Furnace Fan Efficiency??
Furnace Fan Efficiency??
(OP)
I am the first to admit that this is a rather trivial query, but does anyone know the typical electrical fan efficiency of a regular North American furnace fan. ?? I am not seeking anything on the thermal efficiency of the furnace system , just the blower fan. Since these are relatively low cost units, I suspect it is low, and I am well aware that the operating point on the fan curve .... and therefore efficiency.... will vary from one system to another but surely there is a normal expected range.





RE: Furnace Fan Efficiency??
The little forward-curved fan in the poor mounting position might not hit the 60-70 percent mechanical efficiency we see in the big 'uns where the ME selects based on the system curve and BEP. But I bet it isn't a whole lot lower.
http://www.baldor.com/pdf/501_catalog/CA501.pdf
Best to you,
Goober Dave
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RE: Furnace Fan Efficiency??
RE: Furnace Fan Efficiency??
RE: Furnace Fan Efficiency??
RE: Furnace Fan Efficiency??
RE: Furnace Fan Efficiency??
RE: Furnace Fan Efficiency??
RE: Furnace Fan Efficiency??
Anyway, just to make certain we're all thinking about the same thing, I'll ask miningman: We're talking about something like the attached spec sheet shows, right?
That's what I assumed (shame on me for assuming).
Best to you,
Goober Dave
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RE: Furnace Fan Efficiency??
RE: Furnace Fan Efficiency??
Best to you,
Goober Dave
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RE: Furnace Fan Efficiency??
No those are industry terms for our motors.
A 'squirrel cage' motor is the most common type of motor. It gets its name from the rotor design, which is a 'cage' akin to a hamster's wheel formed (typically) from straight copper rods or bars with the ends of the rods being welded or brazed to copper rings. Very large induced currents (hence 'induction motor') flow in the copper cage, resulting a corresponding magnetic field. The rotor field interacts with the stator field causing torque to be produced. A quick look on Google found this: http://www.youtube.com/watch?v=3MbP4t920Is, or alternatvely here's the Wiki entry: http://en.wikipedia.org/wiki/Squirrel-cage_rotor
A shaded pole motor uses a copper loop to distort the magnetic field in an iron yoke forming the stator. Induced currents in the rotor - which is similar to that described above - interact with the distorted stator field and produce torque. The copper loop dissipates a lot of power. They are limited to small sizes because they make poor use of the magnetic materials and have dreadful efficiency; ratings greater than a few tens of watts are uncommon. To drive a circulator fan for a small furnace - which looks like a kiln to me
RE: Furnace Fan Efficiency??
Shaded pole is something I've never investigated. I'm not much of a motor guy. The last time I worked a problem with a motor was when taking my PE exam in 1984.
Everything I see in the US for the fractional-HP residential furnaces is permanent split capacitor. Many are being sold with variable-speed drives now.
Best to you,
Goober Dave
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