You have a sterilization plan. You have a PPE plan. But do you have an air ventilation plan? How to implement an Air Ventilation Plan.
Pandemic restrictions are lifting across the country, and it will soon be time for America’s restaurants to reopen for business. This is welcomed news for an industry that has taken a particularly hard hit during this crisis. To prepare, restaurant owners are developing plans to keep their staff and customers safe. They are following sterilization plans to keep surfaces and hands clean, as well as personal protective equipment (PPE) plans that instruct staff and customers to wear face, eye, and skin protection. To ensure restaurants are combatting COVID-19 on all fronts, we believe an air ventilation plan is just as essential as cleaning and PPE.
As business owners and facility managers prepare to reopen their locations, many have wondered whether their ventilation systems are safe. Some have asked if their HVAC systems could be adjusted to further reduce exposure to COVID-19 for their occupants. We have leveraged our 25+ years of air balancing experience, as well as the latest guidelines from the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE), to provide the following recommendations for restaurant air ventilation plans:
1. Consider Your Air Turnover Rate
Compared to most office spaces, retail shops and even some medical facilities, restaurants by virtue of the design of the ventilation systems may already be a safer environment for their customers and staff in regard to the COVID-19 crisis.
HVAC systems in restaurants are complex. You have the large exhaust hood over your cooking surfaces, supply air grilles in the dining room, exhaust grilles in the restrooms and a make-up-air unit for your kitchen. By design, these systems have a very high air turnover rate.
Air turnover rates are defined as how many times per hour your HVAC supply air retriculates through through your units and filters. The more the recirculation, the healthier the air. Additionally, each recirculation is infused with fresh outside air.
The more the RECIRCULATION, the healthier the air.
These air turnover rates are defined as air changes per hour, or ACH. Health departments do not allow hospitals to open if they cannot meet the minimum required ACH.
To ensure a comfortable environment, a restaurant’s HVAC system typically creates an air turnover rate that is comparable to, or in some cases higher than, that of many medical facilities. The table below shows recommended design criteria comparing hospitals and restaurants
As an example, consider a typical 4,000-square-foot restaurant that has 15-foot ceilings and can serve 150 customers. This space might be designed for 40 tons of cooling, yielding approximately 16,000 cubic feet per minute (CFM) of supply air into the space. (The exact amount of cooling depends on many other factors; this is an approximate example.) Additionally, a 12-foot kitchen hood would deliver approximately 4,000 CFM of outside make-up air to offset the kitchen exhaust fans. This would yield a total of 20,000 CFM of supply air into the space.
By applying the air turnover formula (total supply air CFM x 60 minutes/hour ÷ volume in the space in cubic feet), we calculate 20 air changes per hour. This rate is comparable to most operating rooms. (20,000 CFM x 60 minutes/hour) / (4000 SqFt x 15 Ft) = 20 ACH.
Of course, we are not implying the air quality in a restaurant is as good as a hospital but simply saying that the quanitity of airflow movement is comparable. Many experts have implied that large quantities of air movement help lower the possibility of infection, since the virus particles are “carried” away from people at a much faster rate.
In our example above, this restaurant would be considered to have great air exchange rates compared to many other commercial buildings. With 20 ACH, the entire air space of the restaurant is being circulated once every three minutes.
In addition to air exchanges, all restaurants must introduce a certain amount of outside air to mix with the air that is already in the space. Without detailing the required amount of fresh air for this example, conventional design may state that approximately 15% of the total HVAC air has to be mixed with outside air. We are also introducing outside air to make up the difference of exhaust air from the kitchen hood.
In our example, 15% outside air of the 16,000 CFM of HVAC supply air plus 4,000 CFM from the kitchen hood equals 6,400 CFM of fresh air that must be introduced. That is 6,400 cubic feet of air from the outside pumped into the restaurant every minute. Another way to present this data is that 6.4 out of the 20 air exchanges per hour are directly from the outside.
To verify the quantities of outside air and air exchanges per hour, we reccommend hiring a certified testing, adjusting and balancing (TAB) firm, as they have the proper skills and tools to measure the airflow for your restaurant.
2. Consider a Filter Upgrade
Filters are designed to filter out particles while still allowing as much free air to flow as possible. With today’s added airborne threats, ASHRAE is recommending upgrading to a higher-quality filter, if your HVAC system can support this upgrade.
The HVAC industry uses a rating system called a MERV rating, which stands for minimum efficiency reporting value.MERV values vary from 1 to 16. The higher the MERV value, the more efficient the fileter will be in trapping airborne particles.
ASHRAE is recommending upgrading to a MERV 13 or higher (MERV 14 is preffered) if your HVAC system can support it. These filters are designed to folter out bacteria and some airborne viruses.
However, not all HVAC systems can handle higher-quality filters. Arbitrarily installing higher MERV filters without a TAB technician’s analysis could decrease the heating and cooling effectiveness of your system.
Regardless of what filter you select, it is important to understand that filters will need to be changed regularly to maintain system performance. When you change filters, ASHRAE recommends wearing full PPE: N95 mask, gloves and eye protection. These filters are designed to catach viruses on the filter media, so you need to protect yourself from those contaminants when handling the filter or doing any maintenance on the unit.
3. Check for Filter Frame Leakage
Once you settle on what type of upgraded filter your system can handle, inspect the filter frame to ensure there are no air gaps. The fitler should cover the entire frame space of the air entering the unit. Any gaps found around the frame and between the filters need to be sealed.
4. Double Check Your Building Pressure
To avoid bringing in unfiltered air, restaurants should be operating under positive pressure conditions (more outside air than exhaust air). Your air balancing technician can properly set the outside air intake of each unit to ensure it exceeds the amount of exhaust. This will reset your building back to positive pressure and keep out unfiltered air.
5. Other Sanitization Options
Some systems simply cannot functionproperly with MERV 13 or higher filters. If your system falls into this category, you still have options to sanitize your air in ways that are on par with hospitals.
Most hospitals install ultraviolet (UV) light sanitizers inside their HVAC units. The UV-C spectrum inactivates viral, bacterial and fungal organisms so they are unable to replicate. These UV lights have been shown to destroy related coronaviruses (including MERS), but as of this writing, it has not been conclusively proven to kill COVID-19.
These lights can be installed inside HVAC units, typically by a local HVAC contractor. This method is more expensive than the filter upgrades but provides an added layer of protection restaurants can use as a substitute for, or in addition to, higher-quality filters.
Please note, some images were taken before we required the use of PPE for our technicians.
6. Don’t Forget to Clean Your Ceiling Diffusers
If you are spending time and money to have clean filters installed, do not forget to also clean the ceiling diffusers. Even with regular filter maintenance, ceiling registers tend to get dirty over time, but it’s not because your HVAC unit is delivering dirty air. The dirty build-up is caused by air leaving the register at a high velocity and interacting with dust particles. This is called the Coanda Effect, or smudging.
ASHRAE recommends sanitizing all supply, return and exhaust registers to be safe. This will provide a clean space for your conditioned air to travel and give your occupants the added comfort of seeing clean registers.
Implementing Your Air Ventilation Plan
Many experts have implied that large quantities of air movement help lower the possibility of infection.
Without a vaccine, the best we can do in the fight against COVID-19 is take steps to mitigate the spread of infection. We are all accustomed to sterilization plans and PPE plans. But as we start reopening restaurants, we must start incorporating air ventilation plans to treat our air as well. The more mitigation steps we take, the better off we all are.