Thermal Reduction Experimental Analysis for a Hollow Green Roof
|關鍵字:||中空式綠屋頂;能量平衡;熱傳係數;EnergyPlus;建築隔熱;hollow green roof;energy balance;u-value;EnergyPlus;energy-saving|
Covering building with green roof can reduce roof temperature and result in energy-saving. However, due to some problems associated with the conventional green roof, green roof is not widely promoted in this country. Therefore, this study has established a hollow type of green roof (HGR), which is expected to be publicly acceptable and cost-effective. To carry out this study, a green roof was installed on half of a campus building roof, and the remaining conventional half building roof (CR) without green roof as a comparison. Data such as solar radiation, temperature, heat flux, and water level were monitored. Based on the data collected, the differences between two roofs for surface temperature, interior temperature and heat flux were compared and analyzed. According to ISO 9869 and the LORD model, the U-value of the HGR was estimated based on monitored data. Also, the energy saving of applying the HGR on the other campus building was simulated and estimated by the EnergyPlus model. Finally, an energy balance model was established to analyze the thermodynamic transmission of the HGR. According to experimental results, the surface temperature difference between two roofs during summer is more than 20 degree Celsius. The HGR can decrease roof surface thermal expansion and contraction, and subsequently protect the roof surface. For interior temperature, the differences between the rooms under two roofs are about 2-4 degree Celsius. The U-value of the HGR was estimated to be 0.79 W/m2 under ventilation assumption or 0.86W/m2 under poor ventilation assumption. Although the U-value estimated by measured data is acceptable for the CR, the values estimated for the HGR does not converge due to dynamic microclimate fluctuation. For the same reason, the LORD model cannot obtain a converged result either. The annual HGR energy saving simulated by the EnergyPlus model for the experimental roof with the HGR is approximately 9.71-9.81 kWh/m2. For the conventional roof with a better insulated layer, the annual energy saving is approximately 5.71-5.83 kWh/m2. From the energy balance analysis for the HGR, the latent and sensible heats are about 77% and 4 %, respectively, of the net radiation. The proposed HGR can significantly reduce roof surface sensible and storage heat flux by releasing the latent heat through the plant and water evaporations instead.