Air-to-Air or only Air-to-Water Heat Pump?

[puntloos]

As you passive eg air tight you will need a supply and return in each room it’s normally 2.5-3” duct have a look at zehnder

To be clear we will certainly have central MVHR, but the air volumes that those units produce tend to be only sufficient for keeping the air moving/fresh and not for active cooling.

Main challenge I think is the situations where unexpected heat is generated (aka opening a huge sliding door) and the inbalances that can be locally created. A friend has a new passivhaus and it's super comfortable all year long, except their bedroom in moderately warm summer days.

 

[ShaunCorbs]

It’s all down to how long you leave that door open etc you could design an air con system just for that one door but tbh that’s a waste tbh I think you will be surprised how effective the erv is with a ac coil before it/ ahu

 

[puntloos]

It’s all down to how long you leave that door open etc you could design an air con system just for that one door but tbh that’s a waste tbh I think you will be surprised how effective the erv is with a ac coil before it/ ahu

Yeah but I'm more thinking of the hot bedrooms. Perhaps I'm slightly blinded by close anecdotes but a friend is sweltering in his passivhaus bedroom and he had to retrofit an FCU, and is now getting a second one.

But he indeed is using A2W so perhaps I shouldn't overthink it. I'm just wondering if modern ASHPS can easily switch between heating and cooling. Many older ones required you to go deep under the hood to convince them to reverse...