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Table 1 Range of each parameter used for borehole thermal resistance calculation

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

Parameter Minimum Maximum Average
Water flow rate (L s−1) 0.5 6 3.25
Borehole length (m) 50 250 150
Backfilling thermal conductivity (W m−1 K−1) 0.6 2.8 1.7
Pipe thermal conductivity (W m−1 K−1) 0.1 0.7 0.4
Pipe outside diameter (mm)/thickness (mm) SDR-11 SDR-17 SDR-13.5
31.75-mm (1.25 in.) nominal diameter 42.0/3.8 Not used for U-pipe Not used for U-pipe
50.8-mm (2 in.) nominal diameter 59.7/5.5 60.3/3.6 59.8/4.5
101.6-mm (4 in.) nominal diameter 113.1/10.4 114.3/6.7 113.3/8.5
152.4-mm (6 in.) nominal diameter 166.4/15.3 168.3/9.9 166.8/12.5