Abstract:
A system and method for providing conditioned air to an aircraft cabin. The system combines the benefits of a traditional 4 wheel condensing cycle and dual expansion energy recovery cycles. The energy of a heat load such as aircraft electronic or avionics can be recovered and used in a second turbine while a continuous source of cooling for the heat load is provided for high altitude operation when the first turbine is by-passed. The disclosed invention conditions inlet air using an efficient process that recaptures energy that would otherwise be wasted. Recaptured energy can come from aircraft avionics and from moisture in inlet and cabin air.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to apparatus and methods for conditioning inlet air for use in an aircraft cabin and, more particularly to apparatus and methods for conditioning cabin air while capturing and reusing energy that would otherwise be waste. 
   In aircraft operating in atmospheres with low pressure it is necessary to condition the cabin air to increase pressure and provide temperature and humidity control. 
   U.S. Pat. No. 6,250,097 shows a combined 4 wheel air cycle and liquid cycle system used to cool aircraft cabin air and avionics while recovering some heat energy in the process. In &#39;097, an air cycle includes, inlet air from an aircraft turbine cooled by ambient air, compressed and cooled again by ambient air. The inlet air is then cooled again by use of reheat heat exchangers which route the warm moist inlet air over cooled inlet air downstream in the system. The inlet air is then expanded through a first turbine and water is extracted. The inlet air then enters an air to liquid heat exchanger where warm fluid containing heat energy from a liquid cycle used to cool the aircraft avionics is used to warm the inlet air. Then the inlet air passes through a reheater to gain energy from the next inlet air and is then expanded through a second turbine. The cool inlet air from this turbine is again warmed by the liquid cycle in a heat exchanger and the air is then supplied to the cabin. This arrangement recaptures some of the available energy from the heat of vaporization of the liquid from the air and from reject heat contained in the liquid cycle from aircraft avionics. However, &#39;097 does not disclose a way to continue to cool the aircraft avionics when the avionics heat energy is not needed in the air cycle. Aircraft electronics and avionics must be cooled constantly or they will overheat. Therefore there must be a way to cool the avionics even when the waste energy is not needed. In operation, there are also conditions when it would be desirable to at least partially bypass some elements of an air conditioning system. For example, at high altitude operation when ambient air is cool and dry relative to cabin conditions, the first turbine in air cycles such as that shown in &#39;097, is not needed. The first turbine has a smaller nozzle intake and therefore constricts flow more than the second turbine so the system shown in &#39;097 bleeds air off the aircraft turbine engine that is not required to condition cabin space, wasting energy. 
   Another prior art example of the so-called 4-wheel environment control systems is shown in Warner U.S. Pat. No. 5,086,622. The Warner patent figure shows a bypass valve 72 that bypasses the first turbine during high altitude aircraft performance when the turbine would not be needed. For example, during high altitude performance, when ambient air is cooler and bleed air is less humid than at ground level, operation of the first turbine would waste energy by drawing un-needed bleed air from the turbine engine. The inefficient operation of Warner forces designers to build the system components, particularly heat exchangers, larger than needed which in turn wastes more aircraft fuel in carrying the additional weight. 
   As can be seen, there is a need for an improved condensing cycle energy recovery system that is compact and economical to operate. There is a need for an improved apparatus and method for condensing cycle energy recovery system that makes use of all energy available, including waste energy from aircraft avionics. There is further a need for a condensing cycle energy recovery system that is efficient so that system components can be sized as small as possible and still do the job of conditioning the aircraft cabin space. 
   SUMMARY OF THE INVENTION 
   In one aspect of the invention, an inlet takes air from a supply such as a bleed from an aircraft turbine engine and conditions the inlet air using a first air sub-cycle. The first air sub-cycle cools inlet air in a heat exchanger with ambient air and compresses it. A second heat exchanger and condenser further cools the inlet air and extracts moisture from the air upstream from a first turbine. Air expanded and cooled in the turbine then captures the heat of vaporization in the condenser to warm the now dry inlet air. A third heat exchanger further heats inlet air with waste heat from a heat load, and a second turbine expands the air for use as supply air to a space. An economy valve can be used for bypassing the condenser, first turbine and third heat exchanger, which make up a first air sub-cycle, for supplying inlet air directly to the second turbine. This bypass valve operates at high altitude when the first turbine would otherwise bleed off more air from the aircraft turbine engine than may be required to condition cabin space. 
   In another aspect of the invention, air from the first air sub-cycle can be heated using waste energy from aircraft electronics or avionics. The waste energy can be collected in a closed loop liquid or air sub-cycle and warms inlet air from the first air sub-cycle in an air/air or liquid/air heat exchanger. 
   In a further aspect of the invention, waste energy from the avionics load can be exchanged using an aircraft skin heat exchanger. Thus, when the bypass valve bypasses the first air sub-cycle it can also bypass the third heat exchanger and the un-needed waste energy from aircraft avionics. So at altitude, the waste energy from the avionics can be cooled by ambient air through the aircraft skin heat exchanger and the avionics have the needed constant source of cooling. 
   In a still further aspect of the invention, a method of providing conditioned air for an aircraft cabin is described. The method includes the steps of bleeding inlet air from an aircraft turbine engine, then cooling it, dehumidifying it and compressing it in an air sub-cycle that can recapture at least a portion of the heat of vaporization of the condensed moisture. The method also includes heating inlet air with a third heat exchanger using waste heat from the aircraft. The method includes expanding the inlet air in a second turbine. The method also includes a step of bypassing the first turbine when the aircraft is in ambient air that is cooler and dryer then the condition desired in the cabin. This step saves bleed air that would otherwise be unnecessarily bled from the aircraft engine by the first turbine. The efficiency of this arrangement allows system components to be smaller which saves even more aircraft space and fuel. 
   In another aspect of the invention, the method of conditioning aircraft cabin air includes bleeding inlet air from an aircraft turbine engine expanding, cooling and dehumidifying the inlet air, in a first air cycle. Then heating said inlet air with an air/air heat exchanger using waste heat from aircraft avionics. 
   These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block diagram of the conditioning cycle according to one embodiment of the invention; 
       FIG. 2  shows a block diagram of a second embodiment of the present invention; 
       FIG. 3  shows a block diagram of a third embodiment of the present invention; 
       FIG. 4  shows a block diagram of a fourth embodiment of the present invention; 
       FIG. 5  shows a block diagram of a fifth embodiment of the present invention; and 
       FIG. 6  shows a block diagram of a sixth embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
   It is necessary to cool and condition air for supply to a cabin space of an aircraft. The system used must perform in a variety of conditions including in relatively warm moist air when the aircraft is on the ground and inlet air comes from an auxiliary power source, and in cool dry air when the aircraft is at high altitude. In flight it is common practice to use air bled from a turbine engine as inlet air and to condition the inlet air to cool and dehumidify the air. The disclosed invention conditions inlet air using an efficient process that recaptures energy that would otherwise be wasted. Recaptured energy can come from aircraft avionics and from moisture in inlet and cabin air. 
   Referring now to the Figures, where like elements in different embodiments carry like numbers,  FIG. 1  shows a schematic block diagram of a first embodiment of the condensing cycle energy recovery system  10 . The energy recovery system  10  includes an air cycle sub-system  12  indicated by dashed lines and in this embodiment a liquid cycle sub-system  14  also indicated by dashed lines. The air cycle subsystem  12  may begin with inlet air ‘A’ from supply line  16 . This inlet air ‘A’ in flight may be bled from the turbine engine ‘T’ of the aircraft (not shown). When the aircraft is on the ground air supply line  16  may connect to an auxiliary source (not shown). The inlet air ‘A’ may flow over a primary heat exchanger  20 , which uses ambient air from ambient air inlet  22  to cool the inlet air ‘A’. After the inlet air ‘A’ is cooled it may be compressed by compressor  24 , and then cooled again by a second heat exchanger  28  again using ambient air from inlet  22 . When the aircraft is on the ground, the moist inlet air ‘A’ may flow through regenerative heat exchanger  32  where it can be partially cooled and then the inlet air ‘A’ may flow through condenser  34  where it may be further cooled. Water may be condensed out by extractor  36 , and cold dry inlet air ‘A’ may flow through the cold side of regenerative heat exchanger  32  to partially cool the next flow of air. Dry inlet air ‘A’ may then be supplied to the first turbine  40  where it may be expanded and used to condense water from the next flow of air through condenser  34 . The inlet air ‘A’ may then flow through the liquid/air heat exchanger  50  where it may be further warmed how by the liquid cycle sub-system  14 . The inlet air ‘A’ may then be supplied to the second turbine  60  where it may be expanded and supplied to cabin  70 . 
   At altitudes where ambient air is cool compared to the desired cabin conditions, the economy cooling bypass valve  80  may open bypassing the first turbine  40  and air cycle sub-system  12  as they are not needed and bypassing them saves energy. The heat load  82 , which may include aircraft electronics and avionics may be cooled, in this embodiment, with an aircraft skin heat exchanger  84  when the liquid/air heat exchanger  50  is bypassed. The aircraft skin heat exchanger  84  may include a low altitude bypass valve  85  which may bypass the aircraft skin heat exchanger  84  at low altitude so that the waste energy may be used by the second turbine  60 . The liquid cycle sub-system  14  also may include a coolant pump  86  that can move liquid through the liquid/air heat exchanger  50  to cool inlet air ‘A’. 
     FIG. 1  further shows a second turbine bypass valve  90 . If the bypass valve  80  opens to bypass the first turbine  40 , and if the system  10  still is able to supply more cool air then the cabin  70  requires, the turbine bypass valve  90  may open to at least partially bypass the second turbine  60  as well. Bypassing the second turbine  60  may save additional energy. Also shown in  FIG. 1  is a low temperature control valve  92 . With bypass valve  80  and turbine bypass valve  90  both open to bypass both first and second turbines  40  and  60 , if the system is still supplying air to the cabin  70  that is too cool, then low temperature control valve  92  may open to mix some warm air from compressor  24  with the supply air to cabin  70 . Should the actual first turbine  40  outlet temperature fall and ice form in the condenser  34 , the low limit valve  94  may open to bypass just the first turbine  40 . 
     FIG. 2  shows a second embodiment. In this embodiment auxiliary cooling may be performed by a closed air sub-cycle  114 . As in the first embodiment, cooling may occur at altitude through a skin heat exchanger  184 , but in this case the fluid medium may be air. There may be a heat load  182  and a fan  186  may circulate air in the closed air sub-cycle  114 . An air/air heat exchanger  150  may transfer heat from the closed air sub-cycle  114  to the air cycle sub-system  112 . An inline valve  188  may open when ambient air temperature is below the desired cabin temperature, to allow flow through the skin heat exchanger  184  to cool the heat load  182  when the bypass valve  80  is open. Thus the heat load  182 , which may include aircraft avionics, may have a constant source of cooling from closed air sub-cycle  114 , while heat energy from the heat load  182  may perform useful work through the second turbine  60  when needed. 
     FIG. 3  shows an alternate embodiment. This embodiment is similar to that of  FIG. 1  except for the use of an altitude load cooling valve  200 . The altitude load cooling valve  200  may open up when the airplane is at altitude and when the economy cooling bypass valve  80  may be open. The altitude load cooling valve  200  may allow the portion of the inlet air ‘A’ that flows through turbine  40 , condenser  34  and liquid to air heat exchanger  50 , to bypass the second turbine  60 . Then this portion of the inlet air ‘A’ may be remixed with the supply stream coming through economy cooling bypass valve  80  and the second turbine  60 . This approach may have the advantage of allowing recovery of energy from both the heat of vaporization and the heat load  82  in the second turbine  60  during normal operation. It also may allow the heat load  82  to be continuously cooled during all operating conditions while the second turbine  60  may do useful work using the recovered energy. 
     FIG. 4  presents an embodiment that is similar to  FIG. 3  except that the heat load  382  may be cooled by a closed air loop  314 . A fan  386  may circulate air in the closed air loop  314  over the air/air heat exchanger  350  which may exchange heat with the inlet air ‘A’ from air cycle sub-system  312  just as in the other embodiments. The embodiment of  FIG. 4  also includes an altitude load cooling valve  200  as in the embodiment of FIG.  3 . The advantage of this approach may be that the second turbine  60  may be bypassed to save even more energy by reducing air bleed when the ambient air is cooler then the desired cabin temperature. 
     FIG. 5  shows an embodiment where an air/air heat exchanger  400  may be added to the closed air loop  414 . Heat may be exchanged first through the air/air heat exchanger  450  with inlet air ‘A’ from air cycle sub-system  412  and then again through the second air/air heat exchanger  400  after the inlet air ‘A’ leaves second turbine  60 . A valve  402  may control flow through the heat exchanger  400  and may allow the flow at altitude when the economy cooling valve  80  bypasses turbine  40  and the air cycle sub-system  412  so that the heat load  482  may have a constant source of cooling. By placing the heat exchanger  400  in a circuit location where it may be supplied with the coldest possible supply air temperature, minimum or no engine bleed inlet air flow may be needed to cool the heat load  482  at cool dry ambient conditions. While  FIG. 5  shows an air closed loop  414  for cooling the heat load  482  it will be understood that a liquid closed loop could also be used. 
     FIG. 6  also shows an embodiment where both the heat of vaporization and the energy of the cabin air are recovered in the second turbine  60 . In this embodiment cabin  570  re-circulation air may be provided to an energy recovery heat exchanger  550  downstream of the first turbine  40  of air cycle sub-system  512 . In the second turbine  60  both the heat of vaporization from the condenser  34  and a portion of the cabin heat load energy may be converted to useful energy. The re-circulated cabin air, moved by fan  586 , may then be mixed with fresh inlet air ‘A’ from turbine  60  and with a portion of untreated cabin air in mixer  590 . The advantage of this approach may be that waste energy from the cabin air may be recaptured in the second turbine  60 . 
   It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.