Geothermal heat pumps:
Closed-loop systems

Q: What is a closed-loop system?
A: The term "closed-loop" is used to describe a geothermal heat pump system that uses a continuous loop of special buried plastic pipe as a heat exchanger. The pipe is connected to the indoor heat pump to form a sealed, underground loop through which an antifreeze solution is circulated. Unlike an open-loop system that consumes water from a well, a closed-loop system recirculates its heat transferring solution in pressurized pipe.

Q: Where can this loop be located?
A. That depends on land availability and terrain. Most closed- loops are trenched horizontally in yards adjacent to the home. But any area near a home or business with appropriate soil conditions and adequate square footage will work.

Q: How deep and long will my trenches be?
A: Trenches are normally four to six feet deep and up to 400 feet long, depending on how many pipes are in a trench. One of the advantages of a horizontal loop system is being able to lay the trenches according to the shape of the land. As a rule of thumb, 500-600 feet of pipe is required per ton of system capacity. A well- insulated, 2,000-square-foot home would need about a three-ton system with 1,500-1,800 feet of pipe.

Q: How many pipes are in a trench?
A: Normally, a run of pipe is laid at five feet then looped back over itself at three feet once the bottom pipe is covered with soil. This allows more length of pipe to be put in one trench and has no adverse affect on system efficiency. Other loop designs use four or six pipes and allow for shorter trenches if land area is limited.

Q: What if I don't have enough room for a horizontal loop?
A: Closed-loop systems can also be vertical. Holes are bored to about 125-150 feet per ton of heat pump capacity. U-shaped loops of pipe are inserted in the holes. The holes are then backfilled with a sealing solution.

Q: How long will the loop pipe last?
A: Closed-loop systems should only be installed using high- density polyethylene or polybutylene pipe. Properly installed, these pipes will last 25-75 years. They are inert to chemicals normally found in soil and have good heat conducting properties. PVC pipe should not be used under any circumstances.

Q: How are the pipe sections of the loop joined?
A: The only acceptable method to connect pipe sections is by thermal fusion. Pipe connections are heated and fused together to form a joint stronger than the original pipe. Mechanical joining of pipe for an earth loop is never an accepted practice. The use of barbed fittings, clamps and glued joints is certain to result in loop failure due to leaks.

Q: Will an earth loop affect my lawn or landscape?
A: No. Research has proven that loops have no adverse effect on grass, trees or shrubs. Most horizontal loop installations use trenches about six inches wide. This, of course, will leave temporary bare areas that can be restored with grass seed or sod. Vertical loops require little space and result in minimal lawn damage.

Q: Can I reclaim heat from my septic system disposal field?
A: No. An earth loop will reach temperatures below freezing during extreme conditions and may freeze your septic system. Such usage is banned in many areas.

Q: If the loop falls below freezing, will it hurt the system?
A: No. The antifreeze solution in the loop will keep it from freezing down to about 10 degrees F. Three types of antifreeze solution are acceptable: propylene glycol, calcium chloride and methyl alcohol.

Q: Can I install an earth loop myself?
A: It's not recommended. In addition to thermal fusion of the pipe, good earth-to-coil contact is very important for successful loop operation. Nonprofessional installations may result in less than optimum system performance.

Most closed-loop systems use trenched-in pipe as a heat source.

Q: I have a pond near my home. Can I put a loop in it?
A: Yes, if it's deep enough and large enough. A minimum of six feet in depth at it's lowest level during the year is needed for a pond to be considered. In pond loops, copper, polyethylene or polybutylene pipe can be used.

A pond can be used as a heat source if it has adequate depth.