Development of the Control Algorithm for Automated Roller Shade System Integrated with Daylight Responsive Dimming System : Development of the Control Algorithm for Automated Roller Shade System Integrated with Daylight Responsive Dimming System
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Recently, curtain wall systems have been installed in many office buildings. Therefore, as the amount of direct sunlight entering increases because of a curtain wall, unexpected problems could occur. For example: discomfort of occupants from a glare; and inefficient building energy consumption with a high cooling load in summer because of solar and thermal loads after the inflow of daylight. For these reasons, it is essential to install shading devices such as roller shades or venetian blinds in an office building which uses curtain walls to block excessive direct sunlight. To save electric lighting and cooling load energy in office buildings, the role of an automated roller shade system which can control direct sunlight flowing inside is very important. For efficient operation of the automated roller shade system, implementation of an accurate control algorithm-based system is essential. This study developed an automated roller shade height control algorithm. This algorithm operates automatically in accordance with sky conditions and a profile angle, regardless of an occupant's operations. It creates a refreshing indoor environment with daylight and provides a uniform illuminance distribution. According to a field study using the profile calculation-based algorithm, errors occurred in the Ddepth. Error occurred up to 60% (0.27m) with an average error of 19.6%. An analysis of the causes of the error confirmed that solar position and building azimuth can cause a significant error to the system. To minimize an error from Ddepth, therefore, the penetration depth of direct sunlight was measured, and then a profile angle was obtained. Based on the profile angle obtained from the calculation and the one from actual measurement, a calibration equation was derived. When re-tested after applying this calibration equation to the algorithm, an error declined to 20% (0.09m) (reduced by approximately 40%). With the control algorithm developed in this study, therefore, when the sky is clear or partly cloudy, Ddepth is automatically controlled regardless of the occupant's operation, blocking the excessive inflow of direct sunlight. It is possible to allow daylight flow into the building in overcast, lighting energy could be saved by dimming. When the sky is overcast, in addition, a roller shade is fully up, allowing skylight to flow freely into the building. If daylight responsive dimming systems are applied to save energy, the accuracy of an optical sensor will be significantly improved thanks to uniform illuminance distribution, which will in turn enhance system accuracy. This study connected smart automated control roller shade which is operated after calculating the depth of the direct sunlight penetration and photosensor dimming control system and installed them in testbed. Then, the effects of the system on indoor illuminance distribution and amount of energy saved were analyzed. Data were collected and measured from August to 29 (20 days in total). When sky conditions were classified through measurement of irradiance for twenty (20) days, the ratio of clear sky was 18.90% while partly cloudy sky and overcast study were 26.93% and 54.16% respectively. The ratio of the automated roller shade cycle is the sum of clear sky and partly cloudy sky (45.84%). In other words, it was cycled by 45.84% during the measurement period. Compared to the ratio of other sky conditions, overcast sky was significant high with 54.16%. During the measurement, the roller shade was fully up with this ratio, allowing daylight penetration to the building up to the maximum level. At comparison of illuminance measured at the testbeds 'A' and 'B' for 20 days, the testbed 'B' in which an automated roller shade was installed was higher than the testbed 'A' in terms of maximum value with 96%. Compared to 'A-ES-2,' 'B-ES-2' installed in the middle of the testbed was higher by 41%. Compared 'A-ES-3,' it was higher by 89%. In terms of the minimum value, 'B-ES-1' was 12% compared to 'A-ES-1' while 'B-ES-2' and 'B-ES-3' were 25% each. These results mean that the automated roller shade has a significant effect on indoor illuminance distribution, compared to the manually operated roller shade. In addition, these effects are very helpful in saving energy. According to analysis on the amount of energy saved for twenty (20) days, 54.4% was saved by the manual operation while 76.7% was saved by the automated roller shade. The difference in the amount of energy saved between the two methods was 22.3%. These results were obtained because the automated roller shade was more active than the manually operated one in responding to weather changes. In addition, it was confirmed that the smart roller shade is essential in office buildings with curtain walls. If the smart automated roller shade can't be installed, the manually operated one should be installed because energy could be saved by 54.4% through the manual operation. Because the measurement was done in summer in which irradiance is high, the difference in the amount of indoor lighting energy saved by the two shielding systems could be large. In winter in which irradiance is relatively low, on the contrary, the amount of energy saved could be low.