Fluids & Treatment - Water

Water is the least expensive circulating loop fluid. Its main disadvantages are its relatively high freezing point of 32°F. and that it expands upon freezing, rupturing pipes.

It has a density of 8.334 pounds per gallon at 60°F and a specific heat, for practical purposes, of 1.000 Btu per pound per °F. At 40°F its viscosity is 1.550 centipoise.

The refrigerant temperature in the evaporator runs about 10°F lower than the exit water temperature. Antifreeze protection is required when there is a possibility that the minimum operating evaporator refrigerant temperature will drop to or below 32°F.

The coldest expected evaporator exit water temperature during heating operation determines the required fluid freezing point. The earth coil fluid freezing point should be about 10°F below that exit temperature. This freezing point then determines the solute concentration required to protect the heat pump evaporator from freezing.

The physical properties of the various antifreezes are available from several sources, such as the manufacturer's published data, and the Chemical Engineers' Handbook. Appendix A of the IGSHPA Installation Guide and Appendix B of the ASHRAE Commercial/Industrial Ground-Source Heat Pump Engineering Manual.