Commercial Kitchen Ventilation Systems. The
commercial kitchen is a unique space where many different HVAC applications
take place within a single environment. Exhaust, supply, transfer,
refrigeration, building pressurisation and air conditioning all must be
considered in the design of most commercial kitchens. It is obvious that the
main activity in the commercial kitchen is the cooking process. This activity
generates heat and effluent that must be captured and exhausted from the space
in order to control odour and thermal comfort. The kitchen supply air, whether
mechanical or transfer or a combination of both, should be of an amount that
creates a small negative pressure in the kitchen space. This will avoid odours
and contaminated air escaping into surrounding areas. Therefore the correct
exhaust air flow quantity is fundamental to ensure good system operation,
thermal comfort and improved IAQ. Similar considerations should be given to
washing-up, food preparation and serving areas.
Initial Design Considerations
The modes of heat gain in a space may include
solar radiation and heat transfer through the construction together with heat
generated by occupants, lights and appliances and miscellaneous heat gains as
air infiltration should also be considered. Sensible heat (or dry heat) is
directly added to the conditioned space by conduction, convection and radiation.
Latent heat gain occurs when moisture is added to the space (e.g., from vapour
emitted by the cooking process, equipment and occupants). Space heat gain by
radiation is not immediate. Radiant energy must first be absorbed by the
surfaces that enclose the space (walls, floor, and ceiling) and by the objects
in the space (furniture, people, etc.). As soon as these surfaces and objects
become warmer than the space air, some of the heat is transferred to the air
in the space by convection (see picture 2). To
calculate a space cooling load, detailed building design information and
weather data at selected design conditions are required. Generally, the
following information is required:
• building characteristics
• configuration (e.g, building location)
• outdoor design conditions
• indoor design conditions
• operating schedules
• date and time of day
Heat Gain and Emissions Inside
the Kitchen
Cooking can be described as a process that adds
heat to food. As heat is applied to the food, effluent (1) is released into the
surrounding environment. This effluent release includes water vapour, organic
material released from the food itself, and heat that was not absorbed by the
food being cooked. Often, when pre-cooked food is reheated, a reduced amount of
effluent is released, but water vapour is still emitted into the to the
surrounding space. The hot cooking surface (or fluid, such as oil) and products
create thermal air currents (called a thermal plume) that are received or
captured by the hood and then exhausted. If this thermal plume is not totally
captured and contained by the hood, they become a
heat load to the space. There are numerous secondary sources of heat in the
kitchen (such as lighting, people, and hot meals) that contribute to the
cooling load as presented in table 1.
Load
|
W
|
Lighting
|
21 - 54/ m2
|
People
|
130/person
|
Hot meal
|
15/meal
|
Cooking eq.
|
Varies
|
Refrigeration
|
Varies
|
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