There is no denying the importance of a clean, safe environment in foodservice operations, but what about that which isn’t obvious or seen? Poor indoor air quality not only negatively impacts health but also affects mood, energy levels and concentration.
Healthy environments depend on restaurant operators’ awareness of pollution sources, including those from the back of the house, and the ability to manage contaminants in a space.
Along with contaminants, climate also plays a part in air quality. Studies have found that a 10-degree rise in temperature leads to a 30% reduction in productivity.
The first step in controlling air quality is to monitor pollutants in both the kitchen and dining areas.
The WELL Building Standard is one type of measurement that provides insight on pollutant limits in commercial kitchens. Like how Leadership in Energy and Environmental Design (LEED) looks at energy efficiency, WELL is an international assessment method that not only encourages healthy eating choices and active lifestyles but also promotes natural light and a high standard of air quality based on seven years of scientific, medical and architectural research.
In terms of design, there should not be significant aesthetic changes when controlling air quality. Existing devices, such as supply diffusers, are still the main vehicles for delivering air into a kitchen or restaurant, while exhaust hoods are the primary means of removing air from the space.
What Impacts Air Quality
In restaurant dining areas, indoor air quality is primarily driven by carbon dioxide, but in kitchens, indoor air quality can be impacted by several factors. This includes hoods not properly capturing cooking effluent and appliances with fuel like gas, propane or wood that produce a moderate level of carbon monoxide. Additionally, gas appliances that are not burning correctly or not producing enough oxygen can increase the amount of carbon monoxide produced.
Cooking under a ventilation hood creates particulate matter (PM) and volatile organic compounds (VOC), which tend to be odor-carrying compounds. When this is not controlled, people will smell benzine produced from cooking.
In addition to VOCs, relatively high concentrations of HCHO (formaldehyde), NO2 (nitrogen dioxide) and PM exist in restaurants and are highest in operations that use gas for cooking and allow smoking indoors. Gas cooking equipment also is a source of sulfur dioxide, water vapor, particulates, carbon dioxide, carbon monoxide and oxides of nitrogen.
Particulate matter also exists in high amounts throughout restaurants due to high traffic and cleaning as well as cooking. Some particles, such as dust, dirt, soot or smoke are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope.
Particle pollution includes PM10 or inhalable particles with diameters that are generally 10 micrometers and smaller; and PM2.5, fine inhalable particles with diameters that are generally 2.5 micrometers and smaller. How small is 2.5 micrometers? By comparison, the average human hair is about 70 micrometers in diameter, making it 30 times larger than the largest fine particle.
HCHO is present in outdoor air but concentrations are usually much higher indoors because of formaldehyde sources. For example, dominant formaldehyde sources are manufactured wood products that use formaldehyde-containing resins to glue together pieces or particles of wood. This includes particle board, plywood, oriented strand board, fiberboard and similar items often used in walls, floors, furniture, cabinets, doors and modern manufactured wood beams. Additional sources are some paints, fabrics and insulation materials.
The Temperature Effect
In commercial kitchens, the main air quality challenge is contending with the heat produced from cooking equipment. By reducing heat load or Btus, minimal air conditioning will be needed to achieve an acceptable comfort level in the back of the house.
In hotter states, the focus is on reducing humidity in the air. When this is minimized with a dehumidifier, warmer temperatures will feel more comfortable.
Another consideration is tempering exhaust hood air. It is recommended that tempered air coming into the kitchen be at minimum 60 degrees F in winter and 80 degrees F in summer so there is not as much of a temperature differential. This will help control the amount of heat and air conditioning needed throughout the year.
Operations without makeup air are pulling all the air from the room, which requires HVAC units to work much harder to cool or heat the space.
The goal in kitchen spaces is to reduce the amount of exhaust in the hood. For every 500 cfm (cubic feet per minute) of exhaust that is saved, it is comparable to saving approximately a ton of air conditioning. This can be accomplished by increasing hood depth so there is more volume that can capture hot air. This means air doesn’t have to be pulled out of the space as fast. Also, stainless-steel side curtains can be installed on hoods so less air is being pulled out at once. For energy and utility savings, hoods with variable speed controls for exhaust and makeup air sense the amount of heat given off by cooking equipment and utilize only the necessary amount of exhaust and makeup air.
In addition, equipment with remote air-cooled compressors will keep the atmosphere cooler since the exhaust heat is expressed in a separate area. For equipment using fractional compressors that total up to 2 hp, it takes 2,000 cfm of air to cool the space and remove heat from the compressors; with water-cooled compressors, it’s only 250 cfm.
Taking Measurements
Air changes per hour (ACPH) or air change rate, is the measurement and calculation process assuring air is replaced in a room a specified number of times in an hour. This verifies adequate indoor air quality, ventilation and cleanliness.
Sensors that can monitor indoor air quality and levels of carbon monoxide, carbon dioxide, VOCs, ozone and PM are especially crucial since these represent the particle sizes that are respirable and enter the lungs.
There also are sensors that measure the thermal comfort in spaces, including temperature and relative humidity. When combined with indoor air quality measurements, these calculations are collectively referred to as indoor environmental quality.
Reducing virus transmission in smaller spaces requires targeting four to six ACPH using outdoor air ventilation, recirculated air passing through a filter with a minimum 13 efficiency (MERV 13) rating or utilizing portable air cleaners with high-efficiency particulate air (HEPA) filters.
Options for Better Air
Basically, air quality and cleanliness go hand in hand; the more a space is kept clean with minimal dust and debris, the less a filtration system needs to work.
With new installations, before choosing a system, it’s best to look at how many times air is being exchanged in the room. This will depend on cubic feet and air exchange in the space and how many times per minute that air is taken out and recirculated with new air. The quicker the air replacement, or the more air exchanged, the better.
Also, higher density filters trap more contaminants, improving air quality. Along with highly rated MERV filters (14 or above), HEPA and ULPA (ultra-low particulate air) filters block bacteria and viruses indoors.
Keeping up with HVAC and ventilation hood maintenance and making sure filters are changed on a regular basis are key to maintaining decent air quality.
Those seeking natural ventilation with windows or vents letting in outside air should keep in mind that outdoor contaminants, including pollen and car exhaust, can potentially compromise air quality indoors.
In commercial kitchens, the only way to currently mitigate air quality issues is by manually increasing the maximum exhaust airflow of the ventilation hood or manually increasing the minimum airflow during part-load cooking, which most often occurs when demand-controlled kitchen ventilation (DCKV) systems are used. Kitchens with slight negative pressure ensure odors aren’t being transferred into the dining area or the rest of the building.
Most restaurant dining spaces utilize some form of demand-controlled ventilation, since these units automatically increase the amount of outside air being brought into the dining space in relation to the number of occupants. Indoor air quality (IAQ) monitoring could augment those systems by providing additional information on air quality. Another option for smaller spaces is tabletop air purification systems that are designed to attack viruses, bacteria, mold and pollen, depending on the type of unit.
There is newer technology that can improve air quality. UV (ultraviolet) light and UV-C wavelengths can be used to kill bacteria, viruses, fungi and mold. These can be installed in filtration systems within HVAC ducting or other areas.
Although not widely used in foodservice operations, air or biopolar ionization systems kill viruses through chemical reaction. This works by using high-voltage electrodes to split apart oxygen molecules into negative and positive ions. These bond with and neutralize viruses, bacteria, molds, allergens and other particulates.
In the future, there will likely be systems that automatically increase exhaust airflow on the hoods in the kitchen if contaminant levels are increasing in the kitchen. At the same time, the quantities of replacement air will also increase to maintain space balance, which means that cleaner air will be entering the space. These systems will need to be more energy efficient, actively monitor and improve conditions and automatically increase replacement air.
As there is more public awareness of indoor air quality’s importance and indoor environmental quality concerns, it is anticipated that this will continue to be an expanding area of change with new innovations emerging in the future.