Keep heat pump and ventilation systems separate for best results Best practice is fully decoupled systems: don’t share the ductwork

10 April 2024 by Jason Quinn

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.

Comments 1

  1. Assuming we’re dealing with a client who is inclined not to include MVHR at all (very common) and would choose a heat pump first I’d suggest this advice actually complicates rather than simplifies the application.
    I entirely agree that ventilation is required 100% of the time, would it not also be suitable to advise the client or interlock the fan of the heat pump with the ventilation power to ensure the fan always runs on the heat pump regardless of cooling function? The cost to run an entirely independent duct vs the power usage of the fan only (on a heat pump) would likely take many years to offset.
    Keen to hear your thoughts

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