Next Lon Challenge

[greenleaf360]

I build Andover Controls (now known as TAC). I want to do a standard control scheme a new way. I have 2 hot water pumps with two VFDs. Add a typical controller with typical inputs, outputs and PID programs to modulate pump speed to maintain diff press setpoint, lead/lag, failure recovery, etc. We have all done this a thousand times.

On this project the engineer specifies the VFDs to include a LON interface. My master controller (Netcontroller) is LON ready. I have Lonmaker, Ilon10 and basic beginner Lon skills. Mechanical contractor furnishes 2 Danfoss VLT6000 with LON option card.

I want to:
- eliminate one TAC controller.
- interface to the drives via LON.
- Install two differential pressure sensors as direct inputs, one to each VFD.
- Use the VFD's built in PID control to modulate the pump speed and maintain DP setpoint.
- start/stop, send setpoint and monitor VFD functions/static pressure all via LON.

This all seems pretty straight forward stuff. I've waited for the pieces to fall into place for years. I see a few problems:
- I cannot access or modify the Danfoss PID control, at least not remotely.
- I give the customer a system that is 80% TAC/20% LON. The customer barely understands TAC and will never understand LON.
- My service people will not know how to support it either.
- I am assuming that I can setup the Danfoss PID control. If I get into trouble with the Danfoss I'll have to pay my competitor (they supplied the Danfoss) to program the drive.

Any suggestion or thoughts from the LON specialists out there?

I had one more question, I'm meeting with the specifying engineer next week to discuss the project design. Could the engineer have specified the boiler as LON also? If the boiler were LON I could eliminate most of the TAC controllers and control wiring. Can anyone tell me why, if the VFD is a LON device, why wouldn't the boiler also be a LON device? Does any American Boiler Manufacturer offer a boiler control package that is LON ready?

Cliff

[ctrlguy]

Do you have the xif file for the VFDs? Just wondering what you have for network variables available.

[greenleaf360]

I have a couple of xif files from the Danfoss website. They all look short to me and I'm not convinced I have the right files. I expect I have the standard VFD functional profile stuff plus the VFD input/output values. It doesn't appear to include PID constants.

Cliff

[sysint]

LNS Plugin for VLT6000 (http://www.echelon.com/Products/networktools/plugin/pluginShow.asp?pluginManID=14)

I haven't loaded this in LM but I would think it would be all you need if you can open LNS Plugins.

LON boiler? - I only know of one off the top of my head. Strange to me as there are alot of Lonworks controllers out there that go up to 4096 variables which is more than enough for any boiler plant, ERU, or most chiller plants....

[greenleaf360]

Thanks for the plugin. I'll hand that to Bill. He has the LM and will doing the programming.

Cliff

[ctrlguy]

Viessmann has a LON interface to their proprietary controls. It's terrible and all the NVs are in German. Oh, and it's really expensive.

[sysint]

I thought that was only for their cascade controller.

I should point out there is a difference between a Lonworks DEVICE and a Lonworks INTERFACE. The latter is where you can get into trouble.

[nikko]

Originally posted by ctrlguy
Viessmann has a LON interface to their proprietary controls. It's terrible and all the NVs are in German. Oh, and it's really expensive.

I'm using the Veissman stuff here on a distributed district heating plant and it works well. We simply told them which varoiable we needed and they provided the interface. It was a no-brainer.

Re: VLT-6000 drives. No, I don't believe you can access the on-board PID remotely, but I never wanted to. It's my preference to have the sensors wired to the DDC controller and have the controller do the actual control. You perform start/stop and speed via the LON as well as collect any alarm data or operational data you need.

The advantage of doing it this way is you can use a small (physical) I/O count on your TAC contrloller and use Network Variables to bind to/from the drive. You still get to maintain control of all the math in one place rather than have it distrubuted. This in turn allows for simple remote loop tuning etc.

Nikko

[dapper]

RayPak offers a Lon controller but I believe its primary function is for mutiple boiler operation. If you had an iLON and the boiler has a Honeywell R7800 controller w/Modbus interface, you could access burner functions and alarms etc.

[bradtech]

I used to service and startup Danfoss VLT 6000's and install and design Lonworks system. Didn't have the time to put the two together, as my involvement with Danfoss was not at a high enough volume. But a few things came up when I evaluated how to do what you're talking about. The Danfoss plug in did not expose enough detail to allow Lon control of the built-in in PID directly, as you are interested in. However, the plug in did offer a backdoor of sorts, if one of your controllers had some programming functionality to it (say a Circon UHC 300 and Circon Basic or a TAC Xenta 300 with Menta software). With a little work, you could access the functionality of the VLT from another programmable Lonworks controller. It would be interesting to see if the i-LON 100 could do something like this. Any thoughts on that score, Sysint?

I like it, and would be interested in helping you flesh it out, as it's not my time sheet against the project. If you're interested in doing a little development work, we could explore it a bit. I must caution you that any limitations to this scenario would only become known as you work through them. Trying this on an anctual project with a firm completion date and budget might be playing Russian Roulette, but what's life without a little risk?

[greenleaf360]

Thanks Bradtech, I appreciate your feedback. I expect that the Danfoss will modulate pump speed using its own PID control (probably better than my PID loops) and do not expect to mess with internal Danfoss programs other than what is required for standard Danfoss set-up.

-DP sensor will be installed as direct input to the VFD.
-I will send a start/stop and setpoint signal via LON.
-"KISS" as we say.

I have wanted to do this for years and all the peices have fallen into place with this project. Always seemed silly to add a controller to a VFD that was more sophisticated than my controllers. Saves about $1000 in cost IF, big IF, it works. I meet with the engineer on Thursday to see if he will accept this configuration.

Always a pleasure chatting with y'all, Cliff

[integrationx]

This is the way most projects will go eventually.

On a recent tender (with over 100 VFD/VSD), the DDC had no requirements for AIs or AOs to do with VFD/VSD control. All sensors were to be connected directly to the drives, utilising the drives internal loop, and Lon or Modbus interface.

A quote from a recent LonMark magazine on a similar vein;
"The resulting technical complexity of these systems will eventually put the commissioning component of these systems completely outside the realm of a 'trade labour' skill set, and pull it into an 'engineering-level' skill set"

[greenleaf360]

I met with the specifiying engineer yesterday to discuss the controls and he approved the design. Seems like a no-brainer. I appreciate your feedback.

Next question, I have two pumps, 2 VFD and only one differential pressure sensor. If the DP is 4-20ma signal can I wire the DP to both VFD?

This particular engineer told me that he would be specifying all new project as BACnet. He is an ASHRAE man and bought the line that LON doesn't know anything about HVAC controls. Go figure.

Cliff

[nikko]

Originally posted by greenleaf360
Next question, I have two pumps, 2 VFD and only one differential pressure sensor. If the DP is 4-20ma signal can I wire the DP to both VFD?

This particular engineer told me that he would be specifying all new project as BACnet. He is an ASHRAE man and bought the line that LON doesn't know anything about HVAC controls. Go figure.

Cliff

Nope, you can't. Hard wire it to one input and bind it to the other one, or hardwire it to your controller and bind it to both drives, or put two sensors in that share high pressure and low pressure (physical) ports but have independant signals to each drive (use this as a last resort).

And let your engineer know that he needs to do more research. If LON doesn't know anything about HVAC, I've not had any food in my table for over 12 years. :)

Nikko

[sysint]

I'd be happy to talk to this engineer for you......