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Abstract

The factors that determine the design parameters of ultraviolet germicidal irradiation (UVGI) systems are addressed. The methods that can be used to size systems more effectively are discussed. The information presented may lead the industry back to the path of continuous improvement although the goal of eliminating airborne disease might remain unachievable.
By W.J. KOWALSKI, PE, and
WILLIAM P. BAHNFLETH, PhD, PE,*
Department of Architectural
Engineering,
The Pennsylvania State University,
University Park, Pa.
Lethal to microorganisms, ultra-
violet radiation in the range of
2250 to 3020 angstroms is used
in a variety of disinfection ap-
plications, a process referred to as ultra-
violet germicidal irradiation (UVGI).
Since the first UVGI system was
successfully implemented for disinfect-
ing the municipal water system in Mar-
seilles, France,
1
in 1909, the disinfec-
tion of medical equipment using UVGI
has been a common and reliable prac-
tice. But unlike water- and equipment-
disinfection applications, the disinfec-
tion of air streams using UVGI has a
history of varying success and unpre-
dictable performance.
The first laboratory studies on
UVGI of air in the 1920s showed such
promise that the elimination of air-
borne disease seemed possible. In 1936,
Hart used UVGI to sterilize air in a sur-
gical operating room.
2
In 1937, the first
application of UVGI for a school ven-
tilation system dramatically reduced
the incidence of measles, with subse-
quent applications enjoying similar
success.
3
Experiments by Riley and
O’Grady
4
resulted in the elimination of
tuberculosis (TB) bacilli from hospital-
ward exhaust air.
A plethora of designs that were more
imitative than engineered followed
these early applications. The result was
a mixture of successes and failures. This
experience is reflected in various
guidelines that decline to sanction the
use of UVGI as a primary system. A
1954 study on the use of UVGI showed
a failure to reduce disease in London
schools. Although limited data are
available to determine the causes of
earlier design failures, the apparent
cloning of UVGI systems without re-
gard to operating conditions probably
doomed many installations from the
start.
A review of current industry prac-
tices indicates that information on the
design of UVGI systems lacks the de-
tail necessary for engineers to ensure
performance. This article addresses the
factors that determine the design
UVGI
Design
Basics
for Air and Surface Disinfection
1
Superscript numerals indicate references listed
at end of article.
*William P. Bahnfleth is a member of HPAC
Engineering’s Editorial Advisory Board.
FIGURE 1. Types of UVGI systems
and approximate share of market.
FIGURE 2. Approximate breakdown of
where UVGI air-disinfection systems
are being installed.
Ultraviolet germicidal irradiation lamps
can help clean coils and improve
indoor air quality
Photo courtesy of UltraViolet Devices, Inc.
HPAC
ENGINEERING
100 January 2000 • Heating/Piping/AirConditioning
In-duct systems,
27%
Room
recirculation,
17% Microbial-
growth control,
32%
Upper air,
25%
Shelters,
19%
Hospitals,
41% Clinics,
19%
Other, 3%
Prisons,
19&%
Heating/Piping/AirConditioning • January 2000 101
HPAC
ENGINEERING
parameters of UVGI systems and dis-
cuss methods that can be used to size
systems more effectively.
TYPES OF UVGI SYSTEMS
Figure 1 shows the types of UVGI
systems that are sold for building-air
and air-handling-unit (AHU) applica-
tions and their approximate share of
the market, based on estimates from a
number of major manufacturers. The
use of systems for disinfecting air and
controlling microbial growth is grow-
ing in the United States and Europe,
according to manufacturers. In the
Third World, however, demand for up-
per-air-disinfection systems is high be-
cause of the TB pandemic, strained
economics, and the common use of
natural ventilation.
As shown in Figure 2, health-care fa-
cilities are where the most UVGI sys-
tems are installed. Notably absent are
schools, office buildings, and public
and residential buildings, even though
these are major sources of contagious
respiratory diseases.
AIR-STREAM-DISINFECTION
APPLICATIONS
The first step in the design of an air-
stream- or surface-disinfection system
is to characterize the application. This
includes describing the air stream,
identifying the specific surface, and,
sometimes, targeting specific microbes,
such as TB.
UVGI units commonly are located
in an AHU downstream from the mix-
ing box. Photo A shows a typical air-
stream-disinfection system installed
downstream from the filter bank and
upstream from the cooling coils.
Although UVGI systems also can be
placed in a return-air duct to deal with
recirculated, contagious pathogens,
they are rarely placed in outside-air-
supply ducts. Spores, which hail from
the outdoors, are more efficiently re-
moved by filtration alone. An excep-
tion exists in cases such as AIDS clin-
ics, where environmental bacteria
from the outdoors could threaten im-
munodeficient patients indoors.
SURFACE-DISINFECTION
APPLICATIONS
UVGI for microbial-growth control
has been undergoing much study re-
cently and has enjoyed success in field
applications.
5,6
Microbial growth may
be comprised of fungi, bacteria, or
even algae, but never viruses. In Eu-
rope, microbial-growth control on
cooling coils has been practiced in
breweries since at least 1985. One
manufacturer recommends placing a
15-W lamp 1 m from the surface of
cooling coils or walls where condensa-
tion may occur.
7
Direct UVGI exposure can sterilize
any surface if given enough time.
Theoretically, low-intensity UVGI
could be used for microbial growth
because the exposure time is ex-
tended. In practical applications,
however, microbial growth can occur
in crevices, shadowed areas such as
insulation, and stagnant water where
UVGI may not completely penetrate.
UVGI can control microbial growth
on filters subject to moisture or high
humidity. Photo B shows a test applica-
tion of UVGI for controlling microbial
growth on filters. Photos C and D show
an unirradiated and irradiated filter
bank, respectively. The unirradiated
filters show natural contamination
from various fungal species, including
Aspergillus and Penicillium, while the ir-
radiated filters show no evidence of mi-
crobial growth. The system in photos
B, C, and D used lamps that produce a
rated intensity of 100 mW/cm
2
at 1 m
from their midpoints.
PHOTO A. UVGI array used for air disinfec-
tion. Note the specular reflective surfaces.
Photo courtesy of Lumalier Inc., Memphis.
PHOTO B. UVGI lamp array used to disinfect
a filter bank. The filters are to the left.
PHOTO C (top): Microbial growth on unirra-
diated filters. PHOTO D (bottom): Microbe-
free irradiated filters.
Photo courtesy of Airguard Industries Inc., Louisville.
continued on page 103
TYPES OF MICROORGANISMS
The variety of microbes encoun-
tered by a given UVGI system is essen-
tially unpredictable. It depends to
some degree on the type of facility and
geographic location.
All viruses and almost all bacteria
(excluding spores) are vulnerable to
moderate levels of UVGI exposure. Be-
cause viruses are primarily contagious
pathogens that come from human
sources, they are found in occupied
buildings. Bacteria can be contagious
or opportunistic, with many found in-
doors; however, some are environmen-
tal. Certain facilities, such as agricul-
tural buildings, may disseminate
unique types of bacteria, such as spore-
forming actinomycetes.
Spores, which are larger and more
resistant to UVGI than most bacteria,
can be controlled effectively through
the use of high-efficiency filters. The
coupling of filters with UVGI is the
recommended practice in all health-
care settings
8
and for UVGI applica-
tions in general.
MICROBIAL RESPONSE TO
UVGI
A basic review of the mathematics
of UVGI disinfection will assist design
engineers. The population Sof a spe-
cies exposed to any biocidal factor is
described by the characteristic loga-
rithmic decay equation:
(1)
where:
k= standard decay-rate constant,
cm
2
/mW1s
I= intensity of UVGI irradiation,
mW/cm
2
t= time of exposure (sec)
The standard decay-rate constant
defines the sensitivity of a microorgan-
ism to UVGI and is unique to each mi-
crobial species.
9
It can be thought of as
the rate constant at an intensity of 1
mW/cm
2
, providing a basis for compar-
ing pathogens. The rate constant for E.
coli, commonly used for design pur-
poses, is 0.000767 cm
2
per mW sec.
Equation 1 omits two characteristics
that may impact the disinfection pro-
Circle 365 on Reader Service Card
UVGI DESIGN BASICS
Heating/Piping/AirConditioning • January 2000 103
HPAC
ENGINEERING
St e kIt
() =
FIGURE 3. Survival curve for
Staphylococcus aureus
illustrat-
ing the shoulder portion and two
distinct stages of decay.
(Source: Sharp, G. 1940.
The effects of ultraviolet light on
bacteria suspended in air.
J. Bact. 38:535-547.)
continued from page 101
cess: the shoulder and the second stage.
The shoulder represents the delay in
response (or threshold dose) of a mi-
croorganism subject to UVGI expo-
sure. If air velocity is too high and the
dose is insufficient, a microbe may
have a negligible response or even re-
cover from the damage. Insufficient
data exists to determine the shoulders,
or threshold doses, of most airborne
pathogens.
Most microbial populations exhibit
characteristic two-stage inactivation
curves (Figure 3) in which each stage
has a unique rate constant. The total
survival curve is the sum of a fast-decay
curve (the vulnerable majority) and a
slow-decay curve (the resistant minor-
ity), as follows:
(2)
where:
k
f
= rate constant for fast-decay
population
k
s
= rate constant for slow-decay
population
F= fraction of the total initial pop-
ulation subject to fast-decay response
The resistant fraction of most micro-
bial populations is about 0.01 percent,
although some studies suggest that it
can be as high as 10 percent for certain
species.
3
A distinction exists between the
terms “disinfection” and “sterilization.”
Sterilization is defined as the complete
destruction of all microbial species.
Sterilization sometimes is considered
to be 99.9999-percent eradication, or a
six-log (base-10) reduction in micro-
bial population. Disinfection, on the
other hand, is merely the reduction of
microbial population. Because air
streams are generally disinfected, not
sterilized, this residual second stage
usually can be ignored.
DESIGN PARAMETERS
A number of parameters must be
considered when considering UVGI
products for HVAC designs. The most
important factors are the air-flow or
HVAC equipment that will be disin-
fected, the lamp wattage and distance,
and the ventilation system design
itself.
Air-stream characteristics
The characteristics of an air stream
that can impact UVGI design are rela-
tive humidity (RH), temperature, and
air velocity.
Increased RH is commonly believed
to decrease decay rates under ultravio-
let (UV) exposure. However, studies
on this matter are contradictory and
incomplete at present. Fortunately,
because most UVGI studies have been
conducted under normal indoor con-
ditions, typical room and in-duct ap-
plications are not likely to differ
greatly.
Air temperature has a negligible
impact on microbial susceptibility to
UVGI.
10
However, it can impact the
power output of UVGI lamps if it ex-
ceeds design values.
Operating a UVGI system at air ve-
locities above design will degrade the
system’s effectiveness because of the
cooling effect of the air on the lamp
surface, which, in turn, will cool the
plasma inside of the lamp. UV output
UVGI DESIGN BASICS
HPAC
ENGINEERING
104 January 2000 • Heating/Piping/AirConditioning
St Fe F e
kIt kIt
fs
() ( )=+
1
FIGURE 5. Calculated additional light intensity from reflections and inter-reflections. Total
intensity is the sum of direct, reflected, and inter-reflected UV light.
FIGURE 4. Survival of
E. coli
under mixed flow and unmixed flow in square ducts of in-
creasing dimension.
is a function of plasma temperature
when power input is constant.
Not all UVGI lamps have the same
response to cooling effects. Some
lamps have different plasma mixtures;
overdriven power supplies that respond
to plasma temperature; or UV-trans-
parent, infrared-blocking shielding
that limits cooling effects. Data from
the manufacturer should be consulted
to determine the cooling effects or the
limiting design air velocities and tem-
peratures within which the lamps can
be operated efficiently.
Ventilation system design
A number of ventilation system pa-
rameters can impact UVGI design.
Air velocity and air mixing. Doses are
determined by the time of exposure
and UVGI intensity, both of which
are dependent on the velocity profile
and the amount of air mixing in the
air stream. The velocity profile inside
of the duct or chamber depends on lo-
cal conditions and may be impossible
to know in advance with any cer-
tainty. In any event, the design veloc-
ity of a typical UVGI unit is similar to
that for filter banks—about 400 fpm.
Sufficient mixing will occur at these
velocities to temper the effects of a
non-uniform velocity profile.
The amount of air mixing that oc-
curs will affect system performance to
a degree that depends on system con-
figuration. This is illustrated in Figure
4, which compares survival predic-
tions for mixed- and unmixed-flow
conditions in square ducts of increas-
ing dimension. The error resulting
from the assumption of complete mix-
ing will decrease as system dimensions
increase.
In systems in which the lamps do not
span the duct’s entire width or length,
the assumption of complete mixing
also will result in larger differences,
compared to unmixed flow. The im-
portant point is that system operation
will lie somewhere between these two
assumptions, which provide limits de-
scribing system efficiency.
Using reflectors. Reflectivity can be
an economical way of intensifying the
UVGI field in an enclosed duct or
chamber. A surface with a reflectivity
of 90 percent will reflect 910 of the light
it receives.
The results of a computer-generated
analysis of reflectivity are shown in
Figure 5. The components of reflectiv-
ity—both direct and inter-reflected—
will clearly sum to greater than the ini-
tial direct intensity. This can occur
whenever the surface is mostly en-
closed and highly reflective. Such de-
signs can considerably improve
economics.
Two types of reflective surfaces ex-
ist: specular and diffuse. Specular sur-
faces produce mirror-like reflections
that are directionally dependent on
the source, while diffuse surfaces pro-
duce non-directional reflections that
Circle 344 on Reader Service Card
Heating/Piping/AirConditioning • January 2000 105
HPAC
ENGINEERING
spread equally in all directions. Non-
glossy white paper is a good example
of a diffuse surface. Most materials
possess a combination of specular and
diffuse properties and exhibit a de-
gree of directional dependence. For
UVGI design purposes, the degree of
directional dependence is usually not
critical.
Some materials reflect visible light,
but not UV light. Polished aluminum
is highly reflective to UV wavelengths,
while copper, which reflects most visi-
ble light, is transparent in the UV
range.
No simple method of calculating
the three-dimensional UVGI-inten-
sity field for specular reflectors exists.
Ray-tracing routines using Monte
Carlo techniques are one approach,
but the results do not easily lend
themselves to analysis. However,
they can be rather useful for examin-
ing complex geometries, such as
when cooling coils are irradiated.
Figure 6 shows ray-tracing diagrams
of a UVGI lamp irradiating a bank of
cooling coils from three perspectives.
Note how few of the rays penetrate
the coils, even after 20 reflections.
Also note how the copper tubes ab-
sorb many of the rays—although cop-
per is transparent to UVGI, the water
inside is not.
Combining with filtration. UVGI sys-
tems generally are used in combination
with HEPA filters, a practice usually
recommended for isolation-room ap-
plications. For other applications,
however, HEPA filters do not offer a
significant enough improvement in
microbe-removal rates over high-effi-
ciency filters to warrant their exclusive
use with UVGI.
Circle 372 on Reader Service Card
HPAC
ENGINEERING
106 January 2000 • Heating/Piping/AirConditioning
Circle 373 on Reader Service Card
a
b
c
UVGI DESIGN BASICS
FIGURE 6. Ray-tracing computer model of a cooling-coil bank irradiated with a UVGI lamp. Rays are
color-coded from blue to red in order of decreasing intensity. The staggered 5/4 coil tubes are 0.5-in. dia.
with six fins per in. Five reflections are shown with 90-percent reflective duct surfaces. Perspectives are (a)
isometric, (b) front, and (c) side.
All ray tracings were produced using Photopia software from Lighting Technologies, Inc., Boulder CO.
Recirculation systems. UVGI sys-
tems that recirculate room air or that
are placed in a return-air duct or mix-
ing-air plenum deliver multiple doses
to airborne microorganisms. Al-
though the effect is partially depen-
dent on the air-change rate, the re-
sult is an effective increase in
removal rate in comparison with a
single-pass system.
Calculations of removal rates for
UVGI and associated filters in recircu-
lation systems can be performed by
evaluating the system minute-by-
minute, including filtration rates, out-
side-air rates, and any microbial
contaminants.
Lamp considerations
The hardest part of sizing a UVGI
system is determining the lamp wattage
for the stated disinfection goal. The in-
tensity field caused by the lamp and the
reflectors must be modeled and aver-
aged before Equation 1 is used to pre-
dict the disinfection rate.
Circle 367 on Reader Service Card
Heating/Piping/AirConditioning • January 2000 107
HPAC
ENGINEERING
Calculating the Intensity Field of a UVGI Lamp
The intensity field of a UVGI lamp can be computed using the following
radiation view factor from a differential planar element to a cylinder, per-
pendicular to the cylinder axis (Modest, M.F. 1993. Radiative Heat Transfer.
McGraw-Hill, New York.):
The parameters in the equation at left are
defined as follows:
H
= x/r
L
= l/r
X
= (1 + H)
2
+ L
2
Y = (1 1H)
2
+ L
2
where:
l
= length of the lamp segment, cm
x
= distance from the lamp, cm
r
= radius of the lamp, cm
The intensity at any point will be the product of the view factor and the
surface intensity of the lamp. The surface intensity is simply the UV power
output in watts divided by the surface area in cm
2
.
To compute the intensity at any distance from the midpoint of a lamp,
multiply the above equation by 2. From any location other than the midpoint,
divide the lamp into two unequal segments and add the two view factors.
View-factor algebra (see reference) can be used for other locations. If we
assume that complete mixing occurs, then the intensity field for any duct can
be computed by averaging the field in all three dimensions.
FHATAN L
H
XH
XY
ATAN XH
YH
L
H
ATAN H
H
L
H
d12 2
1
1
21
1
1
1
=
+−−
+
+
π
π
π
()
()
Lamp-intensity field. An exact de-
scription of the lamp-intensity field is
necessary to accurately determine the
dose that is to be delivered to an air-
borne microorganism. Lamp ratings of-
ten are the sole parameter used for siz-
ing a UVGI installation. Although this
may be a conservative approach when
distances to the lamp exceed 1 meter,
oversizing and prohibitive economics
can result.
If complete mixing is assumed, then
any intensity field can be described by
the single value of average intensity.
This requires computing the intensity
at every point in a three-dimensional
matrix defining the duct. We need to
know the field caused by the lamp
and, if necessary, the field caused by
the reflections. Although the inverse-
square law has been used for this pur-
pose, it has proven to be inaccurate
close to the lamp. An improved ap-
proach is to use the radiation view fac-
tor from a differential planar element
to a cylinder as detailed in the sidebar
Calculating the Intensity Field of a
UVGI Lamp. Ignoring reflectivity, the
average intensity field can be conser-
vatively computed by applying Equa-
tion 3 to a three-dimensional matrix.
There are view factors that can be
used for computing the reflected inten-
sity from flat parallel or perpendicular
surfaces. Consult any thermal-radia-
tion textbook for such view factors.
Circle 368 on Reader Service Card
UVGI DESIGN BASICS
Width Height Airflow Lamp Reflectivity
Kill rate, percent
cm cm m
3
/min UV watts percent Minimum Maximum
100 50 60 12 50 45 48
75 63 74
90 74 96
100 50 60 24 50 69 72
75 85 93
90 92 99
100 50 60 36 50 81 86
75 93 98
90 97 99
100 100 120 36 50 61 64
75 72 76
90 79 83
100 100 120 48 50 70 75
75 81 85
90 87 91
100 100 120 56 50 75 80
75 85 89
90 90 94
200 200 480 96 50 47 59
75 56 68
90 62 73
200 200 480 144 50 58 74
75 68 82
90 74 86
Travel time = 0.5 sec; lamp length = 72 cm; radius = 1.9 cm
TABLE 1. Predicted disinfection rates for typical systems.
HPAC
ENGINEERING
108 January 2000 • Heating/Piping/AirConditioning
UVGI Economics
Table 2 summarizes the costs associ-
ated with purchasing, installing, and
operating two types of UVGI systems:
an air-stream-disinfection (AD) system
and a microbial-growth-control (MGC)
system. The ventilation systems for
both are identical. These systems were
sized using the techniques described in
the accompanying article, with
predicted disinfection rates as shown.
The location used in the energy
analysis is Philadelphia, with the heat
added by the lamps resulting in a
cooling energy penalty for 30 percent of
the year. No credit is taken for energy
input during the heating season.
Clearly, the first cost of each of these
systems is minor, with the maintenance
cost eclipsing the energy cost.
Although the MGC system uses less
wattage, it operates continuously, while
the AD system operates only when the
building is occupied. The power require-
ments of the former system are appro-
priate for disinfection of duct surfaces or
filter faces, but not necessarily for
cooling costs.
A critical energy difference between
these systems occurs because the AD
system has an ASHRAE 25-percent
filter, while the MGC system has a dust
filter only. Because the short exposure
time in an AD system may not effec-
tively reduce spore levels, it becomes
cost-effective to use a higher-efficiency
filter to control spores. The MGC
system renders spores inactive with
continuous (24-hr) exposure and, as a
result, needs only a dust filter for
purposes of cleanliness.
TABLE 2. Economic evaluation of typical UVGI systems
(Corrected from original publication, January 2000)
FIGURE 7. A comparison of UVGI air-stream-
disinfection (AD) and microbial-growth-control
(MGC) systems for a 20-year life cycle.
Heating/Piping/AirConditioning • January 2000 109
HPAC
ENGINEERING
Air-stream Microbial-growth
Type of Application disinfection control
Design airflow 10,000 cfm 10,000 cfm
Velocity 413 fpm 413 fpm
Predicted disinfection 90 percent
Serratia
99.99 percent
Aspergillus
UVGI lamp model GPH436T5 TUV18W
Number of lamps 2 1
Height 150 cm 150 cm
Width 150 cm 150 cm
Length 150 cm 150 cm
Lamp total power (each) 36 W 18 W
Hours of operation 3744 hr 8760 hr
Energy costs
Heat generated 0.072 KW 0.018 KW
Cooling load 189 KWH 110 KWH
Total dP (lamps, fixtures, filters) 0.560 in. WG 0.290 in. WG
Total fan energy (80 percent eff.) 8016 KWH 4151 KWH
Electrical energy 270 KWH 158 KWH
Cooling load energy 189 KWH 110 KWH
Total energy 8475 KWH 4419 KWH
Rate 8 cents per KWH 8 cents per KWH
Annual energy cost $678 $354
Maintenance costs
Average tube life 9000 hr 9000 hr
Tube hours per year 7488 hr 8760 hr
Replacements per year 0.83 0.97
Cost per tube $85 $85
Annual cost $71 $89
Annual filter-replacement cost $33 $6
Maintenance (assumed) $200 $200
Annual maintenance cost $949 $642
First costs
UVGI system (AU prices) $765 $550
Labor (estimated) $1000 $1000
Total installation cost $1765 $1550
Life cycle 20 years 20 years
Interest rate 8 percent 8 percent
Life cycle cost $180 $158
Total annual cost $1806 $1154
Economic evaluation of typical UVGI systems
First, use Equation 3 to determine the
intensity at the flat surface. Then, use
the appropriate view factor to deter-
mine the reflected intensity after mul-
tiplying by the reflectivity.
Table 1 presents a comparison of
UVGI systems that were sized using
the view-factor method and may be
used to approximate the performance
of similar systems.
CONCLUSIONS
Although simplistic, the methodol-
ogy presented here is more accurate
than any previously published method
for sizing UVGI systems. The authors
Circle 369 on Card; see HPAC Info-dex, p. 129
UVGI DESIGN BASICS
HPAC
ENGINEERING
110 January 2000 • Heating/Piping/AirConditioning
Circle 506 on reader service card if this
article was useful; circle 507 if it was not.
hope that these principles will lead to
successful applications and avoidance
of the design problems that have ham-
pered the industry and perplexed engi-
neers. Although the goal of eliminat-
ing airborne disease might remain
unachievable, the information pre-
sented here may help lead the industry
back to the path of continuous
improvement.
ACKNOWLEDGEMENTS
The authors wish to thank the fol-
lowing for providing information and
support for this article: Ultraviolet De-
vices Inc., Lumalier Inc., American
Ultraviolet Inc., Steril-Aire Inc., In-
sect-O-Cutor Inc., and Airguard
Industries Inc.
HPAC
REFERENCES
1) AWWA. 1971. Water Quality and
Treatment. McGraw-Hill, New York.
2) Sharp, G. 1939. The lethal action of
short ultraviolet rays on several common
pathogenic bacteria. J. Bact. 37:447-459.
3) Riley, R.L. 1972. The ecology of in-
door atmospheres: Airborne infection in
hospitals. J. Chron. Dis. 25:421-423.
4) Riley, R.L., and F. O’Grady. 1961.
Airborne Infection. The Macmillan Co.,
New York.
5) Shaughnessy, R., E. Levetin, and C.
Rogers. 1999. The effects of UV-C on bio-
logical contamination of AHUs in a com-
mercial office building: Preliminary results.
Indoor Environment ‘99:195-202.
6) Scheir, R., and F.B. Fencl. 1996. Us-
ing UVC Technology to Enhance IAQ.
Heating/Piping/Air Conditioning. February
1990.
7) Philips. 1985. UVGI Catalog and De-
sign Guide, Catalog No. U.D.C. 628.9,
Netherlands.
8) ASHRAE. 1991. Health Facilities.
ASHRAE (ed.), ASHRAE Handbook of
Appl., Atlanta.
9) Jensen, M.M. 1964. Inactivation of
airborne viruses by ultraviolet irradiation.
Appl. Microb. 12(5):418-420.
10) Rentschler, H.C., R. Nagy, and G.
Mouromseff. 1941. Bactericidal effect of ul-
traviolet radiation. J. Bact. 42:745-774.
... UV radiation in the range of 2250 to 3020 angstroms is lethal to microorganisms and has been used in various disinfection applications in a process referred to as ultraviolet germicidal irradiation (UVGI). The first UVGI system dates back to disinfecting the municipal water system in Marseilles, France in 1909 [7]. Besides waste water treatment, "the disinfection of medical equipment using UVGI has been a common and reliable practice. ...
... Besides waste water treatment, "the disinfection of medical equipment using UVGI has been a common and reliable practice. But unlike water-and equipment disinfection applications, the disinfection of air streams using UVGI has a history of varying success and unpredictable performance" [7]. UVGI laboratory studies for air treatment began in the 1920s and showed that eliminating air-borne diseases was feasible. ...
... UVGI laboratory studies for air treatment began in the 1920s and showed that eliminating air-borne diseases was feasible. By the 1930s, UVGI was used to sterilize air in surgical operating rooms and in school ventilation systems, which greatly reduced the occurrence of measles [7]. However, designs began to be imitated instead of engineered for a particular use, which led to some failures. ...
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There are nearly 6 million commercial buildings in the United States. People working in those buildings can fall victim to allergies, sick building syndrome, or building related illnesses caused by poor indoor air quality. Ultraviolet germicidal irradiation (UVGI) in a building's HVAC system is one approach to improving air quality and reducing the health risks of its occupants. When considering the HVAC design of a building, the owner has to take into consideration many factors and the facility's intended use and budget are two major factors. The owner's analysis should consider life cycle costs and the potential impact of design solutions on the future occupants. Indoor air quality can have a significant impact on productivity, absenteeism, and perhaps insurance premiums. UVGI may or may not be a feasible or proper solution for every case, however, the pros and cons of the UVGI technology should be weighed and examined more carefully as a viable solution. The goal of this paper was to review information as it related to positive and negative aspects of the UVGI technology. Areas analyzed included the ability of the UV systems to improve indoor air quality, ozone generation, and economics.
... The efficacy of UV purifiers in reducing or eliminating mold or other pathogens from the air, as compared to our HEPA unit, is also questionable (Olander et al. 1988). UV can potentially deactivate mold, but does not help with spores (Kowalski and Bahnfleth 2000). After upgrading our HVAC filters and adding the indoor HEPA unit, tests showed no detectable allergens or pathogens in the air of Morphology Center. ...
Article
The ornithological collection of the National Fish and Wildlife Forensic Laboratory in Ashland, Oregon includes over 6,800 bird skin and loose feather specimens. These are essential reference material for the morphological identification of avian evidence in wildlife crime investigations by the U.S. Fish and Wildlife Service. In the summer of 2020, these specimens were moved from several locations and installed in a new building dedicated to the laboratory's bird, mammal, and herpetological collections. Following installation in the new building, a severe outbreak of mold was discovered in many of the cabinets containing bird specimens. This paper reports on the likely cause of the mold outbreak and the actions taken to control it, preserve the specimens, and prevent future outbreaks.
... ). (b) Removal of 90% Serratia (bacillus) and 99.99% Aspergillus (fungus) (continuous flow UV sterilizer + filter, air flowrate 4.5 m 3 s −1 , 72 W lamps, 0.5 s exposure time, 413 m s −1 air speed, 3744 h lamp life(Kowalski and Bahnfleth 2000). (c) 99.5 + % removal of Staphylococcus aureus, Staphylococcus epidermidis, Serratia marcescens, Bacillus subtilis, 67% removal of Aspergillus niger (continuous flow UV sterilizer + filter, 0.5 s irradiation time, 254 nm UV lamps)(Nakamura 1987). ...
Article
The technique of air sterilization by thermal effect was revisited in this work. The impact of incorporating a high efficiency heat recovery exchanger to a sterilizing cell was especially assessed. A mathematical model was developed to study the dynamics and the steady state of the sterilizer. Computer simulation and reported data of thermal inactivation of pathogens permitted obtaining results for a proof-of-concept. The simulation results confirmed that the incorporation of a heat recovery exchanger permits saving more than 90% of the energy needed to heat the air to the temperature necessary for sterilization, i.e., sterilization without heat recovery consumes 10-20 times the energy of the same sterilization device with heat recovery. Sanitization temperature is the main process variable for sanitization, a fact related to the activated nature of the thermal inactivation of viruses and bacteria. Heat recovery efficiency was a strong function of the heat transfer parameters but also rather insensitive to the cell temperature. The heat transfer area determined the maximum capacity of the sterilizer (maximum air flowrate) given the restrictions of minimum sanitization efficiency and maximum power consumption. The proposed thermal sterilization device has important advantages of robustness and simplicity over other commercial sterilization devices, needing practically no maintenance and eliminating a big variety of microorganisms to any desired degree. For most pathogens, the inactivation can be total. This result is not affected by the uncertainties in thermal inactivation data, due to the Arrhenius-like dependence of inactivation. Temperature can be adjusted to achieve any removal degree.
... It has already been recognized and recommended for efficient bioaerosol elimination in HVAC systems [11,12], which account for approximately 27% of the UVGI market [13]. As for the application scenarios, it is reported that its primary installations are in healthcare facilities (60%), whereas office, school, public, and residential buildings account for less than 3% of installations, even though these are major infection locations of contagious respiratory diseases [14,15]. In addition, massive growth in the UV disinfection equipment market is anticipated in the next five years (from USD 4.8 billion to USD 9.2 billion) as a result of the COVID-19 combat [16]. ...
Article
The rapid increase in global cases of COVID-19 illness and death requires the implementation of appropriate and efficient engineering controls to improve indoor air quality. This manuscript focuses on the use of the ultraviolet germicidal irradiation (UVGI) air purification technology in HVAC ducts, which is particularly applicable to buildings where fully shutting down air recirculation is not feasible. Given the poor understanding of the in-duct UVGI system regarding its working mechanisms, designs, and applications, this review has the following key research objectives:
Technical Report
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Ultraviolet Light Disinfection for animal facilities.
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There are many types of Ultra Violet Germicidal Irradiation (UVGI) products available in the market used in many applications such as sterilization and disinfection. These products are popular during the spread of pandemic COVID-19 and become an option of disinfection method for surface and air such as in office, hospital, hotel room and car. The objective of the study is to investigate the UVC lamps of the UVGI products based on their wavelength. This is to validate whether the product samples are using UVC lamp as stated in the specification which normally has 253.7 to 254 nm wavelength. Besides that, the UVC intensity level has been measured to determine the irradiance emitted by the lamps. The measurement was carried out at various distance to see the effectiveness of the UVGI in disinfection process at different size of spaces. UVC is categorised as non-ionising radiation and has potential health effects due to excessive exposure specially to eye and skin. The equipment used for the irradiance measurement is IL 1700 radiometer with UVC sensor and the measurement data recorded in microwatt/cm ² . The irradiance level of the samples was compared with the permissible exposure limit to the members of public by International Commission on Non-Ionizing Radiation Protection (ICNIRP).
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Aluminium nitride (AlN) crystalline substrate has emerged as a striking material and received tremendous attention for applications in high power electronics (HPE), deep-ultraviolet (DUV) light sources due to its exceptional properties. Single crystal growth of AlN by physical vapour transport (PVT) technique, and the necessity of large diameter AlN native substrates for the fabrication of HPE and DUV devices are described here. Two competing growth approaches in PVT are utilised to produce initial AlN single crystalline seeds namely, starting with self-nucleation followed by iterative homo-epitaxial growth for enlarging the crystal diameter in steps, and directly seeding on a closely lattice-matched foreign substrate of desired diameter by hetero-epitaxial growth. Both of these approaches are intended to grow bulk single crystals from which wafers might be prepared for further fabrication of devices. The hetero-epitaxial growth approach is specifically and comprehensively reviewed in this present work. A specific attention is given in using 6H- and 4H- polytype silicon carbide (SiC) substrates. The issues in hetero-epitaxially grown crystals such as presence of misfit dislocations, control of low-angle grain boundaries, incorporation of unintentional impurities, are highlighted together with the recent progress made in the achievement of about 2.5-inch dia. free-standing AlN wafer by this approach.
Article
Coronavirus disease (COVID-19) is an infectious disease caused by a newly discovered coronavirus strain (SARS-CoV-2). COVID-19 is an acute respiratory infection that occurs with a wide range of symptoms. The best way to prevent and slow down infection is based on the assumption that we know the characteristics of the SARS-CoV-2 virus, the disease it causes, and the way it spreads. This review has been prepared by the Pediatric Infectious Diseases Unit of the Behçet Uz Children’s Education and Research Hospital in order to share the preparations and strategies to combat the SARS-CoV-2 virus together with other hospitals. What has been prepared in the clinic (physical arrangements, disinfection, regulations for the protection of employees from occupational infections, regulations for patients and companions) is explained under subheadings. The COVID-19 epidemic, which has affected the entire world and caused many people to die, requires the establishment of many new regulations in health services, including new ones to existing patient safety and infection control measures. The treatment and care for children and their families continued without interruption, with various arrangements made in the clinic in cooperation with the team, based on the guidelines updated frequently by the Ministry of Health, international literature, and experiences. Nurses who managed to communicate with children by wearing clothes that looked “like robots” (in the words of the children) used their existing knowledge and equipment in this process and gained new knowledge. It is thought that this review will be useful in guiding future developments of new information emerging during the COVID-19 outbreak.
Article
There are several categories of organisms that can grow and/or spread in modern air handling systems: pathogens--viruses, bacteria, and fungi that cause a range of infectious diseases; allergens--bacteria and mold that cause allergic rhinitis, asthma, humidifier fever, and hypersensitivity pneumonitis; toxins--endotoxins and mycotoxins that cause a variety of toxic effects, irritation, and odors. As HVAC systems move large amounts of outdoor and recirculated air through occupied buildings, they become the conduits by which these unhealthful organisms are spread throughout the spaces they serve. A new UVC technology overcomes previous limitations to enhance IAQ control, effectively and efficiently killing microorganisms that grow, disseminate, and circulate in air handling systems.
Article
Aerosolized viruses were passed through a high-intensity ultraviolet (UV) cell. This cell consisted of a long cylindrical aluminum tube [diameter, 7 in. (17.7 cm); length, 36 in. (91.4 cm)] with a highly reflective inner surface and a longitudinally extending helical baffle system which directed airborne particles in close proximity to a centrally located UV lamp. After having been passed through the UV cell, viral aerosols were collected with an Andersen sampler, and viral concentrations were determined by plaque assay methods on tissue cultures. Inactivation rates of greater than 99.9% were obtained for Coxsackie, influenza, Sindbis, and vaccinia viruses, and slightly less for adenovirus (96.8%), when the aerosols passed through the UV cell at 100 ft(3)/min. At aerosol flow rates of 200 ft(3)/min, inactivation rates were slightly lower; 91.3 for adenovirus, 97.5 and 96.7 for Coxsackie and Sindbis, respectively, and greater than 99.9% for influenza and vaccinia viruses.
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