"Nehmo" wrote in message
...
If a house currently has multiple window air-conditioners,
are these
significantly less efficient than central air, if the house
were
retrofitted with it?

Window AC's typically 10 to 12 SEER (Seasonal Energy
Efficiency).. 12 is not bad... 10 is not so hot.

You can buy central AC's at 14 Seer thats hot.

However there are losses with duct work in a central AC that
you dont have in window AC. (depending on duct leaks etc etc.
in the 5 to 10% range...not so good actually)


Window AC's are dirt cheap to install compared to central AC's
and provide good 'zone control' so can be a lot less expensive
to operate than central AC

Home resale will be better with central AC of course.


I realize the comparison is complicated, so assume all other
factors
equal, and assume: the vents and their position for central
air would be
adequate; about half the rooms are normally in use; nobody's
concerned
about the window-view obstruction, etc.; Chicago climate;
poorly
insulated house.

A companion question is, does the efficiency of air
conditioners
increase significantly with size?

No..efficiency goes down with size because its running
partially loaded most of the time. The window AC's will be
most cost effective across the boards especially if you buy
the high efficiency models (and go to heat pump window
AC's)... zone control is a major advantage with multiple
window AC's

Phil Scott
HVAC contractor/ mech engr since 1905



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