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Table 2 GHE configuration and sizing calculation results for the synthetic load profile

From: Designing coaxial ground heat exchangers with a thermally enhanced outer pipe

GHE configuration       
 Borehole diameter - mm (in.) 152.4 (6) 152.4 (6) 152.4 (6) 152.4 (6) 152.4 (6) 203.2 (8)
 GHE configuration 1 U-pipe 1 U-pipe 2 U-pipe 2 U-pipe Coaxial Coaxial
 Pipe nominal diameter - mm (in.) 31.8 (1.25) 31.8 (1.25) 31.8 (1.25) 31.8 (1.25) 101.6 (4) outer 152.4 (6) outer
50.8 (2) inner 101.6 (4) inner
 Pipe SDR 11 11 11 11 17 outer 17 outer
11 inner 11 inner
 Pipe thermal conductivity - W m−1 K−1 0.4 0.7 0.4 0.7 0.7 outer 0.7 outer
0.4 inner 0.4 inner
 Grout thermal conductivity - W m−1 K−1 1.7 1.7 1.7 1.7 1.7 1.7
Sizing calculation results when applying the full building loads       
 Total flow rate - L s−1 7 7 7 7 9.6 8
 Borehole thermal resistance - m K W−1 0.0955 0.0777 0.0563 0.0443 0.0734 0.0630
 GHE grid 4 × 4 4 × 4 3 × 4 2 × 5 3 × 4 2 × 4
 Individual GHE length - m 159 151 181 203 194 246
 Total GHE length - m 2,544 2,416 2,172 2,030 2,328 1,968
 Total water volume in GHE - m3 4.62 4.39 7.89 7.37 16.43 27.48
 Pumping power for peak conditions - W 246 234 138 213 130 31
 Borehole length reduction - % --- 5 15 20 9 23
Sizing calculation results for a hybrid system with a 55-kW cooling tower       
 Total flow rate - L s−1 4.6 4.6 4.6 4.6 6 6
 Borehole thermal resistance - m K W−1 0.0948 0.0768 0.0547 0.0442 0.0701 0.0587
 GHE grid 2 × 5 2 × 5 2 × 4 2 × 3 2 × 3 2 × 3
 Individual GHE length - m 146 137 158 199 222 198
 Total GHE length - m 1,460 1,370 1,264 1,194 1,332 1,188
 Total water volume in GHE - m3 2.65 2.49 4.59 4.37 9.40 16.59
 Pumping power for peak conditions - W 160 152 77 160 137 19
 Borehole length reduction - % - 6 13 18 9 19