Open Loop Vs. Closed Loop Geothermal

Geothermal systems are some of the most efficient residential and commercial heating and cooling systems available. They use the consistent temperature of the earth’s surface as a heat source in the winter and a heat sink in the summer. The consistent ground temperature provides a dependable constant which is high enough to provide heat for heating applications and low enough to absorb heat for cooling applications. There are many different ways to utilize geothermal energy for heating and cooling applications which fall into two different categories: open loop geothermal systems and closed loop geothermal systems.

Open Loop Geothermal

Open loop geothermal systems use groundwater, which acts as a refrigerant to transfer thermodynamic energy. Because water is an excellent thermal conductor and groundwater is naturally insulated and much closer in temperature to the surrounding ground, open loop geothermal systems are an excellent choice for efficiency. Open loop geothermal systems can be designed to use water from a well as a source and sink, a pond or lake as a source and sink, or a well as the source and a pond or lake as the sink. Every installation is different and various factors of each system determine cost, space needed, and efficiency of the system.

Closed Loop Geothermal

Closed loop geothermal systems are different from open loop geothermal systems in that they use a mix of antifreeze and water which cycles through pipes buried in the ground instead of using fresh groundwater to transfer heat. There are also different types of closed loop geothermal systems.

  • Horizontal - Horizontal closed loop geothermal systems are systems which use the piping laid horizontally in the ground. These systems can take up quite a bit of space as the loops are laid to run length-wise.
  • Slinky - A variation of the horizontal system is the slinky closed loop geothermal system. In a slinky loop system, the piping is laid horizontally, but first it is designed to look like a flattened and spread out slinky. This reduces the length of the trenches in which the pipes will be laid.
  • Vertical - Another type of closed loop geothermal system is the vertical closed loop geothermal system. Instead of running the pipes out horizontally, the pipes are run vertically between 100 and 400 feet deep in several wells and connected at the bottom by a U-bend. The boreholes are then filled with a grout so that the vertical pipes will get good thermal conductivity.

Which to Choose?

In most situations, the open loop geothermal systems are less costly and more efficient than closed loop geothermal systems due to the constant temperature of the ground water and the amazing conductivity of that water in comparison to the antifreeze in a closed loop geothermal system, which absorbs and releases heat through a polyethylene pipe. However, in many situations, open loop applications are not feasible either because there is no groundwater source available, the groundwater contains too much iron, or local code may prohibit open loop systems.

3 comments (view/add)
  • Porsche
    Posted on 1/17/2022

    For a closed loop vertical system, aren't the feed and return pipes usually right next to each other? Doesn't this have a significant reduction in efficiency, where the return pipe cools the incoming water of the feed pipe?

    Also, for an open loop system, depending on the particular mineral content, can the water be filtered to protect the equipment?

  • Rebekah Muller
    Rebekah Muller from Ingrams
    Posted on 1/21/2022

    The outgoing and incoming lines are only next to each other for the short distance required to enter the structure so there will be very little effect on heat transfer for the ground loop[ as a whole. Yes depending on water quality it may be possible to filter or treat the water to make it acceptable.

  • River Bergquist
    River Bergquist
    Posted on 10/1/2020

    Thank you! Very informative and helpful.

* All fields required.

Your email address will not be published. Comments will display after being approved by our moderators. Comments may be edited for clarity.