Patent Publication Number: US-2020300498-A1

Title: A compact heat recovery ventilation system

Description:
The present application claims the benefit of priority of U.S. Provisional Patent Application No. 62/316,325, filed Mar. 31, 2016 the entire context of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to heat ventilation and air conditioning (HVAC) systems for moving air, and/or regulating the temperature, humidity, chemistry and quality of indoor air. More particularly, the present invention relates to air processing devices such as ventilators, including heat ventilators, coolers, air conditioners humidifiers and air purifiers. The present invention is particularly, but not exclusively, useful for systems that are mounted inside a wall or ceiling and constitute a part of room decor; therefore, thickness of the system is a critical factor. Another critical factor is the countercurrent air flow (air flowing in opposite directions) that provides the highest energy recovery efficiency or chemical recovery efficiency. There is also an important field of application related to the indoor automotive air ventilation/conditioning systems. 
     BACKGROUND OF THE INVENTION 
     The countercurrent principle is a vital factor in many ventilation processes. Heating or cooling energy in the exhaust air can be preserved by recovering it and directing it into the replacement air through a heat exchanger. Low indoor humidity levels can also be better maintained in hot and humid environments by extracting the humidity out of the supply air into the exhaust air through various countercurrent processes (like desiccant wheel, water permeable membrane etc.). Same method can be used to help maintain sufficient high indoor humidity level by extracting much of the humidity from the exhaust air into the supply air. Some industrial processes can also benefit from using an extraction method based on a countercurrent (or cross-current) principle, in order to minimize pollution or waste, or to make the process more efficient. 
     In addition to these countercurrent processes, good ventilation systems can also have various other air processing units, such as filters including activated carbon, humidifier, dehumidifier, heater, cooler and others, which may improve the quality of air, while a long duct system may be necessary to efficiently extract or supply the air in the right locations. All these processes and systems (countercurrent, cross-current or in-line) restrict the airflow and contribute to the pressure drop of the ventilation system. Ambient pressure fluctuations due to weather or movement of an enclosure is another source of the pressure load that requires additional power consumption for ventilation system. 
     However, higher power often results in higher sound level, which is one of the reasons why more powerful systems are centralized with long bulky ducts and noisy blowers that need to be closed off in a sound insulated enclosure. 
     This brings up one of the major problems for modern ventilation systems. The powerful ventilation systems are often too bulky, and the small ones are often not powerful enough. Other disadvantages of the smaller systems of lower functionality are that most designs are difficult to conceal, the small size results in higher motor and blower inefficiency and, as they are closer to the user, their noise level can still be a nuisance. 
     This dilemma causes a problem, specifically in projects, where there is only limited space available for the ventilation system, for instance, when older apartments or buildings are being renovated. In these very common cases, there are often simply no good solutions possible. 
     Most of the current Heat Recovery Systems have traditional axial fans, which are often used as air moving devices, have certain limitations because they are not suited to create high static pressure at given airflow when various air processing units are added (heat exchanger, filter etc.) and when affected by ambient pressure fluctuations (e.g., wind loads, vacuum pressure inside the building envelope). Such designs are described in the International Patent Application WO 2005/040686 “Window Type Air Conditioner” and Patent WO2012155913 “Ventilation system with a rotatable air flow generator and one or more moveable registers and method for obtaining ventilation through the ventilation system.” 
     There are also numerous designs of air processing devices for HVAC systems that include radial type blowers as air moving devices, for example, US Patent Application 2005/0257687. Radial blowers for indoor air processing devices create sufficient static pressure at a given airflow, but have relatively small diameter of the impeller. It is well known that for such diameters, the total blower efficiency decreases dramatically. When a flat centrifugal blower is mounted flat on the surface in such way that it fits the structural envelope, the whole design is limited by the suction being in the center on the flat side and, therefore, perpendicular to the structural envelope. This leaves little room for any noise mitigation, like a silencer, unless by compromising the flat design. 
     Crossflow blowers are used in air processing devices more often due to their affordable mounting performance and a well-known ability to achieve relatively high efficiency that does not depend upon diameter size. Moreover, the crossflow blower creates much more static pressure at the same airflow, unlike the centrifugal blower, when other conditions are equal. There are many such designs, for example, International Patent Application WO 2004/085929 “Indoor Unit for Air Conditioner” and Japanese Patent No. JP2000297945 “An Air Conditioner”. According to these designs, air processing devices comprise a base with a flat surface for wall mounting and the axis of the crossflow blower is parallel in respect to that surface. However electric motors for typical crossflow blowers are located adjacent to the impellers, because if a conventional electric motor is placed inside the impeller, it greatly affects the internal aerodynamic structure of the crossflow blower, thus dramatically decreasing performance characteristics. 
     In some cases it may be beneficial to have two blowers rotate on the same axis. Having a single motor rotate two blowers increases the ventilation efficiency benefits, as larger motors are normally more efficient. An example of one such solution is described in the US patent application 2013/0101449(A1) “Double inlet centrifugal blower with peripheral motor”, where a peripheral motor is used to run two concurrent blowers on a single axis. 
     Similar solution is also described in a Japanese patent application 60-75635 “Heat exchanging type fan,” consisting of a casing and two centrifugal fans mounted on the same shaft inside the casing, but oriented in opposite directions in regard to each other, creating concurrent flow through a heat exchanger. Two co-current channels for heat carriers of different temperatures are formed in the casing, separated by a partition separating both fans. The heat exchange element comprises radial fins mounted on both surfaces of the partition beyond the edges of the impellers of the fans. 
     When the fans rotate, the heat carriers enter the inter-blade space of the fans via the suction inlets and further on, passing over both sides of the radial fins of the heat exchange element, are removed from the casing via the respective blower outlets. Heat exchange takes place through the radial fins and the partition itself, but as the flow is co-current, the efficiency is limited. Again a large radial size, inlet perpendicular to the plane and co-current flow should be listed among the disadvantages of such arrangement. A heat exchanger solution for co-current airflow in two channels is described in U.S. Pat. No. 7,837,127 B2 “Ventilation system.” This system overcomes the disadvantages of the co-current airflow by using a very thin “thin wire” heat exchanger, which effectively creates a countercurrent heat exchanger between the channels. The countercurrent fix of the otherwise co-current system has some disadvantages that may limit its use. The heat exchanger relies on using copper wire, resulting in higher cost and low pressure drop over the heat exchanger may cause higher sensitivity to pressure fluctuations. 
     Modern air processing devices have become a part of indoor interior as a wall-mounted system, creating a requirement for thin box-shaped designs, within the structural envelope. However, all known designs do not provide a thin air processing device with the crossflow blower for such wall-mounted air movement systems. The thickness of known devices with the crossflow blower axis parallel to the mounting surface is defined by the impeller diameter. Such solutions are thicker than desired and they do not meet the market requirements. 
     There is a main problem for all known air processing-heat exchanger devices where they cannot resolve the contradiction between the high performance that requires a relatively large impeller diameter on one hand and a small thickness of the whole device on the other hand. 
     Therefore, it is generally desirable to provide a thin, box-shaped air processing device for indoor HVAC systems with thin size relatively large diameter efficient blower unit that produces countercurrent air flow that overcomes such problems in a mechanically feasible manner. 
     Heat-exchanger is one of the most important part of the countercurrent heat recovery ventilation system. 
     There are at least a few options that could be used for this proposed application such as: 
     traditional one made as a central plate with protruded fins or pins from both sides of the center plate. As the center plate forms separation between the two countercurrent air streams along the length of the heat exchanger, the flow is restricted to exit on the other end of the heat exchanger on the same side as it entered. 
     changeable air flow sides could be made in the following ways: designed as folded fins with a center plate divider, or as plate heat exchanger based on the same principals as changing air flow sides. The center plate dividers are only located at the open ends of the heat exchanger but not inside it. This gives additional flexibility in design as the air is free to move between one side of the outside panel at the intake of heat exchanger, to the opposite side of outside panel at the outtake of heat exchanger. In the same time the airstream is separated to plurality of thin airstreams moving in a way that any other thin stream flows in opposite direction. 
     The last design of such heat exchanger is described in patent DE4301296 “Plate heat exchange on countercurrent principle” and incorporated here by reference. 
     Space for the air filter unit in most current systems are included as part of the HVAC treatment box. 
     There are some building solutions which are having ventilation ducts integrated into a wall, a slab or a raised floor. Such solutions are described in patents US 2008 0142610(A1) “Integrated structural slab and access floor HVAC system for buildings “,KR Patent 2010 0002817 (A)”Slab structure” and KR patent 2015 101576615 (B1) “Hollow core slab integrated ventilation deck plate”. There is, however, too little space for air processing units, and blower inside these slabs. 
     Efficient motor is very important part for any heat recovery system as the part that providing energy saving. Several improvements for better motor efficiency level have been done according to US Patent 2004 245866 (A1) “Integrated cooler for electronic devices,” which describes a flat cooling unit consisting of crossflow blower connected to heatsink removing heat from a co-current flow around heat pipes. US Patent 2005 121996A1 “Electric dive for radial impeller” describes a flat peripheral motor with coils printed on a PCB board and magnetic means fixed with the radial impeller and even integrated in the blades. This compact design has high efficiency which is increased further by leaving space in center of the radial blower allowing higher airflow. US patent 2006 0006745A1. “Integrated blower for cooling device” describes a peripheral motor for a radial blower with stator and rotor in the same plane. This arrangement produces lower motor vibration, which results in lower motor noise, higher efficiency and ensures higher airflow. US patent 2006 238064A1 “Flat radially integrated electric drive and method of the manufacturing the same”, describes stator of the motor printed in a PCB board where the motor and the rotor are on the same plane. US 2006 056153 A1 “Multi-heatsink integrated cooling device,” describes flat crossflow cooler connected to two heat sinks. US Patent 2008 101966A1 “High efficient compact radial blower” describes an integrated blower, motor and heat sink, which uses printed coils, and locates the heat sink inside the blower. US Patent 2007 166177(A1) “Thin air processing device for heat ventilation air conditioning system”, describes an efficient design for a single flat cross flow blower and the benefits of connecting it to an air processing unit like purifier, humidifier or temperature regulating means. US Patent 2008 238218(A1) describes an improved method of arranging coils in motor partially printed on a PCB board. This arrangement increases the motor power, and efficiency. 
     All these prior art designs still have some disadvantages that limited abilities to create flat compact heat recovery system capable to be soundless, wall-mounted or even fit inside of the wall or ceiling. It would be highly desirable to use the advantages of the known prior art along with the novelty elements that would be described further per our patent application. 
     SUMMARY OF THE INVENTION 
     The present invention is an approach to resolve in particular situations where only limited space is available for ventilation system, by inventing a ventilation system that can easily be integrated into the structural envelope of an enclosure (building, car, boat, plane or similar). Such configuration is achieved herein by a system, based on the countercurrent principle, with flat countercurrent heat exchanger and flat blowers powerful enough to perform and the system thin enough to fit inside the wall or ceiling. 
     Using a flat countercurrent ventilation system made up of matching flat air treatment modules which all have identical thickness and width and for different countercurrent air treatment processes, provides novelty of the design. 
     An additional benefit of the compact flat system of the invention, is that the system&#39;s length does not have to be restricted. Any air handling unit which has the same thickness and width can be added to the system without compromising aesthetics or style of the system. This gives the system additional functional flexibility (modularity), as each of the air treatment modules can be chosen independently so that it can meet its functional requirements, thus allowing for additional flexibility in design. 
     According to the present invention, the whole heat recovery system is made from two major components, namely a air module assembly and heat exchanger assembly. 
     The air module assembly comprises two radial blowers surrounded by airflow guides, placed on the common axis using peripheral motor. Housing made from two side panels and base plate between these side panels. These blowers along with airflow guides, side panels and base plate form two hydraulically isolated counter flow canals with inlet and outlet openings for each of the canal. 
     Heat exchanger assembly comprises a box with heat exchange elements surrounded by outside panels. The box, further compromises an intake and outtake openings and a center plate dividing the whole heat exchanger assembly in two hydraulically isolated flow conduits with intake and outtake openings. Side panels of the air module assembly are fixed with outside panels of the heat exchanger. Base plate of the air module assembly is fixed with center plate of the heat exchanger assembly. Therefore, such arrangement allows hydraulically connecting canals of the air module assembly to flow conduits of heat exchanger assembly respectively. 
     The air module assembly comprises a base plate fixed with the side panels thru airflow guides and placed parallel between the side panels. 
     Two radial blowers are spaced between side panels from both sides of the base plate, while the other part of the base is fixed to the center plate of the heat exchange assembly. Two radial blowers further comprise two radial impellers spaced from both sides of the base plate, thus each of the radial impellers is located at one of flow passages. Each of the radial impellers comprises a back plate disk with radial blades that are spaced apart. 
     Heat exchanging elements protruding from both sides of the base plate thus spaced inside of each flow passages are forming an exhaust and fresh heat-exchanging sides of the integrated heat exchanger. 
     The heat-exchanger could also done as changing flow side heat-exchanger made as folded fins or plates, thus each of the both flow passages split in many separate flow channels. Every other channel forcing the flow in the opposite direction. 
     The electric drive preferably comprises a flat stator fixed attached to the base plate, and a rotor with magnetic elements integrated with at least one of the back plate disk, thus the double side radial impeller serves as the rotor of the motor. The stator size (diameter) is larger than the radial blower diameter, when electrically powered, creates alternating electromagnetic fields that interact with a magnetic field created by the magnetic elements, thus providing a rotation of the double side radial impeller, causing the exhaust gas flow through the outtake side of the heat exchanger, while fresh gas flows through the intake side of the heat exchanger. 
     The base plate of the air module assembly further comprises volute casings for each of the radial impeller, that formed by flow guides protruding from both sides of the base plate, one of the two flow guides serves as a tongue of the volute casing, while the other flow guide serves as a spiral part. 
     According to the first embodiment, one of the inlet opening (exhaust gas out) is located at the side panel, both radial impellers rotate in one direction and one of the radial impellers operates as a centrifugal blower, while the other radial impeller operates as a crossflow blower. At the same time, the flow guides of the centrifugal blower serve as the volute casings directing the airflow for one part of the flow canal. The flow guides on other of base plate create the second flow canal made by crossflow blower. 
     The Heat Exchanger assembly includes heat exchanging elements located in the line of the intake and the outtake openings in a consecutive way for the flow conduits, thus providing counter-flow heat exchange process. In this case, the electric drive can be made as a conventional electric motor spaced inside of the radial impeller of the centrifugal blower. 
     According to the second embodiment of the present invention, the radial impellers rotate in one direction and operate as crossflow blowers, two flow guides are shifted in view perpendicular to the shaft in angular direction, therefore the fresh gas flows through the intake openings, the heat exchanging elements, inlet, the crossflow impeller and the outlet openings in a consecutive way, while other air flows through the inlet openings, the radial impeller, intake of the heat exchanging elements, outtake in a consecutive way form another flow passage, thus providing countercurrent flow heat exchange process. In this case the electric drive can be made as a peripheral thin motor placed between crossflow impellers. 
     The heat exchanger assembly can further comprise the heat exchanging elements, thus forming two elongated flow passages serving as the exhaust and fresh sides of the integrated heat exchanger. 
     The heat exchanging elements for all embodiments can be made in a few ways: 
     In the most general configuration, when heat exchanging elements protruding from both sides of the center plate thus spaced inside of each flow passages form an exhaust and fresh heat-exchanging sides of the integrated heat exchanger. 
     The heat-exchanger could also be built as changing flow side heat-exchanger made as folded fins or plates, thus both flow passages split in plurality of flow channels. Every other channel would be forcing the flow in opposite direction. 
     The last approach is the most beneficial for our proposed application since the air passages are changing sides inside of the system, thus when the system is installed in the wall or ceiling, the air from the inside of the enclosure travels towards outside of the enclosure naturally, with no special ducts. 
     A preferred heat-exchanger for this design is per patent DE 4301296 A1 with some improvements described further. 
     Several design options for the electric drive can be used here in accordance with the invention. According to one design option the flat stator comprises circumferential arrayed coil windings with magnetic axes coincided with a plane of the flat stator and integrated with the base plate, while the magnetic elements made as circumferential arrayed permanent magnets are placed and magnetized along the plane of the flat stator, thus magnetic axes of the coil windings and the permanent magnets are located at one plane substantially. 
     For all embodiments, when the radial impellers are operating, as crossflow blowers including guides integrated with the side panels correspondingly, the exhaust air flows through the intake opening, the heat exchange elements, the radial impeller, and the outlet openings in a consecutive way for one airflow passage while the other airflow passage of the fresh air flows through inlet opening, radial impeller, heat exchange elements and outtake opening. 
     The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the first embodiment of the compact heat recovery ventilation system for the present invention containing one centrifugal and one crossflow blower. (ducts and filters are not shown) 
         FIG. 2  is a perspective view showing the second embodiment of the compact heat recovery ventilation system for the present invention containing two crossflow blowers. (ducts and filters are not shown). 
         FIG. 3  is an exposed view of one of the crossflow blowers from  FIG. 2  that shows the integrated crossflow blower including motor elements. 
         FIG. 4  is perspective view showing the second embodiment of the current invention including ducts. 
         FIGS. 5-7  are schematic views showing options for mounting inside the wall or ceiling for the compact heat recovery ventilation system using changing side heat exchanger for the present invention. 
         FIGS. 8-10  are schematic views showing options for mounting inside the wall or ceiling for the heat recovery system using traditional heat exchanger for the present invention 
         FIGS. 11-12  are schematic views showing options for mounting on the wall or ceiling for the compact heat recovery ventilation system using changing side heat exchanger for the present invention. 
         FIGS. 13-14  are schematic views showing options for mounting on the wall or ceiling for the compact heat recovery ventilation system using traditional heat exchanger for the present invention. 
         FIG. 15  Flat schematic view showing all connected in length components including blower, heat exchanger, filter, silencers with the exhaust gas duct. 
         FIG. 16  Flat schematic view showing all connected in length components including blower, heat exchanger, filter, silencers with the fresh gas duct. 
         FIG. 17  is a cross section of the two blowers including integrated motor placed inside the housing. 
         FIG. 18 a    is showing a traditional heat-exchanger view from the intake and outtake;  FIG. 18 b    showing a traditional heat-exchanger cross-sectioned along the flow conduit. 
         FIG. 19 a    is showing a changing flow sides corrugated fins heat-exchanger front view from one open end; 
         FIG. 19 b    the same heat-exchanger back view from the other open end. 
         FIG. 19 c    is showing cross-sectioned along one of the odd changing sides flow conduit. 
         FIG. 19 d    is showing cross-sectioned along one of the even changing sides flow conduit. 
         FIG. 20 a    is showing a changing flow sides plate fins heat-exchanger  3   d  section view from the open end (top outside panel is not shown). 
         FIG. 20 b    is showing cross-sectioned along one of the odd changing sides flow conduit. 
         FIG. 20 c    is showing cross-sectioned along one of the even changing sides flow conduit. 
         FIG. 21  is a perspective view showing the second embodiment of the current invention with L-shaped transition duct between heat exchanger and blowers. 
         FIG. 22  is a perspective view showing the second embodiment of the current invention with L-shaped heat exchanger. 
         FIG. 23  is a perspective view showing the second embodiment of the current invention with 2 transition ducts between the heat exchanger assembly and air module assembly. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. 
     A compact heat recovery system  1  ( FIGS. 1-23 ) comprises air module assembly  2  and heat exchanger assembly  3 . Air module assembly  2  includes base plate  4 , two radial blowers  5  and  6  airflow guides  7 , two side panels  8  and  9 . The base plate  4  located between radial blower  5  and  6 , divides the airflow in two hydraulically isolated canals, exhaust gas canal  12  and fresh gas canal  13  with exhaust gas inlet  14 , fresh gas inlet  15  and exhaust gas outlet  16 , fresh gas outlet  17 . 
     The heat exchanger assembly  3  comprises of heat exchanging elements  20 , center plate  21  fixed with outside panels  22  and  23  and withe with heat exchanger sides  18  and  19 . The center plate  21  divides openings of the ends  24 ,  25  of the heat exchanger assembly  3  for two hydraulically isolated flow conduits  28  and  29  with exhaust gas intake  31 , fresh gas intake  32  and exhaust gas outtake  34 , fresh gas  36  outtake located at the ends  24 ,  25 . The base plate  4 , side panels  8 ,  9  of the air module assembly  2  connected respectively to the center plate  21 , outside panels  22 ,  23  of the heat exchanger assembly  3 . 
     The  FIG. 1  shows the option of two blowers  5  and  6 , one of them is a centrifugal blower  41  and the other is a cross flow blower  42 . Both blowers  41  and  42  placed on the common shaft  44  and integrated with electric drive  45 . 
     The  FIG. 2  shows the option of two radial blowers  5  and  6 , both of them made as crossflow blowers  49  and  50 . 
     According to the ( FIGS. 2-4 ) of the present invention both crossflow impellers  46  and  47  placed on the common shaft  44  and integrated with electric drive  45 , rotate in one direction and operate as crossflow blowers  49 ,  50 . Two airflow guides  51 ,  52  are outside the cross flow impellers  46 ,  47  and a guide vain  56  is located inside of each cross flow impeller  46 ,  47 , therefore, exhaust gas flows through exhaust gas inlet duct  54 A, exhaust gas inlet  53 , cross flow blower  49 , in exhaust gas canal  12 , exhaust gas outlet  53 A, exhaust gas intake  31  through heat exchanging elements  20  and exhaust gas outtake  34  of heat exchanger assembly  3  and exhaust gas outtake duct  54 , while fresh gas flows through the fresh gas intake duct  55 , fresh gas intake  32  through heat exchanging elements  20 , fresh gas outtake  36  of the heat exchanger assembly  3 , fresh gas inlet  15 , cross flow blower  50  in fresh gas canal  13 , and fresh gas outlet  17 , fresh gas outlet duct  55 A of air module assembly  2 , thus providing countercurrent heat exchange process. 
     According to  FIG. 17 , the double radial impeller  57  comprises two radial impellers  46  and  47  that are respectively spaced between each side  58  and  59  of the base plate  4  and side panels  8  and  9 , thus each of the radial impellers  46  and  47  located in each of the canal  12  and  13 . Each of the radial impellers  46  and  47  attached to back plate disk  60  and  61  that are fixed to the hub  69  attached to shaft  44  based on bearings  71 ,  73  pressed in the side panels  8  and  9 . One of the back plate disk  61  comprises magnetic elements  62 , thus both of the back plate discs  60  and  61  form the rotor  63 . Base plate  4  is divided in plane perpendicular to its thickness in two parts  64 ,  65  having between them a stator  67  that along with rotor  63  serves as the electric drive  45  of the air module assembly  2 . 
     There are at least two design options for the electric drive  45 . According to a first design option ( FIG. 3 ), the stator  67  comprises of a circumferential arrayed coil windings  72  with magnetic axes coincided with a plane of the flat stator  67  and integrated with the base plate  4 , while the magnetic elements  62  made as circumferential arrayed permanent magnets  70  placed and magnetized along the plane of the flat stator  68 , thus magnetic axes of the coil windings  69  and the permanent magnets  70  located at one plane substantially. Such electric drive  45  is described in details in the U.S. Pat. No. 7,173,353 for the same Assignee. 
     According to a second design option ( FIG. 17 ), the flat stator  68  comprises circumferential arrayed coil windings  72  with magnetic axes perpendicular to a plane of the flat stator  68  and integrated with the base plate  4 , while the magnetic elements made  62  as circumferential arrayed permanent magnets  70  are magnetized perpendicular to the plane of the flat stator  68 , thus magnetic axes of the coils windings  72  and the permanent magnets  70  of the rotor  63  are substantially parallel. Peripheral parts  60  and  61  of the rotor  63  placed inside of cylindrical cavities  91  and  92 , creating a labyrinth  93  hydraulically isolating canals  12  and  13  of air module assembly  2 . 
     All electrical coils made as printed overlapping coils on the PC board in accordance with the U.S. Pat. No. 7,623,013 that is incorporated in this application by reference. 
       FIG. 15  shows the fresh gas passage in a planar section of a compact heat recovery ventilation system  1 , including air module assembly  2 , heat exchanger assembly  3 , fresh air filter assembly  86  and silencer assemblies  87 . Fresh gas flows through filter assembly  86 , silencer assembly  87 , heat exchanger assembly  3 , transition duct  88 , crossflow blower  50  of air module assembly  2 , and through a silencer assembly  87 . 
       FIG. 16  shows the exhaust gas passage in a planar section of a compact heat recovery ventilation system  1 , including air module assembly  2 , heat exchanger assembly  3 , fresh air filter assembly  86  and silencer assemblies  87 . Exhaust gas flows through filter assembly  86 , silencer assembly  87 , crossflow blower  49  of air module assembly  2 , transition duct  88 , heat exchanger assembly  3 , silencer assembly  87  and exhaust gas outtake duct  54 . 
       FIG. 18 a    and  FIG. 18 b    shown one of the options for heat exchanger assembly  3  with traditional heat exchange elements  20  made as a center plate  21  with protruded fins  76  from both sides of the center plate  21 . As the center plate  21  forms separation between the two conduits  28 ,  29  along the length of the heat exchanger assembly  3 . Exhaust gas is restricted to flow through conduit  28  from end  25  to end  24  along the side of the outside panel  22  thus exiting on the same outside panel side  22  as entered. Fresh gas is restricted to flow through conduit  29  from end  24  to end  25  along the side of the outside panel  23  thus exiting on the same outside panel side  23  as it entered. 
       FIGS. 19 ( a,b,c,d ) show changeable gas flow side heat exchangers could be made as corrugated fins with a base plate divider or as plate heat exchanger based on the same principles  FIGS. 20 ( a,b,c,d ). The center plate  21  splits in two end center plates  74 ,  75  located respectively at the ends  24 ,  25  of the heat exchanger assembly  3  for both configurations. 
     Option shown in the  FIG. 19  ( a,b,c,d ) includes the heat exchanger assembly  3  with heat exchanging elements  20  shaped as corrugated fins  78  made as a plurality of channels  79  divided by end center plate  74  and  75  located respectively at the ends  24 ,  25  of the heat exchanger assembly  3 . 
     End  25  has exhaust gas intake  31  and fresh gas outtake,  36  while the end  24  has fresh gas intake  32  and exhaust gas outtake  34 . 
     At the exhaust gas intake  31  at the end  24  every even channel  81  is sealed and every odd channel  82  is open, while at the fresh gas outtake  36  at the same end  24  every odd channel  82  is sealed and every even channel  81  is open. 
     For this particular heat exchanger with heat exchanging elements  20  at exhaust gas flows through the exhaust gas intake  31  next to outside panel  22  at end  24 , through open odd channels  82  to the exhaust gas outtake  34  next to outside panel  23  at end  25 , thus gas is forced to change sides. 
     Fresh gas flows through the fresh gas intake  32  next to outside panel  23  at end  25 , through open even channels  81  out to the fresh gas outtake  36  next to outside panel  22  at end  24 , thus gas is forced to change sides. 
     Option shown in the  FIGS. 20 ( a,b,c,d ) includes the heat exchanger assembly  3  with heat exchanging elements  20 . The heat exchanging elements  20  are of plate type, where at both ends  24  and  25  at exhaust gas outtake  34  and exhaust gas intake  31  plurality of pairs of all odd plates  84  and even plates  83  are bended and sealed together. 
     At both ends  24  and  25  at fresh gas intake  32  and fresh gas outtake  36  pluralities of pairs of all even plates  83  and odd plates  84  are bended and sealed together. 
     At the end  24  of the heat exchanger assembly  3  the exhaust gas intake  31  is separated from fresh gas outtake  36  by center plate  74 . 
     At the end  25  of the heat exchanger assembly  3  the fresh gas intake  32  is separated from exhaust gas outtake  34  by center plate  75 . 
     For this particular heat exchanger assembly  3  with heat exchanging elements  20  the exhaust gas flows through the exhaust gas intake  31  next to outside panel  22  at end  24 , through open odd channels  82  to the exhaust gas outtake  34  next to outside panel  23  at end  25 , thus gas is forced to change sides. 
     Fresh gas flows through the fresh gas intake  32  next to outside panel  23  at end  25 , through open even channels  81  out to the fresh gas outtake  36  next to outside panel  22  at end  24 , thus gas is forced to change sides. 
     This gives additional flexibility in design as the air is free to move between opposite sides of the heat exchanger, and the air can exit on the other end of the heat exchanger on the opposite side than it entered. 
     The principals of such heat exchanger are described in U.S. Pat. No. DE4,301,296 “Plate heat exchange on countercurrent principle” and incorporated here by reference. 
     The heat exchangers described in  FIGS. 19 and 20  are the most beneficial for our proposed application. The heat transfer distance is much shorter, and therefore, the heat exchanger efficiency relies in much lesser degree on heat conductance coefficient of the heat exchanger material. The heat exchanger can therefore be made out of plastic material. By using a vapor permeable material in the heat exchanger folded fins or plate, humidity can be recovered. Thus, upgrading the heat recovery system to an energy recovery system. 
     The changing or sides of the airflow inside the heat exchanger, is also beneficial as it can be used to prevent formation of dead pockets inside the heat exchanger which may accumulate and condensate dirt, hence, having both outlets on the bottom side can help reduce any such accumulation inside the heat exchanger. 
     There are several alignments of heat exchangers assembly  3  and air module assembly  2  that are possible in the compact heat recovery ventilation system  1 . 
       FIGS. 21, 22 and 23  show three different alignments of the compact heat recovery ventilation system  1 .  FIG. 21  shows L-shaped transition  89  where heat exchanger outside panels  22 , 23  and center plate  21  no longer connect directly with the air module assembly  2 , and are no longer parallel with side panels  8 , 9  or base plate  4  of the air module assembly  2 .  FIG. 22  shows a configuration where the compact heat recovery ventilation system  1  has a bent exchanger assembly  3 .  FIG. 23  shows configuration where the compact heat recovery ventilation assembly  1 , has two separate transition ducts connecting heat exchanger assembly  3  to the air module assembly  2 . 
     According to  FIG. 21  of the present invention the air module assembly  2  is connected to the heat exchanger assembly  3  with transition ducts. The exhaust gas flows through the exhaust gas duct inlet duct  54 A, exhaust gas inlet  14 , crossflow blower  49  in the exhaust gas canal  12  of the air module assembly  2 , the exhaust gas outlet  53 A, the exhaust transition channel  90  of the L shaped transition  89 , exhaust gas intake  31  through heat exchanging elements  20  and exhaust gas outtake  34  of heat exchanger assembly  3 , while fresh gas flows through the fresh gas intake  32  through heat exchanging elements  20 , fresh gas outtake  36  of the heat exchanger assembly  3 , fresh air transition channel  91  of the transition  89 , fresh gas inlet  15 , cross flow blower  50  in fresh gas canal  13 , and fresh gas outlet  17 , fresh gas outlet duct  55 A of air module assembly  2 , thus providing countercurrent heat exchange process. 
     According to  FIG. 22  of the present invention the air module assembly  2  is connected to the heat exchanger assembly  3  which is L-shaped. The exhaust gas flows through the exhaust gas inlet duct  54 A, exhaust gas inlet  14 , crossflow blower  49  in the exhaust gas canal  12  of the air module assembly  2 , the exhaust gas outlet  16 , exhaust gas intake  31  through heat exchanging elements  20  and exhaust gas outtake  34  of the L shaped heat exchanger assembly  3 , while fresh gas flows through the fresh gas intake  32  through heat exchanging elements  20 , fresh gas outtake  36  of the L-shaped heat exchanger assembly  3 , fresh gas inlet  15 , cross flow blower  50  in fresh gas canal  13 , and fresh gas outlet  17 , fresh gas outlet duct  55 A of air module assembly  2 , thus providing countercurrent heat exchange process. 
     According to  FIG. 23  of the present invention the air module assembly  2  is connected to the heat exchanger assembly  3  with transition duct assembly  94 . The exhaust gas flows through the exhaust gas inlet duct  54 A, exhaust gas inlet  14 , crossflow blower  49  in the exhaust gas canal  12  of the air module assembly  2 , the exhaust gas outlet  16 , exhaust gas transition duct  95 , exhaust gas intake  31  through heat exchanging elements  20  and exhaust gas outtake  34  of heat exchanger assembly  3 , while fresh gas flows through the fresh gas intake  32  through heat exchanging elements  20 , fresh gas outtake  36  of the heat exchanger assembly  3 , fresh gas transition duct  96 , fresh gas inlet  15 , cross flow blower  50  in fresh gas canal  13 , and fresh gas outlet  17 , fresh gas outlet duct  55 A of air module assembly  2 , thus providing countercurrent heat exchange process. 
     The compact heat recovery ventilation system  1  operates in the following way. When an electric power is supplied to the flat stator  68  of the electric drive  45 , the alternative electromagnetic field is created. This electromagnetic field is controlled by the electronic controllers (not shown on Figs.) and interacts with a magnetic field created by the magnetic rotor  63 . As a result of this interaction, the magnetized rotor  63  causes the double radial impeller  57  to rotate. The exhaust gas flows through the exhaust gas inlet duct  54 A, crossflow blower  49  in the exhaust gas canal  12  of the air module assembly  2 , the exhaust gas outlet  53 A, exhaust gas intake  31  through heat exchanging elements  20  and exhaust gas outtake  34  of heat exchanger assembly  3  and exhaust gas outtake duct  54 , while fresh gas flows through the fresh gas intake duct  55 , fresh gas intake  32  through heat exchanging elements  20 , fresh gas outtake  36  of the heat exchanger assembly  3 , flexible fresh air transition channel  91  of the transition  89 , fresh gas inlet  15 , cross flow blower  50  in fresh gas canal  13 , and fresh gas outlet  17 , fresh gas outlet duct  55 A of air module assembly  2 , thus providing countercurrent heat exchange process. 
     According to the present invention, the compact heat recovery ventilation system  1  due to the mutual arrangement of the hydraulic schemes of the crossflow blowers  42  with the double side radial impeller  75  parallel to the base plate  4  of the air module assembly  2 , provides a thin, compact, highly efficient, simple, reliable and less expensive device that can easily be mounted inside the wall, ceiling or inside a vehicle. 
     These combination of the dual thin blowers with the integrated single motor between them, mounted with the side changeable heat exchanger including additional modules such as filters, silencers, humidifiers, assembled in a flat modular way, allows to create a flat compact heat recovery system capable of being soundless, wall-mounted or even be able to fit inside of the wall or ceiling. 
     While the invention has been described with reference to various embodiments, it should be understood that these embodiments are only illustrative and that the scope of the invention is not limited to just those. Many variations, modifications and improvements of the embodiments described are possible. Variations and modifications of the embodiments disclosed herein may be made based on description set forth herein, without departing from the scope and spirit of the invention as set forth in the following claims. 
     In accordance to the above description of proposed invention first prototype of such system was manufactured, installed in the standard wall and successfully tested.