Key Factors and Problems in the Performance of Kitchen Ventilation Systems Explorative Review Study

FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT Department of Building Engineering, Energy Systems and Sustainability Science

Key factors and problems in the performance of kitchen ventilation systems Explorative review study

Álvaro Ros Hueda 2020

Student thesis, Advanced level (Master degree, one year), 15 HE Energy Systems Master Programme in Energy Systems

Supervisor: Alan Kabanshi Assistant supervisor: Roland Forsberg Examiner: Magnus Mattsson

ABSTRACT

Regarding the great importance of a good working environment, in this research, ventilation systems installed in kitchens of restaurants were studied in order to avoid problems and to understand the key factors that can influence on the performance of the system. The results obtained were taken into account to provide some recommendations to a real ventilation system of a restaurant called Pastaria in Gävle (Sweden). This concrete ventilation system was not performing good, and some calculations based on the kitchen design were made trying to offset the problem. A large number of scientific studies related to restaurant kitchen hoods and ventilation systems were used to get the findings. These articles were obtained from scholar web databases. The main problem found in kitchen hoods is the inadequate exhaust airflow. The minimum required airflow varies depending on the size and shape of the hood. Keil et al. (2004) found in their research that only 39% and 24% of the studied hoods met the minimum recommended airflow from ACGIH and ASHRAE guidelines, respectively. Other key factors found are related to the kitchen design. The kitchen hood is recommended to have incorporated a capture hood covering all the burners. Side panels can be employed to increase the capture and containment. High efficiency filters and rigid ducts are also recommended. The cleaning of the ventilation ducts is also an important factor, they are recommended to be cleaned between 1 to 9 years depending on the activity of the kitchen. Thus, key factors such as disturbing airflows and the presence/movement of the cooks can disturb the kitchen hood performance. A very effective solution, isolating the fumes below the hood, that is getting developed is the installation of an inclined air curtain from the cooking surface. Related to the kitchen hood and the ventilation system of the Pastaria restaurant. Some measurements and information were obtained in a visit to the restaurant. After calculations, it was obtained based on the kitchen design that is required a minimum airflow of 4 140 m3/hour. In order to do that, the heat exchanger Swegon Silver C RX, installed in the system, requires a minimum size of 11/12. The distribution of the kitchen appliances in this restaurant seems to be correct. However, a future study in order to see if there are disturbing airflows affecting the kitchen hood performance must be carried out. If after checking all recommendations the performance of the kitchen hood is not good enough yet, an inclined air curtain may be installed due to their great effectiveness against problems of hoods. In conclusion, it was clearly obtained that a correct kitchen distribution design and calculations must be done for each restaurant in order to install the most adequate kitchen hood with the best characteristics. This way, fumes, odors, moisture and particles will be easily exhausted allowing a better environment out of risks to the establishment and customers health.

Keywords Restaurant kitchen ventilation, kitchen hood, ventilation system, airflow, air quality, heat exchanger, pressure drop, ventilation ducts, hood performance and efficiency.

PREFACE

This master thesis has been possible thanks to:

My parents Ricardo and Teresa, whose unconditional support in good and bad times is the basis of my success.

My sister Irache, the best personal stylist I could ever have.

My girlfriend Nuria, whose delicious meals gave me the strength to carry on.

My aunt Carmen, for her great evolution with new technologies to be able to make video calls when missing me.

My mates from the Erasmus program, for our healthy competitiveness in all 3.5 “beerpong” tournaments, and Yahtzee and frisbee games.

My friends from Estella, for allowing me to belong to the group “Bromeros”.

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NOMENCLATURE

Symbol Description Unit NV Natural ventilation - MV Mechanical ventilation - HV Hybrid ventilation - IAQ Indoor air quality - ACGIH American Conference of Governmental Industrial Hygienists - ASHRAE American Society of Heating, Refrigerating and Air- - Conditioning Engineers 3 Qhood Volumetric flow through the hood m /h

Vair Exhaust air velocity m/s A Extraction area m2 C&C Capture and Containment - DCV Demand control ventilation - HRV Heat recovery ventilation - DMF Deposited particle mass flux - UFP Ultrafine particles - ODA Outdoor air - IDA Indoor air - EA Exhaust air -

TABLE OF CONTENTS

1. INTRODUCTION ...... 1 1.1 Background ...... 5 1.2 Aims and limitations ...... 7 2. METHOD ...... 8 3. RESULTS AND DISCUSSION...... 9 3.1 Reviewed articles ...... 9 3.1.1 Operational problems ...... 14 3.1.2 Design problems ...... 16 3.1.3 Cleaning problems ...... 20 3.1.4 Disturbing airflow problems ...... 22 3.1.5 Technical solutions ...... 24 3.2 Calculations for the current kitchen hood ...... 26 3.3 Discussion ...... 29 4. CONCLUSION ...... 33 4.1 Study results ...... 33 4.2 Outlook ...... 34 4.3 Perspectives ...... 35 5. REFERENCES ...... 36

FIGURES INDEX

Figure 1. Basic components of a local exhaust system...... 4 Figure 2. Styles of Local Kitchen Exhaust Hoods (ASHRAE, 2015)...... 5 Figure 3. Pastaria restaurant...... 6 Figure 4. Kitchen view of the Pastaria restaurant...... 7 Figure 5. Proportion of Hoods Meeting the Airflow Performance Guidelines (Keil et al., 2004)...... 15 Figure 6. Schematic of 21 hood shapes studied (Zhao et al., 2013)...... 17 Figure 7. Schematic of six side panels studied (Zhao et al., 2013)...... 17 Figure 8. Schematic of two exhaust duct arrangements studied (Zhao et al., 2013). ... 18 Figure 9. Comparison of the totally deposited particle mass in the duct for different cases (Zhao and Chen, 2006)...... 22 Figure 10. Comparison of the accumulation time in the duct for different case (Zhao and Chen, 2006)...... 22 Figure 11. The ventilation system principle diagram (Liu et al., 2020)...... 25 Figure 12. Area calculated between the hood and the cooking surface...... 27 Figure 13. Operation diagram of the minimum heat exchanger size required (Swegon Group AB, no date)...... 29

TABLES INDEX

Table 1. Summary of reviewed articles...... 10 Table 2. Typical exhaust flow rates by cooking equipment category for listed type I hoods (ASHRAE, 2015)...... 28

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1. INTRODUCTION

Ventilation is the process of diluting the air inside a building by extraction of old air or injection of fresh air (Sandberg, Kabanshi and Wigö, 2020). Indoor air is polluted from cooking, smoke, formaldehyde and other pollutants that can cause allergies, smells and diseases (Bluyssen, 2013). Additionally, people usually exhale around 19 liters of CO2 per hour of breathing (SIBER, 2016). All of this needs to be taken outside the building.

The main purposes of ventilation are: - To ensure the good quality of indoor air, producing comfort and avoiding harmful effects on health due to polluted air. - To collaborate in the thermal conditioning of the building. - To ensure building integrity by removing moisture.

SIBER (2016) explains that the concern for clean air has been shared by scientists since ancient times. In ancient Rome, a doctor of Greek origin named Gale, who lived between 29 and 210 A.D, synthesized a body of knowledge on the subject by establishing one of the first currents of medicine called Galenism. Gale sought by all means to find what he called the “good air”, discovering the origin of infectious diseases as a result of its contamination. Other researchers such as Florence Nightingale (1820-1910) insisted on the need for ventilation of rooms, which together with food, temperature, lighting, diet, hygiene, or noise formed the basic elements to achieve a healthy indoor environment. To this end, Florence considered essential that the air was periodically renewed as an indispensable condition for the health of people. These studies are framed within the hygienist movements that in Europe brought with them the epidemiology and the study of diseases such as cholera, headed by Dr. John Snow. All these approaches had a significant influence on the architecture of the 20th century, with the inclusion of interior courtyards in homes encouraging cross ventilation. Gaps also began to be included in the structure of the buildings, through which the ducts of the facilities could be installed, thus improving the habitability of the houses (SIBER, 2016).

Today, it is well known that excessive indoor air pollution is the origin of many diseases such as allergies or respiratory infections (Han, Li and Kosonen, 2019). People spend on an average 80 - 90% of their time on working and living indoors, therefore it is vital to maintain the indoor environment in a good quality (Jomehzadeh et al., 2017). That is why, in Sweden, it is highly recommended the inclusion of ventilation systems to properly ventilate all enclosures within and provide a good indoor air quality, as it is said in the Code of Statutes of the Swedish National Board of Housing, Building and Planning (BOVERKET, 2018).

As a result of the research throughout years, due to the need for ventilation inside many places, different forms of ventilation have been developed. These are known as natural ventilation (NV), mechanical ventilation (MV) and hybrid ventilation (HV).

- Natural ventilation: NV is carried out by means of the appropriate location of surfaces, passages or ducts taking advantage of the under pressure or over pressure created in the building envelope by wind, moisture, sun, thermal convection of the air or any other phenomenon, without it being necessary to provide energy to the system in the form of mechanical work. It is undoubtedly the most efficient and widely used passive cooling strategy. In order to control natural ventilation systems, a good understanding of the mechanisms involved is required. Because natural ventilation is highly dependent on the climate and outside weather, it not only needs a supply of sufficient airflow in warm and “still” weather, but it also needs the openings that can regulate the indoor environment in cold and windy weather (Rong et al., 2016).

- Mechanical ventilation: MV, also known as forced ventilation, is the process by which air is supplied to and extracted from a given space, using mechanical devices such as fans in order to control heat levels, extract contaminating gases, dilute particles and dust, and provide necessary oxygen for personnel or inhabitants of the place. It is normally used when natural ventilation is insufficient or does not have the capacity to maintain a certain space in comfortable conditions or even if climate/weather is not adequate.

- Hybrid ventilation: HV, also known as mixed ventilation, is a ventilation system that performs indoor air renewal by natural ventilation when pressure and temperature conditions are favorable and uses mechanical extraction when these conditions are unfavorable (SIBER, 2016). It takes advantage of both natural and mechanical ventilation systems. A well-designed mixed ventilation system enables the integration of a high-level thermal environment with air conditioning and energy savings when the outdoor air conditions are suitable for natural ventilation (Nomura and Hiyama, 2017).

Buildings normally have installed a general ventilation system that can be hybrid or mechanical, so that it provides a sufficient flow of outside air and ensures the extraction and expulsion of air contaminated by the pollutants. Air should be circulated from dry to wet rooms, with inlet openings in dining rooms, bedrooms and living rooms; toilets, kitchens and bathrooms should have extraction openings; partitions between inlet rooms and rooms with extraction should have passage openings (Sola, 2009). These systems have the possibility of integrating a heat exchanger in order to limit the energy losses recovering part of the energy evacuated to the outside and transferring it to the air that is blown inside (Sola, 2009).

In conclusion, it is clear that a good ventilation system is essential in almost every place but even more important in places that are continually producing heat, fumes and gases such as industrial factories or restaurants, because the establishment and employees and customers health is at risk (Han et al., 2019).

Particularly, in restaurant kitchens a well-designed ventilation system, that controls the emissions of gases, vapors, fumes and particles coming from the cooking processes and reduces some different risks, is very important. Some of those risks are fire from grease fumes deposited on surfaces, contamination of food by grease and occupational exposure to chemicals and heat (Keil, Kassa and Fent, 2004a). The small size of the particles of these fumes makes difficult to control them, and that size allows particles to penetrate deep into the lungs of exposed workers (Keil et al., 2004). It has been shown that in some situations, cooking is more dangerous than some other causes of air pollution such as industry, energy or agriculture, because cooking smokes are more probable to be inhaled or come in contact with skin (Han et al., 2019).

In order to control these risks and maintain a healthful work environment, local exhaust ventilation in the form of kitchen hoods is commonly used in restaurant kitchens (Keil et al., 2004). ACGIH (American Conference of Governmental Industrial Hygienists, 1998) explains that the main function of these ventilation systems is to capture the pollutant at or near its source, cooking surface in this case. This is the most useful method of control because it is more effective and requires a smaller exhaust flow rate that results in lower heating costs compared to high flow rate general exhaust requirements. Furthermore, the local exhaust systems result in lower costs for air cleaning devices.

Five basic elements form local exhaust systems (ACGIH, 1998). They are shown next in Figure 1: - The hood(s): Its aim is to collect the contaminant in an air stream directed to the hood. - The duct system: Its function is to transport the contaminated air to the air cleaning device. - The air cleaning device: It removes the pollutant from the air stream. - The fan: It must overcome all the losses due to friction and hood entry while producing the required flow rate. - The stack (duct on the fan outlet): It discharges the air to the atmosphere in a way that it will not be re-entrained.

Figure 1. Basic components of a local exhaust system1.

Kitchen hoods shall be designed for the type of cooking appliance served and shall be designed to confine cooking vapors and residues within the hood (ICC, 2012). ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) guideline (2015) has made different classifications of kitchen hoods. ASHRAE designs are based on the type of cooking process as well as the hood geometry: Type I, are hoods used for processes that generate fumes and grease; Type II hoods are those used with pizza ovens and other operations solely involving baking. Besides, they are further categorized as light, medium, heavy and extra-heavy duty. Depending on hood geometry, ASHRAE, classifies the following categories: wall-mounted canopy, back-shelf canopy, island canopy, pass-over style and eyebrow type. These last categories are shown in Figure 2.

1 http://safetycoursestraininginchennai.blogspot.com/2016/05/local-exhaust-ventilation-lev.html

Figure 2. Styles of Local Kitchen Exhaust Hoods (ASHRAE, 2015).

O. Han (2019) has previously related that high-performance exhaust hoods are required in restaurant kitchens in order to reduce contaminants and keep good indoor air quality. However, exhaust hoods often fail to meet design requirements and their efficacy decreases. Furthermore, C. B. Keil (2004) reported that proper maintenance and cleaning of these systems is needed to maintain fire possibilities low since grease accumulation in hood systems can present localized risk of fire. In order to avoid risks, there are regularly inspections in the restaurants to see if the establishment conditions are optimal. It makes the owners keep the facilities well-kept. But normally, the sanitarians do not put much interest in the kitchen hoods, therefore some of them are not in best working condition.

As curiosity to highlight the real importance of kitchen hoods, Chiang, Wu and Ko (1998) found in a case study, about exposure to mutagenic fumes produced by hot cooking oil, that the risk of contracting cancer for non-smoking women appears to be associated with cooking meals in kitchens not equipped with a fume extractor.

1.1 Background

This project comes from an Italian restaurant called “Pastaria” situated in the city of Gävle (Sweden), which was opened in November of 2019. From the beginning of its operation, this restaurant has presented problems with the ventilation system associated with the inadequate operation of the kitchen hood. Large amounts of fumes and also a bad smell accumulate inside the restaurant every day. This situation is worrying the owners because not only can it be dangerous for their employees and customers health but also because it can give a bad image of their restaurant and may result in loss of customers. Besides, the intention of achieving better air quality, the kitchen hood is working the whole day (24 hours), which is neither economically nor environmentally friendly.

Figure 3. Pastaria restaurant.

The ventilation system of this restaurant corresponds with a mechanical (or forced) ventilation system, where the air is supplied and extracted using mechanical devices to control heat levels, contaminating gases and particles from the cooking process and provide necessary oxygen inside the establishment. Furthermore, a rotary heat exchanger is included in the system to recover the exhaust heat during heating season.

The supply of air is made in the dry locations of the restaurant as it is the food area by means of grilles that allow the supply to be controlled. The extraction of air is made in the wet areas such as the kitchen, by way of a restaurant kitchen hood, and the toilets, employing an extraction fan.

Related to the category of the kitchen hood installed in this restaurant, following ASHRAE (2015) guideline, it belongs to the category Type I (hoods used for processes that generate fumes and grease), medium-duty (control emissions from large kettles, ranges and griddles), wall-mounted canopy. This is the most common type of hoods in restaurants. Next in the Figure 4, a real picture of the kitchen hood installed in the objective restaurant is shown.

Figure 4. Kitchen view of the Pastaria restaurant.

The control system of this kitchen hood corresponds to a demand control ventilation. The level of ventilation, exhaust airflow, is adjusted according to the needs of the moment or demand. Normally, this allow for a big amount of energy savings. However, in this particular case it does not happen since the kitchen hood is not performing as expected due to unknown mistakes.

1.2 Aims and limitations

Initially, the main objective of this project was to investigate and provide solutions for the required operational characteristics of the kitchen hood and the ventilation system for the proper functioning of the extraction system. In order to do that, it was going to be tried to find out what and where are the problems were and how to solve them in the best possible way. However, due to the restrictions imposed by the current COVID- 19 pandemic, it was not possible to perform diagnostic tests or measurements on site and decided not to take any health risks. Visiting the restaurant to inspect the system and to do some measurements of flowrates and air velocities was not an option. Owing to this, the goal of the project changed to an explorative approach.

Therefore, the aim of this study is to look at and analyze important factors and possible problems that are associated with poor performance of restaurant ventilation systems and explore areas of improvement to achieve a high performance. Some of these problems could be affecting the kitchen hood system of the mentioned restaurant and thus this thesis will recommend considerations to take into account in order to solve the problem. Furthermore, some calculations based on the kitchen design will be performed to determine the possible flowrates and velocities to offset the problem.

2. METHOD

This study was carried out in a theoretical way, based on previous studies. Practical experiments and measurements were not performed due to the COVID-19 global pandemic.

Firstly, to carry out this review study, it was necessary to search for information related to this topic. The main information was extracted from peer-reviewed papers found in useful web databases as University of Gävle’s Discovery portal, ScienceDirect or Google Scholar. In these sources of information scientific, technical and medical journals can be found. The search method used, to find interesting studies dealing with this topic, was to write some specific keywords as “restaurant kitchen ventilation”, “kitchen hood”, “ventilation system”, “airflow”, “air quality”, “heat exchanger”, “pressure losses”, “ventilation ducts”, “hood performance” and “efficiency”.

A large number of interesting scientific studies related to restaurant kitchen hoods and ventilation systems were found. Only original studies about problems in kitchen hood performance were selected and used in this thesis project. These studies were used to take into account some of the most typical problems that can disturb the high performance of a kitchen hood, such as insufficient airflow, disturbing airflows, etc.

Secondly, some calculations, about air flow and air velocity, based on the current design of the objective kitchen hood were made, discussed and compared with the results obtained in the studies previously mentioned. In order to have a clear picture of the kitchen design, it was necessary to visit the restaurant and take some measurements of the dimensions of the kitchen hood and the cooking surface.

Finally, some recommendations of what should be done, how and why, in order to solve the problem and achieve a high performance kitchen ventilation system, are given.

3. RESULTS AND DISCUSSION

The main results found in this project after the review of related research studies with the topic are that the design of the kitchen, the selection of the kitchen hood and all the components and factors must to be studied carefully in order to install the most adequate ventilation system for the given characteristics of the kitchen. One of the most important factors is that the fan must be capable of extracting the minimum required airflow. Depending on the characteristics and design of the kitchen this minimum airflow varies. Related to the real kitchen design in the Pastaria restaurant, it was obtained that the installed fan must be able to exhaust at least a minimum airflow of 4 140 m3/hour. It must be checked if the actual fan can extract at least the given airflow value.

The inclusion criteria for the articles considered in this project were that they must be researches of primary source, it means, only original studies from researchers involved with the topic. Also, the studies must be related to typical problems with hood components and to the influence of the kitchen design on the kitchen hood performance. Researches about solutions related to better performances were also taken into account.

Review articles about ventilation systems were excluded, as said before, only original researches were selected. Papers about air quality, suspended particles or human health in kitchens of restaurants were not taken into account.

3.1 Reviewed articles

In this section is provided all the information extracted from the selected articles. Next, in Table 1 is shown a summary of the results extracted from the selected and reviewed articles. In each different row, the reference and year of the article, and its aim and key results can be seen.

Table 1. Summary of reviewed articles.

Reference Aim Key results / recommendations and year 1. Keil et al., Investigate kitchens airflow rates for 60 - Most hoods were not operating at the needed flow rates 2004 different restaurants and 89 kitchen - 39 percent and 24 percent of the hoods met the ACGIH and ASHRAE hoods guidelines, respectively

2. Singer et al., Assess 15 home cooking exhaust devices - 12 of 15 devices could not meet the nominal airflow rate 2011 - The most effective designs include a collection hood and a robust fan - Cover all the burners lead to higher capture efficiency

3. Sobiski et al., Analyze range top diversity, range - Appliances should be positioned so that its thermal plume is inside the 2006 accessories and hood dimensions perimeter of the hood - Heavy-duty appliances should be positioned towards the center of the cooking line - Maximizing front overhang and minimizing rear clearance improve C&C - Bigger reservoir capacity improves C&C - Minimize the distance from cooking surface to the hood improve C&C - Shorter filters improve C&C

4. Zhao et al., Investigate the impact of hood shapes - Traditional Chinese (30º angle) and American and European 2012 and side panels on C&C (rectangular) kitchen hood designs have the better capture efficiency - Installation of side panels leads to higher C&C values

5. Fisher Nickel, Understand the influence of hood style, - Maximizing the front overhang dimension or decreasing distance I. and construction features and positioning of between the back of the appliance and the wall lead to better C&C and Corporation, appliances exhaust rate reduction A.E., 2011 - Heavy-duty equipment should be positioned in the middle of the cook line - Double stacked ovens are beneficial to be located at the end of the hood - The installation of shelving above an appliance may improve C&C

6. Rim et al., Investigate the effects of exhaust flow - Higher hood airflow leads to larger particle reduction 2012 rates, particle size and burner position on - Larger particles are exhausted easily the reduction of ultrafine particles - Using the back burner is more effective reducing ultrafine particles - Oversized hoods lead to additional energy consumption and higher maintenance costs and noises

7. Eric Petersen, Evaluate the performance of range hood - Rigid ducts are more recommended to be used rather than flexible 2015 fans in systems that include ducts and ducts vent caps - A vent cap with smaller loss coefficients in rigid duct ventilation systems can improve the system performance

8. Ben Othmane Calculate the particle deposition velocity - The deposited particle mass flux at the floor is about 2-6 times larger et al., 2011 in ventilation ducts in order to predict the than at vertical walls cleaning time - Ventilation systems would take between 1 to 9 years to meet the cleaning time - Filters have a very strong influence on the maintenance intervals depending on their quality

9. Zhao, B. and Investigate the particle deposition - Larger particles deposit more onto the floor Chen J., 2006 velocity and deposited particle mass flux - Larger air speed cause bigger number of particles to be deposited onto vertical walls - Filters are very important to avoid more particles to be deposited in the ventilation duct - Higher efficiency filters require more time to reach the cleaning code limit of deposited particle mass - Filters need to be checked and replaced regularly to keep its efficiency

10. Chen et al., Study the effects of disturbing airflows on - Disturbing airflows disturb the airflow pushing the pollutants out of the 2012 the flow and spillage characteristics collection hood - The frontal draft induces the most serious pollutant spillage - At the velocity of 0.2 m/sec, the spillage of pollutants is significant

11. Huang et al., Evaluate the effect of chefs and walk-by - Large amounts of fumes and spillages are attracted to the regions near 2010 motion on cooking fumes the body of the chef - When movement of people, cooking fumes are spilled into the environment easily - Increasing the rated flow rates may increase the hood’s robustness

12. Huang et al., Reduce the dispersions of fumes to the - The inclined air curtain presented a brilliant performance by isolating 2011 kitchen environment, developing a new the fumes below the hood type of range hood employing an inclined - Setting up the jet at an inclination angle of 15º obtain the most robust air-cuirtain hood - Provide better protection at a suction flow rate lower than the conventional hood - At an energy consumption rate 50% lower, presented better performance

13. Liu et al., Develop and optimize an integrated air - The proposed ventilation system can maintain good indoor air quality 2020 curtain and air-conditioning system and thermal comfort for kitchens - Air curtains can control the diffusion of the cooking fumes - For the best cases studied the capture efficiency is 98.7% in summer and 97.5% in winter

3.1.1 Operational problems

Keil et al (2004) investigated if the kitchen hoods of 60 different restaurants could meet the airflow recommended level by its size and shape and the dimensions of the cooking surface for adequate ventilation. This is a very important issue since the minimum airflow rates helps to get a better control of the risks of cooking processes.

For that purpose, the authors measured the airflow rates of 89 kitchen hoods and then compared with the main performance guidelines for the operation of kitchen hoods: “American Conference of Governmental Industrial Hygienists” (2001) and “American Society of Heating, Refrigerating and Air-Conditioning Engineers” (1995). These guidelines provide the appropriate airflow rate per linear length depending on the type and geometry of the hood. In this study, hoods of all different types were taken into account. The hoods were classified as hood against wall (HAW), island-type hood (ITH) or low side-wall hood (LSW).

The current volumetric flow (Qhood) for each hood was calculated measuring the average air velocity (Vair) and the slot or face area (A), and then using the following equation: 3 2 Qhood [m /h] = Vair [m/s] * A [m ].

As result, this research study obtained that clearly most hoods were not operating at the needed flow rates. In the Figure 5, the proportion of hoods meeting the airflow performance guidelines for each different type can be seen. It was obtained that only 39 percent and 24 percent of the hoods met the ACGIH and ASHRAE guidelines, respectively.

Figure 5. Proportion of Hoods Meeting the Airflow Performance Guidelines (Keil et al., 2004).

Singer, B. C. et al. (2012) carried out a study about 15 home cooking exhaust devices varying in design and other characteristics. The aim was to assess their performance metrics of airflow, sound and combustion product capture efficiency in order to achieve an effective removal of pollutants generated.

The 15 exhaust devices were: two downdraft exhaust units, two exhaust fan/microwave over-the-range appliances, three installations of the same model of under-cabinet system with no substantial collection hood and grease screens covering the bottom inlet and eight units with collection hood (two island chimney units, one wall-mount chimney unit and five under-cabinet units).

Next, the research method is described. The airflow was measured using two ways for different devices: Releasing sulfur hexafluoride tracer at a known rate into the hood intake and measuring concentrations downstream, and following a calibrated flow hood method described by (Walker et al., 2001). The capture efficiency was calculated using the mass balance of pollutants moving through the exhaust device. The sound was measured with a standard approach for noise with multiple frequencies called A- weighting (dB-A). The influence of airflow and other features on capture efficiency was analyzed using multivariate regression.

After studying all the parameters, the authors found as outcome the following conclusions: - Surprisingly, most of the exhaust devices could not meet the nominal airflow at the highest fan setting (12 of 15 devices). Even the most expensive ones could not achieve expected airflow values. - Higher airflows normally lead to higher capture efficiency. - The most effective designs are those that include a collection hood and a robust fan. - The price is not a very important characteristic to achieve high performance. Many moderately priced devices have almost as high capture efficiencies as the most expensive ones. - The exhaust devices that cover all the burners of the cooking surface have major capture efficiency. Thus, higher capture efficiency is obtained on back burners than on front burners. This means that cooking on rear burners needs less airflow rate and, therefore, this leads to an energy saving.

3.1.2 Design problems

Sobiski, P., Swierczyna, R. and Fisher, D. (2006) analyzed range top diversity, range accessories, and hood dimensions, finding out the effects that they have on hood performance with respect to the minimum exhaust airflow required for complete capture and containment (C&C) of cooking effluent. The experiments were carried out under a 10 foot (3 meters) long wall-mounted canopy hood.

A typical commercial kitchen was constructed at a laboratory near Chicago. The commercial kitchen appliances and hoods were evaluated using shadowgraph flow visualization technology. In order to carry out the C&C testing, the exhaust airflow was reduced until spillage of the plume was observed. Then, the exhaust airflow was gradually increased until C&C was achieved. This C&C rate was used for direct comparisons with different scenarios.

Some of the general results obtained in this study are shown next: - In order to improve C&C performance, appliances should be positioned so that its thermal plume is inside the perimeter of the hood. - Heavy-duty appliances should be positioned towards the center of a cooking equipment line in order to enhance capture and containment. - A design that can greatly improve C&C performance can be achieved maximizing front overhang and minimizing rear clearance. - Increasing hood depth (front to back) can improve C&C performance when this hood depth added is used to maximize the front overhang dimension. - A higher hood with bigger reservoir capacity can improve C&C performance by allowing a concentrated plume to be more regularly distributed along the filter bank. - Minimize the distance from the cooking surface to the hood installing hoods at the lowest height practical (or permitted by code) will improve C&C performance.

- Shorter filters with reduced filter face area and higher relative face velocity will improve C&C performance.

The research carried out by Zhao, Y. et al. (2013), focuses on the importance of the use of an efficient kitchen hood to ensure a comfortable working environment and better energy conservation. In order to achieve a good performance of a range hood, the impact that hood shapes and side panels have on the capture and containment of cooking hoods was quantified to assess their effect. Additionally, the arrangement of the exhaust ducts was investigated. The type of range hoods studied was wall-mounted canopy hood.

Firstly, a commercial kitchen was selected as case study kitchen. The exhaust airflow rate in the case study kitchen was measured based on the face velocity method. Also, CO2 pollution was evaluated. Secondly, CFD simulations (using AirPak 3.0) were conducted of the different hood shapes, side panels and exhaust duct arrangements and then, compared. Also, different air flow rates were employed in the simulation.

Next, in the Figure 6, Figure 7, Figure 8 the different hood shapes, side panels and exhaust duct arrangements studied in this research can be observed.

Figure 6. Schematic of 21 hood shapes studied (Zhao et al., 2013).

Figure 7. Schematic of six side panels studied (Zhao et al., 2013).

Figure 8. Schematic of two exhaust duct arrangements studied (Zhao et al., 2013).

The main results for the different features studied in this research were: - The hood shapes that showed a better capture efficiency were the traditional Chinese (case 1, front lower edge designed at a 30º angle) and the American and European (case 21, rectangular cooking hood). - Higher capture efficiency values were obtained with the side panel in almost all conditions, so it was concluded that the side panel can improve the capture efficiency. The C&C efficiency was enhanced by about 20% by maintaining the minimum exhaust flow rate and adding a side panel. Better values of capture efficiency were shown in the case of rectangular side panels for short exhaust flow rates. For larger exhaust flow rates, the triquetrous side panels had a better performance. Even, a higher C&C efficiency is obtained when the side panel is set to a higher position (1.1 m in this case). - There was not a clear difference on the capture efficiency related to the two exhaust duct arrangements of the hoods. Whether on the rear or on the upper side the results were similar.

Fisher Nickel, I. and Corporation, A. E. (2011) focused on the design details of the layout with respect to hood position. The aim of this study was to understand the influence on the ability of the hood to capture and contain that hood style, construction features and the positioning of appliances beneath the hood have. The understanding of these factors would lead to achieve optimum performance and energy efficiency in commercial kitchen ventilation systems by properly positioning the cooking equipment.

The method followed in this research was to use a 10-feet (3 meters) long wall-mounted canopy hood with sets of three cooking appliances such as ovens, fryers and broilers. Different combinations of layout were tested and compared to obtain the results. The test included the effect of side-to-side appliance position as well as front-to-back under the canopy hood.

The most important results of the testing were: - Maximizing the front overhang dimension can lead C&C exhaust rate reductions from to 9 to 27%. Decreasing distance between the back of the appliance and the wall can also lead to exhaust rate reduction. - Heavy-duty equipment should be positioned in the middle of the cook line. If it is positioned on the end, a side panel must be employed. Broilers and fryers should not be placed at the end of a cook line. Instead, ranges can be located at the end. - Double stacked ovens or steamers are beneficial to be located at the end of the hood because they can assist capture and containment controlling plumes almost similarly as a side panel. Partial-side panels can provide most of the benefit of full-side panels. - Surprisingly, the installation of shelving above an appliance may improve C&C performance slightly. - Wall-mounted canopy hoods were traditionally mounted 6-ft 6-in (2 meters) above the finished floor. Code officials started to require mounting at 6-ft 8-in (2.05 meters). Increasing hood mounting height by 2 inches occasioned a negligible change in exhaust rates.

Rim, D. et al. (2012) found that the effectiveness of kitchen exhaust hoods in reducing indoor levels of ultrafine particles (UFP) is an essential characteristic to achieve indoor air quality and a good performance of kitchen ventilation system. The presence of ultrafine particles in a kitchen is associated with adverse health effects such as respiratory and cardiovascular diseases. The aim of this study is to investigate the effects of exhaust flow rates, particle size and burner position on the reduction of ultrafine particles. Hood against wall was the type of range hood selected to be studied.

The method followed by the authors was to make measurements in an unoccupied house monitored with ultrafine particles (2 nm to 100 nm) concentrations from a gas stove and oven while changing range hood airflow rate and burner position (front or rear position). Two range hoods with different airflow rates were installed at the same height above cooktop, with grease filters and the air extracted was directly exhausted out of the building.

As result, it was found that range hood airflow and burner position can have huge effects on the reduction of UFP in the kitchen, reducing occupant exposure. Higher hood airflow leads to larger particle reduction, although the reduction varies with particle diameter since larger particles are exhausted easily. Comparing front versus rear burner, there was a higher particle reduction for the back burner, so using the back burner is more effective.

In conclusion, it is very important that range hoods have the ability to exhaust required flow rates in order to reduce most ultrafine particles, although range hoods must not be oversized because it leads to additional energy consumption and higher maintenance costs and noises.

Petersen, E. (2015) evaluated the performance of range hood fans in real world systems that include ducts and vent caps. The range hood that exhausts air to the outdoors and ensures that fresh air comes back into the room was the category of range hood which this study was focused in.

The author of this project employed a mathematical modeling about pressure drop for the flexible and rigid duct component, and different models for the bends and the vent caps. Moreover, a mathematical modeling of range hood capture efficiency was used. Airflow tests were performed on range hoods fans to obtain air flow rate data versus pressure drop data to create fan performance curves. The impact of individual components (ducts, bends and vent caps) on range hood system performances was analyzed.

As result, it was obtained for flexible duct systems that the ducting has a bigger influence on the total system pressure drop than the vent cap component. Instead, for rigid duct systems the vent cap has larger impact than the duct component. Thus, it was found that at the same fan speed, rigid duct systems have higher capture efficiency than flexible duct range hood systems. Capture efficiencies do not change considerably for different duct lengths in the same configurations.

In conclusion, rigid ducts are more recommended to be used, rather than flexible ducts, for obtaining a better performance and a higher capture efficiency. Furthermore, a vent cap with smaller loss coefficients in rigid duct ventilation systems can help to improve the system performance.

3.1.3 Cleaning problems

Ben Othmane, M. et al. (2011) referred to the importance of the air quality within factory buildings of food manufacturers. In order to achieve a high level of air quality, ventilation systems must be habitually cleaned to prevent the development of dust, product or condensate that can be a focus for microbial growth. Problems associated with human health are produced by the pollution of ventilation ducts. The aim of this study was to calculate the particle deposition velocity in ventilation ducts in order to predict the cleaning time. Thus, prediction of cleaning time avoids unnecessary cleaning and allows to choose the correct cleaning method.

Ben Othmane, M. et al. (2011) studied three food factories to get different results and made a comparison between them. In order to do that, they needed to know flow conditions, particle mass concentration and characteristics of the ventilation duct. These parameters were provided from a partner (CEMAGREF). An optical particle counter and a cascade impactor were employed to measure the mass and size distributions of aerosols. With all this data, using the equations explained in the paper, the physical characteristics of ducts and mass concentrations were obtained for different cases and then, the particle deposition velocity prediction could be made.

As result, in this study three main conclusions were obtained. The predicted deposited particle mass flux at the floor is about 2-6 times larger than at vertical walls due to the effect of gravitational sedimentation. Ventilation systems would take between 1 to 9 years to meet the cleaning time following the ASPEC criterion (400 mg/m2). Filters have a very strong influence on the maintenance intervals depending on their quality.

Zhao, B. and Chen, J. J. (2006) numerically analyzed the particle deposition in the ventilation ducts of heating, ventilation and air conditioning systems by computational fluid dynamics (CFD). Both, the particle deposition velocity and deposited particle mass flux were investigated. The particle deposition in the ventilation ducts ensures an entirely developed turbulent duct flow. The influence of having an air filter installed or not was also assessed in this research.

The method followed by the authors was to develop a three-dimensional drift-flux model combined with particle deposition boundary conditions. The empirical equations employed are explained in the paper. Twelve groups of particle size and two average air speeds in ducts were taken into account. Once the numerical method was developed, a computational fluid dynamic technique was used to obtain and analyze the research results. To perform this analysis, the criteria of the cleaning code for air duct system in HVAC systems of China were followed.

After studying the results, some conclusions about particle deposition were obtained: - The particle deposition onto the floor is 2 orders of magnitude larger than onto other walls. - Larger particles deposit more onto the floor than onto vertical walls. For smaller particles the deposition level is almost the same. - Larger air speed cause bigger number of particles to be deposited onto vertical walls than onto the floor.

Related to filters, it was obtained that is very helpful to avoid more particles to be deposited in the ventilation duct. Three cases were analyzed: no air filter, 40% of total efficiency filter and 80% of total efficiency filter. Next in the Figure 9 the totally deposited particle mass on the floor for these three cases is shown. Figure 10 shows the time required to get enough particle deposition in the ventilation duct in order to clean it and keep cleanliness below the cleaning code. The filters need to be checked and replaced regularly to keep its efficiency.

Figure 9. Comparison of the totally deposited particle mass in the duct for different cases (Zhao and Chen, 2006).

Figure 10. Comparison of the accumulation time in the duct for different case (Zhao and Chen, 2006).

3.1.4 Disturbing airflow problems

Chen, J. K., Huang, R. F. and Peng, K. L. (2012) analyzed a relevant factor in kitchen hoods performance as it is the cross draft. Kitchen drafts can disturb the airflow pushing the pollutants out of the collection hood. They may be formed by windows opening and closing, compensation air, or by operating fans or air conditioners. The influence of cross drafts from different directions was evaluated for wall-mounted and jet-isolated range hoods. The aim of this project was to see the effects of disturbing airflows on the flow and spillage characteristics.

In order to carry out this study, a wall-mounted and a jet-isolated (with three crossflow fans in a U shape) kitchen hood were employed. A draft generator was installed at three locations to provide cross draft from three different directions: lateral (0º), oblique (45º) and frontal (90º). A laser light beam was employed as a smoke flow visualization technique. Sulfur hexafluoride (SF6) was also employed as tracer gas to evaluate the performance and effectiveness of the range hoods.

As result, it was obtained that the frontal draft forced the pollutants to bifurcate into streams moving toward the left and the right, inducing the most serious pollutant spillage. The oblique draft pushed the pollutants toward the rear wall and the opposite side, and the lateral draft pushed toward the opposite direction, being the oblique draft more harmful. Pollutants spilled to a greater degree when the cross-draft velocity was increased. 0.2 m/sec is the critical draft velocity, at this rate the spillage of pollutants was significant. At no cross drafts, about 3% of pollutants dispersed to the environment, instead, cross drafts can increase this value larger than 30%.

In conclusion, it was found that similarly the design of wall-mounted and jet-isolated range hoods had low ability to prevent considerable release of particles into the environment when confronted with disturbing drafts.

Huang, R. F., Dai, G. Z. and Chen, J. K. (2010) evaluated the effect of chefs and walk-by motion on cooking fumes. Cooking fumes tend to deflect toward the rear wall under the hood, and the body of the cook behaves like another wall with a finite width. The suction flow, the wall effect and the wake combined can affect the efficiency of pollutant removal. Thus, kitchen hoods are very sensitive to environmental drafts. The walk-by motions of kitchen personnel induce a flow that create convective and turbulent currents affecting negatively the performance of the kitchen hood. In this article, how these factors can influence on wall-mounted and jet-isolated range hoods were analyzed.

In order to do that, the method followed by the authors was to install a wall-mounted range hood in a test room. Three crossflow fans were deployed on the countertop for the jet-isolated hood experiments with two different jet velocity values of 3 and 4 m s- 1. A flat plate was used simulating a mannequin, being placed in front of the counter or being sweeping across the front face of the hood depending on the experiment taking place. A laser beam was employed to observe the flow patterns and the SF6 tracer gas concentration was measured to evaluate the performance of the hoods.

As result of this study, it was obtained that for the wall-mounted range hood the tracer gas concentrations around the mannequin showed very high levels of spillages. Large amounts of fumes were attracted to the regions near the body of the mannequin. Instead, the jet-isolated range hood with high suction flow and low jet velocity could reduce these tracer gas concentrations. The capture efficiencies for the unoccupied condition were higher than for the occupied condition. For the experiment simulating the movement of people in the kitchen, it was found that the cooking fumes spilled into the environment easily. The jet-isolated range hood proved a less ability to resist the

23 influence of people moving through the kitchen presenting stronger fluctuating and turbulent motions.

In conclusion, both the wall-mounted hood and the jet-isolated kitchen hood are influenced by the presence of a chef in front of the cooking surface and to the walk-by motions of kitchen occupants. Increasing the rated flow rates may increase the hood’s robustness but this will lead to greater noise and energy consumption. The authors recommended to develop new hood designs in order to overcome the aerodynamic deficiencies of the kitchen hoods.

3.1.5 Technical solutions

The study carried out by Huang, R. F. et al. (2011) is related to the significant dispersions of fumes from the cooking surface to the kitchen environment due to the presence of a chef in front of the counter and the walk-by motion of occupants that reduce the performance of the range hood. The aim of this investigation was to develop a new type of range hood employing an inclined air-curtain, that could improve the performance of a wall-mounted range hood.

The method followed in this research is very similar to the method of the article by Huang, Dai and Chen (2010) where the influence of a mannequin and a simulated walk- by motion were examined, and it was discovered that they have big influence on the dispersion of the fumes. Here, a laser beam and the SF6 tracer gas concentration measurement were also employed. A conventional range hood was installed in an experimental room. A crossflow fan was attached to the countertop near the front edge to supply the slot jet of the air-curtain hood. The velocity at the exit of the slot was during the whole experiment 1 m s-1.

As result, it was found that the inclined air curtain presented a brilliant performance by isolating the fumes below the hood. Apparently, setting up the jet at an inclination angle of 15º would help to obtain the most robust air curtain hood. The SF6 concentrations measured around the breathing zone of the mannequin were about 10-2 order of magnitude smaller than those of the conventional hood. Furthermore, related to resist the influence of the walk-by motion, the conventional hood is extremely weak. Instead of it, the air-curtain hood presented excellent robustness. Besides, the air-curtain hood could provide better protection at a suction flow rate lower than the conventional hood. Even at an energy consumption rate 50% lower, the air-curtain hood, presented better performance.

In conclusion, the air-curtain technique could considerably improve the flow characteristics and performance of the conventional range hood by consuming less energy.

Liu, S. et al. (2020) focused on the importance of a healthy and thermally comfortable kitchen environment. In order to achieve that, a good ventilation system is essential. In a recent survey to Chinese cooks was revealed that 89% of respondents complained about exposure to kitchen fumes (Cao C, Gao J, Wu L et al., 2018).

Exhaust hoods are used in most Chinese kitchens, however they do not have air conditioning or make-up air systems and opening the window will lead to an excessively hot and cold environment in summer and winter, respectively. The use of air curtains could not solve the problem of indoor thermal environment, and the use of air- conditioning could disturb the air distribution around stove and the conditioned air could be discharged directly outdoors. Owing to this, an integrated air curtain and air- conditioning system was proposed and optimized to improve kitchen thermal comfort and indoor air quality.

Firstly, in this article an experiment to better understand the thermal environment and indoor air quality inside kitchens was carried out. Sixteen teenagers participated in the experiment cooking the same food. Measures about cook’s skin temperature, air temperature and indoor air pollutant concentrations during cooking, were taken in different positions.

Secondly, the proposed system was described. It consists of a kitchen hood with a supplied conditioned air from the lower part of cabinet under the cooktop and untreated outdoor make-up air from the two sides and the front edge of the cooktop. It can be seen next in the Figure 11.

Figure 11. The ventilation system principle diagram (Liu et al., 2020).

During the optimization of the integrated system design, the influence of air supply angle was taken into account as well as the air velocity and volumetric flow. This investigation used the commercial CFD program called ANSYS Fluent 14.0.

Finally, for verification of the results obtained from the CFD simulation, experimental measurements were made in a kitchen at Purdue University.

As result, it was found that the air curtains centralized in the stove region, could control the diffusion of the cooking fumes. Furthermore, it was discovered that the conditioned air best angle in summer was 15º with cold air and in winter was 155º with warmer air. These angles led to the most comfortable vertical air temperature difference. In conclusion, all studied cases for this new ventilation system had a capture efficiency higher than 90%. Moreover, for the best cases mentioned before the capture efficiency is 98,7% in summer and 97,5% in winter. This ventilation system design was also compared with other researches about air curtain designs, and this is the one with better capture efficiency.

In conclusion, the proposed ventilation system could maintain good indoor air quality and thermal comfort for kitchens.

3.2 Calculations for the current kitchen hood

In this section, calculations based on the current design of the kitchen hood of the Pastaria restaurant were carried out. The airflow required to be extracted throughout the kitchen hood was calculated. The objective is to maintain an airflow speed between 0.25 – 0.5 meters/second on the frontal planes of the hood (Bruno de Miranda, 2011). In this case, 0.25 meters/second (worst case scenario) was the speed selected to avoid the lack of air extraction and accumulation of fumes and smells without causing a discomfort to the chefs.

Next, the total vertical area between the kitchen hood and the cooking surface had to be calculated. This is the area that the air needs to cross before being extracted. In the Figure 12, this area can be seen.

Figure 12. Area calculated between the hood and the cooking surface2.

Some measurements were taken during a visit to the restaurant. The kitchen hood and the cooking surface have a total length of 3.5 meters and a width of 1 meter. As it is a wall-mounted canopy, one of the long sides is against the wall, so it will not be taken into account for this calculation because the air cannot come from that direction. The cooking surface is divided into two parts, one is the oven (1.5 meters long) and the other one is the griddle (2 meters long). The vertical distance between the hood and the oven is 0.4 meters, and between the hood and the griddle the distance is 1.2 meters.

With all this data the vertical are between the hood and the cooking surface can be calculated: A = Vertical area above the oven + vertical area above the griddle = 0.4 m hood-oven * (1.5 m length + 1 m width) + 1.2 m hood-griddle * (2 m length + 1 m width) = 4.6 m2 total area.

Once all specifications such as the adequate air velocity and face area are known, the minimum required volumetric flow rate can be calculated with the following equation (Han, Li and Kosonen, 2019): 2 3 3 Qhood = Vair * A = 0.25 m/sec * 4.6 m = 1.15 m /sec = 4 140 m /hour.

After this calculation, it is noted in the ASHRAE guideline (2015) that the typical exhaust flow rates for this type of hood (Wall-mounted canopy and Medium Duty) is between 200 and 300 cfm per linear foot of hood. Making the appropriate change of units the obtained values are 339.8 and 509.7 m3/hour per linear foot of hood (1 meter = 3.28 foot). These values can be seen next in the Table 2.

2 https://www.solerpalau.com/es- es/blog/campanas-extractoras-cocinas-domesticas-diseno- dimensionado/

Table 2. Typical exhaust flow rates by cooking equipment category for listed type I hoods (ASHRAE, 2015).

In conclusion, following the ASHRAE guideline and taking into account that the total length of the kitchen hood is 3.5 meters, the minimum exhaust airflow rate should be higher than 3 900.9 m3/hour. Therefore, for this kitchen hood, with that vertical area between the cooking surface and the hood, the minimum speed recommended of 0.25 meters/second would be enough to overcome the recommendations made by the ASHRAE guideline (2015).

This ventilation system has also integrated a rotary heat recovery. This is the most important device of the ventilation system and if it is not well selected, it may be one of the weakness of the system. These systems have been developed to reduce the amount of energy demand on the heating, ventilation and air-conditioning systems (O’connor, Calautit and Hughes, 2016). The model selected was Swegon Silver C RX. It is a complete air handling unit with rotary heat exchanger, direct-driven supply air and extract air fans as well as supply air and extract air filters (Swegon Group AB, 2019). There are different sizes for this heat exchanger depending on the airflow capacity, the range is from size 04 to size 120 (Swegon Group AB, no date). The size of the one that is currently installed in the restaurant is unknown. In order to be able to extract the minimum exhaust airflow calculated before, 4 140 m3/hour (1.15 m3/sec), the minimum size of the Swegon Silver C RX should be size 11/12. Its operation diagram can be seen in the Figure 13.

Figure 13. Operation diagram of the minimum heat exchanger size required (Swegon Group AB, no date).

3.3 Discussion

After the review of numerous research articles, some key factors and common problems that disturb the performance of kitchen hoods were discovered. These articles indicate that the physical devices, the design of the kitchen and the behavior of the workers must be taken into account to prevent fumes from spreading throughout the establishment.

The main problem in kitchen hoods is the inadequate exhaust airflow. The required hood airflow varies for different kitchen hoods depending on their size and shape (ASHRAE, 2015). Its function is to extract exactly the required amount of air from the kitchen, taking out the fumes and hazardous particles produced by cooking operation. The fan is the responsible for extracting the air. It must not be under-dimensioned because it cannot extract all the fumes and odors, nor over-dimensioned because it implies an excess of noise and energy consumption (Rim et al., 2012). Keil et al. (2004) found in their research that most hoods were not operating at the needed flow rates, only 39% and 24% of the hoods met the ACGIH and ASHRAE guidelines, respectively. Also, Singer et al. (2011) found that 12 of 15 devices could not meet the nominal airflow rate. Therefore, periodical evaluations must be done to detect any change in performance and ensure the adequate exhaust airflow.

Furthermore, related to the range hood design, Singer et al. (2011) found that an exhaust device with collection hood is the most effective design since cover all the burners lead to higher capture efficiency. Sobiski et al. (2006) reported that maximizing front overhang and minimizing rear clearance, increasing reservoir capacity, improve capture and containment. And Zhao et al. (2012) concluded that the best hood shapes for the higher capture efficiency are the traditional Chinese with the front lower edge designed at a 30º angle, and the traditional American and European with rectangular shape. Moreover, in order to achieve a better performance of the range hood and to get a higher C&C value, side panels can be installed. Zhao et al. (2012) discovered that C&C efficiency can be increased about 20% by maintaining the minimum exhaust airflow rate and adding a side panel.

There are some other important components in the ventilation system such as the filters and the ducts. The main function of filters is to avoid particles to be deposited in the ventilation duct. Ben Othmane et al. (2011) discovered that filters have a very strong influence on the maintenance intervals depending on their quality. Zhao, B. and Chen, J. J. (2006) found that employing higher efficiency filters the deposited particle mass on the floor of the ducts is reduced clearly. That means that a longer time is required to accumulate enough particles to clean ducts. Filters also need to be checked and replaced regularly to keep its efficiency. Related to ducts, Petersen, E. (2015) concluded that rigid ducts are more recommended to be used for obtaining a better performance and a higher capture efficiency, since they have lower pressure drop than flexible ducts. Moreover, Petersen, E. (2015) also discovered that a vent cap with small loss coefficients is important to improve the system performance. Ben Othmane et al. (2011) also calculated the particle deposition velocity in ventilation ducts in order to predict the cleaning time. Ventilation systems must be habitually cleaned to prevent the development of dust, product or condensate that can be a focus for microbial growth or even fire. Thus, the particle deposition in the ventilation ducts ensures an entirely developed turbulent duct airflow (Zhao, B. and Chen, J. J., 2006). Ben Othmane et al. (2011) found that ventilation systems would take between 1 to 9 years to meet the cleaning time following the ASPEC criterion (400 mg/m2). This interval is big because it depends on factors as the type of cooking, filters, air speed, etc.

Disturbing airflows are also another problem that can badly influence the performance of kitchen hoods. Chen et al. (2012) found that this factor affects disturbing the airflow and pushing the pollutants out of the collection hood. They can be formed by windows/doors opening and closing, compensation air, movement of workers, or by operating fans or air conditioners. The influence of cross drafts can be produced from three different directions as lateral, oblique and frontal, being the frontal draft the most serious pollutant spillage. A draft velocity of 0.2 m/sec generates a significant spillage of pollutants. The causes that produce it must be avoided. In order to reduce the influence of this factor side panels are recommended to be used, protecting the fumes under the hood.

The distribution of kitchen appliances is also an important factor in achieving good performance of kitchen hoods. Sobiski et al. (2006) reported that appliances should be positioned so that its thermal plume is inside the perimeter of the hood. Heavy-duty appliances should be positioned towards the center of the cooking line in order to enhance C&C. Fisher Nickel, I. and Corporation, A.E. (2011) reported that double stacked ovens are beneficial to be located at the end of the cooking line, controlling plumes as a side panel. Moreover, the installation of shelving above an appliance can improve C&C slightly. In addition, Sobiski et al. (2006) found that minimize the distance from the cooking surface to the hood, installing hoods at the lowest height practical (or permitted by code) avoiding fumes from spreading, improve C&C performance.

The behavior of the cooks must also be taken into account. Huang et al. (2010) reported that large amounts of fumes are attracted to the regions near the body of the cooks, reducing the capture efficiency of the kitchen hood. They also found that the movement of people in the kitchen makes the cooking fumes to spill into the environment easily. Moreover, Rim et al. (2012) reported that cooks should use the back burner more frequently because it is more effective reducing particles.

Some researchers as Huang et al. (2011) and Liu et al. (2020) found that the installation of an inclined air curtain is very effective isolating the fumes below the hood. A crossflow fan has to be attached to the countertop supplying the slot jet of the air curtain. This system provides better protection at a suction airflow rate lower than the conventional hood, reducing the energy consumption rate.

Related to the kitchen hood and the ventilation system of the Pastaria restaurant that needs to achieve a good performance of the extraction system some recommendations are made. Firstly, one of the main recommendations is to check if the heat exchanger Swegon Silver C RX installed in this restaurant meets the size required. This model requires a minimum size of 11/12 in order to be able to exhaust the minimum exhaust airflow of 4 140 m3/hour calculated based on the kitchen design. If the size installed in the ventilation system is 11/12 or greater, the airflow should be measured to see if the fan can really exhaust that amount of air or something is going wrong with it. If it occurs one possibility is that the installed filters are not the adequate ones or need to be replaced, making a big pressure drop that does not let the fan to extract that airflow rate.

Another factor that may be affecting is disturbing airflows as it is an opened kitchen. This factor should be studied since it can arise from many different situations. A smoke generator can help to visualize the air disturbance of diffusers, in order to obtain information about the capture efficiency. If it is found that disturbing airflows are badly affecting the performance of the kitchen hood, one recommendation would be to install side panels in the kitchen hood since it is an effective solution against this factor. Moreover, side panels will help to save energy consumption because they let a less exhaust airflow rate for the same performance. Also, in case that there are disturbing airflows the fan should have the possibility to increase the exhaust airflow since this reduce the negative effect of disturbing airflows.

The design of the kitchen seems to be correct. The kitchen hood covers all the cooking surface and the kitchen appliances are well distributed. There is a double oven located at the end of the cooking line and, as said before, it can make a similar effect as a side panel. One recommendation could be to install the kitchen hood at the same height as the oven, thus, the oven will make a bigger effect as a side panel and reducing the distance between the hood and the cooking surface will improve capture efficiency.

After studying the anterior recommendations, if the performance of the kitchen hood is not still at a normal level, the possibility of install an inclined air curtain should be taken into account. As mentioned before, an air curtain presents a brilliant performance isolating the fumes below the hood and controlling their diffusion, and this could completely solve the problem the restaurant is facing to.

4. CONCLUSION

4.1 Study results

In conclusion, this research has found that generalized assumptions and select a kitchen hood from a catalogue, as normally engineers do, does not always lead to a good performance. A correct kitchen distribution design and calculations must be done for each restaurant in order to install the most adequate kitchen hood with the best characteristics. This way, the fumes, odors, moisture and particles will be easily exhausted allowing a better environment out of risks to the establishment and customers health.

Key results obtained about general kitchen hoods are summarized next: - The fan must be able to extract at least the minimum required exhaust airflow. That minimum airflow must to be calculated depending on the kitchen design and the type of kitchen hood installed. - A kitchen hood with capture hood and covering all the burners has a higher capture efficiency. The front overhang may be maximized, and the rear clearance minimized to get higher C&C. - Adding side panels to the kitchen hood increase C&C efficiency about 20% by maintaining the minimum exhaust airflow rate. - Rigid ducts are more recommended to be used for obtaining a better performance than flexible ducts. - Filters with high efficiency are recommended to reduce the number of particles deposited in the ventilation duct. The particle deposition leads to develop a turbulent duct airflow. - Ventilation systems must be cleaned between 1 to 9 years. Before the particle deposition is bigger than 400 mg/m2, following the ASPEC criterion. - Disturbing airflows must be avoided because they affect disturbing the fumes under the hood and pushing the pollutants out of it. Side panels can be employed to avoid this factor. - Kitchen appliances should be positioned so that its thermal plume is inside the perimeter of the hood. Moreover, the distance from the cooking surface to the hood must be minimized. - The cooks attract fumes to the regions near their body, and their movement can also disturb cooking fumes, reducing the capture efficiency. - The installation of an inclined air curtain is very effective isolating the fumes below the hood.

Related to the kitchen hood and the ventilation system of the Pastaria restaurant the findings are: - The installed fan must be able to exhaust at least a minimum airflow of 4 140 m3/hour. In order to do that the heat exchanger Swegon Silver C RX requires a minimum size of 11/12. - Disturbing airflows may be affecting the kitchen hood performance. That is why a study to check if this factor is badly influencing must be carried out. - Side panels can be installed in order to improve the capture efficiency and reduce the energy consumption. A double oven is located at the end of the cooking line and can be doing a similar effect as a side panel. - The kitchen appliances distribution seems to be correct. - Kitchen hood could be installed at the same height as the oven, minimizing the distance with the cooking surface and improving the capture efficiency. - The ventilation ducts must be checked to see if a cleaning is necessary to be carried out. The filters must be also checked to see if they are keeping their effectiveness or a replacement is needed. - If the performance of the kitchen hood is not good enough after checking all recommendations, an inclined air curtain may be installed since it was found in some researches that has a brilliant performance isolating the fumes below the hood and controlling their diffusion.

4.2 Outlook

This project is described as an explorative review study about key factors and common problems in ventilation systems of restaurant kitchen hoods.

As a further development of this work, a monitoring about how the recommendations made to the real ventilation system will affect the hood performance can be carried out. This way, a better knowledge about the influencing factors and recommendations can be obtained and corrections applied. Also, how to improve the efficiency of the devices of a ventilation system are object to a future study in order to get better performance systems.

4.3 Perspectives

Heating, ventilation and air-conditioning devices are systems that require a big amount of energy consumption. That is why it is necessary for them to be as much efficient as possible, reducing their global energy impact.

In this particular project, a review about factors that can disturb the performance of kitchen hoods has been made. It is very important to achieve that all components of the ventilation system are the most adequate and efficiency ones, and to minimize the influence of factors reducing the performance of the system. The ventilation system of a real restaurant in Sweden has been analyzed and some recommendations have been made with the aim of get a better performance of a kitchen hood that is not controlling the fumes produced during the cooking operation. The fact that it is not performing well makes the system to employ a big energy consumption and, moreover, the health of workers and customers is being at risk.

Therefore, the idea of studying the main factors and problems that affect to a kitchen ventilation system entirely match with a sustainable development, reducing the energy consumption, helping to the climate change and protecting people’s health.

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American Society of Heating, Refrigerating and Air-Conditioning Engineers (2015). ‘ASHRAE Handbook: Heating, Ventilating, and Air-Conditioning Applications’. Inch- Pound Edition.

Ben Othmane, M. et al. (2011) ‘Predicting cleaning time of ventilation duct systems in the food industry’, Journal of Food Engineering. Elsevier Ltd, pp. 400–407. doi: 10.1016/j.jfoodeng.2011.03.027.

Bluyssen, P.M. (2013). ‘The healthy indoor environment: How to assess occupants’ wellbeing in buildings’, Routledge.

BOVERKET (Swedish National Board of Housing, Building and Planning) (2018). ‘Boverket’s building regulations - mandatory provisions and general recommendations’. Version: BBR 26, BFS 2018:4.

Bruno de Miranda (2011). ‘Cálculo del caudal de aire de una campana extractora industrial’. [Online]. Available at: https://www.ingenierosindustriales.com/calculo-del- caudal-de-aire-de-una-campana-extractora-industrial/ (Accessed: 1 July 2020).

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