Numerical investigation of the energy efficiency of a serial pipe-embedded external wall system considering water temperature changes in the pipeline

Abstract Pipe-embedded external wall using low-grade energy has been shown to significantly reduce the cooling or heating load of buildings. However, previous studies have generally focused on the heat transfer between water pipes and pipe-embedded wall and paid less attention on the energy use of water distribution. In this paper, a numerical model of serial pipe-embedded wall (SPW) considering water temperature changes in the pipeline is developed, and the load reduction and energy efficiency of the SPW are studied numerically under different climates and structures. The Influence of flow velocity and flow path on the performance of SPW is also investigated. The results show the following: (1) the SPW retains a satisfactory load reduction rate, which is only slightly less than that of the parallel pipe-embedded wall (PPW); (2) the coefficient of performance (COP) of the SPW is 10 times higher than that of the PPW after considering water distribution; (3) the water temperature affects the indoor load more than the sol-air temperature does, and the SPW has load reduction potential compared with the conventional wall when the water temperature is below 30 °C in summer or above 12 °C in winter; (4) increasing the flow path or flow velocity alone will not always result in better energy efficiency for a SPW system. There exists an optimum flow velocity or flow path that will maximize the energy efficiency of a SPW system.