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jeff5may · 01-13-16, 06:15 PM

With the system you propose, it doesn't need two reversing valves. Simply running the compressor discharge pipe through the water heater before it reaches the reversing valve will yield you ample hot water for all intensive purposes. In nearly all home systems, the space heating and cooling load requirements are much larger than the water heating capacity. Unless you are using your hot water for some other form of heating, that is. Or, say you have a family of eight girls, who take hot baths everyday. Or some other abnormal demand.

For the system you have drawn, you would need to size the water heating coil large enough to digest all of the compressor capacity to ensure that the TXV's would see only liquid. As the water tank temperature rises, the system would yield lower and lower performance until the demand is satisfied. Also, the rig would run short cycles at a high temperature differential to satisfy the water heating needs during periods of low (or no) demand. More importantly, the system cannot heat water and air at the same time. Some control would have to be devised to prioritize one over the other, and switch between them. You would definitely want to run some sort of high-limit sensor on the discharge line to make sure the compressor would not burn itself up or rupture some plumbing.

I'm not saying you can't do it that way. If you size everything correctly and account for the unknowns when this or that happens, the rig could do a good job for a long time. I'm just saying that a short (10 - 15 minute or less) cycle time will eat away at your energy efficiency.

01-13-16, 06:15 PM	#21
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	With the system you propose, it doesn't need two reversing valves. Simply running the compressor discharge pipe through the water heater before it reaches the reversing valve will yield you ample hot water for all intensive purposes. In nearly all home systems, the space heating and cooling load requirements are much larger than the water heating capacity. Unless you are using your hot water for some other form of heating, that is. Or, say you have a family of eight girls, who take hot baths everyday. Or some other abnormal demand. For the system you have drawn, you would need to size the water heating coil large enough to digest all of the compressor capacity to ensure that the TXV's would see only liquid. As the water tank temperature rises, the system would yield lower and lower performance until the demand is satisfied. Also, the rig would run short cycles at a high temperature differential to satisfy the water heating needs during periods of low (or no) demand. More importantly, the system cannot heat water and air at the same time. Some control would have to be devised to prioritize one over the other, and switch between them. You would definitely want to run some sort of high-limit sensor on the discharge line to make sure the compressor would not burn itself up or rupture some plumbing. I'm not saying you can't do it that way. If you size everything correctly and account for the unknowns when this or that happens, the rig could do a good job for a long time. I'm just saying that a short (10 - 15 minute or less) cycle time will eat away at your energy efficiency.