How Geothermal systems work

What is Geothermal energy?

There are two types: High & Low. High-grade geothermal energy is the heat of the earth’s pressure that turns water into steam. Old Faithful at Yellowstone National Park is an excellent example. Low-grade geothermal energy is the heat within the earth’s crust. This heat is actually stored solar energy. ECONAR taps into this low grade geothermal energy and delivers big energy savings when heating, cooling and making hot water. 

What is a Geothermal heat pump?

A heat pump is a mechanical device used for heating and cooling which operates on the principle that heat can be moved from a warmer temperature to a cooler temperature. A geothermal heat pump uses the earth to warm us in the winter and cool us in the summer.  You already have a heat pump in your home – your refrigerator. If you put your hand behind it you’ll feel the heat that has been removed from the food inside the refrigerator. This is the same principle that ECONAR uses to move heat to and from the home and earth.

The technical view of the heat pump process.

Remember that the heat pump moves heat from a low temperature source to a high temperature source. The process of elevating low temperature heat to over 100°F and transferring it indoors involves a cycle of evaporation, compression, condensation and expansion. A refrigerant is used as the heat transfer medium which circulates within the heat pump. The cycle starts as the cold liquid refrigerant passes through a heat exchanger (evaporator) and absorbs heat from the low temperature source (liquid from the ground loop). The refrigerant evaporates into a gas as heat is absorbed. The gaseous refrigerant then passes through a compressor where the refrigerant is pressurized, raising its temperature to over 160º F. The hot gas then circulates through a refrigerant-to-air heat exchanger where heat is removed and pumped into the home at about 100º F. When it loses the heat, the refrigerant changes back to a liquid. The liquid is cooled as it passes through an expansion valve and begins the process again. To air condition, the flow is reversed. 

What is an open-loop system?

An open-loop system is used less frequently, but may be employed cost-effectively if ground water is plentiful. Open-loop systems in fact, are the simplest to install and have been used successfully for decades in areas where local codes permit. This type of system uses ground water from an aquifer and is piped directly from the well to the building, where it transfers its heat to a heat pump. After it leaves the building, the water is disposed of by one of three methods.

  1. Surface drainage – to a low area such as a pond, river, lake or stream, etc.
  2. Sub surface – to a dedicated drainfield sized to the required volume of water of the heat pump.
  3. Re-injection or discharge well - water is pumped back into the same aquifer through a separate discharge well.

Local environmental officials should be consulted whenever an open-loop system is being considered. 

What is a closed-loop system?

Closed-loop systems are becoming most common. There are 5 types of closed loop systems. All types use a continuous loop where the heat transfer fluid is circulated.  A horizontal loop is usually the most cost effective when adequate yard space is available and trenches are easy to dig. Using trenchers or backhoes digging trenches three to six feet below the ground, you then lay a series of parallel plastic pipes. The trench is then back filled, taking care not to allow sharp rocks or debris to damage the pipe. A typical horizontal loop will have 400-600 feet of pipe per ton of heating and cooling capacity.

Vertical loops are preferred in many installations where yard space is insufficient and where preservation of existing landscaping is desirable. Contractors bore vertical holes in the ground 150-450 feet deep. Each hole contains a single loop of pipe with a U-bend at the bottom. The hole is then backfilled or grouted to improve the thermal conductivity. Each vertical pipe is then connected to a horizontal pipe underground to and from the heat pump. Vertical loops are generally more expensive to install, but require less piping than horizontal loops.

Slinky loops are used to reduce the heat exchanger per foot trench requirements but require more pipe per ton of capacity. This pipe is coiled like a slinky, overlapped and laid in a trench. Two-pipe systems may require 200-300 feet of more pipe per ton of nominal heat exchange capacity. The trench length decreases as the number of pipes in the trench increases or as slinky overlap increases.

Pond loops are a special kind of closed loop system. Where there is a pond or stream that is deep enough and with enough flow, closed loop coils can be placed on the bottom. Geothermal transfer fluid is pumped just as a closed loop ground system. First cost economics are very attractive and there is no aquatic environmental impact.

Geothermal heating and cooling systems can be connected to the earth in a variety of ways. High system performance is dependent upon good installation practices. ECONAR’s highly trained authorized dealers are professionals who understand local codes and conditions. Visit our where to buy area and you’ll find an ECONAR authorized dealer who can discuss the best system for you.