ASHRAE Journal - November 2014 - 13

TECHNICAL FEATURE

to (°F)

The goal of this article is to discuss
the new Standard 90.1 requirements in context with designing
energy efficient CKV systems that
strive to improve comfort conditions in kitchens. Complementary
to this article is a publication by
the Department of Energy, which
also reviews the requirements in
Standard 90.1 for kitchen exhaust.6
Readers are invited to download
PHOTO 1 Laboratory setup for applying the "Mixed-Duty Appliance Line" for ASTM 1704 (with and without side
panels).9
this publication as a complement
to our perspective on high-performance CKV systems.
97
And just what does "high performance" mean with
Zones:
Cooking
Dishwashing
Preparation
93
respect to a CKV system? We believe that it means a sys90
tem where the exhaust hood completely captures and
86
82
contains cooking effluent, where the associated noise
79
levels and energy costs are minimized, and where ther75
mal comfort in the kitchen is consistent with good engi72
neering practices and workplace standards. The format
68
we have chosen for this article is to copy the appropriate
64
sections in Standard 90.1 (shown in italics), followed by
61
our interpretation and supporting industry informa57
Casual
Institutional
QSR
tion. In some cases, we also have paraphrased rational
that was included in the foreword to the public review
FIGURE 1 Average of operative temperature for kitchen type and kitchen zones
with 95% confidence interval (100 kitchens).5
draft of this addendum as it no longer resides within the
Standard.
of makeup air introduced into the hood reservoir
6.5.7.1 Commercial Kitchen Exhaust Systems
required a proportional increase in the exhaust rate
6.5.7.1.1 Replacement air introduced directly into the hood
to maintain C&C. Anecdotally, this has been referred
cavity of kitchen exhaust hoods shall not exceed 10% of the hood
to as the "bathtub" effect, where the size of the drain
exhaust airflow rate.
[exhaust collar] must to be large enough to accommoThis first requirement ends the practice of specifydate all water pouring into the tub [hood]; otherwise
ing short-circuit hoods, where large percentages (up
the tub overflows [spills].
to 80%) of the replacement (makeup) air is introduced
While the 10% value from this research (stated earlier)
directly into the hood reservoir. Research conducted by
coincides with the 10% maximum stated in 6.5.7.1.1,
the authors7 confirmed the hypothesis that air introanother reason to permit 10% of the replacement air
duced directly into the hood cavity competes directly
requirement to be supplied directly into the hood cavwith the thermal plume rising from the cooking equipity is to allow what can be described as "high-velocity,
ment, thus requiring an exhaust rate that is higher than
low-flow" air curtains. This is a design feature of some
that needed to capture and contain (C&C) this thermal
manufacturers that has been incorporated around the
plume by itself. Laboratory tests under various coninside perimeter of hoods to enhance capture and configurations of appliances and hoods demonstrated that
tainment by essentially extending the lower edge of the
when the volume of short-circuit air exceeded 10% of
hood. As such hoods may be interpreted as a short-cirthe exhaust airflow, the hood would fail to capture and
cuit design by the AHJ, the threshold limit of 10% clearly
contain. From that point on, any increase in the quantity
permits the specification of these hoods.
N OVEM BER 2014

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ASHRAE Journal - November 2014

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