The tone of the discussion surrounding mechanical systems in institutional buildings has changed. In the past, public buildings seemed to take forever to be clean energy pilot projects. The mechanical design is now more precise, especially in new construction, optimizing innovative active systems in balance with solar gain and natural ventilation.
According to Stuart Hood from Integral Group, who designed Surrey’s new Clayton Community Centre systems, “You’re not just cracking a window and thinking of it as a nice-to-have. Now the technology and design are integrated and properly engineered to ensure healthy ventilation cross-flow through the building.” Superior energy performance is an expected prequalification, and in British Columbia standards are high and carbon-free systems are virtually a must.
The Clayton project brings together solar orientation, envelope design, active mechanical, and passive natural ventilation in a harmonic balance. “It’s also a balance between the cost of mechanical systems and the cost of the envelope,” says Hood. “I think Passive House has found its sweet spot. We’ve learned to create an envelope we can trust without backup-this and backup-that.”
Natural ventilation
His HVAC systems description sounds different from what we may have heard a few years ago. He talks about the control system and motorized triple-pane windows that open automatically in the evening to perform a natural night flush as the day’s heat rises and exits through windows on the roof. This process “charges the concrete slab” and Hood knows the R-values of the roof and wall systems in detail.
He describes a common challenge with institutional buildings with high traffic counts like Clayton, in which cafes in atriums become uninhabitable due to comfort problems. “That’s why we put in a huge revolving airport door.” The science of comfort seems to be a key focus. “We wanted the gym and fitness areas to be cooler than the library, so the architect located them on the north side to reduce solar gain. It should feel like 18C, but we can operate at 20C and use 20 or 30 ceiling fans for a cooling effect.”
The 76,000 sq. ft. facility includes an arts centre, library, daycare, gymnasium, and fitness center. There are two Aermec 40-ton heat pumps on the roof and six Swegon heat recovery ventilators with supplementary heating coils.
Conditioning is delivered primarily by hydronic ceiling panels employing 15C chilled water, and displacement ventilation is achieved through floor grilles in some areas. Efficiency is ensured via the very tight (0.3 air changes per hour) Passive House building envelope and plumbing insulation. “Every pipe hanger and all the heating and hot water pipes are carefully wrapped,” says Hood.
Schulich School of Business
If you think the Clayton Centre is a wacky west coast thing that can only work in a temperate climate, you will be interested to learn that many similar strategies are being used on a frigid Toronto campus for the Schulich School of Business. The Rob and Cheryl McEwen Graduate Study and Research Building is designed around an atrium with a cafe, three large classrooms, four seminar rooms, breakout clusters, lounges, research labs, and offices.
A key feature is a dramatic glass solar chimney that rises 27 metres above the atrium to provide energy-efficient natural ventilation. “The incoming air in winter is pulled through the solar chimney, which provides some passive preheat,” says Jesse Dormody, senior associate at Baird Sampson Neuert Architects. “You get the largest temperature delta on the coldest clear days of winter, 10 to 12C before it enters any part of the building—so technically the chimney is outside of the envelope.”
The base of the solar chimney opens into the central atrium through an operable glazed skylight vent driven by rack and pinion technology like in commercial greenhouse glazing. In the shoulder seasons, glass dampers at the base and top of the solar chimney modulate to allow airflow from occupied spaces to be drawn up and out of the chimney through natural stack effect and controlled pressure differential. The mass wall in the upper portion of the solar chimney serves as a passive solar energy absorber, radiating excessive heat gain to enhance exhaust air buoyancy and further augment system effectiveness. It creates air draw levels comparable to mechanically driven ventilation systems.
Smart, green technology
In the winter, the chimney’s south-facing glazing and mass-wall preheat incoming outdoor air as it is drawn through wall openings and the heat recovery wheel of a dedicated outdoor air system (DOAS). It is then distributed throughout the building. This sequence of preheat and heat recovery minimizes the demand for direct heat energy inputs during even the coldest times of the year.
The building automation system manages adjustments between passive hybrid natural ventilation mode in shoulder seasons, active preheat mode in winter, and active cooling mode in summer. It responds to real-time inputs from the building’s outdoor weather station to open, close and modulate dampers and glazed vents of the solar chimney, the DOAS, and 200 fully automated, operable windows found in all occupant spaces, including classrooms and social areas.
A green light signals when occupants are encouraged to manually open windows. “The high-level idea is to use natural ventilation as much as possible to reduce energy use. If all of the windows are open it reduces the cooling load down to below 10 per cent.”
“Engineering was integral to the architectural design. The building itself is like a piece of equipment,” says Dormody. “We had to conduct pressure analyses in each area. Some windows on upper levels have to open 90 degrees, while windows on the ground floor could only have a four-inch opening for security reasons. When it rains, they’re all closed.”
In winter months and on hot summer days windows are closed to maintain efficient conditioning and control humidity. The DOAS system is sized to meet air exchange requirements. Low-speed displacement ventilation grilles at floor level contribute to excellent indoor air quality, as pollutants are conducted up and out via high return grilles.
Unfamiliar territory
The 67,000 sq. ft. building is connected to the campus district steam heat and cooling facility and incorporates a radiant heating and cooling concrete slab system within the floors and ceilings, along with hydronic panels. More than 20 kilometres of radiant heating/cooling pipe is cast into the concrete structure. The radiant system helps separate heating and cooling functions from ventilation. The required pump energy is about 10 per cent of fan energy needed to convey the equivalent amount of heating or cooling.
“It took some time to get the contractor and trades to feel comfortable while putting up this project. They didn’t really understand what they were building,” says Dormody. “People on the operations side were also nervous about the design, but I think they’ve been won over.”
The pandemic interrupted the tracking, but early returns suggest the building is outperforming its modelling, which predicts energy use reductions of 83.2 per cent below Canada’s Model National Energy Code (MNECB) and energy use intensity of under 72.4 KWh/m2. This translates to a 65 per cent reduction in greenhouse gas emissions compared to the MNECB. Solar panels will be added in the future to make up the difference.
Institutional buildings, and really all buildings, are no longer clean energy pilot projects. With continuing threats to our indoor air quality and climate change bearing down on us, we need masterwork of engineering and building science. Are you ready for it?