ASHRAE Journal - June 2012 - 54

rating 95 or higher. The lone school 120 with a rating below 90 was built in 1938. It should be noted that all of One-Pipe Loop Unitary Loop Common Loop these schools are in the same district 100 and the systems were designed by the same engineer. 80 Four systems in the survey were unitary loops connected to indi60 vidual heat pumps with on-off 69% GSHP circulator pumps. As indicated in Figure 5 these buildings received 40 45% GSHP an ENERGY STAR rating above 90, with one achieving a rating 20 29% of 100 (TX-ES2). They are in the GSHP same district and the systems were 0 designed by the same engineering firm. The two older schools (TXMS, 1996 and TX-ES1, 1996) are ES – Elementary School MS – Middle School HS – High School OFF – Office Mfa – Multifamily served by GSHPs in all areas. The classrooms and offices in the two newer schools (TX-HS, 1998 and Figure 5: ENERGY STAR ratings of one-pipe central loop with central & individual pumps. TX-ES2, 2001) are conditioned with GSHPs while the common areas such as cafeterias, • However, 17% (6/36) of the GSHP buildings had ENERgymnasium and kitchens are served by air-cooled equip- GY STAR ratings below 21. ment. Ventilation air energy recovery units are supple• When properly applied, GSHPs offer significant energy mented by non-GSHP equipment. performance advantages compared to buildings surveyed in The school district has been installing GSHPs since 1994 the Energy Information Administration (EIA) Commercial and has 26 GSHP schools that achieved the ENERGY STAR Buildings Energy Consumption Survey3 upon which the ENdesignation, four of which received a rating of 100 in 2010 ERGY STAR rating is based. including TX-ES2. • The survey suggests that GSHP systems on the lower end Five systems in the survey were served by common loops of the performance scale do no better than average HVAC sysconnected to multiple heat pumps inside the building. Three tems. of the systems were located in buildings that were also partially served by conventional unitary equipment as noted in Central Loop GSHP Energy Performance Figure 5. • Buildings with central loop GSHPs and pumps did not Four of the five systems appear to be operating effec- fare as well as overall GSHPs with 10% (2/20) receiving a tively while one is operating well below the average EN- rating above 90 (top 10% of buildings). ERGY STAR rating of 50. One building received a rating • The central loop GSHP buildings performed somewhat slightly above 50 but only 29% of the floor space is condi- better based on the percentage achieving ENERGY STAR tioned by GSHPs. The other two buildings that are partially designation with 40% (8/20) receiving a rating of 75 or heated and cooled by GSHPs rated high enough to merit an above. ENERGY STAR designation. The school building with a • However, 25% (5/20) of the central loop GSHP buildings single common ground loop received an ENERGY STAR had ENERGY STAR ratings of 21 or below. rating of 97. • Central loop GSHPs with central pumps appear to offer only a small advantage compared to the energy performance Summary and Conclusions of buildings in the DOE/EIA CBECS database. • Central loop GSHPs on the lower end of this energy perAll Loop Circuit Types Energy Performance • The GSHP systems in this survey, which varied in age formance scale actually functioned slightly worse than the from three to 23 years, performed well above average ENER- CBECS buildings. GY STAR ratings with 33% (12/36) receiving a rating above 90 (top 10% of buildings) and 22% (8/36) receiving a rating Central One-Pipe Loop GSHP Energy Performance above 95 (top 5% of buildings). • Buildings with central one-pipe loop GSHPs performed • The surveyed GSHP buildings also had a large percentage well above average ENERGY STAR ratings with 83% (5/6) receiving the ENERGY STAR designation with 61% (22/36) receiving a rating above 90 (top 10% of buildings) and 66% having a rating of 75 or above (top 25% of buildings). (4/6) receiving a rating above 95 (top 5% of buildings).
ENERGY STAR Rating
IL – MS TX – MS AL – ES1 TX – ES1 TX – ES2 AL – ES2 IL – ES1 IL – ES2 IL – ES3 IL – ES4 IL – ES5 TX – HS AL – Off AL – MS

ASHRAE Journal

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June 2012

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ASHRAE Journal - June 2012

Table of Contents for the Digital Edition of ASHRAE Journal - June 2012