Methods of calculating targets
You can use any method you like for calculating your targets. Some methods commonly used are:
- Corresponding period the year before
this is a weak and somewhat
unreliable method, based on the assumption that annual seasonal variations
are consistent. While that's true for a small number of cases, the big
problem is that consumption in the period you're comparing with might
itself have been incorrect
- Specific energy ratio
this method assumes that you use energy
or other commodity in direct proportion to the measured product output.
Dividing energy used by product output gives a figure for kWh per unit
produced, which can then be compared with a target ratio. It's a weak
approach because actually there are very few processes which exhibit a
constant SER; most SERs are variable because there is always an element
of fixed, non-throughput-related, consumption.
- Activity-based target
the main method propounded in this Guide,
this explicitly allows for the fixed element of consumption which
SER method ignores. Most commonly it uses a straight-line relationship
or multi-factor model as an
In its more sophisticated manifestations this approach can deal with complex
scenarios, such as irregular batch production, where numerous factors
determine the energy requirement in complex and non-linear fashions.