Page 1
8/11/2019 ASHRAE JOURNAL - Commissioning Kitchens - Making Sure the Equipment Fills the Bill
http://slidepdf.com/reader/full/ashrae-journal-commissioning-kitchens-making-sure-the-equipment-fills-the 1/5
K i tche n Ven t i l a t i on | A Supp l emen t to ASHRAE J ourna l J une 20 03 K23
By Steve Melink, P.E., Member ASHRAE
I n the traditional plan-specification approach to commissioning res-
taurants, the mechanical contractor is responsible for HVAC testing
and balancing (T&B). Because the T&B firm represents the mechanical
contractor instead of the building owner, this approach can result in
finger-pointing between contractor, manufacturer, and engineer. The T&B
firm’s role is weak relative to the other players and to the building owner.
The design-build approach to com-
missioning usually is better for the build-
ing owner. If a problem occurs, the owner
can tell the design-build firm to fix it
without becoming a referee between the
engineer, contractor, and manufacturer.
Unfortunately, most restaurant chains do
not use the design-build approach.
The independent commissioning
model ( Figure 1) is the best approach
based on the author’s experience. By re-
porting directly to the building owner, the
T&B firm is empowered to ensure the
owner receives the HVAC system for which
he paid. When a T&B technician finds a
problem with the design, equipment, or
installation, he can communicate his find-
ings without undue pressure from the en-
gineer, contractor or manufacturer.
Single-Source T&B Firm
Using a single-source T&B firm allows
the engineer to efficiently compare re-
ports from one location to the next, as
well as communicate with the T&B firm
about upcoming changes. A single-
source T&B firm will develop economies
of scale resulting in greater value to the
owner. A T&B firm that approaches a res-
taurant as just another job among a mix
of commercial buildings is less likely to
satisfy the customer.
The certified, independent, and single-
source T&B firm can help the restaurant
chain hone in on the optimal HVAC sys-
tem for its budget. By being the represen-
tative in the field, the firm can provide
invaluable feedback to the engineer. The
T&B firm can document design errors and
omissions that affect installation quality,
document equipment problems so the en-
gineer can decide whether to continue
specifying certain brands and accessories,
and document installation deficiencies so
that the engineer can design these prob-
lems out of the system.
Specifications and Economics
Many engineers use boilerplate speci-
fications for HVAC T&B. These specifi-
cations must suit the restaurant’s needs
so that the scope of work includes only
The following article was published in ASHRAE Journal, June 2003. © Copyright 2003
American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. It is pre-
sented for educational purposes only. This article may not be copied and/or distributed
electronically or in paper form without permission of ASHRAE.
Page 2
8/11/2019 ASHRAE JOURNAL - Commissioning Kitchens - Making Sure the Equipment Fills the Bill
http://slidepdf.com/reader/full/ashrae-journal-commissioning-kitchens-making-sure-the-equipment-fills-the 2/5
K24 J une 2 00 3 Ki t ch en Ve n t i l a t i on | A Sup p l eme n t to ASHRAE Journa l
Flow Hood for Ceiling Diffusers(and Registers When Possible) Vane Anemometer
2 in. from Hood Filters
No
No
Yes
No
No
Yes
Figure 2: Where and how to measure hood airflows.
Owner
A/E MFR GC T&B
MC
Figure 1: Independent commissioning model.
applicable equipment (such as the rooftop air-conditioning
system and kitchen ventilation system).
The T&B firm should quote only on necessary services and
information. For example, duct traverses are good when straight
runs are long enough (i.e., 10 times the equivalent duct diameter)
to make it worth the extra time and cost. However, in restaurantsthe trunks are very short. There is also the issue of drilling into
grease ducts that are supposed to be welded liquid tight. The
additional time and cost to repair the holes to maintain code
compliance makes it even more difficult to justify a duct traverse.
Many restaurant owners try to skimp on test and balance, or
revert to a contractor balance, if
they receive proposals that are
not compelling in value. There-
fore, the engineer and T&B firm
should work together to develop
a scope of work that meets in-
dustry standards and makes eco-nomic sense for the application.
For example, if engineers
specify airflows to be balanced
to within ±5% of design instead
of the normal ±10%, the cost is
significant. In fact, most airflow
measuring devices are accurate
only to within ±10%. Clearly,
specifying ±10% of design
makes more sense.
Unlike laboratories, hospitals,
and commercial aircraft, restau-
rants are not precision-critical
applications. Restaurants are
moving targets. Grease filters
continually load up, doors con-
stantly open and close, and pre-
ventive maintenance is rarely
performed. Restaurant owners do
not want to pay extra for a high
level of precision that is obsolete
as soon as they open their doors.
However, some authorities hav-
ing jurisdiction (AHJ) expect
kitchen exhaust air quantities to
be at or above design, and do not know or care about the accuracy
limitations of air balancing equipment. In these cases, the hoods
should be balanced on the high side to ensure the T&B report is
not rejected. It is more important that a hood is performing well
from a capture and containment standpoint, and not whether it is
measuring at 1,995 cfm vs. 2,005 cfm (942 vs. 946 L/s).
Measuring Airflows
Since it typically does not make sense to perform duct
traverses in restaurants, consider using a simpler and less ex-
pensive method, which is to measure airflows at the terminal
air devices.
Measuring airflows at the terminal air devices (supply dif-
fusers, return grilles, and exhaust hoods) not only avoids drill-
ing and plugging the ducts, it allows for a better understanding
of the complete air distribution picture. While a case could bemade that airflows should be measured in the duct and again at
the terminals to determine if there were any air leakage inside
the duct, this would ignore the existence of short duct runs and
grease ducts in most restaurants. The proactive approach to
minimizing duct air leakage is to specify that all joints be
sealed by the installing contrac-
tor and inspected by the T&B
firm. Additional measuring may
quantify an existing problem
but does not solve it.
If the engineer decides that
measuring total airflow is nec-essary (above and beyond mea-
suring and summing the
individual terminal air devices),
a better way exists than running
duct traverses. Measuring fan
rpm, motor amp draw, and/or
external static pressure provides
enough information to refer to
the fan curve for a given piece
of equipment, and then deter-
mine the cfm. This is a more ex-
pedien t and cost -eff ec tive
method, and is typically more
reliable and accurate than mea-
suring velocities inside a duct
with turbulent airflow.
Supply airflows in a restaurant
should be measured with a flow
hood at each diffuser and regis-
ter ( Figure 2). This is because
no correction factors or calcula-
tions are involved, and thus di-
rect cfm readings are made and
recorded. This also provides a
relatively quick understanding
of how airflows are distributed in a given zone, which dampers
need to be adjusted, and how much the supply fan speed needs
to be increased or decreased.
Exhaust airflows ideally should be measured the same way at
the kitchen hood grease filters. Unfortunately, this is not al-
ways practical due to the size and configuration of the kitchen
hood, as well as interference by fire suppression piping and tall
cooking appliances. Therefore, the next best instrument is a
rotating vane anemometer with an extension handle and spacer
to measure air velocities 2 in. w.c. (500 Pa) from the filter face.
Page 3
8/11/2019 ASHRAE JOURNAL - Commissioning Kitchens - Making Sure the Equipment Fills the Bill
http://slidepdf.com/reader/full/ashrae-journal-commissioning-kitchens-making-sure-the-equipment-fills-the 3/5
K i tche n Ven t i l a t i on | A Supp l emen t to ASHRAE J ourna l J une 20 03 K25
The American Gas Association performed a study several
years ago that determined measuring air velocities at this pre-
scribed distance from most any filter face eliminates the need
for any correction factor. The cfm for each f ilter is calculated
by taking five readings taken per filter and multiplying theaverage air velocity by the net exposed filter area.
At least one hood manufacturer has a pressure port on the
exhaust and supply plenums of its hood, so that a single pres-
sure reading can be taken and referenced to a curve for that
particular hood size to determine air quantities. This is an even
better way than the previous method since no compounding
error is associated with one measurement. In addition, pressure
readings generally are more repeatable than air velocity read-
ings. (It is important that the curves are certifiable or traceable,
and the grease filters are new, clean, and constructed under
relatively tight tolerances.)
After the exhaust and supply airflows are measured and bal-anced to within ±10% of design, the next step is to test the
hoods for proper smoke capture and containment with the cook-
ing appliances turned on. The design typically is a good refer-
ence or starting point, but so many variables exist so it cannot
guarantee the desired end result. For example, it may be neces-
sary to increase the exhaust rate 15% above design due to
supply air diffusers in front of the hood creating air turbu-
lence, resulting in smoke spillage. Hood overhang, hood height,
type of appliances, and the presence or absence of side cur-
tains are some of the other variables that might dictate higher
or lower exhaust rates.In fact, the 2003 International Mechanical Code acknowl-
edges the importance of performance testing kitchen hoods.
Turning on the appliances and using a smoke-generating de-
vice to simulate expected heat and smoke load is now required
to verify the hood will effectively remove cooking effluents
from the kitchen.
Keep in mind that it is as possible for the design air quanti-
ties to be too high as too low. However, one should be careful
about reducing exhaust rate below design because the AHJ
reviewing the T&B report may balk at the numbers. The best
way around this is to have the AHJ witness capture and con-
tainment at the lower exhaust rate and agree to accept the moreefficient hood air balance on the basis of proven performance.
The Commissioning Process
Invariably, all types of def iciencies become apparent during
the initial inspection. The design might not allow transfer air
to move properly into the kitchen; the equipment might be
Advertisement in the print edition formerly in this space.
Page 4
8/11/2019 ASHRAE JOURNAL - Commissioning Kitchens - Making Sure the Equipment Fills the Bill
http://slidepdf.com/reader/full/ashrae-journal-commissioning-kitchens-making-sure-the-equipment-fills-the 4/5
K26 J une 2 00 3 Ki t ch en Ve n t i l a t i on | A Sup p l eme n t to ASHRAE Journa l
missing its outside air intakes; the contractor might have hung
the kitchen hoods too high; and the gas company might be
late in turning gas on to the building. Of course, the number
and type of deficiencies varies significantly with each restau-
rant. The problems should be communicated to the general
contractor immediately so that they can be corrected while the
technician is still there.
Proper scheduling is a key part of commissioning. If the tech-
nician arrives too early or before the mechanical contractor is
finished, then he will probably find more problems and spend
more time on the job. If the technician arrives too late, he may
not give the contractors enough time to correct problems before
the restaurant opens. Frequent status reports from the general
contractor are necessary to ensure a cost-effective T&B service.
If the store is not 100% ready, this does not mean the T&B
technician should reschedule for a return visit. He should take
the test and balance as far as possible. As he starts measuring
airflows, it is likely he will find other problems. Although a
return visit still may be necessary to make final adjustments,
the difference could be a successful store opening vs. a disas-
trous one.
Two scenarios can make for a disastrous opening. First, kitchen
hoods operating improperly can result in smoke spilling into
the kitchen. Second, improper operation of the heating or air-
conditioning systems can result in customer complaints. The
T&B firm must do everything to avoid these possibilities. Ev-
erything else is relatively minor in comparison.
For example, if there is a missing damper, this deficiency
needs to be noted for correction, but is not likely to cause the
restaurant to shut down or suffer major repercussions. Similar
minor problems include a supply fan that has a ¾ hp (0.56 kW)
motor rather than the specified 1 hp (0.75 kW) motor, or a
return duct that has an offset rather than a straight run to the
unit. An experienced T&B technician will focus his energies
so big problems are addressed first. Proper hood capture, a
slightly positive building pressure, and a comfortable dining
room are the essential items when commissioning a restaurant
HVAC system.
Often, restaurants experience a negative building pressure.
Although most restaurants have vestibules, both doors often
are open during busy periods. During the cold weather, out-
side air tends to rush inside, causing discomfort in the areas
between the doors and the hoods.
Commissioning Problems Out of the System
The short-term approach to commissioning problems out of
the system is to view the design and equipment as a constant,
and mainly work with the mechanical contractor to modify the
system as necessary to ensure proper performance for a given
store. An example of this may involve balancing an exhaust
fan at 3,000 cfm (1420 L/s) rather than the design of 2,500 cfm
(1180 L/s) to achieve acceptable hood smoke capture. This
may involve increasing the rooftop unit outside air quantities
from 25% to 30% to prevent a negative building pressure.
The long-term approach is to view the design and equipment
as a variable or work in progress. In other words, the engineer
and T&B firm operate as a team so the lessons learned at one
store can be applied to the design and equipment of the next
Technician measuring hood exhaust (left). Technician adjusting exhaust fan (right).
Page 5
8/11/2019 ASHRAE JOURNAL - Commissioning Kitchens - Making Sure the Equipment Fills the Bill
http://slidepdf.com/reader/full/ashrae-journal-commissioning-kitchens-making-sure-the-equipment-fills-the 5/5
K i tche n Ven t i l a t i on | A Supp l emen t to ASHRAE J ourna l J une 20 03 K27
store. Over time, the HVAC system improves with fewer installa-
tion problems, change orders, balance issues, and complaints
after opening. In the previous example, it may mean relocating
diffusers on the drawings so that the hood can capture properly
at the design of 2,500 cfm (1180 L/s) on future stores.Commissioning should start with the plans and specifica-
tions. For instance, the HVAC system should be designed with
the mechanical contractor in mind. Also, the skill level of the
low bidder’s installers should be considered. Standardizing
the equipment as much as possible can minimize errors such as
installing the wrong fan on the wrong curb. Using rooftop
units rather than split systems wherever possible can minimize
errors associated with improper line sizing and charging. Un-
ambiguous and detailed drawings minimize errors, such as con-
densate traps installed backwards.
One opportunity to improve a system for future applications
includes using automatic multispeed controls, which can savethousands of dollars in fan energy and conditioned air. Exhaust
and makeup fans should not operate at 100% capacity in the
middle of the afternoon when the outside air enthalpy is at a
maximum and the exhaust requirements inside are at a minimum.
Another opportunity is to specify direct drive rather than
belt-drive fans. This improves energy efficiency by eliminat-
ing drive losses and eliminates belt maintenance. Belts are the
notorious weak link in a kitchen ventilation system and most
restaurants do not replace belts until they break. Direct drive
fans and speed controls, i.e., variable-frequency drives, are theway of the future.
Conclusion
Engineers and restaurant owners need professional and ob-
jective advice from the field on how to continuously improve
their HVAC systems. An independent and certified T&B firm is
crucial to filling that need.
The engineer is a key player in the commissioning process.
Feedback from the T&B firm closes the design-construction
loop and allows the engineer to continuously improve the me-
chanical plans and specifications. Errors can be designed out
of the system, and opportunities exist for standardization, re-duced installation labor, improved energy efficiency, and re-
duced maintenance.
Steve Melink, P.E., is president of Melink Corporation in
Cincinnati.
Advertisement in the print edition formerly in this space.