The adage “you get what you pay for” has never been more real, more impactful and more serious than when it comes to the design, specification and selection of foodservice ventilation. What differentiates various systems and manufacturers? How can a stainless-steel box cost so much?!? Why does one system seem costly when there are cheaper systems on the market? These are comments and questions we hear all the time. So, what is the correct answer with the most beneficial solution!
First and foremost, almost all government controlled AHJ (authority having jurisdiction) follow, adhere to and/or mandate certain codes, laws and/or rules which, for public safety reasons, require foodservice cooking appliances to have adequate ventilation and fire suppression. These requirements can vary city to city, state to state, province to province and country to country.
The purpose of cooking ventilation is to safely remove cooking grease and grease laden vapors from the building. This can mean, to the lay person, that they simply need a canopy with a duct and an exhaust fan which supposedly exhausts the smoke and grease laden vapors from their building. This seems like a very simple concept in general but, it is not. Systems can be very simple and very inexpensive, but buyer beware as there are long term costs associated with these systems which make their first cost attractive but life cycle total ownership cost extremely expensive and risky.
To avoid these pitfalls requires knowledge of the systems available and their long-term benefit(s). Most systems on the market work as described above (i.e. a canopy hood, some duct work and a fan). How these systems perform is the big difference. Most systems have low efficiency filters which have a capture ratio of about 55% which means 45% of the grease and grease laden vapor stays in the building and typically gets pulled into the buildings air conditioning and heating system thereby distributing grease throughout the facility. The 55% which passes through the filter then gets exhausted out of the building which can be a violation in some jurisdictions but also can lead to premature failure of roofing systems. High efficiency systems have filters with a capture ratio of 95% materially reducing the amount of discharge to the environment and due to the design and capture aspect of the filter materially reduce grease build up in the duct work. These high efficiency filters can be run through the dishwasher as needed; however, duct cleaning is typically performed by a sub-contractor on a regular basis. These high efficiency systems have been tested by third party independent testing agencies who can attest to the actual performance of these components and systems.
Foodservice exhaust has a material impact to the size and cost of operating the buildings air conditioning and/or heating systems. In almost all jurisdictions there is a requirement to replace (or make up) the air which is exhausted from the building. The make up air requirement is usually 80-100% of the amount of exhaust air and in the US is measured in CFM (cubic feet per minute) and in Europe and other parts of the world is measured in CMH (cubic meters per hour). For example; a small operation with 5,000 CFM of exhaust with a make up air requirement of 80% would require 4,000 CFM of outside treated (air conditioned and/or heated) make up/supply air. The major cost impact to a project is the additional cost to treat the incoming make up air. Therefore, exhaust systems which can operate more efficiently (i.e. exhaust and capture grease laden air at a much lower exhaust CFM) require less make up air and smaller building systems to treat the make up air. The cost for the make up air system is considered a first cost to the client while the long-term energy use and maintenance of the system are considered long term second costs.
An example of a standard exhaust system which may appear to have a much lower first cost may have an exhaust rate of 6,000 CFM along with a make up air requirement (at 80%) of 4,800 CFM. A high efficiency system for the same equipment configuration may have an exhaust rate of 4,500 CFM with a make up air requirement (at 80%) of 3,600 CFM which is a difference of about 30%. Therefore, the client would recognize operational savings for air conditioning and heating costs for the life of an efficient system. Additionally, the overall air conditioning and heating systems sizes/capacity could be reduced based on a lower make up air demand system thus resulting in a much lower overall project cost.
Systems with poor extraction efficiency, capability and capture at the filters create risk to both life and property. If the exhaust system only extracts 55% of the cooking grease through the hood filters resulting in a condition in which 45% of the grease remains in the building, then the residual can create a potentially serious fire hazard while materially shortening the life of the air conditioning and heating equipment. The grease/grease particles which pass through the filters will not all be extracted nor discharged by the exhaust fan. This condition results in a grease build up in the exhaust duct work which in case of a fire creates a hospital, hotel, condominium, shopping mall, casino or office tower it creates a potentially dangerous situation. Certainly, all systems are built to local codes with the installations approved by local inspectors. However, it is an important reminder that the codes are the minimum requirement/standard. Therefore, designing, specifying and building your system should consider all aspects discussed in the blog as there is an extremely high cost and high risk with buying cheap.