Development of a Window Opening Algorithm to Predict Occupant Behavior in Japanese Houses Hom B. Rijal, PhD Michael A. Humphreys J. Fergus Nicol Tokyo City University [email protected] Oxford Brookes University Oxford Brookes University ABSTRACT We investigated window opening behaviour and the thermal environment over a period of more than 3 years in the living rooms and bedrooms of dwellings in the Kanto region of Japan. We collected over 32,000 data-samples from 243 residents of 121 homes. The proportion of ‘open window’ in the free running mode is significantly higher than that in the cooling and heating modes. The window opening is related to the indoor or outdoor air temperature. Window opening behaviour as predicted by logistic regression analysis is in agreement with the measured data. These findings can be applied to develop an adaptive algorithm for window opening behaviour in Japanese residences. INTRODUCTION Natural ventilation from opening windows has been decreasing in houses in recent years because of the increasing prevalence of mechanical ventilation and air-conditioning. However, temperature control by opening and closing windows can reduce environmental impact by minimizing the period of the year when air-conditioning is needed. There has been more research into window-opening behaviour in offices (Rijal et al. 2007~2012, Yun & Steemers 2007, Robinson & Haldi 2008, Kim et al. 2009, Haldi & Robinson 2010) and university buildings (Suzuki et al. 2002, Umemiya & Yoshida 2004) than in dwellings (Dick & Thomas 1951, Asawa et al. 2005, Kubota 2007, Rijal et al. 2013). The findings from research in offices and universities cannot be assumed to apply to dwellings, where people’s behaviour is less constrained. There is evidence that people respond differently in their own homes for a number of reasons, social, economic and cultural (Oseland, 1995). Thus it was necessary to conduct research also on residential window opening behaviour. To explore window opening behavior and develop a window opening algorithm for Japanese residences, thermal measurements were made and an occupant behavior surveys conducted over a period of more than 3 years in the living rooms and bedrooms of dwellings in the Kanto region of Japan. METHODOLOGY Thermal comfort surveys and thermal measurements were conducted in 121 houses in Kanto region (Kanagawa, Tokyo, Saitama and Chiba) of Japan from 2010 to 2013 (Table 1). The detail of surveys 1, 2 A Hom B. Rijal is an associate professor in the Department of Restoration Ecology & Built Environment, Tokyo City University, Japan. Michael A. Humphreys is an associate of Oxford Brookes University and J. Fergus Nicol is emeritus professor at Department of Architecture, Oxford Brookes University, UK.. 30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad 1 and 4 can be found in Rijal & Yoshimura (2011), Katsuno et al. (2012) and Rijal et al. (2014) respectively. Indoor air temperature and relative humidity were measured in the living rooms and bedrooms, away from direct sunlight, at ten minute intervals using a data logger (Fig. 1). The globe temperature was also measured in the living room in surveys 3, 4 & 5. Outdoor air temperature and relative humidity were obtained from the nearest meteorological station. The number of subjects was 119 males and 124 females. Respondents completed the questionnaire several times a day in the living rooms and twice in the bedrooms (“before go to bed” and “after wakeup from the bed”) (Table 2). The thermal comfort survey was conducted several times a day using sevenpoint thermal sensation scales (Table 2). The window opening behaviour was recorded in binary form (0 = window closed, 1 = window open). We have collected over 32,000 samples. Table 1. Description of survey Survey period Survey Surveyed room Measured variables* Number of subjects Number of houses Male Female Number of votes Total Living room Bedroom 1 Start date 06-7-2010 End date 18-7-2011 Living, Bed Ti, RHi 11 16 14 30 3299 2558 2 05-8-2011 06-9-2011 Living Ti, RHi 55 52 57 109 2819 - 3 21-7-2011 08-5-2012 Living, Bed Ti, RHi , Tg 14 11 12 23 463 984 4 25-7-2012 24-6-2013 Living, Bed Ti, RHi , Tg 30 26 28 54 13083 7061 5 10-8-2013 03-10-2013 Living, Bed Ti, RHi , Tg 11 14 13 27 936 1265 Ti: Indoor air temperature (°C), RHi: Indoor relative humidity (%), Tg: Indoor globe temperature (°C), *: Tg is measured only in the living room. Table 2. Thermal sensation scale No. Now, how do you feel the air temperature? 1 Very cold 2 Cold 3 Slightly cold 4 Neutral (neither cold nor hot) 5 Slightly hot 6 Hot 7 Very hot Figure 1 Details of the thermal measurement RESULTS AND DISCUSSION 3.1 Distribution of indoor and outdoor temperatures during voting Table 3 shows the mean and standard deviation of the indoor and outdoor air temperature in each mode. Fig. 2 shows the monthly mean outdoor and indoor air temperature in FR mode in living room and bedroom. The mean outdoor air temperatures during the voting were 19.5 °C, 27.6 °C and 7.2 °C for FR, CL and HT modes respectively (Fig. 2). The mean indoor air temperatures at the time of voting were 24.2 °C, 27.3 °C and 19.2 °C for FR, CL and HT modes respectively. The Japanese government recommends the indoor Figure 2 Monthly mean outdoor and indoor air temperature in temperature settings of 20 °C in winter FR mode. 30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad 2 and 28 °C in summer respectively. The results showed that the mean indoor temperatures during heating and cooling were close to the recommendation. The mean indoor and outdoor temperature difference was 4.7 K, -0.3 K and 12.0 K for FR, CL and HT modes respectively. The results show that the seasonal difference of the indoor air temperature is quite large, and that the data represent a wide range of outdoor temperature. Table 3 Indoor air temperature and proportion of open windows in various modes Outdoor air temp. (°C) Indoor air temp. (°C) Window opening Mode Room N Mean SD 13,454 20.4 7.7 Living 9,054 18.2 8.0 FR Bed All 22,508 19.5 7.9 CL All 6,677 27.6 2.7 HT All 2,982 7.2 4.2 N: Number of observation, SD: Standard deviation N 13,361 Mean 24.8 SD 4.5 N 13,452 Mean 0.46 SD 0.50 9,000 22,361 6,407 2,960 23.3 24.2 27.3 19.2 5.6 5.0 2.0 2.9 9,110 22,562 6,648 3,050 0.30 0.39 0.03 0.00 0.46 0.49 0.16 0.03 3.2 Evaluation of window opening behaviour 3.2.1 Status of window opening (WO) To understand the window opening behaviour, the mean proportions of ‘window opening (WO)’ are compared. Table 3 shows the mean and standard deviation of the windows open in each mode. The mean WO is 0.39, 0.03 and 0.00 for FR, CL and HT modes respectively. The mean window opening in living room is higher than in the bedroom (Table 3). Interestingly, the mean WO in UK office buildings was 0.70 in NV mode and 0.04 in AC mode (Rijal et al. 2007). The mean window opening in Pakistan office and commercial buildings was 0.33 in NV mode. The results showed that the mean windows open is close to the Pakistan value and lower than the UK value. We shall limit the analysis to the FR mode. Season, month and time of the day Seasonal and monthly difference in proportion of windows open in FR mode is shown in Fig. 3. The proportion of open windows (WO) is highest in summer and lowest in winter. The WO in autumn is significantly higher than that in spring. This is possibly due to the fact that people are more adapted in spring to the winter low temperature, and in autumn to the summer temperature. In reality, the indoor and outdoor air temperatures in autumn are higher than in the spring (Fig. 3(b)). Evidently, the proportion of open windows gradually increases towards the summer months (Fig. 3(c)). Conversely, it gently decreases towards the winter months as indoor or outdoor air temperature varies (Figs. 2). The data were divided into four groups, in ascending order of time. Interestingly, the proportion of open windows gradually increases during the morning, and then decreases towards the evening (Fig. 4(a)). Most of occupants open the windows in the morning and shut them at night. These trends are similar for all seasons (Fig. 4(b)). Figure 3 The proportion of open windows, indoor and outdoor air temperature (at 95% confidence level) 30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad 3 Figure 4 Proportion of open windows at 95% confidence intervals of time of day in living room. 3.2.3 Relationship between the open windows and air temperature In FR mode the open window correlated better with the outdoor temperature than with the indoor temperature (Table 4). The correlation coefficient for the living room is higher than for the bedroom. From these observations, it can be inferred that the window opening is related to both indoor and outdoor air temperatures. Fig. 5 shows the proportion of open windows and the corresponding temperatures. The data were divided into ten groups, in an ascending order of temperature. The proportion of the window opening rises as the indoor globe or outdoor air temperature rises. The proportion of window opening in the livingrooms is higer than in the bedrooms. When mean indoor air temperature is 27.1 °C, the proportion of open windows is 0.63 in living room and 0.51 in bedroom (Fig. 5(a)). When the mean outdoor air temperature is 24.3 °C, the proportion of windows open is 0.71 in livingrooms and 0.58 in the bedrooms (Fig. 5(c)). These proportions are similar to the Pakistan study (Rijal et al. 2008), and significantly lower than that of the UK study (Rijal et al. 2007). This is perhaps because the indoor and outdoor air temperature in Japan and Pakistan are condiderably higher than that in the UK. Table 4. Correlation coefficients in FR mode Room Liivingroom Bedroom All Items Window:Ti Window:To Ti: To 0.58 0.62 0.87 13,289 13,382 13,352 Correlation coefficient (r) 0.46 0.50 0.89 Number of samples (N) 8,946 9,000 8,997 Correlation coefficient (r) 0.53 0.58 0.88 22,235 22,382 22,349 Correlation coefficient (r) Number of samples (N) Number of samples (N) Ti: Indoor air temperature (°C), To: Outdoor air temperature (°C)All correlations are significant (p<0.001) Figure 5 Proportion of open windows with 95% confidence intervals at deciles of temperatures. 30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad 4 3.3 Potential of the open window 3.3.1 Indoor air temperature Fig. 6 and Table 5 show the seasonal variation in indoor air temperature for cases when windows are open and closed. The mean indoor air temperature for the window open condition is 27.7 °C in the livingroom which is significantly higher by 5.3 K, than for the window closed condition. In UK office buildings, the mean globe temperature for the window open condition is 23.4 °C which is 1.2 K higher than when the window is closed (Rijal et al. 2008a). Thus, the temperature difference between the cases of open and closed Figure 6 Seasonal variation of indoor window in residential buildings is higher than that of the air temperature for windows open and office buildings. The temperature difference is highest in closed in FR mode. autumn. In winter, the mean indoor air temperature for the ‘open window’ case is significantly lower than that of the ‘closed window’ case. The results showed that window opening is an effective way to control the indoor thermal environment. Table 5. Indoor air temperature for windows open and closed Indoor air temperature Ti (°C) Season Window Closed Living room N Mean SD 1,247 18.0 3.2 Winter Open Closed 55 13.1 4.5 2,025 21.8 2.6 493 24.2 2.2 1,038 27.5 2.4 Spring Open Closed Summer Open 3,685 29.0 2.2 Closed 2,926 22.9 3.3 Autumn Open 1,820 26.5 3.0 Closed 7,236 22.4 4.0 All Open 6,053 27.7 3.3 Bedroom t* Open-Closed 10.8 -4.9 19.2 2.5 19.0 1.5 37.1 3.5 82.1 5.3 N Mean SD 1,261 15.2 4.3 54 12.5 4.7 1,631 20.5 3.6 165 23.0 2.6 1,182 27.7 2.3 1,675 28.5 2.1 2,198 22.9 3.8 780 26.3 3.3 6,272 21.6 5.4 2,674 27.2 3.7 t* Open-Closed 4.4 -2.6 -8.9 2.6 10.0 0.8 22.3 3.4 48.8 5.6 *All open/closed temperature differences are statistically significant (p<0.001) 3.3.2 Comfort temperature The potential of the open window is further analyzed in the context of comfort temperature. The comfort temperatures were obtained by the Griffiths’ method (Griffiths 1990, Nicol et al. 1994, Rijal et al. 2008, Humphreys et al. 2013, Rijal et al. 2014). Tc = Ti + (4 - C) / a* (1) Tc is the comfort temperature by Griffiths’ method (°C), Ti is the indoor air temperature (°C) and a* is the regression coefficient (=0.50). Fig. 7 and Table 6 show the seasonal variation in comfort temperature with windows open and closed. The mean comfort temperature for window open is 26.5 °C in living room which is 3.7 K higher than that of the case of window closed. Brager et al. (2004) Figure 7 Seasonal variation of comfort found 1.5 K higher comfort temperature for the people temperature for windows open and closed in with an access to window operation than the group FR mode. 30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad 5 without in office buildings. The temperature difference is highest in autumn. In winter the mean comfort temperature for the open window condition is significantly lower than for the window closed condition. The results showed that window opening is effective to create the comfortable thermal environment. Table 6. Comfort temperature for windows open and closed Comfort temperature Tc (°C) Season Living room Window Closed N Mean SD 1,247 19.5 2.6 t-value* Open-Closed 14.6 -5.4 Winter Open Closed 55 14.1 4.6 2,025 22.1 2.3 492 23.8 2.2 1,038 26.5 2.1 Spring -14.9 Open Summe r Bedroom Closed -10.8 Open 3,683 27.3 2.1 Closed 2,926 23.5 2.8 Autumn -31.0 Open 1,819 26.0 2.6 Closed 7,236 22.9 3.3 All -69.1 Open 6,049 26.5 2.8 N Mean SD 1,260 17.1 3.8 54 13.3 4.6 1,631 21.0 3.3 165 23.2 2.6 1,179 26.5 2.2 1,675 27.3 2.0 2,196 23.3 3.3 779 25.9 2.9 6,266 22.1 4.5 2,673 26.3 3.2 1.7 0.8 2.6 3.7 t-value* Open-Closed 7.1 -3.8 -8.1 2.2 -9.5 0.7 -19.2 2.6 -44.6 4.3 *All open/closed temperature differences are statistically significant (p<0.001) 3.4 Development of an algorithm to predict window opening behaviour 3.4.1 Logistic regression curves In the previous section, we analyzed the window opening behaviour based on field data and confirmed some general behavioural trends, but no attempt was made to predict the occupant behaviour in housing (Rijal et al. 2013). Such predictions are needed for the thermal simulation of buildings. Nicol and Humphreys (2004) made use of Probit analysis to predict occupant control behaviour in NV buildings. For mathematical convenience they used a Logistic distribution in place of the Normal distribution. The relationship between the probability of windows open (p) and the indoor or outdoor temperature (T) is of the form: logit(p) = log {p/(1–p)} = bT + c (2) (bT+c) (bT+c) p = exp /{1+exp } (3) and where exp (exponential function) is the base of natural logarithm, b is the regression coefficient for T, and c the constant in the regression equation. We have adopted the same method here, using SPSS version 19 for the calculations. The Logistic regression equations, based on the indoor or outdoor temperature, are shown in Fig. 8. The following regression equations were obtained in between the windows open and the indoor or outdoor air temperature: Living room logit(p)=0.394Ti‐10.144(n= 13,289, R2=0.34, S.E.=0.007, p<0.001) (4) logit(p)=0.372Tg‐9.659(n=9,833, R2=0.29, S.E.=0.008, p<0.001) 2 logit(p)=0.258To‐5.675(n=13,382, R =0.38, S.E.=0.004, p<0.001) Bedroom logit(p)=0.291Ti‐8.100(n=8,946, R2=0.24, S.E.=0.008, p<0.001) 2 logit(p)=0.206To‐5.113(n=9,000, R =0.26, S.E.=0.005, p<0.001) All data logit(p)=0.349Ti‐9.235(n=22,235, R2=0.30, S.E.=0.005, p<0.001) (5) (6) (7) (8) (9) 2 logit(p)=0.238To‐5.466(n=22,382, R =0.34, S.E.=0.003, p<0.001) (10) Ti: Indoor air temperature (°C), Tg: Globe temperature (°C), To: Outdoor air temperature (°C), n: 30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad 6 sample size, S.E.: Standard error, p: Significance level of the regression coefficient, R 2: Cox and Snell R2. A regression coefficient of 0.349 is obtained when the indoor air temperature is the predictor. This is higher than that obtained when the outdoor air temperature is used. In the Gifu region of Japan (Rijal et al. 2013), regression coefficients of 0.248 and 0.210 respectively were obtained with indoor or outdoor temperature. In Pakistan (Rijal et al. 2008) and in UK (Rijal et al. 2007) studies, regression coefficients of 0.176 and 0.354 respectively were obtained with indoor globe temperature is the predictor. In Kyoto (Majima et al. 2007) and UK (Rijal et al. 2007) data returned the regression coefficients of 0.119 and 0.181 respectively with outdoor air temperature is the predictor. The regression coefficient in the living room is slightly higer than the bedroom. The predicted window opening is well matched with measured values (Fig. 8). Living room Bedroom All All 0.8 0.6 0.4 0.2 0.0 0 Globe temp. Indoor air temp. 0.8 0.6 Living room Bedroom All All 0.8 0.6 0.4 0.4 0.2 0.2 0.0 5 10 15 20 25 30 35 Indoor air temperature (C) (c) Outdoor air temp. 1.0 Proportion of windows open (b) Temperature (Living room) 1.0 Proportion of windows open Proportion of windows open (a) Indoor air temp. 1.0 0.0 0 5 10 15 20 25 30 35 Temperature (C) 0 5 10 15 20 25 30 35 Outdoor air temperature (oC) Figure 8 Comparison of measured (open circular dots) and predicted value (curved line) in NV mode. Measured values were grouped for every 1 °C for indoor air temperature and for every 2 °C for outdoor air temperature. The grouped data for samples less than 100 are not shown. CONCLUSIONS We have investigated the window opening behaviour and corresponding thermal environment over a period of more than 3 years in the living rooms and bedrooms of dwellings in the Kanto region of Japan and the following results were found: 1. The proportion of the window opening in the free running mode is significantly higher than that of the cooling or heating modes. 2. The window opening is related to the indoor and outdoor air temperature in the free running mode. 3. The window opening behaviour is predicted based on indoor and outdoor air temperature using logistic regression analysis. The predicted window opening matched well with that of the measured value. ACKNOWLEDGEMENTS We would like to thanks to all people who participated in the survey, to Kawamoto Industries, Ltd, Japan for their cooperation and to all students for data entry. This research was supported by Grant-inAid for Scientific Research (C) Number 24560726 and (B) Number 25289200. REFERENCES Asawa, T., Umehoshi, N., Takezawa, T. and T. Shimizu. 2005. Analysis of the behavioral characteristics of both window opening and air conditioning use at detached houses: Relationship between outdoor microclimate and residents’ living open to outdoor Part 2. J. 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