AN-92-16-3
VENTILATION EFFICIENCY AND THERMAL
COMFORT IN COMMERCIAL KITCHENS
J.S. Pekkinen T.H. Takki-Halttunen
Member ASHRAE Associate Member ASHRAE
ABSTRACT TESTING
\ Thermal conditions and indoor air quality of the Testing Setup
working environment in commercial kitchens can be
unsatisfactory. With a properly operating ventilation The operation of various air distribution and exhaust
system, it is possible to raise the level of quality of the methods and their effect on ventilation effectiveness and
indoor climate and, hence, increase working effectiveness thermal comfort were studied under laboratory conditions.
and productivity. The test configuration was built in a special model
This paper presents research that was conducted to kitchen. Two different methods of supplying and four
study thermal comfort and ventilation effectiveness in methods of exhausting air were used. The volume of the
commercial kitchens. Various methods for distributing the model kitchen was approximately 70 m3 (5,900 mm x
supply air and exhausting the kitchen air were investigated 4,000 mm x 2,900 mm).
under laboratory conditions. Ventilation effectiveness was A frying pan and an oven range were used as cooking
examined by marking the air with tracer gas and obser- appliances in the test. Their added average power con-
ving the concentration at different kitchen locations. sumption varied between 6.5 and 6.8 kW. The convective
Thermal conditions were metered with an indoor climate heat developed by the equipment was estimated to be 2.0
analyzer. kW. The convective flow was evaluated to be 280 Lis at
Ventilation effectiveness and contamination removal the lower edge of the hood (2.0 m from the floor)
effectiveness were highest by the cooking appliances when (Pfeiffer and Augustin 1982). Both the exhaust and supply
the supply units were located on the floor. 1he best airflows used during the tests were 360 Lis, which was
thermal conditions were found when the supply air unit 30% higher than the calculated convective flow. The ven-
was placed in the ceiling next to the exhaust hood. tilation rate was 18.5 air changes per hour (ach).
_)/ One ventilation arrangement was also investigated
INTRODUCTION with supply and exhaust airflows at 600 Lis. Six different
air distribution and exhaust combinations were studied. In
Commercial kitchens are working environments that every case the air was introduced to the kitchen with low-
can have indoor air problems. The indoor climate is often velocity supply air units. These units were installed either
unsatisfactory and working conditions can have a sig- on the floor or in the ceiling.
nificant effect on worker comfort and productivity. There were four separate ways for exhausting the air:
Great amounts of impurities (grease, smoke) are
released to the kitchen air during the food preparation 1. Conventional (exhaust-only) hood (3,000 mm long by
process. Excessive heat created by the cooking equipment 2,000 mm wide by 800 mm high-see Figure le).
often causes a major problem in commercial kitchens. The 2. General exhaust from the ceiling, see Figures ld and
impurities and a part of the heat load can be removed lf.
from the kitchen with an efficient ventilation system. 3. Special hood (no. 1) with an air jet to capture the
Airflows used to ventilate commercial kitchens are convective flow (3,000 mm long by 1,200 mm wide
usually excessive. Still, supply and exhaust airflows are by 570 mm high-see Figures la and le).
only two factors affecting ventilation effectiveness or 4. Special hood (no. 2) with a capture air jet (2,000 mm
quality of air in different parts of a kitchen. Besides long by 1,000 mm wide by 570 mm high-see
airflows, local ventilation rates depend on (1) the posi- Figure lb).
tioning of supply and exhaust air units, (2) the efficiency
of the exhaust units, (3) the air distribution method, and Different system variations are presented in Figure 1. It
(4) the temperature difference between the supply and should be noted that no system configuration used tradi-
room air. tional ceiling diffusers for supplying the air.
Jorma S. Pekkinen is director of research and development and Tarja H. Takki-Halttuneo is engineering manager of the Halton
Company, Glasgow, KY.
TiilS PREPRINT IS FOR DISCUSSION PURPOSES ONLY, FOR INCLUSION IN ASHRAE TRANSACTIONS 1992, V. 98, Pt. 1. Not to be reprinted in whole or in part
without written permission of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., 1791 Tullie Circle, NE. Atlanta, GA 30329.
Opinions, finding a, conclualona, or recommendationa expreSBed In this paper are those of the author( a) and do not necessarily reflectthe views of ASH RAE. Written
questions and comments regarding this paper should be received at ASHRAE no later than Feb. 7, 1992.
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A. SPECIAL HOOD l, SUPPLY r:"ROM THE: r:"LOOR
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e:. SPECIAL HOOD I. SUPPLY FROH THE CEILING F'. CiE:NE:RAL EXHAUST, SUP~L Y FROM TME C~ll.lNCi
Figure 1 Model kitchen system variations for supply and exhaust combinations.
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Figure 2 Tracer gas concentration measuring locations.
EXAMINING THE VENTILATION EFFECTIVENESS VENTILATION EFFECTIVENESS
Ventilation effectiveness is the ability of a ventilation
Local Ventilation Rates
system to remove impurities from indoor air:
The model kitchen ventilation rate was studied by E = c.1c, (1)
using a tracer gas technique. The supply air was marked
where
with N 20 (nitrous oxide) tracer gas. Gas concentrations
were followed with a computer-driven data logger in eight
E ventilation effectiveness coefficient(-),
locations (Figure 2). When the steady-state concentration
Ce concentration in exhaust duct (ppm),
was achieved, the tracer gas was shut off. The subsequent
C; average occupant breathing zone concentration
decrease at various locations was observed.
(ppm).
Local ventilation rates were calculated from the
digression curves by dividing the steady-state concentra- Tracer gas was released at the rate of 0.065 Lis through
tion by the area that lies under the curve. An example of a perforated copper ring located on the range. Concentra-
a local ventilation rate measurement is shown in Figure 3 . tions were observed in locations presented in Figure 2.
6Cl ..... ~.
!LPll\.T1 LvaL.'tC ""°'..r1-1s.J c
~ T•&•l4.~ c r~~-~
l h CC>ft.IST1~CZ-. I - > c,am:
c ..........
1WCft -CC
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I
1
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1nua"11n li991 l:S:li!l8 e111zz:e0 IHl:Z9:ea aa:J's:aa
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Figure 3 Example of tracer gas concentration curves.
Examining the Thermal Comfort TABLE 1
Local Ventilation Rates IL/h)
Thermal comfort was measured using an indoor System Location
climate analyur located by the range. Evaluated were 1 2 3 4 5 6 7
thermal radiation, air temperature, air velocity, and
Al 26 23 33 14 28 19 31
humidity. 48 29 30 20 65 15 63
A2
B 25 26 34 16 13 9 25
RESULTS c 21 20 30 8 21 7 14
D 18 22 33 12 20 15 14
E 22 21 19 19 15 14 22
Local ventilation rates that were calculated from the F 21 19 17 13 16 17 12
tracer gas digression curves are presented in Table 1.
System letters (A-F) are presented in Figure 1 and
measuring locations in Figure 2. These results indicate TABLE 2
that Exhaust Effectiveness Factors
System Exhaust duct 1 Exhaust duct 2
supplying air from the floor (systems A, B, C, and
D) generally leads to higher local ventilation rates Al 126 12
B 66 50
than with ceiling distribution, and c 35 19
increasing the exhaust airflow by 1. 7 times (system D 8 5
E 8 3
A2) did not affect the individual local ventilation F 2 2 ,I
rates in the same ratio.
Results of exhaust effectiveness metering are shown Distributing supply air from units located on the floor
in Table 2. These results indicate that leads to better ventilation efficiency than with supply units
in the ceiling. An unwanted result with this installation is
generally, the concentrations were higher by the hood a vertical temperature gradient.
edge and near the ceiling than in the occupancy zone, Distributing air from the ceiling near the hood with
and low air velocity provides local cooling that is a necessity
concentrations with a conventional hood and general because of the strong radiant heat created by cooking
exhaust were much higher near the ceiling than with appliances. Increased airflows did not raise metered
the special hoods. indicators at the same ratio, which proves that good
results in kitchen ventilation can be achieved with careful
Comparing the results of metering thermal comfort design and efficient equipment without excessive airflows.
with the various installations was difficult. Heat accumu- Based on the results of the study, the following are
IAted by the surrounding struc.tures could not be measured some basic principles of commercial kitchen ventilation.
or considered in results for different examination days.
Some factors can be noted: 1. Impurities and excess heat should be removed with
efficient local exhaust.
greater airflows did not noticeably affect indicators of 2. Supply air, at the correct temperature, should be
thermal comfort; brought to the working area in such a way that it first
air velocity in the working zone (by the range) was refreshes workers and then replaces convective flows.
highest with supply air units located in the ceiling, 3. In cases where workers are subjected to large heat
which provides necessary local cooling. radiation, supply air should be introduced directly to
the working space (local cooling).
CONCLUSIONS 4. The permitted supply air velocity varies in different
kitchen areas between 0.3 and 0.5 mis. Velocity for
This study showed that the best results in ventilation local cooling can be as high as 0.8 mis with a supply
effectiveness and thermal comfort were not achieved with air temperature of 18°C.
the same exhaust and supply air system configuration. The 5. In addition to local exhaust, general exhaust is
main purposes of commercial kitchen ventilation are required. General exhaust should be at least 10 % of
removal of odors and removal of grease from exhaust air the total kitchen exhaust flow.
and providing thermal comfort to the workers in the
kitchen. Usina: effective hoods, the main criterion of REFERENCE
design should be thermal comfort because the airflow
rates are adequate to provide satisfactory air quality in the Pfeiffer, W., and S. Augustin. 1982. Absaugluftmengen
breathing zone. This is due to the extreme working con- von Erfassungseinrichtungen offener Bauart. Staub-
ditions, especially near the cooking appliances. Reinhalt. Luft 42(8).
