Building and Environment 56 (2012) 139e150

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Building and Environment

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Measurement of temperature, relative , concentration distribution and flow field in four typical Chinese commercial

Angui Li*, Yujiao Zhao, Dahua Jiang, Xiaotan Hou

School of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an, No.13 Yanta RD., Xi’an, Shaanxi 710055, PR China article info abstract

Article history: An assessment of a current situation of Chinese commercial was carried out to assess the impact Received 22 October 2011 of the typical ventilation systems of four commercial kitchens on their indoor thermal environment in Received in revised form China. To understand the effect of the ventilation system, this study only focused on velocity field, 1 March 2012 temperature field, relative humidity field, and concentration distribution varying with following whether Accepted 2 March 2012 cooking or not. From the data available we could find for the kitchens that use the mechanical air supply system, the temperature and CO2 concentration of the non-cooking area exceeded the value of the Keywords: measurement points that besides the cooking range. For the middle and small scales commercial Chinese commercial kitchens system kitchens, that use the natural air supply system, the temperature and CO2 concentration was far more Indoor thermal environment than the acceptable level. In addition, the variation of relative humidity was contrary to the trend of Measurement temperature variation, which is different to the previous study result. The measurement results indicated the ventilation system in typical Chinese commercial kitchens couldn’t remove the waste heat and impurities effectively. The reason is diversiform. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction smoking, airing, salad, sprinkling, sautéing, baking, scalded, fry and simmer. Some dishes require much oil or lard for cooking. In China has the maximum population, nearly 1.3 billion in the addition, a wide range of seasoning is applied [2], especially for world, and would consume numerous foods cooked by various commercial kitchens. Therefore, the emissions from different styles meals everyday. With the further development of China’s economy, of cooking operation might make a quite significant contribution to catering economy becomes an important pillar of tertiary industry indoor air pollution in China, particularly the fumes emitted from economy. For example, there are over 51 thousand restaurants in vegetable cooking oils during stir-frying and deep-frying. Oils are Beijing [1]. In 2010, the sale of catering was 20012.15 trillion; it was usually first heated to high temperatures in a wok (large metal pan two times of 2005. Great attention should be paid to the working with raised sides) to reduce noxious odors, resulting in large conditions in Chinese commercial kitchens-the indoor air pollution emissions of effluent [3]. The effluent includes smoke, grease borne by cooking process in commercial kitchens in city and particles and vapor, products of combustion, heat, and moisture [4]. country. Concerns over the indoor environment have increased during The Chinese kitchen possesses the most delicate culinary skills recent years as a result of knowledge about the significance of in controlling the degree of cooking (heat, temperature or dura- thermal conditions and air quality on health, comfort and tion). Since China’s local dishes have their own typical character- productivity of the workforce. In a commercial kitchen, working istics, generally, Chinese food can be roughly divided into eight conditions are especially demanding [5] A hot and uncomfortable regional cuisines, which have been widely accepted around. Every kitchen contributes to productivity loss, employee turnover, and cuisine can be cooking 200e300 dishes with 24 common cooking eventually profit loss for the restaurant operator [6]. techniques, including: deep-frying, quick-frying, crisp-frying, Research on the indoor environmental impact of Chinese’s burning, braise, simmering, braising, marinade, pan-frying, stir- cooking mainly focused on the fume produced by cooking oil, frying, boiling, quick-boiling, stewing, steaming, roasting, pickle, which have potential adverse health effects for the presence of certain compounds, such as PAHs, heterocyclic amines and unsat- urated aldehydes. Chinese’s housewives on average spend 3.4e4h

* Corresponding author. Tel.: þ86 29 82202507; fax: þ86 29 82202729. in the kitchen everyday, or about 1/4 of their everyday life [7]. Mili E-mail address: [email protected] (A. Li). Weng [8] analyzed various samples of cooking oil fumes. They

0360-1323/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2012.03.001 140 A. Li et al. / Building and Environment 56 (2012) 139e150 found out that there was high concentration of carcinogens in situation of Chinese commercial kitchen was carried out to assess cooking oil fumes. This was likely the reason for high incidence of the impact of the typical ventilation system of commercial kitchen pulmonary adenocarcinoma in Chinese’s women. Ko [9] reported on the indoor in China. that the risk of contracting cancer for non-smoking women appeared to be associated with the efficiency of the fume extractor. 2. Sites and test conditions Seow [10] results showed that inhalation of carcinogens generated during frying of meat may increase the risk of lung cancer among 2.1. Chinese commercial kitchen smokers. The risk was further increased among women stir-frying meat daily whose kitchens were filled with oily fumes during Xi’an is a metropolis and there are various Chinese cooking cooking. Notami [11] analyzed the association between occupation styles and many restaurants, so it is a perfect place to investigate and cancer of lung and bladder in a caseecontrol study in India. In the thermal comfort of Chinese kitchens. Four Chinese commercial their study, a statistically significant link between the lung cancers restaurants were selected in May 2010. These four restaurants all of cooks was found. havemultiple typesof food, i.e. eight famous Chinese cuisine styles, Though these studies demonstrate quite clearly the health risk like Hunan cooking and Cantonese cooking, so they are quite of cooking, we should realize that in commercial kitchens, venti- popular in Xi’an. The eight styles are usually needed to fried, lation plays an important role in providing comfortable and stewed or braised food. productive working conditions and in securing the contaminant These commercial kitchens are part of four well operated removal. And there are four main factors affecting the thermal restaurants, in which more than 100 people may stay for dinner at comfort in commercial kitchens, these beings: air temperature, the same time, while the food type is mainly Chinese food. All the thermal radiation, air velocity and air humidity [6]. At the same restaurants are sited in a street with little traffic where some other time, the removal efficiency of the total system must be guaranteed restaurants are found. No open chimney or other sources of air and the spread of impurities throughout the kitchen should be pollution were noted nearby. The cooking ranges of the four prevented. kitchens are all located in a line that backup to the wall, and under Only a few measurements of Chinese kitchens ventilation a wall-mounted canopy hood, which is the typical arrangement in system have been reported. Chao’s measurements of indoor air Chinese commercial kitchens. It is a quite usual practice to estimate quality showed monoxide (CO) concentrations in Taiwa- exhaust airflow rates based on rough method that the actual heat nese are at their highest during cooking hours [12]. In Hong Kong, gain of the kitchen appliance is neglected. Thus, the exhaust airflow Chao and Law [13] targeted the individual exposure to NO2 in rate is the same: even under the hood there is a heavy hood like residences and conducted field measurements of exposure. The a wok, or light load like a pressure. In this measurement, the study showed that cooking behavior has a lot to do with one’s exhaust airflow rates of the four kitchens are based on face velocity, exposure to NO2, and kitchen ventilators are essential in order to where airflow rate is determined by selected capture velocity and get rid of the air pollutants produced in the kitchen. Chen [14] used the area of the kitchen appliance under the hood. experiments and numerical simulations to analyze the air envi- The front lower edges of the hoods of the four restaurants ronment in the kitchen. Chiang [15] investigated indoor air envi- overhang are set to the 1.8 m as measured vertically from the ronment focusing on the flow fields, temperature fields and air finished floor. In addition, the smoke from cooking in all restaurants contaminant (carbon monoxide) distributions in conventional was withdrawn through the hood, and the grease and impurities residential kitchens, and looking for effective methods to solve are partly separated from the exhaust air using the baffle-type those problems through natural ventilation techniques. Che-Ming grease extractor. Grease and contaminant that have been Chiang investigated the design and experimental assessment of removed flow into a drain channel and towards the collection tray. side exhaust systems in a full-scale model kitchen. From the This hood style is quite different from American or European way. measurements, they discovered that changes in carbon monoxide In order to avoid the greases that emitted from cooking adhering to (CO) concentration as a result of cooking were not dramatic, the hood and falling into the wok, the front lower edge of the hood making it difficult to observe changes in values. As a result, they is designed at about 30. So the greases can fall down along the chose to target CO2 as the main contaminant for investigation in edge of the hood and flow into a drain channel, and towards the evaluating the performance of the kitchen exhaust systems. Well, collection tap. The baffles and the front edge of the hood constitute instead of commercial kitchen thermal environment, these studies a triangle that would reduce the exhaust efficiency because of the all focused on the resident kitchen. At the moment, none of the small hood volume. A drawing and a photograph of the hood are existing standards are specially tailored for typical Chinese kitchen shown in Fig. 1. (extra-heavy load cooking) environment. In the normal design The scales of kitchen 1, kitchen 2 and kitchen 3 are quite large, practice, empirical knowledge of the existing installations has and they all have regular ventilation systems, i.e. mechanical hood been used for exhaust system determination. Undersized airflow system and mechanical air supply system. In kitchen 1 and 2, the rates could lead to indoor air problems, and oversized ventilation mechanical air supply outlets are installed at the bottom of the air system increases unnecessary energy consumption and the life- . Draft free air distribution directly into the working zone, low cycle costs of the system. velocity supply diffuser. However, for kitchen 3, the air supply The previous studies highlight the importance of well-designed outlets are installed on both sides of the duct. The fresh air is ventilation in the kitchen. In order to estimate the thermal comfort supplied at a 45 angle. This utilizes the higher entrainment effi- in Chinese typical commercial kitchen, a study was undertaken in ciency of a faster jet to induct the room air into the canopy, four commercial kitchens of Xi’an, China, where stir-frying in the reducing the amount of air that normally ‘spills’ out into the kitchen wok is the main cooking method that used. Parameters measured and onto the chefs below which could cause discomfort. In Fig. 2, during cooking mode and idle mode included the following: (1) the test site, mechanical air supply system and the air supply time-integrated measurements of air temperature, air velocity, air diffusers of kitchen 3 are presented. Because of expensive initial relative humidity and emissions of CO2 from Chinese cooking of the cost and maintenance cost, for the middle and small scales entire kitchen, specifically the section near the cooking range. (2) commercial kitchens in China, like: kitchen 4, without a mechanical Continuous measurements of air temperature and air humidity air supply system, the makeup air is supplied by infiltration. In that and their distributions. Therefore, an assessment of the current way, thermal comfort is harder to be satisfied. A. Li et al. / Building and Environment 56 (2012) 139e150 141

Fig. 1. A drawing and a photograph of the hood of typical Chinese commercial kitchens.

2.2. Test conditions made by the air-conditioning Institute of China Academy of Building Research. Each kitchen was divided into three test sections. The distance between cooking range to section 1 was within 1m. Section 2 2.3. Statistical analysis measured 3 m wide that 1 m away from cooking range, and the rest area all called section 3. The measurement points were placed The standard error of the mean (SEM) of the data was analyzed, on the breathing zone of the kitchens that meant 1.5 m above the which is the standard deviation of the sample-mean estimate of floor. The set up of measurement points are illustrated in Fig. 3. The a population mean. (It can also be viewed as the standard deviation measurements were taken before cooking and at rush hour for of the error in the sample mean relative to the true mean, since the dinner at night (lunch at noon) respectively in order to reflect the sample mean is an unbiased estimator.) SEM is usually estimated by difference between them. A sample was collected outdoor. the sample estimate of the population standard deviation(sample Accurate measurement of air velocities with high turbulence standard deviation) divided by the square root of the sample size intensities is difficult. In turbulent flows, the velocity changes its (assuming statistical independence of the values in the sample): magnitude and direction. Rapid velocity changes are not detected by a probe with a long response time. Melikov [16] has pointed out s Where SE ¼ pffiffiffi (1) that a response should be 0.2e0.5 s. In this study, the air velocity is x n measured with SWEMA-3000 probes, which has an accuracy of 0.05 m/s for each velocity component. The response time of the s is the sample standard deviation, and n is the number of the sensor is 0.5 s. We use analyzer TSI-7545 to sample. measure the indoor CO2 concentrations. The range of measurement is from 0 PPM to 5000 PPM with an accuracy of 1 PPM, and the 3. Results and discussion response time is 0.5 s. TSI hot wire air velocity meter is used to measure the indoor temperature and humidity. The range of 3.1. Background conditions temperature measurement is from 18e93 C(0Fe200 F) with an accuracy of 0.1 C. The range of humidity measurement is from 5% During the investigation of kitchen 1, 2 and 3, the weather was to 95% with an accuracy of 0.1%. In order to reflect the changes of sunny and dry, with daytime temperatures up to around 33 C. For temperature and humidity during 24 h in the commercial kitchens, kitchen 4, during the investigation, the weather was rainy and wet, we use Temperature and Humidity Acquisition Instrument that with daytime temperatures up to around 26 C and a relative

Fig. 2. The test site, mechanical air supply system and the air supply diffuser of kitchen 3. 142 A. Li et al. / Building and Environment 56 (2012) 139e150

Fig. 3. Floor plan of the case-study kitchens and layout of the measurement points, the supply air duct and the hood exhaust air duct: (a). Kitchen 1. (b). Kitchen 2. (c). Kitchen 3. (d) Kitchen 4. (The black range mean s it was underfired during the cooking mode, and the return air duct is not drawed in the figure).

humidity of 65e75% RH (day and night). The wind speed was for mode of section 1, 2, 3 were 53 C, 30.8 C and 32 C, respectively, the main part of the time below 5 m/s (calm to slight breeze). The and they were 25.2 C (90.6%), 3.9 C (14.5%) and 3.8 C (13.5%) primary background data is shown in Table 1. higher than the idle mode. The data showed that there was a significant higher value of temperature in section 1 of kitchen 4 as 3.2. Results of measurements compared to other three kitchens and the peak difference is 29.5 C (125.5%). The data also revealed significant difference (26 C From Table 2, we can find kitchen 1, 2 and 3 have the mechanical (96.3%)) in temperature in section 1 compared to the acceptable air supply system, which are quite important for commercial temperature (27 C) [17]. This was mainly because the indoor kitchens. In kitchen 1, the maximum temperatures during cooking environment of kitchen 4 was highly dependent on the outdoor mode of section 1, 2, 3 were 23.5 C, 19.6 C and 19.6 C, respec- environment, and without the cooled air supply system, the waste tively, while they were 2.9 C (14.6%), 0.8 C (4.3%) and 1.1 (6.0%)C heat can’t be removed effectively. It has been well documented that higher than the idle mode. For kitchen 2, they were 4.4 C (21.57%), temperature affects productivity. If the temperature in the space 3.9 C (19.4%) and 3.6 C (17.9%) higher than the idle mode, while increases by 5.5 C above the comfort level, the productivity may the maximum temperatures during cooking mode of section 1, 2, 3 drop as much as 30% [18]. For the CEC study, a thermally neutral were 24.8 C, 24.0 C and 23.7 C, respectively. The maximum temperature is 75 F (23.9 C) [19]. As for kitchen 4, the productivity temperatures during cooking mode of section 1, 2, 3 in kitchen 3 may drop like 147%e164% in section 1 while the comfort level is were 34.7 C, 23.7 C and 22.8 C, respectively, while they were 23 Ce26 C [20]. Besides the productivity losses, high temperature 11.3 C (48.3%), 1.6 C (6.9%) and 0.1 C (0.4%) higher than the idle in a kitchen also contributes to a very high turnover rate, which mode. For kitchen 4, the maximum temperatures during cooking means the ratio of the number of workers that had to be replaced in A. Li et al. / Building and Environment 56 (2012) 139e150 143

Fig. 3. (continued). a given time period to the average number of workers is high. In the of the hood surface and dropped vertically downward, which restaurant industry, on average, four persons per annum will be would tend to disrupt the hood performance as verified by labo- hired and trained for the same job position. It is no wonder that the ratory testing [19]. Secondly, it was evident that drafts were present National Restaurant Association identified the single most critical in the kitchen as a result of the ventilation angle, which would issue facing the restaurant industry to be hiring and retaining further degrade the exhaust system performance, causing more a professional kitchen staff [21]. The reason that the temperature of convective heat to enter the kitchen space and cause discomfort for kitchen 3 was much higher than kitchen 1 and 2 was because of the the employees. ventilation style. First, it was apparent that the air exiting the single From the general view of Table 2, we could not find any signif- deflection grolle travelled across the ceiling, impinged on the front icant difference in the relative humidity and velocity between

Table 1 The main background data.

Site Kitchen 1 Kitchen 2 Kitchen 3 Kitchen 4 Area（m2） 185 208 272 85 Food type Chinese food Layout of cooking range In line Capture velocity 0.5 m/s Number of cook 16 20 25 7 Cooking Equipment input (kJ/hr)a 4.38 105 3.15 105 5.01 105 3.82 105 Air change rate (hr(-1)) 40 30 Outdoor parameters Outdoor temperature (C) 32.5 32.8 33.6 25.6 Relative humidity (%) 45.8 48.9 56.4 68.4 Velocity (m/s) 1.04 0.65 0.84 2.14 Ventilation mode Mechanical air supply system Natural air supply system Supply air temperature (C) 18.0 22.0 22.0 25.6

a A heavy-duty burner range: 1.67 105 kJ/h; a cauldron: 1.48 105 kJ/h; a pot: 1.23 105 kJ/h; a steamer: 2.15 105 kJ/h. 144 A. Li et al. / Building and Environment 56 (2012) 139e150

Table 2 Comparison between idle mode and cooking mode.a

Site Kitchen 1 Kitchen 2 Kitchen 3 Kitchen 4 Supply air temperature(C) 18.0 22.0 22.0 25.6 Section 1（1 m within the cooking range） Temperature (C) Maximum 19.9/23.6 20.4/24.8 23.4/34.7 27.8/53.0 Minimum 18.1/18.2 19.4/23.4 22.3/28.3 26.9/31.5 Mean 19.2/20.1 19.8/24.1 22.9/30.6 27.2/42.9 SE 0.3/0.6 0.6/0.6 0.7/1.3 0.4/1.5 Relative humidity (%) Maximum 66.5/74.0 64.5/62.4 51.6/55.5 70.3/71.5 Minimum 62.3/47.5 61.2/59.2 43.3/27.5 65.6/59.8 Mean 64.7/60.9 63.1/60.9 47.7/38.9 67.4/65.7 SE 1.5/6.7 1.0/1.6 1.8/2.7 1.5/2.3 Velocity (m/s) Maximum 0.36/1.20 0.28/0.53 0.27/0.61 0.20/0.31 Minimum 0.08/0.31 0.21/0.45 0.12/0.38 0.09/0.13 Mean 0.16/0.64 0.23/0.50 0.20/0.50 0.16/0.21 SE 0.10/0.23 0.03/0.03 0.05/0.07 0.05/0.08

CO2 concentration (PPM) Maximum 710.0/985.0 680.0/1235.0 647.0/990.0 673.0/2145.0 Minimum 624.0/813.0 660.0/960.0 598.0/770.0 586.0/725.0 Mean 666.0/871.0 674.0/1049.0 621.0/841.0 610.0/1530.0 SE 32.4/54.6 8.9/10.8 14.5/19.6 21.6/21.3 Section 2 (3 m wide that 1 m away Temperature (C) Maximum 18.8/19.6 20.1/24 23.1/23.7 26.9/30.8 from cooking range) Minimum 17.3/17.5 18.5/23.5 22.1/21.5 24.8/29.7 Mean 17.6/18.7 19.41/23.6 22.5/22.4 25.8/30.3 SE 0.2/0.7 0.1/0.2 0.3/0.6 0.3/0.5 Relative humidity (%) Maximum 71.4/75.0 63.4/60.6 53/45.6 79.8/70.2 Minimum 69.2/69.3 59.4/59.1 43.9/30.5 68.8/58.1 Mean 69.9/71.1 61.5/59.9 47.3/40.6 74.4/63.5 SE 0.7/2.0 0.3/0.6 2.7/2.9 2.6/3.3 Velocity (m/s) Maximum 0.82/0.73 0.31/0.46 0.35/0.31 0.24/0.33 Minimum 0.2/0.16 0.18/0.18 0.14/0.21 0.12/0.04 Mean 0.443/0.33 0.25/0.29 0.20/0.26 0.16/0.19 SE 0.22/0.20 0.05/0.13 0.03/0.04 0.04/0.13

CO2 concentration (PPM) Maximum 697.0/849.0 694.0/956.0 634.0/867.0 710.0/918.0 Minimum 621.0/703.0 684.0/694.0 546.0/762.0 578.0/812.0 Mean 657.0/788.0 688.0/834.0 600.0/796.0 655.0/873.0 SE 21.7/24.5 5.5/25.3 24.9/24.2 26.1/35.9 Section 3 (the rest area) Temperature (C) Maximum 18.5/19.6 20.1/23.7 22.7/22.8 28.2/32 Minimum 18.3/18.5 19.61/23.1 21.2/22.1 22.5/30.2 Mean 18.92/18.6 19.84/23.3 21.8/22.5 25.9/30.9 SE 0.3/0.3 0.11/0.2 0.2/0.2 2.5/0.8 Relative humidity (%) Maximum 72.7/79.9 71.2/68.1 53.7/54.4 72.8/75.8 Minimum 64.5/70.4 62.4/60.6 43.7/43.1 65.5/66.8 Mean 68.0/73.2 65.4/62.6 48.4/48.3 68.6/70.2 SE 2.4/2.7 2.1/1.8 2.8/2.4 3.0/4.1 Velocity (m/s) Maximum 0.65/062 0.21/0.26 0.3/0.24 0.26/0.31 Minimum 0.07/0.12 0.12/0.11 0.1/0.18 0.02/0.05 Mean 0.39/0.25 0.15/0.15 0.17/0.21 0.13/0.16 SE 0.17/0.16 0.02/0.03 0.03/0.05 0.09/0.11

CO2 concentration (PPM) Maximum 714.0/756.0 710.0/741.0 625.0/829.0 813.0/1039.0 Minimum 587.0/649.0 6564.0/654.0 578.0/683.0 502.0/611.0 Mean 651.0/717.0 679.0/682.0 596.0/736.0 632.0/907.0 SE 24.3/20.2 18.7/25.0 14.3/26.0 24.9/18.8

a Idle mode/Cooking mode.

section 2 and section 3 during cooking mode. In section 1, the values of CO2 concentration ranged from 810 PPM (A1) to 980 PPM change trend of CO2 concentration was the same with temperature. (A3) among measurement points during cooking mode. Combined For kitchen 4, the maximum CO2 concentration during cooking of with the floor plan, we could find that there was not any range section 1 was 2145 PPM, while it was 1145 PPM (114.5%) higher between (A3) to (A5). For this reason, the temperature and CO2 than the acceptable level (1000 PPM). In general, the indoor concentration should not exceed the value of the measurement thermal environment of the commercial kitchens that using the points that besides the cooking range. Furthermore, the extremely natural air supply system was the worst. While the commercial high velocity of (A4) (1.04 m/s) indicated the air disturbance was kitchens that using the mechanical air supply system, the thermal severe. “Hood capture and containment” is defined in ASTM 1704 environment was much better. The specific situations of section 1 Standard Test Method for the Performance of Commercial Kitchen in the four kitchens will be described in the next four parts. Ventilation System as “the ability of the hood to capture and contain grease laden cooking vapors, convective heat and other products of 3.3. Kitchen 1 cooking processes”. It seemed that for section 1 the hood managed prevent the heat and air impurities throughout the kitchen, and the In kitchen 1, a heavy-duty burner range, a cauldron and a pot capture and containment efficiency got questioned. This is mainly were used during the cooking mode. Their position can be found in because of the heavy-duty burner range, and cauldron was cooking Fig. 3(a). From Fig. 4, we also could find the mean values of in the end position, while the other appliances were off. Richard temperature ranged from 18.5 C (A1) to 22.8 C (A4) among Swierczyna [22] found out when the end appliance was operated at measurement points during cooking mode. However, the mean cooking conditions, the capture and containment rate was similar to A. Li et al. / Building and Environment 56 (2012) 139e150 145

Fig. 4. Measuring parameters of section 1 in kitchen 1: (a). The variation of temperature across different measurement points of section 1 in kitchen 1. (b). The variation of relative humidity across different measurement points of section 1 in kitchen 1. (c). The variation of velocity across different measurement points of section 1 in kitchen 1. (d). The variation of CO2 concentration across different measurement points of section 1 in kitchen 1. the rate required for operating all the appliances of the class. The contrary to the trend of temperature. Though the CO2 concentra- exhaust rate for cooking on the center appliance was significantly tion beside the hood almost meets the requirements, the air lower than that for the end appliance. From the distribution of CO2, impurities just spread throughout the kitchen, the health of cooks we could confirm that the exhaust rate of the hood over the heavy- was injured. duty burner range was lower than the request level. In addition, the variation of relative humidity was contrary to the trend of temper- 3.5. Kitchen 3 ature. Furthermore, on the right side, the CO2 concentration that generated from the pot was less than the cauldron. However, the In the kitchen 3, three heavy-duty burner ranges were under statistical analysis showed that the thermal environment of kitchen fired during the cooking mode. Their position can be found in 1 was not exceeding the acceptable level (CO ＜1000 PPM, Temp.＜ 2 Fig. 3(c). From Fig. 6, we could find the mean values of temperature 28 C) [17]. ranged from 28.1 C (A7) to 34.5 C (A8) among measurement points during cooking mode. However, the mean values of CO2 3.4. Kitchen 2 concentration ranged from 600 PPM (A6) to 980 PPM (A10) among measurement points during cooking mode. Though the tempera- In kitchen 2, a heavy-duty burner range, a cauldron (shown at ture of supply air (26 C) was the same with kitchen 2, the the right-hand side of the cooking range) was under fired during temperature of kitchen 3 was much higher than kitchen 1 and 2. the cooking mode. The cauldron was used for boiled soup, while the Combined with the floor plan, we could find that all the cooking heavy-duty burner range was used for a fried dish. Their position ranges were evenly distributed and there were not any of them can be found in Fig. 3(b). In Fig. 5. We could find the mean values of beside the point (A11). For this reason, the temperature and CO2 temperature ranged from 24.5 C (A4) to 24.8 C (A1) among concentration of (A11) should not exceed the value of the measurement points during cooking mode. However, the mean measurement points that besides the cooking range. It seemed that values of CO2 concentration ranged from 960 PPM (A2) to 1240 PPM for section 1 of kitchen 3, the plume spilled from the side of the (A4) among measurement points during cooking mode. Combined hood. In addition, the variation of relative humidity was contrary to with the floor plan, we could find that there was not any range from the trend of temperature. When kitchen 3 was tested, the cooking (A4) to (A5). However, the CO2 concentration of A4 (1240 PPM) range beside the measurement point (A8) was frying chili. There- exceeded the value of the measurement points that besides the fore, the highest peak velocity (A8) was corresponding to the cooking range (for example A2: 960 PPM) by 29.2%. The relative highest peak temperature (A8). However, the position of the second high velocity of (A5) (0.51 m/s) indicated the air disturbance was peak of CO2 concentration 940 PPM (A11) indicated that the air severe. It seemed that the side spilling is also quite serious in impurities had already spread throughout the kitchen. Because kitchen 2. In addition, the variation of relative humidity was there was a significant higher value of CO2 concentration as 146 A. Li et al. / Building and Environment 56 (2012) 139e150

Fig. 5. Measuring parameters of section 1 in kitchen 2: (a). The variation of temperature across different measurement points of section 1 in kitchen 2. (b). The variation of relative humidity across different measurement points of section 1 in kitchen 2. (c). The variation of velocity across different measurement points of section 1 in kitchen 2. (d). The variation of CO2 concentration across different measurement points of section 1 in kitchen 2.

compared to (A8) which was frying chili and the difference was 115 environment, and without a cooled air supply system, the hood PPM (12.9%). For kitchen 3, because of its air supply outlet were couldn’t remove the waste heat effectively. In addition, the varia- installed on both sides of the duct, the fresh air is supplied at a 45 tion of relative humidity was contrary to the trend of temperature. angle, so the supply air flowed directly to the head of the chef, In order to fully understand the characteristic of ventilation mode which could cause discomfort. Cold supply air, as it accelerates of kitchen 4, we continuously measured the air temperature and air toward the floor, entrains the plume out from the hood. Part of this humidity for a typical day, and analyzed the distributions in next cold air also impinges on the hot cooking surface and compromises section. the performance of the cook. Figs. 8 and 9 showed the variation of temperature and relative humidity across time for a typical day. The measurement points 3.6. Kitchen 4 were placed on the breathing zone of the kitchens that means 1.5 m above the floor. The distance between cooking range to Location 1 In kitchen 4, one heavy-duty burner range (shown at the right- was within 1m. The probes in Location 1 were set beside the hood. hand side of the cooking range) and one steamer (shown at the left- Location 2 was in section 2 that measured 4 m away from the hand side of the cooking range) was used during the cooking mode. cooking range, and the probes were set beside the chopping board. Their position can be found in Fig. 3(d). In Fig. 7, we could find the Location 3 was 8.5 m away from the cooking range, and the probes mean values of temperature ranged from 41.5 C (A2) to 54.0 C were set beside the entrance. (A1) among measurement points during cooking mode. However, However, the statistical analysis showed that the thermal the mean values of CO2 concentration ranged from 1450 PPM (A2) condition of kitchen 4 was really bad. From Fig. 8, we could find that to 2145 PPM (A3) among measurement points during cooking the temperature of commercial kitchen 4 fluctuated greatly. The mode. For kitchen 4, the maximum temperature during cooking of value of temperature increased as soon as the food was cooked, and section 1 was 25.2 C (218.7%) higher than the idle mode. For this to the highest peak on 12:50 at noon and 19:00 at night. The scenario, the upper body of the chef would be enveloped by hot and maximum temperature during cooking of location 1, 2 and 3 were potentially humid, outdoor air. From the data available we could 55 C, 38.5 C and 35.3 C, respectively. The temperature reached find a significant difference in the section 1 of the four kitchens. It 55 C within a short time, that was because the cooking range seemed that for natural air supply system, the temperature of besides the measurement point was frying vegetables in a tradi- cooking zone was far greater than the acceptable level (27 C), so it tional Chinese way. The oil first heated to high temperature in the was for CO2 concentration. This was mainly because the indoor wok, then put the meat, chili, shallot and vegetable with water in it. environment of kitchen 4 was highly dependent on the outdoor The smoke, grease particles and vapour just spilled out in less than A. Li et al. / Building and Environment 56 (2012) 139e150 147

Fig. 6. Measuring parameters of section 1 in kitchen 3: (a). The variation of temperature across different measurement points of section 1 in kitchen 3. (b). The variation of relative humidity across different measurement points of section 1 in kitchen 3. (c). The variation of velocity across different measurement points of section 1 in kitchen 3. (d). The variation of CO2 concentration across different measurement points of section 1 in kitchen 3.

600 s [7]. For temperature, the increase in maximum value when local discomfort, which is typical in commercial kitchen. The most moving from locations 3e2 was 9.1%. However, the increase in common cause of local discomfort is draught and an abnormally maximum value when moving from locations 2e1 was 42.9%. high vertical temperature difference between the head and Because of expensive initial cost and maintenance cost, for the ankles [20]. middle and small scales commercial kitchens in China, like: kitchen In the following, we report our attempts to evaluate the venti- 4, without the cooled air supply system, the makeup air is supplied lation mode and poor air distribution through the measurement by infiltration. In that way, thermal comfort is harder to be satisfied. parameters. We use three evaluation indicators: Vertical Air That’s why even in the midnight, the heat constantly accumulated. Temperature Difference (VATD), Draught and Contaminant So the temperature in kitchen 4 was still much higher than the Removal Efficiency (CRE): outdoor temperature. In addition, the variation of relative humidity was contrary to the trend of temperature. The minimum relative 1) Vertical air temperature difference humidity during cooking of location 1, 2, 3 were 16 0.0%, 34.0% and 36.0%, respectively, while they were 52.4%, 34.4% and 36.4% lower A high vertical air temperature difference between head and than the outdoor relative humidity. For relative humidity, the ankles can cause discomfort. The percentage dissatisfied (PD) as decrease in minimum value when moving from locations 3e2was a function of the vertical air temperature difference between head 5.6%. The decrease in minimum value when moving from locations and ankles. Determine the PD using Equation (2) 2e1 was 53.0%. For the middle and small scales commercial 100 kitchens in China, like: kitchen 4, the indoor temperature during PD ¼ (2) 1 þ exp 5:76 0:856$Dt ;v cooking was too high and the relative humidity was as well low, a that made the chef felt very uncomfortable. Equation (2), derived from the original data using logistic D regression analysis, should only be used at ta;1 <8 C 3.7. Assessment of ventilation mode Where PD percentage dissatisfied, %; In commercial kitchens, ventilation is the most important Dta,v vertical air temperature difference between head and feet, C. factor in providing comfortable and productive working condi- tions and in securing the contaminant removal. From the analysis 2) Draught above, we can find the reason for poor thermal condition of the case-study kitchens is the ventilation mode and poor air distri- The discomfort due to draught may be expressed as the bution. Thermal dissatisfaction can be caused by unwanted cool- percentage of people predicted to be bothered by draught. Calcu- ing or heating of one particular part of the body. This is known as late the draught rate (DR) using Equation (3) : 148 A. Li et al. / Building and Environment 56 (2012) 139e150

Fig. 7. Measuring parameters of section 1 in kitchen 4: (a). The variation of temperature across different measurement points of section 1 in kitchen 4. (b). The variation of relative humidity across different measurement points of section 1 in kitchen 4. (c). The variation of velocity across different measurement points of section 1 in kitchen 4. (d). The variation of CO2 concentration across different measurement points of section 1 in kitchen 4. 0:62 3) Contaminant removal efficiency DR ¼ 34 ta;1 va;1 0:005 0:37$va;1$Tu þ 3:14 (3)

One of the first indicators that actually define a perceived air For v ; < 0.05 m/s, use v ; ¼ 0.05 m/s; a 1 a 1 Ce Cs For DR>100%, use DR ¼ 100%; quality is the contaminant removal effectiveness ε ¼ [23]. C Cs Where This indicator is based on the room average contaminant concen- e ta,1 is the local air temperature, in degrees Celsius, 20 C 26 C; tration C, the contaminant concentration at supply C , and the v s a;1 is the local mean air velocity, in metres per second; contaminant concentration at exhaust C As an indoor air quality e e Tu is the local turbulence intensity, in percent, 10% 60% indicator, ε provides more informative results for removal of (if unknown, 40% may be used). contaminants with known position [24].

Fig. 8. The temperature of outdoor and the 3 measurement locations of kitchen 4 for Fig. 9. The relative humidity of outdoor and the 3 measurement locations of kitchen 4 one typical day. for one typical day. A. Li et al. / Building and Environment 56 (2012) 139e150 149

In Table 3, we present the result of all the cases in terms of the full-service restaurant spends 33% of their sales on salaries, wages, three evaluation indicators. We know that the best overall perfor- and benefits and has a before tax profit of only 4% of sales. Let’s mance is the one with the minimum vertical air temperature assume that kitchen staff accounts for 50% of salaries, wages, and difference, draught and maximum contaminant removal efficiency. benefits. Reducing the temperature in a kitchen to a comfortable Therefore, it could be seen that for kitchen 1, 2 and 3, given the level would result in 30% increase in productivity of kitchen same air change rate, vertical air temperature differences were very personneldfewer employees would be required to do the same job. different. The reason that the vertical air temperature difference of That will reduce labor costs to 28% of sales, and income before taxes kitchen 1 was bigger than that of kitchen 2 was because the supply will more than double to end up at 9% of sales. air temperature of kitchen 1 was lower. When under the idle mode, In general, the indoor thermal environment of the commercial the of kitchen 1 was lower, and while cooking, kitchens that using a natural air supply system was the worst. The most of the waste heat concentrated in the area above the head. So ventilation system in typical Chinese commercial kitchens couldn’t the vertical air temperature difference became larger. Nonetheless, remove the waste heat and impurities effectively. For the middle for kitchen 1 and 2, the percentage dissatisfied (PD) was still and small scales commercial kitchens in China like kitchen 4, to acceptable. maintain sufficient indoor conditions year-round, the air- The air distribution of Kitchen 3 cannot remove the waste heat conditioning system is always needed in the kitchen. Without effectively, so even with the same air change rate, the vertical air mechanical cooling, the air temperature in the kitchen will be time temperature difference was the biggest. For kitchen 4, without to time over 30 C during summer time. a mechanical air supply system, the vertical air temperature For kitchen 3, it should be noted that it is poor design practice to difference was as high as 23 C, which would make the chef feel place a ceiling diffuser that blows supply air at a hood in close very uncomfortable. proximity to the hood. At a minimum, it is recommended that We used draught to evaluate the thermal dissatisfaction caused diffusers blow away from the hood. However, this is still a common by unwanted air movement. For kitchen 3 and 4, ta,1 exceeded the design practice in the restaurant industry. One reason is that some specified value, so there also couldn’t carry on a comprehensive designers and engineers have the misconception that they can use evaluation. And, the almost the same local mean air velocities of the air from the ceiling diffusers to “cool” the chef, not realizing the kitchen 1, 2 and 3 couldn’treflect the influence of air direction on negative impact this has on hood performance. thermal comfort. Because the sensation of draught was lower at Most conventional kitchens use mixing ventilation to cool the activities and for people feeling warmer than neutral, the natural space, like kitchen 1, 2 and 3. In mixing ventilation systems, cool air supply system of kitchen 4 increased the hot feeling. conditioned air is typically supplied through ceiling diffusers at The contaminant removal efficiency reflects the ability of the a high discharge velocity. This high velocity is required to create ventilation system to remove pollutants. The worst overall perfor- a high momentum air jet for efficient mixing of supply air with mance was kitchen 4. With the same air change rate, contaminant room air. This air distribution system may not necessarily be the removal efficiency of kitchen 2 was worse. This could be related to best fit for a commercial kitchen for two reasons [6]: the smaller hood exhaust rate, because the contaminant had already spread throughout the kitchen. 1 High discharge velocity from mixing diffusers creates unwanted air movement and cross-drafts in the kitchen that make it difficult to capture and contain the plume from cooking 3.8. Discussion appliances with the hoods. 2 All the heat rising from multiple heat sources in the kitchen is High temperature in the kitchen causes thermal discomfort of mixed within the space. employees, leading to productivity loss. As demonstrated in the examples above, it is not uncommon to see temperatures in the However, most designers and engineers in China have the kitchen 10 F (5.5 C) and more above the comfort level. Such a high misconception that the bad thermal condition in the commercial temperature may result in productivity loss of 30% [18]. According kitchen is only related to the hood. If the hood efficiency is per- to 2003 Restaurant Industry Operations Report [25], an average fect,no matter whatkind of air distribution system is the same. They do not realize the negative impact on hood performance. Besides, the results show that the side spilling is also quite Table 3 serious in all the four kitchens. This mainly because when the end Comprehensive assessment of four commercial kitchens.a appliance was operated at cooking conditions, the capture rate was Site Kitchen 1 Kitchen 2 Kitchen 3 Kitchen 4 similar to the rate required for operating all the appliances of the D b ta,v ( C) 4.2 1.7 10.6 23.0 class. On the other hand, it indicated the capture rate is too small for PD (%) 10.3 1.3 N/A N/A c heavy-duty cooking. It is quite comment practice to estimate ta,1 ( C) 20.1 24.1 30.6 42.9 fl va,1 (m/s)d 0.52 0.49 0.51 0.21 exhaust air ow rates based on rough method that the actual heat Tue 40% gain of the kitchen appliance is neglected. Thus, the exhaust airflow DRf (%) 28.0 19.1 N/A N/A rate is the same: even under the hood there is a heavy hood like C (PPM) 792.0 855.0 791.0 1308.0 a wok, or light load like a pressure. This hood style of Chinese’s C (PPM) 585.0 603.0 618.0 537.0 s kitchen makes a smaller hood volume. The baffles and the front Ce (PPM) 984.0 976.0 930.0 947.0 ε 1.9 1.5 1.8 0.5 edge of the hood constitute a triangle that would reduce the exhaust efficiency. a Under cooking mode. b Another interesting sign is the variation of relative humidity is Dta,v vertical air temperature difference between head and feet, <8 C, is specifically referred to section 1. alwayscontrary to the trend of temperature. This is different to the c e ta,1 is the local air temperature, in degrees Celsius, 20 C 26 C. previous study result: if a hood is not able to capture and contain d v a;1 is the local mean air velocity, in metres per second. In order to rule out the the foul air within the kitchen area, both humidity and temperature air turbulence that caused by cooking, in this assessment, the maximum velocity of will increase in the kitchen. The reason for the unusual phenomena section 1 is not considered. e If unknown, 40% may be used. needs further study. However, this maybe due to Chinese tradi- f In this assessment, DR is specifically referred to section 1. tional cooking style, which is mainly deep-frying and quick-frying. 150 A. Li et al. / Building and Environment 56 (2012) 139e150

Instead of boiling and steaming that producing a large amount of [3] He Ling-Yan, Hua Min. Measurement of emissions of fine particulate organic e water vapour, Chinese unique cooking style would generate a mass matter from Chinese cooking. Atmos Environ 2004;38:6557 64. [4] Bramfitt Mark. Supplemental research to ASHRAE 1202-RP effects of range top of smoke and particles, So the humidity would decrease while the diversity, range accessories, and hood dimensions on commercial kitchen temperature increase, during cooking in Chinese commercial hood performance. ASHRAE Final Report; January, 2006. kitchens. [5] Kosonen Risto, Koskela Hannu. Thermal plumes of kitchen appliances: cook- ing mode. Energy and Build 2006;2006(38):1141e8. [6] Livchak Andrey. The effect of supply air systems on kitchen thermal envi- 4. Conclusion ronment. ASHRAE Trans 2005;111. Part 1. [7] Lai Chi-ming. Assessment of side exhaust system for residential kitchens in Taiwan, Building Serv. Eng Res Technol 2005;26(2):157e66. There have been few detailed assessments of the thermal [8] Weng Mili, Zhu Lizhong, Yang Kun, Chen Shuguang. Levels and health risks of comfort of commercial kitchen in China, although the association carbonyl compounds in selected public places in Hangzhou, China. J Hazard between lung cancer and cooking oil fumes in China has been Mater 2009;164(2e3):30. [9] Ko Y-C, Lee C-H, Chen M-J, Huang C-C, Chang W-Y, Lin H-J, et al. Risk factors for reported from many tests. This paper presents an integrated eval- primary lung cancer among non-smoking women in Taiwan. Int J Epidemiol uation of the impact of the typical ventilation systems of four 1997;26(1):24e31. commercial kitchens on their indoor thermal environment in [10] Seow A, Poh W-T, The M, Eng P, Wang Y-T, Tan W-C, et al. Fumes from meat cooking and lung cancer risk in Chinese women Cancer. Epidemiol Biomark China. To understand the effect of the ventilation system, this study Prev November 2000;9(11):1215e21. only focuses on velocity field, temperature field, relative humidity [11] Notani PN, Shah PJ, Kasturi BV. Occupation and cancers of the lung and field, and concentration distribution varying with following bladder: a case-control study in Bombay. Int J Epidemiol 1993;22(2): e whether cooking or not. 185 91. [12] Chao NT, Chiang CM, Wang WA, Chou PC. A study on the coutrol strategies to From the general view, the change trend of CO2 concentration improve indoor sir quality with outdoor air domonstrated by bathroom was the same with temperature. However, the variation of relative design. Proceedings of the 7th Interional Conference on Indoor Air Quality and humidity was contrary to the trend of temperature. The results Climate; 1996. Nagoya, Japan. [13] Chao YH, Law A. A study of personal exposure to nitrogen dioxide using were different to the previous study that both humidity and passive samplers. Building Environ 2000;35:545e53. temperature will increase if a hood is not able to capture and [14] Chen J, Duffy B, Fletcher DF, Haynes BS, Nelson P. FTIR spectroscopy contain the foul air with the kitchen area. measurements and CFD simulations of the pollutants arising from unfueled combustion in a room. Building Environ 2001;36:597e603. For kitchen 3, because of its air supply outlet were installed on [15] Chiang CM, Lai CM, Chou PC, Li YY. The influence of an architectural design both sides of the duct, the fresh air is supplied at a 45 angle, so the alternative (transoms) on indoor air environment in conventional kitchens in supply air flowed directly to the head of the cooks. This would not Taiwan. Building Environ 2000;35:579e85. [16] Melikov AK, Sawachi T. Low velocity measurements: compatative study of only cause thermal uncomfortable, but also decrease the hood different anemometers. Proceedings of RoomVent-92. International Confer- performance. ence, Aalborg Denmark; 1992. [17] Indoor air quality standard of China; 2002 [In Chinese]. The temperature and CO2 concentration of the non-cooking area [18] Wyon DP. Individual microclimate control: required range, probable benefits exceeded the value of the measurement points that besides the and current feasibility. Proceedings of Indoor Air ’96. Tokyo: Institute of Public cooking range. It seemed that for section 1 the hood managed Health; 1996. prevent the heat and air impurities throughout the kitchen, but the [19] California Energy Comission. Design guideeimproving commercial kitchen effectiveness got questioned. The reason is diversiform. ventilation performance. Architectual Energy Corporation and Fisher Nickel, Inc; 2002. [20] ISO 7730. Ergonomics of the thermal environment - analytical determination Acknowledgement and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria; 2005. [21] National Restaurant Association. Restaurant industry Forecast; 2001. Support from the National Natural Science Foundation of China [22] Swierczyna Richard. Effents of appliance diversity and position on commercial through grant No. 51178374 in this study is gratefully acknowledged. performance. ASHRAE Trans 2006;112:591. ProQuest Science Jounrals. [23] Yaglou CP, Witheridge WN. Ventilation requirements, Part 2. ASHRAE Trans References 1937;42:423e36. [24] Novoselac Atila, Srebric Jelena. Comparison of air Exchange efficiency and [1] Beijing Statistics Bureau. The yearbook of statistics in Beijing. Beijing: Beijing contaminant removal effectiveness as IAQ Indices. ASHRAE Trans; 2003. Statistics Press; 2005. p. 385 [in Chinese]. KC-03-4-5(4663). [2] Ishige N. In: Nakayama T, editor. Chinese dietary culture. Beijing: Chinese [25] National Restaurant Association. 2003 Restaurant industry operations report; Social Science Press; 1992. p. 6e13 [in Chinese]. 2003 [Deloitte & Touche].