A couple years ago I sent one of my best techs to a 3 day class on geothermal. He learned how to do everything but design a two-well open loop system, where the second well puts the water right back underground.
We're in Michigan. In a whole lot of places there's groundwater at a 5 to 20 foot depth. That's especially true when you get into more rural areas, as population and buildings are mostly found nearby lakes and rivers (tho most not with frontage on the lake or river). In most cases the houses have domestic water provided by an 1-1/4 inch shallow well with a screened wellpoint at 20-25 feet. They are often hand driven by a HO in a day's time and deliver 5 gpm or more, at 40 psi, with a 1/3 hp shallow well pump. And yeah, the HO doesn't grout them - or permit them.
We've (ground)water, (ground)water everywhere! And it's really very mineral-free at that shallow level. So scale wouldn't be a problem.
Yet, from what my guy learned, everybody is burying long coil loops or sinking deep wells for closed loop vertical systems where space prevents the coil system. That seems to me to be an expensive way to go, rather than quickly sinking a couple (or even six or eight) 20 foot shallow wells. But I'm really dumb on the subject - and can't seem to find much on it (even when I popped $300 for a man to get educated on it.).
I can see that pump horsepower could become an issue in a dual well system, yet it also seems to me if you've two water columns at equal weight and height, the pump hp ought to be the same as on a closed loop, once primed and full. At the shallow level, the water columns are held up under vacuum, so the head is just friction, not height, same as in a closed loop system, tho there'd be some add'l friction at the screen points, I'd guess. But since I can't find any info on it, I sure don't know how I'd calculate it.
I'm in the Detroit area where geothermal is super rare and we currently do virtually no residential work, just commercial service and some retrofit. I started looking into it a few years back, thinking that it was what the future would be, and the direction the company might need to go, just to keep guys working, even if we had to start bidding these systems in other areas.
I guess what got me interested was a single call I ran on one system, the only one I'd ever seen in the area, so even tho it was residential, I took it. The system was water to water and kept freezing up when in "chiller" mode. The factory cure was to glycol fill it and had shipped the HO 15 gallons of glycol. There was an A/H in the attic of the two story house that went air bound when I dumped the water. There were no vents in the piping and no valves or unions either on it or the other A/Hs. So my transfer pump couldn't get it purged. The pump for that A/H was also in the attic, with no valves around it, so I couldn't even use it to purge the air. I could have done it if I was putting water back in, because of the flow rate and pressure from the fill valve in bypass, but not with a transfer pump. It turned into a very expensive call for that HO because the installer - who might have understood how to dig up the backyard to lay a loop, didn't know the basics of hydronic piping regarding vents, valves and unions. So, I started to see a potential in the biz. Plus, the "factory cure" struck me as a bad way around a bad design. But I didn't bother to get into that.
Is the problem with a two-well system code related, where "injection" back in on the second well is barred? Or is it not commonly used because of the "unknown" - where the guy quoting the job has no easy way to determine the water table at the job site?
I'm not the typical dumb boss owner. I've 30+ years of field experience, on everything but geothermal, and we already know water source heat pumps as we maintain a few buildings with boilers and cooling towers on either end of the loop that supplies the heat pumps. So you can talk tech to me!
There have to be some other places in the country where this sort of open loop, two-well, heat source design is - or could be - used.
Can anybody educate me or point me in the right direction?
PS sorry for the long post, but I was trying to cover all I could - and business is really slow around here!