Deceptive Primary Energy

Summary

The UK’s Part L Building Regulations have introduced primary energy as a key performance metric. This shift aims to promote energy-efficient homes, but the calculation method warrants closer examination. The simplified approach, especially for renewables, can misrepresent the true energy landscape and potentially hinder progress towards genuine sustainability.

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** Main Story**

Part L Building Regulations: A Primary Focus on Energy

The UK’s pursuit of energy-efficient buildings has led to significant changes in the Building Regulations, particularly Part L (Conservation of fuel and power). A central element of this update is the introduction of the Target Primary Energy Rate (TPER) as a performance metric. This addition aims to provide a holistic view of a building’s energy consumption, accounting for not only the energy used within the home but also the energy consumed in producing and delivering that energy. This “upstream” consideration marks a shift towards a more comprehensive assessment of energy efficiency.

Understanding Primary Energy

Primary energy represents the raw, unprocessed energy found in nature before any conversion or transformation. Examples include the chemical energy stored in fossil fuels (coal, oil, and gas), the nuclear energy within uranium, and the kinetic energy of wind. In contrast, electricity is considered secondary energy because it results from converting primary energy sources.

The TPER specifies the maximum allowable primary energy use for a dwelling over a year, expressed as kWhPE/(m²·year). This metric evaluates the primary energy needed for various functions within the home, such as heating, hot water, lighting, ventilation, and cooling. The calculation uses the Standard Assessment Procedure (SAP) 10.2 software, which incorporates factors like heating system efficiency, power station efficiency (for electricity), and the energy used in fuel production and delivery.

A Critical Look at the Calculation Method

While the intention behind the TPER is laudable, the way SAP 10.2 calculates primary energy, especially for renewable sources, requires careful consideration. The software assigns primary energy factors to different fuel types. For instance, mains gas has a factor of 1.13, meaning that 1.13 kWh of primary energy is needed to deliver 1 kWh of usable energy to the home.

However, the calculation for renewables raises concerns. The software essentially assumes near-perfect conversion efficiency for wind and solar energy into usable electricity. This simplified approach overlooks the energy required for manufacturing, installing, and maintaining renewable energy systems, as well as the intermittency of these sources and the need for backup power or energy storage solutions. This can lead to an underestimation of the true primary energy consumption associated with renewables, creating a potentially misleading picture of their contribution to overall energy efficiency.

Potential Implications and the Path Forward

This oversimplified view of renewable energy within the TPER calculations may have unintended consequences. It might discourage investments in genuine improvements to building fabric and energy efficiency, as developers could rely on the perceived low primary energy contribution of renewables to meet the targets.

To ensure that the TPER effectively drives genuine progress towards sustainable building practices, a more nuanced approach is essential. Incorporating lifecycle energy costs for all energy sources, including renewables, will create a more accurate representation of their true primary energy impact. This would incentivize developers to prioritize building fabric improvements alongside renewable energy integration, leading to more sustainable and energy-efficient homes.

Aligning with Passivhaus Standards

The shift towards primary energy metrics in Part L brings the regulations closer to standards like Passivhaus, which also utilize a primary kWh target. While the TPER focuses on new builds, Passivhaus commonly applies to retrofits of older homes. Both contribute to the construction industry’s overall drive towards greater energy efficiency.

Implementing the Changes

Developers must meet the dwelling targets for energy efficiency. Given the use of SAP 10.2 in TPER calculations, builds need to comply with the standard and achieve a satisfactory score out of 100. This underscores the increased importance of building efficiency, utilization of renewable energy sources like heat pumps, and integration of renewable systems.

As of today, May 15, 2025, these changes in Part L are in effect. It’s crucial for the construction industry to remain informed about updates and new regulations to ensure compliance and contribute to creating a more sustainable built environment.