Comparison of Thermal Performance for Two Types of ETFP System under Various Operation Schemes

The earth to fluid pipe (ETFP) system has been widely applied to various energy engineering. The numerical model of the heat transfer process in the ETFP system with a shallow -buried horizontal or a deep -buried vertical U -shape pipe adopted in practical engineering was established and the model distinctions were pointed out. The comparison of the thermal performance between the two types of ETFP system under various schemes was conducted on the basis of numerical prediction. The results showed that the thermal parameters of the ETFP system with a shallow -buried horizontal pipe were influenced by the inlet velocity and ground temperature obviously. The variation of the fluid temperature was smooth and the thermal influence zone was limited under the fixed conditions. The proper intermittent operation scheme reduced 53.1% outlet fluid temperature rising. By contrast, the fluid temperature in the ETFP system with a deep -buried vertical U -shape pipe varied dramatically with the operation conditions. The intermittent operation scheme with a relatively short interval led to a less temperature fluctuation of soil around the pipe. The intermittent scheme is beneficial to the recovery of the thermal condition of soil around the U -shape pipe. These results indicated a stark difference in thermal performance between the two types of system. The study can provide guidance for the selection and operation of ETFP system in practical heat exchange engineering.