U.S. patent application number 10/426339 was filed with the patent office on 2003-10-23 for reducing odors with a germicidal lamp.
Invention is credited to Fencl, Forrest B..
Application Number | 20030198568 10/426339 |
Document ID | / |
Family ID | 23474614 |
Filed Date | 2003-10-23 |
United States Patent
Application |
20030198568 |
Kind Code |
A1 |
Fencl, Forrest B. |
October 23, 2003 |
Reducing odors with a germicidal lamp
Abstract
A mechanical ventilation system, which obtains and maintains to
below threshold reduced concentrations of volatile organic
compounds and common organic odors in an air stream. The air stream
has a concentration of volatile organic compounds of at least 100
parts per million and a temperature of between 30.degree. and
70.degree. F. The mechanical ventilation system comprises a duct,
an air moving apparatus and a low-pressure germicidal lamp. The
duct has a volume of at least five cubic feet for temporally
containing and directing the air stream. The air moving apparatus
moves the air stream through the duct at a speed of at least 100
cubic feet per minute. The low-pressure germicidal lamp is
installed with respect to the duct such that the germicidal lamp,
when energized, will irradiate the air stream passing through the
duct. The germicidal lamp, when energized, produces ultraviolet
radiation of approximately 254 nm with a power of at least 300
microwatts/cm.sup.2 at 1 meter for every 4 square feet of duct
area, with substantially no ozone generated. Application of the
ultraviolet light to the air stream reduces concentrations of
volatile organic compounds and other common organic odors in an air
stream to below thresholds such as ordinary olfactory
detection.
Inventors: |
Fencl, Forrest B.;
(Huntington Beach, CA) |
Correspondence
Address: |
SOCAL IP LAW GROUP
310 N. WESTLAKE BLVD. STE 120
WESTLAKE VILLAGE
CA
91362
US
|
Family ID: |
23474614 |
Appl. No.: |
10/426339 |
Filed: |
April 29, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10426339 |
Apr 29, 2003 |
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09373955 |
Aug 13, 1999 |
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6589476 |
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Current U.S.
Class: |
422/4 ; 422/24;
588/303 |
Current CPC
Class: |
A61L 9/20 20130101; Y02A
50/20 20180101; F24F 8/22 20210101; F24F 8/192 20210101 |
Class at
Publication: |
422/4 ; 422/24;
588/210; 588/212; 588/227 |
International
Class: |
A61L 009/20 |
Claims
It is claimed:
1. A method of reducing concentrations of volatile organic
compounds and common organic odors to below threshold limit values
of human detection in a mechanically ventilated space, the
mechanically ventilated space having a mechanical ventilation
system comprising plural ducts, the method comprising the steps of:
(a) identifying a region having a volume of at least four cubic
feet within a given duct of the mechanical ventilation system
through which an air stream passes at a speed of at least 100 cubic
feet per minute, the air stream having a concentration of volatile
organic compounds of at least 100 parts per million and a
temperature of between 30.degree. and 70.degree. F.; (b) installing
a low pressure germicidal lamp with respect to the region such that
the germicidal lamp, when energized, will irradiate the region and
the air stream which passes there through; (c) energizing the
germicidal lamp and exposing the air stream to ultraviolet
radiation of approximately 254 nm with a power of at least 300
microwatts/cm.sup.2 at 1 meter for every 4 square feet of duct
area, with substantially no ozone generated; wherein the UV
radiation destroys volatile organic compounds in the air stream to
thereby lower the concentration of volatile organic compounds to
potentially no more than 10 parts per million.
2. The method of reducing concentrations of volatile organic
compounds and common organic odors to below thresholds in a
mechanically ventilated space of claim 1 wherein the air stream
passes through the region of the duct at between 200 and 600 cubic
feet per minute.
3. The method of reducing concentrations of volatile organic
compounds and common organic odors to below thresholds in a
mechanically ventilated space of claim 1 wherein the germicidal
lamp comprises a single-ended tube and a fixture, the installing
step comprising: (a) opening a hole in the duct wall; (b) mounting
the fixture over the hole on the outside of the duct; (c) inserting
the tube through a hole in the fixture and the hole in the duct
wall; and (d) securing the tube to the fixture.
4. The method of reducing concentrations of volatile organic
compounds and common organic odors to below threshold in a
mechanically ventilated space of claim 1, wherein the thresholds
are comprised of human olfactory detection.
5. The method of reducing concentrations of volatile organic
compounds and common organic odors to below thresholds in a
mechanically ventilated space of claim 1, wherein the thresholds
are less than 100 parts per million.
6. A method capable of controlling low levels of volatile organic
compounds (VOCs) and common organic odors in an air flow and
capable of operation at ambient and cool temperatures comprising:
(a) passing the contaminated air flow through a duct, the air flow
having a speed of at least 100 cubic feet per minute, the air flow
having a concentration of volatile organic compounds of at least
100 parts per million and a temperature of between 30.degree. and
70.degree. F.; (b) generating ultraviolet light of approximately
254 nm without generating a substantial quantity of ozone; (c)
directing the generated ultraviolet light into the duct with a
power of at least 300 microwatts/cm.sup.2 at 1 meter for every 4
square feet of duct area, with substantially no ozone generated;
(d) converting with the ultraviolet light the VOCs into non toxic
materials; wherein organic gas phase compounds are degraded to
below threshold limit values.
7. The method of controlling low levels of VOCs and common organic
odors in an air flow of claim 6 wherein the ultraviolet light is
generated by a germicidal lamp, the lamp comprising a tube and a
fixture, the duct having an inside and an outside, the method
further comprising the steps of: installing the fixture on the
outside of the duct; installing the tube into the fixture, wherein
the tube extends into the duct.
8. The method of controlling low levels of VOCs and common organic
odors in an air flow of claim 6 wherein the air comprises at least
5% oxygen.
9. The method of controlling low levels of VOCs and common organic
odors in an air flow of claim 6 wherein the air comprises at least
25% nitrogen.
10. The method of controlling low levels of VOCs and common organic
odors in an airflow of claim 6 wherein the amount of ultraviolet
light directed into the duct is varied in relation to the
anticipated concentration of VOCs in the air stream.
11. The method of controlling low levels of VOCs and common organic
odors in an air flow of claim 10 wherein the ultraviolet light is
generated by a germicidal lamp, and the amount of ultraviolet light
directed into the duct is varied by varying the intensity of
ultraviolet light source.
12. The method of controlling low levels of VOCs and common organic
odors in an air flow of claim 11 wherein the contaminant is a
member selected from the group consisting of: (a) aliphatic and
aromatic hydrocarbons in a family commonly found indoors, (b)
saturated and unsaturated hydrocarbons containing 28 carbon atoms,
(c) halogen substituted saturated and unsaturated hydrocarbons
containing 28 carbon atoms, and (d) partially oxidized variants of
the hydrocarbons and the halogen substituted hydrocarbons.
13. A mechanical ventilation system which obtains and maintains to
below threshold values reduced concentrations of volatile organic
compounds and common organic odors in an air stream, the air stream
having a concentration of volatile organic compounds of at least
100 parts per million and a temperature of between 30.degree. and
70.degree. F., the mechanical ventilation system comprising: (a) a
duct having a volume of at least four cubic feet for temporally
containing and directing the air stream, the duct comprising at
least one wall which is air-tight and defining an interior through
which the air stream passes and an exterior; (b) an air moving
apparatus for moving the air stream through the duct at a speed of
at least 100 cubic feet per minute; (c) a low pressure germicidal
lamp installed with respect to the duct such that the germicidal
lamp, when energized, will irradiate the air stream passing through
the duct; (d) wherein the germicidal lamp, when energized, produces
ultraviolet radiation of approximately 254 nm with a power of at
least 300 microwatts/cm.sup.2 at 1 meter for every 4 square feet of
duct area, with substantially no ozone generated.
14. The mechanical ventilation system of claim 13 wherein the air
moving apparatus moves the air stream through the duct at between
200 and 600 cubic feet per minute.
15. The mechanical ventilation system of claim 13 wherein the
germicidal lamp comprises: a fixture disposed exterior to the duct;
and a single-ended tube substantially disposed within the duct and
electrically connected to the fixture and supported by the
fixture.
16. The mechanical ventilation system of claim 13 wherein the
threshold limit values are comprised of concentrations specific to
the compound that produces human olfactory detection.
17. The mechanical ventilation system of claim 13 wherein the
threshold comprises 100 parts per billion.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to methods and
apparatus for achieving and maintaining acceptable indoor air
quality.
[0003] 2. Description Of Related Art
[0004] One industry that is mature and economically sensitive to
costs is the heating, ventilation and air conditioning (HVAC)
industry. Because of the competitive nature of both the
construction and HVAC industries, HVAC systems must be inexpensive
to purchase and install. Of a more global interest though, is the
cost to operate and maintain HVAC systems. Often, a building owner
will replace an aging HVAC system as the reduction in operating and
maintenance costs can offset the retrofit cost, sometimes in a
matter of months.
[0005] HVAC systems are typically comprised of a cooling and
heating section for, respectively, cooling and heating the air. An
HVAC system will also include fans and ductwork for moving this
conditioned air where it is needed. In most HVAC systems, air is
drawn in, filtered, cooled and dehumidified or heated and
humidified, and then delivered to a space. The greatest portion of
this air is drawn from the space for recirculation through the HVAC
system.
[0006] One factor impacting design and operation of HVAC systems is
indoor air quality (IAQ). A major consideration in IAQ today is the
amount of outdoor air introduced by an HVAC system into an
otherwise sealed space. The HVAC industry and others have adopted
standards for the introduction of outdoor air into spaces serviced
by an otherwise closed HVAC system. These include offices,
residential, commercial, industrial and institutional spaces, as
modes of transportation such as cars, buses, planes and ships. In
addition to controlling indoor air for occupant comfort, the goal
of most HVAC systems is to provide air with reduced levels of
particulate, gases and bioaerosols, be it for semiconductor,
pharmaceutical or food processing facilities, hospitals, schools or
offices and now the home.
[0007] Various reasons have contributed to the lack of success in
utilizing germicidal lamps for bioaerosol control (IAQ), except for
limited and specialized purposes. The functional implementation of
such devices in air moving systems has been limited generally to
expensive portable units with questionable efficacy. However,
non-moving air devices can be found as wall or ceiling mount
systems where the germicidal lamp is situated in a minimum air
movement, and proper ambient air temperature area. A typical
germicidal tube is designed to operate in still air of
80-90.degree. F. to maintain a tube wall temperature of 105.degree.
F. Germicidal lamps have sensitive physical characteristics
including plasma gas(es), mercury and partial pressures
thereof.
[0008] When a conventional germicidal lamp is used to irradiate
moving airstreams, the air moving across the tube removes heat and
lowers the tube's temperature. The tube's mercury begins to
condense such that the emission of the germicidal wavelength of
253.7 nm decreases. This decrease can be up to 75% when the tube
wall temperature reaches 58.degree. F. Also, at lower internal
temperatures, tube components degrade quicker, shortening tube
life. This phenomenon, known as skin effect cooling, requires a
notable increase in the number of conventional tubes required for a
given level of performance. Increasing the number of tubes reduces
the available square area for airflow. This in turn requires the
airs' velocity to increase, which decreases the dose (time times
intensity) and air volume. If such a system could be made to work,
it would require an increase in fan horsepower, UVC light energy
and in the number of expensive tube replacements.
[0009] Conventional germicidal lamps emit ultraviolet light at both
the primary and secondary emission lines of mercury (254 nm and 187
nm). At mercury's 187-nm line, ozone is created and in many
applications of germicidal lamps, such as in water, this is
desirable. However, ozone has strict threshold limit values in air
due to its strong oxidative properties and harm to humans. Also,
numerous companies have attempted to apply germicidal lamps to HVAC
systems, these conventional germicidal lamps have proved
unsatisfactory. Typically, a conventional germicidal lamp performs
best when installed in a device or room where the air is still
and/or warm. So despite the clear benefits of germicidal lamps,
problems such as decreased output in moving and/or low temperature
air, reduced air changes and ozone production have prevented their
use in all but specialized environments.
[0010] Germicidal fixtures continue to enter the HVAC market.
Recent entries have been sold under the Germ-O-Ray and Germitroll
trademarks. The particular capabilities and design of these devices
is not known to the inventors, though it is believed both devices
use conventional tubes so that when installed in air ducts, they
will suffer from the criteria outlined above.
[0011] For further information concerning improvements in electric
discharge devices, which are directed to overcoming such problems,
reference is made to the above-identified patent applications.
These other patent applications describe excellent devices and
methods for using germicidal lamps to make HVAC systems more
efficient, less costly to operate and maintain, and to provide
better IAQ for a healthier environment.
[0012] Germicidal tubes differ significantly from electric
discharge devices used in ultraviolet gas spectroscopy (VUV tubes).
Germicidal tubes are low-pressure types that emit UV light at the
primary and secondary emission lines of mercury--254 nm and 187 nm.
In contrast, VUV tubes are high-pressure types that operate at high
temperatures and as a consequence, emit different spectral lines
and intensities.
[0013] In occupant air one group of gas phase contaminants are
classified as volatile organic compounds (VOCs). VOCs have been
associated with simple unpleasant odors to serious maladies. Many
people can detect even low part per billion (ppb) concentrations of
VOCs in the air, and VOCs can be found in concentrations of parts
per million (ppm). Numerous studies show the human nose to be the
best gas chromatograph and further that many people have mild to
serious sensitivities to certain or mixed VOCs and their associated
odors. In higher concentrations, some VOCs can cause physical
discomfort and maladies requiring medical attention. Since newer
buildings have become more energy efficient (tighter), internally
generated VOCs are of greater concern.
[0014] Some level of VOCs and other organic odors have existed in
new and old buildings alike for decades. Mechanically ventilated
spaces accumulate simple organic gas phase compounds as a result of
operating office equipment, adding new building materials or
furnishings and using various cleaning agents and solvents to name
a few.
[0015] When attempting to rectify IAQ problems, gaseous
contaminants can be diluted (controlled) through the introduction
of outside air. However, diluting VOCs with outdoor air is neither
efficient nor cost effective. It requires both more heating and
cooling to condition this air and it may bring in more pollutants
than it dilutes.
[0016] Other prior art methods include filtering air through
activated carbon or activated alumina encapsulated by potassium
permanganate, to either adsorb the VOCs or to chemically react with
them in an effort to break them down (oxidize). Both of these
methods have certain disadvantages. Both filtering devices require
additional space and structure within the ventilation system as
they can be 24".times.24".times.24" for every 2000 cfm and weigh
over 110 pounds each. Additionally, they require added system
static pressure (in air horsepower) to move air through them. Both
require lots of natural resources to either reactivate or dispose
of as hazardous waste fill. The initial cost to install these
filters, excluding labor, is approximately $850 for every 2000 cfm.
Their maintenance costs are from $290 to $400 annually. A properly
designed activated carbon system lasts approximately 12 months. A
properly designed potassium permanganate encapsulated activated
alumina system lasts approximately 9 months. Thus, at least once
per year, these special filters require expensive, hazardous and
intrusive service. These systems also require more air horsepower
to move air through them and thus more energy consumed. When they
are added to an existing system, it could necessitate speeding up
the fan and/or changing out the fan and fan motor to a larger
size.
[0017] Outside of HVAC, VOC-control has been pursued through
several techniques. One technique uses liquids to wash VOCs from a
gas stream. However, these liquid systems are inadequate for
treating air in an HVAC system. They can be more costly and
hazardous than the filter systems described above. Heat treatment
using radiant beds or afterburners has been used to partially
catalyze VOCs in certain applications. However, heat treatment is
not compatible with HVAC systems. The amount of heat that is added
would also have to be offset by added cooling capacity.
Photocatalysis has been gaining popularity in high VOC
concentration atmospheres but again first and operating costs are
prohibitive. Solvent recovery systems utilizing high volumes of
activated carbon are the extreme and here we are simply dealing
with a misapplication.
[0018] UVC at predominately 253.7 nm in and of itself has not been
considered for VOC control. One prior art method used ultraviolet
light of 185 nm to produce ozone for breaking down odor. In that
prior art method, an air stream was passed across an ultraviolet
lamp of UV energy at 185 nm where oxygen (O.sub.2) is separated
forming unstable O.sub.1's, which combine with O.sub.2's to form
O.sub.3's or ozone. Also, it was found that when an ultraviolet
lamp was placed in a moving air stream, the reduced UV output was
insufficient enough to reduce the production of both 185 nm
generated ozone and 253.7 nm UVC to have much effect on most VOCs.
Thus, reliance only upon ultraviolet light even when producing
ozone was considered wholly inadequate for VOC-control.
SUMMARY OF THE INVENTION
[0019] The previously described problems are solved in a method and
apparatus for reducing ppb concentrations of volatile organic
compounds and common organic odors to below threshold limit values
in a mechanically ventilated space. The mechanically ventilated
space has a mechanical ventilation system comprising plural ducts
and an air moving apparatus such as a fan. Ultraviolet radiation is
introduced into a duct to treat an air stream passing by the UV
radiation and moving through the duct. The air stream passes at a
speed of at least 100 to over 1500 feet per minute and has a
temperature of between 30.degree. and 90.degree. F. An untreated
air stream could have a concentration of volatile organic compounds
as high as 100 parts per million.
[0020] A low-pressure germicidal lamp is installed with respect to
the interior of the duct such that the germicidal lamp, when
energized, will irradiate the air stream. The germicidal lamp when
energized emits ultraviolet radiation of approximately 254 nm with
a power of at least 30 to 3000 microwatts/cm.sup.2 at 1 meter for
every 4 square feet of duct area, with substantially no ozone
generated. The UV ionization radiation separates many volatile
organic compounds at the molecular and atomic level to water vapor
and carbon dioxide thereby lowering the concentration of volatile
organic compounds to 90 parts per million and down to 10 parts per
billion.
[0021] Still further objects and advantages attaching to the device
and to its use and operation will be apparent to those skilled in
the art from the following particular description.
DESCRIPTION OF THE DRAWINGS
[0022] Further objects of this invention, together with additional
features contributing thereto and advantages accruing therefrom,
will be apparent from the following description of a preferred
embodiment of the present invention which is shown in the
accompanying drawings with like reference numerals indicating
corresponding parts throughout and which is to be read in
conjunction with the following drawings, wherein:
[0023] FIG. 1 is a cross section of a duct having dual,
single-ended germicidal tubes installed therein.
[0024] FIG. 2 is a cross section of a germicidal tube in a duct and
showing the radiation pattern of ultraviolet light from the
tube.
[0025] These and additional embodiments of the invention may now be
better understood by tuning to the following detailed description
wherein an illustrated embodiment is described.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Throughout this description, the embodiments and examples
shown should be considered as exemplars, rather than limitations on
the apparatus and methods of the present invention.
[0027] Throughout this description, the preferred embodiment and
examples shown should be considered as exemplars, rather than
limitations on the apparatus and methods of the present
invention.
[0028] The sun naturally produces ionizing radiation. This
radiation can disturb the electrical properties of most organic
compounds, and at high enough levels will break apart these organic
compounds at the molecular and atomic level. The residual compounds
of such broken organic compounds are mostly water vapor and carbon
dioxide--harmless materials in almost any environment. Yet, for
reasons suggested above, sunlight cannot be used efficiently and
effectively in a mechanically ventilated space for control of VOCs.
A mechanically ventilated space is defined as space which can be
occupied by a person and having a mechanical ventilation system
comprising plural ducts and which modifies air temperature and
possibly humidity for human comfort.
[0029] The inventors have found a way to replicate sunlight's
degradation of VOCs without the problems of sunlight and at a low
cost. That method comprises generating specific wavelengths of
ultraviolet radiation and directing that radiation into a moving
air stream, which flows into the mechanically ventilated and
occupied space.
[0030] Turning now to FIG. 1, there is shown a cross-section of a
duct 100 of a mechanical ventilation system. FIG. 1 also shows a
germicidal lamp 200 comprising two tubes 210 and a fixture 220. Air
passing through the duct typically will have a temperature of
between 30.degree.-70.degree. F. The humidity of this air is also
typically controlled. The relatively low temperature and varying
humidity render the duct a harsh environment for electronic
devices, and particularly for germicidal lamps. For the germicidal
lamp to operate effectively in the harsh environs of an air duct, a
germicidal lamp specifically designed for such an environments must
be employed. In particular, the germicidal lamps sold by the
assignee of this invention, Steril-Air U.S.A., Inc, and sold under
the trademark, "UVC Emitter," are preferred. These germicidal lamps
produce no detectable ozone, which is also highly desirable.
However, germicidal lamps which produce an insignificant quantity
of ozone may be used.
[0031] The mechanical ventilation system includes an air moving
apparatus. This air moving apparatus is preferably a fan 120. The
fan 120 is shown in the duct 100, though the fan or other air
moving apparatus may be located some distance from the germicidal
lamp 200. Other air moving apparatuses which can move an air stream
through the duct as described further below are within the scope of
the invention.
[0032] In determining the spatial relationship between the
germicidal tubes 210 and the walls of the duct 100, the objective
is to obtain a uniform distribution of UV radiation across the duct
100. It has been determined that, for a germicidal tube which is
positioned in accordance with the invention, the spatial
distribution of UV radiation follows precisely that of a diffuse
area source and, surprisingly, not an isotropic point source. The
pattern of UV radiation from the preferred germicidal lamp is shown
in FIG. 2. It can be seen that although the germicidal tube 210 is
a source of radiation, the walls of the duct 100 are effectively a
secondary (reflected) source of UV radiation. The diffuse radiation
of the germicidal tubes 210 and diffuse reflection is therefore
defined as a near field effect, not as an inverse square law. This
finding is contrary to normal expectations, and therefore placement
of germicidal tubes in accordance with the present invention
results in the need for fewer germicidal tubes. Put another way,
when the germicidal tubes 210 are positioned in sufficient
proximity to the walls of the duct 100, the intensity of UV
radiation from the germicidal tubes 210 at a given point is, to a
degree, independent of the distance of the germicidal tubes 210
from the given point.
[0033] As shown in FIG. 2 the photons emitted from a particular
point on the germicidal tube 210 radiate in all directions. Because
FIG. 2 is an elevational view, the global radiation of these
photons is not shown. These photons would, however, also radiate
outwardly and inwardly from the plane of the paper upon which the
planar representation is illustrated and from all surfaces of the
tube 210.
[0034] In accordance with the invention, ultraviolet radiation from
a germicidal lamp is used to reduce concentrations of VOCs and
common organic odors to below threshold limit values in a
mechanically ventilated space. That threshold is preferably an
average person's ability to smell the VOCs and common organic odors
("olfactory detection"). To reduce VOCs and common organic odors
below olfactory detection, it is believed that the concentration of
VOCs must be reduced to below 100 parts per billion. The
ultraviolet radiation is applied within the ductwork of the
mechanical ventilation system of the mechanically ventilated space.
Ultraviolet light of 254 nm will invalidate the molecular structure
of a VOC in a confined air stream. A germicidal lamp is preferably
used to emit ultraviolet radiation of approximately 254 nm, with
substantially no ozone generated. The absence of ozone is a notable
difference from most prior art methods as it is now well understood
that ozone is harmful to human health and more so in the presence
of certain VOCs.
[0035] In order to treat an appreciable quantity of air, the method
includes directing the radiation into a relatively rapidly moving
air stream. As a normal function of the operation of a mechanical
ventilation system, air is passed through the system's ductwork.
Preferably, the air stream has a speed of at least 100 feet per
minute (FPM). More typically, the air stream has a speed of between
100 to over 1500 feet per minute. The air in the duct preferably
has a temperature of between 30.degree. and 90.degree. F, which
though not necessarily ideal for UVC type ionization of the VOCs
and common organic odors, renders the method unobtrusive to
operation of the mechanical ventilation system. The quality of
radiation introduced into the duct is adjusted to achieve the
desired results, rather than adjusting the temperature, air
pressure or humidity of the air stream to be treated. This is more
easily achieved with the product that the inventor offers.
[0036] The air is passed through a region of a duct having a volume
of at least four cubic feet for the irradiation cited. The
inventors have found that the air would have a concentration of
volatile organic compounds of 100 parts per million (PPM) or less
for the method to be useful.
[0037] To generate the ultraviolet radiation, a low pressure
germicidal lamp, such as that shown in FIG. 1, is preferably
utilized. The germicidal lamp is preferably positioned with respect
to the region such that the germicidal lamp, when energized, will
irradiate the region and the air stream which passes there through.
The region preferably is irradiated with a power of at least 300
microwatts/cm.sup.2 at 1 meter for every 4 square feet of duct
area
[0038] The germicidal lamp preferably comprises a single-ended tube
and a fixture as described above. Installation of such a germicidal
lamp includes producing a hole in the duct wall, mounting the
fixture over the hole on the outside of the duct, inserting the
tube through a hole in the fixture and in the duct wall, and
securing the tube with the fixture. The fixture preferably includes
a power supply adapted to receive standard power available within
the mechanical ventilation system. This typically is 115, 208/230
or 277 Vac power. Power consumption for a typical install of
germicidal lamps is preferably less than 150 Watts per each 2000
CFM of duct air.
[0039] The tubes of the germicidal lamp are preferably distanced
from one another such that the duct area is equally irradiated with
the tube centerlines potentially based on a given concentration per
unit volume of offending VOC. Because of the low power consumption
of the germicidal lamps, the germicidal lamps can and should be
operated at any time the mechanical ventilation system is
running.
[0040] The inventors have found that, when so applied, the UV
radiation destroys VOCs and common organic odors in the air stream
to thereby lower the VOC concentration to as little as 10 ppb. At
such a low level, the VOCs and common organic odors are beyond
human olfactory detection and therefore is not a hazard or nuisance
to building occupants.
[0041] In contrast to the cost and problems of the prior art
methods of VOC control described above, UVC irradiation can be less
costly, more predictable and as a monumental benefit, adds nothing
to the environment or the space being served.
[0042] Installation of properly sized single-ended germicidal lamps
requires little mechanical or physical modifications to an existing
mechanical ventilation system. Thus, the method can be used in both
existing and new mechanical ventilation systems, and the germicidal
lamps simply added to the existing structure. The inventors have
found that germicidal lamps which emit UV of approximately 254 nm
without substantial ozone require relatively little energy to
operate, require no changes to mechanical equipment and offer the
additional benefit of killing (inactivating) microorganisms in the
air.
[0043] Using UV light could reduce the amount of outdoor air for
dilution or eliminate the need for adding sorbants to the air
handler. The annual savings, including labor and materials for both
could amount to $0.45 per CFM or more. Building owners and
operators can reduce their dependency on, or eliminate the need
for, increased amounts of outdoor air thus eliminating the need or
requirement to condition that air for acceptable use. Additionally,
productivity would be increased while absenteeism or incapacitation
would be decreased. Savings in both areas would be dramatic.
[0044] Our method is especially non evasive to the typical air
handling system and can be directly related to the regenerative and
restorative properties of our sun . It does not require altering
the mechanical equipment to install or operate. It has lower costs
of installation, operation and maintenance. It adds nothing to the
air stream or environment to control gas phase compounds. It also
provides a significant degree of germicidal control to further
reduce absenteeism and incapacitation. Thus, the invention provides
a more suitable indoor environment for occupants of any
mechanically ventilated space whether at work, school or
leisure.
[0045] The streams in which the above described hydrocarbons are
present as contaminants are described as conditioned spaces
designed for human occupancy. Such streams typically consist of air
or of rather inert gases, such as nitrogen. These gaseous
hydrocarbon contaminants may be present individually or admixed in
concentrations as low as 10 parts per billion (volume basis), and
up to 100 parts per million. However, the present decontaminating
process is sufficiently reactive to be of considerable interest
even well below 100-ppb hydrocarbon concentration.
[0046] As with many chemical reactions, increased temperature
generally accelerates the decontaminating process; however, the
photochemical nature of the present process is rather insensitive
to temperatures significantly below the thermal oxidation
temperatures of the subject hydrocarbons. Consequently, temperature
limitations follow from practical considerations. Similarly, the
decontamination rate will increase with increased ultraviolet
radiation intensity. However, it is important to control the UV so
that a base intensity exists for a given concentration of VOCs. The
inventors have found that an untreated tube wall will allow out the
185-nm wavelength and will generate ozone.
[0047] The pressure at which the decontamination reaction is
conducted is again limited by practical considerations. The air
streams of this process are subject to ordinary gas laws, and the
effective residence time obtained through selection of the air
speed in the duct. The decontamination reaction per se is rather
insensitive to pressure within ordinary limits of 0.01 to 10
Atmospheres.
[0048] Some oxygen must be present, as ultraviolet light is
believed also to react with both oxygen and background ozone to
produce various activated species, including OH radicals,
O.sub.2H.sub.2, O.sub.1, O.sub.2 and O.sub.3 with excited electron
states. The term "oxygen species" refers collectively to these
compounds and elements and their excited allotropes. The duct is
selected to provide sufficient time to oxidize or break apart the
VOCs into simple products such as carbon dioxide, water vapor and
hydrogen halides.
[0049] Although exemplary embodiments of the present invention have
been shown and described, it will be apparent to those having
ordinary skill in the art that a number of changes, modifications,
or alterations to the invention as described herein may be made,
none of which depart from the spirit of the present invention. All
such changes, modifications and alterations should therefore be
seen as within the scope of the present invention.
* * * * *