't want it .. ie. heat loss through a insulated pipe , container , etc is a function of size and dT .. to move the same watts of heat with air requires either larger volume containers (larger size = more loss) , and/or higher temperatures of that air (higher dT= more loss).

After carefully bending the coils out.

I 1st tried the dunk coils (evaporator / condenser) into water bath .. 55 gallon drum .. and it worked .. cold water sinks .. hot water rises .. soo, there was considerable temperature gradient .. which was good for cold side , but bad for hot side.

pic attached.

Then I scaled the dunk bath down to the size of the coil .. ~5Galon and ~8 Gallon. This reduced the temperature gradient effect .. progress .. from there I could then pump the heated / cooled water where I wanted it to go.

pic attached

To further improve the heat transfer from coil to working fluid I blocked off the bottom and sides soo that the water had to flow through the exchanger .. a little better.

pic attached

To further improve the heat transfer from the coil to the working fluid I made a form to go on each side , which will force the water to flow back and forth through the coil (snake like) .. Still tinkering with it .. not 100% done yet.

pic attached.

video
https://youtu.be/HLPhRFaLJXY

- - - - -

I'm still a little on the fence about the number of heat pumps .. But I am leaning toward 2 systems.

One for the inside storage to outside dT harvesting / expelling.
One for the inside storage to living space dT harvesting / expelling.

Something like the attached diagram.

The thermal storage can be regular water (even free rain water) .. the working fluid might be best to be distilled water or such so as to not clog up the heat pump coils .. where it could do bellow freezing (like outside run in winter) , will either need a 'drain back' design .. avoids need for glycol and such .. or , no need to drain back I use Glycol (or such) .. The inside runs will not ever go below freezing , soo that shouldn't be a issue anywhere else.











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Last edited by Daox; 02-01-21 at 04:17 PM..
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