I just went to a geothermal heating/cooling unit for the house, with 2, 300' wells as the heat sync for the geothermal unit. It comes standard with a "desuperheater" that puts waste heat into the std. electric hot water heater in summer, and it alternatively uses part of the heating capacity to more cheaply preheat the hot water heater in the winter. It appears the "desuperheater" is pretty much the same gadget as the "heat recovery unit" mentioned.
I too kept lookiing at this and wondered, isn't there a way to heat the pool???? But the main system already blew the budget to kingdom come, and trenching 100' down the hill to the pool with the geothermal loop seemed just too expensive. Not to mention, geothermal expertise is rare enough, messing with the pool too would go beyond the contractor's commonplace experience....and I prefer not to be on the bleeding edge.... I guess ONE way would be to power off the hot water heater, and top up the pool from HOT water. But with my luck, about the time the hot water heater was truly spent, my wife would go try to take a shower, and I'd be VERY unpopular....
My impression is that the pool would want A LOT of capacity in the spring/fall, possibly while the house still wanted heating.
My "if only money was no object" thought for northeastern Maryland (water eventually gets too hot in summer, but fairly short pool season and lots of snow & ice in winter) would be a second entire geothermal system, with its own wells/trenches/pond/whatever, and use it to HEAT THE POOL in the spring/fall/litle of summer, and to MELT ICE ON THE DRIVEWAY in winter.
Can't afford the thought, of course. So the pool is unheated, as it's been since 1971. FWIW, the pool water's been warmer this summer than ever before.
I just got a full month's bill AFTER BGE's recent 50% rate hike. My avg daily kWH consumption is down 23% from same month last year. Weather was 3 degrees F cooler on avg, BUT last month for half that time the #$%^& pool's been running 24hrs/day instead of 9 hrs/day 'cause of all the algae/other issues I've been having. So my bill went up about $35 instead of about $125. NOT BAD....won't directly pay for the fancy system but it sure helps, and in the meantime I get other advantages....no noisy 3 ton a/c outside, got rid of the underground oil tank (YEA!!), no loss of precious living/storage space to oil storage, etc....
Pardon the non-pool discussion, but I just can't see talk of a/c without going into it this year.... Combining full blown geothermal with pool heating would certainly be interesting....probably really effective....but probably NOT cost effective....