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  1. #1
    Join Date
    Oct 2003
    Location
    s.e. mi
    Posts
    173

    Anyone have experience on open loop

    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!

  2. #2
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    2,416
    I'll give you my 2 cents worth which may be about all it's worth. Here in Nebraska we can do an open loop, well to well, but it is discouraged because of the possibility of injecting foriegn material into the ground water. Generally there are cheaper operating cost wit the closed loop because of fractional pump HP compared to 1-2 hp well pumps needed for open loops {water levels around here are 75+ft}. Normally there are not purge valves, unions or things ormally seen on Hydronic systems. On the standard pump packages I have used a 3-way valve is used for system entry. A 2-hp injector pump is used to purge the loop and pressurize it to 15-30lb. The pump is connected to a tank that has the antifreeze solution in it, a hose is connected from the outlet 3-way and back to the tank. Because of the velocity of the pump the air is purged. The whole process takes about 2 hours.

  3. #3
    Join Date
    Feb 2004
    Location
    Pacific NW
    Posts
    570
    The code and legal issues vary so much state to state and even by county one cannot generalize.

    Here is WA, the first thing you need is a water rights permit.
    System at own house is air-air till it get down to 50 F outside, then pump the well thru evaporator into a pond. There are really stringent rules on anything going back into the water table, have not looked into that here in detail, but assume it is very restrictive.

    Own situation is 2 acre ft per year water rights even though it goes back onto the ground, so at 8 or so GPM you can see it can pretty much be limited to 60 days continuous operation (or at 25% running = the whole heating season below 50F here).

    That said, the COP of my system is 5.6; post over in the pro section (or may be moved anyway by the moderator?) and can give you more details as the water part of the system was 95% shop built and paralled onto the Rheem air-air system. Since it is an experimental system, started out with the water right off the 35 psi potable water supply to the house, COP would be over 6 if not for the extra 30 or so psi pumping losses. A retirement project will be a separate low head well pump to reduce pumping losses.
    One big advantage for the water loop is that the 2nd exchanger is eliminated, hence your low end temp on the mollier diagram is typically more than 10C higher! Now in the exchangers, you have only one film coefficient of water to pipe vs. 3 film coefficients in the ground loop type setup. For the 2 well system, with good design of the return draft tube, pumping losses are less than a ground loop.
    Sounds like you could be on to a highly profitable venture in Michigan if the water rights laws and well point driving laws regulation allow it, techically it is the only way to go IMO, for AC in the summer you probably dont even need the compressor in the loop.


    Michigan sound like an excellemt place for

  4. #4
    Join Date
    Oct 2003
    Location
    s.e. mi
    Posts
    173
    Thanks kls-ccc,

    If I had to go to 75 feet then the multistage well pump HP would instantly convince me that a closed loop would be the only choice - or operational costs would be way too high. Plus, drilling to 75 feet can't be cheap either.

    As long as I've got your ear, what's with the antifreeze? I've worked on probably over 100 chillers. Save for a rare one that is used in industrial process and needs a fluid temperature below 50, they all just use water. The air handlers for space cooling have water coils that are much larger (more rows) than what a DX evaporator would be, simply because the water is warmer than what refrigerant would be.

    I guess I'd need a 2 hp pump, as you say, to be able to purge such a system. But I'm curious on that too. Where do you plug in a 2 HP, 115v pump on the job site. or is it 230 and you just jumper it into the Heat pump circuit?

    My rant on the lack of valves, unions, vents is kinda my status quo, and much of the reason I hate residential work. Residential hydronic boilers seem to get installed without them too, unless they go back to the 60s. We do - and I've always done -mostly service work, so the absence of them can make a one hour component replacement job a near all-day call. But any commercial job always has them. Obviously, I'm gonna be high on a residential bid, because I figure them all into the job. I'm always thinking about 10-20 years from now and what the cost would be, not just to operate it, but to fix it. The people in the market for geothermal must be looking at long term costs, too. I think I could convince them that I'm $1500 higher than the next guy because I'm installing a much better system when it comes to "serviceability." Well, maybe just some of them!

    Thanks again.

  5. #5
    Join Date
    Oct 2003
    Location
    s.e. mi
    Posts
    173
    Thanks Junkhound,

    You're gonna find this a bit nuts, but in the immediate suburban area where I live, water wells are generally prohibited - because it's too likely that you'd hit a natural gas pocket at 20 feet! The mineral rights are all sold off, so the HO can't sink a gas well. Tho there are a few homes a mile south of me that were built 100 years ago where they kept the mineral rights and have their own gas well. Every few years a HO decides to sink his own well for watering the lawn - usually a country boy who moved here. He doesn't ask, sure doesn't try to permit it. Drives a wellpoint down 20 feet and hits a gas pocket at a couple hundred PSI. He dials 911 and gets busted, big time. The local area is kinda unique in the state, as it's clay. Everywhere else in the lower peninsula it's mostly sand under the topsoil. The clay here traps the natural gas into "domes." And yeah, before you ask, yes, I've been tempted!

    Beyond my small local area, I'm not sure tho about injecting water back in. I'm not even sure that a well for water that isn't for domestic use (drinking) even needs a permit in most areas. All I really know is that there are a whole lot of houses (existing) that have a 20 foot domestic water well in operation. And that would mean that they'd be a great candidate for an inexpensive geothermal, two well installation.

    The water tends to run about 50 degrees at that level. Like you, if I was doing for my own place, I'd install an aircooled condenser, oops I mean evaporator, to handle the temperature band between 50 and 65. But on a customer installation, I'm not sure I could justify the add'l costs of that.

    About 25 years back I designed and installed a cooling only well source system. The HO sunk a 20 foot well, but left the pipe buried under the dirt in the crawl space. The building contractor built the house up over it. As soon as we got final inspection on the heating system, I went back and installed a water coil in the duct, 1/3 hp well pump and some simple controls. Worked great. He was cooling near 2000 sq. ft on 1/3 horse! The wasted water just went to a drain in crawl. He was on "city sewers." Thus the need to do it "off permit." But I've always wondered how it would have worked if he'd also sunk an injection well, and whether that would have made it "legal."

  6. #6
    Join Date
    Mar 2009
    Location
    Russell ON Canada
    Posts
    24
    I live outside of Ottawa in Canada and have been on an open loop for over 15 years. My first Geo failed last January, probably due to scale buildup though we are not sure. I should have had it flushed every 3-4 years but did not know at the time. It was a good WF 5 ton unit and heated the house quite well and didn't owe me anything. It's a good thing I had a 15Kw 3'rd stage heater in the unit or we might have frozen to death.

    I replaced it with a 6 ton Climatemaster (do not make a 5 ton) and it is purring like a kitten. I have a great installer which I think is the most important thing.

    An open loop is 15-20% more efficient than a closed loop but you have to deal with any water quality issues. My water is not that bad but I put in a CuproNickel exchanger in the Climatemaster as it is more resistant to iron bacteria and such.

    The slight oversizing will also allow me to convert to closed loop if I ever win the lottery.

  7. #7
    Join Date
    May 2005
    Posts
    161
    I did this exact same thing outside of Jackson, MI a few years ago. I have water 7 ft below my basement floor so I drove a well point down, then put another well about 100 ft away in the back yard. The system worked pretty well for a few years then clogged up with rust and mineral deposits. It was one of the worst weeks of my life in the dead of winter trying to clean out the pipes just to get the system up and running again. That summer I switched to a horizontal closed loop setup and haven't looked back. It's a push as far as costs go because the horizontal loop is less efficient than open loop, but the pump draws less power. The upside is I don't have to worry about the pipes clogging up ever again.

    Also, for what it's worth, I did catch some flack from the county drain inspector for having 3 wells on my property. Apparently it's not legal even in Jackson. If it's not legal in Jackson, I'd have a hard time believing it's legal anywhere.

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