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Geothermal heat pumps (GHPs) have been shown to have a number of benefits over other technologies used to heat and cool buildings and provide hot water, combining high levels of occupant comfort with low operating and maintenance costs. Public facilities represent an increasingly important market for GHPs, and schools are a particularly good application, given the large land area that normally surrounds them. Nevertheless, some barriers remain to the increased use of GHPs in institutional and commercial applications. First, because GHPs are perceived as having higher installation costs than other space conditioning technologies, they are sometimes not considered as an option in feasibility studies. When they are considered, it can be difficult to compile the information required to compare them with other technologies. For example, a life cycle cost analysis requires estimates of installation costs and annually recurring energy and maintenance costs. But most cost estimators are unfamiliar with GHP technology, and no published GHP construction cost estimating guide is available. For this reason, estimates of installed costs tend to be very conservative, furthering the perception that GHPs are more costly than other technologies. Because GHP systems are not widely represented in the various softwares used by engineers to predict building energy use, it is also difficult to estimate the annual energy use of a building having GHP systems. Very little published data is available on expected maintenance costs either. Because of this lack of information, developing an accurate estimate of the life cycle cost of a GHP system requires experience and expertise that are not available in all institutions or in all areas of the country.
The lack of confidence in design methods has also led to the perception that GHPs have a high first cost. For example, ground heat exchangers can account for 20–30% of total system installation costs, and cost-effective design requires that they be sized as accurately as possible. A number of vendors have developed computer software to automate the calculations involved in sizing the ground heat exchangers. As shown in Chapter 5 of this report, these programs are now generally accurate; but because of a lack of confidence in the software, many system designers continue to rely on traditional rules of thumb, such as 150 bore feet per ton of cooling capacity installed. In most cases, this leads to oversized ground loops and a more costly installation.
In 1998, Oak Ridge National Laboratory (ORNL) entered into an agreement with the Lincoln, Nebraska, Public School District and Lincoln Electric Service, the local electric utility in the Lincoln area, to study four new, identical elementary schools built in the district that are served by GHPs. ORNL was provided with complete as-built construction plans for the schools and associated equipment, access to original design calculations and cost estimates, extensive equipment operating data [both from the buildings’ energy management systems (EMSs) and from utility meters], and access to the school district’s complete maintenance record database, not only for the four GHP schools, but for the other schools in the district using conventional space conditioning equipment. Using this information, we were able to reproduce the process used by the Lincoln school district and the consulting engineering firm to select GHPs over other options to provide space conditioning for the four schools. The objective was to determine whether this decision was the correct one, or whether some other technology would have been more cost-effective. An additional objective was to identify all of the factors that make it difficult for building owners and their engineers to consider GHPs in their projects so that ongoing programs can remove these impediments over time.