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Heat recovery ventilation is more energy efficient than an old breathable house. But unfortunately it is not common even in new buildings. If you own a home you

Heat recovery ventilation is more energy efficient than an old breathable house. But unfortunately it is not common even in new buildings. If you own a home you probably can install one but renters are out of luck.

londons_explore 4y ago
Heat recovery ventilation is still a technology in its infancy. 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.
- throw0101c 4y ago
  > Typically only around 90% of the energy is recovered, even in ideal conditions. 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-ventilation-standard-resistance-may-not-be-futile/ https://www.energyvanguard.com/blog/lstiburek-has-new-ventil... * https://www.greenbuildingadvisor.com/article/how-much-fresh-air-does-your-home-need https://www.greenbuildingadvisor.com/article/how-much-fresh-...
  - Dork1234 4y ago
    Most homes are getting 4 to 7 air changes per hour just from leakage, 100cfm is nothing compared to that. It should be tied to the ACH value of the construction, as well as tied to occupancy sensors in each room.
- kyberias 4y ago
  The standard to replace all air is about 2 hours which is 12 times longer than the 10 minutes you stated here.
- valenterry 4y ago
  > That sounds good, but considering that for 'good air', you really want to be replacing the air fully every 10 minutes. That obviously does not make any sense. You at least want to know the volume of the room/house before giving any number...
  - anonymous_sorry 4y ago
    It's not obvious to me why this doesn't make sense. 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.
    - valenterry 4y ago
      > What "Replacing the air fully" equates to in terms of volume is already a factor of the size of the room/house. 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.
- dagw 4y ago
  That sounds good, but considering that for 'good air', you really want to be replacing the air fully every 10 minutes. What country are you in that has such standards? In Sweden the official recommendation in the building standards is once every other hour.
  - alliao 4y ago
    I once heard that Swedes sleep with windows open, sounds like way more ACH than building standards?
    - jeltz 4y ago
      Only during the summers and due to lack of air conditioning. That is no related to air quality.
- Dork1234 4y ago
  HRV have been around for 30+ years. I wouldn't call it infancy, just not main stream.
- changoplatanero 4y ago
  > That means after ~1.5 hours, you've lost nearly all the heat in your home. 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
  - PaulDavisThe1st 4y ago
    Unless you live in an adobe/stone/brick house, the thermal mass of your walls is pretty small. Traditional plaster would add a limited amount to a stud-framed house, but in most US houses, what you've said isn't true.
mharig 4y ago
And the ventilation ducts and filters are nice hotbeds for mold and bacteria.

londons_explore 4y ago

Heat recovery ventilation is still a technology in its infancy. 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.

throw0101c 4y ago
> Typically only around 90% of the energy is recovered, even in ideal conditions. 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-ventilation-standard-resistance-may-not-be-futile/ https://www.energyvanguard.com/blog/lstiburek-has-new-ventil... * https://www.greenbuildingadvisor.com/article/how-much-fresh-air-does-your-home-need https://www.greenbuildingadvisor.com/article/how-much-fresh-...
- Dork1234 4y ago
  Most homes are getting 4 to 7 air changes per hour just from leakage, 100cfm is nothing compared to that. It should be tied to the ACH value of the construction, as well as tied to occupancy sensors in each room.
kyberias 4y ago
The standard to replace all air is about 2 hours which is 12 times longer than the 10 minutes you stated here.
valenterry 4y ago
> That sounds good, but considering that for 'good air', you really want to be replacing the air fully every 10 minutes. That obviously does not make any sense. You at least want to know the volume of the room/house before giving any number...
- anonymous_sorry 4y ago
  It's not obvious to me why this doesn't make sense. 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.
  - valenterry 4y ago
    > What "Replacing the air fully" equates to in terms of volume is already a factor of the size of the room/house. 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.
dagw 4y ago
That sounds good, but considering that for 'good air', you really want to be replacing the air fully every 10 minutes. What country are you in that has such standards? In Sweden the official recommendation in the building standards is once every other hour.
- alliao 4y ago
  I once heard that Swedes sleep with windows open, sounds like way more ACH than building standards?
  - jeltz 4y ago
    Only during the summers and due to lack of air conditioning. That is no related to air quality.
Dork1234 4y ago
HRV have been around for 30+ years. I wouldn't call it infancy, just not main stream.
changoplatanero 4y ago
> That means after ~1.5 hours, you've lost nearly all the heat in your home. 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
- PaulDavisThe1st 4y ago
  Unless you live in an adobe/stone/brick house, the thermal mass of your walls is pretty small. Traditional plaster would add a limited amount to a stud-framed house, but in most US houses, what you've said isn't true.

mharig 4y ago

And the ventilation ducts and filters are nice hotbeds for mold and bacteria.