Well question

On a sand point well, I know water can be pumped from the well. Does it work to reverse the process and put water back into the ground via the sand point? The subsoil is mostly coarse sand. Flow rate should be less than 8 gpm.
On an open loop system it is possible to take water from one well, run it through an exchanger and then put it back into the ground via a separate well. If the sand point works, then it won't be necessary to run a drain to the pond.
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Franz Fripplfrappl
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Yes, but...
The engineering is the sticker. How fast are you going to pull water out and how fasst will it perculate back? You could easily pull more out than will perculate back in.
You don't say what your goal is. Water loop for a heat exchanger?
Harry K
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On Wed, 16 Jul 2008 08:21:44 -0700, Harry K wrote:

The flow rate should be about 6 gpm through a water-to-water heat exchanger.
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Franz Fripplfrappl
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Are you considering a water source heat pump?
Dick

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On Wed, 16 Jul 2008 10:27:25 -0500, Dick Keats wrote:

Yes, a water-to-water heat pump for hydronic radiant floor heat. There's no chance water will get contaminated since there is nothing else on the system.
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I have an open loop ground source heat pump which operates as you describe. You can put the water back - that makes it an injection well. There are a number of ways of screwing up an open loop system and our well driller and installers found several of them.
Open loops are hugely problematical and I would go with closed loops if I had it to do again. I'll assume you have a good reason to reject closed loop systems. I repeat - I wouldn't do an open-loop system again and I wouldn't recommend one to my worst enemy. I had a special case where I did not want to kill a lot of very old trees so I went to open-loop. I should have killed the trees.
Here are some things I learned the hard way.
Flow rates should be approximately 1.5 to 2 gpm per ton of unit capacity - varies from manufacturer and type of unit - so your flow rate is likely OK for a 3 ton unit.
We had an iron bacteria infection because the well driller did not disinfect the wells after he was finished drilling. Also, the installer did not disinfect after installing the pump and discharge pipes. Iron bacteria occur on all ground surfaces and it is impossible to avoid transferring it into the well so disinfection is key. Add a jug of bleach to each well when finished drilling and after installing the pump and pipes - after doing anything to the wells that involves something touching the ground and going into a well.
Once started iron infections are said to be permanent - I have disinfected like crazy doing all the things several experts recommended - came back in 3 months. I will now have a permanent disinfection process and filter cleaning problem. Avoidance is the only cure.
Our injection well started the first winter with water levels 30 feet below ground with the pump running - there was about a 5 foot rise above static level. By January the injection well was overflowing. It would have been a big problem if the overflow had entered a neighbors property but ours is a river lot and it just went down the riverbank. The cause was air locking of the injection well ground formation. Air locking occurs when the installer uses a pressure reducing valve (PRV) to adjust pump flows to the desired rate during the calibration process. PRV's hiss and that sound is air or gasses coming out of solution and those bubbles air lock the well after a while. The negative pressures that occur in a PRV also cause calcium and other minerals to come out of solution and those will plug the injection well and the ground formation. SO don't permit the use of PRV's, no way no how - most installers use them and say they never cause any problems but they most certainly did at our place. We proved it was air locking by putting a pump down the injection well and reversing the flow out instead of in. Nothing happened for 2 days and then there was a shoulder high geiser for about 15 minutes. After that the well rise was almost normal again - 6 feet rise instead of the original 5 feet. The extra rise is due to calcium deposition but allowable for now.
To avoid the need for PRV's you should use orifices at the end of the discharge pipe in the injection well. Size the orifice so the flow rate is what is needed. The pump will be a bit larger than required so an orifice restrictor will be required to throttle the flow. The flow rate is calibrated so the discharge water after the heat pump is no lower than 38 degrees. If you take too much heat out of the water then the heat exchanger would freeze - that would happen if the flow was too slow. If the flow is too fast then there might be extra wear on the heat pump internals. We started with an orifice a bit too small - 3/16 inch diameter - water temp was too low - drilled it larger just a bit - water temp rose but still too low - drilled a bit more - temp rose, repeated until temp was 38 degrees with heat pump in full heating mode. Took 5 tries. A lot of work but the well did not overflow this winter. Also eliminating the loud hissing noise in the basement was a bonus.
Make the discharge pipe in the injection well as long as possible so the orifice at the end is as far below water level as possible. The submergence will avoid any negative pressures in the orifice. Putting the restrictor at the end of the discharge pipe and deep under water keeps the pipe under pressure which avoids calcium and other minerals coming out of solution. That is why the pump should be slightly over-sized and restrictor used to throttle back the flows. If the pump had only the exactly correct capacity the discharge pipe would run under negative pressure and the well screens and ground formations would become plugged after a while - maybe a few years but could be much sooner. Depends on water hardness and how extreme the hydraulics get.
In our province there are no great ground source suppliers and only one good well driller. I asked several senior ground water engineers who they would recommend and they responded instantly "none of them". I didn't use the best well driller because he charged twice as much as the other bidder - big mistake - if I counted the value of my time I would have been money ahead. I am a civil engineer and got a lot of free consulting from groundwater experts so I was able to bebug my system myself but I shudder to think what is happening to normal folk out there. My first ground source installer was only medium recommended by other prople but he turned out to be a crook - police and tax colectors turned up looking for him and he took off. He had been trying to get large deposits but I only gave him a few $thousand. Lost about $2,000. Next installers were good but they insisted on PRV's with promise to remove them if they caused any problems - when well overflowed they fixed it with me working with their guy and sent me a bill for over $2,000 - they reduced it to $900.
Be very careful who you hire and don't give them more than a small deposit. Don't pay the well driller at all until he proves that the well will deliver the required flows with only around 5 feet drawdown in the pump well and maybe 6 or 7 feet rise in the injection well - maximums. Injection levels rise more than the drawdown value because it is harder to pump water into a well than out. So the injection well should be larger, deeper and have longer screen than pump well - unless they easily exceed capacities. Note that capacity is flow at normal changes in level up or down. It is not just a flow value.
The wells should be 250 feet apart for best efficiency. Mine are only 135 feet apart so I had one well cased 25 feet deeper than the other so the groundwater flow between the wells would be partly vertical. We have frcatured limestone so a little vertical separation cause a significant increase in groundwater flow path because the vertical fractures are smaller than the horizontal ones. Sand layers are more homogeneous so vertical separation will only help a bit and the horizontal separation becomes much more important.
When the wells are finished, as part of the capacity proof, measure the static level in each well before starting pumping. Pump to surface initially. The pump well should drop around 5 feet and the other well, just standing there with no flow in or out, should drop no more than 6 inches or so in reaction to the pump out after an hour of pumping. This reaction should be minor to prove that the wells are not hydraulically connected to too great a degree and water will not short circuit between the wells. It is OK for some of the water to flow between the wells, just not a lot. The water will be picking up heat as it goes through the ground.
After proving that the inter-connection is OK then pump from one well into the other - discharge pipe MUST be well below static level before pump starts - no splashing allowed at all. Check that drawdown is in the 5 foot range and rise is a couple of feet greater, say 7 feet. Lower values are better, higher by a bit is OK but higher by a lot is bad. Bad depends on the local experience but most homeowners don't pump at 6 gpm for hours on end like a heating or cooling system would so you may not find much to go by. DO NOT take the drillers word for what is OK - he just wants to get paid and clear out. Consult with state or provincial groundwater departments to get some idea of what sort of reaction to expect. The values I gave you are for my area where we have fractured limestone rather than sand layers to draw from.
Make sure your well casings are PVC and the sand screens are stainless, best grade, don't skimp on quality. Wells need maintenance or they stop working. More so for heating and cooling where you pump thousands of times as much water as simple domestic users. Maintenance is generally just chlorinating whenever working on the wells and once or twice a year. If you notice drawdown or rise problems then you can regain capacity. If the injection well overflows then stop pumping, either relocate the pump from the draw well to the injection well or get another pump of equal or, better yet, more capacity and reverse the well flow until a lot of air comes out. Took me 2 days but sometimes it is a matter of minutes, depends on many factors. If that doesn't work and you suspect mineral deposition has plugged one or both wells then acid treatment would most likely restore capacity. Industrial strength acid is required which is very dangerous to handle so you must get professionals to do it. Try well drillers or geotechnical engineering companies who specialize in groundwater and who are familiar with acid treatment of wells. If your well casing is plain steel then acid would destroy it. Same goes for the screens - anything but the best grade stainless will be destroyed by the acid. Includes clamps and all other parts - stainless or PVC only. Polyethylene is NOT acceptable. Poly pipes and pumps must be removed before acid treatment because they can not tolerate acid.
If your driller uses inferior materials, when you need to acid treat the well at a future date - it is inevitable - then the well would be destroyed and need to be replaced entirely at huge expense. Even chlorination would eat at steel casings and cause them to rust which would then become the source for iron bacteria.
The above rant and rave shows why closed loops are better than open loops. Closed loop may need a cleaning flush every 5 or 10 years. Open loop has no end of hassles. If you don't use the best well driller around you will be sorry and the best guy knows how he compares to the competition and charges much more - the only good guy in our area charges double and triple and is kept busy. There is no way an open-loop system is cheaper to build than a closed loop and the on-going costs and hassles are huge. The majority of the problems are related to the injection well so if you can eliminate the injection well by discharging to a pond it would help. It would cause concerns about groundwater quantities because huge amounts of water are used. If you are close to neighbors who reply on wells there may be concerns about drawdown affecting them. Neighbors could also get warmer water during air conditioning season.
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So 3 tons needs about 3x1.75 = 5.25 gpm, cooling it by about 0.8x36KBtu/h/(5.25x8.33x60Btu/h-F) = 11 F.

Why not just pump some water out of the river and dump it back in cooler? My 1820 farmhouse has a hand-dug well with water 9' below the surface and a nearby creek.
The ground loop can be the most expensive part of a water-source heat pump. Can a $400 18'x48' EZ Set inflatable pool be the heat source for a $5K 3-ton Climatemaster Tranquility 27 heat pump with a COP of 5? It might be solar- assisted where I live in PA, with an average 30.4 F January temp. We might add a little ground water if the ice ever reaches the bottom.
Nick
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