Thread by @marwa_zaatari

🧵 Answers to what the different strategies will result in term of air change rate

Example used throughout the thread:
👉Classroom: 960 ft2: 30' x 32’
👉Number of occupants: 30 (this is the design number, taking into account average classroom density).

Ventilation by code, this classroom should have 415 CFM airflow of outside air or 14 CFM/person.

👉This airflow is being forced through the HVAC system (unit in classroom or mechanical room).

When we check ventilation, the answer is not “yes” or “no”, the answer should be how much?

Many classrooms are at full capacity, meaning that social distancing of 6 feet is not adopted - further highlighting the importance of masks/ventilation/filtration MERV HEPA/UVGI.

Exploring what different combinations of outside air and filtration and UVGI will result in terms of air change rate:

What is the target of air change rate? General agreement 5 or above ACH.

Check different combination ventilation/filtration/HEPA mitigation strategies and the resulting ACH:

Here is some good news:

Mechanical Filtration cost (if there is a place/capability to install filters)
The Yearly cost including two replacements of MERV 13 filters will be $28.
Let's assume it takes $5 of labor cost to install a filter.
Total cost/Year = $48 to get ~5 ACH.

HEPA air purifiers are also a cost-effective measure to get to 5 ACH:

For a 960 ft2,
👉5 ACH: purchasing 2 x air cleaner with CADR = 320 CFM costs ~$17/student for first year.
OR
👉5 ACH: MERV 13 costs $1.6/student each year.