Indoor air quality can be improved by increasing the clean air contribution per hour to the indoor environment. This calculator can be used to compute the contribution of each component that impacts air quality. It is based on a guidance provided by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). By taking all of these components into consideration, it is possible to calculate the eACH or equivalent clean air exchange rate for your environment. The second, connected spreadsheet is a model developed by the Robert Koch Institute, the German CDC, to calculate risk of COVID-19 transmission based on several different factors. This is a modeling tool only and cannot take into account every factor in your specific environment. It should be used for guidance and comparision purposes only.

## INDOOR AIR EXCHANGE CALCULATOR FOR REDUCING SARS-CoV-2 IN THE AIR

#### calculation according to ASHRAE recommendations ^{(1)}

#### Normal/forced natural air circulation

estimated normal circulation [0.35], open windows 5 min every hour [2.0]

^{(2)}

#### HVAC

no HVAC [0]; yes [ACH]

no HVAC [0]; yes [%]

MERV 8 [20%], MERV 9 [35%], MERV 10 [50%], MERV 11 [65%], MERV 12 [80%], MERV 13 [85%], MERV 14 [90%], MERV 15 [90%], MERV 16 [95%]

^{(3)}

Clean/outdoor air contribution (HVAC)

#### Mobile HEPA Filter

no HEPA filter [0], yes [CADR]

Clean air contribution (mobile HEPA filter / UV Air Purifier)

Clean/outdoor air contribution without CASPR

#### Adding CASPR

no CASPR [1]; with CASPR in normal environment

^{(4)}[3.3], with CASPR in hospitals with nominal ACH of >15

^{(5)}[2.4]

Clean air contribution (CASPR)

Total clean/outdoor air delivery rate

^{(1)} see: ASHRAE, guidance: IN-ROOM AIR CLEANER GUIDANCE FOR REDUCING COVID19 IN AIR IN YOUR SPACE/ROOM, January 21, 2021, page 2

^{(2)} see: Lelieveld et al., Model Calculations of Aerosol Transmission and Infection Risk of COVID-19 in Indoor EnvironmentsInt. J. Environ. Res. Public Health 2020, 17, 8114, page 3 of 18 - "In the standard case for a room with closed windows, we assume a passive indoor air volume exchange rate of 0.35/hr. If active blow ventilation with outside air is applied [open windows] for short periods every hour, the rate increases to 2/hr

^{(3)} see: ASHRAE, presentation: ASHRAE EPIDEMIC TASK FORCE FILTRATION & DISINFECTION, Updated 10-20-2020, page 11, range 2, 1-3 µm

^{(4)} see 200812 vitrii-Parish Episcopal School-CASPR Test Report.pdf

^{(5)} see: https://pages.ada.org/en/covidmonograph/photocatalytic-oxidizers-as-a-novel-device-for-bacterial-reduction-in-dental-surgical-bays-dr.-margaret-scarlett-and-colleagues

## COVID 19 INFECTION RISK CALCULATOR FOR INDOOR SPACES

#### calculation according to Lelieveld et al. recommendations ^{(1)}

no mask [0], cloth mask [0.5], surgical mask [0.7], FFP2/KN95 [0.95]

no one vaccinated [0%], all vaccinated [100%]

^{(3)}

0 to 100%

quietly [1], loud [3], singing/screaming [4...9]

**Detailed Input +**

for original Wuhan COVID 19 virus [316], for mutated Delta virus variant, 225% more infectious [140]

**0**

^{(4)}range 7.5 to 10, adult [10]

average [5*10

^{8}], superspreader (10 times more RNA) [50*10

^{8}]

^{(5)}

**Specific results +**

**Normalized results +**

^{(1)} see: Lelieveld et al., Model Calculations of Aerosol Transmission and Infection Risk of COVID-19 in Indoor EnvironmentsInt. J. Environ. Res. Public Health 2020, 17, 8114 - Note: All input assumtions are reflecting the current scientific discussion, and may need to be adjusted as the scientific discussion evolves

^{(2)} Very large room sizes violate the assumption of instantaneaous mixing of the air

^{(3)} This is an estimate that depends on two factors, first, on the probability of protecting the person vaccinated, and second, the probability of carrying and shedding a significantly reduced viral load when infected although vaccinated

^{(4)} multiplied by speaking volume number

^{(5)} Range [1e8...1e11], the reported viral RNA concentration of approximately 5 × 10^{8}/mL represents the category of highly infectious patients and represents approximately 20% of individuals tested positive for SARS-CoV-2

This worksheet includes the Gloassary of Terms, and below, line-by-line instructions for inputing the data needed to calculate clean air change rates and the related infection risk for your environment.

### Glossary of Terms

**ACH** – Air Change Rate, is a measure of the air volume added to or removed from a space in one hour, divided by the volume of that space

**eACH** – equivalent Air Change Rate, is Air Change Rate determined by clean/outdoor air volume added to the space

**CADR** – Clean Air Delivery Rate

**CASPR** – Continuous Air and Surface Pathogen Reduction unit, a device that utilizes a natural catalytic process to clean air and surfaces

**cfm** – cubic feet per minute, is a measure of air volume supplied to or removed from a space per minute

**Clean/outdoor air contribution** – The term clean/outdoor air contribution is a measure of the volume of clean/outdoor air each component contributes

**ft²** – Square feet, a measure of area, calculated by length x width of that area

**ft³** – Cubic feet, a measure of volume, calculated by length x width x height of a volume

**HEPA** – High Efficiency Particulate Air filter, an air filter that can remove 99.97% of airborne paticles with a size of 0.3 microns

**HVAC** – Heating, Ventilation and Air Conditioning

**m²** – Square meter, a measure of area, calculated by length x width of that area

**m³** – Cubic meter, a measure of volume, calculated by length x width x height of a volume

**MERV** – Minimum Efficiency Reporting Value, a measure of quality for HVAC filters, ranging from 1 to 20; the higher the MERV rating, the smaller the particle size it can capture; most buildings use MERV filters ranging from 8 to 13

**min** – Minute

**UV** – Ultraviolet light

### Instructions for Use Sheet eACH Calculation

This calculator can be used to compute the contribution of each component that impacts air quality. It is based on a guidance provided by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).

Please note that the green cells in the spreadsheet are for input and the numbers in bold are automatic calculations. If you don’t have an exact number, an estimate is fine.

**Room size** – Enter the square footage of the room

**Ceiling height** – Enter the ceiling height

**Natural air change rate** – This is to calculate air change that is not from the HVAC system; in a standard room with closed windows you can assume a passive rate of 0.35 changes per hour; if you open a window in the room every hour for five minutes, you can assume 2 air changes per hour; enter the most applicable number

**Nominal air change rate** – Enter current air change rate per hour from HVAC system; if you don’t have an HVAC system, enter zero

**Percentage of outdoor air mixed into the total supply** – Enter percentage of outdoor air mixed by HVAC system into the total air supply

**Filter rating for return air** – Enter the percentage found next to the MERV rating of the filters you are using, e.g. MERV 9 = 35%

**Clean air delivery rate (CADR)** – If using a portable air cleaner with a HEPA filter, please enter the manufacturer’s CADR rating; this number can vary from the manufacturer’s estimate based on the fan speed chosen; if you don’t have a portable air cleaner, enter zero

**CASPR effect ** – CASPR has been shown to effectively triple the clean air change rate in most environments; 3.3 is the effect where air change rates are between 1 and 15; enter 2.4 if your air change rate is higher than 15

### Instructions for Use Sheet COVID 19 Infection Risk Calculation

This modeling tool can be used to estimate the risk of COVID 19 transmission based on several factors. It uses data compiled by the Robert Koch Institute, the German CDC.

Please note that the green cells in the spreadsheet are for input and the numbers in the yellow cell are automatic calculations. If you don’t have an exact number, an estimate is fine.

**Mask efficiency (exhaling + inhaling)** – Enter the number that corresponds to the type of masks required in your environemnt; enter zero if no masks are required

**Number of people in the room** – Enter the average number of people expected to occupy the room

**Vaccination ratio** – Enter the percentage of occupants vaccinated

**Time spent in room (episode)** – Enter the average time spent in room (each block of time is considered an episode for purposes of this calculation)

**Number of episodes per day** – Enter the number of episodes per day

**Number of days with episodes per year** – Enter the number of days with episodes per year, e.g. how many days per year is the room occupied

**Speaking/not-speaking ratio** – Enter the percentage of time that corresponds with the occupants speaking vs. not-speaking; e.g. enter 100% in a choir where all participants are singing; enter 5% in a library

**Speaking volume **– Enter the number that corresponds to the average speaking volume; e.g. enter 9 for fans cheering at a basketball game, enter 2-3 for a teacher or students during class