![]() This is accomplished by adjusting the outside air dampers so they are open slightly more than the exhaust air dampers. To prevent infiltration, a building is kept at a slightly positive air pressure. This infiltrating air is unfiltered and untreated. Infiltration air leaks into a building from the outside, such as through doors and cracks around windows. Low bypass factors are found on high latent heat applications, such as those found in restaurants (especially cooking areas) and bowling alleys.īuilding air pressure is normally between 0.03 to 0.05 in. High bypass factors are normally found on heat pumps in the heating cycle, and on high sensible heat applications like computer room systems. The higher the air speed in fpm, the higher the bypass factor. This is the average percentage of air that bypasses or fails to come into contact with the evaporator as it passes through the evaporator. Bypass air should be at a rate of 0.1 to 0.35, or 10% to 35%.Terminal velocities are the velocities at the end of the run, such as registers or diffusers, where the air enters a room. ![]() Speeds slower than 400 fpm may cause the evaporator to freeze over. Speeds faster than these may cause condensation to be blown off of the evaporator fins and down the duct. These are the recommended velocities for coils.
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