Understanding the basics of certain key features is essential to proper design.
Commercial Kitchen Hoods
Why should one investigate the use of a UL
710-listed hood?
The International Mechanical Code Chapter 507, “Commercial Kitchen Hoods,”
makes exceptions to the Code’s requirements for commercial kitchen hoods for
construction and exhaust CFM level designs for listed and labeled UL 710 hoods.
The main function of the UL 710 test is for safety of the hood during a fire
condition. The test procedure makes sure that, during a fire condition, the
hood is liquid tight and does not allow the grease to migrate through any of
the joints or seams, which would allow for the fire to follow the same path and
spread outside of the hood canopy.
During the fire condition, the test also monitors the temperature of all
electrical components in the hood to make sure they do not exceed their
temperature ratings during a fire condition. The UL 710 test also has a visual
smoke capture test to verify the minimum exhaust flows that the hood will
capture smoke at during the cooking process for different cooking surface
temperatures.
It is important to remember that the visual smoke capture test is conducted by
the laboratory technician’s eyes. It is also important to note that the test is
conducted in a laboratory condition and the room is balanced to a .-02” SP.
Because it is a controlled environment, the test laboratory’s conditions are
not realistic for what is found in a real-life condition in a kitchen or
servery. The exhaust volumes needed for capture and containment in real life
conditions may be 10% to 200% higher than the listing values needed for
complete capture and containment of the smoke, grease-laden vapors, and
convection heat produced by the cooking process.
In recent years, the performance test used and accepted by the kitchen
ventilation industry to show how well a hood captures is the ASTM 1704-05,
Standard
Test Method for Capture and Containment Performance of Commercial Kitchen
Ventilation Systems. The performance reports for most major hood
manufacturers are published at the Food Service Technology Center’s Web site,
www.fishnick.com. The ASTM 1704-05 test utilizes a Schering camera to be able
to visually see the heat produced by the cooking appliance and if it is
captured by the exhaust hood.
There are five types of UL-listed hoods:
Baffle filter type, which utilizes standard baffle filters
with a grease extraction rating of approximately 28% for 8 microns and larger
particulates. This type of hood has the lowest entry cost, but also gives the
lowest grease extraction of particulate of the available
hoods.
High-efficiency extractor type, which utilizes
high-efficiency grease extractor filters with a grease extraction rating of approximately
90%+ for 8 microns and larger particulates. This type of hood has a mid-level
entry cost, but also gives the highest grease extraction of the available
hoods.
Self-cleaning water wash hoods
with stationary filtration, which have a grease extraction rating of
approximately 60% for 8 microns and larger particulates. This type of hood has
a mid high-level entry cost but is the easiest to maintain.
High-efficiency extractor type, which utilizes
high-efficiency grease extractor filters and UVC lights with a grease
extraction rating of approximately 90%+ for 8 microns and larger particulates.
This type of hood has a high-level entry cost, but with proper maintenance will
keep the exhaust ducts beyond the hood virtually grease-free.
Self-cleaning water wash hoods with stationary filtration and UVC
lights, which have a grease extraction rating of approximately 90%+
for 8 microns and larger particulates. The hood has a self-cleaning feature
that cleans the stationary filtration system and the UVC lights in the exhaust
plenum daily. This type of hood has the highest-level entry cost, but is the
easiest to maintain; just a little maintenance will keep the exhaust ducts
beyond the hood virtually grease-free.
Fire Suppression Options
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| Versatile Utility Distribution System (UDS) and
hood with fire protection during an installation. Photos courtesy of Professional
Foodservice Design, Inc. |
|
The kitchen exhaust hood fire suppression system
is the first defense against fire in a commercial kitchen. Let’s take a quick
look at four options for suppression systems under the
hood.
Appliance specific systems. These cost less and target
specific equipment in a fixed location. They allow the offending piece of
equipment to be doused with a wet chemical, by an appliance-specific nozzle, to
extinguish fire and cool down the equipment and reduce the potential for re-ignition.
Full flood/overlapping systems. These are typically more
costly than appliance-specific systems and have a much larger reservoir of
chemical, which provides a virtual zone of protection under the hood by
overlapping wet chemical dispersion coupled with fusible link detection. They
allow the flexibility of a full flood system because equipment can be moved in
and out for cleaning and exchanged with other equipment as desired. For this
reason, it is the system of choice for many food establishments.
Dual agent systems. These typically use a combination of a
quick-acting liquid chemical (to extinguish) and water (to cool down the area
and diminish the chance of re-ignition). In some cases, the water enhances the
characteristics of the liquid chemical used to extinguish the
fire.
Water mist. NFPA 96 (1998 edition) Chapter 7, “Fire
Extinguishing Equipment,” addresses the use of water mist fire protection.
Notes Section 7-2.2.1, “Automatic fire extinguishing systems shall be installed
in accordance with the terms of their listings, the manufacturer’s
instructions, and the following standards where applicable, (b) NFPA 13
Standard
for Installation of Sprinkler System.” The NFPA 13 4-9.8.2 (1999
edition) or 3-9.8.2 (1996 edition) say the same thing: “A sprinkler or
automatic spray nozzle used for the protection of a deep fat fryer, shall be
listed for that application. The position, arrangement, location, and water
supply for each sprinkler or spray nozzle shall be in accordance with its listing.”
The Dualtech nozzle is UL 199E-listed for use over fryers. The UL 199E testing
follows the same criteria as UL 300, except it is more stringent since it
actually requires a kitchen hood to be mounted over the appliance during the
test, whereas UL 300 does not.
Please note that manual activation is not required for an automatic sprinkler
system, per NFPA 96 (1998), sections 7-5.1 Manual Activation, Exception #2.
NFPA 13 (1999) 4-9.3 and NFPA 13 (1996) 3-9.3, say the same thing as Exception
#2: sprinklers or automatic spray nozzles shall not be required where the
entire exhaust duct is connected to a listed exhaust hood incorporating a
specific duct collar and sprinkler (or automatic spray nozzle) assembly
investigated for protection of unlimited duct length of duct in accordance with
UL 300,
Standard for Fire Extinguishing System for Protection of
Restaurant Cooking Areas. The EA-1-1/4” orifice and 65-degree angle
of discharge has been UL tested to standard UL 300 for the protection’s
unlimited length of duct and listed for this purpose when used with listed mist
systems.
NFPA 96 (1998) accepts listed hoods, per Section 2-4, Listed Hood Assemblies.
“Listed hood assemblies shall be installed in accordance with the terms of
their listing and the manufacturer’s instructions.” The UV hood is UL
710-listed, therefore it is accepted by NFPA 96 (1998).
UL attachments to the building sprinkler system have faced much adversity since
UL 300. Other than very specific open fryers listed for coverage by a Dualtech
nozzle, open fryers can no longer be protected by mist
systems.
At this time, the chemical systems seem to be more design friendly to this
problem.
Pre-Manufactured Raceways
When four or more pieces of equipment are placed
under a ventilator, it makes great sense from an engineering and economic point
of view to have a factory-built raceway as an accessory to your UL-listed hood.
The raceway’s cost will approximate the costs of supplying and installing all
necessary components into the building to tie together the power sources and
fire protection.
Pre-manufactured raceways are considered to be pieces of equipment with a
seven-year depreciation schedule in lieu of a 32-year leasehold improvement
building depreciation when utilities are built into a wall. The raceway can be
custom designed by a food facility consultant or others with an encompassing
perspective on the use and needs of both the equipment and the staff using it.
Flexibility in supplying gas, electric, steam or water is the mantra of a
distribution system. Systems vary by manufacturer and patent in how supply and
connection are accomplished to each piece of under hood equipment. The end
result is minimal expense or effort in moving equipment around under your
hood.
The raceway will come complete with a minimum of the following accessories,
with others being available by request.
- Gas hoses w/quick disconnect
- Water hoses
- Power cords and plugs
- Power supply
- Pressure gauges
- Ball valves for plumbing lines
- Main disconnect w/shunt trip
- Water metering
- Fire protection tie-in.
