Determination of economic velocity and economic insulating layer thickness of secondary pump system for central cooling system of underground railway stations

With an actual project, develops an optimal model of the variable secondary pump water system, calculates the economic velocity and economic insulating layer thickness with the minimum annual cost as the principle, and obtains that the major influencing factors on economic velocity are pipe type, power price, temperature in section tunnels, transportation radius, cold load of underground railway stations, price and thermal conductivity of insulation materials while the factors on economic insulating layer thickness are temperature in section tunnels, power price, price and thermal conductivity of insulation materials, system COP, cooling load of underground railway stations, temperature of chilled water supply. The analysis result shows that there is a remarkable distinction of heat loss between water supply and return pipelines in large temperature difference variable secondary pump water systems. Therefore, the economic velocity and economic insulating layer thickness should be calculated respectively in term of characteristics of water supply and return pipelines in different section tunnels.