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Old 11-16-15, 06:33 AM   #1
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Default DIY "Micro GSHP" (on the cheeeeap)

For about 1-1/2 year I lived in a motorhome on my own land while I built my new home. It was originally propane heat, but weighing anchor and going to fill up the propane was a big problem. So I used electric "space-heaters" for a little while. After a month or two I developed the worlds least expensive pump-and-dump GSHP.

This abomination worked well, kept me warm and never failed. I still have it sitting in the shop to re-purpose the compressor for another project.

I saw a substantial reduction in my heating bill vs electric and propane. In cooling mode, these little 5K window units are pretty efficient. In heating mode, you get the ~500 Watts or so back as heat from the compressor, rather than throwing that away. So they actually put out around 6600 BTU/Hr of heat. I measured my LG branded unit with a Fluke 87-V meter and saw around 480 watts of power consumption at peak load. The unit only blows around 85*F - 95*F air in a typical 60* F - 70* F room.

Basically you can get around 12 to 14 BTU / Watt with one of these little guys. I was seeing a COP of approximately 4.05 with mine, not including the well pump that feeds it with water. With the well pump I was estimating around 2.75 COP which is far better than the space-heaters. If you had a small ground loop or bury a coil in a pit with a little Taco circulator you could bring this thing into the 3.5 COP range pretty easily.

When complete I think I had somewhere in the $50 to $70 range in all the materials.

I checked out craigslist and found a couple of 5000 BTU/Hr "Window units". They go between $10 - $50 around here in the fall and winter because people with apartments don't want to store them.

A trip to the local hardware box-store gave me the remainder of the materials I needed.

1) 1/2" NPT sprinkler valve
2) 1/2" NPT x 5/8" ID hose barb fitting
3) 1/2" NPT x 1/4" ID hose barb fitting
3) 3/8 OD x 1/4" ID nylon tubing (transparent & flexible)
4) 1/2 "FPT" x 3/4 "MPT" threaded PVC bushing
5) 3/4 "FPT" x 3/4 "FPT" threaded PVC coupler
6) 1/2 "MPT" x 5/8" ID hose barb 90* elbow fitting
7) Two standard garden hoses, length will vary
8) Assorted hose clamps per the above items...
9) 24V sprinkler power adapter (or a 24v doorbell transformer)
10) Short extension cord with a grounded (3 prong) outlet
11) Thermostat for a baseboard heater ($10 part at lowes / home depot)
12) 15" x 18" x 8" Rubbermaid Tote with lid
13) 16" x 20" piece of scrap plywood, OSB, etc.

Here's a quick tip: Grab the tote first when you get to the store. You can carry all that other little stuff in the tote.

Disassemble the entire window unit and carefully remove the refrigeration assembly (compressor, condenser, evaporator, etc) from the steel chassis plate. (It helps if you label the wires with a sharpie and masking tape, unless you are intimately familiar with how these things wire back up).

Cut the plywood to fit on the top of the Rubbermaid tote, then place the refrigeration assembly on the top of the plywood.

Trace the compressor bolt pattern and condenser mounting bolt pattern on the wood. Drill holes and make sure they bolt down.

Using your best judgement, safety goggles, face shield, gloves, etc. bend the evaporator coil (cold / indoor side) down flat against the wood. (If a line bursts and maims or kills you, don't sue me you cheap f*^@&er. This is a risky deal bending pressurized copper.) Make a guestimate of where the lines need to go through and mark the wood.

Remove the refrigeration assembly from the wood and make your cuts. You need to drill a hole with a hole-saw, router or step-bit big enough for both lines, then connect it to the nearest edge of the board.

Bend the evaporator coil (cold / indoor side) down until it is under the compressor and condenser coil. Slide that assembly onto the board for a test-fit. Adjust your cuts & trim as necessary.

Cut a single hole and slice the Rubbermaid tote lid to mimic the holes in the wood.

Assemble the Rubbermaid lid, wood base and compressor assembly together using bolts and screws.

remove the fan blade off of the evaporator side of the motor. It's usually a centrifugal type fan while the condenser fan is of the axial type. The axial blades are brittle, be careful not to flex it. They are made of glass filled ABS.

Mount the fan and shroud so that the axial blade blows air through the condenser coil as it was designed to do.

Now drill a hole about 3/8" diameter straight down through the wood and the Rubbermaid lid. Opposite corner of the compressor might be a good location.

Drill a large hole (sized for a 3/4" pipe thread) near one corner of the plastic tub about 3/4 of the way up the side (approximately 2" from the top edge).

Install the 90* elbow 5/8" hose fitting and PVC coupler/bushing pair into that hole as a pass-through with plenty of sealant. This will be the drain hose.

Install the 2 feet of nylon 3/8" OD tubing on the sprinkler valve using the plastic barb. Use the 5/8" OD barb on the other side with a length of garden hose. This will be your water supply. The 3/8" nylon tubing goes into the top of the tub in the 3/8" hole you drilled previously.

Remove the "close on rise" thermostatic bulb from the system, you won't need it. Replace it in the wiring scheme with the "open on rise" baseboard heater thermostat from the parts list.

Cut the female end off of the extension cord and wire it to the output from the thermostat (parallel in circuit to the compressor). This will allow you to plug in the 24v sprinkler transformer to power the sprinkler valve.

The sprinkler valve wires up to the transformer. Some solenoid valves need a rectifier diode in circuit, others don't. The green one I used doesn't need it, so 24v AC was fine.

when the compressor comes on, so will the water flow. The 3/8" tubing will probably be too much flow. You can use the tube from an old pen, or some smaller tubing, or kink the 3/8" tubing with a zip tie to create a restriction.

You are shooting for around 1 to 1.5 gallons per minute of source water flow... Here's the math:

Roughly 5000 BTU/Hr refrigeration system.

Target around 10 degrees F water delta-t across the evaporator
Assume 48F source water inlet temp (lowest I saw with that system)

5000 BTU / (10 degrees * 8.34 lbs/gal * 60 minutes/Hour) = about 1 GPM

You can use a 5 gallon bucket and a stop watch. Restrict the flow until you get it up to approximately 2-1/2 minutes to fill the bucket to the top rim.

For you guys in the metric world, that's around 15 - 18 LPM. So fill a 20 liter pail in about 2-1/2 minutes.

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Old 11-16-15, 08:06 AM   #2
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This is an awesome proof of concept experiment for rookie hackers and those who doubt the viability of phase change systems in general for heating purposes. The effectiveness of the lowly 5000 btu aircon unit unit will surprise you. It will heat a large bedroom well, and for the frugal of thermostat, it will keep that gas blaster central unit from running up the cubic feet quite effectively. For a larger home, a larger aircon unit can be modified in the same manner to provide more heating capacity.
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Old 11-16-15, 03:54 PM   #3
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Good use of a 5k unit. Curious where you are pulling the water from. Is it ground sourced or a pond or what? I imagine in Washington the ponds and lakes don't freeze too often.
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Old 11-16-15, 08:19 PM   #4
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Jeff5may, that's what made me decide to post it. I constructed this unit as a self-teaching tool and proof of concept for GSHP. I learned enough to successfully build and install my 4 ton unit.

MN_Renovator, the water was coming from a well I have on the property. I am currently sourcing about 60% of the heat for my 4 ton GSHP from the same well. My land is on a lake and I have some artesian springs that feed a small pond via a stream. They rarely freeze during the winter. When they do freeze, it's very thin ice and only lasts from few days up to a week.
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Old 11-17-15, 08:37 PM   #5
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Originally Posted by TechShop View Post
I constructed this unit as a self-teaching tool and proof of concept for GSHP. I learned enough to successfully build and install my 4 ton unit.




I'm not an HVAC technician. In fact, I'm barely even a hacker...
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