Experimental and numerical study on a novel low temperature façade solar thermal collector to decrease the heating demands: A south-north pipe-embedded closed-water-loop system

•We present an active closed-loop-water-pipes embedded in the building exterior walls.•Harvest the solar energy gain on the south wall and transfer it to the north wall.•A comparative experimental study is carried out to test the system’s performance.•Numerical modeling and simulations are carried out. Recently, more and more research is being conducted on thermo-activated building walls with the use of circulating water or other fluids for the aim of decreasing and shifting the heating and/or cooling loads. In this context, we present a novel concept of the active embedded-pipe envelope systems. The system consists of an active closed-loop-water-pipes embedded in the building exterior walls to harvest and utilize the solar energy gain on the south wall exterior surface to decrease or offset the heat loss through the north wall and enhance thermal comfort. During non-cloudy winter days, a significant amount of solar energy hitting the south (insulated) facade is not transferred to the inside environment. In this study, a comparative experimental set-up is carried out to test the system’s efficiency and compare its performance to that of a static insulated envelope without the system. Also, a numerical model is developed and validated against experimental measurements. Numerical simulations with a parametric study are carried out to examine the active wall loop system’s efficiency for different design and operating parameters. The main conclusion derived from this study is that the system performs very well in the Mediterranean climates (or similar climates) and to a lower extent in the cooler ones. However, its performance is highly dependent on several design, climatic, and operating variables which should be optimized to have the best performance.