new Geothermal heating/AC considered

I will reply to your questions after snipping a quote from your comments;
I had the general knowledge of geothermal
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Geo systems do lose efficiency with drop in incoming water temperature so that is the reason for a correlation to drop in efficiency with distance northwards. Also, why your pond idea would be less efficient. Otherwise the whole system is buried below frost so being farther north should make no difference.
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The tubing would have to be in complete contact with the surrounding earth for efficient transfer of heat from the ground. Backfilling with clay lumps would leave a lot of air pockets and thus very poor efficiency. I have some geo manuals from the Oklahoma geothermal institute that state that the whole pipe should be buried in special thermally efficient grout - gives complete contact plus protects from rocks in the backfill. I found several studies that estimated improvement in efficiency of 5 to 10%. I also found that none of the suppliers of grout in the city had ever ordered in any of this type of grout. Dry sand or soil has low thermal efficiency so your wet location would be ideal, thermally, even if you just backfilled with clean sand to about 6 inches above the tubing to protect it from rocks. Then maybe pump a lot of water into the backfill to break up lumps and improve compaction. Don't pound with packers at all or at least not for the first 2 or 3 feet above the tubing.
Open-loop is indeed more efficient than closed loop - that's one reason I selected it. Major reason was that we are on a sloping clay riverbank that is at risk of slow sliding movement which would have torn apart buried tubing.
Too bad about the rocks - I agree that digging in rocks would be very difficult.
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Yes, closed loop is less efficient but not that much, maybe 5%. All you do is use longer length of collector tubing to get the same incoming energy. So actually, it is not so much less efficient as it simply means you should design the collector tubing correctly.
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I have heard and read about single well installations but they all had one major difference fom this suggestion - use of a rubber seal to separate the water coming back from the house from the groundwater flowing into the well from the formation. The seal forces the incoming water to flow outwards through the formation before it can get back into the well and thus it collects heat from the ground along the way. Without a seal the well is sort of like a 350 ft long vertical heat collector - length from bottom of well to pump. It is helped considerably by the use of 10% bleed water which causes that amount of new water to enter from the formation, plus a small additional amount due to domestic uses. The only new heat comes from water travelliong the 350 ft plus the heat in the 10% inflow. Thus 90% of the water is recycyled for more heat transfer. If the incoming heat does not keep up with the heat extracted by the heat pump then the well water could freeze. Actually freezing would be prevented by sensors that shut down the system if temps fall below a pre-set limit or if frost is sensed on the exchanger. So the system is protected from freeze damage but what happens then is that the auxiliary heat kicks in and you don't get the benefit of geothermal efficiency until the temps rise again. I met one couple whose heating bills were the same as their old house which had gas heat and a much lower standard of insulation. They gained nothing from their investment in geothermal. I think their problems were due to the wells being only about 70 ft apart and at the same depth - water simply flowed quickly along the short path between the wells which was not long enough to collect enough heat to keep the geo going. Their red light indicating that the auxiliary heat was operating stayed on most of each winter. Hopefully you are not going to get the same performance due to recycling of the same water which can only supply a certain amount of heat before it is cooled too low to be useful.
Closed loop systems have anti-freeze in them so they won't freeze and can be operated close to freezing temp - 32 degrees. I met one installer who claimed he had a closed loop buried only 3 ft below a parking lot and it supplied enough heat for a commercial building. I found that hard to believe as parking lots are kept clean of insulating snow and up here frost penetrates 8 ft or more under clean pavement. So this system was supplying heat from a loop that was below freezing temp for most of the winter. The ClimateMaster manuals do show earth loop temps down to 25 degrees so he may well have been truthfull. He had photos of the system being installed.
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We are in Winnipeg which is only 75 miles north of the border but dead center of Canada so we get the coldest winter temperatures of the country going east/west. This winter we had 6 weeks of temps below minus 30 degrees C.
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I am on the second dealer. I researched the first one fairly well and he came highly recommended by my project managers who had used him on several jobs. I checked on two of his jobs and the workmanship was impecable. Unfortunately something was wrong with him on, I think, a personal level. He refused to showup when we needed him and delayed construction by at least 6 weeks because we kept believing his promises to come 'next week'. He then started demanding tens of thousands of dollars for 'progress payments'. We had paid him $5,000 down and I told him progress payments would be after progress was shown, not before. Then the police and tax collectors showed up looking for him and garnisheeing any future payments we might have made to him. Turns out he had collected much money in down payments from many people and never showed up and was way behind on his taxes. I fired him. He had already finished the wells, the well connections and the ducting for the second floor of the house so I think we only lost about $2,000 on the guy, compared to $10,000 and $20,000 losses the police told us he had taken others for. It was a shame because he was a nice person who had done great work in the past. The second installer naturally took no responsibility for the wells because he had not installed them. His warranty only covers his own work which is perfectly reasonable. It does leave me holding the bag for anything well related.
The second installers were the ones who insisted on use of pressure reducing valves (PRV's) despite my insistence that they would lead to air locking based on opinions from two professional geotech engineers. The installer said if the wells air locked they would come back and remove them. The well did air lock by Christmas of the first winter, 2 months of heating. The large air bubbles came and went with turning the PRV's on or off, proving that they were the cause of the air. The installer agreed but had no idea of what Plan B should be. I suggested we use a separate discharge line for each heat pump and put orifices on the ends to restrict flows to the required levels. This was done but they sent me a bill for $2,200 for 'improvements'. I said they were not improvements but corrections to their instalation. Considerable polite discussion ensued. They reduced the bill by half and that was the best they would do. I paid it. That mod lasted through one winter but overflowed again. I did Plan C myself. I now know why it it overflowing and think that either an air separator (degas vessel as suggested by another poster) may help or I have another separator idea. Plan D should work to 90% or better success.
The problem with air entrainment is if it is reduced but not eliminated entirely the solutions become much more difficult and expensive. The large bubbles of the PRV's air locked in 2 months but I solved it with 5 hours of reverse pumping of the injection well which drew the air out of the rock formations. Plan B overflowed in 10 months but it had very tiny bubbles (1 mm in dia). The small bubbles travelled farther into the rock formations and were very difficult to remove. I reverse pumped for 2 weeks with negligible improvement. I then acid treated the well which blew up like crazy but removed all the air plus improved capacity even better than original. Took me 2 weeks of pumping plus a day of setting up the acid program and performing it and then cleaning up the mess from the blow off. Cost $300 for acid and parts and at least 4 days of my time. Also killed some grass that must be re-sodded. I borrowed an expensive acid pump and a lot of fittings. This would have cost a normal consumer quite a bit from a pro company.
If my Plan D leaves only a few miniscule air bubbles it may not over flow for years but when it does the air will have gotten so far into the ground formations that removing them by reverse pumping will be impossible and I will again have to acid treat. Acid is very dangerous to handle and when I get into my 70's (15 years from now) I won't be able to do it alone. Have to train the boys or someone younger but for now I don't want bystanders.
Or do all
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I've found 3 other homeowners with over flowing wells. My geotech friends do about 3 commercial jobs a year to correct over flowing wells. They also get monthly or maybe bi-monthly calls from private residents with overflowing wells who can't afford to hire professional consultants. So they are not uncommon.
I did do a lot of research ahead of time but all I got is answers to my questions. If you don't ask the right questions you don't get the right answers. So I didn't research problems with open loops until I had problems. I didn't researche air locking when I was comparing open loops to closed loops. Then I got no end of hits about air locking and mineral deposition, photos of wells that were essentially lined with rocky mineral deposits until they were unsalvagable, etc, etc. My problems seemed minor compared to a lot of others. All reports say 'maintenance' of wells, like any other piece of equipment, is required 'for proper operation'. But what the heck is well maintenance? The geo companies lead you to believe that you may have to replace a pump every now and then. Simple and cheap and everyone knows well pumps last a long time. They don't tell you that when wells get air locked the pressure drops in the system also cause mineral deposition inside of the heat exchangers, piping and injection wells. Commercial installations are advised to use multiple injection wells so problems are slower to appear and some wells can be used while others are treated. Advice includes cautions that the injection wells may have to be abandoned and new ones drilled. The new ones may have to be far removed from the old ones because mineral deposits may have plugged up a good region near the old wells. Thus you have expenses of new wells and longer connections, assuming you have the land to drill new wells.
If that kind of experience is typical of open-loop systems how
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That's exactly what I am wondering. The professional engineers i know have little respect for the geothermal companies around here. My problems are a constant source of amesement and 'why would any sane person use open loops?' 'Why didn't you ask us first, we could have told you it wouldn't work.' When I consulted them at the beginning they were not eager to bad mouth the industry but then they have had 3 years of bad experiences/observations since then and are now less shy.
I've been too busy fixing wells and trying to make a living to get back to the folks who told me their wells were also over flowing. One guy said he can't afford to fix it and will just let it over flow into a ditch where it seems to infiltrate away. Haven't heard from the others. Most of the people I have contacted with geothermal heating have closed loop systems - the closed loop people are all happy, no exceptions.
I think open loop can be successfull if the groundwater has very low air entrainment and low mineral content - ours is high for both. You should get water tests done at a commercial lab and show the results to your geo dealer. He should be required to state that his design is suitable for those water qualities. I knew I was taking a chance on the minerals but deposition has been slow - a bit of mineral remover down the supply well and flushed through should do it once I need to do it. The air entrainment was not measured so came as a surprise. I don't know how to measure air entrainment but it should be possible - might have to done on sight or with special sample jars. No one - not my geo engineers nor any of the dealers who quoted our place ever mentioned air locking.
Even if you get a quarantee on the water quality it probably won't do you any good at all - mineral deposition takes more than a year and so can air locking if the bubbles are small. If you get a PRV and there is any air in your groundwater it may air lock in a few months like ours did. Where is the over flow going to drain to? If it gets onto your neighbor's property who gets sued? You or the dealer? Bet it's not him. He just says that he has done thousands of installations so it isn't anything to do with his work and thus must be something else. He won't know what but doesn't care. He will have been gone for a year or more and just claims that you or someone did something after he left - no way to prove anything was his fault. Only the owner is left responsible because the water came out of his well and why doesn't matter.
Another question - do you need a permit to discharge the return water back into the well? I know some states don't permit it.
Another question - are you sure the 10% bleed water can be infiltrated into the ground forever? Soils with high clay content have very low infiltration rates. If that location over flows will it cause problems?
In our area there are many well drillers but only one is highly recommended, one is OK and the rest are -----. I overheard one guy say that, of the geo dealers, half are incompetent and three-quarters are dishonest, or it may have been the other way around.
Around here geothermal has only recently gained popularity so it is a business full of Johnny-come-latelys and get-rich-quick artists. Prices are very much over-rated - knowing what I know now I could do our system better and for at least half of the cost. I would never do open loop again.
If you do proceed as stated;
1. get the dealers to show you some sort of computations that the required BTU's can be extracted from the single well concept with only 10% bleed water - I am sceptical of the numbers. Will you run out of new incoming BTU's in short order? It sounds too good to be true - why does one well work fine when everyone else needs two wells or a single well with a complicated design using a separator seal? You may spend a lot of money and not gain much efficiency if you spend most of the winter on the auxiliary system. There is no way to prove that you aren't getting the efficiencies you hoped for and thus no way to recoup anything from the seller. I haven't seen any references to a single well arrangement that did not separate the groundwater from the injection water.
I did a crude estimate of the heat gained by the well. Of the 10 gpm 1.0 gpm would be bled off and thus 1.0 gpm is entering the well. The other 9 gpm is recirculating over and over again with mixing of the 1 gpm. A 1.0 gpm flow has about 5,000 BTU/hr for a 10 degree drop in temp (my heat pumps drop the water temps by 8 degrees). A 350 ft long pipe might collect about 19,000 BTU/hr for a total heat gain of 24,000 BTU/hr by the well. Assuming 100% efficiency of the heat pumps that is all the heat you be gaing from the ground around the well plus the 1.0 gpm inflow. Granted this is a very crude estimate it is not out by 100%. If a 5 ton heat pump is extracting 60,000 BTU/hr then it won't be long before you are making ice cubes.
2. Heating or cooling capacity in tons is 12,000 BTU/hour so a 5 ton unit shoud have about 60,000 BTU/hr. The Tranquility 27 5-ton Model 064 has only 60,000 to 66,000 BTU/hr capacity, for your pumping rate, from the manuals I downloaded, for incoming water temps from 50 to 60 degrees. A lot less than your stated 112,000 Btu's in your first post. The dealer who said you needed two units to get 112,000 BTU's may have been closer to the mark. The 3 ton unit Model 038, capacity is 38,000 to 42,000 BTU's again for 50 to 60 degree incoming water temps. Both together would yield around 98,000 to 108,000 BTU's - could get to 112,000 with higher pumping rate or higher incoming water temps. Is there some confusion of just what is intended? Is one guy assuming the auxiliary would supply half the heat? How big is your house and what is the insulation standard? It sounds like they are recommending as much heat as for our house up here in a Canadian winter. On the coldest nights (minus 36 degrees C and high winds) I set an alarm for every half hour and checked if the auxiliary heat was on and never did find it on (I tested that the indicator light was functioning properly). The auxiliary is electric coils which see so little use that they have a fine coating of dust so when I test them there is a distinct smell of burnt dust in the house - no way the auxiliary is on without us noticing. I put R60 in all ceilings, R20 all walls, extensive sealing of all gaps and all windows are triple pane low E options. The geo sytem is very efficient - we have over 5,000 sq ft on two floors plus a finished basement with an outdoor wall for a walkout, 4 computers running all the time, a hot tub on the deck heated and used all winter, plus every electrical toy we could think of and in the past two very long and cold winters we paid from $300 to $350/month for electricity; heating included. We have very low electricity rates in our province - might be lowest in North America - around $0.065 kw/hr.
Did you actually see the heat requirement computations? I found dealers wouldn't show them to me.
3. Will the state water well permit allow for the 10% bleed water and even the re-injection of water? Find out before it's too late. Phone the state well drilling authority. Most authorities won't allow bleed water wasting. A family of 4 uses about 240 gallons of water a day but 1.0 gpm for around 20 hours run time is 1200 gallons a day - 5 times domestic use or put another way, the waste of water for 5 houses. For sure you wouldn't be permitted such wastage of potable water in the southwest states.
While you are talking to the state well drilling engineer ask him about open loops, who has them, who does the best job of installing them, what to look out for, will your proposed single well arrangement work, does he know any customers of your dealers who have had their systems a few years, etc? In my province the provincial guys are a great source of info - which I learned too late.
4. You are on a potable water acquifer as indicated by the reference to already having the well. That means you are subject to much more stringent rules about potential acquifer pollution and this makes injection of water less likely to be approved. If the dealer says to go ahead without a permit get a better dealer. They'll catch up with you sooner or later and make you stop injecting and then what? I was told by the provincial well guy that I didn't need a permit only because our acquifer was non-potable and there were no users of the acquifer. I was told that I would not have received a permit for an injection well if the acquifer was potable water. That may explain why there are few open loops around here - most other acquifers are potable. Now that I think about it, I may have read somewhere that most states ban injection of water into potable acquifers, some ban all injection.
5. Well performance is critical. It would be a good idea to have the well improved called 'well developement' by some. Your 35 foot drawdown for 10 gpm pump rate is on the high side - OK if it hasn't changed for a long time but makes me wonder. My wells had 45 and 55 foot drawdowns for 16 gpm pump rates which were considered way too high by my geo engineers. I acid treated both wells and got the drawdown to 5 and 3 feet - acid makes a huge difference in our limestone bedrock formations. Don't know your rock characteristics but the state well drilling engineer would be consider the best source for this info. Again a potable acquifer would have more stringent regulations than a non-potable one. Maybe acid treatment would not be allowed on a potable acquifer. You do flush it out very well after the acid is finished doing its work but how do you guarantee that no acid taste reaches the neighbor's well? Works best if you leave the acid in for 24 hours so there is a risk in some acquifers that acid could migrate and not get flushed. Contact with the rock neutralizes the acid but it takes time and much depends on how concentrated the acid is, what type and how much you use. Local practice will dictate.
6. Your 10 gpm pump rate is way more than a domestic well would need so a well that was fine for years will be subject to a much higher rate than ever before for much longer periods of time and pumping much higher volumes. Domestic use is around 60 gal/person/day so 4 people would use 240 gal/day. At 10 gpm the pump would run only 24 minutes a day. Geothermal heating runs for much longer times than LP, gas or electric heat - the supplied air temps are much cooler than from these other heat sources. So a geo system runs most of the day and night in the winter - you could now have the 10 gpm pump running 20 hours per day. That difference could lead to problems that did not occur before like sand being drawn into the well and plugging of well screens if they are used. Well development can help by removing sand from the region near the well, if there are no screens. It could also remove sand and sediment from the bottom of the well that were left over from the original drilling but not removed if the well was not developed at that time. If you are going to make the well a part of the heating system you should make it as good a well as possible.
7. If your dealer does suggest a rubber seal to separate the well supply and injection zones that won't be good enough. The 30 ft drawdown means that the mounding up from the injection flow will be very high, in the same range but lower. Thus the well won't have the capacity to accept the injected water without either overflowing within minutes of turning on the system if the injection is above the seal or just folding up the seal and flowing past it if the injection is below the seal. Normally, supply is below the seal and injection above but that could be switched. I wouldn't want to pull up a pump on 450 ft of pipe with a rubber seal dragging along - that is a heavy pull to be done by hand. The single well systems rely on a good design which takes into account the location and capacity of the fracture zones in the rock formations. The seal is located so that there is enough capacity below the seal to accept the injection flows and enough capacity above the seal to supply the required flows; or vice-versa. It works best if the rock formations are tight enough that there is not much vertical travel of water. Thus the supply water would not be cooled by the injection water as in your proposal.