energy changes are measured.

The way that energy and

ENERGY UNITS

The energy content of foods has been traditionally measured in Calories and more recently in kilojoules (kJ). There is no reason why we could not use either of these units to measure energy use in the home. The Joule, being the official SI unit of energy actually was the favoured unit until a few years ago. However, for convenience, the kilowatt-hour has now become the unit of choice in Domestic, Commercial and Industrial energy measurement.

Electricity companies have long used this unit since it is easy for billing. The reason why, becomes clear as soon as one considers appliance energy use.

To appreciate the size of the kWh of energy, the approximate equivalent values are compared below:

• 1 kWh
• 3,412 Btu (British Thermal Units - units often found on older boilers)
• 3,600 kJ
• 860 Calories

Adult daily nutrition requirements using kWh units become

• Males 3000 Calories = 3.50 kWh
• Females 2200 Calories = 2.55 kWh

For comparison, the average daily use is 9.04 kWh electrical and 22.9 kWh thermal energy per UK household, (derived from the annual use of 3300 kWh and 8000 kWh respectively). We are profligate energy users in the UK !