|06-09-17, 11:14 PM
You can measure the high side pressure to find out. The condensing temperature will follow the high side pressure and vice versa. The corresponding values can be looked up on a PT chart for the refrigerant being used. Any superheated gas leaving the compressor will not fall below its condensation temperature until it has all changed phase. Out of 1000 btu's of heat transfer, 950 or more of those btu's flow as the gas condenses.
On the water side of the heat exchange, it matters which way the water flows versus the refrigerant in the HX. Counterflow yields more heat transfer. Usually, the water will exit a few degrees cooler than the entering refrigerant.
In ChetT's proposed mod to his existing system, a BPHE could be rigged between the outlet of the slab and the inlet of the boiler. When the system first fires up, the water entering the BPHE would be slab dwell temp, and the heat pump would run at max energy savings to preheat the water entering the boiler. As the HP ramps up, the boiler could bridge the gap in capacity. Once the HP provides enough capacity, the boiler could stop for the rest of the cycle. Short cycling the boiler would not cause any adverse side effects.
Last edited by jeff5may; 06-10-17 at 09:20 AM..