Abstract:
A bus air conditioning system with at least one air conditioning module installed on a bus roof The air conditioning system having a pair of supply air openings for conducting the flow of conditioned air downwardly near the outer side of the roof and a return air opening whose position may vary substantially in the lateral direction from a longitudinal central axis of the bus for any given installation. The air conditioning system including a refrigeration circuit for circulating refrigerant serially through a compressor, a condenser coil, an expansion valve and an evaporator coil. The air conditioning system further including an evaporator section including an evaporator blower for causing return air to flow from said return air opening, into a return air compartment of the evaporator section, through the evaporator coil and then to the supply air opening. The air conditioning system further includes a condenser fan for causing outside air to flow over the condenser coil and then to be discharged outside. Where the compressor is a horizontal compressor with a longitudinal axis. The compressor is mounted proximate to the roof of the bus and external to the passenger compartment of the bus and the compressor oriented such that the longitudinal axis of the compressor is substantially perpendicular to the longitudinal axis of the bus.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part application and claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,584 entitled “Modular Rooftop Air Conditioner for a Bus”, filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0002]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,481 entitled “Modular Bus Air Conditioning System” (Attorney docket number 210 — 545), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0003]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,456 entitled “Supply Air Blower Design in Bus Air Conditioning Units” (Attorney docket number 210 — 549), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0004]    This application claims the benefit of priority under 35 U.S.C. § 120 of U.S. patent application Ser. No. 10/429,453 entitled “Bus Rooftop Condenser Fan” (Attorney docket number 210 — 550), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0005]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,455 entitled “Method and Apparatus for Refreshing Air in a Bustop Air Conditioner” (Attorney docket number 210 — 548), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0006]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,454 entitled “Coil Housing Design for a Bus Air Conditioning Unit” (Attorney docket number 210 — 547), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0007]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/430,092 entitled “Integrated Air Conditioning Module for a Bus” (Attorney docket number 210 — 558), filed on May 6, 2003, which is incorporated herein by reference in its entirety.  
         [0008]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,451 entitled “Fresh Air Intake Filter and Multi Function Grill” (Attorney docket number 210 — 554), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0009]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,583 entitled “Integrated Air Conditioning Module for a Bus” (Attorney docket number 210 — 557), filed on May 5, 2003 which is incorporated herein by reference in its entirety.  
         [0010]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,424 entitled “Modular Air Conditioner for a Bus” (Attorney docket number 210 — 561), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0011]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,437 entitled “Modular Air Conditioner for a Bus Rooftop” (Attorney docket number 210 — 562), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0012]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,423 entitled “Evaporator Section for a Modular Bus Air Conditioner” (Attorney docket number 210 — 564), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0013]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,484 entitled “Wide Evaporator section for a Modular Bus Air” (Attorney docket number 210 — 565), filed on May 5, 2003 which is incorporated herein by reference in its entirety.  
         [0014]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,391 entitled “Condensate Pump for Rooftop Air Conditioning Unit” (Attorney docket number 210 — 568), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0015]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,452 entitled “Condensate Removal System Rooftop Air Conditioning ” (Attorney docket number 210 — 551), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0016]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,390 entitled “Modular Rooftop Unit Supply Air Ducting Arrangement” (Attorney docket number 210 — 577), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0017]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,389 entitled “Configuration for Modular Bus Rooftop Air Conditioning System” (Attorney docket number 210 — 595), filed on May 5, 2003, which is incorporated herein by reference in its entirety.  
         [0018]    This application claims the benefit of priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 10/429,388 entitled “Unibody Modular Bus Air Conditioner” (Attorney docket number 210 — 596), filed on May 5, 2003, which is incorporated herein by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0019]    This invention relates generally to air conditioning systems and, more particularly, to an air conditioning system for the rooftop of a bus.  
           [0020]    The most common approach for air conditioning a bus is to locate the air conditioning components on the rooftop thereof Inasmuch as power is available from the engine that drives the bus, it has become common practice to locate the air conditioning compressor near the drive engine such that the drive engine is drivingly connected to the compressor, with the compressor then being fluidly interconnected to the air conditioning system on a rooftop of a bus. This, of course, requires rather extensive piping between the engine compartment and the air conditioning unit, thereby increasing installation and maintenance costs.  
           [0021]    Another problem with such existing systems is that the speed that the compressor is driven is dependent on the speed in which the drive engine is running. Thus, when the drive engine is idling in a parking lot, for example, the compressor is running at a relatively slow speed which may not be sufficient to provide the desired degree of air conditioning. It is therefore generally necessary to oversize the compressor in order to obtain the performance needed under these conditions.  
           [0022]    Others problems associated with such a motor driven compressor system is that the open drive compressor needs a shaft seal and a mechanical clutch, both of which are subject to maintenance problems. Further, since DC power is available on a bus, DC motors have been used for the air conditioning system In general, DC motors are not as reliable as AC motors since they have brushes that wear out, and brushless motors are relatively expensive.  
           [0023]    In addition to the problems discussed hereinabove, it is recognized, that because the wide variety of bus types and application requirements, it has been necessary to provide many different types and variations of air conditioning systems in order to meet these different requirements and vehicle interfaces. As a result, the manufacturing and installation costs, and sustaining engineering resources that are necessary in order to properly maintain and service these units, are relatively high.  
           [0024]    Also associated with the existing bus air conditioning systems is the problem of a component failure causing a complete loss of the air conditioning capacity. That is, with a single large unit as is now customary, failure of that unit such as, for example, a leaking hose causing loss of refrigerant, an electrical failure leading to inoperation of one of the components such as a fan, or a compressor failure, the entire unit is inoperable and no air conditioning can be provided to the unit. In such a situation, it would preferable if partial capacity could be maintained in order to provide a “limp home” capability.  
           [0025]    In addition to the function of cooling the air in a passenger compartment of a bus, it is also necessary to warm the air when the ambient conditions are cold Again, it is common to use the energy that is available at the drive engine, with the heat coming from the engine coolant. But, similar to the case of cooling, less heat will be available when the engine is idling, for example.  
           [0026]    Generally speaking, the capacity of a compressor is typically proportional to the diameter of the compressor. Similarly, the cost effectiveness of a compressor is related to the aspect ratio of the compressor, thus from am cost effectiveness standpoint, it is undesirable to have long skinny compressors. Therefore, typical hermitic, high volume and low cost compressors are only manufactured in discrete aspect ratios.  
           [0027]    A proposed approach, involves locating the air conditioning system for a bus on the roof of the bus. Locating the air conditioning system to the roof of the bus requires that, when installed, the air conditioning system does not cause the height of the bus to exceed operational limits that would cause the bus to strike overhead objects, such as, for example, signs, bridges and overpasses when passing underneath. In addition, bus manufacturers prefer for styling and aesthetic reasons that the air conditioning units protrude above the roofline as little as possible. Likewise, for a cost effective system, the aspect ratio of the compressor must fall within a certain range. For example, for a given diameter and compressor efficiency, the length of the compressor typically will fall within a small range of lengths.  
           [0028]    It is therefore an object of the present invention to provide an improved bus top air conditioning system  
           [0029]    Another object of the present invention is the provision for a bus air conditioning system which is effective at all operating speeds of the bus, while at the same time does not require an oversized compressor.  
           [0030]    Yet another object of the present invention is the provision for reducing the manufacturing, installation, and maintenance costs of a bus air conditioning system  
           [0031]    Still another object of the present invention is that of providing an air conditioning system that is designed for adaptability of use in various types of installation configurations.  
           [0032]    Another object of the present invention is that of providing a “limp home” capability in the event of certain component failures.  
           [0033]    Still another object of the present invention is the provision in a rooftop air conditioning system for effectively providing heat to the passenger compartment, regardless of engine speed  
           [0034]    Yet another object of the present invention is the provision for a bus rooftop air conditioning system which is economical to manufacture and effective in use.  
           [0035]    Yet another object of the present invention is the provision of a low profile rooftop air conditioning system  
           [0036]    Yet another object of the present invention is the provision of an aesthetically pleasing rooftop air conditioning system  
           [0037]    Yet another object of the present invention is the provision of a lower drag rooftop air conditioning system.  
           [0038]    These objects and other features and advantages become more readily apparent upon reference to the following descriptions when taken in conjunction with the appended drawings.  
         SUMMARY OF THE INVENTION  
         [0039]    Briefly, in accordance with one aspect of the invention, an air conditioning module is assembled with its condenser coil, evaporator coil and respective blowers located within the module and so situated that a standard module can accommodate various installation interfaces with different types and locations of return air and supply air ducts on a bus.  
           [0040]    In accordance with another aspect of the invention, rather than a large single air conditioning unit, a plurality of relatively small identical modules can be installed on the roof of a bus, with each being capable of operating independently of the others so as to allow for the relatively low cost mass production of identical standardized units and also provide for a limp home capability in the event of failure of one or more units.  
           [0041]    By yet another aspect of the invention, the modules may include a compressor, such that all the necessary refrigerant piping is located entirely on the module, with electrical power being provided to the electrical components on the module from a motor driven generator.  
           [0042]    By another aspect of the invention, the evaporator section of the air conditioning unit has a relatively wide return air openings so as to be adaptable to use with any of the narrow body, wide body or curved top buses.  
           [0043]    By still another aspect of the invention, heat is introduced into the air conditioning system by way of a heat resistance coil located in the air stream passing to the passenger compartment of the bus.  
           [0044]    By still another aspect of the invention, there is provided a bus air conditioning system with at least one air conditioning module installed on a bus roof The air conditioning system having a pair of supply air openings for conducting the flow of conditioned air downwardly near the outer side of the roof and a return air opening whose position may vary substantially in the lateral direction from a longitudinal central axis of the bus for any given installation. The air conditioning system includes a refrigeration circuit for circulating refrigerant serially through a compressor, a condenser coil, an expansion valve and an evaporator coil. The air conditioning system further includes an evaporator section including an evaporator blower for causing return air to flow from said return air opening, into a return air compartment of the evaporator section, through the evaporator coil and then to the supply air opening. The air conditioning system further includes a condenser fan for causing outside air to flow over the condenser coil and then to be discharged outside. The compressor is a horizontal compressor with a longitudinal axis. The compressor is mounted proximate to the roof of the bus and external to the passenger compartment of the bus and the compressor oriented such that the longitudinal axis of the compressor is substantially perpendicular to the longitudinal axis of the bus.  
           [0045]    In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true sprit and scope of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0046]    [0046]FIG. 1 is a perspective view of a module in accordance with a preferred embodiment of the invention.  
         [0047]    [0047]FIG. 2 is an alternative embodiment of the invention to include a compressor.  
         [0048]    [0048]FIG. 3 is a schematic illustration of both a refrigeration circuit and an electrical circuit within a module in accordance with the present invention.  
         [0049]    [0049]FIG. 4 is a cut away perspective view of a module in accordance with a preferred embodiment of the invention.  
         [0050]    [0050]FIG. 5A-5C are sectional views of modules as applied to various types of bus installations in accordance with a preferred embodiment of the invention.  
         [0051]    [0051]FIG. 6A-6C are sectional views of a module with an air mixing stops in various positions.  
         [0052]    [0052]FIG. 7 is a perspective view with a pair of modules installed in accordance with a preferred embodiment of the invention.  
         [0053]    [0053]FIG. 8 shows a perspective view of four modules installed in accordance with the invention.  
         [0054]    [0054]FIG. 9 is a perspective view of six modules installed in a bus in accordance with the invention.  
         [0055]    [0055]FIG. 10 is a perspective view of an alternative installation of four modules on a bus rooftop. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0056]    [0056]FIG. 1 shows a module  11  with the cover removed to show the various components including an evaporator coil  12 , a condenser coil  13 , a plurality of evaporator blowers  14  and associated drive motors  16 , and a condenser fan motor  17  for driving a condenser fan (see FIG. 3).  
         [0057]    Outside the module  11  is a compressor  18  which is driven by a motor drive  19  to pump refrigerant from the compressor  18  through refrigerant line  21  to the condenser coil  13  and eventually to the evaporator coil  12  by way of an expansion valve  22  (see FIG. 3). The refrigerant vapor then passes back to the compressor  18  by way of refrigerant line  23 .  
         [0058]    The drive engine  19  is also operatively connected to an electrical generator  15 , (or alternator, if desired) for providing electrical power to the module by way of line  25 .  
         [0059]    Also shown in FIG. 1 is an electrical resistance heater  24  which is downstream of the evaporator coil  12  such that, for periods of heating, the air is drawn by the evaporator blower  14  through the evaporator coil  12  and the heater  24  such that the air being delivered to the passenger compartment of the bus is heated The electrical power to the heater  24 , as well as to the evaporator blower motor  16  and the condenser fan motor  17 , is provided by way of the electrical line  25  receiving DC power from the generator  15 . The heater  24  can be powered by either DC or AC currents with the heat output being independent of the speed of the drive engine  19 . With the module as shown in FIG. 1, DC power is available to power all of the motor components and is therefore preferred for the heater  24 .  
         [0060]    Referring now to FIG. 2, a modified module  26  is shown to include all of the components as described hereinabove. Further, it includes a horizontal rotary compressor  27  which is operatively interconnected between the evaporator coil  12  and the condenser coil  13  so as to circulate refrigerant in a manner similar as described hereinabove. The difference over the earlier described system, however, is that the hermetic compressor  18  is driven by an internal electric motor  20 , with the power being provided by way of the generator  29 , driven by the main engine  19 , and an inverter/controller  28  as shown in FIG. 3. The inverter/controller  28 , which receives input from various control sensors  30  and which includes a rectifier and an inverter, receives AC power from a generator or alternator  29  and provides, by way of the inverter, controlled AC power to the evaporator blower motor  16 , the condenser blower motor  17 , the compressor drive motor  20  and the heater  24 . Since the invertor/controller  28  is capable of providing controlled AC power, each of the motors are AC motors, thereby ensuring a more maintenance free system  
         [0061]    With the inverter/controller providing controlled AC power, a preferred type of heat  24  is a positive temperature coefficient (PIC) heater wherein electrical resistance increases relatively fast as the temperature increases. Whereas this type of heater is relatively expensive in it initial installation, it acts as a self limiter and does not require a thermostat to maintain a safe temperature limit.  
         [0062]    In one embodiment of the module  26  shown in FIG. 2 the constituent components of the module are arranged so that when the module  26  is installed on a bus, the horizontal rotary compressor  27  is oriented such that its longitudinal axis  27   c  is substantially perpendicular to the longitudinal axis of the bus. An example of a horizontal rotary compressor is provided U.S. Pat. No. 5,221,191, entitled “Horizontal Rotary Compressor”, assigned to the Assignee of the present application, which is herein incorporated by reference in its entirety. If horizontal compressor  27  is installed such that its longitudinal axis  27   c  is substantially parallel to the longitudinal axis of the bus, then when the bus pitches, i.e., goes up or down hills or grades, the lubricant in the compressor  27  will tend to collect at the lower most end of the compressor. as used herein, the term “longitudinal axis of the bus” is intended to mean an axis extending from the front to the rear of the bus in the direction in which the bus travels when it is traveling in a straight forward or rearward direction. When the lubricant in the compressor  27  collects at one end of the compressor  27 , lubrication of the compressor  27  may become interrupted If the bus remains in a pitched attitude for frequent or prolonged periods, the compressor may become damaged due to the lack of lubrication. Configuring the module  26 , such that when installed the compressor  27  is in a transverse relationship to the longitudinal axis of the bus ensures that inclination of the bus from its normal operating position, such as, for example when it is climbing or descending a hill, the compressor  27  will not cause a lack of lubrication in the compressor  27 . The inventors have discovered that by mounting the horizontal rotary compressor  27  in a transverse relationship to the longitudinal axis of the bus that the bus can negotiate ascending and descending grades in excess of 20 degrees without an interruption in the lubrication of the compressor  27 .  
         [0063]    It will be appreciated by those of ordinary skill in the art of providing conditioning for the passenger compartments of large passenger vehicles that although the module  26  has been described with reference to a horizontal rotary compressor  27 , in view of the teachings of the instant application, that other types of compressors may be adapted for operation in a horizontal mode and may therefore be used in the air conditioning system of the present invention, such as, for example, rotary vaned compressors or scroll compressors.  
         [0064]    Due to the clearance requirements for passing under signs, bridges and the like the overall height of a bus is restricted. Because the module  26  increases the height of the bus when mounted on or about the roof, the height of the module  26  must be carefully controlled to ensure that bus&#39;s height restrictions are not exceeded. The inventors have discovered that by configuring the module  26  such that when installed, less than 200mm of the module  26  extends above the roof line of the bus that the module  26  may be mounted to almost every commercially available bus without exceeding any overall height restrictions. Additionally, the inventors have found that a roof mounted module that extends less than about 200mm does not unnecessarily detract from the aesthetics or aerodynamic efficiency of the vehicle. When using compressors of about 200mm in diameter or less, the inventors have discovered that it is advantageous to construct the bus air conditioning system in a modular fashion with a number of compressor modules. Using a modular configuration allows the installed compressors to have a low profile while meeting important operation efficiency and capacity requirements.  
         [0065]    Referring now to FIG. 4, the module is shown with the various components as described hereinabove enclosed within a housing  29  and including a condenser fan  31 . Also shown are the various openings in the housing  29 , including a return air opening  32 , a condenser outlet opening  33  and a condenser/fresh air intake opening  34 . A fresh/return/exhaust air flap  36  is provided between the condenser coil  13  and the evaporator coil  12  to control the mix of air passing to the evaporator coil  12 , depending on the particular demands of the system, as well as the existing ambient conditions. The air flow pattern, as indicated by the arrows, is thus controlled by the condenser fan  31 , the evaporator fan  14  and the position of the air flap  36 . As the return air enters the return air opening  32 , it is caused to flow out the condenser outlet air opening and/or through the evaporator coil  12  depending on the position of the air flap  36 . Similarly, the fresh air coming in the intake opening  34  passes through the condenser coil  13  and then out the condenser outlet air opening  33  and/or, depending on the position of the air flap  36 , it is allowed to pass through the evaporator coil  12 . Thus, with the use of the air flap  36  it is possible to have all of the return air pass through the condenser air outlet opening  33 , with all fresh air passing into the air intake opening  34  and then through the evaporator coil  12 , or when the flap  36  is placed in the other extreme position, all of the return air passes through the evaporator coil  12  and all of the fresh air entering the air intake opening  34  passes through the condenser coil  13  and out the condenser outlet air opening  33 . A more likely operating condition, however, is an intermediate position of the air flap  36  wherein a selective mix of return air and fresh air are passed through the evaporator coil  12 .  
         [0066]    As will be seen, a filter  37  is positioned in the air flow stream which enters the fresh air intake opening  34  and passes through the evaporator coil  12 . Its purposes is to filter out any debris that may be in the air stream entering the air intake opening  34 . After passing through the evaporator coil  12 , the conditioned air is caused to flow by the evaporator blower  14  out a supply air opening  38  as shown.  
         [0067]    Considering now the manner in which the module  11  is positioned on the rooftop in such a way as to interface with the existing air path openings on the rooftop, reference is made to FIGS. 5 a - 5   c . As will be seen, the position of the various openings on a bus can vary substantially from application to application. For example, in a wide bus application as shown in FIG. 5 a , the supply air duct  39  is located near the outer side of the bus, whereas the return air duct  41  is disposed at a substantial distance from the longitudinal center line thereof In a narrow bus application as shown in FIG. 5 b , the supply air duct  42  is moved a small distance inwardly from the outer side of the bus, and the return air duct is located adjacent the longitudinal centerline as shown. In a curved-roof bus as shown in FIG. 5 c , the supply air duct  44  is moved slightly more inwardly from the outer side of the bus, and the return air duct  46  is located in an intermediate position, somewhat outwardly of the longitudinal centerline, but not as far as for a wide bus application.  
         [0068]    Of course, in all of the bus applications, a balanced arrangement is provided wherein each side of the bus is provided with both a supply air duct and a return air duct, in a substantially mirror image arrangement as shown. Thus, the modules are placed in back-to-back relationship, with the space therebetween being varied to accommodate the individual application requirements. For example, for the wide bus application of FIG. 5 a , there is a substantial space between the two modules wherein for the narrow bus application of FIG. 5 b , they are substantially in an abutting relationship. For the curved roofbus application, they are somewhat angled from a true horizontal position, with the spacing therebetween being at an intermediate degree as shown. It should be understood that the three types of installations shown are presented as a sampling of the possible installation requirements, and there are also others that have heretofore required unique designs in order to meet the particular requirements. The present design, on the other hand, provides a single module which will meet the needs of all of the various applications of rooftop air conditioners.  
         [0069]    As will be seen, the supply air opening is relatively small, and in each of the three cases described above, the module  11  is placed in such a position that the supply air opening  38  is located substantially over the individual supply air ducts  39 ,  42  and  44 . The return air opening  32 , on the other hand is relatively large and therefore can accommodate the various positions of the return air ducts  41 ,  43  and  46  as shown.  
         [0070]    In order to describe the length (i.e., the extent that it spans a lateral dimension of the bus), of the return air opening  32 , it is necessary to briefly review the design features, including the exhaust air flap  36  as shown in FIG. 6 a - 6   c . In FIG. 6 a , the fresh/return/exhaust air flap  36  is placed in such a position that all of the return air coming into the return air opening  32  passes through the evaporator coil  12  as shown, and with all of the fresh air entering the fresh air intake opening  34  passing through the condenser coil  13  and out the outlet air opening  33 . In FIG. 6 b , the fresh/return/exhaust air flap  36  is placed in the other extreme position wherein none of the return air passing into the return air opening  32  is passed to the evaporator coil  12  and the only air entering the evaporator coil  12  is the fresh air, a portion of which passes through the evaporator coil  12  and a portion of which passes through the condenser coil  13  as shown. In FIG. 6 c , the fresh/return/exhaust air flap  36  is placed in an intermediate position wherein a portion of the return air passes through the evaporator coil  12 , and a portion thereof is diverted to pass through the condenser coil  13 . In this case, fresh air is also diverted from the air intake opening  34  and mixed with the return air as it passes through the evaporator coil  12 .  
         [0071]    In all of the three positions of the fresh/return/exhaust air flap  36  as shown, and for any other position thereof, the return air opening  32  of the module is rather extensive in length, with the length thereof being represented by the designation L 1 . It is because of this substantial length L 1 , of the return air opening  32  that the module  11  can accommodate the various installation requirements as described hereinabove.  
         [0072]    The relative size of L 1 , can be established by a convenient comparison with the overall length L 2  of the module. That is the ratio of longitudinal length L 1 , of the opening to the longitudinal length L 2  of the module is  
           18.64                 inches       37.80                 inches       =   .493                         
 
         [0073]    It is therefore greater than 45% and close to 50%. Another reference point is the width of the bus rooftop or more appropriately, the half width of a bus. A wide bus has a half width of approximately 51 inches and a narrow bus has a half width of approximately 48 inches. Thus, for a wide bus (FIG. 5 a ), the ratio of the length L 1  to the bus half width L 3  (i.e. the dimension between a longitudinal centerline thereof and the outer side of the bus) is:  
           18.64                 inches       51                 inches       =   .365                         
 
         [0074]    For a narrow bus (Fig. 5 b ) it is:  
           18.64                 inches       48                 inches       =   .388                         
 
         [0075]    In each case, it is therefore greater than 36%.  
         [0076]    In FIGS. 7-10, there is shown various pairings of modules as installed on various locations of the bus rooftop. In FIG. 7, a pair of modules are positioned in back-to-back relationship near the longitudinal center of the bus. In FIG. 8, there are two such pairings (i.e., four modules) in back-to-back relationship near the longitudinal center of the bus, and in FIG. 9 there are shown three such pairings. In FIG. 10, there is shown a pair of modules in back-to-back relationship, but with a substantial space therebetween, both near the longitudinal center of the bus and near the trailing end thereof with all being aligned along lines parallel to the longitudinal centerline of the bus. In addition to those shown, it should be understood that various other installations can be accommodated with the module as described herein.