An efficient BMS needs customised programmable logic control to automate processes and reap energy savings, says Christopher Edwards.
Lights left on after close of business, heating empty rooms, and unused equipment in standby mode are causing headaches for facilities managers concerned with keeping down operating costs and the carbon footprint.
An efficient building management system (BMS) based on custom-built programmable logic control (PLC) presents a solution by automating operating processes to maximise energy savings.
What is PLC?
PLC stands for programmable logic control. This means a device can control other devices based upon rules, strategies or logic that you create. It is a device that allows you to decide how it works.
PLC devices are programmed using PLC software. Within a PLC strategy, or software program, multiple controllers or devices are linked together and control each other based on the rules the user sets up.
How does it work?
Controllers are used to link together multiple systems that would otherwise not communicate and so would waste energy, such as heating, air conditioning and windows.
Using PLC helps to ensure that all systems in a building work with, and not against, each other - saving energy and smoothing operational processes. For example, if the heating and air conditioning system can communicate with devices controlling the windows, energy could be saved by turning off HVAC systems when the windows are opened. At the same time, manual checks of windows and heating become unnecessary.
Improved efficiency stretches beyond energy savings and can also be used to increase the efficacy of the installed devices. Connecting lighting and security alarm systems results in significantly reduced energy usage when a building is unoccupied as lighting can be automatically shut off when the security system is set to active.
And if an intruder is detected the lights can be set to switch on throughout the building providing security and CCTV with optimal conditions to identify and catch intruders.
How can FMs create their own PLC strategy?
The first thing that FMs need to do is identify the inefficiencies within the building's HVAC and lighting systems. Only when they understand this will they be able to create a strategy to optimise their BMS.
There are many ways to program PLC software, ranging from text strings and ladder systems to the more common object-based platforms.
Object-based solutions allow users to create strategies by dragging objects onto a blank page and connecting them using an array of rule, maths or function-specific blocks. This method has grown in popularity owing to the ease with which programs can both be created and read.
When creating strategies, the user will usually start by simply adding the inputs and outputs to the page. Once this has been completed they will start to set rules using a combination of simple maths, Boolean logic and more advanced 'function' specific blocks.
Specifics will vary between different solutions, but desktop editing software is available for users to create or amend existing strategies in-house.
How can FMs review the PLC strategy's success?
Success can be measured in many ways. Good PLC programs provide a simulation function that allows users artificially to dictate values to gauge the impact they have on the program when it is in operation. If the ambient temperature is changed does the heating come on automatically? If a window is opened, will the heating system shut down?
BMS manufacturers can often provide a development kit in addition to the control hardware. Development kits typically consist of a suitcase-type box with a PLC controller, numerous inputs, switches and LEDs. PLC software can then be fully tested before being put into use on a live site.
The final and most telling sign of a PLC strategy's success is answering: "How does the building perform?" Has your control achieved your targets in relation to energy, customer comfort and overall efficiency? Before implementing the new PLC strategy it is advisable to put a plan in place for measuring the desired data and excluding other factors affecting results.
Christopher Edwards is technical applications specialist at Resource Data Management
