Typically only around 90% of the energy is recovered, even in ideal conditions.
That sounds good, but considering that for 'good air', you really want to be replacing the air fully every 10 minutes. That means after ~1.5 hours, you've lost nearly all the heat in your home.
Combine that with the fact the 90% is an ideal figure - in more typical installations it might be more like 50% because the incoming and outgoing airflows are not balanced, the heat exchanger is full of fluff and dust, and the humidity of the air is such that lots of energy is lost to the latent heat of vaporization.
Is it worth having one if you want a well ventilated house? Yes. Will it be worth replacing it in 5-10 years when more efficient models get designed...? Probably also yes.
That obviously does not make any sense. You at least want to know the volumne of the room/house before giving any number...
What "Replacing the air fully" equates to in terms of volume is already a factor of the size of the room/house.
You might want to know what volume of air that actually was to understand energy usage, but gp was talking about air quality, not energy efficiency.
Exactly. If one person lives in a castle, do we need to replace all the air every hour? Certainly not. If we are talking about a person in a 5sqm room (for sleeping) then replacing all air every hour won't be sufficient.
There are more factors besides the number of people and the air volume, but I really didn't want to go into so much detail.
As opposed to the 0% of energy recovered when a house "breathes" (i.e., leaks like a sieve) and lets out all the conditioned air?
> That sounds good, but considering that for 'good air', you really want to be replacing the air fully every 10 minutes.
[citation needed]
ASHRAE 62.2 does not mandate nearly that much air exchange. A 2,000 sq. ft. (200 sq. m) home is about 20,000 cu. ft. of volume, and needs about 100 cfm of ventilation. And some folks (e.g., Lstiburek) think ASHRAE (at least the newer revisions) is too high:
* https://www.energyvanguard.com/blog/lstiburek-has-new-ventil...
* https://www.greenbuildingadvisor.com/article/how-much-fresh-...
It should be tied to the ACH value of the construction, as well as tied to occupancy sensors in each room.
What country are you in that has such standards? In Sweden the official recommendation in the building standards is once every other hour.
As far as I know most of the heat in my home is stored in solid objects like the walls and not the air. Replace all the air and you still have the heat