Abstract
A forgotten thermosiphon scheme is found in Montreal's former Royal Victoria Hospital and traced back to the original Center Block of Canada's Parliament Hill. This discovery inspires an investigation into the fluid mechanics of heat recovery with buoyancy ventilation, where interior spaces are arranged in an open thermal loop with heat exchange through partition walls. Flow visualizations with physical models are used to corroborate the archival evidence and show how the historical scheme worked. The scheme is then generalized, defining a criterion for steady unidirectional flow (λ > 1) and a heat recovery limit when room temperatures upstream and downstream reach equilibrium (ε ≤ 50%). This mathematical model is validated experimentally, demonstrating steady flow (λ ∼ 2.21) close to the efficiency limit (ε ∼ 0.40) with a balanced thermal design (NTU ∼ 1). Further analysis shows significant heating savings are possible in mildly cold seasons compared to natural displacement (74%) and natural mixing (60%) ventilation.