Saving energy on site, part 5

Messing with our heads… in a good way

This post is part of a series on CSIRO Newcastle’s energy-efficient office buildings. Read all the posts in the series here.

Are you reading this in an office building right now? If so, how’s the temperature? Is the air-conditioning turned up too far or down too low? Are you too cold or too hot? If so, research has shown something surprising: you might be happier if there was no air-conditioning at all – even if it makes the room even colder or hotter than the temperature you’re uncomfortable with right now.

To explain this crazy-sounding result we need to go back to some research that started in the 1980s, and led to some findings that influenced the design of the CSIRO office building that I’m sitting in at the moment.

In the mid-1980s, researchers in the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) began to fund some studies into building temperature and comfort. They were interested to find out what range of temperatures people found too hot, too cold and just right – and how it varied with things like season and climate. With this data, people designing new buildings would have a better understanding of what sort of air conditioning or heating systems they’d need in order to keep most people comfortable and happy. (Note: it’s widely recognised that you can never make everyone happy with the indoor temperature. That’s why building standards generally consider an 80% satisfaction rate to be perfectly acceptable.)

One decade and several additional studies later, ASHRAE had collected around 21,000 sets of data from 160 different office buildings. This included locations over 4 continents, spanning climates from tropical Singapore to sub-arctic Canada. With all this data it became possible to work out a nice equation into which you could feed information about the outdoor temperature, indoor air speed, humidity, metabolic rate and even the sort of clothing people wore inside, and it’d tell you where to set the air-con to make most people happy.

This equation was pretty accurate for most standard air-conditioned offices, which you can see from the image below. If the scientists knew what they were talking about, the thick black line, showing the predictions given by the equation, should match up with the lighter line with white squares, which shows the office temperature people were actually most happy with. As you can see, it’s almost a perfect match. Equations predicted a narrow ‘Goldilocks’ window from 22.5 to 24°C where people would feel not too cold or too hot, but just right – and this is exactly how people behaved (on average) in real life.

Predicted and observed ‘comfortable’ indoor temperatures for air-conditioned office buildings. From de Dear & Brager, 2002.

But something really weird happened when researchers tried to apply the same equations to buildings that didn’t have air-conditioners; buildings in which if people were hot or cold they’d simply open or shut their windows. For these buildings, the wheels fell off, and the equation – which included every factor scientists knew of that influenced thermal comfort levels – couldn’t account for what was being observed. People were, in fact, much more tolerant of higher and lower temperatures than was predicted.

Predicted and observed ‘comfortable’ indoor temperatures for naturally-ventilated offices. (From de Dear & Brager, 2002.)

In short, there seemed to be something mysterious about air that came through an open window that made it better. Natural air seemed comfortable from about 20 C (on freezing cold days) right up to 27 C (on searing hot days), but take the exact same air and deliver it through an air conditioner, and people would generally find it several degrees too hot or too cold.

Clearly, something else was going on that scientists didn’t understand. But Richard de Dear from Macquarie University in Sydney and Gail Brager from University of California, Berkeley had a hypothesis. They proposed that the difference was mainly psychological.

They believed the differences arose partly because people are more tolerant of situations they can control (like being able to open a window) than those they can’t (such as when someone else has set the air-conditioning, and there’s nothing you can do about it!). They also hypothesised that people get used to the narrow temperature variations of air-conditioned buildings, and that this in turn makes them less agreeable to further variation. If you can open a window on a hot day, on the other hand, a hotter office feels more ‘natural’, and likewise for a cold office on cold days. For more information about de Dear and Brager’s work, see this paper from which the above graphs are also taken.

This hypothesis has been fairly well substantiated over the years, and it goes a fair way towards understanding why, when our building has so many smart energy-saving gizmos with computer control, the architects chose to give us windows that could be opened manually. While the temperature control might be more precise if a computer decided when to open and shut them, it turns out people are much less fussy about temperature if they are simply given the ability to open and shut their own windows.

In reality, our building engineers have gone a step further and combined the two. We have manually-opening windows and a computer system that suggests, by changing the colour of an icon in our system tray, when it might be best to have them open and shut.

A colour-coded icon in our system tray tells us when to open our windows (green), keep them closed (blue) or try and reduce energy usage during critical peak periods (red).

Importantly, too, the computer system also accepts feedback from users, who can send instantaneous comfort reports saying if they’re too hot or cold. The computer knows which zone of the building the feedback’s coming from, and takes into account all the feedback to adjust the temperature setting or ventilation mode. All this gives people more control over their environment and increases the chances we’ll feel comfortable.

The electronic comfort survey in our building. If people are feeling uncomfortable, the temperature set-point or ventilation mode is automatically changed.

What’s the message from all this? In a society where buildings account for 20% of all energy usage, and air-conditioning accounts for the largest portion of this, we might be able to use far less energy – and be even more comfortable – if we turn our air conditioning off from time to time and throw open the windows instead.

◊  ◊  ◊

This is the last post in the series I’ve been doing on the energy-efficiency features of our buildings at CSIRO in Newcastle. As you can imagine, what I’ve put here on the blog only scratches the surface. If you’re interested in reading about our building in more depth I’ve uploaded some recent conference papers by our building engineers on the site’s recent performance and on-going improvements:

And finally, you can see a video below that summarises most of what I’ve written about recently. It’s a few years old now but most of the details are still correct.

Remember, too, that Earth Hour is coming up on the last day of March. It’s a chance to take stock of how much electricity you use in your house – and how much of that you could do without. Perhaps the information in the last few posts has given you food for thought about energy reduction and some ideas for your own place. If so, or if you have other energy-reduction strategies that have worked for you, leave a comment and tell us about it!


One Comment on “Saving energy on site, part 5”

  1. Connor says:

    I actually tend to agree with the whole thing that has been written within
    Wood Blinds “Saving energy on site, part 5 | Solar @ CSIRO”.
    Thank you for all the facts.Thanks for your effort,Jerrod


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