EFFECTIVE MANAGEMENT AND ANALYSIS of buildings’ energy consumptions for heating or cooling calls for summary data about how cold or hot the weather has been. Weekly or monthly degree-day statistics provide that information in a convenient manner. But as well as the current values (against which your weekly or monthly energy consumption can be gauged), in the United Kingdom[1] we have two kinds of long-term aggregate value that can be useful for other purposes.

Standard degree-day values

For normalising consumptions we need degree-day values for a ‘reference year’, which allow actual consumptions for buildings in different locations (and possibly measured at different times) to be adjusted back to a comparable basis. Historically, the UK government recommended a standard value of 2,463 heating degree days (to base 15.5C). The source of this number is unknown; it is, in effect, arbitrary but for the purpose of weather-adjustment it does not matter what the number is. This single point of reference was later developed into the following table providing corresponding reference values for different base temperatures, for cooling as well as heating, and disaggregated to individual months:

|     |        Heating       |       Cooling        |
|Month| 18.5'C 15.5'C 10.0'C | 15.5'C 5.0'C -20.0'C |
|     |                      |                      |
| Jan |    488    395    226 |      0    17     705 |
| Feb |    426    342    189 |      0    23     652 |
| Mar |    390    297    134 |      0    64     803 |
| Apr |    319    233     96 |      5   114     837 |
| May |    235    151     39 |     14   192     963 |
| Jun |    148     77      9 |     26   265    1015 |
| Jul |     88     42      4 |     96   380    1155 |
| Aug |    100     45      5 |     57   338    1113 |
| Sep |    162     83     10 |     14   245     995 |
| Oct |    268    177     48 |      1   158     925 |
| Nov |    359    275    124 |      0    53     719 |
| Dec |    439    346    176 |      0    29     755 |
|     |                      |                      | 
|Total|  3,422  2,463  1,060 |    213 1,878  10,637 |

Table 1: standard degree day values

It is important to appreciate that these standard values are fixed and not related to any particular geographical area.

Average degree-day values

If we are forecasting consumption we need to know what future degree-day values we can expect month by month. For this purpose we use 20-year average degree-day values. So the expected degree-day value for next February (for example) is the average of the last 20 Februaries. You can download the UK regional average figures via this link.

In contrast to ‘standard’ degree-day values, ‘average’ values differ from region to region and tend to vary with time thanks to the changing climate. I usually update the table once a year.

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[1] Subject to the availability of suitable historical data, the same principles could be applied in other regions.