- Can't my BMS already tell me all this information?
- How many items can you track?
- How does Demand Logic compare with sub metering?
- "BMS is more trouble than it's worth." Is this true?
- We can already get metering data. Why do we need this?
Can't my BMS already tell me all this information?
In theory, all the data we use is available inside your BMS (Building Management System). That's where we get it from in fact. But there are several reasons why we recommend a separate analysis tool (aside from wanting your business of course!):
Firstly, BMS systems are not very good at number-crunching because it's not really what they were developed for. The typical BMS 'controller' (for example, the digital controller that is attached to each ceiling-mounted air conditioning unit) is excellent at reliable 24-7 control. Once programmed, such units faithfully cycle through a table of simple steps -- predictably and (all being well) indefinitely. But in order to get such units to do other calculations (say to drive displays or test ideas), the whole strategy must be reprogrammed. This puts the main control task at risk and can over-complicate the controller's software, making it opaque to future controls engineers.
Secondly, the needs for display and analysis are dynamic and unpredictable. We believe the most successful approach to eliminating energy wastage in buildings is for people to be free to explore new ideas or hunches, and be able to test them easily against real data. It is simply too time-consuming and expensive to have to reprogram individual controllers in order to see the results of new calculations.
By gathering the data into a central resource, Demand Logic allows for new ideas to be tried out instantly, and the results of investigations shared easily.
Thirdly, there is the matter of logging and storage. Demand Logic (as of December 2014) is streaming around 8 million data points each day. This is because most of the insights we provide require a full 'history' as well as live values. Modern databases make storing and operating on this time-based 'big data' very easy indeed. But we believe it is simply too much to ask for a control system to handle this task. It is true that some BMS systems provide a data-logging facility but again, you have to reprogram the specific controller (and use up its limited memory) in order to make us of this.
We would advise leaving your BMS to do what it's good at (reliable 24-7 control of the plant) and use a separate system for the data-crunching and display.
How many items can you track?
Theoretically, there is no limit to the number of plant items we can track. However, we place a strict limit on the amount of data we stream from your building management system. This is in order to ensure we have no impact on the BMS network. This means that we may need to reduce the polling frequency of some of the data items in order to increase the number of items we track. But in practice this is not usually noticed in the final dashboard.
How does Demand Logic compare with sub metering?
Many organisations are installing "sub meters" to track energy use of specific zones or plant items. Sometimes, these are an ideal option, for example where the data is needed for billing purposes. However, sub meters can be very expensive - often as much as £1000 each when everything is taken into account.
If you are considering sub-metering because you want to find energy savings, we strongly recommend that you first make the most of the data in your building management system. There is so much detail in there showing when plant is running and what is likely to be causing high energy-usage. It just needs a little analysis. Also, we find that "virtual meters" give a more granular picture as you can in principle track every single terminal unit (ceiling-mounted air-con unit). Virtual metering is where you calculate the live energy using say, flow and return temperatures and flow-rates.
"BMS is more trouble than it's worth." Is this true?
In our experience, the BMS equipment itself is hardly ever to blame for problems in buildings. Generally speaking, the leading brands provide highly configurable and reliable controllers, perfectly suited to controlling the plant. The problems are nearly always in how each controller is programmed and whether the mechanical systems and sensors etc have been properly installed or maintained.
In new buildings for example, when budgets inevitably run over, it is often the controls commissioning stage that gets pared down at short notice. This ends up with good BMS equipment going in but with sub-optimal programming (also called 'control strategies') applied to the controllers. Good ideas which may have been in the minds of the designers end up not being implemented in the controls. This can lead to a lack of faith in BMS as a whole -- with critics saying that even new systems don't work properly.
Also, in older buildings, the system quality can be eroded by a series of short-term fixes applied by different people. For example, a facilities team may quite rightly respond to complaints by putting certain items of plant into manual (also called 'in hand') as an emergency measure. But then the vital step of fixing the underlying control problem can be skipped and again people start to lose faith in the BMS itself.
But the good news is that in nearly every building we have looked at, there are low-cost improvements that can be made to the control strategies that lead to immediate and lasting energy savings and comfort improvements.
We can already get metering data. Why do we need this?
It is a common mistake to think that saving energy is a matter of measuring energy consumption. Yes, there are many projects that gather metering data, store it, and display it beautiful ways. And of course, it can be a very important part of an energy-efficiency drive (especially in evaluating the success of projects).
But metering is only a tiny part of the story. If your building has a half-decent BMS, it will know when your boilers and chillers come on, when pumps run, if fans are left running, what each hot and cold water valve is doing -- basically, you are probably in possession of a massive resource of clues about how your plant is behaving over time. And (with proper analysis and display) this is what leads to insights about how to reduce energy consumption. In fact, it is often true that preventing a particular wastage (for example, an extract fan running overnight) is actually easier than measuring its energy consumption.
In summary, if your analysis is based on metering data alone, no matter how clever it is (regression, degree-day correction, etc) you will be missing part of the picture.
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