4 ms·

I saw a Swedish "dream house" TV series where someone installed something like that, it cost a small fortune and I don't see the big benefit in it compared to "

by 2rsf 4y ago

I saw a Swedish "dream house" TV series where someone installed something like that, it cost a small fortune and I don't see the big benefit in it compared to "normal" mechanical ventilation, maybe with heat recovery.

londons_explore 4y ago
The big benefit is that heat recovery units only recover ~80% of the heat. And if you want really good air quality in a room, you want 10 air changes per hour or so. So, that means you are losing 20% of the heat in the air every 6 minutes. If you're doing this in the UK with gas heating and outdoor air of 0C, indoor air of 20C, a 2500 square foot average house and 9 foot ceilings, then it costs a whopping £14/day to heat just the heat lost in the heat recovery unit. Considering that you can buy a CO2+temp+humidity sensor for £15, and then only use as much air as is actually needed for the occupants of the house, you can normally reduce this by 90% typically - saving £4000 per year - well worth it for £100 of sensors. Math: https://www.google.com/search?q=700+J+%2F+kg+%2F+Kelvin+*1.2+kg%2Fm%5E3+*+20+Kelvin+*+2500+square+feet+*+9+feet+*+0.2+*+10+per+hour+*+24+hours+*+0.10+GBP%2Fkwh https://www.google.com/search?q=700+J+%2F+kg+%2F+Kelvin+*1.2...
- walterbell 4y ago
  Is there a good ERV design that is suitable for one room, e.g. the ERV equivalent of a window air conditioner?
  - owenfi 4y ago
    I put a Fantech SE704N in my WFH shed, which is 10x20 feet with 6-7 foot ceilings: Newer ERV: https://www.supplyhouse.com/Fantech-FIT70E-SE-Series-Energy-Recovery-Ventilator-4-Side-Ports-up-to-1200-Sq-Ft https://www.supplyhouse.com/Fantech-FIT70E-SE-Series-Energy-... In stock HRV: https://www.supplyhouse.com/Fantech-SH704-SH-Series-Heat-Recovery-Ventilator-w-Fan-Shutdown-Defrost-4-Side-Ports-up-to-1400-Sq-Ft https://www.supplyhouse.com/Fantech-SH704-SH-Series-Heat-Rec... You can buy the core and swap HRV->ERV (not sure if FIT70E uses the same core). I put it behind a Lutron Caseta Fan Speed controller, it struggles a bit to communicate due to range, but at the low settings I can barely hear it and it keeps CO2 PPM to ~1k if it's just me in here (usually), I turn it up to 3 if I want a gentle wind noise and rarely go to 4 (but would if I wanted to freshen it up). I used the Fantech 4" ducts and it was pretty easy to self-install.
    - owenfi 4y ago
      Oh, and to add, pre-installation the CO2 would hover around 2500ppm if the door and window were closed which was definitely noticeable.
- Retric 4y ago
  You also don’t gain anything by only exchanging outside air with one room. Let’s assume people are willing to let indoor CO2 levels reach X PPM over outside air in a room with N people that takes say 1,000 cubic feet per minute to maintain. The same number of people in a room 50x times as large still takes the same 1,000 cubic feet per minute to maintain. In a larger room it takes longer to reach an equilibrium, but the amount of CO2 you’re removing is a function of the amount of CO2 in the air which reaches the same level. Thus you can setup your air exchanger to vent in response to a single CO2 reading above a fixed level in your HVAC system and automatically adjust for a packed multi hour thanksgiving dinner in your living room or an empty house. Circulating Air within a house is beneficial independent of how much air your venting to the outside. For one thing you can better regulate temperature with increased airflow for another you can filter the air for dust etc. So you really should treat them as separate systems. If it makes you feel better imagine that 10’x10’ room with ventilation to the outside is attached to a sealed 100’x100’ chamber by a ventilation system you can turn on and off. The larger room will only have the same or better air than the 10’x10’ room and thus can’t make the small room worse off. PS: Detecting people in rooms or activity levels does let you adjust temperatures accordingly which may save some money. Also, you may want more ventilation for other reasons thus kitchen and bathroom exhaust fans.
- 2rsf 4y ago
  Intuitively it makes sense, but how do you get to the 90% savings? you still need to keep unused rooms ventilated and heated.

by 2rsf 4y ago

londons_explore 4y ago

The big benefit is that heat recovery units only recover ~80% of the heat. And if you want really good air quality in a room, you want 10 air changes per hour or so. So, that means you are losing 20% of the heat in the air every 6 minutes. If you're doing this in the UK with gas heating and outdoor air of 0C, indoor air of 20C, a 2500 square foot average house and 9 foot ceilings, then it costs a whopping £14/day to heat just the heat lost in the heat recovery unit. Considering that you can buy a CO2+temp+humidity sensor for £15, and then only use as much air as is actually needed for the occupants of the house, you can normally reduce this by 90% typically - saving £4000 per year - well worth it for £100 of sensors. Math: https://www.google.com/search?q=700+J+%2F+kg+%2F+Kelvin+*1.2+kg%2Fm%5E3+*+20+Kelvin+*+2500+square+feet+*+9+feet+*+0.2+*+10+per+hour+*+24+hours+*+0.10+GBP%2Fkwh https://www.google.com/search?q=700+J+%2F+kg+%2F+Kelvin+*1.2...

walterbell 4y ago
Is there a good ERV design that is suitable for one room, e.g. the ERV equivalent of a window air conditioner?
- owenfi 4y ago
  I put a Fantech SE704N in my WFH shed, which is 10x20 feet with 6-7 foot ceilings: Newer ERV: https://www.supplyhouse.com/Fantech-FIT70E-SE-Series-Energy-Recovery-Ventilator-4-Side-Ports-up-to-1200-Sq-Ft https://www.supplyhouse.com/Fantech-FIT70E-SE-Series-Energy-... In stock HRV: https://www.supplyhouse.com/Fantech-SH704-SH-Series-Heat-Recovery-Ventilator-w-Fan-Shutdown-Defrost-4-Side-Ports-up-to-1400-Sq-Ft https://www.supplyhouse.com/Fantech-SH704-SH-Series-Heat-Rec... You can buy the core and swap HRV->ERV (not sure if FIT70E uses the same core). I put it behind a Lutron Caseta Fan Speed controller, it struggles a bit to communicate due to range, but at the low settings I can barely hear it and it keeps CO2 PPM to ~1k if it's just me in here (usually), I turn it up to 3 if I want a gentle wind noise and rarely go to 4 (but would if I wanted to freshen it up). I used the Fantech 4" ducts and it was pretty easy to self-install.
  - owenfi 4y ago
    Oh, and to add, pre-installation the CO2 would hover around 2500ppm if the door and window were closed which was definitely noticeable.
Retric 4y ago
You also don’t gain anything by only exchanging outside air with one room. Let’s assume people are willing to let indoor CO2 levels reach X PPM over outside air in a room with N people that takes say 1,000 cubic feet per minute to maintain. The same number of people in a room 50x times as large still takes the same 1,000 cubic feet per minute to maintain. In a larger room it takes longer to reach an equilibrium, but the amount of CO2 you’re removing is a function of the amount of CO2 in the air which reaches the same level. Thus you can setup your air exchanger to vent in response to a single CO2 reading above a fixed level in your HVAC system and automatically adjust for a packed multi hour thanksgiving dinner in your living room or an empty house. Circulating Air within a house is beneficial independent of how much air your venting to the outside. For one thing you can better regulate temperature with increased airflow for another you can filter the air for dust etc. So you really should treat them as separate systems. If it makes you feel better imagine that 10’x10’ room with ventilation to the outside is attached to a sealed 100’x100’ chamber by a ventilation system you can turn on and off. The larger room will only have the same or better air than the 10’x10’ room and thus can’t make the small room worse off. PS: Detecting people in rooms or activity levels does let you adjust temperatures accordingly which may save some money. Also, you may want more ventilation for other reasons thus kitchen and bathroom exhaust fans.
2rsf 4y ago
Intuitively it makes sense, but how do you get to the 90% savings? you still need to keep unused rooms ventilated and heated.