H.B.Gunay et aL Building and Environment 70 (2013)31-47 with separate upper and lower blinds and reported that upper openings were suppressed with the larger number of window blinds were slightly more frequently used.The upper blinds were openings during the cooling season.However,it failed to explain found to be fully drawn four times more than the lower blinds. the fact that up to 20%of the windows were left open during the However,the relationship between the view and window shade heating season.This shows that the validity of observations may be use was inconclusive due to variability introduced by the presence limited to a particular season.For example,windows may be of anidolic reflectors.Other researchers 32,47,51,65]have also opened for promoting ventilation during the heating season,while acknowledged the view to the outside as a possible predictor var- during the cooling season it may occur in order to achieve both iable,yet a conclusive finding has not been suggested mainly cooling and ventilation [31.33.34.54.This suggests that proposing because of the interferences from other variables.For example, a general window opening model that is valid for both the heating Rubin,et al.[54]stated that the view to the other office buildings and the cooling season may not be possible. can conflict with the preference to maintain a private indoor space. Similar observations were reported in the studies on window Inkarojrit[32]reported that occupants'desire to maintain privacy shades.Mahdavi et al.[49]carried out a survey on three office as a secondary reason for choosing the blind positions.About 12%of buildings,which revealed that the proportion of the mean shade participants stated that privacy and security concerns represent deployment is up to 30%higher during the cooling season than the one of the reasons why they deploy their window shades.More- heating season.This was explained with the relatively higher solar over,Foster and Oreszczyn [55]unexpectedly observed higher radiation on the facade during cooling season.Even after sub mean blind occlusion rates in the north facade than the west stantial changes took place in the solar radiation and illuminance, facade.This was attributed to the fact that north facade of the occupants usually did not react to change the shade position building was facing another office building,which in turn may be [47.72].Window shades were rarely observed to be operated more explained with the efforts of occupants to preserve their privacy. than once a day [53,54]and even then,Bordass,et al.[15]reported Similarly,Reinhart and Voss57]aimed to correct the bias in their that window shades were typically set to mitigate the worst-case observations due to the privacy concerns and suggested that if condition.Thus,Zhang and Barrett [47]stated that window shade blinds were lowered at ambient horizontal illuminance less than position was based on occupants'long term perception and expe- 1000 lux,it would have occurred due to occupants'desire to rience rather than an instantaneous reaction against a particular maintain privacy.Therefore,a major task for BPS users that incor- stimulus.On the contrary,Haldi and Robinson 65 reported that porate occupant behavior into their studies is to predict the bias seasonal effects depend on other independent variables such as introduced by these non-physical variables and adapt the model indoor temperature or daylight level,thus were found statistically accordingly. insignificant.These results suggest that window shade deploy- Heerwagen and Heerwagen [63]carried out a survey on office ment,unlike window opening,may be used to develop a single occupants in a heating and cooling season and revealed that oc- model that is valid for both the cooling and the heating seasons. cupants widely believe daylight is crucial for their general health Begemann et al.[73]suggested that occupant light switch-on and essential for their work environment.Veitch et al.66 preferences were based on the desire to balance the variation be- confirmed that people believe daylight is superior to artificial tween the window brightness and the interior surfaces.Therefore, lighting for health.Participants reported that the quality of light it is expected that on a sunny summer day occupants tend to switch sources is crucial for their well-being and the florescent lighting on their lights to mitigate the large daylight gradients.This expla- can cause headaches and eyestrain [67.Therefore,the occupants nation can justify the lack of seasonal light energy usage variation preference to sit close to the windows can be explained with their in the UK,by inferring that the occupants can tolerate lower health concerns related to the artificial lighting along with benefit workplane illuminances during winter when the daylight level is of view and connection to the outside. lower and expect higher workplane illuminances during summer Visibility of energy use,which can be influenced with the when the daylight level is higher [741.Therefore,the workplane availability of various feedback sources,affects the behavioral illuminance should not be used alone as a predictor variable to adaptation of occupants[68.These direct and indirect feedbacks model the light switch-on behavior and it may be appropriate to may emerge from simple and more intuitive energy use dashboards incorporate window illuminance as a secondary predictor variable. [69].utility bills [70].competitions or awards [70].Darby [71] estimated that savings of up to ten percent can be achieved 2.1.4.Facade orientation through various feedback strategies,which suggests that occupants Facade orientation affects the magnitude and temporal distri- adapt their behaviors to save energy.In other words,the likelihood bution of the solar gains.For example,for the Northern Hemi- of undertaking a manual control action (e.g.turning off the lights sphere,the north facades receive the least solar gains,while south before departure)can be influenced with the visibility of energy facades receive the most useful solar radiation during the winter. use. Also,the solar penetration varies daily in zones adjacent to the east and west facades,but it varies more seasonally in the south zones 2.1.3.Seasonal effects As a result,naturally ventilated south facing offices tend to have Long-term observational studies revealed noticeable variations higher indoor temperatures than the east,west,and north facing in occupant adaptive behaviors between cooling and heating sea- offices [38].In line with this,the likelihood of opening windows in sons.For example,Fritsch,et al.[36]carried out an observational the south facade was observed to be 30%higher than the north study on the occupant control of windows in four offices in a facade [38].Zhang and Barrett [75]reported that the mean pro- heating season and a cooling season.In the heating season,the portion of windows open was 7.3%in the south facade:6.3%,5.6% window opening behavior was found to not follow the outdoor and 3.6%in the east,west,and north facades,respectively.This temperature,while during the cooling season the outdoor tem- implies that window opening behavior in east and west facades perature was a major factor leading to window opening.Similarly, follows a trend more similar to the south facade than the north Rijal,et al.[10]carried out a long term observational study to facade.Moreover,the peak percentage of window opening predict a window opening model,which was based on the aggre- times shifted following the peak solar radiation rather than the gated observations for cooling and heating seasons.The model was indoor temperature [38.This may be explained with the discom- in agreement with the cooling season observations of Fritsch et al. fort due to the transmitted solar radiation incident on the work- 36;perhaps the lower number of heating season window station and occupant.Similarly,mean window shade occlusion waswith separate upper and lower blinds and reported that upper blinds were slightly more frequently used. The upper blinds were found to be fully drawn four times more than the lower blinds. However, the relationship between the view and window shade use was inconclusive due to variability introduced by the presence of anidolic reflectors. Other researchers [32,47,51,65] have also acknowledged the view to the outside as a possible predictor var￾iable, yet a conclusive finding has not been suggested mainly because of the interferences from other variables. For example, Rubin, et al. [54] stated that the view to the other office buildings can conflict with the preference to maintain a private indoor space. Inkarojrit [32] reported that occupants’ desire to maintain privacy as a secondary reason for choosing the blind positions. About 12% of participants stated that privacy and security concerns represent one of the reasons why they deploy their window shades. More￾over, Foster and Oreszczyn [55] unexpectedly observed higher mean blind occlusion rates in the north facade than the west facade. This was attributed to the fact that north facade of the building was facing another office building, which in turn may be explained with the efforts of occupants to preserve their privacy. Similarly, Reinhart and Voss [57] aimed to correct the bias in their observations due to the privacy concerns and suggested that if blinds were lowered at ambient horizontal illuminance less than 1000 lux, it would have occurred due to occupants’ desire to maintain privacy. Therefore, a major task for BPS users that incor￾porate occupant behavior into their studies is to predict the bias introduced by these non-physical variables and adapt the model accordingly. Heerwagen and Heerwagen [63] carried out a survey on office occupants in a heating and cooling season and revealed that oc￾cupants widely believe daylight is crucial for their general health and essential for their work environment. Veitch et al. [66] confirmed that people believe daylight is superior to artificial lighting for health. Participants reported that the quality of light sources is crucial for their well-being and the florescent lighting can cause headaches and eyestrain [67]. Therefore, the occupants’ preference to sit close to the windows can be explained with their health concerns related to the artificial lighting along with benefit of view and connection to the outside. Visibility of energy use, which can be influenced with the availability of various feedback sources, affects the behavioral adaptation of occupants [68]. These direct and indirect feedbacks may emerge from simple and more intuitive energy use dashboards [69], utility bills [70], competitions or awards [70]. Darby [71] estimated that savings of up to ten percent can be achieved through various feedback strategies, which suggests that occupants adapt their behaviors to save energy. In other words, the likelihood of undertaking a manual control action (e.g. turning off the lights before departure) can be influenced with the visibility of energy use. 2.1.3. Seasonal effects Long-term observational studies revealed noticeable variations in occupant adaptive behaviors between cooling and heating sea￾sons. For example, Fritsch, et al. [36] carried out an observational study on the occupant control of windows in four offices in a heating season and a cooling season. In the heating season, the window opening behavior was found to not follow the outdoor temperature, while during the cooling season the outdoor tem￾perature was a major factor leading to window opening. Similarly, Rijal, et al. [10] carried out a long term observational study to predict a window opening model, which was based on the aggre￾gated observations for cooling and heating seasons. The model was in agreement with the cooling season observations of Fritsch et al. [36]; perhaps the lower number of heating season window openings were suppressed with the larger number of window openings during the cooling season. However, it failed to explain the fact that up to 20% of the windows were left open during the heating season. This shows that the validity of observations may be limited to a particular season. For example, windows may be opened for promoting ventilation during the heating season, while during the cooling season it may occur in order to achieve both cooling and ventilation [31,33,34,54]. This suggests that proposing a general window opening model that is valid for both the heating and the cooling season may not be possible. Similar observations were reported in the studies on window shades. Mahdavi et al. [49] carried out a survey on three office buildings, which revealed that the proportion of the mean shade deployment is up to 30% higher during the cooling season than the heating season. This was explained with the relatively higher solar radiation on the facade during cooling season. Even after sub￾stantial changes took place in the solar radiation and illuminance, occupants usually did not react to change the shade position [47,72]. Window shades were rarely observed to be operated more than once a day [53,54] and even then, Bordass, et al. [15] reported that window shades were typically set to mitigate the worst-case condition. Thus, Zhang and Barrett [47] stated that window shade position was based on occupants’ long term perception and expe￾rience rather than an instantaneous reaction against a particular stimulus. On the contrary, Haldi and Robinson [65] reported that seasonal effects depend on other independent variables such as indoor temperature or daylight level, thus were found statistically insignificant. These results suggest that window shade deploy￾ment, unlike window opening, may be used to develop a single model that is valid for both the cooling and the heating seasons. Begemann et al. [73] suggested that occupant light switch-on preferences were based on the desire to balance the variation be￾tween the window brightness and the interior surfaces. Therefore, it is expected that on a sunny summer day occupants tend to switch on their lights to mitigate the large daylight gradients. This expla￾nation can justify the lack of seasonal light energy usage variation in the UK, by inferring that the occupants can tolerate lower workplane illuminances during winter when the daylight level is lower and expect higher workplane illuminances during summer when the daylight level is higher [74]. Therefore, the workplane illuminance should not be used alone as a predictor variable to model the light switch-on behavior and it may be appropriate to incorporate window illuminance as a secondary predictor variable. 2.1.4. Facade orientation Facade orientation affects the magnitude and temporal distri￾bution of the solar gains. For example, for the Northern Hemi￾sphere, the north facades receive the least solar gains, while south facades receive the most useful solar radiation during the winter. Also, the solar penetration varies daily in zones adjacent to the east and west facades, but it varies more seasonally in the south zones. As a result, naturally ventilated south facing offices tend to have higher indoor temperatures than the east, west, and north facing offices [38]. In line with this, the likelihood of opening windows in the south facade was observed to be 30% higher than the north facade [38]. Zhang and Barrett [75] reported that the mean pro￾portion of windows open was 7.3% in the south facade; 6.3%, 5.6%, and 3.6% in the east, west, and north facades, respectively. This implies that window opening behavior in east and west facades follows a trend more similar to the south facade than the north facade. Moreover, the peak percentage of window opening times shifted following the peak solar radiation rather than the indoor temperature [38]. This may be explained with the discom￾fort due to the transmitted solar radiation incident on the work￾station and occupant. Similarly, mean window shade occlusion was 34 H.B. Gunay et al. / Building and Environment 70 (2013) 31e47