Thermal Environment evaluation in Commercial kitchens: Procedure of data collection

Transcription

1 Thermal Environment evaluation in Commercial kitchens: Procedure of data collection Angela Simone *, Bjarne W. Olesen ICIEE-BYG, Technical University of Denmark, Kgs. Lyngby, Denmark * asi@byg.dtu.dk SUMMARY The indoor climate in commercial kitchens is often unsatisfactory and the working conditions can have a significant effect on employees comfort and productivity. The type (fast food, casual, etc.) and climatic zone can influence the thermal conditions in the kitchens. Moreover, size and arrangement of the kitchen zones, appliances, etc., complicate further an evaluation of the indoor thermal environment in kitchens. In general, comfort criteria are expressed in international standards such as ASHRAE 55 or ISO EN7730. But are these standardised methods applicable for such environments as commercial kitchens? There is therefore a need to study the indoor environment in commercial kitchens and to establish standardized methods and procedures for setting criteria that have to be met for the design and operation of kitchens. The present paper introduces a data collection protocol based on physical and subjective parameters. Measurements showed weak and strong points of the procedure in order to evaluate the thermal comfort environment in commercial kitchens and its acceptability. KEYWORDS Thermal comfort, industrial kitchens environment, thermal comfort parameters. 1 INTRODUCTION The main activity in a commercial kitchen is the cooking process that generates heat and effluents that must be captured and exhausted in order to control and guarantee thermal comfort and good air quality for the employees. To evaluate the indoor thermal environment in kitchens is not straightforward. Available studies in commercial kitchens have focused mainly on air-conditioning and ventilation systems. Pekkinen and Takki-Halttunen (1992) showed that the best thermal conditions in kitchens exist when the supply air unit is placed in the ceiling next to the exhaust hood, so that a supply air unit compensates for the high levels of radiant heat. The issue is: are the available HVAC systems for kitchens providing thermal comfort and good air quality for the employees? In general, thermal comfort criteria are defined in international standards such as ASHRAE 55/2010 [1] or ISO EN7730/2005 [2]. However, these standards are intended to be used primarily for sedentary or near-sedentary activity levels. Today there are no specific regulations or even parameters to guarantee that the thermal conditions in commercial kitchens are either comfortable or cost-effective; general evaluation criteria for thermal comfort may be inadequate and unsuitable for practical application. Thermal conditions of the working environment in commercial kitchens are primarily driven by radiant heat that directly impacts the employees. Moreover, appliances, size and arrangement of the kitchen zones, number of employees, variable environmental conditions during business hours, etc., complicate further an evaluation of the indoor thermal environment in kitchens.

2 Based on standardized methods, a procedure for collecting data for the physical environment and subjective reactions in commercial kitchens is presented in this paper. This procedure will then be used in a larger study of the indoor environment in commercial kitchens. 2 EVALUATION OF THE THERMAL ENVIRONMENT IN COMMERCIAL KITCHENS For many years the international standard organisation (ISO) and ASHRAE have been developing standards for the indoor thermal environment. ASHRAE has mainly developed standards for moderate thermal environments (ASHRAE-55) while ISO standards cover the range from cold stress to comfort to heat stress (ISO EN 7730, ISO EN 7933, ISO EN 11079). As the commercial kitchen environment presents different conditions than those studied earlier a measuring procedure was established focusing in particular on the processes characterizing the kitchen space. For example, employees facing high-energy appliances, such as an under-fired charbroiler, ovens, steamers, deep-fat fryers, or to bursts of very humid hot air, are subject to higher radiant conditions than employees working on a preparation line with their backs a few feet from the appliances. A general view of the procedure, from the recruitment of kitchens to the data collection, is summarized in the flow chart reported in Figure 1. Each instruction/activity/entity reported in the boxes requires knowledge and effort of fulfillment for the achievement of reliable results. During the section of data collection (walk in), six environmental parameters (personal and physical) were measured as described in the standards ISO 7726/1998, ISO 9920/2006, and ISO 8996/2004, and recorded in three different kitchen zones: cooking, food preparation, and dish washing. The paper includes the development of instrumentation specifications, data collection protocol during walk-in measurements at peak times of business hours, on-site data collection for a longer period than a day, and questionnaires used to evaluate thermal comfort, thermal stress, and subjective perceptions. Recruitment of Kitchens: (Kitchen Type & Climatic Zone) Sensors Arrange Cooperation between Kitchens Employees and Visiting Expertise 1 st walk in Preparing the Equipment Questionnaires Others supplements Installation of Metering Stations Recording for Long Period Agree for the Spot Measurements Day Distribute and Explain the Long Term Questionnaire 2 nd walk in Physical Spot Measurements and Short Term Questionnaire 3 rd walk in Collection of Metering Stations and Long Term Questionnaires Figure 1. Schema of: Procedure of data collection. Physical parameters The intention is to collect data for the physical environment and personal factors such as clothing and activity, to be able to calculate existing indices for evaluation of thermal comfort and/or heat stress. Therefore the following parameters must be measured: - Air temperature, operative temperature and relative humidity for a whole week, - Air temperature and operative temperature at 0.1 m and 1.7 m close to the workstation during on-site spot measurements,

3 - Air-, operative- and radiant temperature, air velocity and relative humidity at 1.1 m above the floor at the workstation during on-site spot measurement. These data must be recorded both during the summer and the winter and in the identified kitchen zones: cooking, food preparation and dish-washing. Additional data to collect during the walk-in surveys, when possible, should be: Outdoor air temperature and relative humidity, Supply air temperature and relative humidity, Make-up air temperature and relative humidity, Transfer air temperature and relative humidity. Instrumentation The measurements were gathered with the instruments shown in Figure 2. Relative humidity was measured by the HOBO sensor (Figure 2A) that has an accuracy ±2.5%. The air temperature (t a ), and the operative temperature (t o ) (globe and flat) sensors were built according to the results of Simone et al. (2007) obtained by experimental laboratory work. The air temperature sensors (Figure 2B) were built using a thermo-resistance surrounded by an open-ended radiation shield (the cylinder) that enables a free flow of air to come in contact with the sensor. In the range of 10 C to 40 C, t a sensor has an accuracy of ±0.3 C. The globe sensor shape (Figure 2C) was used to evaluate the global temperature perception of the subject and the difference between air and mean radiant temperature that also describes the non-uniformity of the radiant environment. The grayish globe sensor has a diameter of 4 cm with a thermo-resistance placed in the middle of the black cavity, as described in ISO 7726 and suggested by Simone et al. (2007). Consequently, the single value of the mean radiant temperature, representative of the thermal radiation of the occupant with the actual enclosure, can be directly calculated as function of air velocity and air temperature according the equation reported in the annex G of Standard ISO 7726/1998. The mean radiant temperature calculated by the globe operative temperature was a time average value; as a minimum, the temporal average was 12 minutes with 24 equally spaced points over time. The flat shaped sensor (Figure 2D) has two matt grayish faces of 7 cm diameter and two thermo-resistances attached at the conductive flat surface and well insulated from each other. The sensor records two values of operative temperature per time in the same space point, equal or different according to the direction of the plate that faces opposite spaces of the same enclosure. Plane radiant temperature (t p,i ) of six directions and then the mean radiant temperature (t r ) were calculated as reported in equation 1. t pi, t 0.08 (,, ) 0.23 (,, ) 0.35 (,, ) o a t tp up tp down t a p right tp left tp front tp back tr 1 a 2 ( ) (1) with i representative of the direction 1, 2, 3, 4, 5, or 6 of the sensor facing versus up, down, right, left, front, or back. The radiant temperature asymmetry ( T p ), which occurs when the employer faces a higher and reflective temperature surface, e.g. the appliances in the cooking zone, was calculated by equation 17 reported in Annex C of ISO 7726/1998. The average value of temperature calculated by the flat sensor was, as a minimum, the temporal average of 5 minutes with 10 equally spaced points over time. Both t o sensors (globe and flat) have an accuracy of ±0.3 C in the measurement range of 10 C to 40 C. The omnidirectional anemometer has been used for measuring air velocity (Figure 2E). It can measure in a range of to 5 m/s with an accuracy of 0.02 m/s ±1% of readings. The value was recorded in a minimum interval time of 1 second.

4 These sensors were built to read a voltage that was directly recorded by the HOBO logger and afterwards converted by the calibration equations. The storing of data in the HOBO was very convenient for measurements in the kitchens, avoiding any hindrance for the workers, and disturbing them and their work as little as possible. A B C D E RH [%] t a t o t o,flat v a [m/s] Figure 2. Equipment of sensors for measuring the thermal parameters. Data Collection Data collection includes several types of measurement: external temperature and humidity, HVAC-system performance, indoor (thermal) environment, physiological and subjective evaluation. Three different kitchen zones (cooking, food preparation, and dish-washing) were measured; these being considered to have different thermal conditions in the commercial kitchen. Loggers were installed for one week (1 st walk in) to record kitchen temperatures (t o and t a ) and humidity (RH) in time interval of 15 minutes. Other recording devices were used for more detailed spot measurements (2 nd walk in) of thermal parameters (air temperatures, humidity, air velocity, and radiant temperatures) at one foot of the working station where the employees are working and at different heights during the peak operating hours of one working day (breakfast, lunch, and/or dinner time) as shown in Figure 3. Evaluation of clothing and metabolism The thermal resistance and evaporative resistance of clothing can be estimated by ISO 9920/2006. The clothing should be evaluated by registration of the different garments used in the field studies. How often and how much the clothing is changed should be registered and the water permeability evaluated. In particular, during the spot measurements (2 nd walk in), researchers estimated the level of workers clothing insulation as the sum of the individual values of various garments as listed in Table B.2 of the ISO9920/2006. The metabolic rate can be estimated by ISO 8996/2004, taking into account the type of work. The activity level in a kitchen changes a lot during a working day, so it is recommended to estimate a time-weighted average during the previous 1 hour period. During the measuring time in the commercial kitchens, the employees activity level was estimated by observation and by analyses with the assessed employee heart rate of one or more individuals within each kitchen, together with their age, weight and sex. Subjective response (questionnaires) During the field studies the subjects were asked to fill in two questionnaires, one on long-term general effects and one on occupants immediate reactions (2 nd walk in), used to evaluate thermal and working conditions, to support physical data monitoring and to analyze the relationship between the physical parameters of the environment and subjective aspects of the occupants perception of thermal comfort in the kitchen environment. They had to use a 7- point thermal sensation scale and several other questions related to the thermal environment (ISO 10551/2001).

5 3 RESULTS The procedure and the measurements technique were tested in a few commercial kitchens in Denmark. From the spot measurements performed in a fast food type of kitchen, during peack operating time, the average values of thermal environmental parameters measured and estimated at different kitchen zones are shown in Table1. Table 1. Average of measured thermal environmental parameters in a kitchen. Kitchen Kitchen Zone t o t a t mr RH v a I cl M PMV PPD t mr -t a p (f-b) Type [ C] [ C] [ C] [%] [m/s] [clo] [met] [-] [%] [-] [-] cooking QRS preparation dish-washing * PMV and PPD were calculated by using ASHRAE Comfort tool (Huizenga, 2011) Vertical temperature profiles of air and operative temperatures are measured in three kitchen spots and shown in Figure 4. The operative and air temperature trends, measured during a one-week period, in the same kitchen spots are shown in Figure 5. According to the test-results, only the cooking zone presented dissatisfaction with the thermal conditions, as expected. In reality, 50% of the employees assessed dissatisfaction in both cooking and food preparation areas. The walk-in measurements showed that the discomfort in the preparation area was caused mainly by the supplied low air temperature combined with high air speed. height [m] To,cooking To,preparation To,dishwashing 24.0 Ta,cooking Ta,preparation Ta,dishwashing Figure 3. Spot Measurement Stand Placement Temperature [ C] Figure 4. Vertical temperature profiles. 4 CONCLUSIONS A method and procedure for evaluating the indoor thermal environment in commercial kitchens has been established, showing the non-uniform thermal environment in the cooking zone where a high heat radiation from the appliances exists. The method consists of: - Long term measurements of t o, t a, and RH over one week at three work locations: cooking, dish-washing, and food preparation zone. - Short-term on-site measurements of physical parameters (t a, t o, RH, and v a ) at three different heights and in three work locations.

6 - On-site survey of occupants subjective reaction to the indoor environment while the short-term physical measurements are recorded. - General survey of background information employees and their evaluation of the working conditions. 32 To,cookin g Ta,cookin g To,preparation Ta,preparation 30 Temperature [ C] : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :45 Figure 4. Air- and operative temperature trend. Time [h] ACKNOWLEDGEMENT The procedure is used in ASHRAE RP1469 Thermal Comfort in Commercial Kitchens. 5 REFERENCES ASHRAE ANSI/ASHRAE Standard , Thermal Environmental Conditions for Human Occupancy. Atlanta: American Society of Heating, Refrigerating, and Air- Conditioning Engineers, Inc. Huizenga. ASHRAE Thermal Comfort tool ISO ISO Standard , Ergonomics of the thermal environment- Determination of the metabolic rate. ISO ISO Standard , Ergonomics of the thermal environment. Assessment of the influence of the thermal environment using subjective judgment scales. ISO ISO Standard , Moderate thermal environments Determination of the PMV and PPD indices and specification of the conditions for thermal comfort. ISO ISO Standard , Ergonomics of the thermal environment- Instruments for measuring physical quantities. ISO ISO FDIS , Ergonomics of the thermal environment- Estimation of the thermal insulation and water vapor resistance of a clothing ensemble. ISO ISO Standard , Hot environments- Analytical determination and interpretation of thermal stress using calculation of required sweat rate. ISO ISO EN Standard , Ergonomics of the thermal environment -- Determination and interpretation of cold stress when using required clothing insulation (IREQ) and local cooling effects Pekkinen J.S. and Takki-Halttunen T.H Ventilation efficiency and thermal comfort in commercial kitchens. ASHRAE Transaction, 98 (1), Simone A., Olesen B.W., Babiak J., Bullo M., Langkilde G Operative temperature control of radiant surface heating and cooling systems. In: Proc. Clima 2007, Helsinki.