Buildings need fresh air, every single one of them. Even the very best-performing ones will also need some (possibly very little) heating or cooling at peak times of year. Ducting costs money and some people are tempted to combine heating/cooling systems with ventilation.
Don’t do this, is my advice. Best practice is a fully decoupled system design for ventilation (dedicated outdoor air systems, DOAS) and heating/cooling. I would consider it acceptable practice to use a separate fan for each and share some ductwork—but this often adds complexity you don’t want.
It’s not always easy to convince designers and clients why decoupling is the preferred solution. The key point to grasp is that buildings need fresh air ALL the time, while in a well-performing building, heating or cooling is only needed some of the time. For this reason it’s more efficient to keep them separate.
Source: Betterbricks 2024 publication Very High Efficiency Dedicated Outside Air Systems.
Ethos Homes are experienced Passive House builders in Christchurch and their projects exemplify this advice. Principal Pete Bielski is heavily involved at design stage and typically his projects feature a full MVHR system and a fully ducted heat pump system.
Similarly 15 Stout Street (MBIE’s headquarters, owned by Argosy) has a full DOAS with fresh air and heat recovery and a separate fan coil hydronic heating and cooling system, providing for maximum efficiency.
Betterbricks has published some other design strategies specifically for commercial buildings in its 2024 publication Very High Efficiency Dedicated Outside Air Systems.