Are You in the Loop? Open vs. Closed Loop Systems in Geothermal

All homes vary in one way or another, whether it is in size, location, insulation type, or a number of other factors.v Therefore, geothermal heating systems need to be customized in order to operate efficiently.  One decision homeowners must make is whether to install an open or closed loop system. Both types of loop fields effectively link to the geothermal heat pump, however there are some distinct differences in how they function.

Closed Loop System

 

A closed loop system consists of underground continuous piping loops that are filled with an anti-freeze-like liquid that helps transfer the ground temperature to the geothermal heat pump. A closed ground loop system can be installed either vertically or horizontally depending on your yard size (To learn more about vertical and horizontal loops click here). A vertical ground loop is the most common installation for a geothermal heat pump system because it requires minimal space.  A drilling contractor (often a well-driller) will drill the necessary boreholes which run about 5″ in diameter in order to fit the necessary piping.  However, if a homeowner has enough property a horizontal ground loop can be more cost efficient (but not always), since it does not require a drilling rig, only a backhoe or ditch witch.

Open Loop System

 

The primary difference between open and closed looped systems is the use of ground water.  An open loop system is less common, you need to have an ample source of ground water. An open loop system is connected directly to a ground water source such as a well or pond and directly pumps the water into a building to the heat pump unit where it is used for heating and cooling.

Where does the used water go?

There are several ways that open loop geothermal heat systems can dispose of water. One is through surface drainage, where the water is deposited to a low area, such as a pond or river. Another method of ridding of water is re-injection. In this process, water is pumped back into the water source through a separate discharge well. In returning the water back to the earth, it is important to note that there is no pollution generated. The only difference in the water once processed through the geothermal heat pump is a slight change in temperature.

Before installing an open loop system, it is critical to know whether the well contains enough water to power your geothermal heat pump. Although a well may contain the necessary amount of water for your geothermal heat pump, it could also deplete a neighbor’s well source. Make sure to check with your local contractor on whether there is enough water to install an open loop geothermal heating system. Other concerns about open wells are expressed in the post below.

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Comments (19)

 

  1. A closed-loop system is more reliable and requires less maintenance in the long term. With an open-loop you are also taking the risk that the wells drilled on your property will produce as many gallons per minute of clean water necessary to make the system operate at capacity with the proper flow rate. The water should be tested for hardness, acidity and iron content before a heat pump is installed. Even water which has suitable qualities could change with time to poor quality that causes problems with corrosion and scaling. One of the largest concerns people have with open loop systems is the potential for scale build up on the earth loop coil and desuperheater. Mineral deposits can build up inside the heat pump’s condenser. Even if a heat exchanger and filter are inserted to create an interior closed-loop to protect the heat pump, fouling can occur in the primary open loop along with diminished capacity. Impurities, particularly iron, can eventually clog a return well. If your water has high iron content you should be sure that the discharge water is not aerated before it’s injected into a return well. Using water from a spring, pond, lake or river as a source for your heat pump system is a poor choice because of excessive particles and organic matter. They can clog a heat pump system and make it inoperable in a short time. Because of water quality, a geothermal heat pump has a much shorter system life on open-loop. Since a closed loop system simply recirculates a constant volume of clean water, system longevity increases. Additionally, open loop well pumps are considerably larger than the small circulators used on closed-loop flow centers and require considerably more maintenance and cost to replace in the case of mechanical failure. The potential added cost of having to replace a well or its various components could outweigh the cost differential you had chosen it for to begin with.

    A closed-loop system presents absolutely no environmental impact to the earth or our aquifers and this is recognized by environmental authorities. As such, no special permitting or licensing is required. In some localities, all or parts of an open-loop installation may be subject to local ordinances, codes, covenants or licensing requirements. Here on Long Island, we are lucky enough to be independent of the reservoir system for our drinking water because we have abundant clean water beneath our feet. However, this water is threatened on a daily basis by chemical run-off, pollution and aquifer cross-contamination. Typically, the upper aquifer may be unsuitable for drinking purposes and is considered gray water because of fertilizer, chemical, fuel, pollution and storm water run-off. Adding to this contamination should not be taken lightly. An improperly installed open-loop system can have a considerable environmental impact in the case of aquifer cross contamination.

  2. Dr. Thomas Smith, Mechanical Engineer says:

    Everything mentioned about open loop systems above is true. However….

    I designed and engineered my open loop geothermal system over thirty years ago. I bought a 230 year old farmhouse on over 8 acres, that had 3 wells. The first well was the main well used for supplying the house, it’s over 300 feet deep, the other two wells were hand dug wells both at 25 feet deep.

    After conducting tests on all wells, results showed that all wells were producing tons of water… 20-25 gpm! The water quality was good, except for being very hard.

    I brought down the hardness of the water with a good water softener and also installed a heavy duty water filter for sediment from the wells.

    Because the two 25 foot wells produced an abundant amount of water, I chose to use them as my supply and dump for my system. The one well was at the top of my property (supply) and had a root cellar for easy access, the other (dump) was located on the lower side of my property in a big open field.

    After the proper excavation and running the pipes to the wells, it was easy to finish the inside work.

    I live in a rural neighborhood, every house has at least 1-2 acres, while others have 80 acres or more. Most of the major farms are preserved. My land is preserved through a conservation easement I set up, and my neighbors 80 acre farm is also preserved. I didn’t have to worry about more wells being drilled, that might take away from my wells.

    I have never had any problems with my open loop system. Some more maintenance of the these systems are required…

    1. I get the well water tested every 5 years, check hardness, pH, Iron etc.

    2. I used to have to buy salt for the water softener, but replaced that with a simple scale inhibitor system, a lot cheaper than salt and works just as good.

    3. I have to replace my sediment filter every 8 months, could probably get away with once a year, but it gives me piece of mind.

    The above in maintenance costs plus general maintenance on the heat pump, have cost $3500 in 32 years. My system cost $5000 to build.

    My point is, a properly designed and maintained open loop system is every bit as good as a closed loop system and can be a lot less expensive to install.

    My neighbor recently had an 8 ton closed loop system installed and after all the incentives, it still cost $45,000!

    If the right circumstances are present for an open loop system, ie. you have multiple wells on your property, or a lake or pond, and they are big/ deep enough to produce the water you need, then an open loop system might be a VERY cost effective solution for geothermal, instead of a closed loop system.

    Also, I estimated my heating payback to be 5 years, based on oil prices in the 1980s, I did it in 3.5 years.

    My neighbors estimated payback on his closed loop system is 8 years.

    • Gar Eden says:

      Hello Tom ,
      I’m leaning toward a open loop system w/water treatment and was wondering how much salt per month you use. My other alternative is a reverse osmosis system. I’m looking at providing for a building of about 2500 sq. ft. My supply well is 90′ deep with the water table about 18′ . I am in an area where the discharge can be routed to a municipal drain/sewer.Would you offer any advice on this proposal?

    • S andrews says:

      Sounds like a great setup- hard to argue with 30 years of service from anything. I”d love to know what descaler setup you landed on. I am working toward an open loop with a lake water source and feel like a softener is overkill, but a descaler would be good insurance.

  3. Al says:

    Can you provide details on the scale inhibitor and sediment filter you have used.

    I have just purchased a home with an open loop Geothermal and want to try and improve the source water to cut down on wear and tear of valves and system

  4. Benje Estes says:

    I am about finished with open loop geothermal heat pump and ran few tests lately. I noticed that sediment filter clogged after 20 minutes of run time. Dr. Thomas Smith mentioned heavy duty sediment filter. Can you give me the source of where I can get it.

  5. Allen says:

    I also have had and open loop geothermal Waterfurnace and it ran consistently for 25 years without any maintenance except one blower motor. We live in a slide zone where any trenching or shallow wells are not permitted. So we had a choice of geothermal and electric. With a COP of 3.9 and electricity at $.14 per KWH it was an obvious choice. In 25 years we never used the aux electric heat so I finally use that circuit for an RV barn. Sometimes you have to go with open loop and with the cost of horizontal drilling and the amount of pipe needed it takes a long time to payback. Also a deep well produces water at the same temp year around. In my case it is 53 degrees. Closed loop systems do affect the surrounding ground temperatures and under heavy loads your efficiency goes down. Research research research then do more research.

  6. R.E. Potter says:

    Something not mentioned is that the open system’s

    EER is the highest for ALL water-source heat-pumps.

    Consider a closed-loop hovering around 32F in the

    winter versus 55F well water running through the

    heat-exchanger coil…..BIG difference!

  7. norm czepiela says:

    Hi everything said is true, One very important fact is not identified that the cost of running a well pump 15A to supply the water to yr Geo while a circulating pump runds at 1A. The cost of Hydro over a short time exceeds the extra cost of a horizontal loop.

    • Clayton Ross says:

      Norm that’s not how it works, GPM of water moved = energy used, if my heat pump is using 3GPM then my well pump is not used any more electricity than the circulating pump. in fact my pump has much shorted to go with less resistance!! and in the winter warmer water = less pumping in the summer cooler water = less pumping

  8. Kris Cal says:

    Just wanted to chime in that I have a 35 year old Friedrich water to air geothermal system that uses an open loop shallow well system with 1 well pump. In the 35 years I have only had to replace the well pump once. Even if the unit decided to conk out soon, the initially investment and longevity of this open loop system would have been astronomical of service life and reliability.

    Cheers

  9. […] The liquid heat-exchange medium can either be installed in a closed underground loop or an open underground loop depending on the specifics of the project. An open loop requires a nearby aquifer and a well, making closed-loop systems more common. […]

  10. Bob Prudhomme says:

    Hello

    I have been following this conversation with great interest, and now I have a couple of questions.

    Dr. Thomas Smith, the “scale inhibitor” you replaced your water softener with, are these units also referred to as “salt free water conditioners”?

    I have been speaking to sales people about ground source heat pumps, and they are all eager to sell me very expensive closed loop systems. I believe I may have the ideal location here for an open loop system, and would like everyone’s opinion on this.

    I live on the north coast of British Columbia, Canada, just south of the Alaskan Panhandle. Contrary to popular belief, our winters are very mild here, and do not get much colder than Seattle, WA. At present, I have a 23,000 BTU air-to-air heat pump I installed myself that heats my 1800 sq. ft. home through most of the winter. For the 3 or 4 weeks our temperatures drop 6 or 7 degrees below freezing, I turn on a couple of 500-750 watt baseboard heaters to take the chill off. This has more to do with only having one heat exchanger for my heat pump, and heat’s reluctance to travel sideways.

    As I live in a rain forest, there is an unlimited supply of groundwater here in a gravel aquifer (old beach). Wells here have unlimited pumping capacity as the gravel allows almost instantaneous recharge. Groundwater temperature is 46-48° year round, and measuring an old sandpoint well on my property shows the aquifer to be within 7 feet of the surface most of the winter, and never more than 12 feet in the summer.

    Norm Czepiela points out that a circulating pump in a closed loop will consume 1 ampere of electricity, while a well pump suplying an open loop may consume as much as 15 amperes of electricity. Is this a fair comparison? While a well pump must normally pressurize a bladder tank to as much as 60 psi, would an open loop system not require much lower pressures, perhaps as little as 5 psi? Combining this with the very short vertical distance I have to lift the water (7-12 feet), would this not reduce the electricity demand by a great deal?

    I would also be interested to know the gpm required for an open loop, given that my ground water temperature stays at 46-48°.

    Thanks in advance.

  11. We installed a closed loop system after having an open system here since the 1980s. We like the consistency and the money savings, however we have air in the lines that have to be bled every few days and water/antifreeze replenished. How do we avoid this continuing problem? We have air release valves on intake and output lines but do not seem effective.

  12. Hi. I live in Seminole, Florida a stones throw from the intercoastal waterway in Madiera Beach, FL.

    My house was built in the mid 50’s by a gentleman from NY. He had a orchid farm several acres around the house. It is now residential.

    In the center of the house, next to a New York stone wall and fireplace, is a deep well! We bought the house in 2013. Our house inspector and the many people we asked had no clue what this “secret” place was. The builder’s granddaughter drove by the house and asked if she could see it. I asked and she told us about the orchid farm and the well.

    Could we use this as an open geothermal system? If yes, a ball park estimate of the cost… no I won’t hold you to it!

    Thanks, Meredith Slavins

  13. Tom newell says:

    I have a geo system with water pump and large pond for the outflow water. Only broblem is water noise. I recently found the main water pipe is resting on top of the plenum , could the water sound travel through the ducts ?

  14. Paul C Menten says:

    Seems to me that if you have two wells, one for supply and the other for discharge, you could circulate water with a siphon system, possibly aided by a small pump.

  15. Considering Geothermal says:

    I see the open loop’s cost saving mostly from utilizing an existing water source without the digging/drilling job. Can’t you run a close loop in the wells or ponds and get both benefit of a close loop system and cost saving?

  16. Ron Kalvaitis says:

    Be sure to calculate the cost of pumping large amounts of water from the ground. I’ve had an open loop geo thermal system for 2 years and the cost of pumping the water seems to be huge during the winter. We often have minus zero temperatures. I’m getting a Sense power monitor to be sure, but I’m going to look at the cost of converting to a closed loop. I understand the secret of making a closed loop, vertical system work is to put in enough “wells”. At about $.13 a KWh we had an electric bill of between 2 and 3 thousand dollars per winter. Most of it is going, I believe to pumping the water. Our house is only two years old. Our solar panels were designed to get us to net zero but we’ve missed the mark. I believe it is due to the cost of running the water pump (not running the “Water Furnace”).

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