Completion of the workshop, including passing the installer's exam, leads to accreditation as a geothermal system installer.
The comprehensive course includes five manuals: Closed-Loop/Ground-Source Heat Pump Systems: Installation Guide; Soil and Rock Classification manual; Grouting Procedures manual; Slinky Installation Guide; and Design and Installation Standards. A study guide is also provided.
Topics covered include design and material options, cost considerations, ground heat exchanger design, system layout, pipe joining techniques, trenching-drilling processes, air and debris purging, pressure drop calculations, pump and fluid selection, and troubleshooting.
The News sat in on two sessions of the workshop at the conference to learn more about this technology.
For heating, the ground-loop extracts thermal energy from the earth and transfers it to the refrigerant in the system. The compressor compresses the refrigerant gas and puts a small amount of superheat into domestic hot water. The hot gas then goes to the heat exchanger to supply warm air to the conditioned space.
The cooling mode operates in reverse. The cooler temperature of the ground cools the refrigerant, supplying cool air to the space, while building heat gain is rejected as waste heat to the ground.
Eitelman then discussed horizontal and vertical ground loops. A horizontal loop takes up a lot of space and requires a lot of trenching. A vertical loop goes down 200 to 300 ft. "It can get into tight places," he noted.
The colder in winter or the hotter in summer that you let the ground loop get, the lower the efficiency of the system.
There are actually four loops we're concerned with in a geo-thermal heat pump system:
1. The air loop, which is used to distribute conditioned air to the building;
2. The refrigerant loop, which is sealed and pressurized, and transports thermal energy in the circuit;
3. The ground loop, a sealed and pressurized loop of water or antifreeze solution that is circulated below the earth's surface; and
4. The domestic hot water loop, a sealed, pressurized loop that circulates water from the hot water heater to a heat pump's desuperheater for preheating domestic hot water.
Regarding antifreeze solutions, Eitelman stated that "There is no perfect antifreeze."
Available antifreezes include:
For ground loop piping, he said, "It looks like polyethylene is the last one standing for pipe."
A long list of organizations is involved in ground-source heat pump applications, including utilities, contractors, heat pump manufacturers and distributors, plastic pipe manufacturers, fusion-joining equipment manufacturers, trenching and drilling equipment manufacturers, and universities and research organizations.
Benefits that a homeowner can expect with a geothermal system include:
Benefits for contractors are:
The design procedure for the geothermal heat pump system includes the following steps:
A properly designed system is sized so the entering water temperature (EWT) stays within designer-specified limits for the complete season. The minimum EWT is usually 40Â°F above the coldest outside temperature, or 25Â° to 30Â°, whichever is greater. The maximum EWT is 10Â° to 20Â° below the highest outdoor temperature.
Oversizing problems include:
A system should not be oversized by more than 25% of the design sensible cooling load, said Newton. As a general rule, unit-type equipment is designed to operate with a sensible heat factor (SHP) of 0.75 to 0.78.
The steps to design a ground heat exchanger are:
1. Select a ground heat exchanger configuration: horizontal or vertical, parallel or series flow.
2. Select plastic pipe, considering material, size, diameter, and length.
3. Estimate the ground heat exchanger length.
4. Select circulating pumps.
Besides horizontal and vertical systems, Newton said, you also have pond loops, slinky compact systems (for smaller lots), and slinky extended systems.
"There's no black magic in loop design," remarked Newton. Reference information is available to determine soil temperature variations and design variables.
A system should not be oversized by more than 25% of the design sensible cooling load.