GILDERSLEEVE GEOTHERMAL

Open Loop Systems

What is an open-loop system?

The term “Open-Loop” is commonly used to describe a geothermal heat pump system that uses groundwater from a conventional well as a heat source in winter and a heat sink in summer. The groundwater is pumped through the heat pump where heat is extracted (in winter) or rejected (in summer) then the water is disposed of in an appropriate manner. Since groundwater is a relatively constant temperature year-round, it is an excellent heat source/heat sink.

What do I do with the discharge water?

There are a number of ways to dispose of water after it has passed through the heat pump. The open discharge method is the easiest and least expensive. Open discharge simply involves releasing the water into a stream, river, lake, pond, ditch or drainage tile. Obviously, one of these alternatives must be readily available and must possess the capacity to accept the amount of water used by the heat pump before open discharge is feasible.

A second means of water discharge is the return well. A return well is a second well bore that returns the water to the ground aquifer. A return well must have enough capacity to dispose of the water passed through the heat pump. A new return well should be installed by a qualified well driller. Likewise, a professional should test the capacity of an existing well before it is used as a return.

How much groundwater does an open-loop system need?

Geothermal heat pumps used in open-loop systems need differing amounts of water depending on the size of the unit. The water requirement of a specific model is usually expressed in gallons per minute (l/s) and is listed in the specifications for that unit. Your heating and cooling contractor should be able to provide this information. Generally, the average system will use 6-1 0 G.P.M. [0.4 – 0.6 l/s] while operating. An extremely cold day might result in a usage of 6,000-1 0,000 gallons [23,000 – 38,000 liters] of water.

Your well and pump combination should be large enough to supply the water needed by the heat pump in addition to your domestic water requirements. You will probably need to enlarge your pressure tank or modify your plumbing to supply adequate water to the heat pump.

What problems can be caused by poor water quality?

Poor water quality can cause serious problems in open-loop systems. Your water should be tested for hardness, acidity and iron content before a heat pump is installed. Your contractor can tell you what level of water quality is acceptable.

Mineral deposits can build up inside the heat pump’s heat exchanger. Sometimes a periodic cleaning with a mild acid solution is all that’s needed to remove the build-up.

Impurities, particularly iron, can eventually clog a return well. If your water has a high iron content you should be sure that the discharge water is not aerated before it’s injected into a return well.

Finally, you should opt against using water from a spring, pond, lake or river as a source for your heat pump system unless it’s proven to be free of excessive particles and organic matter. They can clog a heat pump system and make it inoperable in a short time.

If water quality is a concern, a closed-loop system should be used.

Does an open-loop system cause environmental damage?

No. They are pollution free. The heat pump merely removes heat from or adds heat to the water. No pollutants are added whatsoever. The only change in the water returned to the environment is a slight increase or decrease in temperature.

Are there any laws that apply to open-loop installations?

In some localities, all or parts of the installation may be subject to local ordinances, codes, covenants or licensing requirements. Check with local authorities to determine if any restrictions apply in your area.