Water to Air Heat Exchange for Summer Cooling
Need someone with Math skills here to calculate the effectiveness of using a Water to Air Heat Exchanger to cool a home in the summer using a system of ground loops circulating glycol with no heat pump involved. Just circulating fluid through the ground loops and running a fan through the heat exchanger. We are in Zone 4 but close to Zone 5. Assuming the temperature of the earth is 56 degrees, and the maximum summer temperature is 95 degrees, how many linear feet of 3/4″ pipe would I need to lay in order to keep the home at a comfortable 74 degrees? We may add a hot water solar panel in the future to add heat if it is feasible. House is roughly 3000 square feet, built in 1960 with R13 in the walls, attic has been reinsulated to R45, all windows are new with U-factor of .30. We have been working at air sealing as well.
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Replies
I don’t think your idea is viable.
You need about 15° if temperature difference to move any real amount of heat. So, your loop will be 15 ° or so warmer than the earth and to move any heat the house would need to be about 15° warmer than the loop. You only get that for the few peak hours a year. Note your earth temp will increase near your tubes over time if you move any heat and every watt hour of electricity you use to pump the water will add 3.4 Btu to the water temp.
If only life were so simple.
Walta
"Assuming the temperature of the earth is 56 degrees" this is the rub - the temperature is stable enough UNTIL you start extracting/adding heat to it. I'd explore solar PV + Heat pump before ground source cooling or solar hot water heating. Generally, your money will go much farther with far less engineering risk.
First step is to calculate how much cooling you need.
This document will tell you the heating and cooling design temperatures for your county:
https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/County%20Level%20Design%20Temperature%20Reference%20Guide%20-%202015-06-24.pdf
There is an article on GBA about how to size your heating system based on your fuel usage. I don't have a link handy. Based on your actual heating load and your design temperature you can estimate your cooling load. Once that is done we can talk.
The article is at: https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler