Table 2.

Estimates of cDGSW performance

Q (kW)To (5 yrs) (°C)QU (5 yrs) (kW)To (10 yrs) (°C)QU (10 yrs) (kW)To (20 yrs) (°C)QU (20 yrs) (kW)
zM = 2000 m; TL = 30°C; TM = 74°C (f ≈ 0.31)
074.00.074.00.074.00.0
2066.913.066.512.966.012.9
4059.924.059.023.758.023.3
6052.832.051.531.150.030.0
8045.835.344.032.942.030.0
10038.329.336.624.834.016.7
12031.79.429.10.026.00.0
zM = 2500 m; TL = 30°C; TM = 90°C (f = 0.25)
090.00.090.00.090.00.0
2084.814.784.514.684.114.6
4079.728.579.028.478.328.3
6074.541.473.541.172.440.8
8069.353.068.052.466.651.7
10064.263.162.662.060.760.6
12059.071.057.068.954.966.5
14053.876.151.572.549.068.2
16048.677.146.071.143.263.6
18043.572.540.662.437.348.1
20038.358.735.140.631.413.1
22033.230.329.60.025.50.0
zM = 3000 m; TL = 30°C; TM = 106°C (f ≈ 0.21)
0106.00.0106.00.0106.00.0
20101.915.6101.715.6101.415.6
4097.930.997.330.896.830.8
6093.845.793.045.592.145.4
8089.759.988.759.787.559.4
10085.673.584.373.182.972.6
12081.586.480.085.778.384.9
14077.598.575.697.373.696.0
16073.4109.571.3107.869.0105.8
18069.3119.366.9116.764.4113.8
20065.2127.562.6124.059.7119.5
22061.1133.958.3128.955.1122.4
24057.0137.953.9130.750.5121.5
26052.9138.849.6128.745.9115.2
28048.9136.045.3121.441.3101.1
30044.8127.641.0106.536.674.4
32040.7111.536.679.432.029.1
34036.684.432.335.127.40.0
36032.641.428.00.022.80.0

Calculations, on the basis explained in the main text, demonstrating the performance issues that result for cDGSW installations operated at nonzero values of f. Values of useable heat output QU and output temperature TO after 5, 10 and 20 years of operation are listed. The calculations assume a = 0.1 m, TS = 10°C, u = 32°C km−1, k = 3.5 W m−1 °C−1, and κ = 1.2 mm2 s−1 (cf. Fig. 4).