Baxi’s Andy Green discusses the success of the strategy with BakerHicks Passivhaus designer David Coulter.
A first-year assessment of Riverside Primary School in Perth, Scotland’s first Passivhaus-certified primary school, has revealed actual energy operational performance of just 43 kWh/sqm/annum, significantly below the classic Passivhaus target of 60 kWh/sqm/annum, while consistently providing excellent comfort levels. Helping contribute to the exceptional standards with energy-efficient hot water provision are Baxi’s Heatrae Sadia point of use electric water heaters.
Passivhaus standards and certification requirements prioritise energy efficiency and minimal heat loss. Passivhaus is particularly popular in Scottish school buildings as projects requiring funding from the Scottish Futures Trust need to meet an energy target of 67 kWh/sqm/annum, similar to a typical new build Passivhaus school. The funding is provided on an outcomes-based approach over 25 years with building energy performance and outcome monitored at set intervals. Where the energy target is not achieved in full, funding is reduced correspondingly, hence the increased uptake of Passivhaus standards to de-risk funding by eliminating a potential performance gap.
When designing Passivhaus and low energy buildings, the focus is placed on the primary building geometry and fabric performance. But careful consideration must also be given to engineering solutions, plant selection, and building user operations, such as hot water delivery. Traditional buildings are often designed with a centralised hot water system, which can result in significant heat losses during distribution and long wait times for water. Both factors contribute to energy waste and increase a building’s overall energy demand – something that Passivhaus and low-energy designs aim to minimise.
So how has the hot water strategy at Riverside Primary School contributed to the building’s impressive energy performance?
David Coulter, Associate Engineer and Certified Passivhaus Designer at BakerHicks (Motherwell), was part of the team that provided mechanical and electrical design services for principal contractor Robertson Tayside on the Perth & Kinross Council project.
“To reduce energy waste, we need a solution that heats water only where and when it is needed,” said David Coulter. “Point of Use (POU) Water Heating is an effective approach that minimises the energy losses of a centralised system. By providing immediate hot water at the source, it ensures availability when required while significantly reducing distribution losses and reheat times.”
Installing a point of use water heater like Baxi’s Heatrae Sadia Multipoint that incorporates anti-legionella functionality, water pasteurisation and anti-tamper design, will ensure that water is adequately stored, cycled and distributed. Baxi’s technical sales and specification team worked with David to identify the multiple Heatrae Sadia POU water heaters required to serve wash hand basins located near classrooms at Riverside Primary School.
When choosing a point of use water heater, selecting a standard model with 10-15 litres of storage volume to serve a single appliance is common practice. However, while the capacity typically provides sufficient hot water and aligns with the principles of point of use water heating, it can often be oversized compared to the actual hot water demand of the appliance. Oversizing can lead to unnecessary energy consumption, reducing the overall efficiency of the system.
As the school wash basins are primarily used for general handwashing, it was possible to reduce both the storage volume and the associated energy consumption (electric kW duty).
“The general guidance for handwashing is 20 seconds per person,” David explained. “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 optimise the design, enhancing efficiency while maintaining functionality.
“We discussed this approach with the client who were pleased that the design was based on actual usage rather than a worst-case scenario, which would be oversized and underused,” David continued. “Collaboration between FES (Stirling), the MEP Engineers, Baxi, the manufacturer, Architype, the Architect, WARM the PH Certifier and the Client was critical in achieving this solution. By understanding how each end user would interact with the sanitaryware, the team were able to generate an operational energy focused solution that delivered energy savings.”
Following this design, the overall water storage for the project was reduced by 25%, with hot water W/K heat loss decreased by 30%, contributing to a more efficient and sustainable design.
With the recent report on energy operational performance demonstrating the success of the solution, BakerHicks now use this design as a template for future projects, even where Passivhaus standards are not applied.
David said: “We are pleased to see these energy results and are delighted that the building is operating far more efficiently than initially projected. The data shows significantly lower energy consumption which demonstrates the importance of strong operational performance and effective energy management. The client team and end users have adapted well to the Passivhaus strategies, learning valuable lessons along the way. This marks a promising step forward for future projects and building services solutions.”
For more information on Baxi’s commercial electric heating and hot water solutions, click here.
This article appeared in the May 2025 issue of Energy Manager magazine. Subscribe here.