Designing and Optimizing Heat Storage of a Solar-Assisted Ground Source Heat Pump System in China

Table 5

Characteristics of the double U-tube heat exchanger.

Pipe
Material		High-density polyethylene
Thermal conductivity	W/(m·K)	0.4
Outside diameter	mm	26.0
Inside diameter	mm	32.0
Number of pipes		4
Distance between pipes (center to center)	mm	50.0
Borehole diameter	mm	140.0
Connection between the two U tubes		Parallel
Grout thermal conductivity	W/(m·K)	2.0
Heat-carrier fluid		50% mixture of propylene glycol