An Experimental Study for the Evaluation of the Environmental Performance by the Application of the Automated Venetian Blind Ji-Hyun Kim 1, Kyoung-Wn Yang 1, Young-Joon Park 1, Kyung-Hee Lee 2, Myoung-Souk Yeo 3 and Kwang-Woo Kim 3 1 Department of Architecture, Graduate School of Seoul National University, Korea 2 Department of Architecture Engineering, College of Natural Resource and Life Sciences, Pusan National University 3 Department of Architecture, Seoul National University, Korea Corresponding email: snukkw@snu.ac.kr SUMMARY Venetian blind can have a major impact on building energy use and occupant's comfort. But manual or motorized Venetian blind has limitations in meeting occupant s needs and in reducing energy consumption. These limitations can be overcome by the automatic control of the Venetian blind. This study aims to analyze the control method of commercially used automated Venetian blind and to evaluate the environmental performance of this type of blind. The environmental performance of an automated Venetian blind was evaluated by a real-scale experiment and occupant s response in summer. The enhancement of environmental performance by the application of an automated Venetian blind was confirmed. 1. INTRODUCTION Recently, cooling loads through the building envelope has greatly increased with the increase of glass area in office buildings in Korea. Windows provide occupants with daylight, direct sunlight, visual contact with the outside and a feeling of openness. While it is desirable to introduce sunlight for natural lighting over a given constant level, the radiation heat of the sun has to be determined to allow its entrance or not according to the weather conditions. The radiation heat from the sun reduces the heating load in the winter season but increases the cooling load during the summer season. Due to the characteristics of solar energy, which is comprised of light and heat, solar energy is not easy to control; that is, daylight introduction and excessive heat isolation have to be considered at the same time. In addition, excessive sunlight will cause glare problems in an office space, which are a major complaint by occupants. These glare problems must also be taken into consideration. In office buildings, since the reduction of the opening ratio and the design of the windows orientation are restricted from the design perspective, Venetian blinds are generally used to control the incoming solar radiation. Venetian blinds are better than roll blinds because they can be controlled to slat angle as well as to occlusion index. Venetian blinds can greatly affect building energy use and occupant comfort, so it is important to control Venetian blinds properly according to the change of the external weather condition for enhancement of indoor environment. But previous studies have shown that in reality, occupants rarely change the position of the manual or motorized Venetian blind [1] [2] [3] [4] [5] [6] [7]. The manual or motorized Venetian blind has limitations in meeting occupant s needs and in reducing energy consumption. To overcome these limitations, the Venetian blind must be controlled automatically. The use of the automated Venetian blind,
controlled automatically by sensors according to the external weather condition, would be more effective than the manual or motorized Venetian blind. During times of peak solar gain, such a blind can reduce cooling loads and overheating. Under cloudy conditions, or in winter, it can be withdrawn to allow daylight and useful solar gains to enter the building, so that the building can reduce its dependence on electric lighting and heating requirement. To achieve this condition, the blind should be properly controlled. Otherwise, unwanted solar gain may enter the building and increase the cooling load. Occupants may experience glare from the sun and be unable to operate the shading to alleviate it. This study aims to analyze the control method of the commercially used automated Venetian blind and to evaluate its environmental performance in comparison to the manual or motorized Venetian blind. The environmental performance of the automated Venetian blind was evaluated by a real-scale experiment and occupant s response in summer. Finally, the potential of energy savings and comfort enhancement by use of the automatic control was confirmed. 2. BLIND TYPE AND OPERATION SURVEY A blind can be categorized into manual, motorized and automated according to its control method. The manual blind is the simplest type of blind without a motorized device. It is controlled directly by the occupant and used generally in modern buildings. But the occupants control the manual blind only when they feel discomfort [8]. In fact, manual blind control has problems because occupants do not control the blind until they feel discomfort such as glare and solar radiation. The motorized blind that can be controlled by a remote controller, and in some buildings, computer are used to control motorized blinds. Though the motorized blind can be controlled easier than the manual blind, it is operated inefficiently in real situations. According to the operation survey of actual motorized blinds, though it is able to control the motorized blind in central control room, central control is not used by the occupants need and 82.6% of all motorized blinds do not move, as shown in Tables 1 and 2. Also, the occlusion index of the stopped blind is usually, almost opened (0 ~ 20%) or closed (80 ~ 100%), as shown in Table 3. An automated blind is automatically controlled by sensors according to the external weather condition to enhance environmental performance. A motorized blind requires higher initial cost than a manual blind but does not produce better environmental performance. Therefore, the application of automated blind is necessary. Table 1. Outline of survey building City, County Number of floors Sky condition Seoul, Korea 22 Cleary sky(2 days) Overcast sky(2 days) Table 2. Frequency of blind operation. (South orientation) Frequency Number Percentage(%) 0 1 2 213 31 14 82.6 12.0 5.4 Total 258 100.0 Table 3. Occlusion index of blind. (Frequency 0) Occlusion index(%) Number Percentage(%) 0 ~ 20 21 ~ 79 80 ~ 100 207 141 172 39.8 27.1 33.1 Total 520 100.0
3. EVALUATION EXPERIMENT ON ENVIRONMEMTAL PERFORMANCE BY AUTOMATED BLIND 3.1 Outline The effects of commercially used automated blind on thermal and visual environment performance and comfort are compared with those of conventional manually operated blinds. The product specification of an automated blind used in this experiment is presented in Tables 4 ~ 6. In the test room, located on the top floor of a building in Seoul National University, Korea, evaluation experiments were conducted to measure the energy saving effect and occupant comfort enhancement for the month of August 2006. Two test rooms of dimensions 5.8m x 4.8m x 2.7m with the same architectural planning were used to reproduce the same conditions. Each room was equipped with an internal Venetian blind of same material and color, and the blind in one room was manually controlled and that in the other room automatically controlled, as shown in Figure 1 and 2. Various instruments were installed inside and outside the rooms to measure and analyze the various environments, as presented in Table 7. Table 4. Product specification of the automated blind Blind Sensor Operation mode Aluminum(gray) Slat width : 50mm Sun sensor (Outdoor vertical illuminance sensing) Energy saving mode(see Table 5) Comfort mode(see Table 6) Table 5. Operation sequence of energy saving mode. Control conditions Operation at ON ON OFF Control time Operation at OFF Exterior Exterior Occlusion delay delay Slat angle Illuminance Illuminance index 09:00 ~ 18:00 16 klux 3 min. 15 klux 15 min 100% 90 Completely open Table 6. Operation sequence of comfort mode. Control conditions ON OFF Control time Exterior Exterior delay Illuminance Illuminance Operation at ON delay Occlusion index 09:00 ~ 10:30 25 klux 3 min. 15 klux 15 min 100% 45 10:30 ~ 12:00 25 klux 3 min. 15 klux 15 min 100% 30 12:00 ~ 13:00 16 klux 3 min. 15 klux 15 min 100% 90 13:00 ~ 13:45 25 klux 3 min. 15 klux 15 min 100% 30 13:45 ~ 18:00 25 klux 3 min. 15 klux 15 min 100% 45 Slat angle Operation at OFF Completely open Figure 1. Plan view of test rooms.
Figure 2. External view of test rooms. Table 7. Measuring equipments. Equipment Interior illuminance Daylight factor meter, Lux meter Room temperature T-type thermocouple Outdoor temperature T-type thermocouple Solar radiation Irradiance meter Exterior illuminance Exterior lux meter Position Room 1, Room 2 Room 1, Room 2 Outside Roof(Outside) Roof(Outside) 3.2 Method In order to investigate the effect of the automated blind on the environmental performances of the rooms in the summer season, experiments were conducted for four cases, as presented in Table 8. In test room 1, the energy saving mode and comfort mode, which were controlled by an outdoor illuminance sensor, were selected. When in the energy saving mode, it was set up to shut out the solar radiation at the maximum level within the control range (see Table 5), and in the comfort mode, the slat angle was controlled to cut off direct daylight (although allowing some daylight to enter), in consideration of the working hours of the occupants and the comfort factor (see Table 6). Table 8. Experiment cases. Case Test room 1 Test room 2 Air-conditioned Remarks 1 Completely open Energy saving mode 2 Completely close ⅹ Evaluate energy consumption 3 Completely open Comfort mode 4 Motorized* Evaluate comfort * Occlusion index 75%, Slat angle: 90 For the set up of the compared blind, three model cases were selected, in which the blind was completely open (occlusion index: 0%), the blind was completely close (occlusion index: 100%, Slat angle: 90 ), and the blind was motorized (occlusion index: 75%, Slat angle: 90 ), respectively. The latter case represented the results of the blind operation survey. In cases 1 and 2, the characteristics of automatic control in terms of energy consumption in comparison with those of the extreme case of manual control were verified by comparing temperature and workplace illuminance. In cases 3 and 4, the conditions (with and without automatic control) were compared by PMV measurement and workplace illuminance, and a questionnaire was conducted four times per day(10:00, 12:00, 14:00, 16:00) to investigate their characteristics with regard to comfort. For each case, the experiments were conducted from 09:00 AM to 18:00 PM, without artificial lighting.
4. EXPERIMENT RESULT AND DISCUSSION 4.1 Case 1 : energy saving mode vs. completely open Case 1 was conducted on August 12th. On this day, the sky was fairly clear but became rather cloudy from 13:00 ~ 14:00. The temperature of the interior zone of the test room is shown in Figure 3 a). The temperature in test room 2 was higher than that of test room 1. Because solar radiation was effectively shut out in the energy saving mode, the temperature in test room 1 was lower than test room 2 by a maximum of 1.0. For the perimeter zone, which is directly subject to solar radiation, the temperature difference was greater. In Figure 3 b), the perimeter zone temperature of test room 1 was lower than that of test room 2 by a maximum of 2.7. Temperature [ ] Difference [ ] a) Interior zone b) Perimeter zone Figure 3. Temperature profile of case 1. In conclusion, the rise in room temperature was effectively reduced by the automated blind. In particular, in the perimeter zone, the automated blind effectively shut out solar radiation to reduce temperature rise. Especially, on clear summer day, the cooling load by the excessive solar radiation can be minimized through the appropriate automatic control of blind. 4.2 Case 2 : energy saving mode vs. completely close Case 2 was conducted on August 16th. The sky was cloudy all day. There was little temperature difference between the two test rooms. Therefore, though the blind was fully opened a few times during the experimental period in response to the external weather condition, the cooling load of test room 1 was slightly higher than that of test room 2, but the lighting energy of test room 1 could be saved by introducing daylight. The room depth meeting the required illuminance profile at the workplace in the two test rooms are shown in Figure 4. Compared to test room 2(completely close), which needed artificial lighting on whole day, test room 1 could satisfy the illuminance criteria( 500lux) during most of the experiment period without artificial lighting because daylight was introduced. So the lighting energy of test room 2 was saved. Consequently, the overall energy consumption, including cooling and lighting energy consumption, could be reduced by using the automated blind. In addition, the automated blind provided an open field of vision and a view of the outside scenery.
4.0 Test Room 1 Test Room 2 Room Depth Meeting Required Illuminance [m] 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 OFF ON OFF ON OFF (0%) (100%) (0%) (100%) (0%) Room 1 Control Room 2 Control Completely Close (100%) a) Room depth within satisfied range b) Workplace illuminance profile Figure 4. Analysis of the satisfied range and measured workplace illuminance of case 2. 4.3 Case 3 : comfort mode vs. completely open Case 3 was conducted in August. The sky was clear. A representative comfort indicator PMV was measured in two test rooms to determine the degrees of comfort of the two test rooms, as shown in Figure 5. In the interior zone, since both rooms were air-conditioned continuously and the PMV meter was installed away from the influence of solar radiation, the difference in the measured values was insignificant, and largely satisfied with the comfort criteria (-0.5 < PMV < +0.5) of the ISO. However, in the perimeter zone, which is directly subject to the influence of solar radiation, the PMV measured in test room 2 remained constant between 1.2 and 1.6, which indicated a discomfort environment. However, the PMV in test room 1 fell by about 0.5 at 10:30 when the blind began to be controlled, and as a result, enhanced the degree of comfort. a) Interior zone b) Perimeter zone Figure 5. PMV profile of case 3. With respect to the overall operation of the blind, 87.5% of the subjects in test room 1 were satisfied, while 62.5% of those in test room 2 were dissatisfied due to the rise in temperature resulting from solar radiation as shown in Figure 6 a). With respect to workplace illuminance, both test rooms showed illuminance of higher than 500lux during entire experiment period, but in test room 2, the illuminance exceeded the recommended upper limit (3,340lux [9]) during most of the experiment period as shown in Figure 6 b). Test room 1, which was operated in the comfort mode, was maintained within the recommended value because slat angle was controlled to cut off direct sunlight but allow daylight to flow in. Since the experiment had been conducted during a period of hot weather and clear sky, solar radiation must have had great impact on the result. Consequently, the degree of direct radiation and direct light should be appropriately controlled with a blind to protect the occupants from glare and to improve comfort.
a) Overall satisfaction b) Illuminance profile Figure 6. Subject response and illuminance profile at workplace of case 3. 4.4 Case 4 : comfort mode vs. motorized The experiment was conducted on August 29th, a cloudy day with rainfall starting from the late afternoon. Motorized blind condition was determined based on the operation survey results. Since the weather was cloudy and no significant influence from solar radiation was likely to be felt, no significant difference of PMV was observed due to the constant air conditioning, and the ISO comfort criteria were largely satisfied in both interior and perimeter zones. With respect to the overall operation of the blind, subjects in test room 1 were satisfied since optimal illuminance could be obtained by automatic control, while subjects in test room 2 were dissatisfied with the brightness, since the blind kept shutting out the daylight greatly during the cloudy weather as shown in Figure 7 a). With respect to workplace illuminance, test room 1 showed illuminance of higher than 500lux during most of the experimental period, but test room 2 under 500lux, as shown in Figure 7 b). Test room 1 was able to introduce more daylight by automatic control of the blind reflecting the outdoor weather condition. Room 1 Perimeter Room 1 Interior Room 2 Perimeter Room 2 Interior Outdoor 12,000 50,000 10,800 45,000 9,600 40,000 8,400 7,200 6,000 4,800 3,600 2,400 Upper Limit of Illuminance 35,000 30,000 25,000 20,000 15,000 10,000 0 0 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 a) Overall satisfaction b) Illuminance profile Figure 7. Subject response and illuminance profile at workplace of case 4. 1,200 Room 1 Control Off (0%) Off 5,000
Based on the questionnaire and measurements, visual comfort could be improved without additional lighting by introducing daylight selectively with the automated blind in accordance with the prevailing weather conditions. Additionally, it was judged that an open field of vision could be provided by automatic control. 5. CONCLUSION In this study, control methods of commercially used automated Venetian blind were analyzed and improvement effects of environmental performance were proven through the experiments on energy saving and comfort. In the energy saving mode, cooling load was reduced more than that with the fully opened window because blind blocked solar radiation according to established conditions under the clear sky condition. In overcast sky, the blind allows daylight to enter according to established conditions and so it can reduce the lighting energy and minimize the cooling load increase, simultaneously. In the energy saving mode, in which the blind is only fully opened or closed, the modification of the occlusion index and slat angle is not considered. Therefore, we need a control method that can consider the lighting and cooling energy saving simultaneously by proper control of the occlusion index and slat angle. In the comfort mode, the slat angle is controlled to cut off direct sunlight and this reduces the discomfort from excessive solar radiation and direct sunlight. Also, in this mode, daylight can be introduced to supply a feeling of openness to the occupant. Because modification of the occlusion index is not considered and modification of slat angle is limited to two times per day in the comfort mode, a more detailed and delicate control method which can consider the control of occlusion index is necessary. The control method discussed in this paper is operated only through external weather condition sensing. But the purpose of blind control is to improve indoor environment, so a more effective and enhanced control method which can reflect indoor environment needs to be developed by sensing internal factors such as workplace illuminance, indoor temperature etc. REFERENCES 1. Rubin, A I, Collins, B L, and Tibbott, R L. 1978. Window blinds as a potential energy saver a case study. NSB Building Science Series Vol. 112. National Institute for Standards and Technology. 2. Rea, M. 1984. Window blind occlusion: a pilot study. Building and Environment. Vol. 19 (2), pp 133 137. 3. Foster, M and Oreszczyn, T. 2001. Occupant control of passive systems: the use of Venetian blinds. Building and Environment. Vol. 36 (2), pp 149 155. 4. Reinhart, C F and Voss, K. 2003. Monitoring manual control of electric lighting and blinds. Lighting Research and Technology. Vol. 35 (3), pp 243 260. 5. Lindsay, C T R and Littlefair, P J. 1992. Occupant use of Venetian blinds in offices. Building Research Establishment contract PD233/92. 6. Rea, M S, Rutledge, B and Maniccia, D. 1998. Beyond daylight dogma, Proceedings of the Daylighting 98 Conference, ON: Natural Resources Canada, pp 215 222. 7. Escuyer, S and Fontoynont, M. 2001. Lighting controls: a field study of office workers reactions. Lighting Research and Technology. Vol. 33 (2), pp 77 96. 8. Inoue, T, Kawase, T, Ibamoto, T, et al. 1988. The development of an optimal control system for window shading devices based on investigations in office buildings. ASHRAE Transactions. Vol. 94, pp 1049 1056. 9. IESNA. 2001. IESNA Lighting Handbook. Illuminating Engineering Society of North America.