©2012 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 10, October 2012
Steve Kavanaugh, Ph.D., Fellow ASHRAE; Mike Green, P.E., Member ASHRAE; and Kirk Mescher, P.E., Member ASHRAE
About the Author
Steve Kavanaugh, Ph.D., is a professor emeritus of mechanical engineering at the University of Alabama, Tuscaloosa, Ala. Mike Green, P.E., is a principal at MEP Engineering in Austin, Texas. Kirk Mescher, P.E., is a principal at CM Engineering in Columbia, Mo.
Part 4: Installation Costs
This article is the fourth installment in a series of articles that summarize a data collection and analysis project to identify common characteristics of successful ground source heat pump (GSHP) systems. This article presents installation cost information that was provided for several of the newer projects.
Performance and cost surveys were collected and site visits were performed at 40 locations. This included 23 building owners, but only four building owners or engineers completed the installation cost portion of the surveys. Fortunately, they provided cost data for multiple buildings, some of which were monitored and several that were too new for performance rating or were under construction. The results are heavily weighted toward the two system types that achieved the highest ENERGY STAR ratings. Costs were available for seven systems with a one-pipe central loop in the building with small pumps that circulate liquid from a common supply and return pipe through the heat pumps. Data for seven unitary loop GSHPs in which each heat pump is connected to an individual loop and circulation is provided by a small on-off pump. Data for three central loop systems were also included along with results from a previous Electric Power Research Institute/Tennessee Valley Authority (EPRI/TVA) project and an ASHRAE research project.
The increase in the HVAC component costs of GSHP systems since the 1995 study has been 177% while the increase in ground loop portion was only 52%. In this recent study, the ground loop portion of GSHP systems accounted for 26% of the total while the HVAC component comprised 74% of the total. Thus, attempts to optimize GSHP cost by focusing primarily on the ground loop seemed illogical. The lack of responses to the cost component of the surveys is disappointing given commercial GSHPs are often avoided because of high cost. Emphasis should be placed on gathering additional detailed cost information to expand the results and further develop the conclusions of this article.
Figure 1 shows the costs for the complete GSHP system and the ground loop portion based on floor area. The Illinois (IL) systems are one-pipe loops, the Texas (TX) systems are unitary loops, and the Tennessee and Georgia (TN/GA) systems are central loops. The ground loop costs for the IL and TN/GA loops include the vertical bore and exterior header costs while the TX systems also include the interior building piping and pump costs.
The average system cost including the ground loop was $20.75/ft2 ($223/m2) with a high of $26.10/ft2 ($281/m2) and a low of $13.34/ft2 ($144/m2). The average ground loop cost was $5.29/ft2 ($57/m2) with a high of $8.89/ft2 ($96/m2) and a low of $3.35/ft2 ($36/m2). The average cost of the ground loop was 25.5% of the total GSHP system cost based on floor area. Costs for the TX systems include non-GSHP equipment. Figure 2 shows the costs for the total GSHP system and the ground loop cost based on the rated capacity of the heat pumps. Again, the ground loop costs for the IL and TN/GA loops include the vertical bore and exterior header costs while the TX systems also include the interior building piping and pump costs. The system cost for the TX systems based on equipment capacity are not included because the common areas were heated and cooled by non-GSHP equipment.
The average GSHP system cost was $7,694/ton ($2,190/kW) with a high of $9,206/ton ($2,620/kW) and a low of $6,291/ton ($1,790/kW). These values include the cost of the ground loop. The average ground loop cost was $2,483/ton ($706/kW) with a high of $4,076/ton ($1,160/kW) and a low of $1,209/ton ($344/kW). As shown in Figure 2, the low value was for the system installed in 1999, which also had a relatively short loop length for the rated capacity of the installed equipment. The average cost of the ground loop was 32.3% of the total GSHP system cost based on rated equipment capacity.
Citation: ASHRAE Journal, vol. 54, no. 10, October 2012
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