Where a building or space incorporates mechanical ventilation systems, including mixed-mode strategies, the selection of future weather files for thermal comfort assessment should be based on the expected service life of the systems installed. This includes systems providing mechanical ventilation, with or without limited comfort cooling, and mixed-mode spaces where natural ventilation is supplemented by mechanical systems within the same space.
For the purposes of this guidance, ‘mechanical ventilation with limited comfort cooling’ refers to systems that may provide some degree of cooling or air tempering but are not designed to fully maintain internal conditions to defined air-conditioned setpoints throughout occupied hours.
Although these systems do not provide full air conditioning, their presence influences internal environmental conditions and overheating risk. As their performance is dependent on mechanical components with defined service lifespans, the future thermal comfort assessment should be aligned with the expected lifespan of these systems (typically 15 years), rather than the overall building lifespan.
For schemes where free‑running buildings are assessed using a longer lifespan for future climate scenarios, a shorter system lifespan should be used where mechanical systems are present
