The Impact of Phase Change Materials (PCM) on the Duration of Spring and Autumn Transitional periods in Residential Buildings

Two of the main issues societies are facing with today are limited fossil fuel resources and increase in energy consumption. A significant part of energy is consumed in residential buildings to obtain thermal comfort, thus so far are, many efforts have been made to improve the indoor thermal conditions and reduce energy consumption simultaneously. One of the issues in this regard is the impact of thermal mass on energy conservation and increase of indoor thermal comfort. Seasonal transition period is a time of year when there is a change of heating to cooling and vice versa. Within this period thermal comfort may be maintained consuming no energy. Lengthening this period will help to conserve energy, and this may be achieved using indoor thermal storage. Common thermal storage materials include high density and heavy materials and sensible heat usage for energy storage. There is a new and light-weight thermal mass (phase change material) especially used in high-rise constructions to reduce the structural load and preserve thermal energy. Phase change materials (PCM) are based on latent heat energy storage. In this paper, the thermal performance of residential buildings in Tehran during seasonal transition period of spring and autumn is studied, in order to maintain the highest reduction in energy consumption without relying on mechanical equipment, and to reduce depreciation of the equipment. The impact of phase change materials (PCM), with various melting temperatures (21, 23, 25, 27 and 29oC), on the duration of seasonal transition period is studied using energy simulation. The dimensions of the studied model are similar to those of a common apartment room in the city. The model was first constructed in Ecotect software and then using EnergyPlus, and Tehran weather data, and its annual heating load was calculated. The temperature set points were 20oC for winter and 28oC for summer. Thermal performance of PCMs with various melting temperatures, regarding the best energy consumption condition during a whole year and the number of the days that were added to the seasonal transition period were identified. In hot -arid climate of Tehran natural ventilation may be used to decrease cooling load and maintain thermal comfort during transition period. To study the impacts of natural ventilation on the period, various ventilation rates, 0, 1, 3, 5, 7, and 10 ach were considered with a constant debi rate. The results revealed that using PCMs as thermal storage material and natural ventilation, energy conservation will be achieved more easily during transition period. It was found that PCM with melting point of 29oC will reduce the annual energy consumption by 15% and will increase the seasonal transition period by 20%, with 5 ach natural ventilation, and has a significant effect on reducing thermal problems of the period and performance of the mechanical equipment. The spring transition period is from 12th March to 19th May. This period for autumn is from 5th October to 5th November, which is 38 days for spring period and 29 days for fall, without any energy consumption which results in shut down of mechanical equipment.