Mechanical air flow switch or current transducer for fan proof?

[air1]

'Cause I lost that battle to politics. We mostly have ABB ACH-550s, and they all have it. But, to standardize, since there are old Grahams out there, and tiny new japanese drives that come in on packaged units, we settled on the
H720.

I am now trying to figure out how to get reliable status from motors with ECMs.

Our ABB VFD rep recommended we setup the VFDs for a relay output to supervise current and get the status over communications. This way you have a virtual CS providing proof through communications.

[Mr_Greenjeans]

I would be wary of the status relays on the drive, without profiling the current, you won't be able to tell if a belt broke, etc. (or you might not care). In general, we don't care.

I agree, network communications (integration) is probably the best way to monitor energy usage (kW/kWh).

.ja.

[orion242]

I would be wary of the status relays on the drive, without profiling the current, you won't be able to tell if a belt broke, etc. (or you might not care). In general, we don't care.

I agree, network communications (integration) is probably the best way to monitor energy usage (kW/kWh).

.ja.

Or the drive is powered off, or running in bypass, etc.

[MatrixTransform]

Or the drive is powered off, or running in bypass, etc.

...use static pressure

[orion242]

I only ask because I myself don't see many of them fail

Ditto. We rarely replace current switches. (RIBXGTAs)

We use them on the vast majority of our projects. They seem to work well and save costs on new projects. This is reflected on bid day and customers seem to respond….

VFD rated units I have tested, never impressed. Installed upstream of a VFD and adjusted properly, they work fine. All and all, my experience with switches has been good. We adjust them close, and more often than not return to the site to decrease the setpoint.

Proper install / adjustment is key with both.

[orion242]

...use static pressure

Also a valid method....

Since universal inputs are becoming popular in my world, almost been thinking of swapping all the current switches over to analog ones. Nicer to be able to adjust them remotely, and use them in poor mans power usage.

[mechdorn]

I prefer the dp over the ct. I have seen the DP's fail but mostly in units that didn't receive proper maintenance and were very dusty. I think they also help if adjusted correctly to send notification that there is an "issue" with airflow like a coil that's froze, failed fan, dirty filter to name a few situations.

I agree with "samwinter" on this one, you could use both wired in series to one input if it's an ultra sensitive install.

[orion242]

Most of the time....move less air, use less power regardless of the cause.

I have not use analog sensors enough yet, but I would think these with custom tailored logic per fan type could provide superior performance to both dp and current switches. Remotely adjustable to boot.

[xarralu]

Or the drive is powered off, or running in bypass, etc.

This is why we use CT's, well CS' technically. We generically call them CT's one way or the other, I guess it's a Texas thing. When someone around here says "get me a coke", the responding person will say, "ok what do you want?"

We use Hawkeye 608's mostly. Half our work is data centers so they will have the e-clipse bypasses and when it's in bypass, the drive goes down.

The problem I see with them is when they are less than 30 Hz. We see the life with 608's is around 5-7 years. Even at that, they have gotten their money's worth out of it!

[orion242]

We typically use the same sensor installed on the line side of the VFD. Adjust the switch with the motor at or near the minimum expected running speed.

1hp motor draws a lot more power at min speed than any of the electronics in the VFD. Bypass is also not an issue.

[Mr_Greenjeans]

This is why we use CT's, well CS' technically. We generically call them CT's one way or the other, I guess it's a Texas thing. When someone around here says "get me a coke", the responding person will say, "ok what do you want?"

Yeah, it's like calling anything hanging on the wall a 'stat. I know better. It's just more quicker.

.ja.

[Mr_Greenjeans]

Or the drive is powered off, or running in bypass, etc.

Now that I think about, most of our drives are specified with bypass. That is how I was convinced to add the separate, external CT. If somebody set it to bypass, we can tell it is running full-tilt from the current reading. The drive won't know.

I guess I'll order a couple of DP sensors for my ECMs. Thanks!

[CraziFuzzy]

Here's the first question to ask when installing ANY control. WHY are you monitoring this point? In this case, what do the operators really care about. Is the air handler doing it's job. The only real thing that shows this is Air flow. There are a few ways to go about this, but first would be, obviously, an air flow sensor. Second best, would be duct static. Odds are, if these units have VFD's, they already have at least one of those things.

Our new units do not have fan DP switches, but do have both duct static AND duct flow. However, we still need actual fan status, because they are fan wall designed units (a couple of them have 9 supply fans). In this case, we also need to know if a single fan fails (they each have their own overload/isolation breaker). For that, we use current switches. however, they are direct drive, so the 'has to be calibrated correctly to detect belt loss' problem is not there. So, the graphic for these units shows status a number of ways. Duct flow and static are shows. The fan animation themselves is from the drive status. Then there are a row of green-red indicators for each individual fan switch. No bypass units on these drives, but they are redundant drives, so there is still logic in there to only check the status of the selected drive.