VS motors on poor ducting

RoBoTeq

Are you sure? I mean, I can never really be sure

Matt Hermanson

All right folks. If you going to be in the HVACR business, you've got to learn about varable speed motors and their applications. It is the big thing in higher effiency units.

Go to www.thedealertoolbox.com. That is the site run by Regal Beloit. R.B. makes about 99% of the VS motors out there in residential systems. No kidding on the 99% thing. Regal Beloit bought the ECM Motor division along with a couple of other divisions from GE back in 2004. You're now going to see the rebranding take place from GE as part of the sale they left the name the same for 5 years and the 5 years is now up. So don't let the "Genteq" name scare you. That is the new branding for the old GE ECM motor division now that the five year name share has expired.

They (Regal Beloit) regularly put on classes at the engineering site in Indiana and at the plant in Springfield, MO. I just took the class at Springfield last week. The trainer, Chris, will also travel, for a fee, anywhere to put the class locally. So you wholesalers need to step up and sponser these classes. And if they don't, you contractors may need to switch to a wholesaler that does. Our local Johnstone is always having classes. Some good, some not so good, but mostly very good. But at least they are having classes. It is the electrical wholesalers that need to step up and offer more classes. We have one that does, but charges around $400 per day for any class, OUCH! But you can see the entire schedule of classes on the web site. If you still have a question, you can e-mail Chris through the web site. AND he does get back to you.

Yes, VS motors will "solve" duct problems. BUT ONLY TO A POINT! You have better be taking SP readings and loking things over closely if you want to keep that customer. VS motors really have major problems at SP of .8 or higher. They are programed to shut down before they get to a point that will cause failure. And if you install them in an application that will see them running at the higher RPM's due to SP issues; they won't last as long and they are more prone to shutting down when that filter gets loaded. And yes, I will grant that there are a lot of customers out there that you would make more money if you never meet them. That's life.

And if you can't sell that new duct job, then you need to go to www.contractorselling.com and learn from the master, Joe Crisara.

And remember, be safe out there when looking for Bambi. Just heard of a 23 pointer harvested in Southern Iowa this year.

cool_air

If your static is to hI then you'll still have problems and could damage the VS motor down the line,so correct the static if possable and try to stay under 0.6

RoBoTeq

Tis true, even though the motor manufacture use .8" SP as the maximum, .6 is safer.

However, with a vs motor you can more safely reduce the amount of air needed and therefore reduce the SP.

beenthere

You can only reduce so much. And then you lose too much sensible heat capacity in cooling mode.

Or, your head is too high in heating mode.

Or, your temp rise is too high on a gas or oil furnace.

For the cost of a VS blower. You can do some duct alterations, and make a system work better with a PSC blower.

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How many times must one fix something before it is fixed?

RoBoTeq

There is no pat solution to every system. A qualified technician will be able to ascertain how much duct correction is feasible and how much a vs blower can be adjusted to make each particular system work the best within a reasonable amount of effort being made to do so.

I really get tired of hearing people making claims that there is only one way to skin the HVAC cat. There is no magic solution for all situations just as there is no magic pill to cure all of our ills. Proper analysis of individual situations will provide viable corrections when done by techs who don't have single minded solutions in their heads.

beenthere

If I'm lowering the CFM to keep the static for a VS motor at or just below .8".
Then a PSC motor would work just as well. And use less electric. The customer wouldn't gain any benefit from the VS blower, as far as more air flow. Or quieter operation when moving the CFM needed for the house to heat or cool to set temp.

They would still gain the slow ramp up benefit. But thats all.

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How many times must one fix something before it is fixed?

RoBoTeq

You keep missing or evading the point I keep making. Only a VS motor is capable of safely running at lowered volumes, so there is no comparison to the psc motor. If something can be done to enhance the ducting to reduce the SP enough to allow a psc motor to operate properly, then adding a vs motor to that system will further enhance the efficiency, comfort effectiveness and overall function of the system.

I am always for correcting ducting issues first and foremost...when it is practical to do so. However, there is no instance where a vs motor will not enhance further any system with a corrected ducting issue. This is not a black and white issue. We must use "ALL" of the tools at our disposal rather then argue that only one tool is a cure all. Just because you beat on things with your wrench doesn't make it a hammer.

beenthere

I'm not missing the point your trying to make.

Where do you get that only VS ECM motors can safely run at lower volumes/speeds?

On a 3 ton system. Moving 1000CFM instead of 1200 CFM, weather moved by a VS motor, or a PSC motor. Is still 1000 CFM. And no harm is done to either motor. No harm will be done to the system by either motor either.

So explain why its safer for a VS blower to move that 1000 CFM, then a PSC motor.

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How many times must one fix something before it is fixed?

RoBoTeq

OK, now I understand why you don't realize the benefits of variable speed motors. Let's assume a system that provides 1200 cfm of air with a psc motor is creating a SP of .8. This is the limit that we want to go and the psc motor has to operate at a higher speed or be of a larger HP motor in order to achieve 1200 cfm at .8 SP.

Now, if we lower the speed of that psc motor in order to provide only 1000 cfm of air in that system, under the exact same conditions, we reduce the SP to about .58. At .58SP the dx coil is going to be colder, producing more condensate. More condensate is going to increase the resistance to the air which will increase the SP, in turn reducing the cfm. As the cfm reduces, the coil gets colder. As the coil gets colder, the condensate increases. During heavy load days, this cycle will continue until the dx coil drops below 32 degrees and freezes the condensate.

Now, take that same .8 SP system (for 1200 cfm of air) and put a variable speed blower on it set for 1000 cfm of air. As the coil condenses more vapor due to being colder from the lowered amount of air, the resistance increases. As the resistance increases, the vs motor speeds up to compensate. Since we are beginning with less air at a lower SP, there is room for the blower to speed up to compensate for the resistance from the condensate. Once the system has decreased the humidity in the air, which it will do more effectively at the lowered amount of air, the coil wil become dryer, reducing the resistance and lowering the SP back down to the .58SP.

A vs blower will maintain the set amount of air it is programmed for. A psc motor will just keep losing volume until the coil freezes up.

beenthere

With the PSC motor. You won't have a continuing decrease in CFM as the coil gets colder. Because as it gets colder, and reduces air flow slightly. The amount of condensate on the coil doesn't increase proportionally. Since your moving less air. There is less moisture that it can remove.

1000 CFM of air at 74°F and 55%RH is 73.2 pounds of air a minute. And 5060 grains of moisture.

950 CFM of air at 74°F and 55%RH is 69.5 pounds of air a minute. And 4807 grains of moisture.


Less CFM means less mass. Which is less water vapor through the coil per minute of run time.


By your description. A PSC motor would never be able to maintain enough air flow for any A/C, at any beginning static.
Because it would move less air as the coil got colder and continue to constantly decrease, and allow the coil to get colder and colder.


Lots of 3 ton systems have been running with PSC blowers for years at static pressures of .8 or more,and only 1000 CFM(some less yet), and are not freezing up.

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How many times must one fix something before it is fixed?

RoBoTeq

You have a lot of wrong information in your head about lowered air "volume" (not flow). You are simply wrong about being to reduce the amount of air with a psc motor and have the same results as reducing the air volume with a variable speed motor.

Since I now rep in your area, maybe we can discuss this over lunch some day. My companies treat.

beenthere

Sounds like a good idea.

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How many times must one fix something before it is fixed?

RoBoTeq

Great! I need to make more variable speed blower equipment sales

Just say when and where. My new cell number is 717-497-6224