Energy efficiency ratings, appliance labelling and various other energy bench-marking systems vs energy efficiency performance… Is there a difference, what does it mean and is it important to understand? Karel Steyn, SAEE* president, investigates.
We often hear of buildings, equipment or appliances being rated as most efficient when it comes to energy consumption. This is usually interpreted to mean that if it is most efficient that it must also use the least energy. However, is this always the case? Buying more efficient equipment (on its own) is not enough to ensure energy efficiency and there are very good reasons for this being the case.
There are many rating systems, labelling systems or benchmarking systems in existence. In addition to appliance and equipment labelling, minimum energy performance standards (MEPS) have been introduced or are proposed, which are also a type of labelling, rating or benchmarking system. Some are well-known and have become familiar to many of us. The fact remains that there are many standards and a variety of tools on energy-labelling or the like. Most of these provide excellent guidance on what would represent energy efficient buildings, appliances or equipment.
The South African energy efficiency label, the Green Buildings Council’s Green Star Rating, the American Energy Star Rating, the SABS standards SANS 941 (air-conditioners, TVs, dishwashers, refrigerators, etc.), SANS 204 (maximum energy efficiency per building type), SANS 10400-XA (for new buildings) and the latest Energy Performance Certificates (EPCs) are all relevant to labelling, ratings or bench-marking for energy efficiency. Some of these have already become mandatory. These systems usually consider the energy use per time period, benchmarked against similar pieces of equipment/appliances/buildings or the energy use against another applicable measure, like the energy use per m2 of floor space (specific use of energy, e.g. kWh/m2 is also a rating).
This makes perfect sense because you cannot be most energy efficient if you are using inefficient and outdated equipment, appliances or buildings. The objective of these energy efficiency rating- and labelling systems is to ensure that you start with the most efficient building envelope, equipment or appliance so that you can ultimately become as efficient as possible! However it does not, or should not, stop here…
Various external energy drivers have to be considered, for example, the geographical location where something is used. You cannot expect two buildings which are exactly the same in all respects, but with one in Cape Town and the other in Upington, to perform the same when it comes to energy consumption. The energy use for buildings is heavily influenced by the ambient conditions (temperatures, relative humidity, direct solar radiation, etc.) around the buildings. The ambient conditions in Cape Town are completely different to those of Upington and the energy use (or building performance) must therefore be different as well. Stated differently, the heating and cooling requirements, and therefore energy consumption for these two locations, are completely different.
Labelling or rating as generally used (in isolation) will therefore not provide a true reflection of real-life building energy performance, because only floor space is considered and not climatic conditions. It does enable the bench-marking of the two buildings against each other which is useful on its own.
Another driver of energy use is the way in which the energy consuming facility or equipment is used. The one building might be fully occupied (or overloaded) while the exact same building next door may be standing empty. It should be obvious that the empty building will use much less energy.
Perhaps this can be even better explained using an analogy to motor vehicles. We all use (drive) our cars differently! I may have the most efficient car available but the energy consumption will depend on the way I am driving it – this will be the case even if I am driving a Hybrid or fully electric vehicle.
I’ve not touched on many other energy drivers, like maintenance, occupancies, behaviour, etc. which will also have an influence on performance.
Of course the design is also important. In this respect: Do you think the new modern shopping malls, some with energy star ratings, are generally most efficient, or even more efficient than all of those built some time ago and not modernised? A very good question! Fact is, the Oriental Plaza in Fordsburg, Johannesburg, with no star ratings, uses less energy per square meter (is more energy efficient) than most of the new malls, many with star ratings, which are built to look and feel like hot-houses. Even the Brightwater Commons Mall in Randburg would be more energy efficient than many of the new malls. Why do think this is so?
What then is the difference between energy ratings and energy performance? I think it is clear from this message. Labelling, ratings, benchmarking and the like refer to the potential of what you buy or have. These are mostly analysed from plans or as built using simulation or detailed analyses. Using the car analogy again, labelling describes the type of car you drive, like a 2ℓ, 3ℓ or hybrid.
Performance refers to the results from the combination of what you have and how you use it (evaluated from actual normal in-use measurements). Both, what you have as well as how you use it or the type/size of your car and how you drive it, will have an influence on the energy use and therefore on the energy efficiency level. Some 6-Star rated buildings may therefore perform worse than some 1 star rated buildings – the same goes for anything else which uses energy. Good measurement and verification should always consider both aspects, e.g. ratings/labelling/benchmarking and the normal in-use performance!
This understanding brings about two very important considerations:
1. It is important to always use energy wisely, always be energy conscious and always consider energy efficiency, even if you already have the most energy efficient equipment, appliance or building.
2. It is more beneficial to manage the actual performance of the facility, equipment and appliance while in use because that will represent the real energy impact and energy efficiency level. (This will then also be the better approach for any incentives or contracts).
*Southern African Association for Energy Efficiency (SAEE)