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 (2)

 

  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.

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