Experimental Investigation on Heat Transfer through the Roof of Air-Conditioned and Non Air-Conditioned Rooms

Building energy consumption in Bangladesh is increasing day-by-day as a result of the increased use of air conditioners. To reduce air conditioning energy consumption, it is required to use energy-efficient building envelopes and properly sized air conditioners. In this respect, it is required to know about the time at which indoor and outdoor air temperatures, and roof surface temperature become peak and heat transfer through building envelopes, especially roofs. The peak indoor air temperature and thermal condition of the roof vary with the indoor air temperature of a room. These data are not available for the Khulna district of Bangladesh. So, the present work has focused on the investigation of such data for air-conditioned room maintained at 25ºC and non air-conditioned room for a typical day in June 2022. From the research work, it is found that the indoor air temperature of the non air-conditioned room reaches peak value at the evening which is higher than that of the outdoor air temperature. As the temperature of indoor air becomes high enough, severe discomfort is felt in rooms on the top floor of the building. For both air-conditioned and non air-conditioned rooms, the outside surface temperature of the roof becomes maximum at noon. In case of the non air-conditioned room, this maximum outside surface temperature is found to be higher than that of the air-conditioned room. On the other hand, the peak value of the inside surface temperature of the roof is found in the evening and this value for the air-conditioned room is higher than that of the non air-conditioned room. Due to maintaining a lower temperature by air conditioners, the peak roof heat gain for the air-conditioned room becomes more than 3 times higher relative to the peak roof heat gain of the non air-conditioned room.