Abstract
Latent heat storage in phase change material (PCM) is an efficient technology that can be applied in building envelopes. Installing PCM in building roof has been effective in altering space cooling loads. However, the heat absorbed by the PCM during the daytime will be released at night; the cooling load is shifted to the night. So, this study proposed a new ventilated roof with form-stable PCM (VRFP). The night cool air is used for ventilation during summer to remove the solidification heat of PCM and to store the cooling energy in the roof. Form-stable PCM is placed in the upper layer and ventilation duct is placed in the middle layer. The inner surface temperature of this roof is reduced sharply compared with the conventional PCM roof. The thermal performance of this PCM roof with night ventilation in Wuhan, a city in southern China, was studied by through Computation Fluid Dynamics (CFD) simulation. A three-dimensional dynamic numerical model of this roof was built. The effects of melting temperature range, thickness of Form-stable PCM layer and ventilation strategy on the thermal performance were analyzed. Results show that, in Wuhan city, the optimal melting temperature range is 35~38 °C, the appropriate thickness of PCM layer is 30~40 mm and the optimal ventilation speed is 2.4~2.5 m/s. This structure can effectively prevent the stored heat of PCM transferring from the exterior to the interior during the summer and reduce cooling energy consumption.
Highlights
With the development of urbanization and the improvement of people’s living standard, the energy consumption of the building sector has been increasing rapidly in recent years
Tolga Pirasaci [39] analyzed the winter energy saving potential of a residential apartment incorporated with a phase change material (PCM) layer; the results showed that annual heating energy requirement decreased by about 6%
The main contributions of this study are two points: First, ANSYS Fluent numerical simulation method was adopted, the key influence factors affecting the thermal performance of ventilated roof with form-stable PCM (VRFP) were explored, the comprehensive effects of melting temperature, PCM thickness and ventilation strategy on thermal performance of VRFP were studied; the thermal performance of this roof was evaluated by analyzing inner surface temperature, latent heat utilization rate of PCM and decrement factor
Summary
With the development of urbanization and the improvement of people’s living standard, the energy consumption of the building sector has been increasing rapidly in recent years. PCMs store energy in the form of latent heat by phase change process between solid and liquid It can prevent overheating in summer, reduce the heat flux through the roof and reduce the energy consumption for space cooling [15,16]; the use of PCM in the building envelope reduces indoor temperature fluctuations, providing better indoor thermal comfort for occupants [17]. The main contributions of this study are two points: First, ANSYS Fluent numerical simulation method was adopted, the key influence factors affecting the thermal performance of VRFP were explored, the comprehensive effects of melting temperature, PCM thickness and ventilation strategy on thermal performance of VRFP were studied; the thermal performance of this roof was evaluated by analyzing inner surface temperature, latent heat utilization rate of PCM and decrement factor. The results provide reference on optimization design of the structure and are of great significance for the application and promotion of the structure
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