Earth Tubes are a way to take advantage of near constant subterranean temperature to warm or cool air. In this case, we are looking at pre-cool/pre-warm the air inlet to the house ventilation system (ERV). With our energy modeling software (do we want to specify Design Builder?), we modeled 8” diameter earth tube buried 4’ underground around the perimeter of the house. The following graph shows the tempered air inlet temperature with the earth tube compared to the outside air temperature without the earth tube. Client could see that the tempered air temperature in red is a lot more stable and milder that would have been without the earth tube in blue.
This tempered air then entered the ERV system. Below are the comparison graph of the cooling and heating capacities with and without earth tube.
The modeling software does not come standard with the capability to model earth tube as a preheat/precool of the outside air inlet to the ERV system. Thus, we worked with the software company to develop a custom script to model this. We faced some glitches in making the scrip works but to see it work, it is quite exciting.
The kWh savings by adding earth tube per year is almost 340 kWh and offset about 220 kg CO2 of carbon footprint.