ASHRAE JOURNAL - Commissioning Kitchens - Making Sure the Equipment Fills the Bill

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.



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.




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.



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).




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.

Documents

ASHRAE JOURNAL - Commissioning Kitchens - Making Sure the Equipment Fills the Bill