Energy Performance Certificates (EPCs) are designed to provide an estimate of a building’s energy efficiency and potential running costs. Traditionally, EPC assessments focus on heating demand, insulation, and building fabric. However, air conditioning (AC) and cooling loads, especially in summer months, are often overlooked — creating what experts call the “summer efficiency gap”. Understanding this gap is crucial for property owners, landlords, and developers to ensure accurate EPC ratings and energy management.

Why EPCs Focus on Heating Over Cooling

• EPC methodology, particularly RdSAP, prioritizes heating demand, as most UK buildings consume more energy for heating than cooling.

• Cooling loads, including air conditioning and passive solar gains, are either underestimated or ignored in many assessments.

• This can lead to EPC ratings that overstate energy efficiency during warmer months, when AC usage significantly impacts electricity consumption.

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The Summer Efficiency Gap

The summer efficiency gap arises because:

1. High Cooling Demand

   • Modern homes with large glazed areas or south-facing windows may rely heavily on AC during summer.

2. Passive Solar Gains

   • Roof pitch, shading, and window orientation influence how much heat enters a building, increasing cooling requirements.

3. Underrepresented in EPC Calculations

   • EPCs often assume moderate summertime temperatures and minimal AC usage, which may not reflect reality.

4. Impact on Energy Costs

   • Overlooking AC loads can underestimate running costs, misleading tenants, buyers, or building managers about actual energy consumption.

How AC Loads Affect EPC Ratings

• Indirect Impact: While AC may not directly change the EPC band, increased electricity use influences cost estimates.

• Building Design Considerations: Poor insulation, roof design, and lack of shading increase cooling demand, indirectly lowering perceived efficiency.

• Potential Misalignment: Buildings with high summer AC use might achieve good EPC ratings but face higher operational costs, creating discrepancies between EPC predictions and real-world energy consumption.

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Strategies to Reduce Summer Efficiency Gaps

1. Enhance Passive Cooling

   • Install external shading, reflective roofing, and ventilated roof spaces to reduce solar gain.

2. Upgrade Insulation

   • Proper insulation slows heat transfer, reducing both heating and cooling energy demand.

3. Optimize AC Systems

   • Use energy-efficient air conditioning units with programmable thermostats and zoning.

4. Consider Smart Controls

   • Automated blinds, smart thermostats, and occupancy sensors can reduce unnecessary cooling.

5. Provide Detailed Data to Assessors

   • Accurate AC load data helps EPC assessors better estimate energy performance and operational costs.