1) About MERV 13 - upgrading filters to MERV13 is the cheapest and most consistent/ practical solution:
For a 10,000 ft2 school buildings or 15 classrooms, it only costs $546/YEAR. This simple upgrade will give you ~5 ACH.
2) About air purifiers, it costs equal or more than $250 to put 1 purifier in 1 classroom (500 ft2) to give ~5 ACH.
Here is a collection of air purifiers available on the market (fan + HEPA filter) compared by cost/ft2 and noise.
3) About ventilation (1/3): if the building open the outside air dampers as designed (per minimum code), you get an extra 4.23 ACH.
-> A lot of studies found that schools are under ventilated because the operators chose to save energy (closing the outside damper on purpose)
(2/3) Starting March, many schools can benefit from economizer mode ( free cooling), meaning that they can open the outside air damper without any taxation on the system.
if units are old or not operational then this will not be feasible.
(3) Many schools do facility assessments. These assessments are key to understanding whether the HVAC system can handle outside air.
We need to be asking for those assessments to make data-driven decision.
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If my school building was running the way it was supposed to be run (compliant to minimum codes), how would it rate per Harvard-CU Boulder Air Exchange Rate Target?
In other words, are we asking too much from school buildings? 🧵
Classroom
- 500 ft2, 12 kids
- served by a central AC system
To obtain the certificate of occupancy (to be allowed to occupy the classroom), this classroom need to have minimum outside air according to building codes. This is by design and should be kept in operation.
1) The minimum outside air equal to 2.7 ACH. 2) The AC system has a filter - mainly installed to protect the heating and cooling coil - of MERV 8 (pretty common in school buildings). The filter + airflow will get you 2.67 ACH.
My school installed an electronic air cleaner system (EAC), what should I do?
1) Ask for the following (part 1):
-Make/model of the system
-What is the basis to choosing the number of units? How many units is needed for the airflow, number of people, ft2?
- How do we verify it is working after it is installed?
Ask for the following (part 2)
- Efficiency test data that correspond to the install (in-room versus duct?)
- By-products test (formaldehyde, ultrafine particles, ozone) test at the SAME conditions of the efficiency test.
Here is a collection of cheating techniques of ionizers when reporting test results 🧵 @jljcolorado
1) Use a small chamber or position their equipment above a tiny surface (example Petri dish) when reporting efficiency to exaggerate the %.
For example, reported efficiency of an equipment positioned above a tiny surface is 93%. Applying to real conditions (duct, with appropriate surface area and contact time), this efficiency will be 0.0016%.