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Old 11-26-12, 06:15 PM   #1341
randen
Uber EcoRenovator
 
Join Date: Apr 2011
Location: Strathroy Ontario Canada
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Default Update for homemade GSHP for the shop

The 3.5 Ton homemade GSHP ran last heating season and provided enough heat to remain comfortable in the shop. A shop temp average of 17-19 Deg C was maintained The beautiful part about it was the heating bill was only about $350.00 as compared to the oil heating $2800.00.

The heat pump had required some additional tweeking. One of the tube and shell heat-exchangers was weeping a little but the whole unit had to be disconnected and disassembled to get at the leak. That annoying little leak had prevented the inclusion of glycol into the system so the HX (ground loop) can operate into the negative loop temps without the HX freezing.

The other tweek was a TXV instead of the capillery tube. This device modulates the amount of refrigerant into the evaporator adjusted by the temp of the refrigerant leaving the evaporator. I had purchased a TXV off ebay for a 3-4 ton air conditioner and I didn't realize not all are adjustable. I thought what the heck I have it now, I will install it maybe I'll get lucky. It's preset during manu., so maybe it will work. NOT.

After installation and purging the air from the loop and air handler the compressor wouldn't give a pressure differential. Damm. The TXV was installed with fittings so it could be removed and replaced with another or hacked. I guess at his point happiness was the pesky little leak was cured!!!

I disassembled the TXV and figured how to make it adjustable by combining a stem from a gate valve and the internal adjustment spool. The new TXV was installed system vacuumed and tested for leakage. All good. Reloaded the refrigerant and turned it on. It is suprising how sensitive the adjustments can be. As of today I'm looking for that sweet spot maximum heat gain with refrigerant charge and TXV adjustment keeping a close eye on temps presures and current draw. I guess the TXV is doing its job the pressure is more steady reguardless of temps.

So far no increase in performance compared to the capillery tube. Here are some of the numbers: Loop temp in 12 deg C return 11.3 Hot water from HX to air handler 33 deg C return 21. Refrigerant suction 70 psi head 275 psi Refrigerant temps Compressor head temp 72 Deg C after TXV 9 deg C suction temp after loop HX 11.3 deg C Compressor Current draw 13A ( this seems a little higher than with operating with the cap tube)

Today with the out-side air temp around -2 Deg C the shop temp made it to 18 Deg C. I would like to see a plus 20 Deg C. with of coarse a good COP. I will continue to adjust the charge and TXV settings to find the sweet spot.

Randen

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