Air conditioning apparatus and method for paint spray booths

An air conditioning system is disclosed for adjusting air temperature and humidity to a predetermined level for the air supply to a paint spray booth. The system includes a multi-section sprayed surface heat exchanger combined with a bypass passage such that a portion of the air flow to be conditioned passes through the multi-section heat exchanger and the remainder of the flow bypasses the same, and is recombined and mixed downstream with the conditioned air to produce a mixture which is at the proper dry bulb temperature and relative humidity. Each multisection heat exchanger may be shut off to increase the proportion of bypass flow. Modulation of the cooling and heating effect of each of the heat exchangers is achieved by modulating valve controlling the flow of heating or cooling medium. Similarly, the humidification effect is controlled by valving controlling a number of water spray nozzles. The system is integrated into an energy conserving system which utilizes the recovered energy from the conditioned air after passing through the spray booth and from other low grade heat energy sources.

TECHNICAL FIELD 
This invention concerns air conditioning systems and more particularly air 
conditioning systems for controlling the humidity and temperature of air 
supplied to paint spray booths. 
BACKGROUND ART 
It is often necessary in industrial and other applications to supply an air 
flow at relatively closely controlled humidity and temperature conditions. 
One such application is in the supply of air to paint spray booths wherein 
water-based paints are to be applied. Such processes typically require a 
75.degree. F. dry bulb air temperature and 50% relative humidity, i.e., 
55.degree. F. wet bulb temperature. 
The use of such water-based paints in such applications as automotive paint 
spraying has become more widespread due to the lessening of the pollution 
problems associated with hydrocarbon solvent-based painting operations. 
Such controlling of temperature and humidity has heretofore required 
relatively extravagant expenditures of energy. For example, if the air 
temperature in the summertime is at a higher temperature than required, 
and if the moisture content is also above the required level (as would 
typically be the case for summertime weather conditions), both the 
temperature and moisture content of the air must be reduced. If such 
moisture is removed mechanically, i.e., by passing such air through a heat 
exchanger where it is chilled to the appropriate dew point, i.e., 
55.degree. F. as per the example given, the air flow must then be reheated 
to the required 75.degree. F. dry bulb temperature. 
Given the enormous volumes of air flow which must be conditioned for 
typical automotive paint spraying installations, i.e., of the order of 
100,000 CFM for each 10 foot length of spray booth, such energy 
expenditures become truly significant. 
For humidifying, moisture may readily be added to flowing air mass by the 
use of high efficiency spray nozzles directed over a heat exchanger in 
which the air can be saturated, i.e., to 100% relative humidity. It is 
difficult however to control humidification by this process at lower 
levels, i.e., to 50% relative humidity. 
Such addition of moisture to the air generally produces an evaporative 
cooling of the air mass such that dry bulb temperature may be below the 
required temperature after humidifying, thus requiring reheating. 
There has heretofore been proposed and practiced dehumidification processes 
which do not cool the total air mass to the required dew point in the 
interest of achieving improved efficiency. In such process, a portion of 
the air flow is bypassed around the cooling coils such that only a portion 
of the air flow is cooled to a lower dew point temperature. This air mass 
thus is reduced to a lesser humidity level than required such that upon 
remixing with the bypass air flow, the combined mixture of the air flow is 
at the appropriate humidity and temperature condition. 
Air conditioning systems of this type typically must accommodate great 
temperature and humidity variations in the ambient air, and the degree of 
modulation of the bypass air flow must be relatively great in order to 
achieve the final controlled air condition. The necessity of a relatively 
large modulation of the bypass air flow volume necessitates a complex 
damper system associated with the cooling coils and the bypass passage and 
greatly increases the bulk of the necessary ducting. 
Also, the air flow characteristics of the system are difficult to properly 
balance particularly for high volume systems due to the flow resistance of 
the cooling coils. 
For similar reasons, it is difficult to properly control the damper system 
modulation such as to closely and stably control the conditioned air flow 
if large variations in flow across the heat exchangers is required. 
In many of these systems, it is difficult to achieve an accurately 
controlled humidification-dehumidification, cooling-heating process such 
that subsequent reheating is not required. 
Such bypass flow arrangements must insure complete mixing of the bypass air 
with the conditioned air such as to avoid stratification in which 
different points within the air mass are at different humidity and 
temperature levels. 
The present inventor's prior U.S. Pat. Nos. 4,173,125 ("Energy Recovery 
System") and 4,173,924 ("Paint Spray Booth With Air Supply System") 
disclose arrangements whereby relatively low grade heat energy may be 
recovered and utilized in air conditioning processes, in the interest of 
improving the overall efficiency of industrial processes. It is of course 
advantageous if any such air conditioning apparatus could utilize low 
grade energy heat source, or the energy value represented by exhausted 
cooled air, to enhance the efficiency of the conditioning process. 
Accordingly, it is an object of the present invention to provide a method 
and apparatus of conditioning air to predetermined temperature and 
humidification levels which is highly efficient in the usage of energy in 
achieving such controlled levels. 
It is yet another object of the present invention to provide such method 
and apparatus in which predetermined dry bulb temperature levels are 
achieved with a minimal amount of reheating of the air flow after 
mechanical dehumidification. 
It is still another object of the present invention to provide a sprayed 
surface cooling-heating coil arrangement for carrying out the 
humidification-dehumidification and heating-cooling of the air flow in 
which the final humidity and temperature levels can be closely controlled. 
It is yet another object of the present invention to provide a sprayed coil 
arrangement for humidification-dehumidification and cooling-heating of the 
air mass combined with a bypass flow damper for remixing unaltered air to 
achieve a given humidity and temperature level, in which the portion of 
damper controlled bypass flow necessary to achieve a given final condition 
is minimized. 
It is still another object of the present invention to provide such sprayed 
coil humidification-dehumidification and heating-cooling of an air mass 
flowing therethrough with minimal bypass flow modulation necessary in 
order to accommodate varying ambient air temperature and humidity levels. 
It is still another object of the present invention to provide a bypass 
ducting arrangement in which thorough mixing of the air passing through 
the heat exchanger and the bypass passage are intimately mixed to provide 
a homogeneous conditioned air mass at appropriate temperature and humidity 
levels. 
It is still another object of the present invention to provide such method 
and apparatus for achieving controlled humidity and temperature levels in 
which low grade energy recovered from waste heat sources and/or the energy 
value in cooled air to be rejected to the atmosphere are efficiently 
utilized in the conditioning process. 
It is still a further object of the present invention to provide an air 
supply system for a paint spray booth in which ambient air either under 
summertime or wintertime conditions can be conditioned to appropriate 
temperature and humidity levels in a highly efficient manner, with a 
minimum of plant equipment. 
SUMMARY OF THE INVENTION 
These and other objects of the present invention, which will become 
apparent upon a reading of the following specification and claims, are 
achieved by the use of air conditioning apparatus including a sprayed 
surface multi-section heat exchanger through which at least a portion of 
the air flow to be conditioned is directed. Each of the heat exchanger 
sections are provided with a modulated flow of heating-cooling heat 
transfer medium to transfer heat into or out of the air flow to establish 
the capability of dehumidifying the air by chilling the air mass to the 
appropriate dew point. This also affords the capability of accurately 
adjusting the air flow temperature to achieve a given final dry bulb 
temperature. 
A bypass flow duct is also provided in which a modulated portion of the 
total air flow may bypass the heat exchanger which is remixed with the 
mass of air flow passing through the coil such that a combined mixture of 
air mass will be at the appropriate humidity and dry bulb temperature 
levels. 
The heat exchanger comprises a plurality of heat exchanger sections 
arranged in banks, each section adapted to be independently turned off 
through the use of three-way valves controlling the flow of warmed or 
cooled heat transfer medium therethrough such as to enable increased 
proportions of unconditioned or bypass air mass flow. 
Thus, the air bypass technique may be utilized which requires only 
relatively small bypass ducting with only a damper control over the bypass 
ducting flow, with substantially unaltered direct flow through the heat 
exchanger. This reduces the bulk of the plant required and minimizes the 
difficulties encountered in attempting to vary substantially the air flow 
through the heat exchanger. 
An array of water spray nozzles is mounted upstream of the heat exchanger 
and across the face thereof to direct water spray onto the surface of the 
heat exchanger sections. The spray nozzles array is arranged in a 
manifolding system with independently controlled shut-off valves in order 
to control the degree of humidification as necessary. Combined with the 
modulation of the temperature of the air passing through the heat 
exchanger section and the proportion of bypass flow, the final condition 
of the remixed air mass may be closely controlled with minimum, if any, 
heating required depending on the incoming air condition. 
The heat exchanger sections are integrated with an energy recovery system 
and also with a preheating and reheating heat exchanger positioned 
upstream and downstream, respectively, of the air conditioning heat 
exchanger such as to efficiently utilize low grade heat recovered from 
waste heat energy sources and also to utilize the energy value of cooled 
air to be exhausted. 
The air conditioning apparatus is incorporated into a supply system for a 
paint spray booth in which air passes through the spray booth and is 
filtered and thence passes through a heat recovery coil in the booth 
exhaust to recover either the heat energy contained in the exhausted air 
or to recover the energy value represented by the cooled air in the event 
that ambient temperature is above the spray booth supply conditions. 
The bypass air flow is remixed into the main air mass through a 
distribution ducting and a series of high velocity jetting nozzles which 
insure complete mixing of the bypassed air into the conditioned air to 
achieve a homogeneous air mass. 
A control system is provided in which the bypass dampers, the spray nozzle 
shut-off valves, the heat exchanger modulating valve, section shut-off and 
the preheater and reheater are all controlled to produce a predetermined 
final dry bulb temperature and humidity level for varying ambient or inlet 
air states so as to efficiently supply air to a paint spray booth. 
DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a diagrammatic representation of an air conditioning system for a 
paint spray booth air supply utilizing an air conditioner apparatus 
according to the present invention. 
FIG. 2 is a detailed diagrammatic representation of the air conditioner 
utilized in the system depicted in FIG. 1. 
FIG. 3 is a perspective view of an air conditioning apparatus of the type 
depicted diagrammatically in FIG. 1. 
FIG. 4 is a diagrammatic representation of the system depicted in FIG. 1 
depicting the control and sensor signals utilized to control the air 
conditioning system as applied to the supply of air to a paint spray 
booth.

DETAILED DESCRIPTION 
In the following detailed description, certain specific terminology will be 
employed for the sake of clarity and a particular embodiment described in 
accordance with the requirements of 35 USC 112, but it is to be understood 
that the same is not intended to be limiting and should not be so 
construed inasmuch as the invention is capable of taking many forms and 
variations within the scope of the appended claims. 
Referring to the drawings and particularly FIG. 1, a diagrammatic 
representation of the overall system is depicted. Such air conditioning 
system is indicated at 10 and is associated with an enclosure, depicted as 
a paint spray booth 12, within which paint spraying operations are to be 
conducted as in the production of automotive car bodies. 
In U.S. Pat. No. 4,173,924, a particular paint spray booth 12 design is 
disclosed of the same general type as that disclosed in U.S. Ser. No. 
851,253, filed Nov. 14, 1977, and assigned to the same assignee as the 
present application. 
This is advantageously combined with the present air conditioning system 
inasmuch as a high efficiency filtration system is incorporated which 
enables the exhaust air flow indicated at 14 to be substantially free from 
overspray paint solids. 
Accordingly, the exhaust flow created by means of an exhaust fan 16 may be 
passed through a heat recovery exchanger 18 disposed in the exhaust 
ducting to extract energy from the air prior to exhausting to the 
atmosphere. 
This heat energy may take the form of heat removed from the exhaust air 
flow prior to exhaust to the outside or may be that energy corresponding 
to that of cooled air prior to its exhaust to warmer ambient temperatures, 
as described more fully in aforementioned U.S. Pat. No. 4,173,924. 
Such filtration system includes a flooded floor pan 13 and exit tubes 15 
through which are caused to be circulated a vortical flow of water to 
produce a "scrubbing" of the exhaust air in a manner more completely 
described in the aforementioned patent application. 
Referring to the air conditioning system 10, this system includes an air 
intake housing 20 positioned to receive air intake from the ambient 
outside air through stack 22 and into a plenum chamber 24. 
Alternatively or additionally, the air supply for the system may be 
pretreated air, i.e., air received from some other source than ambient 
outside conditions to the supply duct 25. Dampers and controllers 28 and 
30 are provided, respectively, to control the air flow into the plenum 
chamber 24. 
The air conditioning system 10 is intended for application to the 
conditioning of air under typical wintertime or summertime conditions, as 
well as intermediate seasonal conditions such that provision is made for 
increasing the temperature of subzero outside air to a temperature 
condition in excess of freezing. 
For such heating, a direct gas-fired preheater 32 is provided comprising an 
array of burners disposed directly in the inlet ducting 34. Such 
preheaters may be of conventional design and are activated whenever the 
outside air temperature declines below the capacity of other heater means 
in the system to be described. 
For moderately low temperatures, preheating means may be provided by a heat 
exchanger 36 through which is caused to circulate warmed water or ethylene 
glycol as by means of a pump 38. Such circulation is under the control of 
a suitable modulating valve 40. 
The energy source for heating such circulated fluid may advantageously be 
provided by an energy recovery system generally indicated at 42. Such 
energy recovery system is preferably of the type disclosed in U.S. Pat. 
No. 4,173,924 in which heat energy is recovered from the air exhausted 
from the paint spray booth 12, the heat recovery means also including the 
heat recovery exchanger 18 which is operatively associated with the 
evaporator and condenser of a mechanical refrigeration unit (not shown) 
such as to enable efficient transfer of heat energy from the exhausting 
air into such circulated fluid. 
A similar but more generalized application system is disclosed in U.S. Pat. 
No. 4,172,125 wherein heat is recovered from various industrial processes 
or other sources of waste heat which typically exist around an industrial 
plant. Such heat energy is likewise caused to be collected and efficiently 
utilized through heat transfer arrangements associated with mechanical 
refrigerator and evaporator and condensing coils of such units. 
The disclosures of the aforementioned patents are hereby incorporated by 
reference into the present specification inasmuch as such energy recovery 
systems are, as noted, preferably employed as the energy recovery system 
indicated at 42 in FIG. 1. 
Downstream of preheating heat exchanger 36 is air conditioning apparatus 44 
according to the present invention in which moisture is added or removed 
from the air mass flowing therethrough to achieve the required level and 
in which the temperature of the air mass is adjusted to the required 
conditions with minimum expenditure of energy required for subsequent 
reheating. 
The air conditioning apparatus 44 includes a multi-section heat exchanger 
45 including sections 46, 48 and 50 contemplated as fin-on-tube coils, 
each adapted to receive a portion of the air mass flowing through the 
ducting 52. 
Arrayed across the front face of the heat exchangers is a series of spray 
nozzles 54, adapted to add moisture so as to saturate the air flow passing 
through the multi-section coil 46. A circulating pump 56 causes water 
disposed in a drain pan 58 to be circulated and thence recollected after 
draining from the respective coil surfaces. A water supply system, not 
shown, adds water as needed to the drain pan 58. 
A portion of the air mass flowing in ducting 52 is caused to be passed 
through a bypass flow ducting 60, which receives a relatively minor 
portion, i.e., on the order of 25%, of the total air flow flowing through 
the ducting 52. A damper and controller 62 are provided to modulate the 
precise volume of air flowing through the bypass flow ducting 60. 
The air is remixed in the ducting 64 immediately downstream of the air 
conditioner apparatus 44 to produce a mixture at or close to the final 
humidity and temperature conditions to be achieved. 
A reheat exchanger 66 is also provided which adjusts the final dry bulb 
temperature of the air mass as necessary after passing through the air 
conditioning apparatus 44. 
If such reheating is required due to operating conditions, the reheat 
exchanger 66 is provided with warm water or other heat transfer medium 
circulated in lines 68 and 70 with a circulating pump 72 provided in the 
modulating valve 74 controlling the precise quantity of liquid in order to 
precisely control the temperature of the air mass exiting through the 
reheat exchanger 66 at the predetermined controlled temperature level. 
Since such temperatures are relatively moderate, it is likewise 
contemplated that the heat energy required would be supplied by an energy 
recovery system 42 of the type described above. 
A filter 76 is provided immediately upstream of the paint spray booth 12 in 
order to remove any solid or liquid contaminants which are suspended in 
the air mass. 
A supply fan 78 is provided drawing flow into the ducting 52 and the 
various conditioning apparatus, and thence into a plenum 80 above the 
ceiling of the paint spray booth 12. 
A supply damper and controller 82 are provided in order to control the 
volume of air flow in the chamber to the system requirements. 
Referring to FIG. 2, the details of the air conditioning apparatus 44 are 
depicted. This typically includes three sections of heat exchangers 46, 48 
and 50 disposed to intercept respective portions of the air flow passing 
through the ducting 52. Disposed upstream of each section of the heat 
exchangers 46, 48 and 50 are corresponding groups of spray nozzles 54 
including respective groups 84, 86 and 88 positioned so as to direct a 
spray onto the front face of each of the heat exchanger sections. Each 
spray nozzle group includes individual spray nozzles 90 located in a 
pattern such as to cover the area of the heat exchanger sections 46, 48 
and 50 in a density of approximately one per square foot of the cross 
sectional area. 
Each of the spray nozzles 90 is controlled with solenoid operated shut-off 
valves 92 such as to allow individual control of water flow to the spray 
nozzles 90. 
Water under pressure is provided via the circulating pump 94 drawing water 
from drain tank 96 pressurizing main lines 98 and feeder lines 100 which 
in turn feed branch lines 102 supplying each of the passages 104 
connecting the shut-off valves 92 and spray nozzles 90. 
The run-off from the heat exchanger sections 46, 48 and 50 is captured in 
drain trays 106 which cascade through a drain arrangement to return the 
run-off to the drain tank 96. 
In order to control the proportion of air flow which is humidified, the 
shut-off valves 92 are operated by a system controller to modulate or 
discontinue the addition of moisture to a corresponding proportion of the 
air flow. Each of the heat exchanger sections 46, 48 and 50 is supplied 
with the heated or cooled heat transfer media such as brine via a 
circulation pump 108 receiving a supply of such liquid through line 110 
and modulating valve 112. 
Modulating valve 112 provides a means for controlling the fluid temperature 
supplied to an outlet line 114 of circulation pump 108. The regulation of 
fluid temperature controls the degree of heat transferred into or out of 
the air flow passing across the heat exchanger sections 46, 48 and 50 such 
as to provide relatively precise degree of modulation. 
Outlet line 114 supplies the inlet line of each of the heat exchanger 
sections 46, 48 and 50 through three-way valves 116 which enable bypass of 
the heat transfer media flow through bypass passages 118 connected to the 
outlet passages 120 of each of the respective heat exchanger sections 46, 
48 and 50, each connected to main return line 122. 
Thus, the heating or cooling of each section may be discontinued to 
effectively increase the bypass flow proportion without affecting the air 
flow therethrough. The step-by-step control afforded by the multi-section 
construction of the heat exchanger 45 also affords an additional level of 
temperature control over that afforded by the modulating valve 112. 
Thus, while only a relatively modest degree of bypass air flow through the 
bypass flow ducting 60 is required with only minor modulation thereof by 
the damper and controller 62, a high degree of continuous control over the 
humidity and temperature levels of the air mass flowing therethrough is 
afforded in a highly efficient manner by the control over the conditioning 
activity carried out in the air conditioning apparatus 44. 
If the air is too humid, mechanical dehumidification is achieved by 
chilling the air mass below its dew point and condensing out a required 
amount of moisture. However, the air mass must be chilled from the 
incoming temperature to the dew point temperature before condensation 
begins to occur and conventionally the entire mass is chilled to this 
level which must be reheated to the appropriate dry bulb temperature. 
If, however, as with the described apparatus, only a portion of the air 
mass is chilled to an appropriately lower dew point, upon remixing with 
the bypassed air, the proper humidity level of the total air mass may be 
achieved. 
An increase in efficiency of the process is thus realized since only a 
portion of the air must be chilled from its incoming temperature to a dew 
point temperature. The degree of chilling required to condense out the 
required weight of moisture would be the same in either case. 
In executing the sprayed surface humidification process, it is relatively 
easy to saturate the air mass to 100% relative humidity. 
However, it is difficult to control such humidification process so as to 
reach some intermediate level, i.e., such as 50% relative humidity. 
However, by utilizing the bypass flow ducting 60, it is possible to 
totally saturate the air mass flowing through the air conditioning 
apparatus 44 and thence recombining the air flow with the bypassed air 
flow which is at a higher temperature and lower humidity to yield a 
mixture of the correct relative humidity, i.e., 50%, and dry bulb 
temperature, i.e., 75.degree. F. 
While the bypass flow ducting 60 itself controls only a relatively minor 
volume of air flow, by utilizing the shut-off valves 92 as described 
above, as well as the shut-off of the bypass valves of the heat exchanger 
sections 46, 48 and 50, an increased bypass proportion can be achieved 
without the necessity for shifting large volumes of air flow from flowing 
through the heat exchanger sections. 
That is, a portion of the flow through each heat exchanger section may in 
effect become a bypass air flow and thus a relatively large proportion of 
the flow can be "bypassed" without flowing through the bypass ducting. 
It can be appreciated that the various controlled components of this 
apparatus afford a great deal of flexibility in achieving given 
temperature and humidity levels. That is, by controlling the incoming air 
temperature by a preheater and varying a proportion of air bypassed into 
the bypass passage or to an activated heat exchanger section, by 
modulating the temperature of the incoming liquid to the heat exchanger 
sections, by control of the nozzle sprays, and by the use of a reheater to 
adjust the final dry bulb temperature, the air supplied to the paint spray 
booth 12 may be controlled in a most efficient manner. 
For example, taking wintertime operation, the air may be heated in the 
preheater 32 or preheat heat exchanger 36 to a temperature in excess of 
32.degree. F. Thence, the bypass damper in activation causes all the air 
flow to pass through the conditioning apparatus 44 wherein the air is 
saturated with the spray nozzles 54. 
At the same time, while circulating warm liquid of an appropriate 
temperature in the heat exchanger 45, this temperature may be increased to 
the appropriate dew point, i.e., in this case 55.degree. F., such that 
there exists 100% relative humidity and 55.degree. F. dry bulb conditions. 
Thence, by being passed through the reheat exchanger 66, an increase to the 
appropriate dry bulb temperature, i.e., 75.degree. F., is achieved. 
In some conditions, it may be possible to entirely eliminate the use of the 
reheater in the interest of improving efficiency. 
Accordingly, if the incoming air is heated to 88.degree. F. presuming the 
ambient air to be at a humidity corresponding to 44.degree. F. dew point 
by controlling the shut-off valves 92 and damper and controller 62, 
one-half of the air may be caused to pass through the air conditioning 
apparatus 44 unconditioned. 
The other half of the air is thus passed through the sprayed sections of 
the heat exchanger sections. This proportion of the air flow will become 
saturated and reduced in temperature due to the evaporative cooling 
effect. Upon remixing downstream thereof, the resultant mixture will be at 
the required 75.degree. F. dry bulb temperature and 50% relative humidity. 
Referring to FIG. 3, an actual physical arrangement of heat exchanger 
sections, spray nozzles and bypass ducting is shown. In this arrangement, 
four sections of the heat exchanger are provided, one half of each section 
arranged on either side of centrally located bypass ducting 124. Each heat 
exchanger section is comprised of a coil, 126, 128, 130 and 132, of a 
fin-on-tube design of conventional configuration adapted to receive 
heating or cooling liquid via inlet lines, one of which is shown for coil 
126 at 134 with a return line 136 receiving the circulated fluid for 
return to the energy recovery system. 
Each coil is provided with independently operated three-way valves 138 
which enables bypassing of heat transfer media through each of the 
individual coils 126, 128, 130 and 132 as described above. 
A modulating valve is also located upstream of the inlet supply 140 to 
control the temperature of the heat transfer liquid to in turn control the 
heating or cooling effect on the air passed through the respective coils 
126, 128, 130 and 132. 
Also provided is a grouping of spray nozzles 142, arranged uniformly across 
the upstream face of each of the coils 126, 128, 130 and 132, each 
receiving water via cross tubes 144 supplied via the supply manifold line 
146 with intermediate shut-off valves 148 provided to enable shut-off of 
the nozzles associated with each of the sections of the coils 126, 128, 
130 and 132. 
A circulating pump 15 is shown having an inlet 152 communicating with a 
drain pan 154 positioned beneath each of the coils. 
Flow through the bypass ducting 124 is controlled by a series of flap 
dampers, one of which shown at 156, to control the proportion of flow 
bypassing the coils entirely. 
On the leaving face of each of the coils, the bypass air is adapted to be 
remixed with the air passing through each of the coils 126, 128, 130 and 
132. As described above, preferably this is accomplished by a series of 
jet nozzles 158 located such as to direct the bypass flow into the air 
mass exiting the coil sections as shown. 
The bypass flow velocity is thereby increased to relatively high rates of 
flow, i.e., on the order of 4000 feet per minute, in order to produce 
thorough remixing of the bypass air and mixing of the air exiting coil 
sections which have been shut-off with air flowing through coil sections 
which have caused humidifying, cooling or heating of the air passing 
therethrough. 
The cross flow direction of the jets and the mixing induced by the jetting 
flow pattern insures thorough mixing thereof in order to produce a 
homogeneous air mass of appropriate humidity and temperature levels. 
Referring to FIG. 4, an overall control system arrangement is depicted in 
diagrammatic form. A microprocessor or other suitable central controller 
160 is provided which receives wet and dry bulb sensor signals from the 
ambient sensors 162 and 164, as well as the supply wet and dry bulb 
sensors 166 and 168. In the event an energy recovery system 42 is utilized 
as a source of energy, available heat signals will also be processed in 
the central controller 160. 
These signals are processed to cause the various controlled components to 
be operated in a mode in which optimum efficiency is achieved. That is, 
control of the preheater 32, the preheat heat exchanger 36, the air 
conditioning apparatus 44 and the reheater 66 are all controlled in order 
to insure a supply of air to the paint spray booth 12 with optimum 
efficiency for the particular operating conditions.