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The Effect of clock changes on energy consumption in UK Buildings

BRE Project

The effect that changing UK clocks from GMT/British Summer Time to Double Summer Time or Central European Time may have on energy use 

A BRE report from 2005, prepared for DEFRA, that expanded on earlier work considering the effect that changing UK clocks from GMT to British Summer Time had on energy use, and the impact that adopting Central European Time (CET) might have on energy use for lighting, heating and cooling.

The report is made available here as there has been recent renewed interest in the subject.

The Executive Summary from the 2005 document reads:


The issue of clock changes has been raised as a potential way of reducing carbon emissions under the current review of the UK Climate Change Programme. An earlier study concentrated on modelling the expected impact of the clock change on the likelihood of artificial lighting being switched off in response to daylight availability. The work presented here expands on this earlier work and looks at the impact of clock change on energy use for lighting, heating and cooling using dynamic simulation modelling to capture the interactions between the energy services.

To determine the effect of a change from the current GMT/BST clock regime to Central European Time (BST/DBST (Double British Summer Time)) and from GMT/BST to BST all through the year (BST/BST) on UK energy consumption in buildings some energy simulation runs were carried out. The simulations were used to determine the impact of a clock change on annual energy consumption for heatingA, and in the case of non-domestic buildings for lighting and cooling as well.

The modelling results were scaled to the UK level for 2010 and 2020 based the projected energy consumption for the reference scenarios developed for the domestic and non-domestic sectors.

The result of this study indicate that both clock change regimes would result in an increase in energy consumption in UK buildings, rather than realise any savings. Overall the changes result in only a small difference to energy for heating, lighting and cooling in UK buildings and were similar for 2010 and 2020. The switch to Central European Time (BBST/DBST) showing 2% increase in both delivered energy use and CO2 emissions (around 40 PJ and 2.5 M Tonnes CO2, respectively). Whilst a switch to BST all year round (BST/BST) would result in a smaller increase of just under 1% (around 20 PJ and 3 5 M Tonnes CO2, respectively).

The only instances where savings are realised are for domestic lighting and non-domestic cooling for the switch to Central European Time. However, these savings are more than offset by the increases in non-domestic heating and lighting, as well as a small increase in domestic heating.

As these results are based on a limited number of simulations, there is uncertainty associated with the final figures. However, it is unlikely that the a switch to either Central European Time (BBST/DBST), or BST all year round (BST/BST) would lead to significant CO2 savings.

The complete report can be downloaded as a PDF document from the link to the right