Heating and Cooling Info From Warmair.net
Return Systems
Imagine heat as a red balloon filled with helium. When you walk through a house,
you would see them collect on the ceiling, peaks of vaulted ceilings,
and upper corners of the room if there is no air turbulence or
drafts. When given the chance, they will drift up open stairways,
for they seek the highest perch.
Heat is a balloon without the plastic wrapper, and where it collects it
exerts a pressure on the surface of the ceiling. The amount of
pressure depends on the difference in temperature between the
inside and outside of the space. The pressure is also greater
than the 68 degrees F used for the heat loss calculation. When
the outdoor temp is 5 degrees F, the difference between inside
and outside can reach 100 degrees F. Just ask any painter who's
had to work on an 8-foot ladder or scaffold. This resulting difference
is almost 50% greater than that calculated, so the ceiling is
losing one and a half times as much heat as calculated.
In multi-level structures, the flow of heat up stairways and through the first
floor ceilings reduces the requirements of the second floor while
increasing the demand on the first floor for heat. On any level,
the collecting points for these "red balloons" become good locations
for return air intakes. Returning the heat increases the efficiency
of the system and reduces the loss to the outside. During the
cooling season, the high returns relieve the stratification that
can develop as cool air tries to settle on the floor. As all supplies
and returns create drafts, high returns will have the least impact
on occupant comfort and increase system efficiency.
Copyright © 1999 Warmair.com, Inc.
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