Geothermal loop and trees

Will planting spruce trees over a geothermal loop affect its performance?

Is it safe to combine a geothermal loop and trees? I installed a hoziontal closed loop system when I built my home in 2007. I was thinking of planting spruce trees over the loop bed and I have two questions: first, is it safe to do this, and second, is it desirable?

My supplier claims it is safe because the pipes are more than six feet down and spruce is not a deep rooted tree. But on the efficiency front I'm not sure what the impacts are. Would a cover of evergreen trees make the loop system more or less efficient? That is, would the trees keep the ground warmer in winter, acting as an insulating layer of tree cover, and thus improve winter efficiency? Would share from the trees keep the ground cooler in summer and therefore improve summer cooling efficiency?

Roy Pegg from Canada

Answer from Green Energy Efficient Homes

According to a relative of mine who has over 40 years experience as a forester, and also spends a fair amount of time at his solar-powered cottage in Central Ontario, combining a geothermal loop and trees should not be a problem if you stick to a shallow-rooted tree such as spruce. Spruce roots do not go much deeper than two feet, usually not even that, so there should be no problem with the spruce tree roots interfering with the operation of the geothermal loop bed, provided the trees are not planted near any tubing near ground level, such as where the tubing enters or exits the house.

As for the efficiency impacts of a geothermal loop and trees, my forester relative felt that spruce trees would likely moderate temperature extremes. The trees would lead to less snow cover, thereby reducing ground insulation, but at the same time increased biomass both above and below ground, which would have the overall effect of increasing ground temperatures in winter. In summer, biomass lessens ground surface temperature. Therefore, overall, planting spruce trees over your geothermal loop bed should enhance efficiency of the system compared to bare ground.

There are two other issues to consider. Horizontal loop beds are usually dug, the tubing laid, and the ground backfilled. First you need to be sure that the backfill was compacted enough to ensure roots don't penetrate deeper searching for water, which will happen if the soil is too loose or porous; the spruce roots may then grow substantially deeper than the two feet suggested above. Second, if the installationwas not done to specification, it is possible that the geothermal loop is not laid as deep in the ground as the six feet you stated in your question, in which case it is also possible that the spruce tree roots could reach down to the loop and cause some damage.

It would be pretty unusual for a bed purportedly dug to 6 feet to be substantially less than that, but if you never saw the loop go in, you have to allow for that possibility. But if you saw the loop go in (or put it in yourself), or you know your installer is responsible and dependable, this should not be a concern.

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