Transient Analysis And Performance Prediction Of Passive Cooling Of Buildings Using Long Wave Nocturnal Radiation In Owerri, Nigeria

ABSTRACT

Transient analysis and performance prediction of passive cooling of buildings using long wave nocturnal radiation in Owerri, Nigeria are presented. Owerri is a typical urban area in southeastern Nigeria lying between latitude 5° 4' and 6° 3' N and longitude 6° 15'and 7° 34' E. The system modeled consists of the room of a building with a radiator panel attached to its roof, water storage tank located inside the room, pump to circulate water through the radiator panel at night and through a heat exchanger in the room during the day. The mathematical model is based on the radiative properties of the local atmosphere, the heat exchange equations of the radiator panel with the sky during the night, and the equations incorporating the relevant heat transfers within the space to be cooled during the day. The resulting equations were transformed into explicit finite difference forms for easy implementation on a personal computer in Matlab language. This numerical model permits the evaluation of the rate of heat removal from the water storage tank through the radiator panel surface area between 11pm – 7am,Qt,out, temperature depression between ambient and the room, and total heat gained from the room space through the action of the room convector into the storage tank during the day (8am – 6pm) Qt,in. The resulting numerical solutions of the model were validated by comparison with actual field performance data taken from Okoronkwo’s work [Experimental study of passive cooling of a building using long wave night sky radiation in Owerri, Nigeria; ongoing PhD thesis, Federal University of Technology, Owerri, 2011]. The resulting rate of heat removal from the radiator, Qt,out, was predicted to within 39 – 57.6 W/m2, temperature depression was predicted to within 1 – 5 oC and the rate of heat gain by the storage water was predicted to within 45 – 60 W/m2. Based on the overall good agreement between the predicted and the measured results, a sensitivity analysis of the above parameters to ±25 % of the base case input values was carried out and the results given as a percentage variation of the above system performance paramers sulting numerical solution was validated with actual field performance data obtained from a test building located at the Federal University of Technology, Owerri.  The results showed a heat removal rate of 57.6 W/m2 and temperature depression (Ta – Tr) was between 1 – 5 oC. Other performance parameters such as total heat gained by the storage water during the room cooling operating period, Qt,in and the heat removed during the night sky cooling period’ Qt,out were 80.2 MJ and 79.5 MJ respectively. The numerical results obtained agreed quite well with an experimental study of this modeled system. The above results show that this passive nocturnal cooling technique is a reliable solution to the cooling needs for food preservation and preservation of other agricultural produce. It is also useful in small office space cooling. This modeled system is undoubtedly an aid to reducing the huge cooling cost requirements of mechanical air conditioning system of cooling.