BMS Control By High Level Interface

In the past 12 months I have noticed a couple of projects where Low Level control is being replaced with High Level control. In other words, controlling equipment over the network rather than using hardwired cables to controller outputs, mostly via BACnet MSTP communication to VSD's.
In this video we discuss 4 things you need to consider if you want to go down this road.
HLI (High Level Interface) control is generally not acceptable, mainly because the introduced reliability risks are not being mitigated.
The points raised in this video do not make HLI control acceptable, however introduce a starting point in moving towards a possible working solution.
Thank you for watching, and please like and subscribe :-)
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[@davidredmond-aes9889]

Some good points there and provides a better understanding of the consultant's position.

[@ytw6832]

Bryce, good works expanding your reach. Victor.

[@Billcasiopost]

Solid advice Bryce

[@bryceanderson17]

Thank you :-)

[@Dogga10001]

Bryce, That is why we are winning less & less projects, we run low level cabling to control low level and try as much as possible to use HLI for monitoring only. Problem #1 our competitors don’t seem to allow for that. Problem #2 too many specs put in their points list that there should be a HLI without detailing what that should do. Example #1 Lighting should have a HLI and that’s it, what do we do with that HLI ? The estimator allows a HLI point in the quote for example monitoring only as no control is mentioned then when it comes to the crunch we are expected to control all lighting points via schedule etc. From experience HLI’s can be a 1 of connection via RS485 or IP and mainly either BACnet or Modbus in our industry. Specs that show in the points schedules usually state a HLI to lighting or generators or security or metering etc etc but don’t elaborate on what it is to do. I have seen generators that have 300+ points available and we bring in the basics then get hit for not including the oil pressure or the emergency stop button etc. each point is time and that is money, why is it we always get hit with additional points that were not documented when someone has an idea for no reason that we should be monitoring all of these points that weren’t specified but are told that we should have allowed for that. Sorry my crystal ball is running out of answers. Specs Now days have to be a lot more thorough to allow the estimators to accurately quote the jobs and to allow for the items that the owner/developer etc are expecting which would save everyone a lot of time and frustration and money in the long run. I could continue......

[@jackhandyside3263]

Please continue, I found that useful.

[@bryceanderson17]

You are a 100% correct. There is no answer that will ever beat a competitor that has allowed for 5 points per HLI. Doing the right thing will never win jobs. The only thing I can suggest is: Think about that generator interface carefully. You allow for a fit for purpose number of points. Not 300, but 50. If it gets pushed back, explain that the spec had zero points listed, you have already gone over and above. Clearly list out these points in the functional description (we don't normally do this well, we usually say to be coordinated with electrical, this leaves us open). The point is, manage the risk. The reason why we end up providing 300 points is because we didn't provide enough fir for purpose points in our submitted design. A consultant can easily reject a submission when it is a poor submission, it isn't easy to reject a fit for purpose submission. Lastly, generally, BMS companies, especially smaller ones, are very accommodating. Be strong in defending your design, but don't be a dick about it. Don't try and defend 5 points, but definitely defect 20 or 30 points. Dave, you lose zero margin from the jobs you don't win. If someone wants to submit a stupid price, then let them have it.

[@davewaterworth8846]

I would have assumed that if the HLI couldn't read a point within a certain number of scans it should have marked it as "stale" - from what I gather that's part of the BACnet standard? So it seems that the BMS retaining the operating status of a failed VSD is due either to an incorrect BACnet implementation, or incorrect logic in the HLI (i.e. acting on the value of a point without considering the quality flags)?

[@bryceanderson17]

Possibly, but that wasn't provided on that project. Maybe if the engineer had thought a bit more about it, the test would have passed. It's still wrong in my opinion, but it would have passed. Some companies, like this particular global manufacturer, builds the BACnet points in their network controllers as proprietary points, not as true BACnet objects. BACnet field controller, BACnet communications, BACnet network controller, but a 3rd party BACnet supervisory device can not discover the points when scanning the network!!!!!!

[@taytzesen7658]

Hi Bryce. If the chiller is connecting to the BMS system with HLI, can the BMS control the chiller like on/off or just can monitoring the chiller data only?. I am quite newbie in BMS. Thanks

[@bryceanderson17]

Sorry Tay, I haven’t been on KZbin for a few months. I just uploaded a video and realised there are a bunch of comments in here. In most cases you can start/stop the chiller via HLI. However, most chiller, boiler, pump, fan start/stop signal goes through a hand/off/auto switch on the mechanical switch board. You need a low level (BMS digital output) signal to do this. Also, important control is best not done via an HLI because the communications between the BMS and the chiller is not always super reliable.