[Goldwingnut]

Originally Posted by BlueStarAirlines

Are the heat pumps for a pool fundamentally different than those used to heat a house? We have had homes in Pennsylvania and Virginia that were solely heated with a heat pump and were fine throughout the most bitter winter. When other wrote they struggle with the cold winters in Florida, I'm just scratching my head.

Fundamentally they are the same, the difference is in the specific heat capacity of water vs that of air and the density differences between water and air.

Water has a heat capacity about 4.25 that of air, this is measured commonly measured in BTUs/lbm/deg F.

Water density is nearly 800 times denser than air.

Together this means that a cubic foot of water hold/requires about 3300 times more energy per degree of change than air.

Comparing a house to a pool - a 2000 sq ft house with 8 ft ceiling is about 16000 cubic ft of air to heat. A 12000 gallon pool is about 1600 cubic ft of water. The pool has about 1/10 the volume of the house but will require 330 times the heat to raise the temperature of the pool water 1 degree as it will take to raise the air temperature in the house 1 degree.

Also, because the humidity is lower in the winter, evaporation increases in a pool, as it evaporates it gives off its latent heat of vaporization of about 970 BTUs per pound mass or about 7500 BTUs per gallon that evaporates. This is more heat that will have to be replaced to keep the pool water warm. When you see the steam rising off the pool in the morning, that is heat that is escaping.

So, if you want to heat the water a lot of energy has to be added, a typical heat pump will add between 50 and 150 thousand BTUs per hour, this is the peak output, and it drops off as temperature outside drops off. A gas heater typically provides between 250 and 500 thousand BTUs per hour, regardless of the outside temperature.

Comparing the operation and outcome of a house heat pump to a pool heat pump, while fundamentally the same machine, is a huge difference in work output required and the resultant heating affect.