Abstract:
A heating, ventilation, and air conditioning (HVAC) module, for a HVAC system, mountable to a work machine, the HVAC module comprising a housing having at least one air outlet and at least one air inlet communicable with ducting on the work machine for conveying air into and out of the operator cab of the work machine. The module also includes a mounting assembly for pivotably attaching the housing to the work machine. The housing is moveable between an operating position where the outlet and inlet are in contact with a ducting interface on the work machine, and a maintenance position, where the housing is pivoted upwards to disconnect from ducting interface of the work machine to allow access to underlying components of the work machine.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates generally to heating, ventilation and air conditioning (HVAC) systems, and more particularly to a modular assembly design for a HVAC system on a work machine. 
       BACKGROUND 
       [0002]    In existing underground mining machines, such as load-haul-dump machines, the heating, ventilation and air conditioning (“HVAC”) components are positioned in various locations around the machine. This can make maintenance of a HVAC system difficult and time consuming. 
         [0003]    Exterior of the cab, a compressor charges a refrigerant fluid to the optimum pressure for cooling efficiency and circulates it around the system. A condenser and fan package is located near the engine radiators. The condenser and fan cools the refrigerant at high pressure, so that at discharge the refrigerant potential thermal energy is well below that of the ambient environment. 
         [0004]    Within the cab of the machine, an evaporator core and blower unit are co-located in a conditioner box, typically attached to the ceiling of the cab. The evaporator core cools air that is pushed through by the blower. Assisting the evaporator core is an expansion valve, which regulates the refrigerant flow within the evaporator. Allowing expansion of the fluid within the evaporator increases the potential cooling capacity, as the expansion further cools the fluid. 
         [0005]    An optional heater core utilises warm engine coolant to heat the same air stream, if the operator is cold. A pressuriser is mounted on the cab outer wall and provides fresh air at a higher-than-ambient pressure to the cab. This ensures that any air leaks result in an outward flow from the cab to the environment. 
         [0006]    The mounting of various components within the cab encroaches on the limited space available for the operator. Having the conditioner box located near the head of the operator can result in possible head injuries and also elevated noise levels. It also makes direction of the air difficult to control, particularly for demisting requirements. 
         [0007]    The spacing out of various components can result in efficiency losses and poor control of the airflow, decreasing performance. It also makes servicing difficult, as mountings and couplings must be in easy-to-reach locations, and can prove time consuming to troubleshoot. 
         [0008]    Whilst there have been a number of HVAC system designs that co-locate more of the components together, these are typically designed for above ground machines. However, underground machines have a further limitation on space due to the restricted width and ceiling height of underground tunnels. As the tunnels do not allow for turning of a vehicle, underground load-haul-dump machines run both backwards and forwards along the tunnel. Load-haul-dump machines are long and narrow and have a relatively low cab, with a driver typically sitting transverse to the direction of travel. The machine is articulated in its centre to provide steering capacity. All of these factors result in poor operator visibility. Therefore, the location of external components on a machine is critical to ensuring sufficient visibility is provided for the operator. 
         [0009]    The present disclosure is directed to one or more of the problems identified above. 
       SUMMARY 
       [0010]    According to a first aspect of the invention there is provided a heating, ventilation, and air conditioning (HVAC) module, for a HVAC system, mountable to a work machine, the HVAC module comprising:
       a housing having at least one air outlet and at least one air inlet communicable with ducting on the work machine for conveying air into and out of the operator cab of the work machine;   a mounting assembly for pivotably attaching the housing to the work machine, the housing being moveable between an operating position where the outlet and inlet are in contact with a ducting interface on the work machine, and a maintenance position, where the housing is pivoted upwards to disconnect from the ducting interface of the work machine to allow access to underlying components of the work machine.       
 
         [0013]    The ducting on the work machine can include a receiver box located on the top deck adjacent the location of the HVAC module. The receiver box preferably includes two channels, an inlet channel and an outlet channel. Connected to the receiver box in fluid communication with the inlet and outlet channels are inlet and outlet ducts respectively. The inlet and outlet ducts may each be comprised of a fixed duct section connected at one end to the operator cab, and a flexible duct section connecting the fixed duct section to the receiver box. 
         [0014]    The fixed duct sections and/or receiver box can be made from sheet steel and have a boxed construction, to ensure adequate strength and robustness. The flexible duct section can be made from rubber hump hose, which typically is robust, yet assists in sealing while allowing axial misalignment. 
         [0015]    The receiver box can be shaped to have a generally rectangular footprint. The inlet channel and outlet channel are preferably aligned one above the other, preferably both running in a generally horizontal direction. The upper channel of the inlet and outlet channels can have a shorter distance to the lower channel; this can result in the upper surface being stepped. In such an embodiment, two upper surface sections are provided having a generally flat surface with an upwardly orientated opening. The upwardly orientated openings may include a honeycomb plate with plurality of hexagonal apertures. The upwardly orientated openings form the ducting interface for the HVAC module. 
         [0016]    The housing may comprise a lower box and an upper lid. The lid may be clamped to the lower box in use and may be pivotally connected to the lower box. The lower box and upper lid can be made from sheet metal. 
         [0017]    The air inlet and/or outlet of the housing may include a hood to create a channel to an opening. The opening is preferably orientated to be downward facing in the operating position. The inlet opening and the outlet opening are preferably located on the same side of the housing; this may be on the side opposite the pivot hinge connection. Surrounding the openings can be a seal, which may compress under pressure. 
         [0018]    In the operating position, the downward facing openings of the HVAC module abut against the upwardly orientated openings of the receiver box, with their respective surfaces aligned. The interface between the respective openings is sealed by the seal located about the downward facing openings, in order to protect the seal from damage while in the service position. However, it will be appreciated that the seal may be located about the upwardly orientated openings. In the operation position, the housing may be clamped to the receiver box ensuring the seal is maintained. When moving the housing into the maintenance position, the housing may be unclamped and lifted away from the receiver box disconnecting the ducting interface. 
         [0019]    The pivotal mounting assembly may include at least one, preferably two, pivot hinges located on one side of the housing. The pivot hinge preferably connecting the housing to the top deck of the work machine. Advantageously, the pivot hinge is a releasable hinge. 
         [0020]    The pivotal mounting assembly may also include at least one lifting linkage on one of more of the sides of the housing perpendicular to the side of the housing the pivot hinge connection is located on. The lifting linkage may be a gas strut. The lifting linkage is configured to assist in raising the housing about the pivot hinges, so that the service technician needs to apply a comfortable load, and so that the articulation angle is limited. The lifting linkage can be releasably connected to the housing. 
         [0021]    On the side of the housing opposite the pivot hinge connection there may be latching elements to secure the housing in the operating position. 
         [0022]    The housing may be mounted to at least partially sit within a recess formed in the top deck of the work machine. 
         [0023]    Advantageously, the HVAC module is a unitary assembly that is removable from the work machine and replaceable. 
         [0024]    The HVAC module may include at least an operational component region, a condenser region and a conditioning region. The operational component region preferably includes at least a motor and a compressor, the motor operable to drive the compressor. The motor is preferably a hydraulic motor that draws hydraulic fluid from a hydraulic supply external to the HVAC module, advantageously regulated by a manifold. 
         [0025]    The condenser region preferably includes a condenser and at least one fan, the fan(s) being operable to draw air from the ambient environment external of the housing. 
         [0026]    The conditioning region preferably includes the at least one air inlet and at least one air outlet, evaporator and heater cores and a blower. 
         [0027]    The evaporator core is preferably in fluid communication with the compressor and condenser to convey refrigerant. A refrigerant flow path is preferably created from the compressor to the condenser to the evaporator core and back to the compressor. Advantageously between the compressor and the condenser there is provided a high pressure charge port. There may also be a pressure sensor. There may be associated with the evaporator a thermal expansion valve. Between the condenser and the thermal expansion valve there is preferably a receiver drier. Running back to the compressor from the evaporator, the refrigerant preferably passes via a pressure sensor and a low pressure charge port. 
         [0028]    The conditioning region may also include an additional inlet for drawing in ambient air from the surrounding environment. A conditioned air flow path is typically created by drawing ambient air through the additional inlet from the external environment into the conditioning region of the housing. The ambient air passes via at least one filter to the evaporator. A pressurizer and/or a temperature sensor may also be located in the path before the ambient air passes through the evaporator. From the evaporator the air may pass via a temperature sensor or freeze-point probe and may then pass via a heater core to a blower. The blower forces the conditioned air through the air outlet to the ducting into the operator cab. Air is also drawn from the operator cab through the air inlet and recycled back through the conditioned air flow path by passing via a filter to the evaporator mixing with the ambient air to continue on the conditioned air flow path. 
         [0029]    Hot coolant for the heater core is preferably drawn from the engine cooling system of the work machine. 
         [0030]    An electronic control module (ECM) may be configured to control all aspects of the HVAC system, for example including the hydraulic components and the electrical functions, and to control the temperature of the airstream reaching the operator cab. 
         [0031]    According to a second aspect of the invention, there is provided a heating, ventilation, and air conditioning (HVAC) system for a work machine, the HVAC system comprising:
       a HVAC module mountable to a work machine, the HVAC module comprising:
           a housing having at least one air outlet and at least one air inlet communicable with ducting on the work machine for conveying air into and out of the operator cab of the work machine, the outlet and inlet having openings that are downwardly orientated;   a mounting assembly for pivotably attaching the housing to the work machine; and   
           a receiver box mountable to the work machine adjacent the housing, the receiver box being connectable to ducting on the work machine and including at least one inlet opening and one outlet opening, both being upwardly orientated;       
 
         [0036]    wherein the module is moveable between an operating position where the downwardly orientated outlet and inlet on the housing are in contact with the upwardly orientated inlet and outlet on the work machine, respectively, and a maintenance position, where the housing is pivoted upwards to disconnect the ducting interface to allow access to underlying components of the work machine. 
         [0037]    As used herein, the term “comprises” (and grammatical variants thereof) is used inclusively and does not exclude the existence of additional features, elements or steps. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]    The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0039]      FIG. 1  is perspective view of an example work machine, a load-haul-dump machine in this case, with a HVAC module according to an embodiment of the present invention installed on its top deck; 
           [0040]      FIG. 2  is a close up view of the HVAC module shown of  FIG. 1 ; 
           [0041]      FIG. 3  is a perspective view of the HVAC module in a maintenance position; 
           [0042]      FIG. 4  is a perspective view of the HVAC module and associated ducting and cables in a partially open position; 
           [0043]      FIG. 4A  is a perspective front view of the HVAC module; 
           [0044]      FIG. 5  is a left view of the HVAC module and associated ducting and cables of  FIG. 4  in a closed position; 
           [0045]      FIG. 6  is a rear view of the HVAC module and associated ducting and cables of  FIG. 5 ; 
           [0046]      FIG. 7  is a cross-sectional left view through lines A-A in  FIG. 6 ; 
           [0047]      FIG. 7A  is a close up view of the area circled B in  FIG. 7 ; 
           [0048]      FIG. 8  is a top view of the HVAC module with the lid removed; and 
           [0049]      FIG. 9  is a boundary diagram of the HVAC module according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    Referring to  FIG. 1 , a work machine in the form of a load-haul-dump machine  2  is shown. A load-haul-dump machine is used in underground mines and runs back and forth to scoop rubble and transport and dump it onto a conveyer. Due to the restricted height and width of underground mine tunnels, load-haul-dump machines have a narrow, long, low profile. The body  4  is centrally articulated about a flexible joint  6  dividing the body into a first body portion  8  and a second body portion  10 . Each body portion includes two opposing wheels  12 . 
         [0051]    The first body portion  8  has a bucket  18  for scooping and hauling rubble from within the tunnel. The second body portion  10  includes an engine, and hydraulic and electrical systems (not shown). The second body portion  10  has an operator cab  20  that projects above a top deck  14 . The operator cab  20  is enclosed, with the operator seated sideways to provide adequate visibility when the machine is moving in either direction. The operator cab includes an operator control station (not shown) of the type that controls a heating, ventilation and cooling (HVAC) system. 
         [0052]    Located generally on the top deck  14  is a HVAC module  22 . Providing fluid communication between the operator cab  20  and the HVAC module  22  is outlet ducting  36  to convey air out of the HVAC module  22  into the operator cab. Inlet ducting  34  conveys recirculated air out of the operator cab  20  back to the HVAC module  22 . This keeps the environment comfortable for the operator. Details of the ducting will be described further below. 
         [0053]      FIG. 2  shows a close-up view of the HVAC module  22  shown in  FIG. 1 . The HVAC module  22  includes a housing comprised of a lower box  24  and an upper lid  26 . The lower box  24  and upper lid  26  would typically be made from sheet steel. The lid has an array of vents  30  located towards a corner of the lid (to be discussed further below). The upper lid  26  is illustrated as being clamped to the lower box  24  with lid clamps  28 . The lid clamps  28  can be released so that the lid can be lifted upwards off the lower box  24 . However, it will be appreciated that hinges may also be provided in addition to clamps, such that the lid may be pivotally joined to one side of the lower box. The lid  26  could then be pivoted open and closed, and clamped in the closed position. A gas strut could be provided within the lower box to assist with lifting of the lid. 
         [0054]    According to the embodiment illustrated, the lower box  24  has a longer side of approx. 874 mm, a shorter side of approx. 790 mm and a height of approx. 350 mm, therefore having a generally rectangular shape. The HVAC module is recessed into the top deck  14  to reduce the impact on the operator&#39;s visibility in that direction compared to if it were positioned directly on top of the deck  14 . The lower box  24  is illustrated as being recessed into the top deck  14  by approx. 154 mm. The recess is indicated by reference numeral  16  in  FIG. 3 . This results in approx. 196 mm of the lower box  24  projecting above the top deck  14 . 
         [0055]    The HVAC module  22  is preferably located directly above the torque converter package (not shown). As the torque converter package is typically serviced daily, the HVAC module  22  is pivotally mounted to the top deck via pivot hinges  32 . To allow seating in the recess  16 , the pivot hinges  32  are located part way down the side wall of the lower box. The HVAC module  22  is pivotable between an operating position, as shown in  FIG. 2 , and a maintenance position, as shown in  FIG. 3 . In the maintenance position, access can be gained to the recess  16  and therefore the torque converter package and other components located underneath for maintenance purposes. 
         [0056]    Enabling the movement between the operating position and the maintenance position is a lifting linkage in the form of a gas strut  48 . The gas strut is connected to one side of the lower box  24  and extends down below the top deck to connect to the chassis. It will be appreciated that whilst only one gas strut is illustrated, another gas strut may be provided on the other side of the lower box. A handle  62  is provided on the lower box to assist in movement of the HVAC module by an operator. 
         [0057]    As can be seen in  FIG. 3 , there are a number of hydraulic hoses  64  connected to the underside of the HVAC module  22 . These hydraulic hoses  64  connect at their other end to the working machine. The hydraulic hoses  64  are provided with sufficient length to be able to be lifted into the maintenance position. The hoses  64  are held in place against the underside of the HVAC module  22  by platework  66 . This allows the hoses  64  to bend as the HVAC module is lowered. Additional hoses  67  are positioned at the bottom of the module to allow condensate from within the module to drip into and then purge from the box  24 . These additional hoses  67  may contain a one-way valve. An array of vents  70  can also be seen in  FIG. 3 , positioned towards a corner of the base (to be discussed further below). 
         [0058]    Also located on the bottom surface of the lower box  24  are electrical cables  68 . The electrical cables  68  run along the underside of the box  24  and are provided with sufficient length to create a loop  69  to allow flexure when the module is elevated to the maintenance position. 
         [0059]    An air inlet opening  50  and an air outlet opening  52  are generally adjacent one another on the HVAC module  22 . Referring to  FIG. 4 , it can be seen that inlet opening  50  is created by a hood  51  that projects above the planar top surface of the lid  26 . The hood  51  creates a channel from the opening  50  to an inlet into the housing. The outlet opening  52  is also created by a hood  53  that projects from the side of the lower box. The hood  53  creates a channel that leads into an outlet in the side wall of the lower box  24 . The hoods  51 ,  53  are formed to orientate the openings  50 ,  52  downwards, when in the operating position. 
         [0060]    Running between the operator cab  20  and the HVAC module is the inlet ducting  34  and the outlet ducting  36 . The inlet ducting  34  includes an inlet fixed duct section  40 . One end  39  of the inlet fixed duct section  40  connects to an upper region of the wall of the operator cab  20 . The other end of the inlet fixed duct section  40  connects to an inlet flexible duct section  42 . The connection makes an elbow in the flow path (see  FIG. 3 ). The inlet flexible duct section  42  then connects to a receiver box  38  mounted on the top deck  14  adjacent the recess  16 . 
         [0061]    Similarly, the outlet ducting  36  includes an outlet fixed duct section  44 . One end  43  of the outlet fixed duct section  44  connects to a lower region of the wall of the operator cab  20 . The other end of the outlet fixed duct section  44  connects to an outlet flexible duct section  46 . Similarly, this connection can make an elbow in the flow path. The outlet flexible duct section  46  then connects to the receiver box  38 . 
         [0062]    The receiver box  38  has a generally rectangular footprint and includes two internal flow paths. The two flow paths are formed by generally horizontal chambers that sit one above the other (to be described further below). The upper surface of the receiver box  38  is stepped creating two upper surface regions  35 ,  37 . The upper surface regions  35 ,  37  include receiver box inlet opening  58  and outlet opening  60 , respectively. These openings  58 ,  60  are upwardly orientated. Extending from the uppermost surface region  35  is a triangular shaped box, or elbow  41 . The elbow  41  allows the connection of the generally horizontal top surface region  35  to the generally horizontally orientated inlet flexible duct section  42 . 
         [0063]    The receiver box is positioned so that upon lowering of the HVAC module into the operating position, the inlet opening  50  and the outlet opening  52  align with the receiver box inlet  58  and outlet  60 , respectively. This can be seen in  FIG. 4  where the HVAC module  22  is being lowered into position relative to the receiver box  38 . As the HVAC module  22  is lowered into the operating position, as shown in  FIG. 5 , the downwardly facing inlet opening  50  and outlet opening  52  abut against the upwardly orientated inlet  58  and outlet  60 , respectively. The receiver box  38  includes two latch clamps  72  that align with latches  73  on the inlet and outlet hoods  51 ,  53 . Once fully lowered, latch clamps  72  are fastened to latches  73  locking the HVAC module  22  to the receiver box  38 . 
         [0064]    The receiver box inlet  58  and outlet  60  are created by a plurality of hexagonal apertures arranged to form honeycomb plates. The honeycomb plates may be integrally formed with the upper surfaces  35 ,  37  or may be separate overlying plates. Such a honeycomb aperture structure maximises airflow whilst maintaining structural integrity to the top of the receiver box  38  and also provides sealing surface area. Located about the inlet opening  50  and the outlet opening  52  are seals  54 . The seals  54  typically comprise a pad of 5-10 mm thick low porosity neoprene foam. However it will be appreciated that any suitable seal may be utilised. As the HVAC module is fastened to the receiver box  38 , the seals  54  are clamped against the top surface of the receiver box  38  about the edge of the honeycomb plates. It will be appreciated that the seals could alternatively be connected to the receiver box. 
         [0065]    A rear view of the clamped operating position is shown in  FIG. 6 . A sectional front view is taken through lines A-A and shown in  FIG. 7 .  FIG. 7  illustrates the two flow paths through the receiver box  38 . Conditioned air from the HVAC modules travels along air flow path A into the operator cab  20 . The conditioned air flows out of the outlet opening  52  through the receiver box outlet  60  into the lower receiver box chamber  61 . From the receiver box chamber  61  the air flows to the outlet flexible duct section  46 , through the outlet fixed duct section  44  to the end  43 , and into the operator cab  20 . Return air from the operator cab  20  travels along the return air flow path B from the end  39  of the inlet fixed duct section  40 . The air travels along the inlet fixed duct section  40  to the receiver box  38  via the inlet flexible duct section  42 , turning at elbow  41 . The air enters the upper receiver box chamber  59  flowing to the receiver box inlet  58  through inlet opening  50  along hood  51  into the HVAC module  22 . As shown in  FIG. 7A , a sealed connection is created between the HVAC module  22  and the receiver box  38  by downward clamping of the HVAC module  22  to the upper surface of the receiver box  38 . The seal  54  prevents the escape of air between the components. 
         [0066]    To minimise the downtime of work machines if the HVAC module requires repair, the HVAC module is fully removable from the work machine. This is accomplished by employing releasable pivot hinges, where a pin  63 , held in by a circlip  65 , can be removed to allow disconnection, as best seen in FIG 8 . The gas strut  48  is connected to the housing with a ball joint, such that it can be quickly disconnected. The hydraulic hoses  64 , and electrical cables  68 , can be disconnected. The HVAC module can then be lifted out of the recess  16  and replaced by another HVAC module. 
       Industrial Application 
       [0067]    Referring to  FIGS. 8 and 9 , the internal components of the HVAC module  22  and operation of the HVAC system will be explained.  FIG. 8  shows a top view of the lower box  24  with upper lid removed. The lower box  24  is partitioned into three regions using sheet steel walls. The three regions are the operational component region  74 , the condenser region  76  and the conditioning region  78 . This is diagrammatically illustrated in the boundary diagram of  FIG. 9 . 
         [0068]    The operation region  74  includes a hydraulic motor  80  and a hydraulic compressor  82 . The motor  80  drives the compressor  82 . The motor  80  draws hydraulic fluid from a hydraulic supply external to the HVAC module (typically associated with the work machine torque converter pump stack) and is regulated via a manifold  84 . The hydraulic fluid flow path E is illustrated in  FIG. 9 . 
         [0069]    Also housed in the operational region  74  are a high pressure charge port  86  and a low pressure charge port  102 , together with a receiver drier  96 . A thermal expansion valve  77  (commonly referred to as a TX valve) is also housed in this region. A number of pressure sensors  100  and temperature sensors  108  are also located in the operational region  74 . An electronic control module (ECM)  118  and a water valve  56  complete the preferred components housed in the operational region  74 . However, it will be appreciated that other components associated with the HVAC system may also be housed in the operational region. 
         [0070]    The condenser region  76  contains a condenser  90  and two axial fans  92 . The axial fans  92  draw fresh air from the ambient environment through the vents  30  in the upper lid  26 . This air blows over the condenser  90 . The air is then ejected out of the lower vents  70  into the underlying transmission bay. 
         [0071]    The conditioning region  78  includes an evaporator  94 , a heater core  114  and a blower  116 . Fresh air filter  106  and secondary filter  110  are also housed within the conditioning region, together with temperature sensors  108 . A fresh air inlet  104  is located in the sidewall of the lower box  24  (see  FIG. 4A ). The evaporator typically communicates with the TX valve  77 , which regulates the flow rate through the evaporator, controlling the superheating of the refrigerant within the evaporator. 
         [0072]    The components are generally adapted to work in concert to produce HVAC cooling and/or heating, as will be appreciated by those skilled in the art. The ECM is configured to control all aspects of the HVAC system, including the hydraulic components and electrical control functions, as illustrated in the boundary diagram in  FIG. 9  by the dashed connection lines. 
         [0073]      FIG. 9  schematically illustrates the refrigerant flow path C. Refrigerant in a gaseous state moves from the compressor  82  to the condenser  90  via high pressure charge port  86  and AC pressure sensor  100 . The refrigerant enters the condenser  90  where it is cooled from its superheated state and condenses into a cooled liquid phase. The liquid refrigerant passes through the receiver drier  96 , which dries the refrigerant, increasing the heat rejection capacity of the fluid. The refrigerant then passes through the TX valve  77 , which meters the amount of refrigerant flowing through the evaporator  94 , allowing a low entropy liquid and vapor mixed refrigerant to enter the evaporator. The refrigerant evaporates and returns to a gaseous state, gaining energy from the air flow, where it is returned to the compressor  82  via an AC pressure sensor and low pressure charge port  102 . The refrigerant continues to cycle through the flow path C. 
         [0074]    Hot coolant is drawn from the engine cooling system of the work machine  2  and supplied to the heater core  114 . The engine coolant flow path D is illustrated in  FIG. 9  whereby the hot coolant passes via a water valve to the heater core. The water valve is ECM position controlled, whereby the position of the internal ball valve controls the flow rate and hence heat exchange to the airstream. A receptacle  120  and relay  122  are required for the water valve  56 , to take the low-power signal outputs from the ECM  118  and boost the signal to the required voltage for the water valve solenoid to actuate. 
         [0075]    Within the conditioning region  78  air is circulated. Fresh ambient air is drawn in through air inlet  104  in the front of the housing and passes through a fresh air filter  106 . Concurrently, return air is circulated back into the conditioning region  78  via inlet opening  50 . The mixed fresh air and return air is then passed via temperature sensor  112  through a secondary filter  110 . The filtered air is passed through the evaporator where it is cooled, if cooling is required in the operator cab  20 . It then passes through the heater core  114 , where it is heated, if heating is required in the operator cab  20 . Air at the desired temperature air is then blown into the outlet ducting by a blower  116 , which transfers the air to the operator cab  20 . 
         [0076]    The advantage of utilising substantially fixed ducting is that the cross-sectional profile of the ducting is more controllable, enabling minimalisation of pressure loss from surface friction in the airstream and allowing turbulence control. Turbulence commonly exists in flexible hoses, particularly those that are ribbed. By limiting the amount of flexible ducting to a small section, the required flexibility between fixed bodies is provided to allow for vehicle movement and vibration, whilst minimising turbulence. Use of the static receiver box to create the duct interface with the HVAC module inlet and outlet ensures a good seal is maintained, whilst allowing the easy disconnection to move the housing into the maintenance position. By utilising opposing downwardly and upwardly orientated openings at the duct interface, a positive clamping force can be applied to ensure an equilibrant pressure across the seal interface, for optimal sealing and pressurisation. 
         [0077]    Although aspects of the present disclosure were described with reference to underground loaders, it should be appreciated that many of the features and advantages described herein may have broad applicability across a wide range of machines. For example, many of the features described herein may be applicable to different types of loaders and trucks, whether for above ground or underground use. 
         [0078]    It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.