[leoedin]

I think that summer/winter distinction is really important. In the UK where most houses don't have air conditioning, you really don't want heat recovery for 1/3 of the year. On really hot days you might want to use heat recovery during the peak few hours, but otherwise you are trying to cool the house down with colder outside air.

I would love some sort of intelligent house ventilation system which could do all that. Heat recovery when it makes sense, normal ventilation when it doesn't. All automated based on dT and relative humidities.

[ZeroGravitas]

I think with this model you can do this as long as you install them in a synced pair (which I think is the baseline assumption).

Normal (heat recovery mode) you have them reverse flow every 60 seconds or so to swap heat.

In cooling mode you just run then continually. One is bringing in fresh air and the other is removing stale air.

The heat store in the intake will soon cool to the outside temp and the heat store in the output is irrelevant (apart from maybe slowing the air flow and creating noise).

If you manually control the system you could combine with a few open windows to create cross breezes even on still evenings.