Thermal performance analysis of a passive hybrid earth-to-air heat exchanger for cooling rooms at Mexican desert climate

Abstract

This research incorporates two passive technologies selected to offer thermal comfort conditions in a room exposed to extreme desert climatic conditions (Hermosillo, Sonora, Mexico). On the one hand, a rectangular earth-air heat exchanger assisted with PCM (REAHE + PCM) is implemented. Its job is to supply cooled air to the room at temperatures below the comfort temperature. On the other hand, a room with PCM on its ceiling (room + PCM) is proposed, to reduce the thermal load towards the room and shift the thermal peak load, acting as thermal insulation. Hoping that the benefits of this combination of passive technologies provide the thermal comfort conditions required in a building in this region and thereby eliminate or reduce the consumption of electrical energy in conventional refrigeration systems. This article reports a detailed transient study of the thermal behavior of a passively cooled room. The effect of position, thickness, latent heat, and phase change temperature of the PCM in the room was investigated. Also, the different room configurations reported the time evolution of heat fluxes, temperatures, coefficient of performance (COP), and liquid fraction. A comparison between the proposed system and a room without PCM was made. Adding PCM to the roof can drop the peak heat flux in the ceiling by up to 33%. It was found that the most favorable system was with the PCM placed on the top of the room with a thickness between 1.5 cm and 2.0 cm. The best configuration kept an average room temperature of 0.6 K below the comfort temperature. The maximum temperature in the room only exceeded the comfort temperature by 0.33 K. The average COP varied between 264 and 288 for the room systems, while the average COP for the REAHE-PCM was 307. This combination of technologies is satisfactory for the climatic conditions studied.