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Long-Term Commercial GSHP Performance--Part 6--Maintenance and Controls

©2013 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 55, no. 1, January 2013.

By Steve Kavanaugh, Ph.D., Fellow ASHRAE; and David Dinse, Member ASHRAE

About the Authors
Steve Kavanaugh, Ph.D., is a professor emeritus of mechanical engineering at the University of Alabama, Tuscaloosa, Ala. David Dinse is a senior project manager in Technology Innovation at the Tennessee Valley Authority, Chattanooga, Tenn.

This article is the sixth in a series summarizing a data collection and analysis project to identify common characteristics of successful ground source heat pump (GSHP) systems. This article presents results from maintenance personnel assessments of GSHP including controls. Occupant perception of maintenance responsiveness and controls also are provided.


Maintenance Personnel and Occupant Survey Results

Near the end of this project it became apparent that many of the operation and maintenance (O&M) personnel servicing GSHPs had useful insights into the long-term performance of these systems. A survey was distributed to 15 personnel who had been assigned to serve as guides during the site visits. Maintenance and energy managers from four school districts responded. The survey consisted of providing the information in Table 1 and spaces for responses to the following queries:

  1. List the operation and maintenance advantages of GSHPs;
  2. List the operation and maintenance disadvantages (or problems) of GSHPs; and
  3. Provide recommendations for future GSHPs to improve O&M.

An unexpected result from the survey, shown in Table 1, is that a single HVAC service technician is responsible for three to eight buildings.

Occupant satisfaction with the responsiveness to maintenance issues and ability to control has previously been presented in relation to ENERGY STAR rating. Figure 1 displays the occupant satisfaction with maintenance responsiveness results by date of system installation and distinguishes results by control type. Systems with room thermostat controls had average ratings of "satisfied" and levels remain relatively constant with system age. GSHPs with building automation system (BAS) controls had slightly lower maintenance response satisfaction ratings but there is a notable decline for newer systems.

Figure 2 plots occupant satisfaction with ability to control by date of system installation. Systems with thermostat controls had average ratings approaching "satisfied," but levels decline somewhat with newer installations. GSHPs with building automation system (BAS) controls had average satisfaction ratings below "acceptable" and ratings also decline for newer systems.


Maintenance and Operation Personnel Comments

When Jeff Monahan, maintenance and construction coordinator for McLean County (IL) Unit No. 5, learned that several older schools would be converted to GSHPs, he was sure he would have to hire additional maintenance staff to deal with all the compressors. “Nothing could be further from the truth. We rarely make service calls at the older schools with the geothermal heat pumps.”

The survey responses from the McLean County district, which incorporate the one-pipe building loop design, were the most positive of the four received. The advantage listed in the survey was “very low maintenance” while the main disadvantage was “our newer schools with more complex controls have been more problematic.” The primary recommendation was “keep the control systems simple as they perform better.”

Energy manager Bruce Boswell realizes that the ENERGY STAR ratings at the three newer schools are lower (91, 75, 75) than the ratings for the five 1950s vintage schools with thermostats (98, 98, 97, 95, 95), but he expects things to improve as he and the operators become more familiar with the controls. Monahan is less optimistic, “…with decreasing school budgets and a reduced supply of experienced technicians, why would you put something complicated in our buildings that uses more energy? The engineers are shoving these controls down our throats.”

Citation: ASHRAE Journal, vol. 55, no. 1, January 2013


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