U.S. patent application number 12/080452 was filed with the patent office on 2008-08-07 for heated replacement air system for commercial applications.
This patent application is currently assigned to Supplier Support International Inc.. Invention is credited to David Krupp.
Application Number | 20080184991 12/080452 |
Document ID | / |
Family ID | 35094991 |
Filed Date | 2008-08-07 |
United States Patent
Application |
20080184991 |
Kind Code |
A1 |
Krupp; David |
August 7, 2008 |
Heated replacement air system for commercial applications
Abstract
Apparatus and a method for providing heated replacement air to a
paint spray booth or other commercial process which requires heated
make-up air to replace exhausted air. A blower draws outside air
through a filter and an injection chamber prior to delivering the
air to the process. Hot gases from a burner are injected into the
injection chamber and mixed with the replacement air to adjust the
temperature of the replacement air. The burner uses combustion air
which is separate from the replacement air. The flow rate of the
exhaust air and the replacement air can be adjusted to meet
changing needs of the process. The BTU output from the burner is
adjusted to maintain a desired replacement air temperature.
Inventors: |
Krupp; David; (Hiram,
GA) |
Correspondence
Address: |
MACMILLAN SOBANSKI & TODD, LLC
ONE MARITIME PLAZA FIFTH FLOOR, 720 WATER STREET
TOLEDO
OH
43604-1619
US
|
Assignee: |
Supplier Support International
Inc.
Hiram
GA
|
Family ID: |
35094991 |
Appl. No.: |
12/080452 |
Filed: |
April 3, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11088664 |
Mar 24, 2005 |
7360534 |
|
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12080452 |
|
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60556097 |
Mar 25, 2004 |
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Current U.S.
Class: |
126/99R |
Current CPC
Class: |
B05B 16/60 20180201 |
Class at
Publication: |
126/99.R |
International
Class: |
F24H 3/02 20060101
F24H003/02 |
Claims
1. An apparatus for supplying heated replacement air to a process
in which air is exhausted, the apparatus comprising: an air intake
connected to an injection chamber from which an adjustable volume
of replacement air flows to the process, a source of BTU energy
positioned outside and connected to the injection chamber and
configured to inject heated gas into the injection chamber, wherein
the adjustable volume of air through the injection chamber can
change without affecting the air-to-fuel ratio of said source of
BTU energy; and, at least one process fan configured to: i) draw
the replacement air through the air intake and into the injection
chamber based upon the variable requirements of the process, and
ii) deliver a predetermined and adjustable volume of the heated
replacement air to the process
2. The apparatus for supplying heated replacement air to a process,
as set forth in claim 1, further including a mixing device located
between the injection chamber and the at least one fan.
3. The apparatus for supplying heated replacement air to a process
as set forth in claim 1, wherein the source of heated gas is a gas
burner positioned outside the injection chamber, the gas burner
including a dedicated blower connected to the gas burner to supply
the combustion air and inject heated gases from the gas burner into
the injection chamber.
4. The apparatus for supplying heated replacement air to a process,
as set forth in claim 1, further including an adjustable mode
changing damper configured to be moveable between a first position,
wherein replacement air from a first location is drawn by the at
least one fan from the air intake into the injection chamber, and a
second position, wherein air from a second location is drawn by the
at least one fan into the injection chamber.
5. An apparatus for supplying heated replacement air to a process
in which air is exhausted, the apparatus comprising: an air intake
connected to an injection chamber for supplying a desired volume of
replacement air to the process; a source of BTU energy positioned
outside and connected to said injection chamber and configured to
inject heated gas into said injection chamber; at least one
delivery fan configured to: i) draw replacement air through the air
intake and into said injection chamber, ii) mix the heated gas with
the replacement air to form the heated replacement air, and, iii)
deliver a predetermined adjustable volume of the heated replacement
air to the process, wherein the volume of the heated replacement
air is substantially the same volume as the exhaust air from the
process, and wherein the volume of the replacement air does not
affect the air-to-fuel ratio of the BTU energy that is injected
into said injection chamber.
6. The apparatus for supplying heated replacement air to a process,
as set forth in claim 5, and further including multiple gas burners
positioned outside the injection chamber wherein the gas burners
would each have a dedicated blower with the gas burners having the
same or different BTU output with controls to engage the gas
burners adjust the injected BTU energy.
7. The apparatus for supplying heated replacement air to a process,
as set forth in claim 5, and further including an indirect heat
exchanger mounted in the injection chamber configured to be
moveable between first and second positions during the operation of
the apparatus, wherein when the indirect heat exchanger is in the
first position heated gas is injected directly into replacement air
drawn through the injection chamber; and, wherein when the indirect
heat exchanger is in the second position heated gas flows through
the indirect heat exchanger and out through a vent in the apparatus
which is engaged as the indirect heat exchanger is moved into the
second position and replacement air drawn through the injection
chamber is indirectly heated by the indirect heat exchanger.
8. The apparatus for supplying heated replacement air to a process,
as set forth in claim 7, and further including an adjustable intake
damper mounted between the air intake and the injection chamber;
the adjustable intake damper having a position permitting an
unrestricted flow of air from the first location through the air
intake when the indirect heat exchanger is in its first position
and the intake damper blocking air flow from the first location
through the air intake when the indirect heat exchanger is in its
second position to force the flow of air from a second
location.
9. The apparatus for supplying heated replacement air to a process,
as set forth in claim 5, wherein the source of BTU energy is a gas
burner, the gas burner including a dedicated blower connected to
develop a proper air-to-fuel ratio and inject hot combustion gases
from the gas burner into the injection chamber thereby preventing a
change in the volume of replacement air from directly affecting the
air-to-fuel ratio in said gas burner.
10. The apparatus for supplying either direct heated replacement
air to a process or indirect heated air as set forth in claim 5,
the apparatus further including: a mode changing damper having a
first position, wherein replacement air from a first location is
drawn by the at least one fan from the air intake into the
injection chamber, and having a second position, wherein air from a
second location is drawn by the at least one fan into the injection
chamber across a movable indirect heat exchanger mounted in the
injection chamber, the indirect heat exchanger being in the first
position when the damper is in the first position and heated gas is
injected directly into replacement air drawn through the injection
chamber; and, the indirect heat exchanger being in the second
position when the damper is in the second position and heated gas
flows through the indirect heat exchanger and replacement air is
drawn through the injection chamber and is indirectly heated by the
indirect heat exchanger.
11. A method for providing heated replacement air to a process in
which air is exhausted comprising the steps of: a) drawing an
adjustable volume of replacement air through an air intake and an
injection chamber; b) injecting a flow of hot gas from a BTU source
located outside the injection chamber into the replacement air as
it is drawn through said injection chamber to heat the replacement
air to the desired temperature where the injected hot gas is
produced with an optimum air-to-fuel ratio not affected by changes
in the replacement air volume, and, c) mixing the replacement air
and the injected hot gas to provide a substantially uniform
temperature to the heated replacement air.
12. The method for providing heated replacement air at variable air
volumes to a process, as set forth in claim 11, and further
including the steps of: d) sensing the temperature of the heated
replacement air after it is mixed; and, e) adjusting the BTU's
output in the injected flow of hot gas to maintain a desired
temperature in the heated replacement air delivered at different
air volumes to the process.
13. The method for providing heated replacement air to a process at
variable air volumes, as set forth in claim 12, and further
including the steps of: adjusting a flow of replacement air
delivered to the process in response to changes in the amount of
air exhausted from the process; and adjusting the BTU's in the flow
of hot gas injected into the injection chamber by the engagement of
a plurality of burners with the same or differing output levels
where the burners would be located outside the injection chamber
and each burner would have a dedicated blower to produce a BTU
output at an optimal air-to-fuel ratio where the burners are
engaged to maintain a desired temperature in the heated replacement
air.
14. The method for providing heated replacement air to a process,
as set forth in claim 12, including converting from directly
heating replacement air to indirectly heating replacement air with
the use of a mode changing damper and a moveable heat exchanger in
the injection chamber, injecting the hot gas into the heat
exchanger, and heating the replacement air with the heat exchanger.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Applicants claim priority to U.S. Provisional Patent
Application Ser. No. 60/556,097 filed Mar. 25, 2004. This
application is a continuation of Ser. No. 11/088,664 filed Mar. 24,
2005, which is expressly incorporated herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
TECHNICAL FIELD
[0003] The invention relates to a system for providing heated
replacement air to a commercial or industrial process, such as to a
paint spray booth.
BACKGROUND OF THE INVENTION
[0004] The process of applying atomized liquid coatings and
adhesives generates potentially dangerous gaseous and particulate
by-products that are controlled or managed by confining them in an
enclosure known as a spray booth and conveying them away from the
process by entraining them in a moving air stream. This exhaust air
stream typically passes through one or more stages of filtration to
remove the particulates before the gaseous or vaporous by-products
are exhausted into the atmosphere. The volume of the exhaust air
stream varies according to the size of the spray booth and may
range, for example, from 3,000 cubic feet per minute (CFM) to more
than 50,000 CFM. This equates to 30 to 150 lineal feet per minute
within the spray booth in the direction of air flow. Provision may
be made to replace the exhausted air volume.
[0005] Since most coating processes are vulnerable to quality
rejects caused by dirt or other foreign airborne objects, prudent
finishing process operators equip their facilities with air make-up
unit. Air make-up units have a three fold function. First, they
supply the process with the required replacement air. Second, they
filter the replacement air. Third, they heat or condition it. An
air make-up unit may be directly coupled to the spray booth or it
may dump replacement air to the area surrounding the booth. Air
make-up units are designed to include a heat source with sufficient
thermal capacity to warm the volume of replacement air to the
desired temperature on the anticipated coldest day. Typically, a
fan or blower in the air make-up unit pushes or pulls the entire
replacement air stream through a complex assembly that includes
filters, dampers, and a heat source which is usually a gas
burner.
[0006] Historically, environmental and worker health and safety
regulations have empirically established minimum air velocities for
spray booths. The overwhelming majority of installed spray booths
are equipped with fixed speed exhaust fans or blowers. While
exhaust air velocities change as the particulate filtration system
loads, the pressure drop increase across the filtration system is
usually limited to 0.5 inches of water column and produces a
corresponding reduction in exhaust air volume in the range of 20%.
Since the spray booth exhaust air volume is essentially fixed in
any given installation, the volume of air the associated air
make-up unit is required to provide also is fixed. Hence, the air
make-up unit like the spray booth is usually equipped with a fixed
speed fan or blower. In addition, the gas burner's operating
efficiency is dependent on maintaining a predetermined air velocity
through the burner mechanism. This precludes making significant
changes to a given air make-up unit delivered air volume without
mechanically reconfiguring the unit.
[0007] The attempts of placing a premix burner in the air stream in
the early days of air replacement technology were short lived
because the panel fans that were used were loud and could not
handle the static loads of the supply plenum filters. Once the
capability of the blower with the ability to handle additional
static was introduced the most effective method for air replacement
was established as the paradigm. Direct fired inline burners with
associated profile plates that adjust the airflow across the burner
proved to be the most efficient technology. These profile plates
were first considered as fixed, as was the airflow through the
unit. With changes in technology these profile plates have now
become adjustable and the range of acceptable airflow across the
burner has been increased.
[0008] In a traditional air make-up unit system, all of the
replacement air is drawn across the burner assembly and any change
in the delivered air volume will change the burner's air supply.
This causes it to operate under less than optimum conditions. For
this reason, traditional air make-up units are designed with fixed
speed fans. Any reductions in delivered air volume are usually
accomplished by partially closing a damper on the output of the air
makeup unit (AMU) to reduce the output volume or changing the speed
of the blower with a variable frequency drive (VFD). A VFD adjusts
the rotational speed of the fan motor to keep the ventilation
system balanced. The cost to apply a VFD to control the motor for
the unit with an in-line burner is significant because a larger
motor size is needed for a system with an in-line burner due to the
higher static load.
[0009] In an enclosed booth system, the air make-up unit discharges
directly into the process within the booth. Based upon the
assumption the air make-up unit operates at a fixed speed, the
exhaust fan speed is varied as required to keep the booth balanced.
Prior to the advent of electronic VFD units, a damper was placed in
the exhaust stack. This damper added an adjustable static load to
the fan. The damper was reduced as the overspray arresting filters
loaded to maintain a constant air velocity through the booth. The
range of actual air velocity changes under this or other schemes is
limited.
[0010] Unfortunately, the resulting somewhat arbitrarily
established, fixed volume air flow found in a typical spray booth
system is not the optimum environment for efficiently applying a
consistent high quality finish. Significant process economies, as
well as improvements in the quality of the applied finish, can be
achieved by reducing the air velocity in any given spray booth. A
few astute finishing process owners have "tuned" their finishing
process by adjusting the exhaust air volume of individual spray
booths and making corresponding adjustments in the volume of
replacement air delivered by the associated air make-up unit as
well as the necessary mechanical changes to the air make-up units
configuration. However, no one has designed an air make-up
unit/spray booth system that can be mass produced, yet economically
facilitate the tuning of individual installations to the precise
needs of their respective finishing processes while simultaneously
maintaining optimum air make-up unit operation.
[0011] In prior art spray booths, replacement air flow is either on
or off because the effort required to vary its volume was complex
and time consuming. The burner required a fixed combustion air
velocity to achieve the necessary clean burn characteristics and
therefore the overall replacement air volume couldn't be
changed.
BRIEF SUMMARY OF THE INVENTION
[0012] The invention is directed to a direct gas fired heat source
arrangement for air replacement or make-up units used in
conjunction with spray booths and other industrial and commercial
processes. The invention permits the replacement air volume to be
varied over a wide range without compromising the integrity of the
burner's combustion process and without requiring the expensive and
somewhat tedious mechanical reconfiguration of the burner assembly.
The invention utilizes a plurality of smaller burners positioned
outside of the primary replacement air passage. The burners are
operated to inject a controlled amount of heat into the primary
replacement air passage to control the temperature of replacement
air flowing through the passage. Each burner is individually
configured in such a manner that it is always supplied with the
necessary volume of air to insure complete combustion. When coupled
with a modified spray booth and the appropriate controls, this
invention allows the exhaust air flow rate and total volume to be
optimized for the finishing process it protects, thereby increasing
the process' coating application transfer efficiency, decreasing
the emission of volatile organic compounds (VOC's) and
particulates, increasing the quality of the applied finish, and
significantly reducing the process operating cost. The invention
provides the production economics associated with the manufacture
of standard equipment packages while simultaneously enabling
individual finishers to customize their air make-up unit--spray
booth systems to the processes ventilation requirements solely by
programming system controls.
[0013] Similar air handling systems are used to replace the
significant quantities of process air exhausted to control the
potentially hazardous build-up of gaseous and/or particulate
emissions generated by other mid-sized and large commercial and
industrial processes including, but not limited to wood working
dust collection, welding fume collection, fiberglass reinforced
plastic lay-up, sandblasting, commercial/industrial dry cleaning
and cooking. The invention offers substantial process and economic
benefits in these applications.
[0014] The invention allows the replacement air units to be thought
of as modular components, not part of a unit that is shipped to the
jobsite on a flatbed truck. Processes that require very clean air
now have the ability to have the filtration system designed
specific to the application and not to be always contained within
the confines of the AMU. The balance problem that existed when a
single blower had to push air down different interconnecting duct
work sections can now be better controlled by decentralized
distribution fans that can have their speeds adjusted via the drive
pulleys at start-up. This can achieve the desired balance, or the
motors can be operated with variable speed drives (VFD's) which
would better address the changes in static loads caused by filter
loading.
[0015] The air replacement system of the invention can produce
significant energy savings that are not possible with current
systems. Although the cost of the self contained burner is greater
than the simple in-line burner, the ability to let the process have
less restrictive limits with regard to the volume of air required
and to allow the process to demand only the volume that is required
is a feature of the invention. Efficiencies that can now be gained
by altering the air volume will produce significant savings in
energy costs.
[0016] The replacement air system of the invention improves the
overall efficiency and effectiveness of a process which consumes
high levels of fossil fuels to reduce the energy cost for those who
use the system. It also reduces emissions from burning excessive
amounts of fossil fuels. The system is unique because it allows
optimization of air being consumed by the spray booth or other
process that contaminates the air, thereby opening a new concept to
improve efficiency. It has been thought that no improvement could
be made to the direct fired burner since all the heat goes into the
air. However, with the invention the volume of air being consumed
can be adjusted, which has a direct relationship to the overall
fuel consumption.
[0017] Various objects and advantages of the invention will become
apparent from the following detailed description of the invention
and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a diagrammatic view of a paint spray booth with a
heated replacement air system according to one embodiment of the
invention;
[0019] FIG. 2 is a diagrammatic view of a paint spray booth with a
heated replacement air system according to a second embodiment of
the invention;
[0020] FIG. 3 is a diagrammatic view of a dual mode heated
replacement air system according to a further embodiment of the
invention, showing the system operating in a direct fire
operation;
[0021] FIG. 4 is a diagrammatic view of the dual mode heated
replacement air system of FIG. 3, showing the system operating in
an indirect heat operation;
[0022] FIG. 5 is a perspective view of a multi-port digital gas
flow control valve;
[0023] FIG. 6 is a perspective view of a multi-burner apparatus for
injecting heat into a flow of replacement air for an industrial or
commercial process such as a paint spray booth; and
[0024] FIG. 7 is an exploded perspective view of the apparatus of
FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The invention is directed to a heated replacement air system
for an industrial or commercial process, and to apparatus which
allows for the independent adjustability of the replacement air
volume flow and the BTU energy applied to that air volume flow. The
system is described herein specifically for use with industrial and
commercial spray paint booths. However, the system also can be used
with similar processes where varying the air volume being moved
through the system and the temperature of the air during some
periods of the process might allow the process to still function
well within all process and safety requirements.
[0026] Turning to FIG. 1 of the drawings, an industrial paint spray
booth 10 is shown incorporating a heated replacement air system 11
according to one embodiment of the invention. The spray booth 10
includes a work chamber 12 where objects are painted. The size of
the chamber 12 will depend on the size of the objects which are
painted. During painting, air and any entrained overspray particles
and solvent fumes are exhausted through a filter 13 into a plenum
14. Exhaust air is withdrawn from the plenum 14 through an exhaust
stack 15 by a motor driven exhaust fan 16. The apparatus for
filtering and exhausting air from the spray booth 12 may be of any
conventional type. For example, the filter 13 may be as simple as a
replaceable glass fiber filter, or may be a water system which
washes the exhaust air, or may include an advanced system for
removing VOC's from the exhaust air.
[0027] Normally, the exhaust air is vented to the atmosphere
outside of a building housing the spray booth 10. As air is
exhausted from the building housing the spray booth 10, it is
necessary to provide an equal amount of replacement air. If the
ambient temperature is sufficiently high, the replacement air may
be filtered ambient air drawn from outside of the building.
However, on cooler days and especially in northern climates, it is
necessary to heat the replacement air to the temperature required
by the painting process.
[0028] The system 11 draws replacement air for the finishing
process from the area surrounding the perimeter of the facility
where the spray painting booth 10 or process contaminating the air
is housed. Replacement air is drawn in through an air intake hood
17 or louvers which rejects rain. A screen 18 prevents birds and
animals from entering the air intake hood. The replacement air is
drawn through inlet filters 19 to remove airborne particulates that
can cause defects in the uncured paint film should they be
deposited thereon.
[0029] The outside air is separated from the process during times
of non-operation by a motorized damper or shutter 20. The location
of the damper or shutter 20 will be a function of where the
building boundary is located with the desire to prevent outside air
from entering the building perimeter when replacement air is not
required. The controls for the replacement air system 11 will
ensure the damper or shutter 20 is full open prior to the need for
replacement air. Preferably, the damper or shutter 20 is of a type
which keeps the static load on the system to a minimum during
operation of the system 11.
[0030] A variable speed fan 21, preferably a tube axial
distribution fan, draws normally cool to cold ambient air through
the hood 17, the filter 19 and the damper or shutter 20 into a
connecting injection chamber 22. In the chamber 22, the replacement
air is blended with a stream of high temperature gas 23 which is
injected into the replacement air flowing through the chamber 22 by
a nozzle mix gas burner 24. Although only one burner 24 is
illustrated, it will be appreciated that a number of burners may be
provided to inject high temperature gas into the chamber 22 to
provide the required BTU's. The BTU energy in the high temperature
gas 23 is controlled by a modulating gas valve 25. Combustion takes
place in the gas burner 24. The gas burner 24 includes a blower 26
which supplies the combustion air and also produces sufficient
pressure to inject the high temperature gas stream 23 into the
chamber 22.
[0031] The variable speed distribution fan 21 pulls the replacement
air through the injection chamber 22 to meet the air volume
requirement of the spray booth 10. The distribution fan 21 also
thoroughly mixes and blends the high temperature air 23 from the
system burner(s) 24 before being discharged into the spray booth
10. A tube axial distribution-fan 21 can be used with this
invention because the static load placed on the system is within
the operation parameters for a tube axial fan. However, the
invention is not limited to its use and would function well with
other forms of air moving devices.
[0032] An optional muffler 27 can be mounted after the distribution
fan 21 to reduce the noise level. If the injection chamber 22 and
the distribution fan 21 were to be located outside the building,
the muffler would also add to the insulation factor of the
interconnecting duct work. Due to the higher frequency noise
generated by a tube axial fan, the noise from a tube axial fan is
easier to attenuate than the noise generated from a blower.
[0033] If only one distribution fan 21 is used in the system 11, a
temperature sensor 28 used for temperature control is located after
the distribution fan. If desired, the distribution fan 21 can be
moved to a location significantly remote from the burner 24 to
improve the overall effectiveness of the air replacement system.
This invention allows the distribution fan(s) 21 to be placed at or
near one or more supply points 29 to a spray booth supply plenum 30
to better control the distribution of the air. The spray booth
supply plenum 30 is connected through filters 31 to deliver clean,
heated replacement air to the work area 12. The prior art
technology forces a single blower to be located close to the burner
because the area between the burner and the blower is under
significant static load. This restriction forces the air to be
pushed down the interconnecting duct work.
[0034] FIG. 2 shows a downdraft paint spray booth 35 incorporating
a heated replacement air system 36 according to a modified
embodiment of the invention. Components in the spray booth 35 and
in the replacement air system 36 which are identical to those in
FIG. 1 are labeled with the same reference numbers. The spray booth
35 is quite large, and may be in excess of 40 feet in length. Such
a spray booth may be used, for example, for painting an automobile
body. Due to the size of the supply plenum 30, replacement air is
delivered through multiple points. Although two supply points 37
and 38 are illustrated, it will be understood that the number of
supply points will depend on the spray booth size and air flow
requirements.
[0035] When multiple discharge points from the air replacement
system are required to service the spray booth replacement air flow
requirements, the splitting of the air from a single centralized
distribution fan such as the fan 21 in FIG. 1 can present problems.
The replacement air system 36 has multiple distribution fans
located at or near the discharge points to the supply plenum. The
chamber 22 is connected to a duct 39, which is shown as splitting
into two ducts 40 and 41. A fan 42 is connected between the duct 40
and is shown mounted in the duct 40 near the discharge point 37 and
a fan 43 is shown mounted in the duct 41 near the discharge point
38. When multiple distribution fans 42, 43 are located remote from
the injection chamber 22, a mixing device 44 must be used to blend
the air to provide a uniform temperature to the air flowing to the
ducts 40 and 41. The temperature sensor 28 is mounted downstream of
the mixing device 44. This mixing device 44 may be, for example, an
arrangement of mixing fins designed to create turbulence to mix the
air without adding significant static load to the system.
Alternately, the mixing device 44 may be an additional fan which
both blends the air and assists in addressing the static load of
the system. While tube axial fans can be used with the system, the
invention is not restricted to the use of any type air moving
device.
[0036] There are also multiple options to inject heat utilizing
this invention. There are different types of burners that can be
applied to this concept. The embodiment of this invention includes
the injection of BTU energy in the form of high temperature air
from sources where the efficiency of the BTU injection will not be
affected by the air volume through the injection chamber. The air
for the self contained burner is a small percentage of the total
volume of air. At designed maximum air volumes the burner for the
typical system will inject less than 5% of the air volume. This air
will be pulled from the area around the nozzle mix burner 24 by a
self contained blower 26 that puts the optimum amount of air
through the burner to achieve an efficient combustion.
[0037] The burners used to inject heat for the system also can be
used with a heat exchanger to allow the system to be converted to
an indirect fired unit to prevent any byproducts of combustion to
be passed into the air stream. This allows the system to
recirculate air in a facility for comfort heat. The conversion from
a direct fired heat mode to an indirect heat mode may be needed
when the area being serviced by the system is a multi-purposed area
such as a tech center or a demonstration area that needs comfort
heat at times and also houses processes that at times require air
to be exhausted from the facility. Rather than having multiple
heating systems the system can be adapted to perform both heating
modes. Due to the efficiency of direct heat and the increased
capability for heat rise with a direct fire burner in the system
the conversion capability has significant benefits.
[0038] FIGS. 3 and 4 show a dual mode heated replacement air system
48 according to a modified embodiment of the invention. The system
48 is shown operated in a direct fired mode in FIG. 3 and is shown
operated in an indirect heat mode in FIG. 4. The system 48 includes
an injection chamber 49 through which replacement air flows. In the
direct fire mode shown in FIG. 3, fresh outside air is drawn
through a screen 50 in a hood 51, through a filter 52 and through
an open damper or shutter 53 into the chamber 49. An indirect heat
exchanger 54 is located in a retracted position, allowing the
replacement air to flow below the indirect heat exchanger 54 where
it is impinged by a hot gaseous jet 55 from a burner 56. The heated
replacement air is then forced by a fan 57 into a duct 58. The fan
57 mixes or blends the air before it flows past a temperature
sensor 59 before it is delivered through a plenum chamber 60 to a
spray booth or other process requiring heated replacement air.
[0039] In the indirect heat mode shown in FIG. 4, the indirect heat
exchanger 54 is moved to extend across the chamber 49 and the
damper or shutter 53 is closed to prevent outside air from entering
the building. A damper 61 is moved to a position which allows
ambient air from inside the building to be drawn into the chamber
49. The fan 57 draws the inside air through the indirect heat
exchanger 54 where it is heated, and delivers the heated air to the
duct 58. The hot gaseous jet 55 from the burner 56 is directed into
the heat exchanger 54 where it indirectly heats the replacement air
flow. The gaseous jet 55 is then exhausted through a vent stack 62
to a location outside of the building. In the indirect heat mode,
combustion production products from the burner 56 do not enter the
spray booth. It will be appreciated that the indirect heat mode may
be operated for heating either interior air or exterior air,
depending on the position of the damper 61.
[0040] If the burner 56 for the system is located outdoors the
blower 63 that supplies combustion air to the burner 56 is enclosed
to protect it from the elements. The combustion air required for
the burners 56 used in the system is filtered separately or the
enclosure 64 that houses the blower 63 that forces the heat into
the air stream is connected to the air inlet chamber after the
filters 65.
[0041] Preferably, the burner used to inject high temperature air
into the replacement air stream is a self contained burner with a
separate blower having the capability of manage flame control as
part of the self contained system. The preferred burner is a known
nozzle-mix burner with a modulating gas valve. These burners are
capable of producing as much as 1 million BTU per foot and work
well under most conditions.
[0042] The nozzle-mix burner also can be used with a digital gas
control valve 66 of the type shown in FIG. 5. The valve 66 has a
gas inlet port 67 which connects to an inlet manifold 68 and a gas
outlet manifold 69 which connects to a gas outlet port 70. The gas
control valve 66 has a plurality of individual open/closed solenoid
operated gas valves connected between the inlet manifold 68 and the
outlet manifold 69, with five valves 71-75 illustrated. A
calibrated orifice is positioned in each flow path between the
inlet manifold 68 and the outlet manifold 69. The orifices control
the gas flow between the manifolds 68 and 69 for each of the valves
71-75. An orifice 76 is shown for limiting the gas flow when the
valve 71 is opened; an orifice 77 is shown for limiting the gas
flow when the valve 72 is opened; and an orifice 78 is shown for
limiting the gas flow when the valve 73 is opened; an orifice 79 is
shown for limiting the gas flow when the valve 74 is opened; and an
orifice 80 is shown for limiting the gas flow when the valve 75 is
opened.
[0043] The orifices 76-80 may be of uniform size. Alternately, the
orifices 76-80 may be calibrated to provide different gas flow
rates to control the burner's BTU output. For example, the orifice
76 may be calibrated to provide a 50,000 BTU burner output, the
orifice 77 may be calibrated to provide a 100,000 BTU burner
output, the orifice 78 may be calibrated to provide a 200,000 BTU
burner output, the orifice 79 may be calibrated to provide a
400,000 BTU burner output, and the orifice 80 may be calibrated to
provide an 800,000 BTU burner output. By selectively opening one or
more of the valves 71-75, the burner output may be controlled in
50,000 BTU increments to inject between 50,000 BTU's and 1,550,000
BTU's of heat to the replacement air flow. Substitution of the
multi-port digital gas control valve 66 in place of the traditional
analog gas valve in the gas line supplying the burner allows a
single burner to provide quick response to changes in air volume to
precisely maintain the set point temperature of replacement air
irrespective of the temperature of the air being drawn into the
system's inlet.
[0044] The multi-port digital gas control valve 66 enables the
system to quickly and independently adjust the temperature during
changes in air volume by pulling the system out of a closed-loop
control and calculating the amount of gas that is needed to reach
the set point temperature based upon the incoming air temperature
and volume flow rate. The initial calculated setting may be the
starting point for the closed loop system when control is given
back to make minor adjustments. The snap action of the multi-port
digital gas control valve 66 allows the volume of replacement air
to change quickly without the significant hysteresis that is caused
by the proportional integral derivative (PID) input device loops of
the traditional analog method. The traditional analog method limits
the transition speeds that can be used when changing the air volume
to prevent out of tolerance temperature swings during times of ramp
up and ramp down in air volume.
[0045] FIGS. 6 and 7 show details of an exemplary self contained
multi-burner unit 86 for injecting heat into a flow of replacement
air to a paint spray booth or other process which requires heated
replacement air. The unit 86 is designed as a stand alone unit
which can be shipped as a unit separate from a spray booth to an
installation site. The unit 86 has four heat injector burner units
87-90 mounted within a housing formed, for example, from sheet
metal side panels 91, top panels 92, bottom panels 93 and an end
panel 94. The end panel 94 has a replacement air outlet opening 95
which is adapted to be connected to ducts leading to the spray
booth (not shown). One or more fans (not shown) for drawing
replacement air through the unit 86 is mounted in the spray booth
ducts. The side panels 91 are shown as including service doors 96
for providing access to the burner units 87-90. A replaceable inlet
air filter 97 is mounted in channels 98 to cover the end of the
unit 86 opposite the outlet opening 95. The unit 86 also includes a
frame structure 99 for supporting the burner units 87-90 and the
panels 91-94.
[0046] The system may have multiple burners of the same size or of
different sizes and of different types to inject heat into the
replacement air. Self contained premix, nozzle mix and venturi
burners along with other known burners that meet the specification
of being self contained units also can be used in the system. In
actual practice, the number and size of the individual burners
depend upon the maximum anticipated heat requirement of the process
the system is supporting.
[0047] Multiple nozzle mix burners can be used where a fixed BTU
rate is provided when the demand for heat was greatest and the
smaller burner is modulated to address fine temperature
adjustments. The turn-down ratio for the nozzle mix burner is rated
at 40:1 so having multiple units where larger burners are required
will allow improved temperature control when low levels of BTU
energy are required.
[0048] For example, in very frigid climates that have sub zero
daytime temperatures, a typical 33,000 cfm unit will have a 4
million BTU burner to produce a 110.degree. F. heat rise which will
bring the -20.degree. F. air up to 90.degree. F. The minimum BTU
level that can be supported by the burner is 100,000 BTU (4
million/40). At 33,000 cfm the temperature rise of 2.8.degree. F.,
but if the air volume is reduce to 25% that heat rise would be
11.2.degree. F. This is most noticeable when the outside
temperature is more moderate. With an outside temperature of
67.degree. F., the minimum air temperature supplied to the process
with the burner at its lowest setting becomes 78.2.degree. F.
(67.degree.+11.2.degree.). The turn down ratio of the in-line
direct fired burners is rated at 30:1 so the low level sensitivity
is worse.
[0049] If the tolerance on air temperature for the process is
tight, the capability of the system to develop finer resolution can
be improved by providing multiple nozzle mix burners. By
incorporating dual 2 million BTU burners where one with a simple
on/off control (the "drone") is engaged at full output once the
maximum of the modulated unit has reached its maximum output.
Better control may be achieved if the drone burner is slightly
smaller than the modulated burner to allow for fine tuning once the
drone burner is turned on.
[0050] Other self contained direct fired burners can be used if
they produce a clean and efficient combustion, so long as the
combustion by-products are not incompatible with the process and
the personnel involved. A 225,000 BTU venturi burner is not the
preferred burner since it does not have a very significant turn
down ratio (2:1 vs 40:1 for the nozzle mix burner) and the injected
air volume injected is triple the air volume injected by a nozzle
mix burner. Multiple venturi style burners which inject heat into
the main air stream also can be used. Instead of modulating them,
they can be turned on in stages based upon the need for heat which
causes a stepped heat rise. The burners may be equal sized, or they
may of differing sizes such as, but not limited to, a binary
progression.
[0051] System controls can be as simple as a heated replacement air
temperature sensor which controls the burner output and a
differential pressure sensor to control the speed of the
distribution fan. This is typical for a manually controlled system
that operated as an air replacement unit which delivers a manually
adjusted amount of air into a facility with a general dump
distribution head to replace air being exhausted by various devices
such as sanding benches, fume hoods, multiple small spray booths
and any other process which exhaust air from the facility.
[0052] The system controls also can be a sophisticated software
driven, microprocessor based system which monitors and controls a
number of primary and ancillary process variables and is programmed
to precisely deliver the right volume of clean, conditioned air, at
the predetermined temperature. It can respond to the demand to
replace the process air being exhausted by the spray booth or any
other high volume air exhausting process.
[0053] A key to the efficiency of the system is its ability to vary
the airflow through the system without changing the products of
combustion. With this capability the spray booth is now able to
control the volume and temperature of air being consumed over a
wide range based upon the requirements of the process. Temperature
conditioning is required on less volume of air and produces
significant energy savings. The advances in technology to vary the
speed of the fans and the increased cost of fuel have caused the
system to become a practical approach to the replacement air
process.
[0054] The system can have multiple modes of operation. Either the
exhausted air volume or the replacement air volume can be set as
the master. The exhaust air volume can be set as the master when
the volume can be applied to the process elements which contaminate
the air. The replacement air volume can be set as the master
maximizing the air flow through the process given the variables in
the replacement air system such as outside temperatures and limits
in fuel available. This mode causes the exhausted air volume to
become slave.
[0055] The most typical operating mode allows the process to
dictate the amount of air required. Changes in the volume of air
can be triggered by the process variables or in response to the
sources that contaminate the air. For example, the exhaust air flow
can be increased while coatings are being applied to a workpiece
and decreased when the coating operation is stopped or a
predetermined time after the coating operation is stopped. Or, the
exhaust air flow rate can be controlled in response to the level of
VOC's in the spray booth air. While monitoring specific process
variables and using these as drivers for safety interlocks and/or
as the stimuli to adjust the overall replacement air flow, the
system uses these inputs to automatically optimize the performance
of the entire system including the process it is serving. The
invention focuses upon the requirements of the process with regard
to the safe and effective levels for each aspect of the process and
develops methods to determine when those processes take place.
[0056] When looking at the painting process, typical modes are
idle, prep, low speed paint, high speed paint, low temperature
cure, high temperature cure and cool down. The most significant
energy savings from the system over prior art systems is in the
idle, prep, low speed paint and low temperature cure modes. A focus
of the system is to allow a reduction in the total volume of air
that is exhausted per day, which in turn reduces the energy needed
to heat replacement air.
[0057] The idle mode is used to start the unit and to operate after
a low temperature cure. The BTU's of heat delivered to the
replacement air may be set, for example, to about 15-25% of the
normal operating level. In the prep mode, the BTU's may be
adjustable, for example, over a range of 25-40% of the normal
operating level, and in the low temperature cure mode the BTU's may
be adjustable, for example, in the range of 40-60%. It will be
appreciated that the replacement air flow rate and the BTU's
applied to the replacement air for different operating modes can be
adjusted as needed.
[0058] In any climate that requires temperature or humidity
controls, the benefits of the heat injector can be seen. When the
cost of replacement air is not a factor due to temperate outside,
the system will still have a benefit because the amount of air
moved through the system, even without temperature conditioning,
will have an affect upon the amount of electrical energy used. In
these climates, the addition of an evaporative cooler option might
prove to be a benefit. The option to cool the air by utilizing
evaporative cooling panels is possible with the reduced static of
the system. The same climates that need heat in the winter could
use evaporative cooling in the summer. Evaporative cooling coils
for dehumidifying and/or cooling the air can be placed immediately
after the inlet filters and before the heat injector.
[0059] Commercial benefits of the different embodiments of the
invention, provide one or more of the following:
[0060] Only as much make up air is supplied as the process actually
needs. The unique design of the system enables it to deliver only
as much replacement air as the process is actually discharging.
Therefore, a single system can serve a facility equipped with
multiple spray booths, economically responding to the varying load
as individual spray booths are brought on-line or taken off-line
without compromising the system's combustion efficiency of the
system and without either over or under ventilating the
process.
[0061] Cold start conditions are nearly eliminated. Burner safety
regulations require the presence of combustion air before the fuel
is turn on. Since traditional direct fired air make-up units use
the same air mover to supply both the combustion air and the
replacement air, they require a flow of cold air at full volume
before the burners can be ignited. When the incoming replacement
air temperature is low, this results in significant volumes of
uncomfortable cold air being dumped into the process area every
time the system is started. To avoid this start-up chill, operating
personnel keep their air make-up units operating during down
periods, thereby wasting significant quantities of power and fuel.
The combustion air, which is typically 10% or less of the
replacement air volume, is separate from the replacement air. The
primary air mover does not need to be energized until the burner is
fired and producing warm replacement air.
[0062] Electrical power consumption is reduced. Since the burners
are located outside the primary air passage, the internal pressure
drop is a fraction of the pressure drop of a traditional direct
fired air make-up unit. The system can deliver a comparable volume
of air with significantly less (approximately 30-50% less)
horsepower, resulting in a significant savings in electrical power
consumption.
[0063] A typical 15,000 CFM prior art air make-up unit requires a
10 HP motor. Due to its unrestricted air passage, a system
according to the invention of the same capacity only requires a 5
HP motor to move the air plus a fractional horsepower motor to
provide combustion air for each burner. The average annual savings
in electrical power due to the reduction in motor horsepower alone
can exceed 40%.
[0064] Energy consumption during non-spray operations is
significantly reduced. In installations where a single spray booth
has a dedicated air make-up unit, the variable volume air supply
makes it possible to add a properly sized, variable frequency motor
controller to the spray booth's exhaust fan. This allows the entire
air replacement/ventilating system to be programmed to exhaust the
normal required volume of exhaust air during the spraying and
flash-off operations. The exhaust air volume can be stepped down to
a substantially lower level during non-regulated activities such as
the time when the parts are being prepared for painting, while the
paint is being prepared, while the equipment is being set-up or
maintained, during break periods and during the cure cycle, thereby
achieving significant savings in both electrical power and heating
fuel.
[0065] Better temperature control when outside temperatures are
moderate: While a traditional constant volume air make-up unit
typically includes a modulated gas valve, the inherent design of
the air make-up unit does not allow for a good gas flow at low
settings. Units sized to provide the typical 70.degree. or
90.degree. F. temperature raise required in colder locations have
difficulty maintaining the desired output temperature when the
outside temperature is more moderate and the unit has to repeatedly
toggle on and off. Consequently, the replacement air tends to be
either too hot or too cold. The multiple burner option of the
invention and its focus to treat the BTU energy separate from the
air volume required for the process allows a better adjustment
irrespective of the temperature of the incoming air.
[0066] Coating transfer efficiency can be safely maximized by
optimizing air flow for each discrete finishing operation conducted
within a spray booth. The system enables the spray booth
ventilation to be tuned to safely maximize the overall transfer
efficiency for the finishing process. The savings associated with
the reduction in coating consumption associated with a 10% increase
in the finishing transfer efficiency can conservatively exceed
$10,000 per year for each production spray booth.
[0067] The control system for such a system or spray booth system
can be equipped with VOC and/or LEL sensors that will automatically
increase the exhaust air flow if it detects the higher than desired
concentrations of gaseous and/or particulates within the process.
When the concentrations decrease or when the finishing process is
taken off-line, the exhaust air volume can be automatically
reduced.
[0068] Airflow can be optimized at any given temperature setting.
When the incoming air temperature drops below its designed
temperature rise range, a traditional air make-up unit system will
deliver replacement air at a temperature below the desired process
set point. Under these circumstances the thermal load of the fixed
air delivery volume is beyond the burner's capacity. Users have two
options, neither of which is good. They can suspend operations
until the outdoor temperature moderates, or they can operate with
the process below the desired temperature. The system has the
ability to produce the maximum air volume at the set point without
compromising the burner's combustion efficiency.
[0069] Some traditional air make-up units are built with a dual air
velocity feature to facilitate spraying and curing in a single
location. In the spraying mode, the air make-up unit delivers its
rated airflow at a predetermined temperature, usually 70.degree. F.
In the curing mode, the air flow rate is reduced to a fraction of
the spraying, while the temperature set point will be
proportionally higher, typically in the 125-150.degree. F. range.
The clean burn characteristics are lost at this point because the
required airflow across the burner has been significantly reduced.
A colder than normal ambient temperature can also be a problem in
the curing mode even with the reduced air flow. The unit may have
enough capacity for the painting process, but not enough capacity
to achieve the desired cure temperature. The system can be
programmed to reduce the airflow to a level within the unit's
capacity to achieve the programmed cure temperature within the
process area. Again, this can be done without jeopardizing the
minimum airflow requirements of the burner.
[0070] The system's variable volume capability enables it to handle
these out of tolerance situations well and provides process
advantages that are not currently available. The system gives the
operator the ability to control the curing cycle by further turning
up the thermostat set point and simultaneously lowering the volume
of process air or increasing the airflow at a reduced set point.
The system provides the optimum control for flashing off and then
curing sensitive waterborne coatings.
[0071] The design can facilitate automatic conversion between
direct and indirect heat transfer. The system is ideally suited to
processes that require large volumes of heated replacement air at
times and require an indirect air heater recirculated heat source
at other times. A typical application would be a plant or lab area
with open face spray booths. In this situation, the direct fired
burner is used when the outside replacement air is required and the
indirect fired unit is used when the exhaust dampers close to
recycle the exhaust air within the process.
[0072] This unit also can be used in a continual state as a
recirculated burner. It can be configured to operate in a direct
fired mode allowing the process area to be quickly and efficiently
heated, then, when the area is nearly up to temperature and the
burner is normally turned down, the system is switched to the
indirect fired mode to isolate the process area from the buildup of
harmful by-products of combustion.
[0073] The system allows the process area to be brought up to
temperature quickly by utilizing the high efficiency and the clean
burn of the direct fired burner at its normal high gas flow. Once
the space has reached the desired temperature, the burner controls
can be programmed to be automatically turned down to reduce the air
flow, and to automatically convert to an indirect heat source to
maintain the temperature by injecting the heat into the process
through a heat exchanger. This will prevent injecting any harmful
combustion by-products at the lower burner levels. This capability
provides the advantages of both a direct and an indirect fired
burner, while eliminating the disadvantages of each. The system's
dual-mode option provides significant energy efficiency gains and
eliminates the need to purchase dual heating systems with the
expense of multiple building penetrations and gas lines.
[0074] The indirect option also allows the system to be used as a
post-heater in a humidity controlled system. When humidity control
is required, the system in the indirect heating mode can be added
downstream of the cooling coils to act as a post-heater to bring
the super chilled air back to the desired temperature set point. In
the indirect heat mode, the burner combustion byproduct gases are
isolated from the process air stream and cannot add moisture to
it.
[0075] During the heating season, the system operates in the direct
fired mode. This is the most energy efficient mode and the direct
fired combustion will increase the process air's humidity, reducing
the amount of additional moisture required to bring it up to the
required relative humidity level. The direct fired burner can be
downstream of the cooling coils because any escaped gas from the
cooling coils will not be exposed to the burner flame.
[0076] Overall reduction in capital costs: The system is
significantly lighter than the comparable air make-up unit it
replaces. Typically the electric motor is half the horsepower size
of that of an equivalent sized traditional unit. The air supply fan
is correspondingly smaller than the traditional air make-up unit.
The substantial weight of the traditional air make-up unit often
requires the construction and installation of a costly steel
reinforced supporting structure.
[0077] The modular nature of the system allows the replacement air
unit to be broken into segments to provide greater flexibility in
where components are located and sometimes in eliminating the need
to have an expensive crane to set it in place. This flexibility can
also simplify ductwork as well as make it more convenient to
service.
[0078] Modularity facilitates combining with other process air
condition technologies: The modular design of the system is
adaptable for use with a variety of heat sources such as steam and
the heat thrown off by environmental emissions abatement systems
and thermal oxidizers. Heated air from these sources of energy can
be injected into the air stream as the only source of BTU energy,
or to augment a gas fired burner. Since the heat source is not in
the middle of the air stream, the system can safely and easily be
coupled with an evaporative cooler, a dehumidification chiller or
any other air conditioning device or system.
[0079] It will be appreciated that various modifications and
changes may be made to the above described preferred embodiment of
a heated replacement air system without departing from the scope of
the following claims.
* * * * *