Determining the optimum economic insulation thickness of double pipes buried in the soil for district heating systems

The insulation thickness(IT)of double pipes buried in the soil(DPBIS)for district heating(DH)systems was optimized to minimize the annual total cost of DPBIS for DH systems.An optimization model to obtain the optimum insulation thickness(OIT)and minimum annual total cost(MATC)of DPBIS for DH systems was established.The zero point theorem and fsolve function were used to solve the optimization model.Three types of heat sources,four operating strategies,three kinds of insulation materials,seven nominal pipe size(NPS)values,and three buried depth(BD)values were considered in the calculation of the OIT and MATC of DPBIS for DH systems,respectively.The optimization results for the above factors were compared.The results show that the OIT and MATC of DPBIS for DH systems can be obtained by using the optimization model.Sensitivity analysis was conducted to investigate the impact of some economic parameters,i.e.,unit heating cost,insulation material price,interest rate,and insulation material lifetime,on optimization results.It is found out that the impact of sensitivity factors on the OIT and MATC of DPBIS for DH systems is different.

Energy Saving Model and Calculation Example of Three Cooling Schemes for Data Center in Hot Summer and Cold Winter Area

In order to achieve the goal of “carbon peak” in 2030 and “carbon neutralization” in 2060, the task of energy conservation has risen to the national strategic level, and its work is urgent. It focuses on energy saving and energy consumption in data center, 5G network and other fields. The gravity heat pipe double cycle air conditioning is a kind of room air conditioning which uses natural cooling source with high efficiency. According to the outdoor meteorological parameters of ten typical cities in China, the calculation model of unit hybrid refrigeration mode is established by using integral method. A simplified algorithm for statistical summation is proposed. Then it compares with the same type of refrigerant pump air conditioner, water-cooled chiller and natural cooling plate. The results show that the annual operation time of gravity heat pipe double cycle air conditioner is 50.8% longer than that of refrigerant pump air conditioner. Then the calculation model is verified by the annual actual operation data of a data center in Changsha. The results show that the double cycle air conditioner with gravity heat pipe can save about 34% energy compared with the chiller. The accuracy of the calculation model is 17.5%, which meets the engineering accuracy requirements. The application of gravity heat pipe double cycle air conditioning in hot summer and cold winter area is a scheme worthy of popularization and application.