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An open loop geothermal heat pump is a superb option for homeowners interested in low-cost, ultra-comfortable heating and air conditioning. Not only can an open loop ground-source system be simpler to install than a closed loop, but open loop technology often delivers the most energy efficient performance available.
Of course, there is a catch.
Open Loop Geothermal is Not One-Size-Fits-All
The main difference between an open loop geothermal and closed loop geothermal heat pump is the nature of the ground installation. A closed loop system relies on a buried network of piping to conduct heat in and out of the building. An open loop geothermal system pumps water from a well, runs it through the system, then dumps it back into the ground. As previously mentioned, an open loop geothermal unit can be highly efficient and doesn't need elaborate piping, but....
Water Quality for Open Loop Geothermal
How high quality is your groundwater? Groundwater with too high or too low a pH level is bad for an open loop geothermal system. Inferior water can cause scaling or even completely corrode and dissolve a heat exchanger. Which, as you might imagine, is not what you want. You really need 'Goldilocks' (i.e. - just right) water for an open loop. When you can't get it, don't bother.
And even if you do....
No Pumping, No Dumping
Numerous municipal governments across the country have made "pump and dump" open loop geothermal units illegal. In many, many places, you can't just pump well water out of the ground, run it through your system, and dump it back out. The government just won't let you do it.
Now, pumping the water back into the well via injection is fine most places, but....
Capacity Needed for Open Loop Geothermal
A geothermal unit on an open loop needs a lot of water to operate. Roughly speaking, it needs about one and a half gallons of water per minute, per ton of operating capacity. To run a 5 ton system you would need 7.5 gallons per minute. Heck, an average system could use a million gallons of water or more in a year!
Which is definitely a lot. Fortunately, that water is not polluted, so it can just go right back into the ground. BUT, if you don't have enough ground water to supply the open loop, which large portions of the country do not, then you have a problem. And that problem is basically unsolvable as it relates to open loop geothermal installation.
So?
So, if you meet all the requirements for open loop geothermal, then great! You can get a wonderful heating and cooling system with ultra-awesome energy efficiency.
But, if you can't, don't worry about it. You can still used a closed loop geothermal, and their efficiency is still way better than any conventional system.
Still Have Questions About Open Loop Geothermal?
Just ask us in the comments below, on Facebook, or on Twitter.
My house is on a shallow tidal saltwater river (max depth about 10 ft). In the winter when it reaches single digits, there is sometime a 1/4” layer of ice that forms on top but is ice free in normal winter conditions. Could saltwater be used for an open loop system?
Most home equipment manufacturers do not allow the use of saltwater directly for geothermal units. However some people have done so on boats anyway, even though manufacturers will not warranty the equipment.
I have an open loop geothermal system with one well at 75 foot depth for the input water and another well of the same depth about 100 feet away for the discharge water. It appears to me that this should be "water neutral" in terms of use of water, but an article I was reading says that an open system uses more than 1,000,000 gallons of water a year. Which is correct?
I am about to start construction of a home near Tulum Mexico, and want to look into an open loop system that pulls from an underground water system called a Cenote, which runs right under my home being built. The average temperature of the cenotes are around 74 degrees, I would like to pull from one area and then re inject it back into the Cenote. Has anyone at your company heard of this, and if so could I get some insight on it. I have heard of using open loop marine AC's as well and running this cold water throughout the house to all of the AC's
I have an open loop units -the unit continues to dump in a pond after the unit is shut off. Seems like great waste of water when it is not pumping to cool the house. Is there a check valve system on the in flow to the unit when it i is not cooling.
Hi looking into open loop .Was thinking of using spring feed open loop and discharge into another spring closer to house where water can warm before entering enviroment.My question is what are acceptable limits for water quality,ie hardness ,iron ,ect.Is there a "rule of thumb" or are all systems /,manufacturers proprietary Thanks for this info
I am told that I acquired the first open loop permit in Virginia from DEQ. I drilled a separate well for the sole purpose of serving a geothermal system. The system has been working flawlessly for five years (use Water Furnace). When I say open loop, the source of water is the well which is then deposited back into the well. No waste of natural resources or depletion of the water table. A win-win for us and the environment (I say this modestly).
I have a discharge valve to redirect output from the Water Furnace in the event that the water temperature exceeds acceptable limits certain (which it has not since operation and suspect that it will not). If a discharge were necessary, the water would be discharged (via a pipe) into a creek that empties into our pond. I have to produce a quarterly report to VA DEQ that shows if there has been any discharge (so far the report says "0" discharge as registered by our gauges and valves). My home is on shale and it would have been extremely expensive to install a closed loop system. Originally, even the supplier sales person of the HVAC and Water Furnace equipment said that it could not be done and fought me all the way; I stood my ground and was fortunate to have good people locally and a collaborative DEQ to make it happen. Encouraging others to fight for an economical implementation that is also environmentally sound and very, very cost effective.
I’ve been irrigating my large lawn with a well drilled 30 years ago; the water has always been clear and fresh I live near a wetlands with a high water table and sandy soil. Can I simply drill another, deeper well and use for open loop geothermal system?
You may be able to do that. In most of the country, including the north, a pond of at least 10 feet in depth is required to maintain a 50-60 degree year round temperature. The goal is to stay below the frost line. A pond with at least 10 feet in the middle is the rule of thumb. This is where the polyethylene piping will be rolled up and sunk. For more information on geothermal products, please give us a call at 270-575-9595.
In a cold weather climate, have we reached the point where Air Source Heat Pumps (ASHP), like the Mitsubishi Zuba, make more sense than a geothermal installation, including an open loop (well-to-well) system, especially if they're roughly the same price? Taking the likelihood of additional maintenance of the open loop, compared to what appears to be typically durable Mitsubishi ASHPs? The closed loop is going to cost about 20 more. Electricity bills will likely be slightly less on the open loop system, but the higher maintenance and other vulnerabilities make me a bit nervous.
It truly depends on what you need. Geothermal systems are very reliable and likely the most efficient way to keep your home comfortable, but do require a lot of upkeep. If you were to go with the Mitsubishi unit, you might find that its upkeep is easier and there are a lot more professionals able to service it. If you'd like, please give us a call at 270-575-9595 so that we can help you in choosing the best unit for your needs.
Hey I’m having trouble finding this answer anywhere online but is use Geothermal open loop water still clean and potable? I’ve seen that you can shower with it as well as heat your water but is that water that has been pulled from the ground then used in the heat pump drinkable after that process?
There is no guidance in any manual that we've researched on this, so we cannot specifically provide an answer in regards to the drinkability of geothermal open loop water. If you are still considering drinking it, we would recommend that you contact someone to come out and test the water, like from a water treatment facility.
Thanks for the helpful article. Have an unused well, 246 feet deep, piped into our home in Rhode Island. Who should i contact to see if this is feasible to use for geothermal radiant/baseboard heating? Assuming we have to check the water ph, mineral content, and flow. And make sure injection return is allowed.
For the best advice, you'll want to contact a geothermal HVAC contractor in your area. You can use our Contractor Assistance page at https://iwae.com/support/contractor-assistance/ to help you in your search.
What is the typical change in water temperature when the geothermal unit is heating? Meaning if it comes in at 55 does it leave at 50? 45? 35? Just want some kind of educated estimate
Water flow is adjusted on a geothermal unit to produce:
Cooling- 10-12F temp rise
Heating-8-10F decrease.
If the temp differential is correct in one mode it will also be correct in the other mode.
I have a customer with an open loop moodiness geo. Previously it was a Florida heat pump geo. Never had an issue with old unit. New unit freezes. I put a flow restrictor in the supply line that delivers 8 gpm. My ? Is should that restricted be on the discharge line instead?
In all local installations, we restrict flow only on the outgoing side. The 8 gpm would normally be sufficient volume for a 3 ton unit however it will vary. I am not sure what you mean by freezing. If it is the main water heat exchanger that freezes, then you do not have enough flow for the unit.
Doing back-of-the-napkin calculations for a small cottage. Like Mr. Nearing I am thinking of using a stream for an open loop system. In my case a large stream in Maine, with about a 10 foot head : a 1" pipe would deliver up to 210 gallons per minute. Enough for a 5 ton system.
Does a 5 ton system suffice for a small house?
I assume I would (1) first check Ph of the water: too high or two low is disqualifying; (2) will pipe will be dug through dirt or as is common in Maine, granite, cost may be disqualifiying; (3) check with the local code office if I can take out 210 gallons a minute and return it to my stream -- all before I start to get serious about a geothermal design?
As long as the stream does not freeze in winter, you can use it. You will likely need some filtration for biological materials. The industry standard is 3 GPM per ton, so 5 ton would require 15 GPM. Final flow adjustment would probably be a lower rate. Whether a 5 ton is adequate for your structure is an engineering question that we can't answer. A Manual J heat loss/ heat gain calculation would give you the specific btu requirement for the structure. The “guesstimate” that has been used in the past is 400 to 500 sq ft per ton, for a well-insulated structure, of normal construction method, in an average climate.
Yes, you will need to check your water quality for Ph as well as hardness and type of mineral content. While there are some local codes regarding open loop systems, large parts of the country have no regulatory requirements. But, as you say, always check your local codes.
Hi,
I replaced my geothermal system 5 years ago. I just had someone out as I have a pinhole leak in the copper pipe coming out from the heat exchanger. I am told it's because of high acidity in my well water. Am I wrong in thinking that when this new system was being installed the company installing it (the ones that sold it to me) should have tested the water? I am from the UK and had no idea about geothermal systems and so didn't know to ask at the time.
Yes, the water should definitely have been tested prior to installation. I'm not familiar with UK geothermal-related regulations, so I can't tell you who the onus of testing would be on.
I have purchased a 4.5 ton water to air system that was used in open loop system. I have a pond 30 ft from house can I just suck water in and pump it back to the pond? I dug the pond with the intention of using it for geothermal heat and cooling. I made the deep part over 18 ft deep and shallows are about 4-6 depending on water levels. It's mostly rock lined and usually very clean,(we had alge this year) its approximately 1 acre the house is About 1400sqft and there's a huge garage that if there is any "extra" output I would like to use to warm it up. We also have 2 wood burning and a pellet stove as well as propane 75k forced air furnace that can all be used as back up or to assist. I know that's a lot to take in. I would just really like to go to geo only and wood back.
You need to make sure that it is pulling from fairly deep in the pond. That way it does not affect the temp as much during the winter and summer. If in a real cold climate at winter, you need to make sure the discharge water is able to fully drain and not build up ice (in the pipe or on top of the pond) when the unit shuts off or the discharge is deep enough to not worry about freezing.
I pull my irrigation from a private, deep spring fed lake. Instead of reworking my existing well to be able to meet the water demands of a 4-5 ton geothermal heat pump, would I be better off just pulling directly from the lake, or even a closed loop lake set up?
A closed loop lake installation means you don't have to do a lot of digging. That can get expensive. I would certainly prefer a lake loop over doing all the excavation for a horizontal or vertical ground loop.
I have an open loop Geo system and the recently it started consuming all of the water our well could pump. My bladder tank drops from 60 all the way down to 30 lb within 5 minutes of use. My well is still producing 20 GPM. My question is what if anything will I harm by restricting the water flow manually at the ball valve to the Geo unit? Will it trip a high pressure or low pressure fault code before anything gets damaged? Or should it at least
That will depend on what size your unit is, and how low you are wanting to restrict it. But, I would use a gate valve on the outgoing side of the Geo instead of a ball valve. You will also need to have a spot to check the water temps on the incoming and outgoing of the Geo.
My house is near a steep slope with a small stream running close by. Could a geothermal system run on gravity system from a inground tank supplied from the stream? Tank would be located at a higher elevation than the house.
Here's what Jacob, our in-house geothermal guy, had to say:
It would depend upon a couple variables: the size of the tank, the PSI of the water coming to the geo unit, the rate the pump was able to fill the tank from the stream, and the size of the geothermal unit. If all the variables were ok, then it probably would work fine. The biggest concern would be PSI fluctuation causing the GPM to go up and down, but as long as his stream was able to provide enough water to never allow the tank to go down below the amount needed to provide standard water P.S.I. rate for the incoming water on the geothermal, then he should be fine. He needs to remember it takes 2-3 gallons per minute per ton. So a 5 ton unit can empty a 600-900 gallon tank in 1 hour if its not replenished. Also, depending upon where they are located and how far the tank is from the house, he may need to bury the pipe from the tank up to 10' in extreme temps.
My plan on installing open loop system myself, Although I have an extensive background in HVAC but nothing in Geothermal heat pumps. It appears to me that there is not much information or that information is guarded as far as do-it-yourself, looking for install information.
Geothermal manufacturers typically do not allow iron content over 1 PPM, and some even less. If you cannot reduce the iron content below this level, I would not suggest using an open loop geothermal system. Closed loop is, of course, still an option.
