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

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