# Performance of Solar Control Films on Building Glazing: A Literature Review
## 5 Discussion of Existing Studies on the Performance of Solar Control Films
### Performance Assessment  
When assessing the potential of the application of SCFs to building glazing, existing studies focus on the following types of performance: thermal, luminous, energy, economic and environmental. To assess the thermal performance of building glazing with SCFs, existing studies commonly analyze the indoor air temperature and the indoor/outdoor glass surface temperature with and without SCFs. Indoor temperature levels are lower in the presence of SCFs due to the reduction in the transmittance of solar radiation through the glazing. However, external SCFs are found to have better thermal performance since internal films can absorb and irradiate heat towards the indoor environment and contribute to temperature increase [44; 46; 49; 50]. SCFs increase the surface temperature of the glass they are applied to due to the absorption of solar radiation, particularly in clear glazing [46; 49; 50]. The research studies evaluate the luminous performance of SCFs through the analysis and comparison of indoor illuminance levels with and without films, and indoor and outdoor levels. Vertical illuminance levels, related to potential glare, are rarely measured and/or computed by existing studies. Even though some studies suggest that SCFs have higher efficiency in reducing solar radiation through the glazing under a clear sky than an overcast sky [43; 48; 50], no existing research study focuses on the luminous performance assessment of SCFs under different sky conditions. The horizontal distribution of illuminance levels on the indoor environment, which is of particular importance for large plan spaces, is poorly explored in the literature. In terms of energy performance, existing studies analyze energy needs, energy consumption and peak values with and without SCFs. Cooling and heating energy needs are commonly analyzed to better comprehend the impact of SCFs on the need of climate control. The discrepancy between thermal setpoints, type of climate control devices and respective efficiency make the comparison of results between studies difficult. Since SCFs can reduce indoor daylight levels, some studies also consider artificial lighting needs/consumption, in addition to climate control needs/consumption. [PERSON] et al. [56] conducted a more complex study, computing the life cycle energy of different SCFs against a new window and concluding that films presented a life cycle energy value up to 40% lower than the new window. To evaluate the economic performance of SCFs, the research studies followed different approaches. Some studies [46; 52; 54; 55] conducted a simple analysis by calculating the cost of the energy consumed (or energy savings) using prices and charges of the local energy suppliers. [PERSON] et al. [40] and [PERSON] et al. [41] conducted a cost-benefit analysis considering the film cost, in addition to the energy cost, assessing different scenarios and determining payback periods. [PERSON] et al. [56] and [PERSON] et al. [57] conducted more complex studies by performing a life cycle cost analysis of buildings with SCFs installed. [PERSON] et al. [57] concluded that the relatively high price of low-E films and the contrasting low price of district heating resulted in a long payback period of around 30 years, which is longer than the service life of these films. [PERSON] et al. [56] concluded that a reflective film exhibited lower economic costs, but it has a worse energy and environmental performance compared with the other alternatives (spectrally selective films and new window). Regarding the assessment of the environmental performance of SCFs, the majority of the existing studies [35; 41; 46; 54; 55] poorly explore the topic by simply calculating the emissions of carbon dioxide that result from the energy consumption with and without SCFs. [PERSON] et al. [56] conducted a more correct and complex study by performing a life cycle analysis considering different SCFs versus the replacement of the existing window.