|03-30-09, 10:11 AM||#1|
Join Date: Mar 2009
Location: Portland, OR
Thanked 722 Times in 534 Posts
The Homemade Heat Pump Manifesto
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I live in an older small house (< 1000 square ft.) built in 1892. I am going through the whole house, meticulously insulating it with expanded poly styrene board. I tore off the lath & plaster, increased the thickness of my walls, and I'm layering in 6 inches of rigid foam into the walls, ceiling, and under the floor.
So I'm thinking ahead to a highly efficient heating system. As best as I can determine, a Ground Source Heat Pump (AKA: GSHP) running warm water through a thin (1.5 inch), radiant concrete floor is my best bet.
[* NOTE: Subsequent study suggests that a 'sandwich' style hydronic floor with close-spaced aluminum spreaders will be easier to build and at least as efficient as a thin suspended concrete floor, but that comes much later in the story. *]
I don't have much money, but I am resourceful and very stubborn.
I have found out that the approximate size of a heat pump I'll require is slightly under 12,000 BTU/hr. In HVAC speak they call 12,000 BTU/hr a 'Ton' of Air Conditioning. Your mileage may vary.
I have also found out that here in Western Oregon (Portland), a GSHP will require a borehole about 200 feet deep. It could also be two boreholes about 100 feet deep, etc... Again, your mileage may vary.
I also found out that heat pumps are classed as Air-to-Air, Water-to-Air, and Water-to-Water.
The kind I need is Water-to-Water. The kicker is, that the smallest I have been able to find is four ton (48,000 BTU/hr). So this means that in order to proceed with the project, I'll have to build my own heat pump. In HVAC, bigger is not better... just slightly smaller than big enough is best, economically speaking.
I have built a proof of concept unit that works. Here's a photo:
I built this unit last summer and did some testing. Here's a performance graph:
The COP is calculated for each measurement period, and changes quite a bit, but the overall COP is quite good.
So, is anyone interested in such a project? I have already built a prototype heat pump, it is working and I have tested it and the test results are very encouraging. I have attached photos and performance data at the end of this post.
I am now in the hole drilling phase. I built an earth auger, which would have worked really well in other parts of the country, but in Oregon, where I live the drilling is not so easy. I have increased the power of my auger 20X and I'm getting ready to dive back in.
A properly designed system as I'm describing should be able to operate at an efficiency of over 300%. My prototype has actually shown efficiency over 400%. In HVAC, efficiency can go over 100%, because the electrical energy that is input is not directly converted to heat, but is being used to move heat from one place to another. Strange but true.
So, there are four parts to the project:
0. Determining your heating load.
Free software is available on the web for this. It is also possible
to measure directly, the energy you are using. I have done both.
1. The Ground source loop field.
Here in Oregon, where I live, an 80 foot long, three foot wide,
by four foot deep trench containing about 300 feet of slinky
loops of plastic pipe, per Ton (12,000 BTU/hr) is required.
(* or *)
Two hundred feet of borehole per Ton is required.
2. The Heat Pump.
I have found that air conditioners and de-humidifiers can serve
as a starting place for DIY heat pumps. These can be had for
cheap to free. German children are using Propane gas as a
refrigerant for cooling CPUs so they can play video games faster.
What a concept!
3. The radiant floor system.
From all I have read, nothing beats PEX in concrete for efficiency.
This is seriously messy, but the technology involved is very
I'd really like to get other people interested in this kind of project. Commercial units installed run $15,000 to $45,000 and up. I'm estimating that I can get mine going for under $2,000. Maybe under $1,000. So far I've spent about $400.
So, let me know if there's interest... I have loads and loads of information I'd like to share.
If we are not the people who can re-purpose pieces of junk that are now headed to the scrap yards and turn them into state-of-the-art high-efficiency home heating systems, who's going to do it?
P.S.: Here's a link to a PDF which will serve as a good overview to our project:
Last edited by AC_Hacker; 09-11-17 at 04:14 PM.. Reason: in-line images, better performance graph
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