BMS systems

loadz

I have asked some questions on this before but i was wondering what kind of bms system people found best for monitoring and also controlling things. What do you find as the best value for money. Do you need separate interface units (Or what are they called) to monitor say energy and another separate one for getting the system to do an action. In other words are the monitoring controllers and the command controllers diffferent or is it the same controller. I don't know a lot about the system but i like the idea of how limitless it is and would like to learn a little about it so that i can speak to installers of these systems with some bit of knowledge on it. Any thoughts or advice would be great.

gan23

Hi Loadz,
I have worked with a couple of different PLC/BMS systems overs the years, mostly on the hardware side of things rather than programming. The most common manufacturers used for building management systems (that I have come across) seem to be TREND, HONEYWELL, ALLEN BRADLEY and SIEMENS etc.
Each has their own pros and cons. The "Best" would depend on the application its being used for i.e. the amount of I/O required, the complexity of of the control tasks (Simple on/off control, PID control, Cascade control), the monitoring tasks its required to perform (Historical trending, alarming functions, remote monitoring etc.) Value for money also depends on the application I suppose but i'm not an engineer so would not be involved in designing or pricing of such systems.
"do you need seperate interface units"
"are the monitoring controllers and the command controllers diffferent or is it the same controller"
Small plc systems have a CPU unit mounted on a rack and different types of input and output (I/O) cards also mounted on the rack controlled by the cpu. So if by interface units you mean I/O cards then yes different ones are required depending on what you are connecting to the the system i.e
digital input/output (swithces, relays, open/close valves etc)
Analogue input/output (transmitters, meters, control valves etc.)
You can connect any device that will send or receive an appropriate signal (4-20 mA, 1-5V etc) to the plc once the program has been set up correctly.
So in short you need different I/O cards but they would generally be contolled by the same CPU (controller).
Larger systems can have many CPU's and field devices connected together over a network such as a profibus network.

loadz

Thanks gan23,

As i say i don't know a lot about this subject but i would like to get a little base knowledge so that i can go from there. What would you need if you were to monitor energy with graphs and so on and what would you need to do control actions. Outside of labour what would you need to put in a system with basic control and a few energy monitors but with the option to expand the system as time goes on. An expandable type system.

Would you need the following and what else:

• Some metering points at every panel you meter with a cable from these brought back to your bms panel. Socomec meters or other type of meter
• Some kind of interface unit to translate this info and put it on PC
• Do you need a software licence
• For turning off say the air con do you need another interface unit or will the energy monitoring interface unit do for this as well
• Software guy needed to set up the program
• If you want to add to the system afterwards will you need the software guy to come back again?
• Is there a unit needed to generate 4-20mA or 1-5 volts
• Is there some unit needed to tie the system to the company IT network

2011

loadz wrote: »

Thanks gan23,
What would you need if you were to monitor energy with graphs and so on and what would you need to do control actions.

That is a hard question to answer without lots more information. Frequently nowadays a SCADA system would be used as a user interface. This is a powerful graphical tool can provide realtime and historical data shuch as graphs. It can also look at several PLCs at one time on a network and rescale values etc...

SCADA systems can be used to show the "live" status of many instrumets across an entire plant. This information (temperatures, pressures, flow rates etc...) would often be displayed on some sort of schematics that over several Windows type pages.

Outside of labour what would you need to put in a system with basic control and a few energy monitors but with the option to expand the system as time goes on.

Most if not all modern systems are expandable (to a point). Something like this would be a good example where additional I/O cards can be added as required, but it ain't cheap!

Would you need the following and what else:

Some metering points at every panel you meter with a cable from these brought back to your bms panel. Socomec meters or other type of meter

First figuer out exactly what you want to achieve. Next select the appropiate instrumentation (type and quantities). Then look at a suitable control system.

Some kind of interface unit to translate this info and put it on PC

You could keep it simple and use classic I/O which would be:
Digital Inputs (DI)
Digital Outputs (DO)
Analgoue Inputs (AI)
Analogue Outputs (AO)
These will be compatiable with just about any industrial PLC made in the last 10 or even 20 years.
You can pick up some 2nd hand ones on E-Bay!

Nowadays many people use field bus communications such as "profibus". Using this vast amounts of information and signals can be sent on a single cable, but it is expensive. For HVAC systems it is often used between the PLC and VSDs (variable speed drives).

Do you need a software licence

Strictly speaking, yes.

For turning off say the air con do you need another interface unit or will the energy monitoring interface unit do for this as well

You can use I/O to drive contactors to do anything you like.

Software guy needed to set up the program

Yes.

If you want to add to the system afterwards will you need the software guy to come back again?

Yes

Is there a unit needed to generate 4-20mA or 1-5 volts

Not really. Most analogue signals connected to a aPLC nowadays are a current signak (4 to 20mA) rather than a voltage signal (0 to 5 or 0 to 10V). This is because over an "instrument loop" the current does not drop where as the voltage does over long runs.

For example, 24VDC will connected to a temperature transmitter (TT). The transmitter is connected to a temperature sensor such as a PT100. The TT is range from say 0 to 300 DegC. So at 0 DegC it will adjust the current on the loop to 4mA. At 150 DegC the current will be 12 mA and at the top of the range the current will be 20mA. So it is the measuring instrument itself that determines what the current is.

The PLC will check what the current determined by the instrument (in this case a temperature transmitter) is periodically (the frequecny of checking the current is determined by the programmer). This current measurement will corrispond to a value that the PLC will write into a data register. By rescaling within the PLC the temperature can be determined by the PLC.

Is there some unit needed to tie the system to the company IT network

Yes