Ventilation in a Classroom

bungaro79

Hi all
just looking for information on ventilation options for a classroom for the upcoming winter. Guidelines now suggest that we are to have windows and doors open to create a natural airflow but with winter coming down it looks like the current guidelines are to still do the same even with dropping temperatures and cold winds.
So I'm wondering if there is some option out there that could create a change of air in the class for say 5-10 mins an hour but then you could close the windows again to keep in the heat and keep the kids warm? I've seen MEV mentioned on here and I've also seen portable fans which you could put in windows but not sure how efficient these are.

Calahonda52

expelling stale warm bug laden air from a class room is never going to be an energy efficient activity.
.
Just putting a fan on the window without providing a properly located fresh supply point is only going to suck bug laden air from other rooms.

bungaro79

Thanks for the reply Calahonda. There is going to be a big discussion on this in the next few weeks as the weather gets colder and something will have to give i.e. heating, energy bills increase, etc. All of the classes in our school have at least one wall with windows to the outside so at least we can use that as our fresh air source. My own daughters school have sent out a message to wear extra layers as the windows will still be left open in her school so we are just trying to see if there are other options out there

Lumen

I would consider single-room HRV specified with flow rates capable of producing the required number of air changes per hour for the number of occupants.

These flow rates will be quite high for class of 30 kids.

Smaller units are around 500 euros, but I don't know whether the flow rates will be high enough.

It is critically important to position the units such that air flows are not carrying virus particles. There are a number of superspreader studies done early in the pandemic which highlight the risks. One I read mapped out infections in a restaurant and these aligned with the air flows from mechanical ventilation - if you were downstream of a spreader you got it.

In any case this ought to be consistent with building regs which specify that ventilation should be well above head height.

The single room HRV units I looked at fell into one of several types:

- Alternating flow, where the unit switches from extract to supply every 30 seconds or so. This type can be problematic under certain weather conditions where the air pressure differences prevent either extract or supply working effectively.

- Simultaneous extract and supply, typically through a single large divided pipe or two smaller (e.g. 3 inch) pipes.

I'm going for the second type cos it seems better.

Obvs these solutions require a hole in the wall, although I guess in theory you could put it through a glazed unit.

bungaro79

Great info there Lumen, thanks!

Not sure if these will fit into our budget unfortunately as we've 35 classes which would need fitting and half the budget has been spent on perspex screens and hand sanitizer already!

Calahonda52

Re
- Simultaneous extract and supply, typically through a single large divided pipe or two smaller (e.g. 3 inch) pipes.

there will have be decent cross flow from these, paradoxically, the much maligned portacabins are easier to do, roof extract, open windows, thermal jocks

Lumen

Calahonda52 wrote: »

here will have be decent cross flow from these

Virus loves cross flow!

That's what makes this particularly tricky. You want air changes without too much lateral air movement, which is kind of hard, particularly when there is no money.

Calahonda52

Lumen wrote: »

Virus loves cross flow!

That's what makes this particularly tricky. You want air changes without too much lateral air movement, which is kind of hard, particularly when there is no money.

Yep, its a tough ask
https://www.trend-uk.com/en/IE/product/AIR_PRO_EUR/2/124/airshield_pro_apf_20_respirator_230v_euro_plug__authorised_distributors_only.html

bungaro79

Calahonda52 wrote: »

Re
- Simultaneous extract and supply, typically through a single large divided pipe or two smaller (e.g. 3 inch) pipes.

there will have be decent cross flow from these, paradoxically, the much maligned portacabins are easier to do, roof extract, open windows, thermal jocks

Can't find a portacabin for love nor money anywhere apparently!