That is amperage draw not power consumption.
The GE ECM units don't have any PFC so they have the same roughly .6 power factor as any old computer power supply that just has a diode bridge and capacitor at the input. That 6.3x120x.6 is roughly 454 watts. Since 1hp is
746 watts that puts the efficiency at about 82%
The fun part is on an induced draft furnace with an in-shot burner set you can't reduce the gas flow without also slowing down the inducer motor so modulating furnaces and I assume your 2 stage have a small ECM for the inducer too that varies speed/flow to match the fuel flow.
One place switching shunt regulators ARE used is on permanent magnet brushless "alternators" on small engines and some motorcycles.
With per-mag "alternators" or "dynamos" the output cannot be controlled, so shunt regulators are used. Linear shunt regulators have proven rather short-lived in some apps, so the higher-end units have gone to switch-mode regs.
Pound for pound iron is a LOT cheaper than the copper that is also required - and MUCH cheaper than silicon.
It's just you need so much LESS silicon to do the job - and less iron and copper when the frequency is in the khz or mhz range.
Which, of course, is a *silly* argument.
Ran across one lately that runs at 180MHz so the (isolation) transformer could be integrated on the chip.
snipped-for-privacy@snyder.on.ca unnecessarily full-quoted:
You might be right.
The motor in my furnace is this:
Emerson SA55NXTE-4513
1/3 HP, 1725 RPM, 5.4 AIt's got a 5" pulley wheel on it, driving a fan with a 7" pulley wheel.
But the motor can't possibly know how many CFM of air is being moved with each turn of the fan rotor.
Actually, once you get the air in the house moving, you should also see a reduction in load. Also, I'm guessing that load will not increase linearly with air-speed or CFM.
If my existing motor is turning at 1725 RPM, and if I'm satisfied by the breeze generated by that RPM, then I sure as hell wouldn't want an ECM motor making it's own decisions about what RPM *it* wants to operate at.
The point of an ECM motor is that its supposed to be more efficient than a PSC motor at ALL rpm's. So if I drop in an ECM motor and wire it up for single-speed operation, I sure as hell would want that speed to be a constant 1725 RPM.
All you ECM-motor apologists are saying that ECM motors are *always* more efficient than PSC motors regardless what RPM they operate at. So now you're backtracking by saying that there's no savings when you replace a PSC motor with ECM if you force the ECM motor to operate at same, constant RPM that the PSC motor did.
What you're saying is that I'm supposed to allow the ECM motor to "learn" and to reduce it's RPM.
That's no different than if I were to replace my 1/3 hp motor with 1/4 hp and put a smaller pulley on the motor vs what I have now. I will use less electricity and the fan speed will be reduced.
It doesn't have to - it's a relative thing - the motor adjusts itself by RPM and current to the most efficient point - at least that's what I gathered. If it runs too fast so the fan is "throttled" the current drops for the speed it is running at, so the motor can slow down 'till the current/rpm ratio ballances out.
You are right - partly. The inertia of the air is not much af a factor, what with air being compressible and all, so there is not much change in power required from "startup" to "air moving" - but the load is not necessarily linear with air-speed or air flow. The counterintuitive thing is the load DROPS when the back-pressure increases. (partly because the actual air movement drops and partly because of the way air behaves in a centrifugal blower (any fluid, actually - look at cavitation in a water pump)
And it would be if that is the right speed - but it MIGHT move just as much air at 1500, or 1375. It might actually move marginally MORE air at a lower speed, because the blower itself may be more efficient at a lower speed.
No, not saying that. It will be somewhat more efficent at the same speed, but may be considerably more efficient, while movong the same amount of air, at a lower speed.
And , depending on your furnace and setup, it may actually be more effective that way.(as well as more efficient)
Sure, the motor can know a lot about it's own current useage as a function of it's own RPM.
But it can't know anything about RPM and fan CFM - without getting feedback from air-flow / air-pressure sensors mounted in the ductwork.
ECM motors can't reduce their RPM to, say, 1600 RPM and magically give me the same CFM as my motor running at 1750 RPM - both given the same fan to turn in the same duct system.
Who says what the right speed is?
Ok, you need to step back and re-think this.
Within a normal range of operation, there is no way that I can turn a given fan at a slower speed and yet get more CFM being moved by that fan.
Again, you think that ECM motors can magically make a given fan move more (or even the same) CFM at a slower rotational speed than a PSC motor at the same speed. You're going to have to explain the physics behind such a phenomena.
The right speed is the speed that 1) - moves the most air with the least power or 2) allows the most heat to be extracted from the heat exchanger by optimizing the air flow.
Moving more air does not necessarily translate to providing more heat.
Counterintuitive, yes - but if YOUR fan is turning too fast, turning it slower CAN provide the same or even higher air flow - and use less power to do it.
I didn't say that. If you could slow down the PSC motor you could have the same effect.. You could use a brushed DC motor and variable voltage to get the same effect - but ECM motors are less maintenance intensive, longer lived, and (can be)more efficient.
A drop-in replacement ECM motor that's replacing a single-speed PSC motor can't know how much air it's moving, because it doesn't know the size of the fan it's turning nor does it have duct-mounted sensors to tell it the CFM of air being pushed through the ducts.
A drop-in replacement ECM motor can't know anything about how much heat is being extracted by the heat exchanger, because it doesn't have temperature sensors telling it the input and output furnace air temperature.
A drop-in replacement ECM motor can "learn" it's energy-useage vs RPM curve is once it's been installed into a given home's furnace, but that doesn't mean that the most efficient RPM will be satisfactory for the comfort or desire of the home owner.
A drop-in replacement ECM motor will not be getting any feedback from any temperature sensors, so that point is moot.
You actually believe that a 1/3 HP motor running at 1750 rpm though a reduction pulley is going to be turning the furnace fan too fast - to the point that it's actually pushing *less* CFM through a "normal" home's duct system as compared to if it was turning slower?
I said given a normal range of operation - not given some ridiculously high RPM.
What effect?
If I slow down any motor, the fan will turn more slowly, and I will get less CFM.
You keep wanting to insist that in every case where there is a PSC motor, that it's almost certainly turning it's fan faster than it needs to, or faster than the home-owner wants.
Just because an ECM motor *can* run slower than a PSC motor doesn't mean that the resulting CFM is what the home-owner wants.
Tell me why an ECM motor is longer lived - given that we've really only had them in consumer furnaces for the past 10, 15 years max.
PSC motors don't have brushes, nor do they have sensitive electronics that are vulnerable to power surges and nearby lightning strikes, nor do they care much about pushing air though high-resistance ductwork.
What is it about the construction of a PSC motor can you point to as being more sensitive or less durable or more prone to failure vs an ECM motor?
That is not NECESSARILY true.
I didn't say in EVERY case
And the homeowner is often too stupid to realise that what the FURNACE wants is more important than what he thinks he wants, in some instances.
Lets see. How long have electronically commutated motors been in common use elsewhere???? DC "muffin" fans have been in use in computer power supplies since before the IBM PC came on the market some 30 years ago. If the bearings don't seize up they run virtually forever.
And the ECM, or "Smart Motor" was first marketted for furnace use by general electric in 1969. That's FORTY TWO YEARS of history.
And nor are they anything approaching anyone's definition of efficient.
Because of lower efficiency they tend to run hotter.
Installed PSC motor efficiency is generally in the 12-45% range, which means a LOT of heat is produced. ECM motors generally run 65 to 72% efficiency as installed.. That means a LOT LESS HEAT. Add to this the FACT that a majority of the heat in a PSC motor is produced in the rotor, whech means a lot of heat is transferred out of the motor through the shaft and bearings. This reduces bearing life and stresses bearing lubrication.
I'm not saying PSC motors are failing at extremely high rates - but I have had them fail in signiificantly less than 20 years, and I reject yout hypotheses that ECM motors are either "puny", short lived, or intrinsically trouble prone.
I just saw a few weeks ago a ECM less tham 4 inches in diameter and less than 4 inches long that will put out 14 HP.
In the 20-200 HP range, Brushless DC motors (ecms) are actually less costly than brush DC motors or any other variable/controlable speed AC motors and are extensively used in industrial applications
Furnaces with ECM motors generally have a larger blower wheel and housing so they can turn slower and move the required volume of air. Air volume and velocity is set up for specific amount of heat temperature rise in furnaces and 400cfm per ton for heat pumps and air conditioning. Also because the ECM motors are turning slower, there is a whole lot less blower noise, but the ductwork has to be correctly sized. If everything is right with the world, the system is correctly designed, sized, and installed, it should have minimal energy usage, be nearly silent, no drafts, and no more than 1F temp difference between any 2 rooms.
If you want to continue screwing with your furnace, have at it...... just as soon as you get done using the hand crank to start your car.
ECM motors are being marketed to replace common evaporator fan motors in commercial refrigeration. Those refrigerated cases you see in the grocery store are getting ECM fan motors.
TDD
Hey, I could hand crank my 1967 Renault 10 with the screw jack handle. :-)
TDD
Unless you can show where someone has made some blower CFM measurements in a real house, then you have no real evidense to support that paradoxical statement.
And in any case, an ECM motor has no way to know how much CFM is being moved by the fan its running, especially as a drop-in replacement for a PSC motor.
And I bet that modern furnaces that come with ECM motors also don't know how much CFM they're actually pushing. They probably only know indirectly by monitoring return-air and output-air temperature difference. Do any of them have an integrated wind-speed sensor?
Then put a number on it.
The home-owner is "often" too stupid ... in some instances. ?
That's a mixed message. You want to say that some arbitrarily large fraction of home-owners would (or are) choosing a fan-speed that too high (you'd have to show me how they have any real control over that, btw) then you back away by saying "in some instances".
You are showing a strange bias against homeowners that is affecting your ability to think rationally about this.
Yes, let's compare these other situations, where micro-power DC motors have been used:
So you think that these tiny, micro-power DC motors make for a good analogy when we're talking about the furnace fan motor market eh?
Tell me how many consumer furnaces were available in 1985 with ECM motors.
And you haven't told me anything to support your claim that ECM motors last longer.
Saying that the first ECM motor was made a hundred years ago, or that GE supposedly actually sold a furnace with an ECM motor in 1969 (which maybe they withdrew from the market a few years later ?) is not an answer to why ECM motors last longer (your claim).
Don't change the subject. We're talking about longevity, not efficiency.
Yes, they run hotter. They are also constantly cooled by the airflow generated by the fan.
Tell me which motor is more likely to survive constant use in a high-resistance duct system? Or survive a fan bearing that gets gummed-up over time? Or a filter that's not properly cared for? Or a power spike or brown-out on the AC grid?
That depends on how many PSC motors are multi-speed vs single speed.
And you can get high-efficienty PSC motors in the range of 62%, as claimed here:
It's clear that when we're talking about 1/4 and 1/3 hp single-speed PSC motors, efficiencies up to 60 - 65% are obviously the norm, and bring us much closer to ECM motor efficiency than most people think possible.
It's clear that some furnace makers are using puny or wimpy ECM motors in their furnaces. But none of the HVAC regulars reading this will chime in and agree.
ECM motors have sophisticated electronics that PSC motors don't have. When-ever you include additional components into any system or device, you have more points of failure. You stubbornly refuse to believe that the electronics in an ECM motor represents an addition point-of-failure that PSC motors simply don't have.
Ok homer, so when are you going to start you new job with the manufacturers and/or governing bodies to redesign and reclassify furnaces so that you can turn a multi billion dollar industry back in time 20 years??
At least ONE. I'm done. You are too stupid to be teachable.
Excuse me, but I think the points Home Guy are raising are perfectly valid and you can't just dismiss them. You claimed that slowing down a fan motor may not lead to less airflow. I agree, thatis possible, IF the fan is turning so fast that it's no longer moving air, ie cavitation has occured. But that isn't the abnormal case we're discussing now, is it? We're talking about a normally operating home forced air funace or AC.
Also, HG raised a perfectly valid question of how a drop in replacement ECM motor could learn anything about air flow. It can't directly measure the CFM being moved. He asked a question I'd like to know the answer to, which is in new furnaces with ECM, do they have air flow sensors?
Also, to add to HG's case, I think all the hoopla about constantly circulating air 24/7 is a bunch of BS. Why? Let;s look at my house, which I'd say is typical. Furnace is in the basement, returns are uninsulated and some to upstairs even flow through outside walls. Those ducts have no insulation, because the wall cavity is used for the ducts and the insulation that the normal cavities would have is absent. Also, typical ducting is far from perfect, with leaks in botht the returns and supply commong.
So, now I'm to believe that running a blower 24/7 when it's 20F outside, drawing the air through the cold basement, the cold furnace that is not fired up, through ducts that are in outside wall, etc, is a smart thing? I don't care how much you think you save in an ECM motor. Even if the energy to run the blower is free, the rest of the above equation spells loss to me.
It is an all too common occurence when guys who do not understand what is happening try to "fix" their furnace.
Which someone has screwed around with
In most cases, if not all, no.
Not all basements are cold. A very large percentage of urban basements are heated, finished living space.
To you it might be. To me, and many others, it is not.
And I've checked the air temp from the heat outlets on the outside walls of my house - they are room temperature or better with the burner not firing
I've stood up for HG on many issues - but he'll never get it. The days of the model "T" are long gone - and the day of the standing pilot light, atnospheric burner, PSC fan gas furnace are pretty well gone too. Taking all the "advancements" off of today's equipment will not make it a) last longer b) work better c) cost less long term or d) run better.
He first argues for resizing the jet - which I agreed with him about, and adjusting the air dampers, which I also agreed with him on, then he starts talking about putting the gas valve "between settings" - referring to the 3 position gas valve as "variable", and adjusting the flame by adjusting the gas shutoff valve on the 1" iron pipe feeding the furnace. Sure he can reduce the flame that way - but it is sure not the right, or even an adviseable way to do it.
We've beaten to death "modifying" furnaces to improve efficiency. It can be done with older furnaces because they just weren't designed with efficiency as a high priority. The priority was quick heat on demand. I wouldn't try modifying a modern "efficient" furnace. Correct sizing is what you want, so more heat goes through the heat exchanger and less up the stack.
Beyond that - and insulation - I've found the best way to reduce gas use is to not heat where it isn't needed. Working vents are important, as are just closing/opening doors. All depends on where the thermostat is, and that can be moved if it makes sense to your needs. I like the idea of zoned heat, though I have no experience with it. I just close or open vents and doors depending on what current needs are.
--Vic
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