Note the substantially higher average borehole depth reported in the slides from Sweden. The graph suggests 580' (178m) average if I am interpreting it correctly. That's almost double the average depth in the US. (from the slide set Erin shared)
Yes, that is correct. Note that the use of GSHP's is primarily for heating. Depths of 300m (980ft) are also not uncommon.
Just to clarify the slide from my talk (below) - The "All boreholes" data represent Sweden, not the whole EU. But it includes both residential and commercial projects. Over much of Sweden, granite bedrock is fairly shallow and the boreholes are constructed more like water wells, cased to bedrock, with a U-tube suspended in the water column. Boreholes are registered in Sweden, so the data set, courtesy of Dr. Signhild Gehlin of the Swedish Geo-energy Center, is reasonably complete. As Roshan mentioned, the systems are often heating only
The red data (for the USA) comes from Ryan Carda of GeoPro. It was collected from commercial project databases and represents only projects that are publicly bid, with the average number of boreholes being about 100. So, I would guess that this is average is probably higher than the actual average, if we could include much smaller projects. But, this is the best data I know of for the USA. If any readers know of other sources, please let me know.
Dr. Gehlin will present a more detailed analysis of the Swedish situation, including a breakdown between residential and commercial project borehole depths, at the IGSHPA meeting in Denver next March.
Thanks Ryan and Sigge for the data!
It's like deja vu all over again (I miss Yogi), being located in the Northeast US, many years ago I was being strongly encouraged by our PE pipe manufacturer to use 3/4" loops because that's what the rest of the country uses.... However, the rest of the country has a very good chance that "mud" drilling is the most cost-effective and appropriate drilling technique. However, in the northeast, "every hole is a new adventure" with bedrock being anywhere from 1 to hundreds of feet below the surface, where having air-rotary and setting casing is required the optimum depths quickly go to the 400 too 500 foot range. New York State has a arbitrary 500' limit only because an additional permit is required to go deeper than 500'. Outside New York we have designed to 600'. We have also adopted 1 1/2" when we go deeper than 450' just to aggressively attack pressure drop.
My point is that the appropriate depth is dictated by local geology, available real estate, and possibly regulations, rather than any real concern regarding performance.