August 21, 2019
Authored by Guy Tomberlin, Senior Regulatory Engineer
Pollution control units (PCUs) have an interesting history in the commercial cooking industry. They were developed many years ago to help meet the needs of challenging termination locations for commercial kitchen exhaust and to help improve environmental air quality.
PCUs are installed directly into a commercial kitchen exhaust system. Their primary functions are to reduce emission impurities such as grease and smoke and to control odors associated with commercial cooking operations. PCU design is based on both the appliances it will serve and the desired air quality for the final exhaust. Over the years, PCUs have been referred to as exhaust filtration systems, air filtration systems and air purification systems for commercial cooking operations
PCUs typically consist of a filter bank that can perform varying functions to reduce unwanted emissions. The filters may be electrostatic precipitators, metal mesh, media types and may include disposable filters. The units typically have built-in static pressure sensors with monitoring to identify when airflow has been compromised because of filter loading or other system malfunction.
Depending on location and climate, PCUs can be factory fitted with internal fire suppression and cleaning or wash systems. The kitchen exhaust fans can be located completely independent of the PCU or incorporated directly into a PCU housing. When incorporated outside of the PCU housing, the fans are evaluated and certified separately. PCUs can be installed indoors or outdoors, depending on their design and certification.
Originally, manufacturers worked with UL to establish certification requirements for PCU operations and performance to deliver at least the same level of safety as the kitchen exhaust systems in which they are installed. The applicable requirements from UL 710, the Standard for Safety of Exhaust Hoods for Commercial Cooking Equipment, and UL 1978, Standard for Safety of Grease Ducts, were applied to enable listed units to become available in the marketplace.
PCU plan review and inspection
As this industry evolved over time, there has been widespread demand for improved air quality. Previously, PCUs and their components were evaluated and certified to several different standards, leading to the realization that a single standard dedicated to this specialized technology was needed. In response, UL developed UL 8782, the Outline of Investigation for Pollution Control Units for Commercial Cooking, to more effectively meet user needs as well as address the diversity of PCU installation and use.
The 2018 edition of the International Mechanical Code (IMC) has incorporated requirements for PCUs that include comprehensive installation criteria. The 2018 Uniform Mechanical Code (UMC) also permits the installation of listed PCUs. Finally, 2017 NFPA 96 contains PCU provisions.
With the popularity of town center-type construction (co-mingled residential and commercial occupancies in the same structure and building footprint), the options for kitchen exhaust terminations are often limited. In addition, many cities and localities are enacting more stringent air quality control measures. If a jurisdiction has not yet adopted a current edition of model mechanical regulations, they may be of great value when evaluating a code modification request for alternate materials and methods to enable use of a PCU.
The model codes and standards, along with UL certification criteria, reference the use of the manufacturer’s installation instructions. In addition, the 2018 IMC has prescribed 15 specific installation requirements pertaining to PCUs. Below is a suggested checklist for code officials performing plan reviews and inspections for commercial cooking systems that include a PCU. The checklist includes are items that have been updated for the 2021 IMC noted with the designation 2021 IMC; specific UMC and NFPA 96 provisions are mentioned as well.
Inspection and plan review PCU checklist
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- 2021 IMC replaces the reference to UL 1978 with UL 8782
- The exhaust fan serving the system must be listed to UL 762.
- Refer to the building code for structural mounting guidance.
- 2021 IMC includes more specificity on the mounting requirements including seismic provisions.
- Where an extra-heavy-duty appliance is intended to be exhausted through a PCU, the PCU shall be listed and designed specifically for use with solid fuel burning appliances. Indoor and outdoor PCUs must be listed for the intended location.
- Outdoor units installed on a roof must be at least 18 inches above the roof surface. A challenging aspect of an indoor PCU installation is to ensure availability of a code compliant installation location. If the grease duct system is required to be located in a fire-resistant rated enclosure, the PCU must also be located in a space that meets the same rating. Bear in mind that the unit requires access and service space for cleaning and maintenance and the space must have ventilation for the PCU.
- 2021 IMC has added requirements for listing to UL 2221 and ASTM E2336 to determine that an enclosure’s fire resistance rating and through-penetration methods are consistent with the grease duct requirements.
- A clearance of 18 inches from combustible material to the PCU is required.
- 2021 IMC requires that clearances be maintained in accordance with the PCU listing.
- Exhaust terminations are required to meet the same requirements as traditional commercial kitchen exhaust.
- An airflow pressure differential sensor must be installed in the filter space to indicate pressure loss across the filters. An alarm located in the cooking area served by the PCU must be activated when inadequate airflow is detected.
- PCUs must have a fire suppression system and the water supply protected from freezing.
- The UMC and NFPA 96 require that the ductwork downstream of the PCU include an approved automatic fire-extinguishing system.
- Duct-to-PCU connections must be made with bolt-on flanges with gaskets rated for not less than 1500°F (816°C)
- If a wash down system is provided:
- It must discharge through a grease interceptor. There are additional requirements for the drain to prevent air emission during unit operation and evaporation between cleanings.
- The water supply serving the wash down system must be protected from freezing.
- Where water from the wash down system can enter the connecting duct(s), the duct(s) must be installed to slope towards the PCU drain provided in the housing.
UL certification requirements and certified PCUs can be found in the UL product category for Pollution Control Units for Commercial Cooking (YZHK). Additional guide Information about this category can be found by using our Product IQTM search tool. Product iQ is free, but a one-time registration is required.
UL is currently working with manufacturers to determine that their products will comply with these new requirements by April 30, 2020. UL Listed products manufactured after this date will be assessed for compliance to the UL Outline of Investigation for Pollution Control Units, UL 8782.
For more information, please contact ULRegulatoryServices@ul.com.