By Mary James

Since the early days of Passive House, the project types that feature Passive House performance levels have expanded steadily, from a core of mostly residential buildings to museums, fire stations, hospitals, and even recreation centers. Each of these novel building types required extensive research into all of the energy uses particular to that typology and sparked new challenges. How could fire stations with their many bays and doors large enough to accommodate fire engines be kept comfortable and meet their requisite heating demand targets? Could hospitals find diagnostic and ventilation equipment that would be sufficiently energy efficient to help achieve their primary energy targets? And what about recreation centers, especially those with pools? Or hotels and schools with indoor pools? The high humidity, temperature, and pool water quality needs in these buildings present challenges that are daunting indeed—and yet not insurmountable, thanks in part to Passivhaus Institute (PHI) research and the several pilot projects that were led by committed clients. 

Back in 2008, when Jessica Grove-Smith coincidentally was a new hire at PHI, the institute received a grant from the German Federal Environmental Foundation to conduct a baseline study for a proposed community center in Lünen, Germany that included a pool. The study encompassed deep dives into the various energy uses in that type of building, what makes them so energy intensive, and then effective measures for bringing down that energy demand. That baseline study brought home the significance of the building fabric when dealing with the need to maintain very high temperatures inside—around 86°F (30°C) in the pool hall—and high humidity. Of course, other factors also have significant roles. 

“The building fabric is the starting point, but there's so much more to it that you can do by, for example, optimizing the ventilation systems, by bringing down the evaporation and dealing well with those humidity loads, and by reducing the electricity needs of the water treatment system that includes pumps circulating pool water 24/7,” says Grove-Smith, who contributed to that research and is now senior scientist and joint managing director of PHI. “There’s really a lot of potential there,” she concludes. As a huge bonus, the research team then got to work closely with that municipality and their design team and implement those initial research ideas in a real-life project, the Lippe Bad.

The research caught the interest of the Exeter City Council when the municipality decided to investigate pursuing Passive House for its new St. Sidwell’s Point (SSP) recreational facility. Completed in 2022, the roughly 72,000-ft² (6,700-m²) building contains two large swimming pools, a shallower toddlers’ pool, a 150-station gym, a spin studio, a fitness and dance studio, a health spa with a hydrotherapy pool, changing rooms, a café, and administrative offices. So many uses, so many PHPP sheets! 

“It was absolutely great to work with them, because they were so committed and so behind this vision and this goal of having an energy-efficient leisure center,” Grove-Smith says of the Exeter City Council. This commitment was crucial in carrying the project through to certification, in spite of its complexity and novelty. 

To model the project, PHI again produced a custom multi-zone PHPP that accounted for heat transfer between the various spaces and the additional energy needs for the swimming pools. The latter requires supplementary calculations in a specialized “pool tool” developed by PHI based on earlier and ongoing research, as pool water energy balance is not accounted for in a standard PHPP. One of the project goals set by the Exeter City Council was to assess, and ideally ensure, energy and comfort resilience for the present, as well as for the decades to come, even extending into projected 2080 temperatures. 

An important starting point for any energy-efficient recreational center is careful consideration of the building’s layout and the orientation of the pool halls. The design team of SSP fine-tuned the layout with the north-facing side of the building harboring the fitness rooms, where enthusiastic exercisers tend to generate high levels of internal heat gains. The changing rooms and hallways were placed in the central areas. The pool areas were designed to face south, as the pools continuously require heating and therefore benefit year-round from solar heat gain. A stepped façade was chosen for aesthetic reasons, and also because this design choice, in combination with clerestory glazing, helped bring daylight further into the building’s interior spaces, thus assisting the Council in achieving its daylighting goals and reducing lighting energy loads. 

A dynamic simulation model was carried out by the project team to help inform the building’s summer comfort. A natural ventilation model was used to maximize this strategy’s contributions to summertime comfort, with planned window openings at the top and ground floors, as well as door openings when needed. Ventilation plays a crucial role for such projects and should be carefully sized and operated based on demand to ensure high quality while keeping fan power and ventilation losses low. At SSP, high-efficiency HRVs are controlled by a demand-based system that responds to continuously monitored levels of carbon dioxide, humidity, and room temperatures, ensuring optimal indoor air quality and comfort throughout the building. 

Modeling of the structure’s thermal bridges was unusually complex, given that there are a variety of wall types and, therefore, many different curtain wall and roof connections. The wall types include masonry block, CLT, and a structural frame system (SFS), all padded with 9.8 inches (250 mm) of mineral wool and external cladding. The attachments required to adhere the mineral wool and the external cladding resulted in many penetrations, each of which had to be calculated. 

For this typology, slightly higher targets are set for air tightness, and the metric used references the building’s surface area (qe50 < 0.4 m³/(hm²))—mainly for quality assurance and to protect the building fabric from warm and humid pool air. For St. Sidwell’s, the airtightness layer varied, depending on the wall and roof composition. The SFS walls’ airtightness layer was both the sheathing board and a fully adhered membrane. Plaster provided the airtight layer on the masonry block walls, while a membrane was used in the roof assembly. The final airtightness test came in at 0.3 qe50 — a result of careful planning and execution, including constructing mock-ups of critical junctions and testing for leaks during the build process with smoke machines and thermal imaging cameras. 

With the implementation of a host of other sustainability strategies, St Sidwell’s has become a leader not only in energy efficiency but also in water savings. Thanks to the reduced evaporation from the pools, a greywater harvesting system, and other measures, the recreation center was designed to use 50% less water than a conventional project would. 

The experience gained at St. Sidwell’s and the previous recreation centers are gradually inspiring other project teams working on pool centers to pursue Passive House, thanks to the many benefits that this approach can bring. “We have a number of follow-up projects—at least five across the UK. Some of them are in the final steps of certification, and some are just starting out, so that’s a wide range,” Grove-Smith says. While the UK may be in the forefront with this typology, other countries are not lagging far behind. “There are ongoing projects in Germany and also interest from France and Spain, including hotels with pools,” she notes, “And, yes, we do have the first inquiries from North America.” 

As with other Passive House firsts, Vancouver, B.C., is out in front of other locales on this continent. So, in the not-too-distant future, some fortunate Vancouverites should be able to splash around comfortably instead of experiencing a cold plunge, while the facility operator is reaping well-earned reductions in carbon emissions and operational costs.