ASHRAE Journal - November 2014 - 22

TECHNICAL FEATURE

to move from "best practice" to "standard practice"
within the design of commercial kitchens.1
It is important to recognize that not all CKV systems
can be operated at 50% of design flow when appliances
are in an idle or ready-to-cook mode (regardless of the
control system installed). This is due to the fact that
some cooking appliances, such as under-fired charbroilers, exhibit a thermal plume under "ready-to-cook"
conditions that is almost as aggressive as the plume generated by the cooking activity. But there is also the condition (of hood operation) when several appliances have
been turned off (including the charbroiler) yet operation of the hood must be maintained (for one appliance
remaining on or during the cool-down and cleanup
periods). In such cases, it may be feasible to reduce the
exhaust rate to the 50% level without repercussion. The
question for the designer is which DCKV systems on the
market can be responsive to this operating scenario and
be in compliance with the Standard 90.1 requirement?

6.5.7.1.4 Energy Recovery
The third option in Section 6.5.7.1.4 recognizes listed
air-to-air energy recovery equipment (also referred to a
heat recovery ventilation or HRV) as a compliance path
for 90.1. Thermodynamically, exhaust air heat recovery
from kitchen ventilation is very attractive. In practice,
however, this waste heat stream is challenged by the fact
that the exhaust air is grease laden and subject to NFPA
96 jurisdiction, potentially requiring fire protection
and/or wash down systems. Consequently, these systems
are more expensive to install ($/cfm) than other HRV
applications, challenging the ROI equation. There also
is a conflict with Section 514.2 of the IMC that does not
permit HRVs in kitchen exhaust. However, there is now
an exception stating "that ERV equipment is not limited
by this code section if such equipment recovers only sensible heat and utilizes only coil-type heat exchangers."
This would allow loop or "runaround coil" type energy
recovery systems for kitchen exhaust.
One positive attribute of this HRV application is the
typical unbalanced flow condition (i.e., more exhaust
than supply air). This inherently increases the thermal effectiveness of the HRV. If applied in combination with a DCKV system, the effectiveness further
increases under part-load (reduced airflow) conditions.
The elevated exhaust air temperatures combined with
the unbalanced flow condition makes heat exchanger
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frosting unlikely. (Heat exchanger frosting or freezing
is an issue in cold climates and a defrost strategy often
required.) The unbalanced flow conditions also make
meeting the 40% effectiveness threshold very attainable
with a runaround-coil style heat recovery system.
The DOE article6 states that DCKV will be a more economically attractive option than heat recovery for 90.1
compliance. We agree. However, the combination of a
DCKV system with an HRV may completely eliminate the
need for makeup air heating-a definite attribute for a
LEED building design and the future of CKV energy efficiency. We hope that further research and case studies
will build a much needed knowledge base for the HRV
potential in CKV design.
6.5.7.1.5 Performance Testing: An approved field test method
shall be used to evaluate design air flow rates and demonstrate
proper capture and containment performance of installed commercial kitchen exhaust systems. Where demand ventilation systems are utilized to meet 6.5.7.1.4, additional performance testing
shall be required to demonstrate proper capture and containment
at minimum airflow.
This section is fundamental to the kitchen exhaust
system commissioning and performance verification
that protects public health and safety. Hood systems
are a field assembly of various components including
hoods, fans, replacement air systems, duct and distribution systems and require testing, once installed, to
ensure specified system performance is met. This section requires verification of hood system performance
and operation, and supports Standard 90.1 purpose
and scope.
The evaluation of design airflow rates can be determined by applying ASTM F2975 Standard Test Method
for Measuring the Field Performance of Commercial Kitchen
Ventilation Systems.15 Protocols have been developed
within the standard to measure velocities and apply
correction factors to determine exhaust and makeup
airflow rates.
An approved field test method used to demonstrate
capture and containment performance can be found in
ASHRAE Standard 154-2003 Ventilation for Commercial Cooking
Operations, Section 4.8.2, Type I Hood Capture and Containment
Test. In that, it describes a field test where all the appliances
under the hood are at operating temperatures, all sources
of outdoor air providing makeup air for the hood are operating, and all sources for the recirculated air providing
conditioning for the space are operating.

ASHRAE Journal - November 2014

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