Publishing their findings in an article in iScience, the researchers from McGill University’s Peter Guo-hua Fu School of Architecture examined the potential for heat recovery with buoyancy ventilation by configuring architectural space – which involves spaces arranged in an open thermal loop, with heat exchange through partition walls.

Their inspiration came, in part, from their investigations into the original ventilation system planned for Montreal’s Royal Victoria Hospital, which they suggest could be adapted to transform modern temperature control and ventilation design.

“These historical insights could help us to design less equipment-heavy solutions today with a new approach to energy-sufficient architecture and healthy indoor environments,” explained co-author Professor Salmaan Craig.

In the plans for the Royal Victoria Hospital, which dates back to 1893, the team found an early precedent for ventilation heat recovery – described as an efficiency measure that recovers heat from the exhaust air so that stale, indoor air can be constantly replenished with fresh, outdoor air without the need for too much extra energy to heat up the incoming flow.

Open thermosiphon loop

The paper explains that the flow cycle worked without mechanical fans, which weren’t reliable at the time, and instead used the motive force of heat – a form of ventilation that could be described as an “open thermosiphon loop with heat recovery”. The main purpose of the technique was to “raise the temperature of the incoming outdoor air safely above the freezing point of water. Only then was the fresh air allowed to pass over the hot water heating pipes, embedded in flues leading to the wards.”

Anna Halepaska, PhD candidate and the study’s first author, elaborated: “Ventilation heat recovery is vital for healthy, energy-efficient buildings but needs miles of ductwork. The supporting infrastructure causes substantial emissions during manufacture, maintenance, and disposal.”

Through archival research and laboratory experiments, the researchers verified the ventilation rate and extent of heat recovery. They found that by modernising the 19th-century technique by eliminating ductwork and fans, it’s possible to recover heat through partition walls and floors while maintaining a steady ventilation flow.

Trawling through design correspondence at the time the hospital was being planned, the researchers discovered how and why the system was designed in such a way originally. The study also confirms that far from being a 20th-century innovation, heat recovery techniques were being explored by engineers in the century previous – before electrification and the widespread use of mechanical fans.

“Fuel economy and clean indoor air were real concerns in the 19th century, especially in hospitals,” said Prof Craig. “However, this early heat recovery innovation responded to the harsh Canadian winter on very pragmatic terms. It provided a means to pre-heat outdoor air, which stopped the pipework in the air heating system from freezing in cold snaps.”

Design dispute

By scrutinising the archives, the researchers were also able to clarify the role of British hospital specialist Henry Saxon Snell, who was commissioned to design the new Royal Victoria Hospital but withdrew from the project after developing its original designs.

Prior to the building’s completion, Snell became embroiled in an argument with local hospital administrators and engineers about the best way to heat and ventilate the patient wards. Snell proposed long and narrow patient wings. In winter, patients would be warmed by fireplaces in the wards while fresh air, pre-heated to room temperature, would arrive from a plenum on the ground floor. Naturally rising through flues in the exterior walls, this warm air would circulate through the wards, before exiting through a trunk in the attic.

Local architects and engineers, however, advised against Snell’s concept, describing it as “quite unsuitable to this climate”. The row eventually led to Snell stepping down.

In the hospital’s final design, the open thermosiphon loop concept was similar to the approach used for the Old Center Block of the Parliamentary Complex in Ottawa, except for expensive excavation and ground tempering. The paper states: “The wards’ thermosiphons likely operated until at least 1900, when the construction of a new boiler plant in the hospital complex saw the removal of the original heating furnaces and steam boilers from the wards. It is unclear how well the original system ran or why it was decommissioned.”

Prof Annmarie Adams, co-author and architectural historian, commented: “It’s also surprising that much of the ventilation design was inspired by a completely different building type, namely the Canadian Parliament building. Architectural historians sometimes think of hospitals as unique, but this work shows those crucial connections.”

The paper, ‘19th-century thermosiphon ventilation and its potential for heat recovery in buildings today’, by Halepaska, A, Adams, A, and Craig, S, was published in iScience.