Dynamic Heating System of Multiphase Flow Digester by Solar-Untreated Sewage Source Heat Pump

Table 1

Comparison of different biogas heating systems.

Heating system	Digestion temperature (°C)	CH4 yield (m^3 m^-3 d^-1)	System unit cost (yuan m^-3)	EER	Reference
Electric boiler	23.5	0.472	/	1.38	[20]
Biogas boiler	35	0.482	2000	1.01	[19]
Solar+biogas boiler	19.82-23.5	0.389-0.472	314.39	2.01	[6]
Solar direct heating system	26-37	0.63-1.08	2145.16	6.17	[7]
Solar direct heating system	7.02-27.14	0.314-0.569	300	5.56	[21]
Ground source heat pump	32	0.6	408.37	2.7	[9]
Solar-air source heat pump	35	/	3750	3	[14]

The value is the system initial cost divided by the volume of the digester.