3 ms·

This is a pretty cool project, it's basically a retrofit approach to what in industry is known as "displacement ventilation" or "stratification ventilation". In

This is a pretty cool project, it's basically a retrofit approach to what in industry is known as "displacement ventilation" or "stratification ventilation". In the US our typical approach is "mixing ventilation" where you try to mix and equalize the air everywhere within a space, then cycle a portion of the air through an air conditioner to get the temperature and humidity to the desired level. This is mechanically intensive, needs big ducts, and has the downside that contaminants in the air tend to get spread everywhere. Displacement ventilation uses the fact that hot and humid air rise, instead of mixing everything together it removes the most stale air at the top of the room and replaces it. Trickier to get right, but quieter and more effective in many cases. Here's a blog post with illustrations: https://blog.hoffman-hoffman.com/blog/the-basics-of-displacement-ventilation https://blog.hoffman-hoffman.com/blog/the-basics-of-displace...

kurthr 2y ago
For efficiency you need to minimize leakage of outside conditions, but you also really need a heat/energy exchanger (HRV/ERV) at the fresh air input so that you're not recirculating stale air.
- toast0 2y ago
  School buildings with operable windows often don't condition the air. This design collects / guides air from around the pupils towards an exhaust window and suggests leaving a door or opposite site window to get fresh air in. It's not a solution for highly conditioned spaces.
  - kurthr 2y ago
    Just thinking about Germany, I'm wondering when peak infections occur. I'd guess that it's during the winter? I have not heard that Germany's winters have become particularly mild. In fact Mainz, where this was developed, often has high temperatures below freezing during the winter months. Having significant airflow without an HRV might make people a bit chilly in the morning. Or would this still require the expensive filtration system in the winter?
    - hedgehog 2y ago
      I'm not sure what the overall calculation looks like but if you remove 10-15 liters per minute per occupant to match normal respiration that's a pretty small loss of heat. Maybe a net win if it reduces need for other ventilation and dehumidification enough. It's not just an infection control thing, the building needs some fresh air anyway to get fresh air in and remove CO2 + all the other nasties that accumulate indoors (cleaning chemicals, radon, various solvents plasticizers, even stuff wafting out of the floor if like some major offices in the valley you're built on contaminated ground).
      - kurthr 2y ago
        So call it 400 liters/min at 30C delta with air's heat capacity about 1kJ/kg/C and 800 liters/kg. You're at 15kJ/min or 250W just for that airflow. Figure there are 40 rooms and you're at 10kW of heating just for that fresh air flow. An ERV can cut that by 90%. You just saved 9kW of continuous power for the building during the winter with an ERV.

kurthr 2y ago

For efficiency you need to minimize leakage of outside conditions, but you also really need a heat/energy exchanger (HRV/ERV) at the fresh air input so that you're not recirculating stale air.

toast0 2y ago
School buildings with operable windows often don't condition the air. This design collects / guides air from around the pupils towards an exhaust window and suggests leaving a door or opposite site window to get fresh air in. It's not a solution for highly conditioned spaces.
- kurthr 2y ago
  Just thinking about Germany, I'm wondering when peak infections occur. I'd guess that it's during the winter? I have not heard that Germany's winters have become particularly mild. In fact Mainz, where this was developed, often has high temperatures below freezing during the winter months. Having significant airflow without an HRV might make people a bit chilly in the morning. Or would this still require the expensive filtration system in the winter?
  - hedgehog 2y ago
    I'm not sure what the overall calculation looks like but if you remove 10-15 liters per minute per occupant to match normal respiration that's a pretty small loss of heat. Maybe a net win if it reduces need for other ventilation and dehumidification enough. It's not just an infection control thing, the building needs some fresh air anyway to get fresh air in and remove CO2 + all the other nasties that accumulate indoors (cleaning chemicals, radon, various solvents plasticizers, even stuff wafting out of the floor if like some major offices in the valley you're built on contaminated ground).
    - kurthr 2y ago
      So call it 400 liters/min at 30C delta with air's heat capacity about 1kJ/kg/C and 800 liters/kg. You're at 15kJ/min or 250W just for that airflow. Figure there are 40 rooms and you're at 10kW of heating just for that fresh air flow. An ERV can cut that by 90%. You just saved 9kW of continuous power for the building during the winter with an ERV.