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An experimental study on the environmental performance of the automated blind in summer
Building and Environment 44 (2009) 1517–1527
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Building and Environment journal homepage: www.elsevier.com/locate/buildenv
An experimental study on the environmental performance of the automated blind in summer Ji-Hyun Kim a, Young-Joon Park b, Myoung-Souk Yeo b, Kwang-Woo Kim b, * a b
Daewoo Institute of Construction Technology, Daewoo Engineering & Construction Co., Ltd., 60, Songjuk-dong, Jangan-gu, Suwon, Gyeonggi-do 440-210, South Korea Department of Architecture, College of Engineering, Seoul National University, San 56-1, Shillim-dong, Kwanak-gu, Seoul 151-742, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 March 2008 Received in revised form 29 July 2008 Accepted 4 August 2008
Blinds are used widely in numerous buildings to conserve energy and provide for occupants’ comfort in the perimeter zone. However, manual or motorized blinds are limited in their ability to reduce energy consumption and to provide comfort because occupants themselves must operate blinds to block direct solar radiation. Thus, the use of automated blinds would more fully exploit the full benefits of blinds. This study aims to find out whether the environmental performance of a building can be improved by the application of an automated Venetian blind in comparison to a manual or motorized Venetian blind and whether occupants may feel discomfort by the application of an automated Venetian blind in the summer season. This study also aims to find out the insufficiency of the automatic control algorithm of that automated Venetian blind for future study of the development of that algorithm. Through this study, the potential energy savings and the comfort enhancement when using the automated blind was confirmed and the insufficiency of the automatic control algorithm of that was also found out. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Venetian blind Manual blind Motorized blind Automated blind Automatic control Environmental performance Energy consumption Comfort Blind operation survey
1. Introduction Recently, numerous glass-skin office buildings have been constructed in Korea and more interest has arisen regarding the appearance of the building envelope. While the glass-skins of a building envelope can provide occupants with daylight, visual contact with the outside and a feeling of openness, they also represent an opportunity for heat to enter the building. While it is desirable to introduce sunlight for natural lighting over a given comfortable level, solar radiation caused by the introduction of sunlight may not be desired under certain conditions or on, for example, a hot summer day, and the decision to introduce it must be made based on these conditions. Radiant heat from the sun reduces the heating energy consumption in the winter season but increases the cooling energy consumption 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. Moreover, illuminance that is too strong in the workplace can cause glare and should be avoided in an office space. As the glare problem is a major factor that has a great
* Corresponding author. Tel.: þ82 2 880 7065; fax: þ82 2 871 5518. E-mail address: [email protected] (K.-W. Kim). 0360-1323/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2008.08.006
effect on the comfort of occupants, it too must be taken into consideration. In office buildings, as the reduction of the window ratio of envelope and the orientation of the window are restricted from a design perspective, the use of blinds is a common means of controlling incoming solar radiation. If blinds are controlled properly according to variations in the outdoor and indoor environmental conditions, excessive energy use and the level of occupant discomfort due to direct solar radiation can be greatly reduced. In the case of Venetian blinds, environmental performance that is more effective can be achieved because additional controls pertaining to the slat angle are available. However, studies in this area [1–7] have shown that in reality, occupants rarely change the occlusion index1 of blinds, regardless of whether manual or motorized Venetian blinds are used. Manual or motorized Venetian blinds are limited in their ability to meet occupants’ needs and in reducing energy consumption, as occupants tend to change the occlusion index only when direct solar radiation makes conditions uncomfortable. To overcome these limitations, Venetian blinds must be controlled automatically. The use of automated Venetian blinds
1 The ratio of a lowered blind to the total window area, which is between 0% (blind fully opened) and 100% (blind fully closed).
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that are controlled automatically by sensors according to the outdoor weather condition is likely more effective compared to the manual or motorized Venetian blinds. In summer, automated blinds can reduce cooling energy consumption and overheating by blocking solar radiation. In winter, they can be opened to allow daylight and required solar gains so that the building can reduce its dependence on artificial lighting and its heating system. To achieve these outcomes, the blinds must be properly controlled; otherwise, unwanted solar gain may enter the building and increase the cooling energy consumption. Moreover, occupants may experience glare from the direct solar radiation. This study aims to find out whether the environmental performance of a building can be improved by the application of an automated Venetian blind in comparison to a manual or motorized Venetian blind and whether occupants’ may feel discomfort by the application of an automated Venetian blind in the summer season. This study also aims to find out the insufficiency of the automatic control algorithm of that automated Venetian blind for future study of the development of that algorithm. For this purpose, the manner in which occupants of buildings with blinds operate their blinds was surveyed firstly. The pattern used with manual blinds was established based on the previous research review [1–7] and the pattern used with motorized blinds was established based on the blind operation survey. The environmental performance of the manual, motorized and automated Venetian blind was evaluated through thermal and visual experiments in a real-scale test rooms and through reports by the occupants of the dwelling in summer. 2. Backgrounds Blinds can be classified into the manual, motorized and automated type according to the control method, as shown in Fig. 1. A manual blind is the simplest type of blind as it does not incorporate a motorized device. As occupants operate it manually, the initial investment is small and the installation of the blind is simple. However, direct operation of the blinds according to environmental variations is an inconvenient factor from the perspective of building occupants. Additionally, considering effective countermeasures is difficult as weather conditions can change dynamically. Occupants operate blinds only when glare makes conditions uncomfortable. Aside from this condition, they tend not to operate the blinds but rather to use artificial lighting,
even when daylight comes into the building sufficiently without glare. Motorized blinds are operated by motors, implying that remote or central operation is possible. Compared to manual blinds, operation and management is easy and convenient. However, the initial investment requirements have increased and effective countermeasures according to environmental changes are difficult because the operation is determined according to decisions by occupants. The motorized blind may become less economically efficient considering the high initial investment. Previous studies [1–5] that investigated the present conditions of actual blinds have shown this. Rea [1] analyzed the operating patterns of a 16-floor building in Ottawa, Canada, according to orientation of the building, the time and the weather condition. The orientation of the building and the weather conditions are important factors that have an effect on the operation of blinds. The occlusion index facing east is high when the sky is clear compared to when it is overcast, while the occlusion indexes facing south and west show little difference. Inoue et al. [2] studied the operating patterns of for high-rise office buildings in Tokyo, Japan. In an eastern exposure, it was found that occlusion index increases before noon as occupants enter the room and that occlusion index decreases in the afternoon. In a western exposure, the operating patterns of blinds have the opposite characteristics. In overcast conditions, blinds have a little movement because radiation is not influential. In addition, they conducted a survey involving 336 occupants. About 90% of those who responded reported that visual comfort affects the operation of blinds, while 50–80% reported that thermal comfort affects their operation. It was also found that the blinds were operated to change an uncomfortable indoor environment to one that was comfortable. The most common factor that led to an uncomfortable environment was direct solar radiation and glare. Lindsay [3] concluded that daylight that comes in at 65 below the perpendicular line of a facade causes the occlusion index to increase. His study also suggested that future studies of blind movements have to consider indoor measurement factors such as the level of illumination, the temperature and the presence of artificial lighting. As the occlusion index can change according to the facade, additional study of the behavior of occupants is required. According to Oscar Faber Associates [4], occupants change the occlusion index when the outdoor radiation exceeds 300 W/m2. Blind operation was found to be a function of solar radiation and altitude.
Fig. 1. Classification of the blind by the control method.
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Fig. 2. Concept of the split blind.
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daylight [8]. These blinds can be more useful compared to manual or motorized blind since daylight can be introduced through the upper section though lower section is closed to prevent from glare (see Fig. 2). But those blinds are also operated by occupants. If once the lower section is closed, the lower section tends not to be opened although outdoor condition has changed. Therefore, automatic control strategy of those blinds has to be developed to maximize environmental performance. Automated blinds are automatically controlled by sensors according to the outdoor weather condition to enhance environmental performance. They utilize a built-in control algorithm that maintains comfortable indoor conditions. They can provide optimum indoor conditions as dynamically changing weather conditions are checked continually. In addition, productivity is increased because occupants can concentrate on their work without operating the blinds. Manual or motorized blinds, though commonly used, have limitations to their level of potential improvement because proper countermeasures according to changes in indoor and outdoor conditions are difficult. To overcome these limitations, blinds need to be controlled automatically. 3. Blind operation survey
Vine et al. [5] studied 14 occupants’ actions concerning automated blinds, a mix of automated and manual blinds, and manual control modes of blinds in a real-scale experiment. In the results, occupants were found to prefer higher illumination to standard levels (700–1500 lux), and a majority answered that glare affects their work. There are blinds that allow closing the lower section of the blinds and leaving the upper section in horizontal position for
To evaluate the environmental performance of automated blinds compared to manual or motorized blinds, the manner in which occupants of buildings with blinds operate their blinds need to be surveyed. For this purpose, the pattern used with manual and motorized blinds was established for use in the experiment. The pattern used with manual blinds was established based on the previous research review [1–7]. Occupants rarely operate the
Fig. 3. A survey building applied with the motorized blind.
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Fig. 4. Blind operation frequency analysis.
blind and only when they feel discomfort because of glare etc., they operate the blind to be fully closed. After that, they do not operate the blind even when daylight comes into the building sufficiently without glare. So, the blind is fully opened or fully closed during most of the day. Operation data regarding the motorized blinds is collected and the pattern used with motorized blinds was established based on this survey because there are few researches about the pattern used with the motorized blind. The results of this survey are summarized below.
In order to investigate the motion and frequency of the operation of the blinds along with the relationship of these factors to other influential factors, operation data for 468 blinds on 16 floors which is occupied was collected via central operation room PC. Of these, 182 blinds faced to the east, 185 to the west, and 101 faced to the south. There were no blinds on the north wall, and the core space was connected to this wall. For 2 clear and 2 cloudy days (for a total of 4 days) at 10-min intervals from 09:00 to 18:00, the occlusion index was recorded, and the sky’s condition throughout was photographed and weather data were collected.
3.1. Outline
3.2. Survey results
The blind operation survey was conducted at a 22-floor building in Seoul, Korea. The building had east-, west-, and south-facing windows equipped with ivory colored roll blinds operated using a remote controller as shown in Fig. 3(a). The blinds in each room were operated by the occupants themselves or a PC in a central operation room housed in the basement, with the position of each blind indicated on a monitor as shown in Fig. 3(b) and (c).
Over a period of 4 days, the operation frequencies of each of the 468 blinds in the building were analyzed. The frequencies are classified into four categories whose rates are shown in Fig. 4. More than half of the blinds were not operated throughout the entire day, though if the blinds that moved only once a day were included, the percentage then rises to 95%. This shows that the occupants rarely operated the motorized blinds and that they appeared to be
Fig. 5. Occlusion index with the highest frequency.
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Table 1 Control sequence of Energy Saving Mode Control time
Control condition
Control at ON
On
09:00–18:00
Control at OFF
Off
Exterior illuminance
Delay time
Exterior illuminance
Delay time
Occlusion index
Slat angle
Occlusion index
Slat angle
16 klux
3 min.
15 klux
15 min
100%
90
0%
–
unconcerned about the status of the blinds. Compared to previous studies, though the operation frequency of motorized blinds tends to be slightly higher than that of manual blinds, it is not sufficient to meet the energy saving requirements and environmental demands for comfort. Therefore, for the correct operation of blinds in such a way that considers environmental performance, an automatic system for the control of blinds is required. The operation frequencies of the blinds show distinctive differences depending on the orientation of the blinds and the condition of the sky. Blinds facing to the south tend to Type A, while the blinds facing west were operated more frequently compared to those facing in other orientations. When the sky was overcast, the percentage of Type B usage increased as shown in Fig. 4. Overall, more blinds were raised in the morning and more drawn down in the afternoon. For the blinds facing south, they were more frequently drawn down between 13:00 and 14:00 when the solar position was at its highest. For the blinds facing east, they tended to be lowered in the morning and raised in the afternoon. For the blinds facing west, they tend to be raised in the morning and lowered in the afternoon, in contrast to those facing east. The occlusion index was divided into 10 sections whose frequencies were analyzed by classifying them into either a morning or an afternoon group as shown in Fig. 5. The occlusion index changed according to the condition of the sky. The occlusion index with the highest frequency in terms of orientation, time, and sky condition is shown in Fig. 5. Under a clear sky, the occlusion index for blinds facing east decreases from the morning to the afternoon. Generally speaking, blinds with an occlusion index in the range of 90–100% change to 0–10% status, while those of occlusion index 70–80% show almost no change. The occlusion index for blinds facing east under a clear sky ranges from 0 to 0%. Thus, as less solar radiation enters when the sky is overcast than when it is clear, there is less glare and discomfort and occupants naturally tend to open the blinds to have a feeling of openness. For blinds facing west under a clear sky, the occlusion index increases from the morning to the afternoon, as the level of direct solar radiation entering through the windows facing west increases in the afternoon. Under an overcast sky, the occlusion index also tended to increase in the afternoon. However, more blinds were lowered to an occlusion index of 50% in the afternoon as there is less solar radiation compared to when there is a clear sky. Compared with those facing east or west, the differences between the morning and afternoon are not significant in case of
blinds facing south. This implies that more of the blinds facing south belong in the Type A group, which remain fixed and are not operated at all throughout the day. However, the occlusion indexes differ under clear and overcast skies. Under a clear sky, the occlusion index of most of the blinds range from 70 to 80%, while under an overcast sky, most range from 50 to 60%. This is thought to be due to the lower amount of direct solar radiation entering under an overcast sky, as in other orientations. In this study, considering the results of the operation survey, the occlusion index of motorized blinds was determined to be 75% as shown in Fig. 5, as the test room of the experiment was facing south. 4. Experiment on the environmental performance of automated blinds 4.1. Outline In this study, the effects of commercially used automated blinds on thermal and visual performance were compared with those of manual and motorized. Internal Venetian blinds were used in this experiment and the blind specification was as follows. Blinds: internal Venetian blinds (slat material: aluminum, slat width: 50 mm). Sensor: sun sensor (sensing outdoor vertical illuminance). Control: Energy Saving Mode (see Table 1) and Comfort Mode (see Table 2) of S company [9]. Experiments were carried out in two side-by-side mock-up test rooms located on the top floor of a building at Seoul National University in Seoul, Korea, to measure the energy consumption and rate of occupant comfort enhancement. The experiment was conducted in August of 2006. Two test rooms with the identical dimensions of 5.8 m (W) 4.8 m (D) 2.7 m (H) with the same heat loss and gain were used to reproduce identical conditions, as shown in Fig. 6. The thermal performance of the blinds was evaluated by analyzing the average temperature difference and the rate in which the temperature decreased over time. To this end, as shown in Fig. 6, a total of 40 (20 in each room) thermocouples were installed in addition to a thermocouple that was attached on the exterior wall to measure the outdoor temperature. The visual performance of the blind was
Table 2 Control sequence of Comfort Mode Control time
Control condition
Control at on
On
Off
Exterior illuminance 09:00–10:30 10:30–12:00 12:00–13:00 13:00–13:45 13:45–18:00
25 25 16 25 25
Control at off
klux klux klux klux klux
Delay time (min)
Exterior illuminance
3 3 3 3 3
15 15 15 15 15
klux klux klux klux klux
Delay time (min)
Occlusion index (%)
Slat angle ( )
Occlusion index (%)
Slat angle
15 15 15 15 15
100 100 100 100 100
45 30 90 30 45
0 0 0 0 0
– – – – –
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Fig. 6. Outline of test rooms.
evaluated by whether it met the standard average room illuminance. Illuminance measuring devices were installed at the exterior and interior measuring points, as shown in Fig. 6, to measure the actual illuminance, and the sky conditions were analyzed by measuring the outdoor illuminance of the overall condition of the sky along with the diffuse illuminance. The different instruments used in the experiment are shown in Table 3. 4.2. Experiment method In order to investigate the effect of the automated blind on the environmental performance, experiments were performed for six
cases, as presented in Table 4. In Cases 1–4, an Energy Saving Mode of S company [9] was utilized in test room 1. This was controlled automatically by an exterior sun sensor. The Energy Saving Mode was set up to shut out the solar radiation at the maximum level within the control range (see Table 1). In test room 2, for the arrangement of the comparison, two model cases of manual blind were selected, in which the blinds were fully opened (occlusion
Table 4 Experiment cases Case Date Test room 1 1
Table 3 Measuring instruments
2
Item
Equipments
Position
Interior illuminance
Interior lux meter daylight factor meter
Exterior illuminance Solar radiation Room temperature
Exterior lux meter Exterior irradiance meter T-type thermocouple
Outdoor temperature
T-type thermocouple
Test room 1, test room 2 Roof (outside) Roof (outside) Test room 1, test room 2 Outside
Test room 2
Cooling Remarks
8/12 Automated blind: Manual X Energy Saving Mode (fully opened) X 8/16 (see Table 1) Manual (fully closed) B 8/19 Manual (fully opened) B 8/20 Manual (fully closed) B 8/18 Automated blind: Manual Comfort Mode (fully opened) a B 8/29 (see Table 2) Motorized
3 4 5 6 a
Occlusion index 75%, Slat angle: 90 .
Evaluate temperature difference Evaluate temperature difference Evaluate energy consumption Evaluate energy consumption Evaluate comfort Evaluate comfort
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Fig. 7. Temperature profile of Case 1.
index: 0%) in one and the blinds were fully closed (occlusion index: 100%, slat angle: 90 ) in the other. Through the experiments, the characteristics of automatic control in terms of energy consumption compared with those of the manual blind were verified by comparing the temperature, cooling energy and lighting energy. In Cases 1 and 2, the effect that isolating solar radiation according to excessive exterior illuminance changed the room temperature is compared to the manual blind. In Cases 3 and 4, cooling and lighting energy were estimated using the measured data of the temperature difference between the supply air and the return air in addition to the interior illuminance. In Cases 5–6, the Comfort Mode of S company [9] was utilized in test room 1, which was controlled automatically by an exterior sun sensor. 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 (09:00–18:00) and the solar position (see Table 2). In test room 2 for the set up of the compared blind, two model cases were selected in which a manual blind (fully opened) and a motorized blind (occlusion index: 75%, slat angle: 90 ). The latter case represented the results of the blind operation survey (see Section 3.2). Through the experiments, the conditions (with and without automatic control) were compared in terms of PMV measurements and workplace illuminance, and a questionnaire was conducted four times per day
(10:00, 12:00, 14:00, 16:00) to investigate these factors with regard to comfort. A total of 24 persons answered the questionnaire in turn and their age ranged from 24 to 36 years. Fourteen persons were men and 10 persons were women. For each case, the experiments were performed from 09:00 to 18:00 without artificial lighting. Prior to the beginning of the experiments, two rooms were air-conditioned to ensure that the two rooms were in identical condition.
5. Results and discussion 5.1. Case 1: Energy Saving Mode vs. manual (fully opened, no cooling) The temperature of the interior zone of the test room is shown in Fig. 7(a). During the experiment, the temperature in test room 2, where the blinds were fully opened, was higher than that of test room 1 where the blinds were controlled automatically. Due to the effective blockage of solar radiation according to the increase of the exterior illuminance in the Energy Saving Mode, the temperature in test room 1 was lower than that in test room 2 by as much as 1.0 C. For the perimeter zone, which was directly subjected to solar radiation, the temperature difference was greater. In Fig. 7(b), the
Fig. 8. Temperature profile of Case 2.
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Fig. 9. Cooling energy consumption of Case 3 and Case 4.
perimeter zone temperature of test room 1 was lower than that of test room 2 by a maximum of 2.7 C. This experiment demonstrated that with automatic control, more effectively manage of increases in room temperature is possible compared to when blinds are fully opened. In particular, in the perimeter zone, solar radiation can be shut out effectively by automatic control, thereby, offsetting a rise in temperature and providing uniform temperature distribution throughout the room. 5.2. Case 2: Energy Saving Mode vs. manual (fully closed, no cooling) The temperatures of the two test rooms for this case are shown in Fig. 8. Compared with test room 2, where solar radiation was shut out all day, the temperature in test room 1 was approximately 0.3 C higher in the interior zone. When comparing the room temperatures in the perimeter zone, the temperature in test room 1 was higher than that recorded in test room 2 by approximately 0.5 C, which is comparable to that recorded in the interior zone. When compared with the results obtained in Case 1, this shows that the rise in the perimeter zone temperature can be reduced by using automatically controlled blinds. Therefore, though the blinds were fully opened occasionally during the experimental period in response to the outdoor weather conditions, the temperature of test room 1 was not significantly different from that of test room 2.
5.3. Case 3: Energy Saving Mode vs. manual (fully opened, cooling) During the experiment, the air supply, return temperature and flow rate through the cooling units were measured to measure the heat that was removed from the room. On the basis of these measurements, the cooling energy consumption of the test rooms was calculated to be 23.3 kWh/day for test room 1 and 26.4 kWh/ day for test room 2. A graph of this data is shown in Fig. 9(a). Therefore, the energy saved when using the automated blinds was 3.1 kWh/day, or approximately 12%, compared with the value obtained when the blinds were fully opened. Fig. 10(a) shows the room depth when meeting the required room illuminance of 500 lux [10]. In test room 1, the required room illuminance could not be met part of the time because the blinds were lowered automatically. Test room 2 was able to meet the required illuminance nearly all of the time, as no blinds were used. However, in test room 2, the room illuminance continuously exceeded the upper limit of 3340 lux [10], which is the threshold for discomfort caused by glare (see Fig. 11(a)). Therefore, in an actual situation under these conditions, it would be reasonable to assume that, during these times, the blinds would have been fully closed and artificial lighting should have been used. Assuming that lighting is used where the required illuminance cannot be met, the lighting energy consumption derived from the heat generated from the lighting was calculated by applying the lighting power consumption of 20 W/m2 in a typical office building
Fig. 10. Room depth meeting the required illuminance of Case 3 and Case 4.
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Fig. 11. Illuminance profile of Case 3 and Case 4.
of Korea [11]. Consequently, test rooms 1 and 2 were shown to consume 4.12 kWh/day and 2.83 kWh/day of lighting energy, respectively. Lighting is electrical energy, while cooling is thermal energy, which has to be divided by a COP of typically 3 to obtain electrical energy. Based on this fact, the overall energy consumption of two test rooms are as follows. Test room 1 (automated): (23.3 kWh/day)/3 þ 4.12 kWh/ day ¼ 11.89 kWh/day. Test room 2 (manual): (26.4 kWh/day)/3 þ 2.83 kWh/ day ¼ 11.63 kWh/day. The overall expenditure was 0.26 kWh/day less when manually controlled blinds were used, but occupants in test room 2 must feel discomfort by glare during most of the day (09:00–15:00). As mentioned above, in an actual situation under these conditions, it would be reasonable to assume that, during these times, the blinds would have been fully closed and artificial lighting should have been used. On the basis of the experimental results, we might conclude that the automatic control of blinds can reduce the cooling energy consumption compared with an environment in which blinds are not used.
and 14.3 kWh/day, respectively (see Fig. 9(b)). Consequently, the use of automated blinds in Energy Saving Mode consumed 2.4 kWh/day (or 16.4%) more cooling energy than when the blinds completely covered the window. Room depths meeting the required room illuminance in test rooms 1 and 2 are shown in Fig. 10(b). Lighting energy was calculated on the basis of the experiment results using the method used in Case 3. Test room 1 consumed 3.12 kWh/day and test room 2 consumed 6.59 kWh/day of lighting energy. The overall energy consumption of two test rooms are as follows. Test room 1 (automated): (16.7 kWh/day)/3 þ 3.12 kWh/ day ¼ 8.69 kWh/day. Test room 2 (manual): (14.3 kWh/day)/3 þ 6.59 kWh/ day ¼ 11.36 kWh/day. This experiment, by virtue of the fact that the cooling load was higher than that obtained for the closed blinds, demonstrates that using automated blinds can reduce the overall energy consumption, including the lighting energy, by 2.67 kWh/day. In addition, the automated blinds can provide an open field of vision and a view of outside scenery. 5.5. Case 5: Comfort Mode vs. manual (fully opened, cooling)
5.4. Case 4: Energy Saving Mode vs. manual (fully closed, cooling) Using a method identical to that of Case 3, the cooling energy consumption of test rooms 1 and 2 were found to be 16.7 kWh/day
During this experiment, the sky was clear. The representative comfort indicator PMV was measured in two test rooms to determine the degrees of comfort of the two test rooms. This is shown in
Fig. 12. PMV profile of Case 5.
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Fig. 13. Subject response and illuminance profile of Case 5.
Fig. 12. In the interior zone, as both rooms were air-conditioned continuously and because the PMV meter was installed away from the influence of solar radiation, the difference in the measured values was insignificant and the two rooms largely satisfied the comfort criteria (0.5 < PMV < þ0.5) of the ISO [12]. However, in the perimeter zone, which was directly subjected to the influence of solar radiation, the PMV measured in test room 2 remained between 1.2 and 1.6, which indicates an uncomfortable environment. However, the PMV in test room 1 fell by approximately 0.5 at 10:30 AM, when the blinds began to be controlled. As a result, the degree of comfort was enhanced. With respect to the overall operation of the blinds, 87.5% of the subjects in test room 1 were satisfied, whereas 62.5% of those in test room 2 were dissatisfied due to the rise in the temperature that resulted from solar radiation, as shown in Fig. 13(a). In terms of workplace illuminance, both test rooms showed illuminance that was higher than 500 lux during the entire experiment period. In test room 2, however, the illuminance exceeded the recommended upper limit (3340 lux [10]) during of the majority of the experimental period, as shown in Fig. 13(b). Test room 1, which was controlled by Comfort Mode, was maintained within the recommended value as the slat angle was controlled to cut off direct sunlight while allowing daylight in. As the experiment was conducted during a period of hot weather and clear skies, solar radiation likely had considerable impact on the results. Consequently, the degree of direct radiation
and direct light should be appropriately controlled using blinds to protect the occupants from glare and to improve their comfort. 5.6. Case 6: Comfort Mode vs. motorized (cooling) During the experiment, clouds and rainfall started from the late afternoon. The motorized blind condition was determined based on the operation survey results. As the weather was cloudy and no significant influence from solar radiation was likely to be felt, no significant difference in the PMV was observed due to the constant air conditioning. Moreover, the ISO comfort criteria were mostly satisfied in both the interior and perimeter zones (see Fig. 14). With respect to the overall operation of the blinds, subjects in test room 1 were satisfied as optimal illuminance could be obtained via automatic control. In contrast, subjects in test room 2 were dissatisfied with the level of brightness as the blinds continued to shut out most of the daylight during the cloudy weather, as shown in Fig. 15(a). With respect to workplace illuminance, test room 1 showed illuminance that was higher than 500 lux during most of the experimental period. Test room 2, on the other hand, was under 500 lux, as shown in Fig. 15(b). Test room 1 was able to introduce more daylight through automatic control of the blinds, in keeping with the outdoor weather condition. Based on the questionnaire and measurements, visual comfort could be improved without additional lighting by introducing
Fig. 14. PMV profile of Case 6.
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Fig. 15. Subject response and illuminance profile of Case 6.
daylight selectively with the automated blinds in accordance with the prevailing weather conditions. Additionally, it was judged that an open field of vision could be provided by automatic control. 6. Conclusion In this study, the manner in which occupants of buildings with blinds operate their blinds was surveyed and operation data regarding the motorized blinds is collected. Based on this survey, the environmental performance of the automated Venetian blind was evaluated through thermal and visual experiments in a realscale test rooms and through reports by the occupants of the dwelling in summer. Through this study, the potential energy savings and the comfort enhancement when using the automated blind was confirmed and the insufficiency of the automatic control algorithm of that was also found out. In terms of cooling energy consumption, automated blinds reduced the cooling energy consumption compared to manual blinds which is fully opened as the automated blinds blocked solar radiation according to the outdoor weather conditions while consuming more energy compared to manual blinds which is fully closed. However, if the additional lighting energy consumption is considered, such as that needed due to the interception and blocking of sunlight, the overall environmental performance of the automated blinds is nearly equal to that of manual blinds which is fully opened. But the room illuminance continuously exceeded the upper limit of 3340 lux [10]. Therefore, in an actual situation under these conditions, it would be reasonable to assume that the blinds would have been fully closed and artificial lighting should have been used. And if the additional lighting energy consumption is considered the overall environmental performance of the automated blinds is better than that of manual blinds which is fully closed. From the viewpoint of comfort, in the case of the automated blinds, the slat angle is controlled to cut off direct sunlight, which reduces the discomfort from excessive solar radiation and direct sunlight. In addition, daylight can be introduced to supply a feeling of openness to the occupants. As modification of the occlusion index is not considered and modification of the slat angle is limited to two times per day in the Comfort Mode, a more detailed and
delicate control method that can consider the control of the occlusion index is necessary. As the blinds are only fully opened or closed in the Energy Saving Mode, the modification of the occlusion index and slat angle is not considered. Therefore, a control method must be devised that can consider the lighting and cooling energy saving simultaneously via proper control of both the occlusion index and the slat angle. The control method discussed in this study was based solely on detecting outdoor weather conditions. However, a more effective and enhanced control method that can also respond to an indoor environment by sensing indoor factors such as illuminance and temperature needs to be developed, as the main purpose of blind control is to improve the indoor environment.
References [1] Rea M. Window blind occlusion: a pilot study. Building and Environment 1984;19(2):133–7. [2] Inoue T, Kawase T, Ibamoto T, Takakusa S, Matsuo Y. The development of an optimal control system for window shading devices based on investigations in office building. ASHRAE Transactions 1988;104:1034–49. [3] Lindsay CRT. The use of adjustable shading devices: an experimental methodology. IBSE National Lighting Conference, Building Research Establishment (BRE), 1989. [4] Oscar Faber Associates. Occupancy data for thermal calculations in nondomestic buildings. Building Research Establishment (BRE); 1992. [5] Vine E, Lee E, Clear R, DiBartolomeo D, Selkowitz S. Office worker response to an automated Venetian blind and electric lighting system: a pilot study. Energy and Buildings 1998;28:205–18. [6] Rubin AI, Collins BL, Tibbott RL. Window blinds as a potential energy saver – a case study. Washington DC: U.S. Department of Commerce, National Bureau of Standards; 1978. [7] Lindsay CRT, Littlefair PJ. Occupant use of Venetian blinds in offices. Building Research Establishment (BRE); 1993. [8] IEA. Daylight in buildings – a source book on daylighting systems and components. IEA SHC TASK 21/ECBCS ANNEX 29; 2000. [9] Somfy SAS. Animeo IB þ operating software. Somfy; 2003. [10] IESNA. IESNA lighting handbook. Illuminating Engineering Society of North America; 2001. [11] Kim KW. Research and development of technologies for environment-friendly smart building systems. Seoul: Korea Ministry of Construction & Transportation; 2003. [12] ISO. ISO 7730: ergonomics of the thermal environment – analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria. ISO; 2005.
Contents lists available at ScienceDirect
Building and Environment journal homepage: www.elsevier.com/locate/buildenv
An experimental study on the environmental performance of the automated blind in summer Ji-Hyun Kim a, Young-Joon Park b, Myoung-Souk Yeo b, Kwang-Woo Kim b, * a b
Daewoo Institute of Construction Technology, Daewoo Engineering & Construction Co., Ltd., 60, Songjuk-dong, Jangan-gu, Suwon, Gyeonggi-do 440-210, South Korea Department of Architecture, College of Engineering, Seoul National University, San 56-1, Shillim-dong, Kwanak-gu, Seoul 151-742, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 March 2008 Received in revised form 29 July 2008 Accepted 4 August 2008
Blinds are used widely in numerous buildings to conserve energy and provide for occupants’ comfort in the perimeter zone. However, manual or motorized blinds are limited in their ability to reduce energy consumption and to provide comfort because occupants themselves must operate blinds to block direct solar radiation. Thus, the use of automated blinds would more fully exploit the full benefits of blinds. This study aims to find out whether the environmental performance of a building can be improved by the application of an automated Venetian blind in comparison to a manual or motorized Venetian blind and whether occupants may feel discomfort by the application of an automated Venetian blind in the summer season. This study also aims to find out the insufficiency of the automatic control algorithm of that automated Venetian blind for future study of the development of that algorithm. Through this study, the potential energy savings and the comfort enhancement when using the automated blind was confirmed and the insufficiency of the automatic control algorithm of that was also found out. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Venetian blind Manual blind Motorized blind Automated blind Automatic control Environmental performance Energy consumption Comfort Blind operation survey
1. Introduction Recently, numerous glass-skin office buildings have been constructed in Korea and more interest has arisen regarding the appearance of the building envelope. While the glass-skins of a building envelope can provide occupants with daylight, visual contact with the outside and a feeling of openness, they also represent an opportunity for heat to enter the building. While it is desirable to introduce sunlight for natural lighting over a given comfortable level, solar radiation caused by the introduction of sunlight may not be desired under certain conditions or on, for example, a hot summer day, and the decision to introduce it must be made based on these conditions. Radiant heat from the sun reduces the heating energy consumption in the winter season but increases the cooling energy consumption 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. Moreover, illuminance that is too strong in the workplace can cause glare and should be avoided in an office space. As the glare problem is a major factor that has a great
* Corresponding author. Tel.: þ82 2 880 7065; fax: þ82 2 871 5518. E-mail address: [email protected] (K.-W. Kim). 0360-1323/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2008.08.006
effect on the comfort of occupants, it too must be taken into consideration. In office buildings, as the reduction of the window ratio of envelope and the orientation of the window are restricted from a design perspective, the use of blinds is a common means of controlling incoming solar radiation. If blinds are controlled properly according to variations in the outdoor and indoor environmental conditions, excessive energy use and the level of occupant discomfort due to direct solar radiation can be greatly reduced. In the case of Venetian blinds, environmental performance that is more effective can be achieved because additional controls pertaining to the slat angle are available. However, studies in this area [1–7] have shown that in reality, occupants rarely change the occlusion index1 of blinds, regardless of whether manual or motorized Venetian blinds are used. Manual or motorized Venetian blinds are limited in their ability to meet occupants’ needs and in reducing energy consumption, as occupants tend to change the occlusion index only when direct solar radiation makes conditions uncomfortable. To overcome these limitations, Venetian blinds must be controlled automatically. The use of automated Venetian blinds
1 The ratio of a lowered blind to the total window area, which is between 0% (blind fully opened) and 100% (blind fully closed).
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that are controlled automatically by sensors according to the outdoor weather condition is likely more effective compared to the manual or motorized Venetian blinds. In summer, automated blinds can reduce cooling energy consumption and overheating by blocking solar radiation. In winter, they can be opened to allow daylight and required solar gains so that the building can reduce its dependence on artificial lighting and its heating system. To achieve these outcomes, the blinds must be properly controlled; otherwise, unwanted solar gain may enter the building and increase the cooling energy consumption. Moreover, occupants may experience glare from the direct solar radiation. This study aims to find out whether the environmental performance of a building can be improved by the application of an automated Venetian blind in comparison to a manual or motorized Venetian blind and whether occupants’ may feel discomfort by the application of an automated Venetian blind in the summer season. This study also aims to find out the insufficiency of the automatic control algorithm of that automated Venetian blind for future study of the development of that algorithm. For this purpose, the manner in which occupants of buildings with blinds operate their blinds was surveyed firstly. The pattern used with manual blinds was established based on the previous research review [1–7] and the pattern used with motorized blinds was established based on the blind operation survey. The environmental performance of the manual, motorized and automated Venetian blind was evaluated through thermal and visual experiments in a real-scale test rooms and through reports by the occupants of the dwelling in summer. 2. Backgrounds Blinds can be classified into the manual, motorized and automated type according to the control method, as shown in Fig. 1. A manual blind is the simplest type of blind as it does not incorporate a motorized device. As occupants operate it manually, the initial investment is small and the installation of the blind is simple. However, direct operation of the blinds according to environmental variations is an inconvenient factor from the perspective of building occupants. Additionally, considering effective countermeasures is difficult as weather conditions can change dynamically. Occupants operate blinds only when glare makes conditions uncomfortable. Aside from this condition, they tend not to operate the blinds but rather to use artificial lighting,
even when daylight comes into the building sufficiently without glare. Motorized blinds are operated by motors, implying that remote or central operation is possible. Compared to manual blinds, operation and management is easy and convenient. However, the initial investment requirements have increased and effective countermeasures according to environmental changes are difficult because the operation is determined according to decisions by occupants. The motorized blind may become less economically efficient considering the high initial investment. Previous studies [1–5] that investigated the present conditions of actual blinds have shown this. Rea [1] analyzed the operating patterns of a 16-floor building in Ottawa, Canada, according to orientation of the building, the time and the weather condition. The orientation of the building and the weather conditions are important factors that have an effect on the operation of blinds. The occlusion index facing east is high when the sky is clear compared to when it is overcast, while the occlusion indexes facing south and west show little difference. Inoue et al. [2] studied the operating patterns of for high-rise office buildings in Tokyo, Japan. In an eastern exposure, it was found that occlusion index increases before noon as occupants enter the room and that occlusion index decreases in the afternoon. In a western exposure, the operating patterns of blinds have the opposite characteristics. In overcast conditions, blinds have a little movement because radiation is not influential. In addition, they conducted a survey involving 336 occupants. About 90% of those who responded reported that visual comfort affects the operation of blinds, while 50–80% reported that thermal comfort affects their operation. It was also found that the blinds were operated to change an uncomfortable indoor environment to one that was comfortable. The most common factor that led to an uncomfortable environment was direct solar radiation and glare. Lindsay [3] concluded that daylight that comes in at 65 below the perpendicular line of a facade causes the occlusion index to increase. His study also suggested that future studies of blind movements have to consider indoor measurement factors such as the level of illumination, the temperature and the presence of artificial lighting. As the occlusion index can change according to the facade, additional study of the behavior of occupants is required. According to Oscar Faber Associates [4], occupants change the occlusion index when the outdoor radiation exceeds 300 W/m2. Blind operation was found to be a function of solar radiation and altitude.
Fig. 1. Classification of the blind by the control method.
J.-H. Kim et al. / Building and Environment 44 (2009) 1517–1527
Fig. 2. Concept of the split blind.
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daylight [8]. These blinds can be more useful compared to manual or motorized blind since daylight can be introduced through the upper section though lower section is closed to prevent from glare (see Fig. 2). But those blinds are also operated by occupants. If once the lower section is closed, the lower section tends not to be opened although outdoor condition has changed. Therefore, automatic control strategy of those blinds has to be developed to maximize environmental performance. Automated blinds are automatically controlled by sensors according to the outdoor weather condition to enhance environmental performance. They utilize a built-in control algorithm that maintains comfortable indoor conditions. They can provide optimum indoor conditions as dynamically changing weather conditions are checked continually. In addition, productivity is increased because occupants can concentrate on their work without operating the blinds. Manual or motorized blinds, though commonly used, have limitations to their level of potential improvement because proper countermeasures according to changes in indoor and outdoor conditions are difficult. To overcome these limitations, blinds need to be controlled automatically. 3. Blind operation survey
Vine et al. [5] studied 14 occupants’ actions concerning automated blinds, a mix of automated and manual blinds, and manual control modes of blinds in a real-scale experiment. In the results, occupants were found to prefer higher illumination to standard levels (700–1500 lux), and a majority answered that glare affects their work. There are blinds that allow closing the lower section of the blinds and leaving the upper section in horizontal position for
To evaluate the environmental performance of automated blinds compared to manual or motorized blinds, the manner in which occupants of buildings with blinds operate their blinds need to be surveyed. For this purpose, the pattern used with manual and motorized blinds was established for use in the experiment. The pattern used with manual blinds was established based on the previous research review [1–7]. Occupants rarely operate the
Fig. 3. A survey building applied with the motorized blind.
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Fig. 4. Blind operation frequency analysis.
blind and only when they feel discomfort because of glare etc., they operate the blind to be fully closed. After that, they do not operate the blind even when daylight comes into the building sufficiently without glare. So, the blind is fully opened or fully closed during most of the day. Operation data regarding the motorized blinds is collected and the pattern used with motorized blinds was established based on this survey because there are few researches about the pattern used with the motorized blind. The results of this survey are summarized below.
In order to investigate the motion and frequency of the operation of the blinds along with the relationship of these factors to other influential factors, operation data for 468 blinds on 16 floors which is occupied was collected via central operation room PC. Of these, 182 blinds faced to the east, 185 to the west, and 101 faced to the south. There were no blinds on the north wall, and the core space was connected to this wall. For 2 clear and 2 cloudy days (for a total of 4 days) at 10-min intervals from 09:00 to 18:00, the occlusion index was recorded, and the sky’s condition throughout was photographed and weather data were collected.
3.1. Outline
3.2. Survey results
The blind operation survey was conducted at a 22-floor building in Seoul, Korea. The building had east-, west-, and south-facing windows equipped with ivory colored roll blinds operated using a remote controller as shown in Fig. 3(a). The blinds in each room were operated by the occupants themselves or a PC in a central operation room housed in the basement, with the position of each blind indicated on a monitor as shown in Fig. 3(b) and (c).
Over a period of 4 days, the operation frequencies of each of the 468 blinds in the building were analyzed. The frequencies are classified into four categories whose rates are shown in Fig. 4. More than half of the blinds were not operated throughout the entire day, though if the blinds that moved only once a day were included, the percentage then rises to 95%. This shows that the occupants rarely operated the motorized blinds and that they appeared to be
Fig. 5. Occlusion index with the highest frequency.
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Table 1 Control sequence of Energy Saving Mode Control time
Control condition
Control at ON
On
09:00–18:00
Control at OFF
Off
Exterior illuminance
Delay time
Exterior illuminance
Delay time
Occlusion index
Slat angle
Occlusion index
Slat angle
16 klux
3 min.
15 klux
15 min
100%
90
0%
–
unconcerned about the status of the blinds. Compared to previous studies, though the operation frequency of motorized blinds tends to be slightly higher than that of manual blinds, it is not sufficient to meet the energy saving requirements and environmental demands for comfort. Therefore, for the correct operation of blinds in such a way that considers environmental performance, an automatic system for the control of blinds is required. The operation frequencies of the blinds show distinctive differences depending on the orientation of the blinds and the condition of the sky. Blinds facing to the south tend to Type A, while the blinds facing west were operated more frequently compared to those facing in other orientations. When the sky was overcast, the percentage of Type B usage increased as shown in Fig. 4. Overall, more blinds were raised in the morning and more drawn down in the afternoon. For the blinds facing south, they were more frequently drawn down between 13:00 and 14:00 when the solar position was at its highest. For the blinds facing east, they tended to be lowered in the morning and raised in the afternoon. For the blinds facing west, they tend to be raised in the morning and lowered in the afternoon, in contrast to those facing east. The occlusion index was divided into 10 sections whose frequencies were analyzed by classifying them into either a morning or an afternoon group as shown in Fig. 5. The occlusion index changed according to the condition of the sky. The occlusion index with the highest frequency in terms of orientation, time, and sky condition is shown in Fig. 5. Under a clear sky, the occlusion index for blinds facing east decreases from the morning to the afternoon. Generally speaking, blinds with an occlusion index in the range of 90–100% change to 0–10% status, while those of occlusion index 70–80% show almost no change. The occlusion index for blinds facing east under a clear sky ranges from 0 to 0%. Thus, as less solar radiation enters when the sky is overcast than when it is clear, there is less glare and discomfort and occupants naturally tend to open the blinds to have a feeling of openness. For blinds facing west under a clear sky, the occlusion index increases from the morning to the afternoon, as the level of direct solar radiation entering through the windows facing west increases in the afternoon. Under an overcast sky, the occlusion index also tended to increase in the afternoon. However, more blinds were lowered to an occlusion index of 50% in the afternoon as there is less solar radiation compared to when there is a clear sky. Compared with those facing east or west, the differences between the morning and afternoon are not significant in case of
blinds facing south. This implies that more of the blinds facing south belong in the Type A group, which remain fixed and are not operated at all throughout the day. However, the occlusion indexes differ under clear and overcast skies. Under a clear sky, the occlusion index of most of the blinds range from 70 to 80%, while under an overcast sky, most range from 50 to 60%. This is thought to be due to the lower amount of direct solar radiation entering under an overcast sky, as in other orientations. In this study, considering the results of the operation survey, the occlusion index of motorized blinds was determined to be 75% as shown in Fig. 5, as the test room of the experiment was facing south. 4. Experiment on the environmental performance of automated blinds 4.1. Outline In this study, the effects of commercially used automated blinds on thermal and visual performance were compared with those of manual and motorized. Internal Venetian blinds were used in this experiment and the blind specification was as follows. Blinds: internal Venetian blinds (slat material: aluminum, slat width: 50 mm). Sensor: sun sensor (sensing outdoor vertical illuminance). Control: Energy Saving Mode (see Table 1) and Comfort Mode (see Table 2) of S company [9]. Experiments were carried out in two side-by-side mock-up test rooms located on the top floor of a building at Seoul National University in Seoul, Korea, to measure the energy consumption and rate of occupant comfort enhancement. The experiment was conducted in August of 2006. Two test rooms with the identical dimensions of 5.8 m (W) 4.8 m (D) 2.7 m (H) with the same heat loss and gain were used to reproduce identical conditions, as shown in Fig. 6. The thermal performance of the blinds was evaluated by analyzing the average temperature difference and the rate in which the temperature decreased over time. To this end, as shown in Fig. 6, a total of 40 (20 in each room) thermocouples were installed in addition to a thermocouple that was attached on the exterior wall to measure the outdoor temperature. The visual performance of the blind was
Table 2 Control sequence of Comfort Mode Control time
Control condition
Control at on
On
Off
Exterior illuminance 09:00–10:30 10:30–12:00 12:00–13:00 13:00–13:45 13:45–18:00
25 25 16 25 25
Control at off
klux klux klux klux klux
Delay time (min)
Exterior illuminance
3 3 3 3 3
15 15 15 15 15
klux klux klux klux klux
Delay time (min)
Occlusion index (%)
Slat angle ( )
Occlusion index (%)
Slat angle
15 15 15 15 15
100 100 100 100 100
45 30 90 30 45
0 0 0 0 0
– – – – –
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Fig. 6. Outline of test rooms.
evaluated by whether it met the standard average room illuminance. Illuminance measuring devices were installed at the exterior and interior measuring points, as shown in Fig. 6, to measure the actual illuminance, and the sky conditions were analyzed by measuring the outdoor illuminance of the overall condition of the sky along with the diffuse illuminance. The different instruments used in the experiment are shown in Table 3. 4.2. Experiment method In order to investigate the effect of the automated blind on the environmental performance, experiments were performed for six
cases, as presented in Table 4. In Cases 1–4, an Energy Saving Mode of S company [9] was utilized in test room 1. This was controlled automatically by an exterior sun sensor. The Energy Saving Mode was set up to shut out the solar radiation at the maximum level within the control range (see Table 1). In test room 2, for the arrangement of the comparison, two model cases of manual blind were selected, in which the blinds were fully opened (occlusion
Table 4 Experiment cases Case Date Test room 1 1
Table 3 Measuring instruments
2
Item
Equipments
Position
Interior illuminance
Interior lux meter daylight factor meter
Exterior illuminance Solar radiation Room temperature
Exterior lux meter Exterior irradiance meter T-type thermocouple
Outdoor temperature
T-type thermocouple
Test room 1, test room 2 Roof (outside) Roof (outside) Test room 1, test room 2 Outside
Test room 2
Cooling Remarks
8/12 Automated blind: Manual X Energy Saving Mode (fully opened) X 8/16 (see Table 1) Manual (fully closed) B 8/19 Manual (fully opened) B 8/20 Manual (fully closed) B 8/18 Automated blind: Manual Comfort Mode (fully opened) a B 8/29 (see Table 2) Motorized
3 4 5 6 a
Occlusion index 75%, Slat angle: 90 .
Evaluate temperature difference Evaluate temperature difference Evaluate energy consumption Evaluate energy consumption Evaluate comfort Evaluate comfort
J.-H. Kim et al. / Building and Environment 44 (2009) 1517–1527
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Fig. 7. Temperature profile of Case 1.
index: 0%) in one and the blinds were fully closed (occlusion index: 100%, slat angle: 90 ) in the other. Through the experiments, the characteristics of automatic control in terms of energy consumption compared with those of the manual blind were verified by comparing the temperature, cooling energy and lighting energy. In Cases 1 and 2, the effect that isolating solar radiation according to excessive exterior illuminance changed the room temperature is compared to the manual blind. In Cases 3 and 4, cooling and lighting energy were estimated using the measured data of the temperature difference between the supply air and the return air in addition to the interior illuminance. In Cases 5–6, the Comfort Mode of S company [9] was utilized in test room 1, which was controlled automatically by an exterior sun sensor. 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 (09:00–18:00) and the solar position (see Table 2). In test room 2 for the set up of the compared blind, two model cases were selected in which a manual blind (fully opened) and a motorized blind (occlusion index: 75%, slat angle: 90 ). The latter case represented the results of the blind operation survey (see Section 3.2). Through the experiments, the conditions (with and without automatic control) were compared in terms of PMV measurements and workplace illuminance, and a questionnaire was conducted four times per day
(10:00, 12:00, 14:00, 16:00) to investigate these factors with regard to comfort. A total of 24 persons answered the questionnaire in turn and their age ranged from 24 to 36 years. Fourteen persons were men and 10 persons were women. For each case, the experiments were performed from 09:00 to 18:00 without artificial lighting. Prior to the beginning of the experiments, two rooms were air-conditioned to ensure that the two rooms were in identical condition.
5. Results and discussion 5.1. Case 1: Energy Saving Mode vs. manual (fully opened, no cooling) The temperature of the interior zone of the test room is shown in Fig. 7(a). During the experiment, the temperature in test room 2, where the blinds were fully opened, was higher than that of test room 1 where the blinds were controlled automatically. Due to the effective blockage of solar radiation according to the increase of the exterior illuminance in the Energy Saving Mode, the temperature in test room 1 was lower than that in test room 2 by as much as 1.0 C. For the perimeter zone, which was directly subjected to solar radiation, the temperature difference was greater. In Fig. 7(b), the
Fig. 8. Temperature profile of Case 2.
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Fig. 9. Cooling energy consumption of Case 3 and Case 4.
perimeter zone temperature of test room 1 was lower than that of test room 2 by a maximum of 2.7 C. This experiment demonstrated that with automatic control, more effectively manage of increases in room temperature is possible compared to when blinds are fully opened. In particular, in the perimeter zone, solar radiation can be shut out effectively by automatic control, thereby, offsetting a rise in temperature and providing uniform temperature distribution throughout the room. 5.2. Case 2: Energy Saving Mode vs. manual (fully closed, no cooling) The temperatures of the two test rooms for this case are shown in Fig. 8. Compared with test room 2, where solar radiation was shut out all day, the temperature in test room 1 was approximately 0.3 C higher in the interior zone. When comparing the room temperatures in the perimeter zone, the temperature in test room 1 was higher than that recorded in test room 2 by approximately 0.5 C, which is comparable to that recorded in the interior zone. When compared with the results obtained in Case 1, this shows that the rise in the perimeter zone temperature can be reduced by using automatically controlled blinds. Therefore, though the blinds were fully opened occasionally during the experimental period in response to the outdoor weather conditions, the temperature of test room 1 was not significantly different from that of test room 2.
5.3. Case 3: Energy Saving Mode vs. manual (fully opened, cooling) During the experiment, the air supply, return temperature and flow rate through the cooling units were measured to measure the heat that was removed from the room. On the basis of these measurements, the cooling energy consumption of the test rooms was calculated to be 23.3 kWh/day for test room 1 and 26.4 kWh/ day for test room 2. A graph of this data is shown in Fig. 9(a). Therefore, the energy saved when using the automated blinds was 3.1 kWh/day, or approximately 12%, compared with the value obtained when the blinds were fully opened. Fig. 10(a) shows the room depth when meeting the required room illuminance of 500 lux [10]. In test room 1, the required room illuminance could not be met part of the time because the blinds were lowered automatically. Test room 2 was able to meet the required illuminance nearly all of the time, as no blinds were used. However, in test room 2, the room illuminance continuously exceeded the upper limit of 3340 lux [10], which is the threshold for discomfort caused by glare (see Fig. 11(a)). Therefore, in an actual situation under these conditions, it would be reasonable to assume that, during these times, the blinds would have been fully closed and artificial lighting should have been used. Assuming that lighting is used where the required illuminance cannot be met, the lighting energy consumption derived from the heat generated from the lighting was calculated by applying the lighting power consumption of 20 W/m2 in a typical office building
Fig. 10. Room depth meeting the required illuminance of Case 3 and Case 4.
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Fig. 11. Illuminance profile of Case 3 and Case 4.
of Korea [11]. Consequently, test rooms 1 and 2 were shown to consume 4.12 kWh/day and 2.83 kWh/day of lighting energy, respectively. Lighting is electrical energy, while cooling is thermal energy, which has to be divided by a COP of typically 3 to obtain electrical energy. Based on this fact, the overall energy consumption of two test rooms are as follows. Test room 1 (automated): (23.3 kWh/day)/3 þ 4.12 kWh/ day ¼ 11.89 kWh/day. Test room 2 (manual): (26.4 kWh/day)/3 þ 2.83 kWh/ day ¼ 11.63 kWh/day. The overall expenditure was 0.26 kWh/day less when manually controlled blinds were used, but occupants in test room 2 must feel discomfort by glare during most of the day (09:00–15:00). As mentioned above, in an actual situation under these conditions, it would be reasonable to assume that, during these times, the blinds would have been fully closed and artificial lighting should have been used. On the basis of the experimental results, we might conclude that the automatic control of blinds can reduce the cooling energy consumption compared with an environment in which blinds are not used.
and 14.3 kWh/day, respectively (see Fig. 9(b)). Consequently, the use of automated blinds in Energy Saving Mode consumed 2.4 kWh/day (or 16.4%) more cooling energy than when the blinds completely covered the window. Room depths meeting the required room illuminance in test rooms 1 and 2 are shown in Fig. 10(b). Lighting energy was calculated on the basis of the experiment results using the method used in Case 3. Test room 1 consumed 3.12 kWh/day and test room 2 consumed 6.59 kWh/day of lighting energy. The overall energy consumption of two test rooms are as follows. Test room 1 (automated): (16.7 kWh/day)/3 þ 3.12 kWh/ day ¼ 8.69 kWh/day. Test room 2 (manual): (14.3 kWh/day)/3 þ 6.59 kWh/ day ¼ 11.36 kWh/day. This experiment, by virtue of the fact that the cooling load was higher than that obtained for the closed blinds, demonstrates that using automated blinds can reduce the overall energy consumption, including the lighting energy, by 2.67 kWh/day. In addition, the automated blinds can provide an open field of vision and a view of outside scenery. 5.5. Case 5: Comfort Mode vs. manual (fully opened, cooling)
5.4. Case 4: Energy Saving Mode vs. manual (fully closed, cooling) Using a method identical to that of Case 3, the cooling energy consumption of test rooms 1 and 2 were found to be 16.7 kWh/day
During this experiment, the sky was clear. The representative comfort indicator PMV was measured in two test rooms to determine the degrees of comfort of the two test rooms. This is shown in
Fig. 12. PMV profile of Case 5.
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Fig. 13. Subject response and illuminance profile of Case 5.
Fig. 12. In the interior zone, as both rooms were air-conditioned continuously and because the PMV meter was installed away from the influence of solar radiation, the difference in the measured values was insignificant and the two rooms largely satisfied the comfort criteria (0.5 < PMV < þ0.5) of the ISO [12]. However, in the perimeter zone, which was directly subjected to the influence of solar radiation, the PMV measured in test room 2 remained between 1.2 and 1.6, which indicates an uncomfortable environment. However, the PMV in test room 1 fell by approximately 0.5 at 10:30 AM, when the blinds began to be controlled. As a result, the degree of comfort was enhanced. With respect to the overall operation of the blinds, 87.5% of the subjects in test room 1 were satisfied, whereas 62.5% of those in test room 2 were dissatisfied due to the rise in the temperature that resulted from solar radiation, as shown in Fig. 13(a). In terms of workplace illuminance, both test rooms showed illuminance that was higher than 500 lux during the entire experiment period. In test room 2, however, the illuminance exceeded the recommended upper limit (3340 lux [10]) during of the majority of the experimental period, as shown in Fig. 13(b). Test room 1, which was controlled by Comfort Mode, was maintained within the recommended value as the slat angle was controlled to cut off direct sunlight while allowing daylight in. As the experiment was conducted during a period of hot weather and clear skies, solar radiation likely had considerable impact on the results. Consequently, the degree of direct radiation
and direct light should be appropriately controlled using blinds to protect the occupants from glare and to improve their comfort. 5.6. Case 6: Comfort Mode vs. motorized (cooling) During the experiment, clouds and rainfall started from the late afternoon. The motorized blind condition was determined based on the operation survey results. As the weather was cloudy and no significant influence from solar radiation was likely to be felt, no significant difference in the PMV was observed due to the constant air conditioning. Moreover, the ISO comfort criteria were mostly satisfied in both the interior and perimeter zones (see Fig. 14). With respect to the overall operation of the blinds, subjects in test room 1 were satisfied as optimal illuminance could be obtained via automatic control. In contrast, subjects in test room 2 were dissatisfied with the level of brightness as the blinds continued to shut out most of the daylight during the cloudy weather, as shown in Fig. 15(a). With respect to workplace illuminance, test room 1 showed illuminance that was higher than 500 lux during most of the experimental period. Test room 2, on the other hand, was under 500 lux, as shown in Fig. 15(b). Test room 1 was able to introduce more daylight through automatic control of the blinds, in keeping with the outdoor weather condition. Based on the questionnaire and measurements, visual comfort could be improved without additional lighting by introducing
Fig. 14. PMV profile of Case 6.
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Fig. 15. Subject response and illuminance profile of Case 6.
daylight selectively with the automated blinds in accordance with the prevailing weather conditions. Additionally, it was judged that an open field of vision could be provided by automatic control. 6. Conclusion In this study, the manner in which occupants of buildings with blinds operate their blinds was surveyed and operation data regarding the motorized blinds is collected. Based on this survey, the environmental performance of the automated Venetian blind was evaluated through thermal and visual experiments in a realscale test rooms and through reports by the occupants of the dwelling in summer. Through this study, the potential energy savings and the comfort enhancement when using the automated blind was confirmed and the insufficiency of the automatic control algorithm of that was also found out. In terms of cooling energy consumption, automated blinds reduced the cooling energy consumption compared to manual blinds which is fully opened as the automated blinds blocked solar radiation according to the outdoor weather conditions while consuming more energy compared to manual blinds which is fully closed. However, if the additional lighting energy consumption is considered, such as that needed due to the interception and blocking of sunlight, the overall environmental performance of the automated blinds is nearly equal to that of manual blinds which is fully opened. But the room illuminance continuously exceeded the upper limit of 3340 lux [10]. Therefore, in an actual situation under these conditions, it would be reasonable to assume that the blinds would have been fully closed and artificial lighting should have been used. And if the additional lighting energy consumption is considered the overall environmental performance of the automated blinds is better than that of manual blinds which is fully closed. From the viewpoint of comfort, in the case of the automated blinds, the slat angle is controlled to cut off direct sunlight, which reduces the discomfort from excessive solar radiation and direct sunlight. In addition, daylight can be introduced to supply a feeling of openness to the occupants. As modification of the occlusion index is not considered and modification of the slat angle is limited to two times per day in the Comfort Mode, a more detailed and
delicate control method that can consider the control of the occlusion index is necessary. As the blinds are only fully opened or closed in the Energy Saving Mode, the modification of the occlusion index and slat angle is not considered. Therefore, a control method must be devised that can consider the lighting and cooling energy saving simultaneously via proper control of both the occlusion index and the slat angle. The control method discussed in this study was based solely on detecting outdoor weather conditions. However, a more effective and enhanced control method that can also respond to an indoor environment by sensing indoor factors such as illuminance and temperature needs to be developed, as the main purpose of blind control is to improve the indoor environment.
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