ASHRAE Journal - July 2011 - 31

One-Pipe Loop Pump
Central Pump 190 gpm | Central Pump Oversize 0% | Minimum Pump 50 gpm| Minimum Pump Used Yes | Head 28 ft of Water Circulating Power 130 W | Minimum Pump Head 20 ft of Water | Central PumpmpEff 70% | Minimum PumpmpEff 60%

Circulating Pumps FL Fraction Minimum Hours 6,350 0.25 0.5 0.75 1 1,200 600 360 250 Number On 0 6 13 19 25 kWh 0 936 1,014 889 813

Central Pumps Number On 1 1 1 1 2 kWh 3,144 594 1,309 785 1,090 Electrical Energy
(kWh)

Heat Rejection
(Btu × 106)

3,144 1,530 2,323 1,674 1,903 10,574 7,430

10.7 5.2 7.9 5.7 6.5 36.1 25.4

Pump Electrical Energy and Heat to Ground = Energy and Heat to Ground (Pump Off at No Load) =

Table 3: Predicted one-pipe loop pump electrical energy use and heat rejection to ground loop.
One-Pipe Loop Pump
Central Pump 285 gpm | Central Pump Oversize 0% | Minimum Pump 50 gpm| Minimum Pump Used No | Head 28 ft of Water Circulating Power 130 W | Minimum Pump Head 20 ft of Water | Central PumpmpEff 70% | Minimum PumpmpEff 60%

Circulating Pumps FL Fraction Minimum Hours 6,350 0.25 0.5 0.75 1 1,200 600 360 250 Number On 0 6 13 19 25 kWh 0 936 1,014 889 813

Central Pumps Number On 1 1 1 1 2 kWh 20,773 3,926 1,963 1,178 1,636 Electrical Energy
(kWh)

Heat Rejection
(Btu × 106)

20,773 4,862 2,977 2,067 2,448 33,127 12,353

70.9 16.6 10.2 7.1 8.4 113.0 42.2

Pump Electrical Energy and Heat to Ground = Energy and Heat to Ground (Pump Off at No Load) =

Table 4: Predicted one-pipe loop pump electrical energy use and heat rejection with two larger pumps. tions. Building owners and engineers with good results are more likely to share it willingly and those with poor results are not. The ongoing project to obtain field data9 has obtained results in which the engineers and owners have been willing to share data of buildings with good results. The project has also experienced some who have restricted information after they realize it does not compare well with buildings that have been normalized by the ENERGY STAR rating. The ENERGY STAR rating is used to determine the success of the building’s energy performance because the key metric of the procedure is measured energy consumption (corrected for several key variables). Results are compared to the Commercial Building Energy Consumption Survey10 database of measured building energy use. To receive an ENERGY STAR designation, a rating of 75 is required, which means the building consumes less energy than 75% all the buildings of that particular type. Figure 2 presents the results of the GHP field measurement project categorized by loop type (unitary or central) and pump control (on-off, VSD, continuous):
July 2011

• Energy results from 24 commercial buildings with GHPs have been obtained and 22 achieved ENERGY STAR rating (>75). • Four of the 21 GHP school buildings with unitary loop onoff pump control in south central Texas are shown in Figure 1. The 21 schools had an average ENERGY STAR rating of 97. They range in age from one to 15 years, and four schools rated a 100 in 2010.1 • Five 1950s vintage schools in central Illinois that were retrofitted with one-pipe GHPs obtained an average ENERGY STAR rating of 96 without the benefit of lighting or envelope upgrades. A 1938 vintage school obtained an ENERGY STAR score of 82.11 • The average ENERGY STAR rating of the buildings with central loop VSDs was 79. • One building with unitary loops with on-off pump control for the classrooms and a central loop with a VSD for the common areas received an ENERGY STAR rating of 89. • Two of the four buildings with subcentral loops and on-off pumps received an ENERGY STAR designation, even though only 50% of the floor space was conditioned with GHPs. A third building with 30% of the floor space with GHPs received an
ASHRAE Journal 31
ASHRAE Journal - July 2011

Table of Contents for the Digital Edition of ASHRAE Journal - July 2011
