The deeper the better? A thermogeological analysis of medium-deep borehole heat exchangers in low-enthalpy crystalline rocks

Geothermal Energy

Science – Society – Technology

Table 2 Summary of borehole heat exchanger parameters adopted in this study

1. Borehole depth (m) and type	600, U-tube	600, coaxial	1000, coaxial	2000, coaxial	3000, coaxial
2. Borehole diameter (mm)	160	160	0–300 m: 311; 300–1000 m: 215.9	0–300 m: 311; 300–2000 m: 215.9	0–300 m: 311; 300–3000 m: 215.9
3. Collector thermal conductivity [W/(m*K)]	HDPE, k = 0.42	VIT, k = 0.02	VIT, k = 0.02	VIT, k = 0.02	VIT, k = 0.02
3. Collector thermal conductivity [W/(m*K)]	HDPE, k = 0.42	HDPE, k = 0.42	HDPE, k = 0.42	HDPE, k = 0.42	HDPE, k = 0.42
4. Collector inner/outer diameter (mm)	51.4/63	VIT, 50/89	VIT, 76/114	VIT, 76/124	VIT, 76/124
		VIT, 76/114	VIT, 76/114	VIT, 76/124	VIT, 76/124
		HDPE, 80/100	HDPE, 100/120	HDPE, 100/120	HDPE, 100/120
5. Casing length and thickness	No	No	300 m, 33 mm	300 m, 33 mm	300 m, 33 mm
6. Flow rate (L/s)	1–3	1–3	1–5	VIT, 1–5	VIT, 1–5
6. Flow rate (L/s)	1–3	1–3	1–5	HDPE pipe, 2–10	HDPE pipe, 2–10

All borehole and pipe diameter values are from the Drilling data handbook (Gabolde et al., 1999)