I recently blogged on the topic of reducing after-hours energy use and highlighted what an enormous opportunity it presents for those of us looking for ways to reduce energy use.
By way of a quick recap, our data crunching found that most commercial buildings are empty for over 6,000 hours a year (72% of the time), and will typically consume over 50% of their annual energy budget whilst standing empty! You can download our free ebook on the topic here.
The focus of that article was largely around when your building uses energy, and helping ensure that consumption is tightly aligned to hours of operation. In this article we’re going to explore that a little further and look at where all that energy is going – highlighting the easiest ways to reduce energy.
Modern buildings are pretty complex things. Even a structure as simple as your own home will most likely have a fairly extensive electrical system with dozens of energy consuming devices installed. Once you move up the food chain to commercial buildings that complexity increases enormously. However, if you have serious aspirations to be more energy efficient then it’s something worth thinking hard about.
Most of us would like to think we have a reasonable idea about where the energy we use in our buildings is going and I’m sure we’d all list off the usual suspects like HVAC and lighting. If you stop and think about it for a moment, you’ll probably throw in plug loads too. If you got those three, then well done. For most commercial and government office buildings that pretty much covers it.
Taking it a step further, there’s no shortage of published information out there providing high-level breakdowns of usage, with figures for HVAC 50%, lighting 25% and plug loads 25% often quoted*.
The problem with these numbers is that they’re necessarily imprecise, representing an average across a huge dataset of buildings, large and small, young and old. The reality for your building or portfolio is likely to be quite different, and it’s in the detail that the real opportunities for ways to reduce energy are revealed.
To help illustrate what I mean, we’ve pulled some data from our own data warehouse. The chart below shows a week’s worth of energy consumption from back in March 2013 for one of our clients, a commercial office building. We’re monitoring energy use through the building split up by HVAC, lighting and plug loads. We’re also separately monitoring the server room.
So what is the data telling us?
Even to the untrained eye, it’s clear that the HVAC and lighting are automated as they power up and power down at the same time every day, regular as clockwork. This is actually a very healthy looking profile, with a nice fast ramp up of the building in the morning, an equally fast shut down at night and next to no HVAC and lighting use outside of operating hours.
Equally, you can see that plug loads vary to a much lesser extent, indicating that a significant portion of these loads remain on, even when the building is empty at night times on over weekends. Just look at all that orange on Saturday and Sunday!
Whilst there may be a number of efficiency opportunities to be unearthed by further tuning the HVAC and lighting for the building, the one opportunity that clearly stands out from the data is to reduce plug load consumption, especially outside of office hours.
The rise of plug loads
Over the past few years there have been significant improvements in the efficiency of the larger, centralised building systems such as lighting and HVAC. This is well illustrated in the example above. Over the same period there has been a steady increase in plug loads which are responsible for a significant, and steadily increasing, proportion of energy consumption in commercial buildings. In fact, the more efficient your building is, the greater the relative contribution of plug loads will be.
According to the US Energy Information Administration this trend is likely to continue over the next few years, as illustrated in the chart below.
What constitutes plug loads will vary a bit from building to building but, in a typical office building, the main culprits will be (in order): PCs, monitors, imaging equipment, other things like projectors, coffee makers and desk fans.
Power to the people
One of the most interesting elements to the plug load story is that this is typically the chunk of electricity consumption over which building occupants have the most control. Plug loads are not normally managed by the building; rather, they are managed by you and I. Even allowing for the rollout of power management software and hardware for PCs, this is one of the ways to reduce energy where occupants have almost total control.
The most immediate challenge for building owners and tenants wanting to explore ways to reduce energy use will be gaining access to data. The nature of this challenge can be both technical – “Do we have sufficient metering to tell us what we need to know?” – as well as political – “Are we allowed access to metering data for our tenancy?”. This can be particularly troublesome for tenants in large commercial buildings where data on their energy consumption is often carefully guarded by the building manager.
Thankfully, with an ever increasing focus on efficiency, sub metering is becoming much more common and the attitudes of building managers are softening a little, although there is still much work to be done and we encourage you to proactively engage your building manager around data access.
Putting in the effort to understand when and where you’re using energy within your buildings will be the best energy efficiency investment you make.
Buildings are complex and, whist occasionally energy waste may be widespread, in many cases it will be limited to a handful of areas, with the rest of the building performing quite well. The trick is to identify which areas represent the best ways to reduce energy use and then to set performance targets against those areas so that you can track improvement.
Plug loads should be a focused and deliberate part of energy efficiency strategy, for three reasons:
- Collectively, plug loads represent a significant proportion of your energy consumption, anywhere from 25% to 45%.
- Plug loads are often the biggest contributor to out of hours consumption
- Plug loads represent a great opportunity to include building occupants in the energy efficiency process. Real and significant savings can be made through education and awareness campaigns for staff about efficient behaviours and usage patterns.
* 2006 review of LEED-NC v2 energy modeling
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