Energy and exergy study of unglazed transpired collector-2stage

•Study of UTC-2stage in terms of energy and exergy approaches.•Investigating the effects of UTC’s and cover’s height on the first and second law efficiency.•Investigating the effects of important parameters on the optimum (Hu/H) value.•By increasing electrical to thermal ratio, the efficiency analysis becomes proportional to exergy analysis. Unglazed transpired collector-2stage (UTC-2stage) is a type of solar air heater constructed of two collectors. The first stage is an unglazed transpired collector (UTC), and the second is a tilted transpired collector covered with a transparent cover. In this paper, a mathematical model has been developed for the purpose of analyzing the system, cover and UTC’s height impact on energy and exergy efficiencies are investigated. The model’s solution is compared with experimental results in order to be validate. The experimental results manifest acceptable commensurability with the present work results. After validation, the effect of key parameters such as hole diameter, hole pitch, sun radiation, suction velocity, wind velocity, plenum depth and inlet air temperature on the ratio of UTC’s height to the total height of the system (Hu/H) at points where the equivalent thermal efficiency or second law efficiency is maximum have been investigated. With regards to the results of this paper, designers should take these key parameters into consideration in selecting the heights of UTC and the cover.