Thursday 24 March 2016
What does making a house “energy efficient” actually mean? by Richard Fitton, Lecturer in Energy Efficiency
Efficiency programmes range from the provision of low energy light bulbs to whole-house retrofitting. As researchers in the field, the one question we are always asked is: “If I do this, how much energy will it save?” To which we give the helpful answer: “It depends”. There is lots of advice out there, after all, and the media, charities and local authorities all provide guidance. But just how much of it is based on real scientific evidence?
Often, when a home is made more energy efficient, people simply decide to absorb the savings – in both money and heat – by keeping their houses warmer. Energy consumption may even increase. This is known as the “take back effect”, or Jevons Paradox. In the UK, this effect accounts for an average of 35% of the initial saving, although individual homes may be more extreme. This further confounds the predicted models that the improvements may have been sold on.
Turning an entire house into an experiment
Given we know exactly how the house was built, how it is “used” (by our researchers), and the “weather” it is exposed to, we can get a very good idea of how efficient it is. When we add curtains, better thermostats or other improvements, we can compare results with those from the original, unimproved house and try to find the difference. Our tests are extensive, detailed and give us data that would be impossible in the field – no actual homeowner would want nearly 300 sensors attached to their house.
However, if we are questioned as to how much a particular action or improvement will make to a homeowner, it still “depends”. This is because every home and family is different: some people are home all day, some people are rarely in; others, such as those who have chronic illnesses, need different internal temperatures to those who don’t.
Fond of inefficiency?
Closing your curtains may save lots of heat, but the number and type of windows, location of radiators, and when they are opened or closed will greatly influence this saving on an individual home. Houses come in all sorts of sizes, shapes and levels of efficiency, particularly in the UK, where we are fond of our older, energy inefficient housing stock.
We can give guidance based on data, but when it comes down to an individual home there will always be confounding variables that might mean actions or improvements will not perform as expected. Even in our energy house, where we can compare one action or improvement against another to a high level of detail, we are really only able to give a miles-per-gallon perspective – much of it will depend on your car and how you drive.