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I have an ECM motor in my furnace, I was under the impression that with these kinds of motors, the fan should be on 24/7 when the a/c or heat turns off, as it will help keep temps more even throughout the house on different floors.
Is that an accurate understanding? If so, what would be needed to have the fan turn automatically on when the a/c or heat turns off? Would that be a function of the thermostat?
No, there are currently no residential systems that run the fan 24/7. A handful of systems have a microprocessor that takes inputs from a humidistat as well as the thermostat to adjust fan speed & run time, but these are the exception. There are some retrofit kits that will also use additional sensors to theoretically increase efficiency / comfort but I have not seen independent analysis that suggests the costs yet make sense -- Swapping ECM for PSC fan motor | GreenBuildingAdvisor.com
they are really geared to controlling fan speed based on conditions and demand.. they are quite complex and to be frank the first time you have issues they will cost you big dollars to trouble shoot and repair.
while typically on larger installations the use of a speed controller like a vfd can save alot of money im not so sure its worth governing fan speed in a small residential installation.
the beauty of using an ac drive in my business which is factory automation controls is you can effectively take any off the shelf motor and use it with out having special motors.
thats not true with these dc electronic motors. you may have one crap out and wait weeks , these are the special motors we strive to get away from in my business..
matt-united electric power
Last edited by mathjak107; 08-20-2012 at 04:03 AM..
Odds are in residential ac the ability to regulate fan speed and torque is more marketing then any real value when energy savings and difficulty in trouble shooting and and parts may be a bigger issue.
The difference between high and low will be barely a noticeable factor. residential ac units dont really have a long enough cycle to really matter.
on paper they look pretty good, they are more efficiant, you can program them to run at speeds for better dehumidification , etc, but resi systems are usually small in size and the benefits shrink with the size and area .
many studies have shown that while they do save energy the energy they do save is much less than the manufacturers lead you to believe under their lab conditions .
figuring a price of 600 bucks for a 1/2 hp ecm motor and a 1 or 2 year warranty the energy savings just isnt great enough in my opinion with all that can go wrong because of the complexity of them.
you also have standard and premium ecm motors. the standard are little more than electronic replacements for the standard psc motor.
the premium are a little smarter actually even being programmable for the geographic location.
as an example longer run times at slightly warmer temps to enable more dehumidification in humid areas.
they do have the ability to be a benefit but right now cost vs savings vs reliability are the issues.
Last edited by mathjak107; 08-20-2012 at 07:21 AM..
ECMs are matched with multi and variable speed compressors so that the system runs to match the heat load put on the system. The biggest advantage with the system running all the time in low speed and only kicking up to high speed when needed is it's basically a dehumidifier which will allow you to keep the indoor temperature higher.
Above is an example of a GE ECM trouble shooting guide and also an wet bulb enthalpy chart so you can see some examples of normal operation and compare the various conditions in low medium and high humidity applications.
That's a wet bulb and dew point calculator that you can use to see the differences using dry bulb, relative humidity and atmospheric pressure. Use 29.92 in hg for atmospheric pressure for sea level or pick from the closest pressure from this chart for your altitude.
While vfd technology and ecm technology has been coming down in price over the years the real benefits of multi-speed operation from sensors of all sorts requires that the application be a lot more demanding .
As an example i sell alot of vfd (variable frequency drives) with pressure transducers for apartment hot water systems.
instead of just off and on or high and low the pressure transducers have a variable 4-20ma output that can make a vfd controlled motor have many many speeds inbetween. in fact we can even have the motor run faster then its base speed.
When everyone is home taking showers the demands on the circulating pump are very heavy. As more and more folks leave for work demand tapers down gradually.
By being able to work that pump not just high and low but everything in between that really increases the savings in energy..
we are talking big pump motors and complex situations.
But a home with 4 people would be a waste for that much technology.
Alot of what we get trickling down is more an exercise in technology then really useful on a small scale.
Matty-united eletric power
Last edited by mathjak107; 08-22-2012 at 06:51 AM..
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