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Annual simulation of in-duct ultraviolet germicidal irradiation system performance


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In-duct ultraviolet germicidal irradiation (UVGI) systems treat moving air streams in heating, ventilation, and air-conditioning (HVAC) systems to inactivate airborne microorganisms. UVGI system performance depends on air temperature, velocity, cumulative operating time, variations in exposure time and other factors. Annual simulations of UVGI efficiency and space concentration that accounted for these effects were performed for a hypothetical building served by a VAV system. The UVGI device was assumed to be located in the supply air stream and exposed to a near constant temperature, but variable flow. UVGI performance was compared with enhanced ventilation and infiltration. Large seasonal variations in UVC dose due mainly to the effect of airflow variation on residence time were observed. UVGI air treatment resulted in much lower predicted space concentrations of Staphylococcus aureus than ventilation according to ASHRAE Standard 62.1 and levels comparable to those achieved by high efficiency, but sub-HEPA, particulate filtration. Transient variations in space concentration due to lamp output variation were small, but adjustment of lamp output to the design operating condition was very important for modeling accuracy.
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William Bahnfleth, Bruno Lee, Josephine Lau, and James Freihaut
Indoor Environment Center, Department of Architectural Engineering,
The Pennsylvania State University, University Park, PA, USA
In-duct ultraviolet germicidal irradiation (UVGI)
systems treat moving air streams in heating,
ventilation, and air-conditioning (HVAC) systems to
inactivate airborne microorganisms. UVGI system
performance depends on air temperature, velocity,
cumulative operating time, variations in exposure
time and other factors. Annual simulations of UVGI
efficiency and space concentration that accounted for
these effects were performed for a hypothetical
building served by a VAV system. The UVGI device
was assumed to be located in the supply air stream
and exposed to a near constant temperature, but
variable flow. UVGI performance was compared
with enhanced ventilation and infiltration. Large
seasonal variations in UVC dose due mainly to the
effect of airflow variation on residence time were
observed. UVGI air treatment resulted in much
lower predicted space concentrations of
Staphylococcus aureus than ventilation according to
ASHRAE Standard 62.1 and levels comparable to
those achieved by high efficiency, but sub-HEPA,
particulate filtration. Transient variations in space
concentration due to lamp output variation were
small, but adjustment of lamp output to the design
operating condition was very important for modeling
Ultraviolet germicidal irradiation, UVGI, UVC lamp
performance, Airborne contaminant control, Indoor
air quality.
Transmission of respiratory diseases by airborne
pathogens is a major problem of indoor air quality
(IAQ). Droplet residues generated by talking,
coughing and sneezing can be suspended in the air
for hours, entrained into HVAC ductwork, and
distributed throughout a building (Sehulster et al.,
2004). In-duct UVGI systems treat air streams as
they pass through HVAC ductwork.
UVGI systems use electromagnetic energy in the
UVC spectrum to damage and prevent replication of
microbial DNA and RNA (Noakes et al., 2004).
Low-pressure mercury vapor lamps used in UVGI
systems produce most of their output at 254 nm,
which has ~85% of the effect produced by the
optimal 265 nm wavelength (Philips, 2006).
To a first approximation, the survival of a population
of microorganisms exposed to UVC is
The surviving fraction S, defined as the ratio of the
surviving population, Nt to the initial population, N0,
is a decreasing exponential function of the UVC
fluence, I; the exposure time, t; and a microorganism-
specific rate constant, k. The product “Itis the dose
received by the microbial population. For example,
using the rate constant value of 0.0035 cm2/µJ for
Staphylococcus aureus measured by Sharp (1940),
Equation 1 predicts that a dose of 542 µJ/cm2, is
required to achieve 85% inactivation. This dose may
result from any combination of fluence and exposure
The UVC output of a UV lamp is rated in still air at a
temperature approximating typical room conditions
after a burn-in of 100 hours (IESNA 1999). Output in
application may be very different because of the
effects of operating conditions and aging. In-duct
UVGI design methods are not standardized and
account for these effects in a variety of ways,
generally through a combination of lamp selection
and sizing based on perceived worst-case conditions.
This paper describes the investigation, via hourly
annual simulation, of the performance of a typical in-
duct UVGI system for a range of scenarios and
operating conditions.
Figure 1. Lamp UVC output as a function of cold-
spot temperature (Philips, 2006)
UVC Lamp Characteristics
With small but important differences, low-pressure
mercury vapor germicidal lamps are essentially
identical to fluorescent lamps used for illumination.
Eleventh International IBPSA Conference
Glasgow, Scotland
July 27-30, 2009
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Lamp UVC output is a function of the mercury vapor
pressure, which varies with the temperature of the
coolest location on the lamp surface. Depending
upon the lamp type, maximum output occurs when
cold-spot temperature is between 39˚C and 50˚C
(103˚F and 122˚F) (ASHRAE, 2008). Figure 1 shows
a typical performance curve with peak UVC output at
40˚C (104˚F).
Cold spot temperature is a function of the energy
balance relating input power, useful UVC emission,
thermal radiation, and convection. Because the main
determinants of cold spot temperature are ambient air
temperature and velocity, the variation of capacity
with environmental conditions is commonly called
“wind chill”. Figure 2 illustrates the importance of
the wind chill effect by comparing two geometrically
similar lamps operating in a 21˚C (70˚F) air stream.
One lamp is a “standard output” model with 36W of
input power while the other is a “high output” lamp
with an input power of 60W. The high output lamp
must dissipate more energy through the same surface
area, therefore, it runs hotter. Consequently, the
maximum output of the high output lamp occurs at a
higher velocity than the standard output lamp.
Figure 2. Wind chill effect on two germicidal lamp
types a 21˚C air stream (Philips, 2006)
Figure 3. Study lamp ambient condition response
characteristics (Lau, et al. 2009)
The lamp considered in this study is a widely used
single-ended twin-tube high-output hot cathode lamp
(Philips TUV PL-L 60W HO) for which a validated
polynomial cross-flow performance model was
developed by Lau, et al (2009). Figure 3 shows
contours of predicted relative output (actual UVC as
a fraction of maximum UVC) as a function of air
temperature and velocity.
UVC output also diminishes (depreciates) over the
life of a lamp in a manner that can be easily modeled.
Figure 4 presents the depreciation of a typical lamp,
in which output falls by 15-20% during the first 2000
hours of operation and then levels off.
Figure 4. Typical mercury vapor lamp depreciation.
(Philips, 2006)
UVGI Device Characteristics
For in-duct application, one or more lamps are
installed in an air distribution duct, in an air-handling
unit, or in a factory-fabricated assembly. Several
properties of these assemblies have a strong effect on
the dose delivered, including enclosure geometry,
lamp configuration, and reflectivity. Design airflow
rates may vary from 5 m/s (1000 fpm) or more in air-
distribution ducts to less than 2 m/s (400 fpm) in air-
handling units (AHU). Much lower velocities may
occur during part-load operation of variable air
volume (VAV) systems.
The combined effects of lamp output, device
geometry and surface reflectivity determine the
irradiance distribution while the combined effects of
geometry and airflow determine the single-pass
exposure time for air passing through a device. On
average, exposure time is the air change rate of the
device, i.e., the irradiated volume divided by the
volume flow rate.
A single-pass inactivation efficiency can be derived
from Equation 1:
UVGI =1S=1ek(It)
A design UV dose for a particular value of S can be
obtained by rearranging Equation 1:
By combining Equations 2 and 3, the expression for
device efficiency at off-design condition becomes:
(T = 5 to 0)
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Taking into account both the effects of temperature
and velocity on lamp output and of geometry and
flow rate on residence time, the dose for an off-
design condition in Equation 4 can be expressed as a
fraction of design dose as follows:
Parametric simulations were performed for a
hypothetical four-storey office building located in
New York, NY. Each floor of 2380 m2 (25,600 ft2)
was served by an independent AHU capable of
delivering a supply air flow rate of 8 m
3/s (17,000
cfm) and constant ventilation air flow of 1.8 m
(3837 cfm), i.e., 22.5% of design supply air flow.
Figure 5 shows the general arrangement of a typical
system. For the purposes of this study, only one
system from a middle floor was studied in detail.
A UVGI device was located in the supply air of each
AHU downstream of the cooling coil and assumed to
operate only during business hours (9 a m. 5 p m.,
Monday through Friday, a total of 2008 hours per
year). It should be noted that the selected UVGI
location is only one of several typical locations. It is
also common to install UVGI upstream of the
cooling coil in an AHU.
The microorganism treated by the system was
assumed to be S. aureus with the k value measured
by Sharp (1940). It was chosen somewhat arbitrarily
because it is a well-characterized reference. In a
typical design process intended to provide protection
against a range of infectious agents, the lowest k
value of concern (i.e., the most UVC-resistant) would
be chosen.
Figure 5 Typical HVAC system schematic
Varied parameters included particulate filtration
(MERV 6, 12, and 13) and UVGI sizing strategy, as
discussed below. In all cases, the design single-pass
efficiency of the UVGI device was assumed to be
85%. For simulating removal of S. aureus by
filtration, a 1 µm, diameter particle size was
assumed, for which the efficiencies of typical MERV
6, 12, and 13 filters, respectively, are approximately
15%, 82%, and 90% (Kowalski and Bahnfleth 2002).
The modeling methodology had three components: 1)
whole building energy simulation to determine
energy use air flow rates, and air temperatures, 2)
UVGI device modeling to determine annual
distribution of single pass efficiency using air flows
and temperatures passed from the whole-building
simulation, and 3) modeling of airborne contaminant
concentration using a well-mixed space model
incorporating UVGI device efficiency results.
The governing equation for concentration of a
contaminant in a single well-mixed zone of volume V
with dilution ventilation and with UVGI and
filtration of specified efficiencies in the supply air
stream is:
dt =G11
( )
( )
( )
{ }
Where G is the source strength of the contaminant
and FOA is the fraction of outside air in the supply air.
Equation 6 expresses that the rate of accumulation of
the contaminant in the space is equal to the rate of
generation less the rate of removal by all three
mechanisms noted.
In UVGI performance simulations, the depreciation
and ambient condition response of lamps were
modeled and compared with predictions of
performance when these effects are neglected. In
space concentration calculations, a distributed source
of S. aureus was assumed. Results of these
calculations are presented in normalized form (ratio
of concentration to a maximum reference
concentration), so that the specific value of source
strength is not significant.
The eQUEST implementation of DOE2 (Hirsch
2009) was used for whole building energy modeling
and other calculations were programmed in a general
purpose computing environment, MATLAB
(MathWorks 2009). From these simulations, it is
possible to compare different scenarios on the basis
of energy use, UVGI device efficiency, and exposure
in occupied spaces.
UVGI sizing strategies
Two sizing strategies were considered: “average
condition” sizing and “worst case” sizing. Average
condition sizing is defined to refer to selection of a
system for a desired single-pass efficiency at mean
values of temperature and air flow at the installation
location. Based on analysis of simulation results the
“average” conditions for the study building were a
temperature of 10.1˚C (50.2˚F) and velocity of 1.7
m/s (380 fpm). The output of the study lamp under
these conditions was 31.7% of maximum.
It was noted previously that the dose required for
85% inactivation of S. aureus is 542 µJ/cm2. With an
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Heating Coil
Cooling Coil
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assumed “average condition” exposure time of 0.39
s, and 31.7% lamp output, the nominal average
spherical irradiance (fluence rate) required for this
system would be 4,384 µW/cm2.
The “worst case” sizing strategy is based on an
extreme condition for which the combination of air
flow and air temperature yields the lowest
inactivation efficiency (or some statistically extreme
value). For the study building, the worst case
combination identified by simulation was 10.8˚C
(51.4˚F) temperature and 2.7 m/s (540 fpm) velocity,
which yielded a lamp output of 29.5% of the
maximum. The spherical irradiance required to
achieve the target single pass efficiency was 6,695
µW/cm2 50% more than that for the average
condition approach.
Figure 6. Air velocity at UVGI device location
Figure 7. Air temperature at UVGI device location
Lamp environment
Figure 6 shows the air velocity distribution at the
UVGI device location obtained from energy
simulation. Figure 7 is a similar plot of air
temperature results.
Results are presented in a monthly box and whisker
format. For each month of data, the line inside the
box denotes the median of all data. The ends of the
box bound the quartiles above and below the median.
The ends of the whiskers attached to each end of the
box show the high and low values. Asterisks and
circles indicate data outliers, i.e., unique conditions
outside the range in which large numbers of data
points are distributed.
Air velocity varies over a wide range as the VAV
system adjusts air flow to meet the space cooling
load. Air temperature, on the other hand, fluctuates
within a small range, since this temperature is under
control continuously during operating hours.
Lamp output, UVC dose, and inactivation
Figure 8 shows the impact of air temperature and
velocity on lamp output. These data reflect only
lamp ambient condition response and not
depreciation. The monthly median varies around 32%
with most of the data between 29% and 33%.
Figure 8. Monthly variation in lamp output,
excluding depreciation
Figure 9. Dose ratio for average condition sizing,
excluding depreciation
Although lamp output is relatively stable, the UVC
dose and microbial inactivation efficiency will vary
because of the effect of air flow on residence time.
The variation of dose for the average condition sizing
strategy is shown in Figure 9 in the form of a dose
ratio, RDose, defined as the ratio of the actual dose to
1 2 3 4 5 6 7 8 9 10 11 12
V [m/s]
1 2 3 4 5 6 7 8 9 10 11 12
T [˚C
1 2 3 4 5 6 7 8 9 10 11 12
Lamp Output [%]
Studen Ve sion of MATLAB
1 2 3 4 5 6 7 8 9 10 11 12
Dose Ratio
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the design dose. The median value is below 1 for
three months during summer, while median values
higher than 1 occur during colder months and
shoulder months on either side. The effect of air flow
is quite significant. In July (month 7), dose ratio falls
below 0.75 for more than 25% of the operating hours.
Figure 10 shows the implications of dose variation
for inactivation of S. aureus. Recalling that the
design target was 85%, it is clear that the system
generally meets the requirement during the winter but
fails to do so during the summer. However, the low
monthly median is still above 80%.
Figure 10 Inactivation efficiency for average
condition sizing, excluding depreciation
Depreciation progressively reduces lamp output over
time. When the depreciation effects shown in Figure
4 are included in the simulation, the outcome in
terms of inactivation efficiency is worse, with the
median for some months now less than 80%.
Figure 11 Duration curves of inactivation efficiency
for various operating scenarios
Figures 8-11 are not replicated for the worst case
sizing strategy as the results would be similar in trend
to those for the average condition approach. Instead,
the more conservative worst case strategy is
compared with the average condition strategy in
Figures 11 and 12 using “duration curve format. A
duration curve shows the distribution of a quantity of
interest plotted against the fraction of time that a
given value is exceeded. The value at 0% is never
exceeded and the value at 100% is always exceeded.
Figure 11 shows duration curves of inactivation
efficiency for four cases:
Design inactivation efficiency (reference);
Average condition design, excluding depreciation
Worst case design;
Manufacturer selection. 50°F, 2.5 m/s (500 fpm)
The “manufacturer” selection scenario reflects the
conditions that a manufacturer lacking more detailed
data, such as the results of an energy simulation,
might reasonably use to select lamps.
From Figure 10 it is clear that average condition
design results in performance that is below that
intended for many hours per year. Whether this
matters is an important question that does not have a
simple answer, and which is discussed further below.
True worst case design substantially oversizes the
system. Although the design target is only 85%
inactivation, more than half the annual operating
hours are at efficiency greater than 95%. It appears
that neither approach is truly satisfactory in that one
(average condition design) performs poorly a
substantial fraction of the time while worst case
design results in unnecessary first cost and annual
cost penalties due to oversizing. In this case, the
manufacturer’s selection conditions are conservative
and very close to the worst case in their implications
for sizing.
Figure 12 Duration curves of occupied hour
inactivation efficiency for the “99%” design strategy
An alternative sizing approach not currently in use
that could strike a suitable balance between economy
and performance is, with the help of simulation, to
select the system so that design lamp output is
achieved for a high percentage of operating hours,
say 99%. This is analogous to the approach taken in
HVAC load calculations to size heating and cooling
Figure 12 illustrates the application of sizing for the
study building system based on the 99% condition,
which for the study building corresponded to a
velocity of 2.5 m/s (500 fpm) with an air temperature
1 2 3 4 5 6 7 8 9 10 11 12
Inactivation Efficiency [%]
Student Version of MATLAB
1 2 3 4 5 6 7 8 9 10 11 12
Inactivation Efficiency [%]
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of 10.7˚C (51.3˚F). To achieve 85% inactivation at
this condition, an irradiance of 6,042 µW/cm2 is
required. This is about 10% less than the requirement
for worst-case design. The device sized for the 99%
lamp output condition meets the single pass
efficiency requirement 90% of the time. For non-
critical applications, a somewhat less conservative
target would result in further initial cost and power
Space microorganism concentration
The preceding discussion has focused on single pass
efficiency of the UVGI device. The more important
issue, and one generally not addressed in design, is
the effectiveness of the UVGI device within the
system comprised of the building and its HVAC
systems. In application, UVGI is only one of three
modes of control, the others being particulate
filtration and dilution. Further, the impact of a filter
or UVGI device depends on where it is located in
system airflow paths. Results of contaminant
concentration modeling illustrate some of the
characteristics of these effects.
Figure 13 depicts a typical day of normalized space
concentration resulting from the distributed,
business-hour release of S. aureus under several
different operating scenarios. The base case that
defines the scale factor for normalized concentration
is one with no UVGI, minimum outside air flow rate
as required by ASHRAE Standard 62.1, and the
MERV 6 filters also required by ASHRAE Standard
62.1 (ASHRAE 2007). Other cases considered
include enhanced ventilation (30% above Standard
62.1), enhanced filtration (MERV 12 and 13), UVGI
(85% efficiency, manufacturer selection condition
sizing) with and without depreciation, and enhanced
UVGI (98% design single pass efficiency).
Figure 13. July 16 space concentration for various
air treatment scenarios
Figure 13 shows that 85% efficient UVGI results in
much lower space concentrations than MERV 6
filters with Standard 62.1 or Standard 62.1 + 30%
outside air. However, increasing UVGI design
efficiency from 85% to 98% has little impact on
maximum concentration in this case.
Figure 14 illustrates the effect of ambient condition
variation and depreciation on July 16 space
concentration predictions. The “constant output” case
is assumed to provide design irradiance at all times.
The “new” lamp case is adjusted for wind chill but
not depreciation, and the remaining case includes
both depreciation and wind chill effects. The most
significant effect in this comparison is the wind chill
correction of the lamp. However, depreciation also
reduces the effectiveness of the system, such that the
space concentration increased by 5%.
Figure 15 compares the effect of other air cleaning
mechanisms--such as ventilation with 30% more OA,
or higher efficiency filtration (MERV 12 and MERV
13) with UVGI operation. It was seen previously that
30% additional OA is far less effective than 85%
UVGI. Figure 15 shows that additional ventilation
added to a system with UVGI has almost no effect.
MERV 12 and 13 filters without UVGI bracket the
performance of UVGI with MERV 6 filters. This
suggests that it is important to perform a thorough
cost analysis of the two approaches that considers all
operation and maintenance cost impacts.
Figure 14. Effect of ambient condition response and
depreciation on July 16 concentration results for min
OA, MERV6, and 85% UVGI scenario.
Figure 15. Comparison of enhanced ventilation and
filtration effects on July 16
The preceding discussion has focused on a
representative 24 hour period. The annual
performance of the system from the prespective of
space concentration control is also of interest.
Figure 16 shows annual duration curves of
normalized space concentration during occupied
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hours comparing the effects of the baseline case of
minimum outside air ventilation + MERV 6
filtration, baseline case + variable output UVGI with
depreciation, and baseline case + constant lamp
output UVGI.
Figure 16. Duration curves of occupied hour space
Figure 16 indicates that the difference in impact on
space concentration between a constant output lamp
and a lamp for which adjustment is made for wind
chill and depreciation is small in this application. In
part, the relatively small difference is due to the
incremental effect of UVGI in combination with
filtration and dilution.
This result should not be over-generalized. As
shown in Figure 8, the combined effect of
temperature and air flow is to maintain lamp output
within a quite narrow range. Under other
circumstances, for example, if the UVGI device was
located at a point in the system with different
temperature and flow profiles, more sensitivity to
wind chill might be expected. Finally, it should also
be noted that both the constant output and wind chill
+ depreciation cases shown in Figure 16 were
compensated for wind chill at the design point, so the
full impact of neglect of wind chill is not indicated.
The analysis presented in this paper is illustrative of
an approach that could improve the application of
UVGI to in-duct systems through the use of
simulation-based design. The advantage this
approach offers over existing methods is the
opportunity to optimize performance by
understanding, for example, the consequences of
locating UVGI in various points in an HVAC system
or the annual distribution of performance resulting
from a particular sizing decision. In particular,
simulation permits the analysis of the performance of
a UVGI device in a system in terms of its effect on
airborne contaminant levels. This is a distinctly
different approach than that frequently applied in
design, which focuses on the single pass efficiency of
the device.
In addition to other sources common to building
simulations, uncertainty in k values adds a potentially
large component of error to calculations of UVGI
system performance. In some cases, k values for a
particular microorganism span orders of magnitude.
This is true of S. aureus, for which measurements
have been made in many media under a variety of
conditions. The value used in this study is among the
lowest in the literature and, therefore, gives a
conservative estimate of UVGI effectiveness.
Although conclusions may be drawn for the specific
system modeled in this study, these should be viewed
as definitive guidance. Only one HVAC system
type, one lamp type, one microorganism, one UVGI
location, etc., were modeled. Even with this very
limited set of parameters, a number of important
phenomena were demonstrated, but a far wider range
of conditions remains to be investigated.
Based upon the results of this study, a number of
conclusions can be drawn:
Both air temperature and air velocity play
important roles in determining the UV dose
delivered by a UVGI device through their
influence on lamp output and residence time.
The impact of age and ambient conditions on the
single-pass inactivation efficiency of in-duct
UVGI systems may be large. In this study, dose
ratio varied by more than 20%.
Design for typical or “average” conditions is
likely to result in a system that delivers less than
its intended design dose much of the time.
Design for worst-case conditions tends to result
in a system that requires substantially more input
power and exceeds design dose significantly
most of the time.
Knowledge of the full range of conditions under
which a UVGI device will operate may permit
informed reduction in installed lamp power
while still meeting performance targets for
contaminant levels.
Until a UVGI device is evaluated in a system
model that accounts for the effect of ventilation
and other modes of air cleaning, its impact is
uncertain. In some cases, differences in
performance measured in terms of dose or single
pass efficiency have a smaller than expected
impact because of such interactions.
Consequently, system performance calculations
may lead to more economical design.
Ventilation quantities would need to be
increased drastically to equal the effect of a
moderately efficient UVGI device on airborne
microorganisms. High efficiency filtration can
equal the performance of UVGI, but potentially
at a greater cost.
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C concentration of microorganism in space (m-3)
F fraction of a substance
G microorganism generation rate in space (s-1)
I the effective (germicidal) irradiance received
by the microorganism (µW/cm2)
k microorganism-specific rate constant
(cm2/ µW-s)
N size of a microbial population of the
Q volume flow rate (m3/s)
S Nt / No , survival fraction of the microorganism
R ratio between two values
t exposure time (s)
T air temperature (˚C)
V airflow velocity (m/s)
V space volume (m3)
η efficiency (%)
design design values
f filter
0 initial value
OA outdoor air
t value at time t
UVGI ultra-violet germicidal irradiation
This work was supported in part by a Graduate
Grants-In-Aid from the American Society of Heating,
Refrigerating, and Air-Conditioning Engineers. The
authors also appreciate the advice of Katja Auer,
UltraViolet Devices, Inc. regarding typical sizing
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Systems and Equipments : Ultraviolet Lamp
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2007. American Society of Heating,
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Media, Summer: 13-17.
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(accessed April 29, 2009).
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Presence of Ultraviolet Light." Aerosol Science,
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Sehulster, L.M., Chinn, R.Y.W., Arduino, M.J.,
Carpenter, J., Donlan, R., Ashford, D., Besser,
R., Fields, B., McNeil, M.M., Whitney, C.,
Wong, S., Juranek, D. (2004). "Guidelines
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on Bacteria Suspended in Air." Journal of
Bacteriology, 39(5), 535-547.
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... Combining Equations 3 and 4 allows for the comparison of risk between different contaminant mitigation strategies, such as increased ventilation rate or better filters. This approach has been used by Fisk et al. (2005) to analyze the health benefits of airside economizers, and by Bahnfleth et al. (2009) in a comparative analysis of UVGI and high-efficiency filtration. ...
Ultraviolet germicidal irradiation of cooling coils controls biofouling that increases airflow resistance and decreases heat transfer coefficient. Though lower in power than air disinfection systems, coil ultraviolet germicidal irradiation systems should provide some collateral air treatment benefit. This benefit is estimated through monetization of simulated nonfatal illness spread in a group of commercial buildings. Benefits were quantified using appropriate metrics for each building type: work-loss days for office buildings, hospital acquired infections for healthcare facilities, and disability adjusted life years for schools. The pre-ultraviolet germicidal irradiation annual cost of occupant illness was the same order of magnitude as annual energy cost. Area-normalized cost was similar in magnitude for all buildings. The collateral air disinfection of coil surface ultraviolet germicidal irradiation reduced baseline illness costs by 3.5% or less, but the resulting cost savings exceeded the energy cost to operate the coil ultraviolet germicidal irradiation systems by as much as a factor of 20. The effectiveness of air cleaning methods already in place, such as ventilation and filtration, directly influences the incremental benefit of additional air cleaning measures.
... adding material at a constant rate of 1/min, or having an initial concentration of 1/m 3 ) . Th e si n gl e pa s s inactivation efficiency of the UVGI systems was set at 85% based on manufacturer' s typical practice as reported in previous work by Bahnfleth, et al (2009). Filtration was varied based on single pass removal efficiencies of MERV 6 and MERV 12 filters for 1 m particles (Kowalski and Bahnfleth 2002). ...
Conference Paper
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Air cleaner effectiveness (ε) is the fractional change in concentration of an air contaminant resulting from the addition of an air cleaner to a system. Unlike component single-pass efficiency, it takes into account the aggregate effect of all contaminant removal mechanisms as well as the effects of air cleaner placement in the system. The usefulness of ε in the analysis and application of air cleaners, as well as its shortcomings, is illustrated by the modeling of in-duct ultraviolet germicidal irradiation (UVGI) in a hypothetical two-zone building served by a constant volume system. The impact of design parameters such as the location of UVGI units, particulate filter efficiency, and the nature of contaminant release are investigated, with calculated ? values ranging from 5% to 90% depending on the nature of these parameters.
... A rigorous economic analysis of a UVGI system requires simulation of both its performance relative to design air quality control targets and its annual energy use. This study combines results of hourly annual simulations described in a companion paper (Bahnfleth, et al., 2009) with economic analysis to estimate the life-cycle cost of in-duct UVGI in a representative building. The primary objectives of the study are to provide an example of UVGI economics and to illustrate basic components of a simulationbased design procedure for UVGI systems. ...
Ultraviolet Germicidal Irradiation (UVGI) systems use 254 nm UVC radiation to inactivate microorganisms in the air and on surfaces. In-duct UVGI systems are installed in air-handling units or air distribution systems to inactivate microorganisms "on the fly" and on surfaces. The literature contains few investigations of the economic performance of UVGI. This study presents a simulation-based life- cycle cost analysis of in-duct UVGI in a hypothetical office building served by VAV systems. Three scenarios are considered: UVGI in the mixed air stream upstream of the cooling coil, UVGI downstream of the coil, and equivalent enhanced filtration without UVGI. The upstream location results in lower first and operating cost for UVGI due to a more favorable thermal environment for UV lamps. UVGI in either location is much lower in annualized cost than equivalent enhanced filtration. The methodology presented could serve as a model for an improved design process.
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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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In this article a modified single fiber model of filtration is described and used to generate filter performance curves that can be fit to MERV data in the 0.3-10.0 micron size range and that can be extended down to the size range of viruses. Coupled with the summary of logmean diameters of airborne microorganism included here, these models will enable estimation of filtration rates for viruses and bacteria.
Ultraviolet germicidal irradiation (UVGI) uses UVC radiation produced by low pressure mercury vapor lamps to control biological air contaminants. Ambient air velocity and temperature have a strong effect on lamp output by influencing the lamp surface cold spot temperature. In-duct UVGI systems are particularly susceptible to ambient effects due to the range of velocity and temperature conditions they may experience. An analytical model of the effect of ambient conditions on lamp surface temperature was developed for three common lamp types in cross flow from a convective–radiative energy balance assuming constant surface temperature. For one lamp type, a single tube standard output lamp, UVC output and cold spot temperature data were obtained under typical in-duct operating conditions. Over an ambient temperature range of 10–32.2°C and an air velocity range of 0–3.25m/s, measured cold spot temperature varied from 12.7 to 41.9°C and measured lamp output varied by 68% of maximum. Surface temperatures predicted by the heat transfer model were 6–17°C higher than corresponding measured cold spot temperatures, but were found to correlate well with cold spot temperature via a two-variable linear regression. When corrected using this relationship, the simple model predicted the cold spot temperature within 1°C and lamp UVC output within ±5%. To illustrate its practical use, the calibrated lamp model was employed in a simulation of the control of a contaminant in a single-zone ventilation system by an in-duct UVGI device. In this example, failure to account for the impact of ambient condition effects resulted in under-prediction of average space concentration by approximately 20% relative to a constant output system operating at maximum UVC output.
The effectiveness of any ultraviolet germicidal irradiation (UVGI) system is governed by the passage of airborne microorganisms through the UV ÿeld. This paper describes a new method for evaluating the perfor-mance of UVGI devices using computational uid dynamic (CFD) simulations. A microorganism inactivation equation is combined with a scalar transport equation to describe the concentration of airborne microorgan-isms in the presence of a UV ÿeld. The solution of this equation, in conjunction with the momentum and turbulent energy equations, allows the eeect of both the airrow and the UV ÿeld on the microorganism distri-bution to be examined. Solutions are shown for the airrow and microorganism concentration through a bench scale ow apparatus, at ÿve diierent UV intensities. The results from the CFD model are validated against the experimental data, obtained from the ow apparatus, for aerosolised Pseudomonas aeruginosa microorganisms. Good comparisons are seen, giving conÿdence in the application of the technique to other situations.
IESNA Approved Method for Electrical and Photometric Measurement of Fluorescent Lamps
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