The purpose of supplying outdoor air is to replenish the oxygen (O 2) content of the indoor space which is being converted into carbon dioxide (CO 2) by the occupants in the space and also to dilute pollutants generated in the space. CFM per square foot (area) of the spaceĬFM per Person is used in most commercial building applications.Ventilation (outdoor) Air requirements are determined using one or more of the following methods. Exfiltration amount is small and usually neglected in HVAC calculations. Since commercial buildings are pressurized, the air flow leakage is from the inside to the outside. The natural air flow direction is therefore from inside to outside. In summer the air inside is colder (air-conditioned) and therefore denser (heavier) than the hotter air outside.
#DOES THE FURNACE EFFECT STACK WITH CUBE WINDOWS#
Commercial air-conditioned buildings are designed to be air-tight (the windows cannot be opened) and pressurized. In the case of high-rise buildings the stack effect also causes infiltrationĮxfiltration Air refers to the flow of indoor air from an enclosed building space to the outdoors. It depends on wind velocity, wind direction and the air-tightness of the building envelope. Infiltration occurs mainly in winter when the air outside is colder and heavier than the air inside. The outdoor air entering through open doors and windows is considered infiltration although the purpose of opening the door or window might be ventilation. Infiltration occurs through cracks in the building envelope and due to pressure differences between inside and outside. Infiltration Air is the unintentional and uncontrolled entry of outdoor air into an enclosed space. The total air supplied to a space consisting of outdoor air and indoor recirculation air is not ventilation air either. The entry of outdoor air through an open door or window is considered infiltration and not ventilation. Ventilation is provided using mechanical systems such as fans. It is the intentional controlled introduction of outdoor air into an enclosed occupied space. In modern commercial buildings, the term ventilation refers to mechanical ventilation. Ventilation Air can be natural or mechanical. In the case of industrial applications, the outdoor air quantity also depends mainly on the amount of pollutants generated in the space. For example, 20 cubic feet per minute (CFM) per person. For a typical office building, the outdoor air supply quantity is determined on the basis of the number of occupants and process pollution. Indoor air must therefore be cleaned and it's oxygen content maintained by adding outdoor air. Indoor Air in an enclosed occupied space loses it's oxygen due to the occupants and it can also be contaminated from within the space with organisms such as bacteria and viruses and with pollutants from the processes that occur in the space. The outdoor air must be cleaned and filtered before it is supplied. The oxygen level in an enclosed occupied space must therefore be replenished by supplying outdoor air. People breathe in oxygen and breathe out carbon dioxide. Nitrogen and the other gases are inert and not harmful to animal life. People and all animal life need oxygen to live. Outdoor Air is assumed to be fresh, clean air made up of the right combination of oxygen (21%), nitrogen (78%), and other gases (1% hydrogen, argon, carbon dioxide, water vapor).
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