The popularity of Food Halls and Mixed-Use Retail properties has created a significant challenge for property developers and designers. The nature of the foodservice operations is to design for the unknown in many instances. Although the overall concept may be known, the needs of individual tenants may not be. Planning the base building infrastructure for future tenants is design around several unknowns.
With proper planning and execution, virtually all these unknowns can be addressed. The nature of these types of projects requires a system capable of adapting to changes in tenants or vendors. With building planning and construction timelines covering several years and the useful life of the buildings estimated to be anywhere between 15 and 30 years or more, a system that is put in place should be able to accept or be updated to the latest generation.
The questions that should be asked to determine the kitchen ventilation base building requirements for Food Halls or Mixed-Use Retail properties are;
- How many vendor or tenant spaces need to be accommodated?
- Is there a mix of QSR (Quick Service Restaurant), Fast Casual, and Fine Dining (this relates to how much overall exhaust may be required to meet the demand from the various tenants)?
- In the case of Food Halls, how many stalls or vendor spaces need to be accounted for?
- What is the most efficient path for the exhaust duct to route through?
- Is it cost-effective to run the duct vertically through revenue-producing spaces or is there sufficient infrastructure space carved out to allow for it?
- Is it more cost-effective to run ductwork through a side wall?
- Can the system be manifold together to allow for one or two main trunk lines and have tenants or vendors connect to the system?
- If a manifold system is available, can the vendors or tenants operate independently?
- When consideration is given to sidewall discharge at the lowest levels of the building, are there residential properties or adjacent spaces that might generate complaints about odors?
The number of vendor or tenant spaces and the allowance for what type of foodservice operation play into the estimate for the exhaust needs. Assuming a 10-space food hall or mixed-use property. The developer has determined that they would like to have 5 QSRs, 3 Fast Casual, and 2 Fine Dining establishments. The exhaust requirements tend to increase by operation type. It is fair to estimate that a typical QSR, whether branded or not, would have the lowest exhaust burden. They are characterized by close-coupled style hoods requiring the lowest airflows.
Fast Casual concepts have a slightly larger footprint and would require an increase in available exhaust capacity. Lastly, Fine Dining has the greatest exhaust requirements and appliance load.
In general terms a fair estimate would be to allow the following:
- QSR 2000 CFM
- Fast Casual 3000 CFM
- Fine Dining 5000 to 7500 CFM
In the example provided, the overall exhaust for the 10 spaces would be 34,000 CFM. This is a crucial piece of information. It does not necessarily mean that exhaust will be required all the time, but exhaust infrastructure, ductwork size, exhaust fan, and make-up air requirements need to be sized to accommodate that amount of exhaust air.
Once the estimate for total exhaust is calculated, then a determination for the exhaust duct routing and if a pollution control unit is needed.
Considerations for the pollution control unit are:
- If Filtration needs are contemplated
- Number and type of foodservice operations
- Cooking processes from bakery to a steakhouse
- Operational hours
- Estimated loading and maintenance cycles
- Odor Mitigation
- Area of discharge
- Best available technology
- Odor monitoring capabilities
- Avoidance of residential complaints
Assuming a manifold duct system allows a central exhaust fan or Pollution Control Unit (PCU) to serve multiple tenant spaces. Vendor ductwork would typically exit the vendor space and tie into the manifold duct. Where the ductwork discharge is located is a function of the location of the tenants and the most direct access to the outside of the building. This can be either a horizontal sidewall discharge (assuming the appropriate PCU technology is used) or a vertical stack to the roof. A cost comparison can be made to determine the most cost-effective means of discharge. Routing ductwork vertically may be impractical due to the number of floors and impact on removing revenue-producing square footage.
- The hood and control package for the vendor would be supplied as part of the vendor space fit-out as detailed in the lease agreement. A combination of varying components on the system would not be allowed to avoid compatibility issues with the base building exhaust system or controls. There are systems and controls available that can easily manage multiple vendor systems on common ducts and operate independently of each other.
- The control package manages the operation of the base building exhaust system. It monitors affected ductwork for grease deposition, the operational status of the Pollution Control Unit (PCU) (if so equipped), and maintenance intervals, receives signals from the vendor space hood system to determine exhaust and makeup air levels required. The controls must be able to adjust with updated programs to reflect any new vendor requirements for exhaust volumes. Care must be taken to estimate the overall exhaust volume on the base building system can accommodate future vendors. “Moving” exhaust levels between vendors is a simple program change for those systems capable of these adjustments.
Pollution Control Units (PCU’s)
There are Media Filter units and Electrostatic Precipitators as the filtration methods for PCU’s. The effectiveness of the filtration method is a function of the filter rating.
Media Filter units are lower first cost but higher maintenance cost as the filters are disposable and need to be replaced when full. Most systems have filter monitoring capability to indicate when the filters need to be changed. These can be effective systems on lighter load applications. An allowance for ongoing maintenance and filter replacement should be accounted for in the operational budget.
Electrostatic Precipitators (ESPs)
ESP’s are higher first costs but typically lower maintenance costs. They remove particulate by charging the grease particles positively. As the particles travel between parallel, positive, and grounded plates, the particles are repelled from the positively charged plate, pushing them toward the ground plates they collect. These systems also have a wash system that can clean the plates daily. Periodic inspection of the ESP “cells” should be undertaken to ensure efficient operation.
ESP units can come in a single pass, double pass, and, in some instances, triple-pass configurations. The number of passes is a function of the volume of loading the system would see. Typically, solid fuel application or other very high grease production would necessitate a double or triple pass.
Smoke particles vary in size from less than 0.1 microns up to 2 microns – solid fuel operations can produce much finer smoke particulate than other operations. Depending on your cooking processes, higher efficiencies of filtration may be required to remove visible smoke. It is recommended to use a HEPA filter employed with a minimum efficiency of 99.97% for a particle size of 0.3 microns for solid fuel operations. Absolute filters with a lower efficiency rating (such as 95% for a particle size of 0.3 microns) may be used if smoke removal is not as crucial or less visible smoke from the cooking operation.
Cooking Odor Mitigation
As previously stated, odor from cooking processes is the primary complaint of residential tenants residing in mixed-use developments. Although appealing in limited exposure, chronic odor migrating to residential tenants has led to devaluing properties and litigation to mitigate odor generation.
There are several odor abatement systems and some very promising new technologies on the market. These technologies run the gamut from odor masking sprays to UV/Carbon with odor sensing “noses” that monitor the carbon life and effectiveness.
Odor Spray is a masking spray that is injected into the airstream on a timed interval cycle. This type of system may be effective for minor or “non-critical” odors such as baking. The odor spray is a solution that is consumed and must be replaced. It is paired with paper filter units.
Permanganate is an adsorbent chemical compound that is used for odor abatement in combination with carbon. It is purple. It is a strong oxidizing agent but requires a chemical reaction that is not always present in cooking effluent; therefore, it is not as effective as activated carbon on most cooking processes.
Carbon Panels. The most effective carbon-based odor absorbent material tested is activated carbon made from coconut shells. The amount, by weight, is a determining factor in its life and effectiveness. Carbon is a porous material, and it traps the VOCs that cause odor. Once the carbon is “full,” it must be replaced. If not replaced, it will start to “off-gas” and impact odor emissions.
UV/Carbon Panels, The most effective combination of odor mitigation technology available. The UV lamps generate UV light, which acts on the VOC’s and the carbon adsorbs them. The ozone from the UV lamps continues to reduce odors after the effluent is discharged from the PCU. New technology now uses an odor sensor or “nose” that can detect the efficiency of the odor abatement and the life of the carbon. These types of systems should be considered for Odor Critical applications where residential tenants will be exposed to foodservice tenant exhaust systems and, in turn, become “odor critical.”
Fire Risk Mitigation and Fire System Requirements
The labyrinth of ductwork that is often created with a multi-vendor system has the potential for fire risk. All fire codes must be adhered to, including access points and fire wrap. Periodic inspections are required based on the NFPA96 and International Mechanical Code standards. Some technologies can monitor grease buildup in the ductwork and alert the building management that critical maintenance (cleaning) of the ductwork is required. It will also verify the work is done properly.
There are two methods to protect the affected ductwork, PCU and tenant hoods, with a manifold duct system. The first is to have an electric actuation of the individual tenant hood and the manifold duct. Local requirements would dictate whether the PCU needs to activate its fire system if there is an event in a tenant space. This method isolates the fire suppression discharge to the individual tenant and the manifold duct (possibly the PCU dependent on local requirements). The other method is to have all tenants’ fire systems activate when an event occurs in one space. Refer to NFPA 96, Chapter 10, and your local code authority for their specific requirements.
With a base-building configuration in place, the developer has significant flexibility in assigning the tenant space based on exhaust demand. Exhaust can be shifted from a space using less of the exhaust allowance to a space requiring slightly higher exhaust values.
Should you require help in planning your Food Hall or Mixed-Use Retail properties, the experts that manufacture these types of systems and solutions can guide you on the proper selection and any accessories needed to meet your local requirements.
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