Energy Efficient or Energy Efficiency? 28 Term Definitions

Using the term energy efficiency (noun) or energy efficient (adjective) can mean many different things!

Energy Efficiency

1. Energy efficiency = rooftop solar. Yep. When I tell people I work in energy efficiency often the response is, “oh, so you work with solar systems.”
2. Energy efficiency = the first fuel. A term used by those frustrated with energy efficiency playing 2^nd 3^rd 4^th violin to solar, wind, coal, gas, hydro, nuclear…
3. Energy efficiency = “negawatts”. A term used to show that power stations can be replaced by energy efficiency. Used by policy wonks.
4. Energy efficiency = minimum energy performance standards, or MEPS. Originating out of California, these standards for fridges, air conditioners, washing machines etc have quietly generated oodles of real negawatts. An unsung hero of energy policy.
5. Energy efficiency = to do with retrofitting existing buildings so that they use less energy. With carbon neutrality a 2050 goal for many, probably half of the buildings existing today will still be here in 2050. Usually the focus of an energy auditor.
6. Energy efficiency = to do with green buildings. A green building is one that should be comfortable, have good indoor air quality, and not use much energy. The term green building is usually applied to the design intent of the building, not its actual performance. Although there is growing interest in verifying actual performance.
7. Energy efficiency = energy conservation = choosing to use less energy = behaviour change. e.g. turning the lights off in empty rooms.
8. Energy efficiency = designing a system to use energy efficiently. For example, choosing efficient light fixtures and an efficient light source and carefully selecting the position of these fixtures, such that a night time workspace is comfortably illuminated and the brightness of different parts of the workspace matches the need for illumination in that particular area. E.g. desk spaces need more light than circulation spaces.
9. Energy efficiency = demand response = demand management = supply responsive. As electricity supplies move away from fossil fuels and towards intermittent sources of energy, such as solar and wind, a supply responsive building is one whose energy use can be matched to that of the available supply. An emerging frontier and opportunity for those involved in energy efficiency.
10. Energy efficiency = smart design that enables the frugal use of resources.

Energy Efficient

11. Energy efficient. The advertising of a new housing estate that has yet to be built but where the street light poles have solar panels mounted on them.
12. Energy efficient. Skype, Zoom, Whatsapp or similar instead of travelling for a meeting. If the time and money avoided by not travelling is put into a great video conferencing system, its almost as good as travelling, but with a fraction of the carbon footprint.
13. Energy efficient. Designing a building that uses very little energy and incorporates a solar system to offset all energy use, or so that the building uses “net zero energy”. Ideally the design intent is followed through to ensuring actual zero net energy performance.
14. Energy efficient = A building designed to efficiently use electricity, but with no natural gas connected to the building, enabling the transition away from fossil fuels in energy supply.
15. Energy efficient = being frugal with your use of resources.
16. Energy efficient = an aerodynamic electric sedan that uses 14 kWh per 100 kms, vs an electric SUV that uses 25 kWh per 100 kms.
17. Energy efficient = a bicycle with a 200 watt electric assist, used instead of the electric car to commute 20 kms to work.
18. Energy efficient = a can of baked beans and an ordinary bicycle to go commute 20 kms to work.
19. Energy efficient. A 30 square (approx 300 m², 3000 ft²) home that has been designed to exceed the regulated minimum energy performance for a new home
20. Energy efficient. A 10 square (approx 100 m², 1000 ft²) new home that just meets the minimum regulated energy performance for homes in relation to a “highly efficient” 30 square home.
21. Energy efficient. A 15 square (approx 150 m², 1500 ft²) new home where during each phase of its construction the proper installation of energy efficiency measures, such as insulation, has been checked off. Will likely use less energy for heating and cooling than the 10 square home built to the same energy efficiency standard which has been building without verifying that the energy efficiency measures are properly fitted.
22. Energy efficient = the 500 litre, 4 door fridge you are being sold to replace your 250 litre 20 year old fridge. Yes, that’s true, the new fridge, although twice the size, will likely use a bit less energy than your old fridge, thanks to MEPS. But a new 250 litre fridge with a high efficiency rating will use around half that of the old fridge.
23. Energy efficient. A building with a high NABERS – National Australian Built Environment Rating System – compared with one with a poor NABERS rating. A NABERS rating is based on the actual energy use of the building. Not to be confused with a building with a high green building (e.g. LEED, GreenStar, etc) score, which is based on the predicted energy use of the building.  
24. Energy efficient = description of a building which won a sustainability award back when it was built in the 2000s due its novel use of mixed mode ventilation. Or in other words an uncomfortable high-energy using building with complicated controls that are supposed to do things like open the windows automatically when its cool outside and hot inside, but don’t, because building construction costs went over budget and there was no money left to get the bugs in the control system ironed out.
25. Energy efficient = an SUV that uses twice as much fuel as a hybrid sedan but less than other SUVs.
26. Energy efficient = any LED light. Whether it generates 50 lumens per watt, or 180 lumens per watt.
27. Energy efficient. Any air conditioner with the word “inverter” stamped on it. See preceding definition.
28. Energy efficient = delivering the same outcome but using less energy.

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