Air Conditioning Efficiency
Are air conditioning units energy efficient?
A question we get asked a lot.
The simple answer is YES – VERY! And here’s why…
Firstly, lets understand what energy efficiency is. Energy efficiency is defined as:
The use of less energy to perform the same task or produce the same result.
Gov.uk
So now let’s have a look at some real world comparisons.
A 1kW electric heater uses 1kW of electricity every full hour it is switched on and running.
Energy efficiency in electrical appliances is usually measured as a percentage (%), and electric heaters are generally considered to be 100% efficient; meaning for every 1kW of electricity they use, they emit the same 1kW as heat.
Therefore, if your energy supplier charges you lets say 26p/kWh, your 1kW heater costs 26p/hour to run for 1 hour.
If your heater was rated at 2kW, you’d get twice as much heat for twice the cost, i.e. 52p.
If you have that 2kW heater on for 6 hours a day, it would cost 6hrs x 2kW = 12kW x 26p = £3.12
Running a 2kW electric heater for 6 hours a day would cost £3.12/day – £21.84/week – £94.64/month – £1,135.68/year.
Now let’s compare that to an air conditioning system.
A 2kW air conditioning unit only uses 0.47kW, (470Watts) of electricity every full hour it is switched on and running.
Energy efficiency in air conditioning systems is measured as a COP (Coefficient of Performance). The COP figure is a measurement that indicates the ratio of heating provided by your air conditioning unit relative to the amount of electrical input it requires to generate it.
In simple terms a COP of 1 would mean for 1kW of electricity you would get 1kW of heating. Just like the eclectic heater, this would be 100% efficient.
A COP of 2 would mean for 1kW of electricity you would get 2kW of heat. Sounds unbelievable I know, but keep reading!
The latest range of Mitsubishi Heavy Industries 2kW air conditioning systems have a COP of 5.74!
That means for every 1kW of electricity the system uses you get 5.74kW of heat out.
But the benefits don’t stop there. Air conditioning systems are rated on their cooling output. A 2kW air conditioning system actually produces 2.7kW of heating output from the same unit. That’s 30% more heat output than the 2kW electric heater!
If we divide our 2.7kW output by our COP of 5.74 we get a power consumption of just 0.47kW.
So to have our 2.7kW air conditioning unit on for 6 hours a day, it would cost 6hrs x 0.47kW = 2.82kW x 26p = 73p.
Running a 2.7kW air conditioning unit for 6 hours a day would cost 73p/day – £5.11/week – £22.14/month – £265.72/year.
This is the specification table for a 2kW air conditioning system taken directly from the Mitsubishi brochure:
The area highlighted in ORANGE is the MODEL NUMBER of the system. The ’20’ refers to this being a 2.0kW system.
The area highlighted in BLUE is the system’s COOLING capacity. We can see that like the model number references, this system is capable of providing 2kW of cooling capacity.
The area highlighted in RED is the system’s HEATING capacity. We can see that although this is referred to a 2kW system, it is actually capable of providing 2.7kW of heat.
The area highlighted in YELLOW shows the system consumes 0.47kW of power in heating mode.
And finally the highlighted GREEN area shows the system has a COP of 5.74 in heating mode. You’re getting 5.74kW of heat for every 1kW of electricity you pay for.
N.B. The cost figures given above for both the electric heater & air conditioning system are meant for comparison purposes, and while they are as accurate as possible, they are subject to some variation depending on the cost of your electricity from your energy supplier, and how long the systems run for.
For instance, you may have your air conditioning system switched on for 6 hours, but once the room is at the set temperature, the system will just run in a low power mode to keep the room at that temperature. In that situation, the air conditioning will cost substantially less to run over the 6 hour period.
Looking back at the definition of Energy Efficiency:
“The use of less energy to perform the same task or produce the same result.” We can safely say…
The air conditioning system is over 4 x more efficient than the electrical heater.
But how can an air conditioning system be so efficient?
Great question. And I’m sure many of you may be thinking these figures are impossible. You can’t get more energy out than you put in, that’s contrary to the laws of physics!
Well, the magical energy efficiency figures come from that fact that air conditioning systems actually harness energy that is already present in the air temperature all around us. Basically – FREE ENERGY!
Air conditioning systems do not make heat, they simply move it around. Heat is energy and Cold is less heat or energy.
If you want to cool your home or office space, the air conditioning system takes the heat from inside and moves it outside. And similarly, if you want heating, the system takes heat from outside and moves it inside.
But what when it’s cold outside? I hear you ask, how can I heat my home when the air temperature outside is colder than I want it inside?
Even when you think it’s really cold outside, in physical reality there is still lots of energy in the air, and an air conditioning system can still harness this energy. It may be below zero outside but an air conditioning system can still still extract energy from the atmosphere and blow air out at over 50°C.
The energy you pay for to power your air conditioning system is not to create heat or cold, it is to move it from one place to another. The energy is already there, for free, all around us!
The best way to think of an air conditioning system is it’s basically a HEAT MOVER.
And that’s how incredible air conditioning efficiency is achieved. If you want to read more about how the actual magic occurs inside the system, you’ll find all the information in our easy to understand article on the refrigeration cycle.
I really appreciate the great example and diagrams that was given to me on the Refrigeration cycle. It help me understand the air condition and refrigeration better. Thanks
Thank you for taking the time to comment Gerald, I’m glad our article has furthered your understanding of the refrigeration cycle – an amazingly clever and useful process!
Very interesting article, thanks for the provided information