ACHRNEWS

Taking the Geothermal Certification Track

June 5, 2000
STILLWATER, OK -- Normally offered as a separate three-day workshop, this year the International Ground Source Heat Pump Association (IGSHPA) included its Installation Workshop as part of its 2000 Technical Conference here.

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.

Tap Into The Source

The opening session, "Introduction to the Ground Source System and Economics, Marketing, and Demand Reduc-tion," was taught by Larry Eitelman of Florida Heat Pump. He talked first about the basic heating and cooling cycle.

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:

  • Salts -- calcium chloride and sodium chloride; "But salt is corrosive," he said.

  • Glycols -- ethylene and propylene; "But these are pricey chemicals and they get more viscous when cold."

  • Alcohol -- methyl, ethyl, and isopropyl; "They're cost effective but toxic."

  • Potassiums -- acetate and carbonate. Eitelman thinks acetate is going to be the winning antifreeze.

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:

  • Utility savings;

  • Energy conservation;

  • Cleanliness;

  • Long system life;

  • Low system maintenance; and

  • Low noise generation.

Benefits for contractors are:

  • The ability to compete in areas with low-cost fossil fuels for those consumers who desire electric heating;

  • The fact that geothermal is a higher-priced system with excellent paybacks, so you make a good profit; and

  • The fact that it is simple in operation with a long lifetime.


Make Your Selection

The session on "Selecting, Sizing, and Designing the Heat Pump System" was taught by Howard Newton of The Trane Company.

The design procedure for the geothermal heat pump system includes the following steps:

  • Determine the heating and cooling loads.

  • Select a properly sized heat pump system.

  • Select an indoor air distribution system.

  • Select proper air supply diffusers, registers, and return grilles.

  • Size the indoor air distribution system.

  • Estimate the building's energy requirements.

  • Estimate the ground heat exchanger loads.

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 40°F above the coldest outside temperature, or 25° to 30°, whichever is greater. The maximum EWT is 10° to 20° below the highest outdoor temperature.

Oversizing problems include:

  • Poor comfort;

  • Frequent cycling;

  • High average coil temperatures;

  • Poor moisture removal;

  • Reduced life; and

  • Reduced operating efficiency.

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.