Early simulation for new building plays key role in halving energy requirement

Exploiting the capabilities of simulation software from the earliest stages of the design of a new headquarters for the Irish Office of Public Works in Eire has halved energy consumption compared with other possible designs. Using IES Virtual Environment software for the building in Trim, County Meath, an annual energy consumption of 185 kWh/m2/a was calculated. This is 59.4% less than a type 4 ECON 19 building and 48.5% over an equivalent notional building. Associated reductions in carbon-dioxide emissions have also been estimated. IES also worked with the winning tender team, Bennett (Construction) Ltd, during the later stages of the process and will be involved throughout construction, assessing the impact of last-minute design changes. The OPW is responsible for developing a series of new buildings that form part of the Irish Government’s decentralisation strategy. Taking the opportunity to lead the way in the design of green buildings in Ireland, the new headquarters is the flagship project and will house 275 staff. The involvement of IES from the earliest stages made possible a structured simulation approach —including external wind studies, thermal, airflow and lighting studies. 10 key design features that significantly enhanced the thermal performance of the building were identified. • Triple opening façade strategy.
• Night cooling. • Exposed mass.
• Improving the ratio of façade glazing.
• Atrium.
• Enhanced shading system.
• Solar-control glazing system.
• Intelligent placement of airflow obstructions such as cellular offices.
• Identifying localised cooling requirements.
• Atrium-independent solution created for the minister’s office. This configuration was validated and further optimised using internal CFD studies to predict micro air movement and radiance studies to predict daylight distribution in the atrium and open-plan offices. The design was found to be effective during summer at moving air, and therefore heat gains, away from the perimeter of the building and into the atrium to achieve a typical uniform temperature of about 23/24°C across the office floorplate. During winter, underfloor heating in the atrium and a high-level extract system generate a positive flow to promote uniform temperature distribution and minimise draughts on people near the atrium. The building was also shown to be successful at using all available daylight. With sunny conditions, daylight delivers 450 to 500 lx internally. Overcast conditions achieve a daylight factor of 1 to 3 and a good distribution across the working plane. The Virtual Environment analysis at the early stages of the design verified that the initial thermal configuration could not maintain comfort conditions in line with CIBSE best-practice guidelines. The final configuration resulted in 25°C (dry bulb) being exceeded for an average of 41 h a year, compared with 125 h in CIBSE guidance and 416 h for the original design. CIBSE guidance also recommends that internal temperatures should not exceed 28°C for more than 25 h a year. Vincent Murray, lead IES consultant on the project, said, ‘The OPW has really taken on board the capabilities of our Virtual Environment software. We have been able to work closely with the design team right from the early stages to ensure that maximum impact on energy consumption was achieved. All too often, performance modelling is carried out after many key design decisions have been made, limiting the scope for performance-enhancing alterations.’
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