The challenge of making an accurate and comparable energy calculation!


As anyone who has made a few building-energy calculations might know, it is quite easy to ruin or tamper with the results if you are not careful with the data you use as input.

MeasuresAnd if you have been trying to compare the results of calculations from different countries then you might have found that it is not always easy to tell which building that really uses the least energy, depending on what is included in the different calculations.

In the european countries we have different views of which posts that are to be included in a buildings energy use. Not even the areas are measured the same way! This results in different “specific energy use” (kWh/m2and year) for the same building, depending on which energy that is included and which area that is used. Area definitionTherefore I consider one of the greatest challenges of building simulations to be how to choose your user-defined input data!

And, to present the results in such a way that it is easy to recognize what is included in the calculation and what is not.

What does an energy-calculation show?

The result of a calculation is totally dependent of the input data, and the user defined data such as the amount of people in the building and their behaviour influences the results a lot!

For example: A classroom with all the pupils and teacher present all day, five days a week gets less heating demand and more cooling demand than the more reallistic case wen on average 30% are absent from colds, vacations, breaks etc.Energy balance in classroom (IDA-ICE)

How to do it

To make a good calculation that is as close to reality as possible and, not least, comparable to calculations of other buildings, it is good if we can try and find standard values for the user related inputs that schould be used.

In Sweden we have come a bit down that road by the project SVEBY ( ) that aims at standardizing and verifying the energy performance of buildings.

But there is still a lot of work to do…..

Some key-rules for high quality calculations:

  • Specify the different posts of the energy balance separately
  • Document who made the calculation, when and with what program.
  • Document the input data assumed along with the results
  • Document where the data comes from.
  • Use standardized input data if possible

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