Heating and Cooling Info From Warmair.net
System Design Considerations
The first thing to determine when designing a central heating and cooling
system is whether it will primarily be a heating or a cooling
system. This may sound ridiculous at first, but here's what it
means. A system installed in a house in Florida is primarily a
cooling system, while a system installed in Vermont will be a
heating system. The systems will supply both heating and cooling
according to the season, but will operate most of the time in
the primary mode due to the length and extremes of their particular
climate.
There are many more days in Vermont that require heating than cooling, and
vice versa for Florida. The reason for determining the type of
system is based on the reasoning that one system cannot effectively
supply both heating and cooling through the same ductwork. The
demands of certain rooms for heating cfm can vary significantly
from that same room's cooling cfm needs even when different blower
speeds are factored into the equation. The heat loss for a room
peaks at the coldest hour of the day, which is in the early morning
darkness, while the heat load for that same room reaches its peak
in the mid-afternoon sun. The contribution of solar radiation
throws a wrench into the formula and disconnects the calculations
from a pure temperature driven equation.
A window which faces west will gain more heat in the afternoon than a window
facing north, but a window facing west will not lose more heat
than the same size window facing north. If delivered enough air
to that room to meet the peak heat gain requirement during the
cooling cycle, the room will receive too much air flow, and therefore
too much heat during the heating cycle. This condition is acceptable
if the system is primarily a cooling system with only minor time
periods spent in the heating mode, but if the system is operating
in the heating mode most of the time, the occupants will not be
comfortable. This system should be designed on its heat loss figures.
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