Propane (R-290) heat pump heating a hydronic loop

A single-stage vapor-compression heat pump delivering heat to a space-heating water loop — the same cycle as a refrigerator, read from the hot end. Propane evaporates at 4.7 atm (273 K, an air- or ground-source evaporator at 0 °C), is compressed to 21 atm (condensing at 333 K, 60 °C) and condenses against the heating water in a real two-sided exchanger, so the delivered heat is a water stream you can read: 40 °C return warmed to 59 °C. A small makeup feed and purge close the refrigerant mass balance around the recycle, as in the refrigeration examples. Two numbers define the machine: 80 kW delivered for 28 kW of compressor work, a heating COP of 2.9 — 52% of the Carnot limit for this 60 K lift, which is where a real R-290 unit sits. Read COP on the flowsheet as the user variable cop_heating, or sweep the condensing pressure: from 18 to 27 atm the COP falls 3.2 → 2.6 as the lift grows, the trade every heat pump makes between water temperature and electricity. Honest scope: the compressor is a fixed isentropic efficiency, the condenser outlet is a specified subcooling, and there is no defrost, part-load or refrigerant-charge model. Below ~18 atm the specified 326 K condenser outlet sits above saturation and the cycle stops condensing — the sweep starts where the physics does.