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Primary Energy – Not the only consideration whilst designing NZEBs

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By the 31st December 2020, the built environment must ensure it is only constructing Nearly Zero Energy Buildings (NZEBs) to comply with the Energy Performance of Buildings Directive (EPBD).

This national requirement for all new buildings to be designed to use very little energy, and to provide for this low energy demand using largely renewable sources, will be the next step for the built environment to take as it aligns with new European and UK energy legislation.

However, the EPBD goes further than just setting this target for new developments – it also sets certain requirements that member states must adhere to, such as measuring the achievement of NZEBs through primary energy.

Moving to a primary energy focused compliance system for new developments would require a shift in mindset for building service engineers, who will need to adjust their specifications and building design to minimise energy use, consider different systems as ‘energy users’, and meet a new primary energy target.

When defining the criteria for measuring NZEBs, the EU were keen to make their definition flexible to allow member states to put into their laws a system that worked for their unique construction industries. Two such factors include the presence of a renewable energy strategy (RES) and whether there will be supporting compliance indicators alongside the primary energy target.

What is primary energy?

Primary energy is a reflection of how much raw fuel is used to generate a unit of final energy. This includes the energy used to create, transform and transport the energy from its raw form to where it is used.

Currently, the UK primary energy factors are listed as 1.122 for gas and 1.738 for electricity. These factors are likely to be used to calculate a building’s overall energy primary energy use, with a target which must be achieved before construction can commence.

 

 

Other compliance indicators

Application of supporting compliance indicators has been varied amongst other EU member states, with the majority combining a primary energy target with compliance indicators such as a carbon emissions target, smart controls, envelope performance criteria, renewable contribution and analysis on the performance of technical systems.

With the UK’s current compliance system based on carbon emissions, it is likely that Government would combine this with the new primary energy target to ensure progress made under the previous compliance system would be retained, rather than discarded in favour of whatever systems meet the primary energy requirements.

This is made more likely when the legally-binding Carbon Budgets are considered – which the UK transposed into law in the Climate Change Act 2008.

Renewable energy solutions (RES)

The EU’s definition for NZEBs is clear on the importance of renewable sources in providing a large proportion of a building’s energy demand. This is why the EU is eager for member states to have a RES to aid in the achievement of this.

As with the supporting indicators, there has been a vast difference in how member states have approached their own renewable energy strategy.

Some member states have requested a direct RES contribution (share in percentage, or minimum amount of kWh/m² per year); whilst others have only included an “indirect” RES requirement by setting very low primary energy targets that can only be met with RES contributions1.

With governmental strategies (e.g. Clean Growth Strategy) in support of utilising more renewable energy solutions, such as heat pump technology, this seems like a potential avenue for future compliance within the UK.

In some cases, new developments are already required to provide on-site renewable contributions under powers granted in the National Planning Policy Framework to local authorities – making this route to compliance more feasible for the industry to adopt in the narrowing timeframe before the NZEB 2020 deadline.

Whether the UK Government decide to implement a direct or indirect renewable energy strategy to meet the NZEB target, it is clear that new developments will need to utilise more renewable energy under the terms of the EPBD than they currently require.

                                

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Staying on target: Combining nearly zero energy buildings and low carbon HVAC solutions

Using the primary energy factors listed within the draft SAP 10 methodology and software, we were able to model what a primary energy based compliance system could mean for HVAC specification.

These results were then combined with legally-binding targets and the aims of governmental strategies to provide recommendations on how this could be approached, and the key decisions that Government needs to make in defining nearly zero energy buildings for the UK.

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