ASHRAE Journal - October 2023 - 15

COLUMN INFECTIOUS AEROSOL CONTROL
2021 and Feb. 2022. Given that
almost all people are infectious
for about fi ve days5 and that the
respiratory virus season lasts 112
days, we assume each day about
1% of the population is infectious.
We multiplied the per-person perhour
infection probability by the
occupancy rate and operation time
to fi nd the total infection risk per
site under normal operation and
Standard 241's IRMM operation.
To improve the accuracy of
the cost-benefi t analysis, I fi rst
multiplied the expected number
of infections in some spaces,
especially health-care spaces, by a
factor of two or three to represent
the increased vulnerability of
the people in those spaces. Then
I calibrated the model results to
the American Time Use Survey,
which lists the amount of time the
average person spends on activities
in the average day. I applied an
adjustment factor to adjust the
model output, so a person spending
the average amount of time in each
space, without IRMM operation ,
has a 25% chance of being infected.
I put a dollar value on the
infection reduction using the U.S.
Department of Health and Human
Services' methodology for public
health regulations,6 which values
each life-year gained at about
$500,000. Briggs, et al.,7 shows that
an average death causes about eight life-years to be lost,
so the value of preventing a death is $4 million.
To calculate the expected future infection fatality rate, I
assumed future deaths would be similar to the 2022 - 2023
virus season, when roughly 30,000 Americans died of
COVID.8 With 25% of the U.S. population infected and
30,000 dying, the infection fatality rate is 0.04%.
Counting only the fatality-reduction benefi t, the
monetized value of preventing an infection is then
about $1,400. To account for nonlethal health effects of
Correctional Facilities
Cell Block
Dayroom
Commercial/Retail
Food and Beverage Facilities
Gym
Offi ce
Retail
Transportation Waiting
Educational Facilities
Classroom
Lecture Hall
Industrial
Manufacturing
Sorting, Packing, Light Assembly
Warehouse
Health Care
Exam Room
Group Treatment Area
Patient Room
Resident Room
Waiting Room
Public Assembly/Sports & Entertainment
Auditorium
Place of Religious Worship
Museum
Convention
Spectator Area
Residential
Common Space
Dwelling Unit
1,200
2,000
12
6
90%
92%
0.6
0.6
$1,100
$1,200
$52
$82
an infection, such as the chance of suffering from long
COVID, I added $500 to this value, based on the ratio of
estimated COVID morbidity and mortality costs.9 The
expected value of preventing an infection is then $1,900.
Table 1 lists estimated costs and monetized COVIDreduction
benefi ts for several model spaces. The areas,
ceiling heights and default occupancies of all spaces are
taken from ASHRAE Standards 62.1, 62.2 and 170 . The
additional ECAi required is the difference between the
currently required rate and the Standard 241 IRMM rate.
O CTO B E R 2 0 2 3 ashrae.org ASHRAE JOURNAL
15
150
1,000
300
300
1,000
2,000
2,000
10,000
10,000
3,000
3
20
3
3
30
150
180
400
400
100
66%
39%
68%
82%
25%
26%
27%
34%
34%
56%
1.3
6.1
1.2
0.4
33
13
4.8
27
27
4.2
$2,500
$55
$11,000 $1,000
$2,200
$680
$99
$23
$62,000 $2,100
$25,000 $7,500
$9,000
$8,700
$51,000 $21,000
$51,000 $21,000
$7,900
$4,800
10,000
1,000
1,000
70
20
20
93%
89%
89%
0.7
0.6
0.6
$1,300
$1,100
$1,100
$870
$210
$210
1,200
2,000
30
150
59%
26%
3.8
13
$7,000
$820
$25,000 $7,500
TABLE 1 Annual costs and COVID-prevention benefits of Standard 241 in model sites.
OCCUPANCY CATEGORY
AREA
(ft2)
1,200
1,000
1,000
5,000
10,000
10,000
10,000
DEFAULT
OCCUPANCY
30
30
50
180
50
150
100
RELATIVE
RISK
56%
50%
33%
35%
87%
60%
63%
INFECTIONS
PREVENTED
11
2.6
11
39
1.0
12
13
MONETIZED
VALUE
COST
$20,000 $730
$4,900
$1,100
$21,000 $2,600
$72,000 $11,000
$1,900
$500
$22,000 $4,500
$24,000 $5,300
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ASHRAE Journal - October 2023

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