How can we (actually) save energy in buildings?

After a few weeks’ break — working, resting, and following the disturbing news coming from the Middle East (and the Wild West) — I’ve been back in touch with my newsletter subscribers.

For this edition, I’ve focused on what seems likely to matter most in the coming months, years, decades? Who knows…

I’ve focused on how we can actually save energy in buildings.

And by “actually” I mean energy measured in real-life meters, and paid in real-life bills. Not just saved in theory or in our models.

Basically, we won’t save energy just by:

🔴 talking about energy saving measures

🔴 analysing their economic ROI in optimistic scenarios

🔴 preparing presentations in early project stages

🔴 creating energy models on computers

🔴 meeting some targets in theory

We may even not save much energy by:

🟡 specifying more insulation or more efficient systems

🟡 getting projects to comply with more demanding regulations or standards

🟡 using the smartest tools and AI to generate optimal designs

We actually save energy in real life when:

🟢 the boilers/chillers/heat pumps/heaters/fans/pumps are not running

🟢 they run efficiently when needed

🟢 other equipment in the building is on only when needed

🟢 lights are off if nobody needs them

That might sound silly, but it’s exactly what we are not achieveing in many cases when trying to save energy in buildings.

And it’s the reason why there is often a notorius gap between the energy-efficency credentials of a building and its performance in real life.

It’s not that we need more accurate models, or better standards, or better technology (which seem to have become the “raison d’être” of energy efficiency professionals).

These might help to some extent, but they are not the essence of the problem.

The essence is that we need to relearn how to focus on using less and not more. An ability that many of us have lost in the last decades of overabundance.

Once the focus and priorities are clear, we should be able to align all available methods to serve that purpose most effectively.

Now, let’s look at some measures we could apply to have better chances of achieving real-life energy savings. As well as their order of priority in my view.

If you think about it, it’s quite surprising how little we know about how buildings are used in real life. Especially when it comes to making design decisions. And even more when these decisions are related to energy efficiency.

This becomes flagrant when you undertake an operational energy model. Which, if you are not familiar, is basically an attempt to make a reasonably accurate prediction of the future energy consumption for the different uses in a bulding to inform design decisions.

🙋‍♂️ You ask the architects about how spaces will be used:

— No idea, just vague descriptions or intentions. They might just ask or point you towards the M&E engineers.

🙋‍♂️ You ask the M&E engineers:

— If anything, they’ll give you the peak loads they use for sizing the systems. Which, if you are not familiar, are the typical, decades-old, worst-case parameters they use to estimate the maximum loads the systems might need to handle someday.

🙋‍♂️ You try with the developer representatives:

— If you are lucky, they might tell you the expected opening times and a basic schedule (but you are more often unlucky).

If it is a retrofit of an existing building, you might be a bit luckier and someone from the building management may provide some more details of how spaces have been used. But they won’t collaborate much in putting together potential future scenarios.

Some people (especially in the UK) think that standards like TM54 or NABERS DfP are the solution for more realistic energy analyses, but when you work with them you realise they are just a starting point for understanding what you’d really need, rather than providing actionable information.

However, understanding how buildings are used in real life, with sufficient detail, is an essential first step in making better decisions on how to optimise energy use.

In my view, government energy departments or other relevant institutions should lead large-scale studies on how buildings are used that can inform more realistic energy-saving analyses. It is that important.

Once the real use of the spaces, equipment, and system controls is well understood (in existing buildings) or likely scenarios are established (in new buildings or retrofits), we can focus on the available measures for optimising energy use to achieve the building’s objectives.

And, before any “hard” measures involving changing or defining insulation and systems are determined, “soft” measures involving reducing the demand from the building activities should be also analysed.

Soft measures are normally much cheaper and can often achieve bigger savings than the hard ones.

Examples of soft measures for existing buildings could be:

💭 reviewing that the operating times of systems match the occupancy requirements

💭 reviewing the set points at which the heating/cooling is operated

💭 making sure there isn’t equipment using energy when not needed

💭 reviewing lighting needs

💭 analysing if activities can be distributed differently in the building so some areas can be turned off at certain times

💭 putting together an energy saving strategy and people responsible for fine-tunning it

💭 adding smarter controls and managing demand times to avoid higher grid strain and tariffs

Similarly for new buildings, based on lessons learned from existing buildings, these measures could be incorporated during the design. And further developed throughout the construction and handover stages. Developing an energy strategy for the building from its inception that goes further than just defining glazing ratios, U-values, and HVAC systems.

There’s often a debate on what should go first for energy efficiency: fabric (passive) measures or active measures (renewables, efficient HVAC systems, etc).

The debate is usually focused on economic analyses, more or less rigurous technical arguments, or even political agendas.

In my view, what should be incorporated first depends on the characteristics of the building and the project.

Actually, to achive more optimal designs, the options of both passive and active measures should be considered together, using an integrated and iterative approach.

In general, we should forget about generic rules and avoid oversimplifying building performance if we want to be serious about saving energy.

There are several aspects worth mentioning when deciding and defining the systems in order to achive real-life savings:

⚠️ The efficiency figures provided by manufacturers are based on standard test conditions, which may be quite different to the real dynamic conditions in each project and climate.

• Where possible, their performance should be modelled incuding the specific project details or considering measured data in similar projects and weather.

⚠️ How the systems are controlled in reality can have a significant impact on their efficiency, as well as how flexible they are to adapt to variable demands.

Examples:

• Heat pumps that lose their theoretical efficiency by starting and stopping too often.

• Centralised HVAC systems that use the same energy regardless of how many rooms are occupied.

• Buildings used occasionally served by systems most suitable for continuous occupancy.

• Systems that require active management to be efficient, but without anyone responsible for management.

Again, modelling with sufficient detail and common sense, considering realistic use patterns of the buildings, is key to making good energy-saving decisions on systems.

Of course, significant energy savings can also be achieved through good insulation of the building’s thermal envelope.

However, as we’ve seen, this is not necessarily always the first or most important measure when looking at overall, real-life energy consumption. Since it only influences heating and cooling energy, and the importance of these can vary significantly in different buildings and climates.

For example, in buildings with high internal gains and cooling requirements for several months, after certain level is achieved, adding more insulation can be unnecessary or even detrimental for energy consumption or thermal comfort.

And when considering insulation we shouldn’t just focus on adding more and more thickness. The type of insulation and the details, shuch as minimising thermal bridges and airtightness, can be as important for optimal performance.

🧐 For some projects, it can be also important to consider the limitations of the modelling methods in representing the real performance of the thermal envelope. Since U-values are just a simplification of the real performance of materials. And even more-advanced dynamic simulations, which take into account both thermal conductivity and thermal mass layer by layer, don’t consider other influential variables, such as moisture content or variations in conductivity with temperature.

🧐 When calculating energy from thermal envelope options (especially when they involve glazed façades) it can also be important to check that the values obtained correspond to actual thermal comfort conditions (e.g. looking at the operative temperatures achieved rather than just air temperature). Otherwise, there’s a risk the actual set points used in real life are different to those modelled, and then energy consumption can also be quite different.

We should always consider the intersection between energy saving and other important aspects for building performace, such as:

• Ventilation requirements
• Moisture management
• Daylight levels
• Internal and external pollutants
• Noise levels
• Safety and health in general

All important but sometimes overlooked in the pursuit of “cheap” energy efficiency.

And, at this moment in time, with all the uncertainties floating around on energy security, climate change, etc, it might also be wise to think about building additional resilience in our buildings for much worse scenarios.

E.g. Would they still be habitable with no energy supply and rising (or falling) temperatures? For how long?

I think that’s all for this edition (not so bad for a return 😁)

I guess I haven’t reinvented the wheel here, but I believe further improvements in energy efficiency won’t come so much from inventing anything new as from being more honest with ourselves and applying more common sense.

If you’d like to see anything more specific to be discussed, feel free to let me know.

Have a nice day!

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