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Frequently Asked
Questions about FanHandler operation
If you have
questions of your own, please call us at 877-414-2169
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Why change the operation of a
machine that was carefully designed to do a specific job so that it
no longer runs the way the designer intended?
First, we are not operating it contrary
to the design intent. The design of any A/C system is to meet maximum
load conditions. A three-ton system sold by a major manufacturer has to
meet the heat and humidity conditions found in the Florida Keys, the
altitude, heat and dry conditions of Mesa, Arizona, the damp,
cool conditions of the Oregon coast, the cottonwood & milkweed seeds and
mosquitoes of Minnesota and every natural condition on either side of
these. The same machine has to stand up to the unnatural forces of
misapplication, dirty coils, improper installation, poor service, low
refrigerant, overcharge, over sizing, under sizing, mold, mildew,
improper pan drainage, setting the thermostat up and down and many other
human factors. Because of these widely varying conditions, the system
has to be way over built. That is why there has been so much
increase in fan top speeds over the years.
Heat gains of homes do not fit neatly
into 2.5 ton, 3 ton, or 5 ton slots. The sizing is an approximation of
the maximum load conditions. Maximum load condition happens maybe 10% of
the time in Florida and maybe 1% of the time in Northern Michigan. At
all other times the overbuilt unit is also oversized. So the answer to
the question is: The HVAC system is designed for worst-case conditions.
The FanHandler is designed to fine-tune the HVAC system for the
intermediate conditions that are present most of the time.
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How does the FanHandler control the
motor’s speed? If you simply cut the voltage the amperage goes way
high and the motor will burn out.
I’ll answer the second
part first. This is true with a split phase motor found on belt
drive blowers. Even those can be modulated a little bit. Usually the
reason why this statement is correct is that the questioner is
thinking in terms of no change in load. Of course if you cut voltage
and do not change the load, you’ll burn out the motor.
We control the motor’s speed through
phase control. This means
clipping the sine wave both above and below the zero line. The very
critical aspect here is that the FanHandler cuts the sine wave at
exactly the same voltage above the zero as it is below. If you do not do
this precisely, you end up with a direct current component to the AC
signal. AC to an induction motor drives it forward and a DC component
acts as a brake. (The way big screw machines and lathes are stopped is
to hit them with DC; they stop within a few revolutions.) DC in our
application will cause heat and burn up the motor. The FanHandler’s
circuitry avoids the DC component. We’ve been building just about this
same circuit since the early 1960’s (GE helped us develop the control).
Many companies have tried to do the same thing but with cheap triggering
methods (like dimmer switches). These cheap controls will ruin a
motor.
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The literature states that some
motors will not work with the FanHandler. Why not?
First off, the FanHandler is designed to
control shaded pole or permanent split capacitor motors, the types most
commonly found on direct drive HVAC blowers. The FanHandler cannot
be used with belt drive blowers.
It is true that some shaded pole or PSC motors
will not work well with the FanHandler. Often this is because the motor
is old and worn, but it also happens with brand new motors that are
cheaply designed and built. The most common problem is an objectionable
“growl” at low speed, but there are also some motors that, because of
poor design, do not follow the fan laws. If a motor does not reduce
amperage when you reduce speed, you must replace the motor. We
offer super high quality Baldor motors at very competitive prices,
should you need one.
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If the coil is dirty, it will
freeze-up due to reduced airflow. Even if the coil is clean it will
freeze-up due to low airflow.
Whether the coil is dirty, clean or in between doesn’t matter. The
air speed is slow only until the air temperature begins to drop.
What happens to the speed of the FanHandler controlled motor when
the temperature drops? The FanHandler drives the speed up to a level
that it needs to reach its speed/temperature point. The FanHandler
will drive the fan as fast as it has to be driven, even if that is
top speed.
The FanHandler responds to the load
on the fan as well as the temperature of the delivered air. If a dirty
filter or coil restricts airflow, the load on the fan motor is reduced.
The FanHandler senses this and speeds up the motor. The FanHandler
automatically makes up for loading filters, coils etc. Just like any
other part of the system, it can’t make up for totally clogged.
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If the compressor shuts down and the
fan keeps running, all the water on the coil and in the pan will end
up being re-evaporated or end up in the blower housing or supply
ducts and promote mold growth.
No, it won’t. First let’s look at the present condition, with no
FanHandler. You have the high-speed fan. The compressor shuts off.
Water adheres to the fins in inverse proportion to the temperature
of the coil. (The colder the coil the tighter it sticks. The warmer
the coil the less it sticks) The A/C designers put that fan speed up
to the max so that the fan/coil combination under normal
circumstances is just bumping up against the point where when the
compressor and the fan are both running, the water doesn’t strip off
the coil. Shut the compressor off and leave the fan run and the coil
no longer holds the water as tightly so it strips off the coil and
into the ductwork. With the FanHandler, as soon as the compressor
shuts off, the air temperature off the coil begins to rise. When the
temperature rises, the fan speed slows (not in a few minutes, but
immediately). Therefore there is no stripping of water. The speed
typically drops to somewhere about 1/3 of the way between the
minimum speed setting and full speed. At this point, the FanHandler
takes advantage of the refrigerating effect of the pressure
equalizing cycle, which is liquid refrigerant under high pressure
traveling to the evaporator, which is under low pressure. In some
systems you’ll get about 10 minutes of additional cooling at a small
rate but which would be cooling that normally is wasted, plus it
takes out lots of humidity during this period.
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Since most homes have duct leakage,
running the fan all the time is a bad idea. With the fan running,
the house will be under negative pressure. Replacement air will be
sucked in through undesirable channels, such as crawl spaces, attics
or water heater flues.
Sure air will be continually pulled into
the home if duct leaks cause a negative pressure. With the FanHandler
running at very slow speed most of the time, pressure in the supply
ducts is reduced, and some leaks may disappear at this reduced
pressure. However, right now with the full speed fan running ½ the time
you are pulling in more air than you would be with a fan that averages
less than half-speed all the time. And when you’re running under
FanHandler control you’re pulling a lot more humidity out of the air.
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With cooler coil temperatures, the
blower compartment or supply plenums will reach dew point, promoting
mold growth.
This won’t happen. The dew point
or saturation point is at the coil, the air temperature is maintaining
the roughly 20° differential that it had before. The exciting thing
about FanHandler operation for cooling is that the coolness of the coil
is first used for the removal of moisture. This uses compressor capacity
for condensing water at about 1,000 BTU’s (actually about 1076) per
pound or 8,333 BTU’s per gallon.
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A properly designed system requires
full speed in order to move air across the ceiling to the furthest
reaches of the room.
This refers to register “throw” and just
about nobody incorporates it in the design unless for an engineered
system in commercial or larger buildings. However, throw is required
in an off/on system to get the air mixed when the part time fan is
running. The FanHandler action of mixing air is like Italian
dressing. You shake it to get it mixed-up but from then on you just
have to jiggle it to keep it mixed.
How
it Works
Installation
FAQs
Read Humidity and Air Conditioning
by Richard Peters, PE, CM
Learn about FanHandler products for...
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