Simple Calculations to show quantitative
impacts of equipment use
In the current economic climate, opportunities to save money are
often pounced upon. The following calculations will show how easy
it is to save a lot of money through energy efficiency.
Signage
Figure 1

A lot of appliances and equipment have
energy efficiency stickers on them.

In the picture you can see that it tells
you the energy consumption for a year
(based on being on for 24hrs a day (it’s
a fridge)) = 602 KwH

Knowing how many KWhs a piece of
equipment uses allows you to make lots
of useful calculations!
How do I calculate the cost of electricity used by equipment?
A typical current campus cost of electricity is 10p / kWh including Climate Change Levy and
charges.
The calculation you need: KWh of electricity usage x £cost of electricity
Following the fridge example in Figure 1: 602KWh x 0.10 = £60.20
How do I calculate the amount of carbon emitted by equipment usage?
The average volume of CO2 (including other GHGs too) released into the atmosphere per kWh
of electricity is 0.543. (DEFRA Guidelines August 2010)
The calculation you need: KWh of electricity usage x kg of CO2 emitted
Following the fridge example in Figure 1: 602 kWh/year x 0.543 kg = 327 kgCO2/year
I don’t have a sticker telling me the KWhs, what do I do?
KWh = KW (1000 Watts) x Hours used
Watt = Volts x Amps
For example, the bottom of a laptop often has this sticker:
Figure 2
This tells you the laptop uses 19.5 Volts and a
maximum of 4.6 Amps. The calculation is
therefore:
19.5V x 4.62 A = 90.09W/ 0.09Kwh
Calculating Energy Consumption: putting this into practice
•
A union has 44 x 50W tungsten filament halogen bulbs (energy inefficient type) in the
male washroom of its nightclub.
•
They are on for eight hours, four nights a week for 31 weeks a year. Assuming an
average electricity tariff of £0.15 per KWh, what is the value of the energy they
consume in a year?
•
And what is their carbon footprint? (Remember, 1 KWh equals 0.543 kg carbon)