Experiment Research On The Dynamic Thermal Performance Of Low-e Glass Curtain Wall And Its Indoor Environment

The glass curtain wall is widely used in modern buildings in China.Under the background of reducing building loads,energy efficiency technologies like Low-e glass and external shading have developed rapidly.The thermal behavior of glass curtain wall is different from opaque building envelope,its indoor environment is unstable and significantly affected by solar radiation.Low-e glass and external shading technologies not only played an important role in reducing solar heat gain and improving indoor environment,but also in the design and control of central air conditioning system.But the research on glass curtain wall’s inertia or its transient thermal behavior was rarely reported.It’s necessary to evaluate the dynamic performance of a Low-e glass curtain wall and its indoor environment under solar radiation,which is essential to optimize air conditioning system control and improve indoor environment.The paper defined 4 thermal inertia factors: temperature amplitude,response time,attenuation factor and time lag,which are useful to determine the transient thermal behavior of the building.Then an experimental study was carried out in a full-scale glass fa?ade room with Low-e glass curtain walls and external shading systems.Temperature was measured at varying radiation intensity and at different venetian blinds positions.At last,the dynamic response rules,and the heat flow rules of Low-e glass curtain walls under the effect of radiation intensity and tilt angle were analyzed.The conclusions are as following:(1)The newly defined evaluation factors are convenient for characterizing the investigated walls’ ability to maintain thermal stability against outdoor thermal disturbance.(2)The fluctuation of the walls’ outer surface temperature is linearly dependent on the value of solar radiation and varied for different shading angle.The temperature of the outer surface lagged behind incident solar radiation when shading blinds opened small(about 5 min).(3)The response time of the Low-e glass inner surface was 35~48 min,7~17mins lagging compared with the outer surface,the attenuation factor of inner surface temperature amplitude against outer surface temperature amplitude is about 3.With an external shading the response time delayed about 20% and the temperature amplitude decreased notably,both changed with shading angle.(4)The response time of indoor air was about 60 min and rarely changed with radiation intensity.The temperature amplitude was around 2~4℃.With the external shading,the response time delayed 30%,and the temperature amplitude dropped 1.5℃.(5)The convective heat flow from the glass inner surface to indoor air and the radiation heat flow from the glass inner surface to indoor walls increased linearly with the value of solar radiation.The ratio of radiation heat flow was around 80%~90% of the radiation and convective heat flow.With the external shading,the convective heat flow was 25%~60% of no shading conditons,and the radiation heat flow dropped 10%~50%.Above all,the time lag(7~17min)of Low-e glass inner surface temperature was close to the control period of(5~30min)central air conditioning system,and its temperature amplitude is significant.Therefore,it’s necessary to consider the influence of inner surface temperature or the dynamic response character of glass curtain walls.