3 ms·
The question with that system is: where is the replacement air coming from? To be effective for disease particle controls, it needs to come from outside, other
by danans 6y ago
The question with that system is: where is the replacement air coming from? To be effective for disease particle controls, it needs to come from outside, otherwise you'd just be sucking dirty air from the rest of the building into the classroom - or even worse: backdrafting CO2 and CO from any combustion appliances within the building envelope.
You can achieve a clean air supply by opening another window in the classroom, but then you also let hot or cold air into the classroom (depending on the season), making the heating/cooling systems work even harder.
The answer to this is to run the exhaust/intake air channels through a heat recovery ventilator (HRV), which transfers energy from the hotter to colder airstream, while also introducing fresh air back to the space.
- tpmx 6y agoAlso: How do you make that system work in the winter?
- danans 6y agoA heat recovery ventilator works fine in the winter. Its whole purpose is to introduce fresh air into the conditioned space while preheating it with the heat in the dirty exhaust air stream.
- jessaustin 6y agoHRVs have been designed to exchange heat, and ERVs to exchange heat and moisture, but have either specifically been designed not to exchange virus particles? One wouldn't want to make any assumptions...
- danans 6y agoAt least with heat recovery ventilators, the air streams do not mix at all. Unless the virus finds a way to penetrate the metal fins of the heat exchanger, it should be completely fine.
- bluGill 6y agoThere are several different designs, some there is a mix of streams. Most are sadly not particularly efficient overall, but still much better than leaving a window open.
- danans 6y agoIs it really an HRV if the air streams mix? [1] The primary function of an HRV is ventilation. Any air stream mixing would nullify that objective. 1. https://www.greenbuildingadvisor.com/article/misconceptions-about-hrvs-and-ervs https://www.greenbuildingadvisor.com/article/misconceptions-...
- bluGill 6y agoThere are a few different types. One type blows air out "across rocks" to warm them up, and then reverses the fan pulling air in "across the same rocks" I simplified a lot in the above, but the idea should be clear - there is some mixing of streams in this style.
- theptip 6y agoIs there a reason you can’t just recirculate through a HEPA filter? They capture viruses AFAIK. Seems easier than recovering exhaust heat and refilling from outside.
- peteretep 6y agoNo reason at all. That's basically how most existing air purifiers work, they're a big fan attached to a HEPA filter.