Harvard-CU Boulder Portable Air Cleaner Calculator for Schools.v1.3

	A	B	C	D	E	F	G	H	I	J	K	L	M	N
1	HARVARD - CU BOULDER PORTABLE AIR CLEANER CALCULATOR FOR SCHOOLS.v1
2	AUTHORS	Joseph Allen		Healthy Buildings Program, Harvard T.H. Chan School of Public Heatlh
3		Jose Cedeno-Laurent		Healthy Buildings Program, Harvard T.H. Chan School of Public Health
4		Shelly Miller		Mechanical Engineering, College of Engineering and Applied Science, University of Colorado Boulder
5	ABOUT	This tool supports the Harvard 'Schools for Health' report on risk reduction strategies for schools and should not be used in isolation
6		Link to full report: https://schools.forhealth.org/risk-reduction-strategies-for-reopening-schools/
7		This guidance does not supercede guidance from CDC, WHO, state and local guidance, or other bodies
8		It is provided to support efforts to supplement outside air ventilation with air cleaning using well established particle filtration strategies
9		To input values from your indoor spaces of interest, download the calculator as .xlsx file.
10	DATE	November 8, 2020
11	VERSION	v1.3
12	LINK TO FILE	https://docs.google.com/spreadsheets/d/1NEhk1IEdbEi_b3wa6gI_zNs8uBJjlSS-86d4b7bW098/edit#gid=0
13	SHORT URL	https://tinyurl.com/portableaircleanertool
14		check back often for updates!
15	IMPORTANT	This tool is intended to simplify decision-making around portable air cleaners in schools for airborne transmission control (it can also be applied to residential or office air cleaning, noting differences in ventilation practices and occupancy).
16		Airborne transmission is not the only mode of transmission, therefore additional risk reduction strategies are required
17		UNIVERSAL MASK WEARING SHOULD BE REQUIRED AND SOCIAL DISTANCING MORE THAN 6 FEET (~2 meters) IS EMPHASIZED
18		Read the DISCLAIMER at bottom of this worksheet
19		Schools should open when community spread is controlled and this guidance should come from the local public health officials
20		For information on when to open based on community spread: https://globalhealth.harvard.edu/path-to-zero-schools-achieving-pandemic-resilient-teaching-and-learning-spaces/
21	NOTES
22		Quick 'rule of thumb' selection guide for portable air cleaners
23			Look for portable air purifier with HEPA filter
24			Look for high clean air delivery rate
25			Avoid add-ons (e.g., ionizers, ultraviolet lights)
26		Placement of the device matters
27			The calculations are based on a simple-box model that assumes equal-mixing in a room
28			Avoid having air blow across individuals
29			In the absence of additional information place air cleaner in the middle of the room
30		Basis for targeting 5 total air changes per hour (ACH) from outdoor air ventilation + portable air cleaner
31			Goal is a total of 5 air changes per hour
32			5 air changes per hour means that the air inside will be exchanged with clean air on average 5 times an hour
33			And it will take (1/5)603=36 min to clear the air from contamination completely
34			The design standard for minimum ventilation in classrooms is approximately 3 ACH (see below)
35			Many classrooms do not meet this minimum; a few will provide higher ventilation
36			The impacts of ventilation and air cleaning are additive (e.g., ventilation of 3 ACH + air cleaning of 2 ACH = 5 ACH)
37			You can add multiple air purifiers to a room to achieve a higher ACH (e.g., putting in two devices, each with 2 ACH, will equal 4 ACH total)
38		Understanding CADR
39			Clean air delivery rate is a combination of filter performance and also how much air passes through that filter (e.g., a device with a great filter but no air passing through is not effective)
40			HEPA filters capture >99.97% of airborne particles, so look for devices with HEPA filters
41			Next, look for a high CADR, which is in units of cfm, or cubic feet per minute
42			CADR is determined for different particle sizes; use the smoke or dust rating
43		Filter types and when to change them
44			Look for devices with HEPA filters, and change them according to manufacturer recommendations
45			Many devices come with a charcoal filter. This treatment can be useful for reducing concentrations of gas-phase pollutants.This filter needs to be changed often and has no impact on viruses.
46		Basis for assuming ~3 ACH of outdoor air ventilation as the design standard for schools is ASHRAE 62.1 (2019)
47									Calcs based on ASHRAE
48			ASHRAE						500	sq ft room*		1000	sqft room*
49					cfm/person	cfm/sq ft	Default occupancy (per 1000 sq ft)		cfm	cfm/person	ACH	cfm	cfm/person	ACH
50			Classrooms	5-8 year olds	10	0.12	25		185.0	14.8	2.8	370.0	14.8	2.8
51				9+ years old	10	0.12	35		235.0	13.4	3.5	470.0	13.4	3.5
52									*assumes 8 foot ceiling			*assumes 8 foot ceiling
53									** metric units at the bottom of README page
54	ADDITIONAL HELPFUL RESOURCES
55
56		Air cleaner guidance, effectiveness
57			Kirkman, Zhai, Miller		Effectiveness of Air Cleaners for Removal of Virus-Containing Respiratory Droplets. Recommendations for Air Cleaner Selection for Campus Spaces
58					https://shellym80304.files.wordpress.com/2020/06/air-cleaner-report.pdf
59			Offermann et al. 1985		Control of respirable particles in indoor air with portable air cleaners
60					https://www.sciencedirect.com/science/article/abs/pii/0004698185900034
61			Miller et al. 1996		Effectiveness of in-room air filtration for tuberculosis control in healthcare settings
62					https://shellym80304.files.wordpress.com/2020/06/miller-leiden-et-al-1996.pdf
63			Shaughnessy and Sextro 2006		What is an effective portable air cleaning device? A review
64					https://www.tandfonline.com/doi/full/10.1080/15459620600580129?casa_token=90BksVnsPBcAAAAA%3ALI6QfCsrlFVElAHpOtdgvVOt9OjRQ1PN5aMvJbnn5ohUg58Hy1H3DZ8HjfJybl3K9vRO6XyK5HUeXg
65			California Air Resources Board		https://ww2.arb.ca.gov/our-work/programs/air-cleaners-ozone-products/california-certified-air-cleaning-devices
66			Association of Home Appliance Manufacturers			https://ahamverifide.org
67		General information on air cleaners
68			U.S. EPA		Air cleaners and air filters in the home
69					https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home
70					https://pubmed.ncbi.nlm.nih.gov/16531290/
71		Typical ventilation rates in schools
72			Shaughnessy et al, 2006		A preliminary study on the associations between ventilation rates in classrooms and student performance
73					https://pubmed.ncbi.nlm.nih.gov/17100667/
74		Resource for parents and teachers
75			Allen, Corsi, Gall, Clevenger, Lang, Jone		20 questions to ask before sending your kid back to school
76					https://schools.forhealth.org/risk-reduction-strategies-for-reopening-schools/faqs/
77
78
79	DISCLAIMER
80	This tool is provided for informational and educational purposes only. It is intended to offer guidance regarding questions about best practices regarding the general selection of portable air cleaners in schools in an effort to reduce the risk of disease transmission, specifically novel coronavirus SARS-CoV-2 and the disease it causes, COVID-19. Adherence to any information included in this tool will not ensure successful treatment in every situation, and the user should acknowledge that there is no “zero risk” scenario, that each building and situation are unique and some of the guidance contained in this document will not apply to all buildings, or countries outside the United States.
81	Furthermore, the tool should not be deemed inclusive of all proper methods nor exclusive of other methods reasonably directed to obtaining the same results. The tool is in no way intended to override or supersede guidance from government and health organizations, including, without limitation, the Centers for Disease Control and Prevention, the World Health Organization, the United States Government, and or any States. The information contained herein reflects the available information at the time the document was created. The user recognizes that details and information are changing daily, and new information and/or the results of future studies may require revisions to the document (and the general guidance contained therein) to reflect new data. We do not warrant the accuracy or completeness of the guidance in this document and assume no responsibility for any injury or damage to persons or property arising out of or related to any use of the report or for any errors or omissions.
82
83	ACRONYMS
84		ACH	air changes per hour
85		cfm	cubic feet per minute
86		sq ft	square feet, measure of area
87		cfm/p	cubic feet per minute per person
88		ASHRAE	American Society of Heating, Refrigerating and Air-Conditioning Engineers
89		HEPA	high efficiency particulate air
90		CADR	clean air delivery rate
91		AHAM	Association of Home Appliance Manufacturers
92
93
94	ASHRAE in metric units							Calcs based on ASHRAE
95		ASHRAE						50	m2 room*		100	m2 room*
96				l·s/person	l·s/m2	Default occupancy (per 100 m2)		l·s	l·s/p	ACH	l·s	l·s/p	ACH
97		Classrooms	5-8 year olds	5	0.6	25		92.5	7.4	2.8	185.0	7.4	2.8
98			9+ years old	5	0.6	35		117.5	6.7	3.5	235.0	6.7	3.5
99								*assumes 2.4 m ceiling			*assumes 2.4 m ceiling
100
101	VERSION CONTROL
102	Version	Date	changes
103	v1	August 4 2020
104	v1.1	August 5 2020	unit system selection added
105	v1.2	August 19,2020	correction to metric units in README ASHRAE table

	A	B	C	D	E	F	G
1	SIMPLE TOOL FOR SCHOOLS FOR SELECTING PORTABLE AIR CLEANER FOR ROOMS (input fields are bright yellow)
2
3	STEP 1	HOW BIG IS THE ROOM?
4		Select units of preference	feet
5		How big is your room?	500	Input your room size here in square feet
6		How tall are your ceilings?	8	Input your room size here in feet
7
8	STEP 2	WHAT IS THE 'CLEAN AIR DELIVERY RATE' OF THE AIR PURIFER? (you get this from the manufacturer)
9
10		What is the clean air delivery rate of the air cleaner?	300	Find the CADR from the manufacturer in units of cubic feet per minute, or cfm; if they report multiple numbers, use the one for 'dust'
11
12	STEP 3	HOW MUCH OUTDOOR AIR VENTILATION DO YOU HAVE?
13
14		How is the ventilation in my school?	Low ventilation	Good ventilation	3	ACH	This is the approximate minimum air exchange rate that schools should be designed for, but most don't achieve (see 'README')
15				Enhanced ventilation	4	ACH	Select this only if your school has made enhancements beyond code minimums
16				Typical school	1.5	ACH	This is an approximate average air exchange rate in many schools based on research studies
17				Low ventilation	1	ACH	Select this if your school has poor ventilation or you're not sure (for reference, a typical U.S. home is 0.5 ACH)
18
19	STEP 4	COMBINING AIR CLEANING AND VENTILATION, IS YOUR ROOM MEETING THE TARGET?
20
21		Air changes from outdoor air ventilation	1		TARGET IS AT LEAST 5 TOTAL AIR CHANGES PER HOUR
22		Air changes from air cleaner	4.5			Ideal (6 ACH)
23		Total air changes in the room per hour	5.5			Excellent (5-6 ACH)
24						Good (4-5 ACH)
25						Bare minimum (3-4 ACH)
26						Low (<3 ACH)
27
28	STEP 5	WHAT SIZE ROOM WILL WORK FOR THIS PORTABLE AIR CLEANER?
29
30		Cubic feet per minute (cfm) of clean air from cleaner	300	This is from the manufacturer (see cell 'c10')
31		Cubic feet per minute (cfm) of outdoor air from ventilation	67	This is calculated from air changes per hour and volume of room
32		Total cfm of air cleaning and ventilation	367
33
34		Recommended room size for this air cleaner (in square feet)	550	This is the recommended maximum size of the room for this air cleaner to achieve 5 total ACH
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	A	B	C	E	G	I	J	K	M	N	O
1	EXPANDED TOOL FOR SCHOOLS FOR SELECTING PORTABLE AIR CLEANERS (WITH EXAMPLES) (input fields are bright yellow)
2
3		STEP 1: How big is the room?		STEP 2: What is CADR for device?	STEP 3: How is the ventilation in the room?	STEP 4: Is room meeting target ACH?			STEP 5: What size room for this air cleaner?
4	Portable Air Cleaners Under Consideration	Floor area (square feet)	Ceiling height ( feet)	CADR for dust, in cubic feet per min (cfm)	How would you rate outdoor air ventilation currently?	Calculated ACH from Outdoor Air (from Step 3)	Calculated ACH from Air Cleaner (from Step 2)	Total ACH (DOES TOTAL MEET MIN 5 ACH?)	Calculated cfm from outdoor air (from Step 1 and Step 3)	Calcualted cfm from air cleaning (from Step 1 and Step 2)	Room area (square feet; assuming celing height in Step 1)
5	Levoit Vital 100 True HEPA Air Purifier	250	10	130	Typical school	1.5	3.1	4.6	63	130	231
6	Whirlpool® WPT80 Whispure™ Large Tower Air Purifier	250	10	142	Typical school	1.5	3.4	4.9	63	142	245
7	Oransi OV200 Air Purifier	250	10	150	Typical school	1.5	3.6	5.1	63	150	255
8	Conway Airmega 150	250	10	161	Typical school	1.5	3.9	5.4	63	161	268
9	BioGS 2.0 Ultra Quiet Air Purifier	250	10	180	Typical school	1.5	4.3	5.8	63	180	291
10	Honeywell True HEPA Large Room Air Purifier With Allergen Remover	250	10	190	Typical school	1.5	4.6	6.1	63	190	303
11	MinusA2 Ultra Quiet Air Purifier	500	10	200	Typical school	1.5	2.4	3.9	125	200	390
12	Coway Airmega AP-1512HH	500	10	246	Typical school	1.5	3.0	4.5	125	246	445
13	Levoit LV-H134 Tower Pro True HEPA Air Purifier	500	10	312	Typical school	1.5	3.7	5.2	125	312	524
14	Honeywell True HEPA Bluetooth Smart Air Purifier With Allergen Remover	500	10	320	Typical school	1.5	3.8	5.3	125	320	534
15	Whirlpool® WPPRO2000 Whispure™ Air Purifier	500	10	328	Typical school	1.5	3.9	5.4	125	328	544
16	Oransi EJ120 Air Purifier	500	10	333	Typical school	1.5	4.0	5.5	125	333	550
17	Alen BreatheSmart 75i True HEPA Air Purifier	1500	10	347	Typical school	1.5	1.4	2.9	375	347	866
18	Blueair Blue Pure 221	1500	10	350	Typical school	1.5	1.4	2.9	375	350	870
19	Blueair Classic 605 with Particle Filter	1500	10	500	Typical school	1.5	2.0	3.5	375	500	1050
20	Medify MA-112 V2.0 Air Purifier	1500	10	560	Typical school	1.5	2.2	3.7	375	560	1122
21											*assumes target is 5 ACH
22
23	Note: We are not making recommendations for or against any of these products, and this should not be considered an endorsement.						TARGET AT LEAST 5 TOTAL ACH
24								Ideal (6 ACH)
25								Excellent (5-6 ACH)
26								Good (4-5 ACH)
27								Bare Minimum (3-4)
28								Low (<3 ACH)