BREEAM New Construction: Energy Modelling and Heat Pump Trade-off
A new 12,000 m² office building is targeting BREEAM Excellent. The design team proposes an air-source heat pump (ASHP) system with a seasonal coefficient of performance (SCOP) of 3.2, but the local grid has a carbon intensity of 0.25 kgCO2e/kWh. To meet the Ene 01 credit, the team must demonstrate a 40% reduction in regulated energy use compared to the notional building. The energy model predicts a 35% reduction with the ASHP, but the client is reluctant to increase insulation due to cost. The assessor suggests adding on-site solar PV to compensate. The PV system would generate 80,000 kWh/year, but the building's annual regulated electricity demand is 250,000 kWh. The client asks whether the PV can be used to claim the credit, and whether the ASHP's SCOP of 3.2 is sufficient given the grid carbon intensity. The project is in the UK and uses BREEAM UK New Construction 2018.
1. Can the proposed on-site PV system enable the project to meet the 40% reduction target for Ene 01? Justify your answer with calculations and reference to BREEAM methodology.
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The PV system generates 80,000 kWh/year, which is 32% of the regulated electricity demand (80,000 / 250,000 = 0.32). However, BREEAM Ene 01 assesses the reduction in regulated energy use compared to the notional building, not just the supply from renewables. The PV can contribute to the reduction, but the energy model must account for the building's total regulated energy consumption. The predicted reduction without PV is 35%, which is below the 40% target. Adding PV reduces the net regulated energy use by 80,000 kWh, but the baseline notional building energy use must be known. Assuming the notional building energy use is 250,000 kWh / (1 - 0.35) = 384,615 kWh (since 35% reduction means actual is 65% of notional). With PV, the net energy use becomes 250,000 - 80,000 = 170,000 kWh, which is a 55.8% reduction (1 - 170,000/384,615). This exceeds the 40% target. However, BREEAM may have specific rules on how PV is treated; typically, on-site renewable generation can be deducted from the regulated energy demand. Therefore, the PV can enable the credit, provided the energy model is updated and verified. The assessor must ensure that the PV is not double-counted with other credits (e.g., Ene 04).
2. Evaluate whether the ASHP with SCOP 3.2 is a suitable low-carbon heating solution given the grid carbon intensity, and explain how it affects the BREEAM Ene 01 credit.
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The ASHP's carbon intensity is calculated as grid carbon intensity divided by SCOP: 0.25 / 3.2 = 0.078 kgCO2e/kWh. This is lower than the grid average (0.25) and lower than a gas boiler (approx. 0.18 kgCO2e/kWh). Therefore, the ASHP is a low-carbon solution. However, BREEAM Ene 01 is based on energy consumption, not carbon, so the SCOP affects the energy model's predicted energy use. A higher SCOP reduces the electricity consumption for heating, improving the reduction percentage. With SCOP 3.2, the ASHP is likely to contribute positively. But the assessor must check that the SCOP is realistic for the building's climate and that the energy model uses the correct seasonal efficiency. The credit requires a 40% reduction in regulated energy use; the ASHP's efficiency helps achieve that, but it may not be sufficient alone, as shown by the 35% reduction. The PV addition can compensate. The ASHP is suitable, but the overall energy strategy must include additional measures to meet the target.