ASHRAE Journal - November 2014 - 16

TECHNICAL FEATURE

16

ASHRAE JOURNAL

ashrae.org

N OVEM BER 2014

Generic Hood
Max Overhang
Manufacturer 1
Manufacturer 2
Manufacturer 3
Manufacturer 4
Manufacturer 5
Manufacturer 6
Manufacturer 7
Manufacturer 8

5,000
Capture and Containment Exhaust Airflow Rate (cfm)

accordance with ASTM 1704. In the first set of data
the hoods are without side panels while in the second
set the hoods have partial side panels. The generic
unlisted hood did not include any of the performance
enhancing features that the high-performance hoods
incorporated (e.g., flow-enhancing flanges). Figure 2
shows that the capture and containment exhaust airflow rate for all eight of the high-performance hoods
are at or below the maximum limit of 280 cfm per
linear foot of hood (2,800 cfm total) set in Standard
90.1. The variations in the C&C exhaust rates are due
to the differences in individual hood designs. Note that
the generic hood exceeded the maximum and that
Manufacturer 8's hood was at the limit for the condition without side panels (due to convective spill from
the side of the hood). However, in both cases, the addition of side panels reduced the exhaust rate below the
threshold. The bottom line is that many listed hoods
will meet the Standard 90.1 exhaust rate requirements
for wall-canopy hoods based on both UL 710 listings
and ASTM F1704 performance testing. Note, however,
that the UL 710 listing "cfm" numbers must be met in
cases where the ASMT F1704 "cfm" values are lower.
The same may not be said for the specification of single-island hoods operating over heavy-duty appliances,
which are typically being used for exhibition cooking
stations in modern food service facilities. The strong
effluent plume that is generated by the heavy-duty
appliances is very susceptible to cross drafts, reduced
overhang and high-velocity makeup air introduction.
As a result, the exhaust airflow rates required to capture
and contain such thermal plumes increased significantly. ASHRAE RP-1480, Island Hood Energy Consumption
and Energy Consumption Strategies,12 explored the C&C
exhaust airflow rates for single-island canopy hoods.
One style of island canopy hood (10 ft by 4 ft [3 m by 1.2
m]) had the filter bank along the rear of the hood while
the second style of hood (10 ft by 6 ft [3 m by 1.8 m]) had
a V-bank down the center of the hood. The replacement
air was supplied through 14 floor-mounted displacement diffusers to emulate transfer air from adjoining
spaces and provide a low-velocity air supply, which has
been proven to minimize the influence of replacement air
on hood performance. The results are shown in Figure 3.
The difficulty in capture and containment is evident
by the high exhaust airflow rates. While side panels
mitigate some of the cross drafts and improve C&C

4,000

ASHRAE Standard 90.1
280 cfm/ft

3,000

2,000

1,000

0

Combination-Duty Line-Broiler

Combination-Duty Line w/
Side Panels-Broiler

FIGURE 2 Published manufacturers' ASTM test data for the C&C exhaust airflow
rates for a 10 ft (3 m) wall-mounted canopy hood over a heavy-duty
appliance line.

performance, the data show that it is very difficult for
single-island canopy hoods to stay below the 420 cfm/
ft (650 L/s·m) limit imposed by Standard 90.1. However,
it is important to note that the data in Figure 3 is for
generic, unlisted hoods. Unfortunately, not many manufacturers have used ASTM F1704 to report airflow rates
for high-performance island hoods. Our message to the
design engineer: Proceed with caution!
6.5.7.1.4 If a kitchen/dining facility has a total kitchen hood
exhaust airflow rate greater than 5,000 cfm then it shall have one
of the following:
a) At least 50% of all replacement air is transfer air that would
otherwise be exhausted.
b) Demand ventilation system(s) on at least 75% of the exhaust
air. Such systems shall be capable of at least 50% reduction in
exhaust and replacement air system airflow rates, including controls necessary to modulate airflow in response to appliance operation and to maintain full capture and containment of smoke,
effluent and combustion products during cooking and idle.
c) Listed energy recovery devices with a sensible heat recovery
effectiveness of not less than 40% on at least 50% of the total
exhaust airflow.

6.5.7.1.4 Maximizing Transfer Air
The replacement air required for commercial kitchen
ventilation systems is always 100% of the exhaust air;



ASHRAE Journal - November 2014

Table of Contents for the Digital Edition of ASHRAE Journal - November 2014

Contents
ASHRAE Journal - November 2014 - Cover1
ASHRAE Journal - November 2014 - Cover2
ASHRAE Journal - November 2014 - 1
ASHRAE Journal - November 2014 - 2
ASHRAE Journal - November 2014 - Contents
ASHRAE Journal - November 2014 - 4
ASHRAE Journal - November 2014 - 5
ASHRAE Journal - November 2014 - 6
ASHRAE Journal - November 2014 - 7
ASHRAE Journal - November 2014 - 8
ASHRAE Journal - November 2014 - 9
ASHRAE Journal - November 2014 - 10
ASHRAE Journal - November 2014 - 11
ASHRAE Journal - November 2014 - 12
ASHRAE Journal - November 2014 - 13
ASHRAE Journal - November 2014 - 14
ASHRAE Journal - November 2014 - 15
ASHRAE Journal - November 2014 - 16
ASHRAE Journal - November 2014 - 17
ASHRAE Journal - November 2014 - 18
ASHRAE Journal - November 2014 - 19
ASHRAE Journal - November 2014 - 20
ASHRAE Journal - November 2014 - 21
ASHRAE Journal - November 2014 - 22
ASHRAE Journal - November 2014 - 23
ASHRAE Journal - November 2014 - 24
ASHRAE Journal - November 2014 - 25
ASHRAE Journal - November 2014 - 26
ASHRAE Journal - November 2014 - 27
ASHRAE Journal - November 2014 - 28
ASHRAE Journal - November 2014 - 29
ASHRAE Journal - November 2014 - 30
ASHRAE Journal - November 2014 - 31
ASHRAE Journal - November 2014 - 32
ASHRAE Journal - November 2014 - 33
ASHRAE Journal - November 2014 - 34
ASHRAE Journal - November 2014 - 35
ASHRAE Journal - November 2014 - 36
ASHRAE Journal - November 2014 - 37
ASHRAE Journal - November 2014 - 38
ASHRAE Journal - November 2014 - 39
ASHRAE Journal - November 2014 - 40
ASHRAE Journal - November 2014 - 41
ASHRAE Journal - November 2014 - 42
ASHRAE Journal - November 2014 - 43
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ASHRAE Journal - November 2014 - 45
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ASHRAE Journal - November 2014 - 49
ASHRAE Journal - November 2014 - 50
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ASHRAE Journal - November 2014 - 54
ASHRAE Journal - November 2014 - 55
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ASHRAE Journal - November 2014 - 58
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ASHRAE Journal - November 2014 - Cover3
ASHRAE Journal - November 2014 - Cover4
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