Table 2 Design parameters of 2U-type BHE

BHE depth/H (m)

80

Borehole diameter/ψ (m)

0.13

Outer diameter of branch pipe-in(out)/d_i(o) (m)

0.032

Wall thickness of branch pipe-in(out)/b_i(o) (m)

0.0029

Adjacent branch pipe distance/w (m)

0.05

Thermal conductivity of pipe-in(out) material/λ_pi(o) (W m⁻¹ K⁻¹)

0.60

Thermal conductivity of refrigerant (water)/λ_r (W m⁻¹ K⁻¹)

0.65

Volumetric heat capacity of refrigerant (water)/c_rρ_r (J m⁻³ K⁻¹)

4.18 × 10⁶

Volumetric heat capacity of grout/c_gρ_g (J (m⁻³ K⁻¹))

2.19 × 10⁶

Thermal conductivity of grout/λ_g (W m⁻¹ K⁻¹)

1.90