New gas furnace/AC recommendations?

[The Daring Dufas]

>>

I'm sorry, I should have written linear, I stand corrected. I've worked on enough of the darn things. It used to be everything had a linear regulator and heavy transformer but the power supplies were simple and reliable. The 78xx series regulators and LM317's make it so easy to put together a regulated supply for a project. I was working in TV shops back in the 70's when RCA, if I recall correctly, came out with a TV set that used the flyback transformer as a newfangled power supply for the whole set. The company rep had one of the new "all solid state" sets hooked to a variac transformer which he used to run the voltage up and down. We were all impressed by the fact that the set would show a clear but slightly shrunken picture when the power to the set was turned down to 80 volts AC. I knew then that things were know going to get very interesting in the field of consumer electronics. Most of the sets we were working on had hybrid circuitry using transistors and IC chips for low power and low voltage then tubes for the high voltage horizontal output stage. I remember when a horizontal output tube was under $5.00 and a horizontal output transistor was $25.00 or more. Gasoline was also

30 cents a gallon back then. Gosh darnit! I think I'm getting old. :-)

I just had a flashback to the good old Radio Shack 12 volt DC power supplies the company sold for powering up a car or CB radio out of a vehicle. The early units used a TO-3 power transistor and a zener diode as a voltage reference in the circuitry. The latter versions used the LM317 and 78xx series regulators. I get the same power now from a wall wort that feels so light for the power it will supply. Oh yea, some of those Radio Shack power supplies were unregulated. :-)

TDD

[clare]

It's been a long time since I've seen a 1/4hp residential blower motor

1/3 seems to be pretty well standard for heating, with 1/2 HP being very common with A/C

It knows how fast it is turning and how much current it is drawing. The current draw is a direct function of the load on the motor, which decreases as the flow decreases

If you have a belt drive blower you will need to replace it with a direct drive blower, or cobble together some kind of mount and pulley setup.

That's all you do - the learning" is built in.

For more economy of operation. Turning the fan too fast can just draw more power, without moving any more air.

That's fine if you are not trying to enhance efficiency.

Moving less air does not provide fewer BTUs - it just makes the air hotter. Adjusting the amount of flame is what the motherboard you have been cuesing for the last week or two can do. Mine is a 2 stage burner, but there are "modulating" burners as well, that CAN control the amount of heat produced, according to the number of BTUs required (delta between current and desired temperatures)

You just don't (and won't - ever, by the looks of things) get it.

[clare]

>>

And the switch mode regulator can take the place of both. It is GENERALLY used in a series configuration because it is more efficient that way.

[krw]

>>>

Switching shunt regulators are exceedingly rare because the gain generally isn't worth the cost. Another topology almost always wins.

[The Daring Dufas]

>>>>

I came across a ferroresonant transformer power supply in a piece of gear a friend had and he was mystified by the darn thing and why it wasn't working. I obtained a replacement oil filled capacitor from an electric motor rewind shop and got the equipment working again. He had worked with all manner of DC voltage regulators but had never seen an AC voltage regulator. I guess it helps to broaden your horizons in a search for knowledge. :-)

TDD

[krw]

>>>>>

They also are not often used anymore because it's cheaper to use a switcher of some sort. Iron is expensive. Silicon is cheap.

[The Daring Dufas]

>>>>>>

I have a notion that the constant voltage transformer is a lot less susceptible to voltage spikes and lightening strikes than a switcher. I've installed a lot of them to protect phone systems power supplies. The things work well as AC line filters and isolators.

TDD

[Daniel who wants to know]

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%

[Daniel who wants to know]

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.

[clare]

>>>>

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.

[clare]

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.

[krw]

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.

[Home Guy]

[e-mail] unnecessarily full-quoted:

You might be right.

The motor in my furnace is this:

Emerson SA55NXTE-4513

1/3 HP, 1725 RPM, 5.4 A

It'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.

[clare]

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)

[Home Guy]

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.

[clare]

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.

[Home Guy]

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?

[clare]

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

[Steve]

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.

[The Daring Dufas]

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