Air Conditioning, Inc.
method of distributing heating and cooling throughout a house.
This includes the most popular systems that blow air through
ducts and other systems that use water (e.g., radiant floors and
hot water radiators) and electricity (e.g., baseboard heaters).
Studies by LBNL and other researchers have shown that forced
air systems have the potential for significant energy losses
because of air leaks and their installation outside the heated and
cooled parts of the house. Recent research funded by DOE and
CIEE through LBNL has therefore concentrated on forced air
distribution systems and found that typically a quarter of the
energy (and therefore money) used for heating and cooling is
wasted through duct system energy losses.
to
Residential
Duct
Systems
1. They are installed outside. In many places in the country the
ducts (and the furnace and air conditioning coils) are located in
attics, crawlspaces, garages, basements and other locations
outside the heated or cooled parts of the house. Ducts in these
locations not only leak air to and from outside, but any heat lost
through the walls of the duct (by heat conduction) is also lost to
outside instead of heating and cooling the house. This
combination of air leaks and heat conduction losses means that a
great deal of the energy (and money!) used to heat or cool the
house actually ends up outside. It should be noted that in some
places basements are lived in and are considered part of the
conditioned space of the house. It is also common for these
houses with conditioned basements to have all the ducts, the
furnace and the air conditioner in the basement where any air
leaks or heat conduction losses go to the basement and are
therefore NOT lost to outside. In these cases the energy (and
monetary) penalty for leaks and conduction losses is negligible.
However, systems with lots of leaks will not supply sufficient
heating or cooling to rooms in the house located far from the
furnace or air conditioner, making these rooms uncomfortable for
the occupants. In other words - losses from ducts count, even if
they are not lost directly to outside.
2. They leak. Air leaks in and out of ducts at all the connections
within a system (e.g. at plenums and behind registers). This
leakage means that air that occupants have paid to have heated
or cooled escapes from the heating or cooling system and does
not heat or cool the house. Also, air leaks into the heating or
cooling system increase the amount of outside air that must be
heated or cooled. Outside air is usually cooler (for heating) or
warmer and more humid (for cooling) than air inside the house
and the heating or cooling capacity of the system is then used to
heat or cool this outside air instead of the air in the house. Even
with the heating and cooling system off, the leaks in the ducts
increase the ventilation rate of the house - increasing the need
for heating or cooling. The "leakage" from water and electric
based systems is much rarer due to the somewhat catastrophic
nature of leakage from these systems. In fact, building codes are
extremely sensitive to leakage from water and electric based
systems and there are strict controls regarding construction and
installation of these systems due to the safety problems
associated with their possible failure.
