At a cheeky lunch the other week, James Palmer from Metrikus, quite rightly, told me I was stupid. Being the engineering nerds that we are, we were fighting over the best way to measure the efficiency of a building...

I’m a disciple of the LETI (London Energy Transformation Initiative) and their incredible design guide. They have reminded everyone working in built environment sustainability of the need to determine operational carbon performance using Energy Usage Intensities (EUIs). EUIs are measured in kilowatt-hours (kWh) per meter squared of space. This tells you exactly how much energy is needed to operate a building relative to each other. It allows for direct comparison and that means we can see which buildings are performing well, and which ones aren’t.

Today, most building owners need to use Energy Performance Certificates or EPCs. However, there's a growing consensus amongst experts that EPCs, while well-intentioned, have significant shortcomings when it comes to accurately assessing and improving the energy efficiency of buildings. Some of these reasons include:

  • They’re too theoretical: they’re based on simulations of a building's energy performance under standardised conditions. That means that they often fail to account for real-world complexities such as variations in occupancy, weather, and maintenance.
  • They’re a snapshot in time: there’s no real-time data that’s used. Having a good day in favourable conditions doesn’t mean it’s good all year round
  • Limited future accountability: EPCs last for years, and the building could have deteriorated substantially since the last assessment.

Given the scale of the net zero carbon challenge in front of us and the substantial financial impact of having a stranded asset (from new energy performance regulations lurking just around the corner), many have already shifted their focus from traditional building performance ratings like BREEAM (which looks at design performance) to NABERS that uses real-time data to demonstrate real-world performance.

That’s why James, and now I, think that some kind of energy efficiency index would be better than an EPC. Knowing your EUI is a great start. Knowing how the building responds to cold days and sunny summers helps us understand whether it’s a leaky box or a greenhouse. Knowing the amount of heating and cooling days (when you need an energy system to bring the building's internal temperature up or down to something comfortable) helps solve that. Good performance in one season is only half the story.

Furthermore, energy performance looks better when no one’s in. It makes the plug load lower. But that’s actually terrible for energy performance in the grand scheme of things as we’re still heating the office, and the people are somewhere else using even more energy. That’s why normalising the number based on occupancy gives a true picture of how well that energy is consumed in a space.

It sounds more complicated than it is. To come up with that metric, it’ll only take three pieces of tech:

  1. An energy meter to measure actual energy consumption
  2. A thermometer to measure temperature to allow us to calculate the number of heating and cooling days and therefore how ‘energy leaky’ the building is
  3. A people counter to know the occupancy levels of the building and how much ‘usage leakage’ there is.

If there’s one thing that smart buildings can easily help us improve, it’s how sustainable our buildings are and could be.

In Dr Marson’s monthly column, he’ll be chronicling his thoughts and opinions on the latest developments, trends, and challenges in the Smart Buildings industry and the wider world of construction. Whether you're a seasoned pro or just starting out, you're sure to find something of interest here.

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About the author:

Matthew Marson is an experienced leader, working at the intersection of technology, sustainability, and the built environment. He was recognised by the Royal Academy of Engineering as Young Engineer of the Year for his contributions to the global Smart Buildings industry. Having worked on some of the world’s leading smart buildings and cities projects, Matthew is a keynote speaker at international industry events related to emerging technology, net zero design and lessons from projects. He was an author in the Encyclopaedia of Sustainable Technologies and a published writer in a variety of journals, earning a doctorate in Smart Buildings.