Quote:
Originally Posted by MEMPHIS91
Ron, thank you. Yes I am still looking for a slightly larger compressor. But seeing as I can't find one right now, I am going to go ahead and braze on the txv I have. I was kinda worried that I would have to much pressure drop in the DX loop field for an internal equalized, but after running some numbers it looks like I'll be fine.
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Check out the attached document. For an external vs internal equalized valve, as long as you don't have a huge pressure drop, the extra superheat is not that significant. Unless you have a double digit psi drop, for R-22 or 290 the added superheat (aka loss of effective surface area) is going to be less than 7 degF. Figure 4 and figure 5 illustrate the difference. If you have a straight-through evaporator that's not seriously clogged or undersized, at the flow rates we use in nearly all of the builds on this forum, there will be pressure drops well below the example. For a 1 ton unit, a 5% drop in capacity is like 180 Watts on the refrigerant loop and like 50 Watts on the compressor side. The somewhat mismatched txv still beats the holy moly out of a perfectly matched cap tube in real life.
Now if we were talking about a 40 or 50 ton machine, the loss of capacity would make a difference. 5 or 10 percent of half a million BTU per hour is a lot of lost capacity. In large systems like that, cap tubes are not even considered due to the economics of scale. These systems are often regulated to target superheat values within a few inches of water column to save operating dollars. FWIW, there are 28 inches of w.c. in 1 PSI. The powers that be have moved on in the direction of electronic valves and programmable controllers to tackle this realm (think Tyson foods, Sysco, Smithfield, etc.) since every penny they can save effects their profit margins.