©2018 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 60, no. 11, November 2018.
By Toshiya Iwamatsu, Ph.D., Associate Member ASHRAE; Wataru Urabe
About the Authors
Toshiya Iwamatsu, Ph.D., and Wataru Urabe are research scientists in the Energy Innovation Center (ENIC) at the Central Research Institute of Electric Power Industry (CRIEPI), Kanagawa, Japan.
In commercial kitchens, there are two types of exhaust hoods: wall-mounted hoods and island hoods. In general, the ventilation requirements of island hoods are larger than that of wall-mounted hoods. According to ASHRAE Standard 154-2011, the ventilation requirements for medium duty cooking appliances are about 1.7 times larger than that of wall-mounted hoods. VDI 2052 also describes the ratio of the ventilation requirements between wall-mounted hoods and single island hoods. The ventilation requirements of island hoods are 1.6 times larger than that of wall-mounted hoods.
On the other hand, in Japan, the face velocity of 60 fpm (0.3 m/s) at the exhaust hood opening is usually adopted as the typical ventilation rate for commercial kitchens. There is no distinction between the ventilation requirements of wall-mounted hoods and single island hoods in the Japanese conventional ventilation design guideline.
In general, the thermal plume from cooking appliances is expanded by the airflow derived from cooking behavior and the supply of air conditioners. In the case of single island hoods, the expanded thermal plume due to the air disturbance from cooking appliances easily strays from the exhaust hoods compared to that in the case of wall-mounted hoods, because there is no wall behind the cooking appliances. However, the ventilation requirements described in both ASHRAE Standard 154-2011 and VDI 2052 do not seem to consider the influence of air disturbance in commercial kitchens.
Therefore, this study investigates the ventilation requirements for electric cooking appliances installed under wall-mounted hoods and single island hoods in an environment with air disturbance.
Method to Estimate the Ventilation Requirements of Exhaust Hoods
The definition of ventilation requirements for exhaust hoods in this study is the same as that in our previous research. The ventilation requirements of exhaust hoods should be sufficient to adequately exclude heat, moisture, and effluents from cooking appliances, such that the thermal environment and air quality are maintained. When the capture efficiency is too low to exclude the thermal plume, problems occur, such as condensation on the external surface of exhaust hoods and deterioration of the thermal environment in the kitchen. In particular, the release of carbon monoxide following the incomplete combustion of fuel is problematic in that it is toxic to the occupants of the kitchen. This means that the ventilation rate is sufficiently large to completely exclude the thermal plumes from cooking appliances. However, electric cooking appliances do not produce combustion pollutants. Therefore, a minor leakage of the thermal plume from an exhaust hood can be acceptable in adequately air-conditioned kitchens. The necessary and sufficient capture efficiency for electric cooking appliances is not revealed; therefore, a threshold capture efficiency of 90% is assumed. The measured data were interpolated to estimate the ventilation rate when the capture efficiency approached the threshold. The ventilation rate at a capture efficiency of 90% was defined as the ventilation requirement in this study.
Read the Full Article
ASHRAE Members have free access to the full-text PDF of this article as well as the complete ASHRAE Journal archives back to 1997 in the Free Member Access Area.
Non-members can purchase features from the ASHRAE Bookstore. Or, Join ASHRAE!
Return to Featured Article Excerpts
Return to ASHRAE Journal Featured Article Excerpts