The current periodic table of chemical elements contains 117 substances divided into four categories—solid, liquid, gas, and unknown. This is a great departure from the original Greek philosophy which named water, air, fire, and earth as the only elements. Yet, the Grecian quartet is the basis for alternative energy methods. Water is used for hydroelectricity; air creates wind power; and fire is the sun and the source necessary for solar energy. But what about the earth? How can energy be extracted from the ground in order to heat and cool a facility? The answer is a geothermal heat pump (GHP).
GHPs (also known as GeoExchange, earth coupled, ground source, or water source heat pumps) use the constant temperature of the earth instead of fluctuating outside air temperature as the exchange source. A few feet below its surface, the earth maintains a fairly constant temperature year round—from about 45 degrees F in northern climates to about 70 degrees F in the Deep South. GHPs use this consistency to their advantage.
During winter, fluid (either water or an antifreeze solution) in pipes collects heat from the earth and brings it through the system and into the facility. Inside, an indoor unit compresses the heat, concentrates it, and then releases the warmer air. The opposite takes place in the summer—building heat is pulled out, transferred through the heat pump to a loop, and absorbed back into the earth. The only electricity necessary assists with operating the heat pump, ground loop pump, and distribution fan or pump.
Geothermal energy is not new. Paleo-Indians tapped hot springs at least 10,000 years ago and are considered the first humans in North America to make use of these resources. GHPs were created over 60 years ago. Carl Nielsen of Ohio State University developed the original GHP for use at his home in 1948. An engineer from Portland, OR, J.D. Krocker was the first to install one for commercial use the same year.
What To Choose
The three main parts of a GHP are the air delivery system (ductwork), heat pump unit, and the liquid exchange medium, also known as the loop. Depending on where a facility is geographically, a facility manager (fm) can choose from four types of loop systems. Costs, climate, soil conditions, and available land can all impact which one is the most appropriate for a particular site.
Closed loop horizontal: This set up is considered the most cost-effective for residential installations, especially where land is plentiful. Trenches at least three feet deep are dug, and a series of parallel pipes are set. Pipes need to be made of high density, polybutylene or polyethylene. They can be buried at different depths or side by side. Pipes can also be coiled, like a Slinky toy, to save money and assist with horizontal installation where it would normally be difficult.
Closed loop vertical: This configuration is more suitable to facilities such as schools and large commercial buildings. Vertical loops are necessary in locations where the soil is too shallow for trenching. Four inch diameter holes are bored approximately 20′ apart and from 100′ to 450′ deep. A pipe is inserted into each hole and connected by thermal fusion to form a U-shape at the bottom. These are then connected to underground horizontal pipes (manifolds), which carry fluid to and from the heat exchanger. Vertical loops tend to be more expensive but require less piping since the Earth’s deep temperature is warmer in winter and cooler in summer.
Pond/lake: Of all the choices, this one often makes the most economical sense. However, a nearby water source is required to make it function. Long sections of pipe leaving a facility are submerged under the water and coiled deep enough below the surface to prevent freezing. If using a pond loop, fms need to be sure that the water level does not drop below 6′ to 8′ at its minimum to ensure proper heat transfer.
Open loop: This method is arguably the simplest to install. However, it functions with the use of well or surface body water. Ground water is the heat exchange fluid and goes directly through the GHP. The water returns to the ground through another well. An abundance of clean water is needed for this system, and local authorities must be contacted regarding environmental regulations.
It’s Not Free
Whether installing a GHP for a new facility or retrofitting one to an older building, initial costs vary. Some may cost double, especially if drilling rather than digging is required. Buildings in cold climates may need multiple capacity units to handle the gaps between cooling and heating loads. Others may see little variation when compared to the price of a four pipe boiler/chiller system.
A GHP could be even less expensive than low quality traditional HVAC systems. Much also depends on the size of the building slated for the GHP. The systems pay for themselves over time due to other savings, such as the need for 50% to 80% less mechanical room space and no chiller or boiler maintenance.
“The payback period is anywhere between three and seven years depending on the existing system and the old one versus the new one,” says David Goldsholl of Glen Rock, NJ-based Eastern Natural Resources Group. “With more tax credits on the way (courtesy of the five year extension of the Energy Efficient Commercial Building Tax Deduction), it will be quicker payback.”
The biggest savings come on energy use since GHP heating efficiencies are 50% to 70% higher than other heating systems; cooling efficiencies can be anywhere from 20% to 40% better than traditional air conditioning systems. The U.S. Environmental Protection Agency (EPA) estimates that schools using GHPs are saving $25 million in energy costs.
Land Of Lincoln Installation
One facility making use of GHPs is the Sherman Hospital, currently under construction in Elgin, IL. Mechanical, Inc. decided to use an open loop lake system for the building’s heating and cooling needs. There was only one problem—no lake. So Mechanical decided to build one.
The 15 acre, 17′ deep body of water will hold the largest lake loop heat pump system in the nation (275,000 feet of 2″ piping) while the hospital is the first in Illinois with a geothermal lake. The system will heat and cool every part of the hospital, except the emergency room and surgical suites (which require colder temperatures and use a traditional HVAC system). The system will save nearly $1 million annually in utility costs.
Fms may want to consider some of the other benefits of a GHP, including being able to set up multiple zones (with each zone having an individual room control), having a maintenace free piece of equipment with a 40 plus year service life, and doing away with any above ground equipment.
However, GHPs are not a cure all to HVAC needs. All systems require an emergency back up. A contractor decides what portion of the heat should be generated from the heat pump and how much should come from the auxiliary source. Also, there are additional installation fees for any required facility adaptations, such as ductwork, electrical work, and water hook up.
GHPs have a positive impact on the environment. According to the U.S. Department of Energy Office of Geothermal Technologies, nearly 40% of all U.S. emissions of CO2 are a result of facilities using energy to provide hot water, cooling, and heating—equal to the amount generated by the transportation sector. Because GHPs conserve natural resources, emissions are lowered. Ozone layer depletion is also minimized, because the refrigeration systems are sealed.
The International Ground Source Heat Pump Association (IGSHPA) estimates current systems are eliminating three million tons of CO2 from the air, equal to removing 650,000 cars from the road. The EPA estimates the U.S. can reduce oil imports by 61 million barrels annually and offer the same environmental impact as converting nearly four million cars to zero emission vehicles or planting eight million acres of trees if every U.S. school converted to GHPs. The agency said nothing about the implementation costs to school districts.
GHPs can assist with obtaining LEED credits from the U.S. Green Building Council. These systems are helpful in the category of LEED Energy and Atmosphere Credit 1, Optimize Energy Performance, which is worth one to 10 points for 10.5% to 42% energy cost savings.
While solar and wind seem to get most of the attention when it comes to alternative energy sources, GHPs may be making up some ground, says John Turley, president and owner of Middleton Geothermal Services, LLC, based in Akron, OH.
“In our area, we see many facilities moving toward ground source systems,” says Turley, who is also the IGSHPA Advisory Council president. “In past years, public buildings have seen a greater share of the market than the private sector. The private sector will see more rapid growth with the recent passage of federal tax credits for commercial systems. The future is very bright.”
Goldsholl says, “I believe it is the sleeping giant of alternative energy.”
Whether fms agree is a different story. Budgets do not appear to be increasing in 2009, and large projects for alternative HVAC systems, such as GHPs may be put on hold. That does not mean the future for GHP is dimming. After all, geothermal use has been going on for thousands of years, so what’s a few more?