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One of the proposed models for the Green Deal has been to evaluate energy savings based on individual measures installed. In this posting we’ve presented a worked example calculation showing the importance of evaluating installed energy saving measures as packages in evaluating savings and paybacks e.g. for the Green Deal.

When we look at all the options for a property we first of all evaluate the individual effects that each will have if carried out on their own.  Importantly we then use our judgement to build packages or suites of complementary measures to understand the net effect of them on the energy consumption and CO2 emissions.

To begin with we looked at 6 things that were possible for the house using our domestic energy modeling software (3 bed end of terrace Victoria solid wall….again).  This isn’t an exhaustive list obviously.  The modelled energy cost of the house is £1,766 a year – its a pretty inefficient house.The measures evaluatded were:

  1. Upgrading the boiler from one with a permanent pilot light to a top specification boiler – install cost ~ £2,000
  2. Installing 300mm of mineral wool loft insulation – install cost ~ £300
  3. Internally insulating the solid external walls with 50mm of PIR insulation – install cost ~ £4,000
  4. Zoning the house using thermostatic radiator valves to keep upstairs 2 degrees lower than downstairs – install cost ~ £0
  5. Sealing the leaky ground floor floorboards – install cost ~ £2850
  6. Insulating under the ground floor suspended floorboards – install cost ~ £1,300

The first graph shows the savings that you could expect by making each of the amendments on their own and keeping everything else constant – the boiler and the walls each are expected to save over 25% of energy bills.


If you add all of these up the total is not far off the total fuel bill costs of the house – yet none of them affect the electricity – alarm bells should be ringing.Next we built a range of packages of measures and evaluated the net effect of each package.  The results and comparisons to what you would get if you just added the individual savings for the measure in each package together are show in the graph below.As you can see the variance increases the more measures you add into the package – by the package with 7 measures the variance is around 30% of the actual savings.  In our Masterplans we often build packages with upwards of 30 measures so it’s clearly essential to calculate the combined effect of recommended measures rather than just adding up the individual savings.