Underfloor Heating Manufacturers' Association chairman Rex Ingram highlights the difficulty of predicting the energy profile of buildings
THE path to a low carbon economy is anything but straight.

Legislation introduced for the most altruistic of reasons, can make life difficult for the building services professional - at times even seeming to stand in the way of a more energy efficient solution.

Unfortunately underfloor heating can be an apparent victim of this anomaly. Designers have actually been denied building control approval because their scheme employs this type of heating, now recognised as being one of the most efficient available.

To understand how this can be possible and how the problem can be overcome requires some background information.

Since January 4 2006, all nation states within the EU have had to comply with the Energy Performance of Buildings Directive. This requires all member countries to introduce a methodology for measuring the energy performance of buildings.

The objective is to encourage more efficient use of energy in both new buildings and those being extensively refurbished. The directive introduces procedures for certification of buildings according to their energy use - so that a potential purchaser can see how a building is rated. It also requires procedures to ensure that these more energy-efficient structures are kept running efficiently long into the future.

All well and good; the problem is that different countries have chosen different ways of complying with these requirements.

In the UK our response was to change Part L of the Building Regulations.

Residential buildings are now covered by Part L1 and we must all use SAP software to determine Target Emission Rate (TER) and then calculate Building Emission Rate (BER) The name of the game is to ascertain which particular combination of elemental U values, air-tightness, cold bridge details, heating systems and controls will ensure BER is less than or equal to TER.

The required SAP software is supposed to be obtained from authorised or approved suppliers.

Non-residential buildings are covered by Part L2 and we are advised to calculate TER and BER in much the same way as with SAP but using SBEM software which is downloadable from DCLG.

Now all this is great in theory, but the theory isn't working.

In the case of SAP software, the Building Research Establishment is sending out a stream of updated algorithms to approved SAP software suppliers as mistakes in the original are uncovered.

Unfortunately software suppliers have widely differing commercial attitudes towards updating their software packages. Some are diligent and update their package straight away and issue a new version.

Others have elected to accumulate a bundle of algorithm updates and combine the lot in a single update once every six-12 months.

Moreover, Building Control officers get updates at different times depending on their individual council's policy on updating software.

And, if all that's not bad enough, not all the software suppliers started out with their software packages in absolute agreement on TER and BER in the first place!

So, it is hardly surprising that we have disagreements over whether a particular recipe for a building is or is not compliant. It all depends on whose package you use and which version you've got.

The situation of non-residential buildings is even more bizarre. If you run your proposed building's geometry and services 'recipe' through SBEM, you get a set of TER and BER projections. However if, instead of SBEM, you run the same data through one of the long-established building simulation programs such as TAS or IES, you may get a set of BER projections around half of what SBEM predicts.

The difference is so great that TAS will often say that a building is compliant with its TER while SBEM says it is not.

Building Control is instructed to accept the TAS result because SBEM is what it says on the tin - a Simplified Building Energy Model - and is known to have deficiencies.

So, if you have a project where either SAP software or SBEM come up with BER predictions that seem to be too high, consider running the building geometry and recipe through TAS or IES instead. This approach is more than worth the small cost premium involved.

On the wider European front, most European countries seem to be experiencing the same kind of confusion as we are with our SAP and SBEM. A major new project called CENEMIS is being planned to try and bring some order out of the chaos.

It seeks to combine the resources and knowledge of the major European centres of academic expertise on building energy efficiency matters with the six major pan-European Trade Associations involved in this area, namely EURAD, EUBAC, EURO-VENT, EURO AIR, ELVHIS and EU-RAY.

The objective is to develop practical ways in which we can predict a building's energy efficiency, whatever form of heating/cooling it has and wherever it is built.

This won't be easy. It is anticipated that CENEMIS will take at least three years to complete.

In the meantime we will have to struggle on in the knowledge that the first answer is not necessarily the correct one.