Heat losses in directly buried solar heat collection networks in high-altitude regions

Abstract

Due to the fluctuations in the medium temperature, the solar collector system (SCS) based on temperature difference control currently lacks a medium temperature value for accurately calculating the operational heat loss of directly buried solar heat collection pipelines. This research proposed a method for calculating heat loss utilizing an equivalent medium temperature (EMT). Initially, a computational model is established for assessing the heat loss of directly buried solar collector pipelines in Xizang plateau. Based on the primary factors influencing heat loss, the study investigated the temperature drop and operational heat loss patterns of directly buried solar heat collection pipelines. The ranges of regional equivalent medium temperature (REMT) and condition equivalent medium temperature (CEMT) were optimized using the gradient descent algorithm and heat loss calculation theory. The variations of REMT and CEMT with different regions and key heat loss factors were analyzed, and a CEMT association model was obtained. The EMT is highest in Lhasa and lowest in Gar, related to the ambient temperature for heating design and collector field operation time. For REMT, Lhasa ranges from 50.4 °C to 52.8 °C, and Gar from 31.1 °C to 33.4 °C. CEMT decreases with increasing flow rate coefficient and nominal diameter, ranging in Lhasa from 77.1 °C to 35.5 °C, and in Gar from 54.9 °C to 18.5 °C. The study aims to provide fundamental data and theoretical support for heat loss calculation and designing the insulation thickness of directly buried solar heat collection pipelines in high-altitude regions.