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In a remarkable stride towards energy efficiency, Riverside Primary School in Perth, Scotland, has emerged as a beacon of sustainable architecture, being the first Passivhaus-certified primary school in the region. A recent first-year assessment of the school’s energy performance has unveiled an impressive operational figure of just 43 kWh/sqm/annum—substantially lower than the classic Passivhaus target of 60 kWh/sqm/annum. This exceptional performance is not merely a statistical triumph; it directly correlates with the comfort levels experienced by students and staff alike, thanks in part to the innovative hot water solutions provided by Baxi’s Heatrae Sadia range of point-of-use electric water heaters.

The Passivhaus standards are designed to significantly enhance energy efficiency and reduce heat loss, making them particularly advantageous for educational institutions in Scotland. Notably, projects funded by the Scottish Futures Trust are required to meet an energy target of 67 kWh/sqm/annum, akin to the benchmarks set for a typical new build Passivhaus school. This funding model is based on outcomes over a 25-year period, where building performance is monitored at predetermined intervals. Any failure to meet the energy targets leads to a corresponding reduction in funding. Thus, the adoption of Passivhaus standards serves to mitigate risks associated with funding by effectively closing any potential performance gaps.

When it comes to the design of Passivhaus and low-energy buildings, considerable emphasis is placed on the geometry of the structure and the performance of its fabric. However, it is equally crucial to evaluate engineering solutions, plant selection, and the operational needs of the building’s users, such as the delivery of hot water. Traditional designs often rely on a centralised hot water system, which not only results in significant heat losses during distribution but also leads to prolonged wait times for hot water. These factors ultimately contribute to energy waste and escalate the overall energy demand of the building—issues that Passivhaus and low-energy designs strive to rectify.

The Hot Water Strategy: A Game Changer

So, what has contributed to the impressive energy performance at Riverside Primary School? To shed light on this, we turn to David Coulter, Associate Engineer and Certified Passivhaus Designer at BakerHicks, who played an instrumental role in providing mechanical and electrical design services for the principal contractor, Robertson Tayside, on this ambitious project.

“To minimise energy waste, we require a solution that heats water only where it’s needed, when it’s needed,” David explains. “Point of Use (POU) water heating is a highly effective approach that drastically reduces the energy losses associated with a centralised system. By delivering immediate hot water right at the source, it guarantees availability when required while simultaneously cutting down on distribution losses and reheat times.”

By installing a point-of-use water heater such as Baxi’s Heatrae Sadia Multipoint—which incorporates anti-legionella functionality, water pasteurisation, and an anti-tamper design—the school ensures that water is stored, cycled, and distributed efficiently. Baxi’s technical sales and specification team collaborated with David to determine the number of Heatrae Sadia POU water heaters necessary to serve wash hand basins situated near classrooms at Riverside Primary School.

Typically, when selecting a point-of-use water heater, a standard model with a storage volume of 10-15 litres is considered adequate for a single appliance. Although this capacity generally suffices for providing hot water and aligns with POU principles, it can often be oversized compared to the actual demand of the appliance. Such oversizing can lead to unnecessary energy consumption, ultimately reducing the system’s overall efficiency.

In the case of the school’s wash basins, primarily used for general handwashing, it was possible to optimise both the storage volume and the associated energy consumption (electric kW duty). “The general guidance for handwashing is approximately 20 seconds per person,” David clarifies. “By comparing this timeframe with the available storage volume in the POU water heater and the maximum flow rate of the wash hand basin, we identified an opportunity to further enhance the design, boosting efficiency while maintaining functionality.”

“We communicated this approach to the client, who appreciated that our design was based on actual usage rather than a worst-case scenario that would have resulted in oversized and underused equipment,” David elaborates. “The collaboration among FES (Stirling), the MEP Engineers, Baxi, the manufacturer, Architype, the Architect, WARM the PH Certifier, and the Client was crucial in achieving this solution. By understanding how each end-user would interact with the sanitaryware, the team formulated an operational energy-focused solution that facilitated significant energy savings.”

As a direct result of this innovative design approach, the overall water storage for the project was reduced by an impressive 25%, while hot water heat loss decreased by 30%. These outcomes have contributed to a more efficient and sustainable design, showcasing the potential for significant advancements in energy performance in building projects.

With the recent report on energy operational performance highlighting the success of this solution, BakerHicks now intends to use this design as a blueprint for future projects, even in cases where Passivhaus standards may not be applicable. David reflects on the success, stating, “We are thrilled to see these energy results and are delighted that the building is operating far more efficiently than we initially projected. The data indicates substantially lower energy consumption, underscoring the importance of robust operational performance and effective energy management. The client team and end users have adapted remarkably well to the Passivhaus strategies, learning valuable lessons along the way. This represents a promising step forward for future projects and building services solutions.”

Looking Ahead

As we continue to strive toward a more sustainable future, the lessons learned from Riverside Primary School serve as a compelling case study in the potential of innovative energy solutions. The collaboration between various stakeholders—from engineers to architects to the client—demonstrates the power of teamwork in achieving ambitious sustainability goals. It is clear that the future of building design lies in the integration of energy-efficient technologies and strategies, paving the way for a greener tomorrow.

For more information on Baxi’s commercial electric heating and hot water solutions, click here.

This article originally appeared in the May 2025 issue of Energy Manager magazine. To stay updated on the latest in energy management and sustainability, subscribe here.

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