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Old 09-05-17, 11:18 AM   #31
jeff5may
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With your buddy's window shaker rig, I would definitely run a water source ground loop. I say this because of the ease of drilling you have experienced. Also, the whole thing would be much easier to construct and debug. Water has much more heat capacity than air per cubic inch, so a half inch pipe carrying a few gallons per minute would move the same heat as a 4 inch earth tube carrying many cubic feet of air per minute. The squirrel cage fan required to pump hundreds of CFM through the earth tubes to the air conditioner would most likely cancel out any efficiency gain, where a much much smaller water pump would take a much smaller bite.

The rule of thumb is to start off with 200 feet of borehole per ton of refrigeration. So you would want to start with 4 holes 50 feet deep. Even though the ground loop would not be digesting the whole heat load, the more surface area underground the better. Testing the modified window shaker before drilling holes would give you a better starting point, but if drilling holes is simple, the added cost isn't such a huge concern.

For the interface with the window shaker, I would do the helical wrap on the existing plumbing. Due to the small diameter of the compressor discharge and liquid line, it would be easier to use two or three tubes in parallel to wrap the plumbing. The tubes are laid flat next to each other and then bent in a spiral fashion like a ribbon cable. Cold inlet next to the condenser HX and hot outlet near the compressor discharge.

Adding a "subcooler" HX could net more efficient operation, but the potential gain is much diminished compared to the hot discharge line. How much really depends on the weather and the ground loop efficiency. If the evaporative cooling done by the condenser and its integrated water slinger brings the liquid temperature below that of your ground source, the subcooler HX would be counterproductive.
For preliminary testing, the "desuperheater" HX could be run with well or tap water to determine effectiveness and optimum flow rate. The flow rate and Delta T of the water passing through the add-on HX is easy to measure. The airflow and Delta T through the existing condenser is not. However, the Delta T of the evaporator is. So the way to figure out how effective the add-on HX is regarding added cooling is to log the Delta T of the evaporator plumbing. First u-bend past the cap tube vs exiting suction line temperature. Change in cold discharge air indoors is somewhat misleading, as the latent energy cannot be directly measured.


Last edited by jeff5may; 09-05-17 at 11:56 AM..
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