Environmental Information Exchange

Energy self-audit

In order to manage and reduce energy usage, an organisation must first be aware of how much energy systems and appliances are currently consuming on the premises and how this is controlled by building users.


Organisations should consider each area of energy use in the building, which commonly consists of:

The state and fabric of the building is highly relevant, as this will affect:

Perhaps of most importance is the way energy use is managed by building users, for example:

When energy efficiency measures such as insulation, draught-proofing and energy management controls have been implemented, organisations can then consider if technology upgrades would further increase their energy cost savings. For example, upgrading lighting fitting and fixtures, purchasing new, more efficient appliances, and additional features such as sensors or more sensitive thermostatic controls.

Basic Energy Calculations

Understanding how your energy bill has been calculated is a first step in reducing energy use and cutting costs. The use of many electrical and gas devices makes it necessary for businesses to be aware of how much they pay and how they are charged in order to allow them to cut costs and save energy. The UK Government has several representations of energy use in different sectors.

Measuring Consumption

Energy consumption is measured in kilowatt hours, kWh (kilowatts multiplied by hours)

The cost of using energy can be calculated by multiplying the energy consumption of the device by the tariff by the number of hours it is used over a period of time.

Cost = Price (per kWh) x wattage x hours / 1000

Some devices use more or less energy than their labels suggest. For these exemptions, the formula used is:

Cost = Price (per kWh) x wattage x hours x E / 1000

(Where 'E' is given by the amount of time a device is on e.g. 0.25 for an device that is on 25% of the time or where the energy label suggests is used to drive circuitry , e.g. for standard ballast fluorescent tubes E=1.25 and for high frequency or fast state tubes E=1.1))

Wattage indicates the rate of energy use and production consumed by electrical device. Many devices provide only volts (energy per unit charge) and amps (amount of electricity charged per second). To calculate wattage from volts and amps:

Wattage (W) = Volts (V) X Amps (A)

1000 Watts (W) = 1 kilowatt (kW)

Gas consumption is recorded in hundreds of cubic feet but needs to be billed in terms of kilowatt hours. One gas unit is equivalent to 1000 watts of power used for one hour.

Gas units x 31.6


Gas units
x 2.83 (metric conversion factor)
x 1.02264 Factor (volume conversion) *
x 39.3 (calorific value) *
/ 3.6 (Kilowatt hour conversion factor)

* These values will vary depending on your location and supplier - see your gas bill for full details.