Carrier variable speed motor, duct transitions - any problems?

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I've had a Carrier dealer discourage use of a variable speed motor with my ductwork in a 15 year old home. As he explained, the transitions from square duct to round can confuse the sensors in the variable speed motor to cause it to ramp up to higher speeds unnecessarily. Does this make sense? I ask because other dealers of different equipment have not expressed this concern.
This led me to wonder how specifically Carrier variable speed motors determine what speed to run at. What is the algorithm for speed control--are there sensors put in the plenum, on-board sensors, are they looking at temperature and inferring airflow from that, directly measuring airflow, or. Are there fixed intervals involved like run at X% for Y minutes, if tstat isn't satisfied ramp up to blah% for Z more minutes, if not tstate, ramp up further? Or is airflow involved/measured somehow?
Other dealers who've quoted have not expressed any concern with the duct situation, even when directly asked. It's always possible they'd love to sell a variable speed motor setup.
Of course, one of those dealers (a Frigidaire dealer) had no clue how their variable speed motors worked and couldn't explain it other than mentioning DIP switches for low and high speeds. Based on their knowledge, I don't think I'll be using them I'm afraid.
A Ruud dealer explained that their variable speed sensed airflow somehow (he said he wasn't sure precisely what was being mesured) but did offer the anecdotal evidence that he had forgotten to change his filter at his house once and the clue he had was that his variable speed motor was running faster than normal due to the airflow blockage.
Thanks for sharing and info you know on various manufacturer's variable speed motor operation.
Best Regards, -- Todd H. http://www.toddh.net /
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Paul,
The guy asked some good questions that I've also asked here in some variety.
They deserve some answers, but I doubt he'll get them. The manufacturers hold this information so close that it's ridiculous.
Now to Todd....
I'm a electrician and a controls engineer that has been around this NG for a couple of years. My business has gotten more into the management of small/medium HVAC systems for existing industrial & commercial clients. I've learned a great deal about how HVAC systems work from the contributors here.
That said... I'm going to tell you that the majority of VS systems out there today are 'dumb', and take very little feedback from the real-world into consideration during operation.
Airflow is a good example. It's usually extrapolated from a computation of how much energy (amperage) the blower motor needs to operate at X speed. This is done on-board at the motor... a expensive-to-replace proposition that, as an engineer, I totally disagree with.
Some... better systems also will take readings from the refrigeration circuit into consideration. Do a Google to learn more about how a refrigeration circuit works.
Sensors might measure line temperatures or pressures at key points by which things like airflow can be 'roughly' extrapolated.
Bottom line is... VS... by itself... does not gain you much efficiency. How it effects the 'circuit' on the other hand... might yield great cost savings. Remember, the biggest user of energy in your system is the compressor and not the fan.
Jake
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Jake wrote:

I would disagree with you.
The average leakage in a 15 yr old duct system ranges 30-45%.
people are delusional thinking they're getting 13 seer by buying equipment but not replacing or sealing, sizing & insulating duct work.
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I might buy that... I'll take your word for it (-;.
On the other hand, I was talking strictly about the equipment and not the system as a whole.
SO... is there a problem with VS in a duct-transitioned system the OP described?
I'm not convinced of that... yet.
Jake
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Jake wrote:

oh bs. you said system. system implies every component. :)

it seems the problem exists only in the mind of that one carrier dealer.
somehow, magically, VS motors work in every other similiar situation for thousands if not millions of people.

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snipped-for-privacy@gonefishin.net writes:

That's what I'm wondering.
Anyone here been through the Carrier factory training gauntlet or have installation notes for the Carrier variable speed motor and recall any mention of potential issues when dealing with typical substandard builder-grade ductwork transitions?
The dealer in question tends to be among the more clueful in the area, so it'd be surprising if they were making something up that would make them less money. But then again, there seem to be plenty of folks willing to install variable speed into this duct system too, albeit from other manufacturers whose blower design may differ.
Best Regards, -- Todd H. http://www.toddh.net /
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snipped-for-privacy@gonefishin.net wrote:

Sort of throws a wrench in all those fancy heat loss/gain calculations, no wonder everyone is undersizing today
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Cool. Nice to meet you. BS EE here, so we can talk geek to geek. :-)

Poo.

Agreed.

I figured that'd conceptually be a better way to do it than with circuitry on the fan alone.

It's not efficiency I'm after with VS I guess. The big selling point of it is comfort, quietness, and evenness of heat distribution, for me anyway. To have some air ciculating to even out the temperature in the house is why I'm considering it, though getting that benefit without having to run a motor full bore would also be welcome.
Thanks for your response. I'll see if anyone can shed some light on why the Carrier dealer is steering me away from VS. Given that it's probably a decent markup item, I suspect there's got to be some truth to it. This dealer appeared to be the most clueful of the 3 outfits that were here, but I'm holding out hope that variations among how various manufacturers' VS works might also account for the differences in recommendations.
Best Regards, -- Todd H. http://www.toddh.net /
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Not. You are talking about a Ho Moaner system, not a commercial system where you can dedicate a machine to do the monitoring and control of multiple air handlers. Really... How many flow, temperature and pressure sensors do you think they can hang on a system involving a tiny amount of duct?

There is. But it's a Ho Moaner system.....

Because he's probably been doing this in the real world long enough that he doesn't think it will make a difference in your case, and he doesn't want to spend six months at the EE's house after installing the system. Or, maybe he doesn't have much more of a clue how it works than the Frigidaire dealer who knows how to set the dip switches.

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Todd..
think about the EMI and surge suseptability issues of the variable speed control electronics... and how much they cost to repair after the lightning storm...vs how much energy savings/comfort they may or may not buy you...
Mark
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Yeah... it's true. Although with a 10 year warranty (Bryant anyway), it gets a little easier to stomach. :-) And with underground service here, we've been pretty lucky thus far with being (relatively speaking) strike and surge free. But it is certainly a risk vresus the tried and true single speed systems.
The Fanhandler+Baldor route might be worth investigating further. But given the temp differences in this Colonial here, variable speed has some compelling appeal to me. Like anything it's a calculated risk right?
I agree though that the cost savings argument is a red herring with variable speed. It's really mostly about comfort while reducing energy use. Whether that reduction in energy use translates to money savings depends on whether the damned thing breaks and requires repair. :-)
Best Regard,s -- Todd H. http://www.toddh.net /
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A Fanhandler with a good motor will give you the same or better results than a OEM VS setup... I'd bet on it. It does the same thing, but the design is not on-board the motor and can be more efficient... and reliable.

A integrated, on-board VS will break, Todd. It's an frequency chopper mounted on a motor housing, for Gods sake.
It also makes things more difficult for the standard field service guy to diagnose. I don't know the specifics here but it looks to me like the test is "go" or "no go". The tech doesn't know if it's the controller, or the "chopper", or the motor. He'll just replace them all in one neat package for $800.00... so it can fail again in a few years.
Note how tricky a PWM power supply is.... These guys are not gonna have a 'scope out there. Thing is.. if you did... the thing could probably be fixed for $10 bucks instead of $800.
From the cheap plug-in control wiring harness, to the inadequate assurance of ventilation... it's a bad design, and time will prove it.
The OEM's should have gone with a separate 'module' complete with on-board diags... but they didn't because the field training is weak on this stuff (in resi) and they can make a killing on motors.
Sorry... I'm not sold. And I'm grouchy tonight.
Jake
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Jake posted for all of us...

Constipation?
--
Tekkie "There\'s no such thing as a tool I don\'t need."

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Jake wrote:

NEWS FLASH Jake. Every fucking thing built by human beings will break. The highly touted ABB VFD's you put in? There gonna break someday, bet your life on it.

Once again, unadulterated horseshit. Competent techs have a VS motor tester kit that tells them whether its the GE motor or the propriatary electronics package thats defective.

Now I'll bet you're gonna tell us the VFD's you push dont utilize PWM as well......a VFD is a frequency chopper for Gods sakes....

more horseshit.. The VS motor in my furnace has been running non-stop 24/7 for the last 10 years. I run constant fan, and I MAY remember to change the 2" pleat filter 2x yearly.

more horseshit. What would an electrician from Indianna know about nationwide HVAC field training? Perhaps you have links to back up your biased opinions?

Who cares if you're sold or not? When you get 15-20 years under your belt as an HVAC service tech, you MAY have a little more credibility with people who are actually in the trade today.
ps- if you're still grouchy, wait til morning before you read this. :))
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On Sat, 16 Sep 2006 02:00:18 GMT, snipped-for-privacy@gonefishin.net wrote:

And some of us lucky soles have that tester and another much less expensive one called a "9 volt battery" and 2 or 3 alligator jumper wires. Work like a charm. Bubba

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snipped-for-privacy@gonefishin.net wrote:

They're usually replaced with newer technology long before they break, Fish. I have some in the field for 20+ years running 100+ hp motors. They're over-engineered, for sure... but I've seen very rare failures.

Really... and what do you do when you find it's the motor or the driver? I'm curious?

A VFD is an inverter... not a chopper. It's capable of running the motor faster than the line frequency... something a chopper cannot do. It's also capable for delivering more torque, and ramping the motor... under control.. up and down. Something a chopper cannot do.

I really don't buy that. Real VS motors have not been around that long in resi applications, have they? You'd have to give me some more info before I believe that.

I know that many HVAC techs I've run into... particularly in the resi trade... have little skills about discrete controls in general and even less about something as advanced as analog. Granted, that's in my little corner of the World here but I suspect factory training is the same throughout the country.

Fish.. you know me. I don't discuss things I don't understand. I ask for help when I need it. Don't throw that HVAC trade stuff at me... this is a controls problem of which I am very familiar. I don't care whether it's running a fan or a 500 hp. compressor motor... the concepts are the same thing.
Building these controls onto a easy-replace motor that the customer will be forced to pay exorbitant rates to replace is a scheme. It makes ill-trained techs have a easy answer... and it makes the likes of GE-Regal/Beloit a lot of money.
I'm not fooled.
BTW, the McQuay units we installed last year have Toshiba drives in them. I'm happy with that...
Jake
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wrote:

yup
Replace the part thats bad

Rheem has had ECM blower motors in high end, resi equipment since 1997

They might make a killing on the motors, but the manufacturers are clamping down on swapping out (warranty)"bad" ECM motors because BJJB hasn't been to the classes that the manufacturer puts on that tells you how/what to do with them.

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Jake wrote:

well my one and only experience was to remove the defective electronics from the end of the motor and get a new one under warranty. It was a piece of cake to remove & reinstall.

In a vfd, isnt the waveform chopped before its inverted?

Jake, every single vendor I have offers training, alot of it free. Equipment vendors regularily have classes on their products.
A local trade organization is sponsoring free Nate training leading to certification. Classes are booked solid
One major manufacturer I know of offers factory training online to techs thru participating contractors.
The Utility Co's offer free training, on every imaginable topic. http://www.socalgas.com/construction/freeresources.shtml

your problem is you're a professional in your trade, but not necessarily a professional at making money, and therefore resent? those that are. alot of us suffer from that syndrome. it infuriates me to pay the exorbant prices for most carrier parts, but the customer pays for everything, right?

easily.

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snipped-for-privacy@gonefishin.net wrote:

What would that service call have cost a consumer... just curious?

Actually, the sequence usually is that the AC is rectified to DC and held via a cap bank on a bus. The Inverter then changes the DC back to AC by firing it into a AC waveform at very specific rates. Newer drives produce something very close to a true sine wave. >

How many REQUIRE training, though... and how many contractors take advantage of free training in the HVAC field for resi. equipment?

Fish... this kind of "the customer pays for everything" attitude is what's driving manufacturing offshore and leaving us with only cheap, disposable products that we throw away at regular intervals.
No, I'm not a pro at making money... but I've done very well for myself and for my employees and their families. I don't have 4 homes in different states, but I sleep well at night knowing that my company, my vendors, and my customers all got good value for their dollar at the end of the day.
Carrier (and other OEM's) charge a lot of money for their parts because of attitudes just like yours.. that "the customer pays for everything".
Well, one of these days (coming soon to a town near you), the customer will no longer be able to afford it and will be buying $100.00 window shakers at Wal-Mart and heating their homes with wood stoves.
When that happens, the 'money professionals' will be out of business and the people who provide a real service, for a fair price... will still exist.
Jake
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Jake wrote:

personally I dunno. maybe Bob P will chime in with his FR price. I usually include a 5 or 10 yr p&l warranty with any install, so its a moot issue.

Major US equipment vendors are moving in the direction of requiring their resi dealers to employ Nate certified techs, to the tune of at least 50% of the tech & installer work force. Its happening today Jake.
Remember, the whole industry had to be retrained for 13 seer, not to mention 410a.

get real Jake. carrier and a whole slew of others are in china because thats where future profits are at. billions as I understand it. with cheap labor, profits are even greater.
we live in a disposable society only because our labor (to repair) exceeds any other countries combined manufacturing & shipping costs....
some people are in business to service peoples needs, some businesses are in business to make money.
ever notice how high on the hog charitable organizations live?
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