I ran a test this weekend to measure how fast the basement floor will heat cold water. I purchased 60 pounds of ice and put it in the first tank. Next I added water from the garden hose and let the mixture sit for a while. Once almost all of the ice was melted I pumped the water into the second tub and measured the water temperature in thirty minute intervals. Here are the results:
0.0 32.3 0.5 34.2 1.0 38.3 1.5 38.6 2.0 39.9 2.5 41.1 3.0 42.1 3.5 42.9 4.0 43.7 4.5 44.5 8.0 54.9
All of the measurements above are in Fahrenheit, but I converted them to Celsius for the rest of the calculations.
The tub contained 88.3 liters of water and in the first hour the temperature rose 3.33 degrees Celsius. Using the equation
E = cp dt m
E = (4.2 kJ/kgoC) ((3.50 oC) – (0.166 oC)) (88.3 liter) (1 kg/liter)
E = 1,298 kJ => 0.36 kWh
So in the first hour the foundation of the basement added 0.36 kWh of energy to the water. Given the tank can hold up to 378 liters it has the potential to store the following amount of energy.
E = cp dt m
E = (4.2 kJ/kgoC) ((12.72 oC) – (0.166 oC)) (378 liter) (1 kg/liter)
E = 19,924 kJ =>5.53 kWh
Estimating that the tank can heat up from 0 to 12.6 degrees Celsius in 8 hours it would have the potential to provide 500 kWh of energy per month to provide hot water.
While this test provides some very positive data I should bring up the rate of heat transfer will depend on many factors that might not be reflected in this initial test.
The surface area of the bottom of the tank: The larger the surface area the faster the heat will transfer to the water. Flooding the entire basement with water would provide the optimal heat transfer rate but could pose logistical problems for homeowners.
Rate of heat transfer: This value will depend on many factors such as the materials used in the tank, the amount of fluid movement in the tank, and the rate of heat transfer in the foundation.
Volume of water in the tank: I didn’t completely fill the tank for this test, so the rate of heat transfer will be different for a larger volume of water. Adding water in the tank would allow the compressor to run less frequently, but also adds complexity to the system in terms of structure and cost.