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Degree days

Learn more about how climate-measuring data, known as degree days, can be used for energy management.  How you can use degree days to account for the effect of weather on energy consumption, to monitor and measure your organisation's energy efficiency.

Digital thermostat

Using degree days for energy management

Four valuable uses of degree days in energy management are:

  • Constructing control charts that compare benchmarked and actual energy usage (the closer they are, the greater your energy efficiency)
  • Evaluating success of savings measures
  • Detecting faults in heating systems and their control
  • Preparing annual budgets

The Degree days for energy management (CTG075) publication (updated from CTG004) provides an introduction to degree days and shows how simple analysis can be a powerful tool in understanding weather-related energy consumption.

Degree days: technical details

The base temperature used to calculate degree days in the UK is 15.5ºC, because at this temperature most UK buildings do not need supplementary heating.

Degree days is a measure of the difference between the baseline and the actual outdoor temperature multiplied by the number of days. For example - the temperature measured hourly records a temperature of:

7.5ºC for 48 hours the degree days total would be: (15.5 - 7.5) x 2 = 16

Note - it is not possible to have a negative degree day value as when the outdoor temperature exceeds 15.5ºC no heating is needed. When the outdoor temperature does exceed the 15. 5ºC baseline, then the degree days are set to zero.

Degree days for energy management

Degree days for energy management

Our 22-page guide to degree days for energy management shows how to use degree days to:

  • Monitor changes in heating system operation
  • Determine actual savings from energy saving measures
  • Produce realistic heating budgets.

Used with care, the methods described in the guide will provide an overview of overall trends in energy performance, an indication of whether significant changes have occurred in the operation of the building or plant affecting the building’s energy consumption, and a methodology for budgeting energy costs.  The guide deliberately limits its discussion of theory to the minimum necessary to enable users to apply the techniques described in it.

Guide contents:

  • Introduction
  • What are degree days?
  • Using degree days
  • Worked example (step-by-step approach to degree-day analysis of energy consumption)
  • Budget setting and benchmarking
  • Sources of information

Publication date March 2012; Publication code CTG075

Information in this guide was correct at the time of publication


Download degree day data

The Carbon Trust no longer supplies this data, but it is freely available from other websites, including:

Degree (opens in new window)
The Energy Management Register (opens in new window)

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