You’ve probably heard stories about pesky building occupants who just won’t go along with what the clever designers intended for their low-energy building.
There has been much head-scratching about how to deal with this problem, both in influencing occupant behaviour and the amount of control they should be given, such as the ability to open windows and control over heating/cooling.
Changing occupant behaviour
Occupant behaviour has a significant impact on the overall energy consumed by a building. It remains a challenge for those trying to design buildings for energy efficiency, with well-intentioned efforts often thwarted by the behaviour of occupants.
In addition, the effect of occupant behaviour on energy consumption is difficult to quantify for methodological reasons. Any research on the topic is challenging because of the many and varied factors that influence behaviour.
Research shows that three things can make a big difference on behaviour: energy use feedback, social interaction, and gamification.
There is evidence that behaviour changes are only short-term. This is because people sometimes react in unexpected ways to eco-feedback, which can lead to undesired consequences, such as cold homes or even increased levels of energy consumption.
Rebound effects (where the money saved by reducing energy use is spent on something else that uses energy) and other unintended consequences depend largely on user engagement.
Research is starting to recognise the importance of user engagement, with one piece of research in the UK recommending to the government that it reconsider a proposed investment in in-house displays because they become out-dated faster than apps on smartphones and websites.
The study also recommended the use of carefully designed feedback. Another more recent study reported that normative messaging could have a positive influence on behaviour in the long-term.
A large-scale study of 2000 households and a study of utility eco-feedback programs concluded that users responded well to real-time feedback on their energy use. Energy savings of 15 per cent and seven per cent, respectively, were reported.
Other research has come to the conclusion that because people hate to be forced into habit change, a participatory process is preferred. This means involving both the occupants of buildings (such as offices) and energy managers or designers to come to an agreement about how to best cooperate with the building design to save energy.
As well as self-monitoring, energy use apps can provide comparisons to neighbours’ usage, which has shown to be an effective instrument in changing behaviour. Adding advices and tips on the dashboard has also been shown to improve the impact of eco-feedback and provide greater energy savings. There are now many apps like this on the market.
But most people don’t think in terms of kilowatt-hours or CO2 emissions. They need something more user-friendly that is easy to get their heads around. A visual means of giving feedback is important, with images of trees one ideaalready demonstrating success because people tend to associate trees with carbon dioxideabsorption.
Leafully is one app that converts energy consumption into the impact in trees and other interesting units such as cow flatulence.
The app allows users to set targets based on these metrics, gives some advice on saving energy, and allows users to compare their energy use with neighbours.
Building size
For planners and designers it’s important to factor in the correlation between building type, size, occupation level and energy use. Average annual electricity consumption typically increases with floor area.
Furthermore, the monthly electricity consumption of terraced (row) houses is between 70 and 75 per cent that of detached houses, while semi-detached houses use about 90 per cent that of detached houses. In winter this rises so that the difference in the annual demand on the grid between detached and terraced (row) houses is between 24 and 30 per cent (in Northern Ireland, at least, where this study was done).
Electricity consumption per person also decreases as the number of occupants increases. Large dwellings with smaller numbers of occupants use the most per person. It should not be surprising that richer people use more electricity, but the poor can also use a lot because household energy efficiency features are not always affordable.
Apartment blocks will usually give the lowest per person energy usage, however, in these situations it is the heating, ventilation and cooling which would need the most attention because it will form a significant part of the overall energy usage.
Predicting energy use at scale
As we all know, what gets measured gets saved. For authorities working at the neighbourhood or district scale, urban building energy modelling can be a useful tool for analysing the building stock, but the accuracy and relevance of the input data is crucial.
It also depends on what data is available in each country. Data that is available is potentially time-consuming to aggregate, with data access often limited due to privacy concerns.
In Denmark, a hierarchical bottom-up model of residential building stock using public building data has been used to predict the annual heating energy consumption with some degree of accuracy.
This experiment tested over 10,000 randomly selected single-family dwellings in the city of Aarhus, Denmark, and found that half of the energy use was explained by just four easy-to-discover building characteristics.
These are: the construction year of the building, the heated floor area, the refurbishment status, and the presence of supplementary heating installations in addition to district heating, such as heat pumps, electric radiators, fireplaces or wood-burning stoves. These characteristicsare detailed in the Danish Building and Dwelling Register.
This meant that predictions of energy use could be made with a mean absolute error of about a quarter. But at the city-wide level, a regression-based model enabled aggregated predictions with a mean bias error of less than just ±2 per cent.
Single-building predictions remain somewhat imprecise but comparable to current state-of-the art high fidelity UBEM, meaning that if the purpose of a given urban modelling task is to calculate the aggregated energy use on an urban scale, a simple regression-based approach will be adequate.
Should we let occupants open windows?
So, should building occupants be allowed to open windows? What if they were given visual nudges as to when this might be a good idea? In the Syracuse Centre of Excellence (a LEED Platinum test-bed facility) small green and red lights are situated above eye level near to windows as part of a building maintenance system.
The green lights glow on warm days, indicating that opening a window or two would increase the comfort level, while the red lights come on when the sun goes down and the temperature drops –prompting inhabitants to close the windows. The lights operations are based on outdoor temperature, humidity, air quality, and wind speeds. Of course, the inhabitants need to be told what the lights are for and reminded to look at the lights every now and then.
If occupants can open windows – a good idea for internal air quality and general well-being – then the air conditioning controls must be able to tell that a window is open and turn off the cooling air supply to that zone.
It might also be a good idea for some windows to be remotely controllable so that they can be opened at night to promote night ventilation cooling.
Narrow buildings with natural ventilation are less negatively impacted by times when ventilation systems are inactive (such as power outages), as they are less dependent on daylight and artificial cooling.
Finally, screens to keep insects out, ceiling fans, and openable windows can minimise use of air conditioning. The Infosys office in Hyderabad, India (above) has openable windows and ceiling fans that offer a perceived cooling effect of up to 5.6 degrees Celsius, enabling a temperature increase in the workspace while maintaining comfort.
David Thorpe’s two new books are Passive Solar Architecture Pocket Reference and Solar Energy Pocket Reference. He’s also the author of Energy Management in Building and Sustainable Home Refurbishment.