Curbing Your Consumption:
Q: Should I buy a DC furnace fan?
By John Ford
People who want to circulate air in their homes even when the furnace
or air-conditioning is off often install two speed or variable speed
fans in their furnace. Running a fan continuously gives some
advantages to comfort especially in homes with variances in heat loss
as it evens out the temperature. Multi-speed fans can run quieter
since they run longer at slower speeds.
Fans require energy however, so how you intend to use it should be a
factor in what type of fan to buy. There are a few choices:
traditional AC induction motor (PSC) with two speeds, variable speed
AC (SCIM and SRM), and variable speed DC (ECM). variable speed motors
are more efficient than single or dual speed motors, but the
controller is typically on all the time. Compared to a standard single
speed AC induction motor , a high efficiency PSC can save 14%, an ECM
25%, and a variable speed ECM 75%. If you intend only to use lower
speeds for a small number of months or weeks of the year, it may not
be cost effective to pick a variable speed motor which has an always
on controller and costs more to buy.
If you are a heavy user of air-conditioning, keep in mind that
inefficient motors give off that energy not used as heat, which
creates a bigger load on your A/C (and more cost). An inefficient
blower motor could be the equivalent of running a 200 watt heater
inside your air-conditioner. That's the same reason a newer, and more
efficient refrigerator will also lower your A/C costs. An old fridge
could be putting out 500 watts in the form of heat into your kitchen
which then requires 1000 watts of A/C to cool.
Before you make your decision, speak to your heating and cooling
company and compare the numbers for the available options based on
your own usage patterns.
Ask the Miser
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John Ford is a technology consultant, and owner of a small energy