ECM or PSC blower for zoned WaterFurnace Legend?

[tipsrfine]

You missed my point George2. Your previous statement seems to imply that a x13 is not an ecm motor;at least that is how I read it. Thanks.

[skippedover]

Following up on what George2 was saying, you need to first understand that when any blower/fan comes on, there is a certain amount of resistance to airflow. In a ducted system, we refer to all of the resistance outside of the equipment jacket as External Static Pressure (ESP). In a single zone system, the ESP is what it is based on the design and installation. Ideally it would be, in a residential application, about .5 IWC (inches water column).Anything above 1.0 IWC is huge and a definite no-no. The ways to reduce ESP are to keep all filter and coils clean, as well as a properly designed and installed duct system. If the duct system is too small, the ESP goes up quickly.

Now to the zoned system. Clearly if the system has an ESP of .5 IWC with all zones open, then closing one or more zone will serve to decrease the overall size of the duct system and the ESP goes up. Recognizing this issue, the designer of the zone control system must design in some sort of 'relief strategy' to eliminate the excess static pressure. A common solution for basic zoned systems is to install a barometric by-pass damper that responds to high static by opening and therefore limiting the ESP to some tolerable value. However, a modulating zone system can accomplish the same thing but without the damper. This is done by some sort of 'intelligent' controller that controls ESP by opening zone dampers as needed to keep ESP below a specific value. In the case of modulating zone systems, a by-pass damper is not used. Likewise, with the modulating system, the variable speed blower motor is directly regulated by the system controller and also aids in keeping ESP under control.

Now come the complication of a by-pass damper. Since a variable speed blower is regulated primarily based on ESP (the resistance to airflow is reflected in motor RPM and amps) a by-pass damper will first open, reducing ESP, causing the ECM motor to increase in speed to keep ESP within set parameters but some of the increased airflow will travel through the by-pass and into the return air, thus reducing the return static, causing the ECM motor to slow down, which causes the by-pass to close, increases the ESP, increases the return air static, which causes the ECM to increase. This is a never ending 'hunt' for the variable speed (ECM) motor. This is also the reason that ECM motors are NOT allowed on 'twinned' systems, where more than one blower motor operates in the same static environment as another. Hope this helps. SO

[George2]

Skipper..............I don't know if Arzel came out with it first, but about 10 years ago they introduced a modulating by-pass damper. All of their other dampers did not (modulate) change. The duct dampers either opened or closed. The mod. by-pass sensed the ESP and opened as needed. It is a very slick item.

I know that Carrier, and others, now have the systems that your explaining.

[George2]

You missed my point George2. Your previous statement seems to imply that a x13 is not an ecm motor;at least that is how I read it. Thanks.

Sorry..........the X13 is based on a ECM platform but doesn't have the "brains" to be variable-speed.

Thus the reason the a barometric by-pass will work with a PSC or X13 but not recommended with a "true" ECM motor.

Skippedover explained it (maybe) better than I in post #15.

[tipsrfine]

Sorry..........the X13 is based on a ECM platform but doesn't have the "brains" to be variable-speed.

Thus the reason the a barometric by-pass will work with a PSC or X13 but not recommended with a "true" ECM motor.

Skippedover explained it (maybe) better than I in post #15.

Hate to harp on the subject, but there are several ECM motors out there that are not variable speed ECM motors. The X13 is a ECM motor. The evergreen motor is a ECM motor. Your previous postings seem to indicate that all ECM motors are variable speed ECM motors, and anything that is not variable speed is not an ECM motor. There are ECM motors that are not variable speed.

[seandarcy]

I'm learning a huge amount, and I do appreciate all the comments.

But I'm still confused: can I use the X13 (ECM?) motor from WF if I have a barometric bypass installed? I think I understand that you shouldn't use a standard ECM with a baromteric bypass. Is the WF X13 different enough from a "standard" ECM to allow it to be used?

Is X13 a WF brand, or a specific type of ECM motor?

Or would I need to install a modulating bypass? Is changing from a barometric to a modulating bypass a major undertaking?

[beenthere]

Yes, you can use the X13 with a barometric bypass.

[George2]

Hate to harp on the subject, but there are several ECM motors out there that are not variable speed ECM motors. The X13 is a ECM motor. The evergreen motor is a ECM motor. Your previous postings seem to indicate that all ECM motors are variable speed ECM motors, and anything that is not variable speed is not an ECM motor. There are ECM motors that are not variable speed.

Yes, I agree. That is what I thought I was said. It's not always easy to write an explaination and have other interpret it correctly.
We should call a ECM motor a "variable-speed" motor, a X13 motor a hi-eff. motor and a PSC a good and inexpensive motor.

[George2]

I'm learning a huge amount, and I do appreciate all the comments.

But I'm still confused: can I use the X13 (ECM?) motor from WF if I have a barometric bypass installed? I think I understand that you shouldn't use a standard ECM with a baromteric bypass. Is the WF X13 different enough from a "standard" ECM to allow it to be used?

Is X13 a WF brand, or a specific type of ECM motor?

Or would I need to install a modulating bypass? Is changing from a barometric to a modulating bypass a major undertaking?

Yes. I agree with B. L., you'll have no problem with a X13 motor and a barometric by-pass.

As I tried to explain earlier, a X13 is a hi-eeff., ECM motor without the ability to be
"variable-speed", i.e; cannot adjust airflow to different ESP changes.