Abstract:
There is provided a controller for a heat capture and storage system configured to capture and store energy from heat expelled in engine exhaust. The controller includes a plurality of inputs, a plurality of outputs, and at least one processor coupled to a memory for storing within the memory instructions executable by the at least one processor. The controller is configured by execution of the instructions stored in the memory to: receive signals at one or more of the plurality of inputs, the signals representing at least one operating parameter of the heat capture and storage system; and based on at least one operating parameter, generate signals at one or more of the plurality of outputs for controlling at least one component of the heat capture and storage system to capture and store the energy from the heat expelled in the engine exhaust.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/601,723 filed Jan. 21, 2015, which is a divisional of U.S. patent application Ser. No. 13/395,049 filed Sep. 28, 2012, which is the National Stage of International Application No. PCT/CA2011/000315, filed Mar. 30, 2011, and claims the benefit of U.S. Provisional Patent Application No. 61/319,923, filed Apr. 1, 2010. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to energy storage, and more particularly to a system and method for capturing and storing thermal energy as a source of auxiliary power in a vehicle. 
       BACKGROUND 
       [0003]    Conventional vehicles that use internal combustion engines, such as transport trucks, either require heat from a running engine to power a heating system of the vehicle to supply heat during the winter or require mechanical energy generated by a running engine to turn a compressor in order to power an air-conditioning system in order to supply cooling during the summer. Truck drivers often leave their engines running while the truck is parked for extended periods of time in order to supply this heating or cooling while taking a break or sleeping overnight. Since trucks typically have diesel engines, this prolonged idling results in significant amounts of pollutants being released into the atmosphere. Additionally, many jurisdictions are now implementing anti-idling legislation, which prohibits trucks from being left to idle and leaves the drivers with few options for heating or cooling while taking a break inside the cab. 
         [0004]    It would be desirable to have a system and method for capturing and storing thermal energy as auxiliary power in a vehicle that addresses at least some of the shortcomings of the conventional systems. 
       SUMMARY 
       [0005]    One aspect of the present disclosure provides a system for capturing energy from heat expelled in an exhaust of an engine of a motor vehicle and storing the captured energy. The system comprises a generator, a condenser, an evaporator, and an absorber. The generator captures heat from the exhaust of the engine and may be configured for circulating a first solution having a solute that is vaporizable by heat captured by the generator. The condenser may be coupled to the generator for receiving vaporized solute and condensing the vaporized solute to a liquid. The evaporator may be coupled to the condenser and have an orifice between the condenser and the evaporator, the evaporator having a first fluid passage for circulating the solute and a second fluid passage for circulating a second solution. The first and second fluid passages may be configured such that solute running through the first fluid passage is vaporizable by heat absorbed from the second solution running through the second fluid passage, thereby cooling the second solution. The absorber may be coupled to the evaporator and the generator. The absorber may be configured to return the solute to solution by mixing the solute with a solvent of the first solution supplied by the generator, and for returning the first solution to the generator to complete a cycle of the system. 
         [0006]    Another aspect of the present disclosure provides a method for operating in cold storage mode a system for capturing energy from heat expelled in an exhaust of an engine of a motor vehicle and storing the captured energy. The method comprises absorbing heat from the engine exhaust into a solution and vaporizing a solute of the solution, leaving behind the solvent of the solution; cooling and condensing the solute back into a liquid; injecting the liquid solute into an evaporator, allowing the solute to absorb thermal energy, thereby cooling a second solution flowing through the evaporator; and further absorbing the solute back into the solvent to reconstitute the solution for further use in the absorbing step. 
         [0007]    Another aspect of the present disclosure provides a method for operating in heat storage mode a system for capturing energy from heat expelled in an exhaust of an engine of a motor vehicle and storing the captured energy. The method comprises absorbing heat from the engine exhaust into a solution and vaporizing a solute of the solution, leaving behind a solvent of the solution; circulating the solute through an evaporator to enable the solute to dissipate thermal energy, thereby heating a second solution flowing through the evaporator; and absorbing the solute back into the solvent and reconstituting the solution for further use in the absorbing step. 
         [0008]    Another aspect of the present disclosure provides a controller for controlling a system for capturing energy from heat expelled in an exhaust of an engine of a vehicle and storing the captured energy. The controller may have at least one processor coupled to a memory for storing within the memory instructions executable by the at least one processor and a plurality of inputs and a plurality of outputs. The controller may be configured to execute instructions stored in the memory and thereby receive signals at one or more of the inputs and generate signals at one or more of the outputs for controlling components of the system to capture energy from the heat expelled in the exhaust of the engine of the vehicle and store the captured energy. 
         [0009]    Another aspect of the present disclosure provides a heat exchanger for use in a system for capturing energy from heat expelled in an exhaust of an engine of a vehicle and storing the captured energy. The heat exchanger may have an outer conduit and an inner conduit. The heat exchanger captures heat from the exhaust of the engine travelling through the inner conduit and transfers the heat to a solution circulating through the outer conduit, a solute of the solution being vaporized as heat is absorbed by the solution. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Reference will now be made to the drawings, which show by way of example, embodiments of the present disclosure, and in which: 
           [0011]      FIG. 1  shows in block diagram form a thermal auxiliary power unit according to one aspect of the present description; 
           [0012]      FIG. 2 a    shows in block diagram form a thermal auxiliary power unit operating in a cold storage mode according to one aspect of the present description; 
           [0013]      FIG. 2 b    shows in flow chart form the process of a thermal auxiliary power unit operating in a cold storage mode according to one aspect of the present description; 
           [0014]      FIG. 3 a    shows in block diagram form a thermal auxiliary power unit operating in a heat storage mode according to one aspect of the present description; 
           [0015]      FIG. 3 b    shows in flow chart form the process of a thermal auxiliary power unit operating in a heat storage mode according to one aspect of the present description; 
           [0016]      FIG. 4  shows in block diagram form a process executed by the controller of the thermal auxiliary power unit according to one aspect of the present description; and 
           [0017]      FIG. 5  shows a front view and a related sectional view of a generator for use with a thermal auxiliary power unit according to one aspect of the present description. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Thermal auxiliary power unit systems are described that store and release thermal energy in a controlled manner to enable a vehicle such as a truck to continue to provide heating and cooling to the passenger compartment and/or to other systems within the vehicle when the main engine is not running. Such systems may thereby reduce fuel consumption, emissions, and make it easier for drivers to comply with existing and/or upcoming anti-idling legislation. During the winter months, heat may be captured from the engine&#39;s exhaust and/or engine cooling system and may be stored in an insulated tank for later use. During the summer months, the heat from the vehicle exhaust system may be used to drive an absorption refrigeration unit that cools a liquid and/or creates ice, which are stored. Some aspects of the functioning of the systems may be similar to a combined cycle used in power plants but are suitably modified and applied to a motor vehicle. The ice may be melted at a later time giving up its latent heat to provide a source of cooling. In neither case is any significant additional fuel used to create the heating or cooling storage, thus reducing fuel cost for the operator who wishes to have heating or cooling available at a time that would normally require leaving an engine idling while the vehicle is not being driven. The system may therefore make use of waste heat expelled by an internal combustion engine by capturing the waste heat in a bottoming cycle and storing it in an absorption cycle. 
         [0019]    The term bottoming cycle is used herein to refer to the process of capturing energy from exhaust heat and the term absorption cycle is used herein to describe a style of refrigeration, which is a thermal process and not a mechanical process. For example, an absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive a cooling system. 
         [0020]    Systems according to the invention may include an insulated storage vessel capable of storing up to, for example, 10 kWh of thermal energy, an absorption refrigeration unit, a battery to store sufficient electricity for pumping, air circulation and control purposes, and heat exchangers to acquire and dispense the thermal energy through an absorption cycle under the control of an energy management controller. One form of such systems may include a photo voltaic array that generates electricity during daylight hours for storage in the battery. Another form of such systems may simply utilize a high output mechanically-coupled alternator which charges the battery during vehicle use. 
         [0021]    Systems in accordance with the invention may provide an advantage over conventional truck heating, ventilating, and air-conditioning (HVAC) systems that use some fuel during driving to power a cooling or heating system and that also use fuel in a direct fire heater during periods when the main engine is shut off. Other systems use a small auxiliary engine and present problems with noise and vibration, maintenance, and also use fuel and create additional emissions. Systems in accordance with the invention may also provide a life cycle cost that uses and stores thermal energy directly with little or no operational penalty to vehicle operation. Such systems may use little or no fuel and, in some embodiments, may even reduce fuel consumption while driving. In long haul trucks, the system may pay for itself in as little as two years due to reduced fuel consumption from reduced idling. The system itself may be emission free and silent or nearly silent in operation. 
         [0022]    Referring now to  FIG. 1 , a block diagram is shown illustrating a thermal auxiliary power unit or system  100  according to one aspect of the present description. The system  100  generally includes an exhaust diverter valve  102 , a generator  104 , a valve  106 , a condenser  108 , an evaporator pre-cooler or heat exchanger  110 , a spray orifice  112 , an evaporator  114 , an absorber  116 , an absorber pre-cooler or heat exchanger  118 , a thermal storage tank  120 , a thermal tank input coil and circuit  122 , a thermal tank output coil and circuit  126 , a controller  128 , and a valve  130 . 
         [0023]    The exhaust diverter valve  102  may be coupled to an exhaust pipe of a vehicle and the generator  104  and the valve  102  may ensure the thermal energy from the engine exhaust is appropriate for the system  100  by regulating the flow of exhaust to the generator  104 . In  FIG. 1 , the exhaust arriving from the engine to the system  100  is indicated by arrow  103  and the exhaust leaving the system  100  after passing through the generator  104  is indicated by arrow  105 . A bypass path controllable by the valve  102  is indicated by arrow  107 . In one example, the valve  102  may be a 3-way, 2-position type valve and may be able to completely divert the exhaust to or away from the generator  104  or blend between the generator  104  and bypass path  107  to achieve the proper heat load passing through the generator  104 . Optionally, the valve  102  may be omitted, but this may compromise performance on different driving cycles 
         [0024]    The generator  104  may include a heat exchanger that receives the hot exhaust from the engine and captures heat expelled in the exhaust from the engine of the vehicle and transfers that energy to a solution (e.g., water/ammonia (H 2 O/NH 3 )) that circulates through the generator  104 . The solution may be heated to a point where the solute (e.g., the ammonia) boils out of the water sending the ammonia at a high pressure and temperature out through a line to the next component in the system (e.g., either the condenser  108  in cooling mode or the evaporator  114  in heating mode). In one example, the heat exchanger component of the generator  104  may be the liquid to air type and may capture the heat from the exhaust of the vehicle engine. However, a liquid to liquid heat exchanger may also perform the same task and recover the thermal energy from other heat sources of the engine such as the cooling circuit of the engine. While the generator  104  is referred to throughout as a generator, the term heat exchanger is equally applicable and the generator  104  may accurately be referred to as a heat exchanger. The generator  104  is described in more detail below in connection with  FIG. 5 . 
         [0025]    The valve  106  may provide the system  100  with the ability to switch between heating and cooling mode by changing the fluid flow path through the system  100 . For example, the valve  106  may be of the 3-way 2-position type and may direct the flow of ammonia through the condenser  108  prior to the spray orifice  112  and evaporator  114  and the system  100  may function using an absorption cycle when cooling is desired. If heating is desired, the valve  106  may be configured to direct the flow of ammonia through a secondary circuit bypassing the condenser  108  and the spray orifice  112 , which eliminates the cooling portion of the system  100  and sends hot ammonia directly to the evaporator  114 . The heating and cooling modes of the system  100  will be described in greater detail below in connections with  FIGS. 2 and 3 . 
         [0026]    The condenser  108  may include a heat exchanger that condenses the hot ammonia gas back into a liquid while still under high pressure by cooling the ammonia below its boiling point while the system  100  is operating in cooling mode. In one embodiment, the heat exchanger portion of the condenser  108  may be of the liquid to air type and may remove thermal energy from the ammonia and releases it to the surrounding environment. It is also possible to implement the condenser  108  as the liquid to liquid type and discard the excess thermal energy elsewhere to a liquid, however this could lower the coefficient of performance of the condenser  108 . The condenser  108  may optionally have a fan (not shown) configured to pass air through the condenser  108  thereby increasing the efficiency of the condenser  108 . 
         [0027]    The evaporator pre-cooler  110  may include a heat exchanger and aims to increase the coefficient of performance of the system  100 , therefore allowing other components to operate more efficiently. In one embodiment, the heat exchanger portion of the evaporator pre-cooler  110  is of the liquid to liquid type and transfers thermal energy between a fluid passage going from the condenser  108  to the evaporator  114  and from a fluid passage going between the evaporator  114  and the absorber  116 . In one example, the fluid passages may be implemented using fluid coils within the exchanger portion of the evaporator pre-cooler  110 . It is also possible to omit the evaporator pre-cooler  110  from the system  100 , but performance may be reduced. 
         [0028]    The spray orifice  112  may include a restriction placed in the flow passage in the cooling circuit. As the ammonia leaves the evaporator pre-cooler  110  before the ammonia arrives at the evaporator  114 , the orifice  112  causes the high pressure ammonia to be sprayed into the relatively low pressure cavity of the evaporator  114 , resulting in the ammonia being vaporized. The loss in pressure of the ammonia also causes a temperature drop of the ammonia. 
         [0029]    The evaporator  114  includes a heat exchanger for transferring thermal energy between the absorption system containing the ammonia and a circuit that transfers that thermal energy to the thermal storage tank  120 . In one embodiment, the heat exchanger portion of the evaporator  114  is of the gas to liquid type with the ammonia flowing through a first fluid passage (e.g., a fluid coil) of the evaporator  114  and solution (e.g., glycol/water) flowing through a second fluid passage (e.g., a fluid coil) of the evaporator  114 . 
         [0030]    The absorber  116  includes a heat exchanger that allows the ammonia solute to dissolve back into the water solvent by cooling both fluids to a temperature where such can occur. The absorber  116  may include a spray bar at its lower end. The ammonia is fed through the spray bar and since ammonia is lighter than water, the ammonia bubbles through the water to the top and is largely absorbed in the water. In one embodiment, the heat exchanger portion of the absorber  116  is of the liquid to air type. It is also possible to use a liquid to liquid type heat exchanger in the absorber  116  at a lower overall system performance. 
         [0031]    The absorber pre-cooler  118  may include a heat exchanger for increasing the coefficient of performance of the system  100  and therefore allowing other components to operate more efficiently. In one embodiment, the heat exchanger portion of the absorber pre-cooler  118  is of the liquid to liquid type and transfers thermal energy between the ammonia/water fluid passage connected between the absorber  116  and the generator  104  and the return water fluid passage going back from the generator  102  to the absorber  116 ; however it may be possible to create a system that would operate without the pre-cooler  118  be it at a lower coefficient of performance. 
         [0032]    The thermal storage tank  120  may be, for example, a sealed storage tank that houses and insulates thermal storage fluid and the thermal energy the fluid stores until that energy is needed for transfer elsewhere at a later time. In one example, the thermal storage fluid may be a water/glycol blend. The thermal storage tank  120  may include an input fluid passage  122  (e.g., a fluid coil and circuit) and an output fluid passage  124  (e.g., a fluid coil and circuit). 
         [0033]    The input fluid passage  122  may form part of a heat exchanger and may have a corresponding fluid circuit and pump for transferring thermal energy from the evaporator  114  to the thermal storage tank  120 , or vice versa. In one example, the heat exchanger portion of the input fluid passage  122  may be of the liquid to liquid type with, for example, a glycol/water blend used for the fluid in the fluid passage  122  flowing back and forth from the evaporator  114  to the thermal storage tank  120 . The thermal storage tank  120  may have fluid present within the thermal storage tank  120  in which the input fluid passage  122  is submerged. In one example, the fluids of the fluid passage  122  and the thermal storage tank  120  are of different concentrations to achieve different effects. However, any glycol concentration in the water may be used to meet the design criteria of a particular application. 
         [0034]    The thermal tank output fluid passage  124  may form part of the heat exchanger and the fluid passage  124  may be driven by a pump and may be responsible for transferring thermal energy from the thermal storage tank  120  to the HVAC  126  unit of a vehicle. In one example, the heat exchanger portion of the thermal tank having output fluid passage  124  and input fluid passage  122  may be of the liquid to liquid type with, for example, a glycol/water blend being both the fluid in the fluid passage  124  and the thermal storage fluid present within the thermal tank  120  in which the thermal tank fluid passage  124  is submerged. In one example, the fluids of the tank output fluid passage  124  and the thermal storage tank  120  are of different concentrations to achieve different effects. However, any glycol concentration in the water may be used to meet the design criteria of a particular application. 
         [0035]    The valve  130  may be, in one example, a 3-way 3-position dual circuit type valve and may direct the flow of the solution (e.g., glycol/water) between the vehicle&#39;s HVAC  126 , the vehicle&#39;s engine, and the thermal storage tank  120 . For example, if the solution in the thermal storage tank  120  is hot because the vehicle is currently being operated in a cold environment such as during the winter, the valve  130  may control three possible operating modes. First, the valve  130  may be closed, connecting the engine to the HVAC unit  126 , for example when the vehicle is moving and the heat source from the thermal storage tank is currently not needed while the system  100  is heating the solution in the thermal storage tank  120  for later use. Second, the valve may be in a first open position allowing the solution to pass from the thermal storage tank  120  to the HVAC unit  126 , thereby allowing the HVAC  126  to use the stored heat such as when the vehicle is parked with the engine off and a user of the system  100  desires the cabin of the vehicle to be heated. Third, the valve may be in a second open position directing the flow of solution to the vehicle engine. This may be useful during a cold start of the engine during cold conditions, allowing the user of the system  100  to pre-heat the engine before starting the engine, thereby reducing engine wear and emissions emitted by the engine during a cold start and allowing the user to immediately use the vehicle heating system once the engine is started. 
         [0036]    The system  100  further includes a controller  128  programmed with suitable code for controlling the overall operation of the system  100 . The controller  128  generally includes a processor coupled to a memory for storing and/or executing program code stored in the memory and a number of inputs and outputs for communicating with various parts of the system  100 . While interconnections between the components of the system  100  and the controller  128  are shown in  FIG. 1  in limited detail, outputs of the controller  128  may be electrically connected to any part of the system  100  controlled by the controller  128  and inputs of the controller  128  are electrically connected to any suitable or desired transducers, feedback loops, or other components of the system  100  responsible for supplying input signals to the controller  128 . 
         [0037]    Pumps may also be used in the system  100  where gases or fluids need help flowing in a particular direction, for example where pressure gradients do not automatically cause fluid flow to occur in a desired direction. Pumps may be suitably implemented anywhere, according to the design criteria of a particular application. As an example, pump  128   a  is shown aiding the flow of the water/glycol blend in the output fluid passage  124 , pump  128   b  is shown aiding the flow of the water/glycol blend in the input fluid passage  122 , and pump  128   c  is shown aiding the flow of the water/ammonia blend from the absorber  116  towards the higher pressure portion of the system  100  where the absorber pre-cooler  118  and generator  104  reside. 
         [0038]    The system  100  may also have a battery (not shown) to store sufficient electricity for pumping, air circulation (e.g., fans) and/or control purposes. Optionally, the system  100  may have a photovoltaic array that generates electricity during daylight hours for storage in the battery. 
         [0039]    Referring now to  FIGS. 2 a  and 2 b   , collectively referred to as  FIG. 2 ,  FIG. 2 a    shows in block diagram form a thermal auxiliary power unit or system  100  operating in a cold storage mode according to one aspect of the present description. In  FIG. 2 a   , the line from the valve  106  to the evaporator  114  is greyed out illustrating that this path is not used when the system  100  operates in cold storage mode.  FIG. 2 b    shows in flow chart form the process  200  of a thermal auxiliary power unit operating in a cold storage mode according to one aspect of the present description. At a first block  202 , exhaust from an engine of a vehicle flows through the generator  104 , as indicated by arrows  103  and  105 , and the generator absorbs heat from the exhaust gas and transfers this heat to a solution, for example water with dissolved ammonia, being circulated through the heat exchanger portion of the generator  104 . As a result, the solute (e.g., the ammonia) boils out of solution and is vaporized and ammonia gas progresses through valve  106 , which is configured to direct the ammonia gas towards the condenser  108  while the system  100  operates in the cold storage mode. The solvent of the solution (e.g., water) is left behind at the generator  104 . As an example, dividing line  130  illustrates the division between the portion of the system  100  where an ammonia/water solution is circulated (e.g., through the absorber  116 , the absorber pre-cooler  118 , and the generator  104 ) and the portion of the system  100  where substantially only ammonia is circulated (the valve  106 , the condenser  108 , the evaporator pre-cooler  110 , the orifice  112 , and the evaporator  114 ). 
         [0040]    Further, exemplary test results provide an approximate indication of the temperatures and pressures that may be observed at various stages in the process  200  and in the system  100  when operating in a cooling mode. For example, typical exhaust gas from a diesel powered truck may enter the generator  104  at a temperature of about 400 degrees Celsius and may exit the generator  104  at a temperature of about 300 to 380 degrees Celsius, assuming the diverter valve  102  is not diverting any of the exhaust gas through the bypass path  107 . Pressure in the heat exchanger portion of the generator  104  may reach about 120 to 250 psig, resulting in ammonia gas travelling towards the condenser  108  at a pressure of about 120-250 psig and a temperature of approximately 130 degrees Celsius. While specific examples and/or ranges of observed temperatures and/or pressures and provided here and further on in the description, these temperatures and pressures are dependent on the exact design and operating mode of the system  100  and may vary substantially depending on the desired design criteria and operating mode of the system  100 . In other words, the examples of observed pressures and temperatures in the system  100  are provided as examples only and are not intended to be limiting. Further, while an ammonia/water solution is provided as an example as a suitable solvent/solute for operating the system  100 , any suitable solvent/solute combination may be used, depending on the design criteria of a particular application. 
         [0041]    Next at a block  204 , the ammonia arriving at the condenser  108  is cooled and condensed into a liquid to surrender some of the heat carried by the ammonia gas. In a cooling mode of the system  100 , it may be the pressure of the ammonia gas that is desired to act as an energy source at the evaporator  114 , however the resulting high temperature assumed by the ammonia is not needed and the ammonia is therefore cooled before arriving at the evaporator  114 . For example, the condenser  108  may cool the ammonia to approximately 50 to 60 degrees Celsius by transferring the heat to the surrounding air using a coil and fan design liquid to air heat exchanger. The ammonia may remain at 120-250 psig on exiting the condenser  108  and travelling towards the evaporator pre-cooler  110 . 
         [0042]    Next, at a block  206 , the ammonia liquid is further cooled, for example in a first fluid passage (e.g., a fluid coil) at the evaporator pre-cooler  110 . The heat exchanger portion of the evaporator pre-cooler  110  may be of the liquid to liquid type and transfers thermal energy between the first fluid passage going from the condenser  108  to the evaporator  114  (e.g., the first coil) and from the fluid passage going between the evaporator  114  and the absorber  116  (e.g., a second coil). The ammonia leaving the first coil of the evaporator pre-cooler  110  will be cooler than the ammonia liquid entering the second coil of the evaporator pre-cooler  110 . For example, the ammonia liquid leaving the first coil of the evaporator pre-cooler  110  may be at a temperature of about 50 degrees Celsius and a pressure of about 120-250 psig. 
         [0043]    Next, at a block  208 , the ammonia gas passes through the spray orifice  112  and passes into or is injected into the evaporator  114 . The orifice  112  creates a boundary between the high pressure side of the system  100  and the low pressure side of the system  100 , illustrated by line  132 . As the ammonia passes through the orifice  112  into the cavity of the evaporator  114  (e.g., through a first fluid passage of the evaporator  114 ), the ammonia vaporizes because the ammonia encounters an area of lower pressure, which also forces the temperature of the ammonia down significantly. In the process of vaporizing, the ammonia absorbs thermal energy through the heat exchanger portion of the evaporator  114  from the water/glycol mixture being circulated through a second fluid passage (e.g., a fluid coil) of the evaporator  114 , thereby cooling the water/glycol mixture, which travels onwards to the thermal tank input fluid passage (e.g., a coil and circuit)  122 . The ammonia that enters the evaporator  114  after passing through the orifice  112  may have a temperature of approximately −10 to −5 degrees Celsius and a pressure of approximately 0-5 psig. The ammonia gas that leaves the evaporator  114  and travels back to the evaporator pre-cooler  110  may have, for example, a temperature between −5 and 0 degrees Celsius and a pressure of approximately 40 to 55 psig. 
         [0044]    Next, at a block  210 , the ammonia gas passes again through the evaporator pre-cooler  110 , this time through the second fluid passage and absorbs heat surrendered by the first fluid passage at block  206 . The ammonia gas may leave the second coil of the evaporator pre-cooler  110  at temperature of about 10 degrees higher than on entering the second fluid passage of the evaporator pre-cooler  110 , and the ammonia gas travels onwards through the low pressure side of the system  100  towards the absorber  116 . Blocks  206  and  210  of the process  200  work in conjunction with each other since blocks  206  and  210  make use of the evaporator pre-cooler  110  and are optional and aim to increase performance of the system  100 . 
         [0045]    Next at a block  212 , the ammonia is absorbed back into the water. The water that the ammonia absorbs into may be the nearly ammonia free water produced at the block  202  when the ammonia boils out of the ammonia/water solution. The ammonia gas travels through the absorber  116  that includes a heat exchanger that allows the ammonia gas to dissolve back into the water by cooling both fluids to a temperature where such can occur. The absorber  116  may include a spray bar at its lower end, which the ammonia is fed through where the ammonia bubbles to the top and is largely absorbed in the water. The water/ammonia solution may be pumped up to a higher pressure and temperature (e.g., across line  132  by pump  128   c ) and arrive next at the absorber pre-cooler  118 . 
         [0046]    Next at a block  214 , the water/ammonia solution passes through the absorber pre-cooler  118 . Block  214  that uses the absorber pre-cooler  118  may be an optional step in the process  200  that aims to increase the efficiency of the system  100  and the absorber pre-cooler  118  may be an optional feature of the system  100 . Hence, the block  214  and the absorber pre-cooler  118  may not be needed for the functioning of the system  100 . In embodiments that do use the pre-cooler  118 , the water/ammonia solution travelling towards the generator  104  through a first fluid passage (e.g., a first coil) of the pre-cooler  118  absorbs heat while the water travelling from the generator  104  to the absorber  116  (e.g., water that has had the ammonia boiled out of solution) through a second fluid passage (e.g., a second coil) of the pre-cooler  118  is cooled to bring the water closer to the temperature where re-absorption of ammonia will occur at the absorber  116 . The water/ammonia solution arriving at the generator  104  completes the cycle of the process  200  and the process  200  returns to the block  202 . 
         [0047]    Referring now to  FIGS. 3 a  and 3 b   , collectively referred to as  FIG. 3 ,  FIG. 3 a    shows in block diagram form a thermal auxiliary power unit or system  100  operating in a heat storage mode according to one aspect of the present description. In  FIG. 3 a   , the path from the valve  106  to the condenser  108  to the pre-cooler  110  to the evaporator  114  is greyed out, illustrating that this path is not used when the system  100  operates in heat storage mode.  FIG. 3 b    shows in flow chart form the process  300  of the thermal auxiliary power unit or system  100  operating in a heat storage mode according to one aspect of the present description. 
         [0048]    At a first block  302 , exhaust from an engine of a vehicle flows through the generator  104 , as indicated by arrows  103  and  105 , and the generator absorbs heat from the exhaust gas and transfers this heat to the ammonia/water solution being circulated through the heat exchanger portion of the generator  104 . As a result, the ammonia is vaporized and boils out of solution and ammonia gas flows through valve  106 , which in the present example is now configured to direct the ammonia gas directly towards the evaporator  114  while the system  100  operates in the heat storage mode. As an example, dividing line  130  illustrates the division between the portion of the system  100  where an ammonia/water solution is circulated (e.g., through the absorber  116 , the absorber pre-cooler  118 , and the generator  104 ) and the portion of the system  100  where substantially only ammonia is circulated (e.g., through the valve  106  and the evaporator  114 ). Water solvent is left behind and is directed towards the absorber pre-cooler  118 . The low pressure/high pressure dividing line  132  shown in  FIG. 3 a    should be ignored, as relatively little pressure differentials exist in the system  100  when operating in the heat storage mode as opposed to when operating as an absorption cycle. 
         [0049]    Exemplary test results provide an approximate indication of the temperatures and pressures that may be observed at various stages in the process  300  and the in the system  100 . For example, typical exhaust gas from a diesel powered truck may enter the generator  104  at a temperature of about 400 degrees Celsius and may exit the generator  104  at a temperature of about 300 to 380 degrees Celsius, assuming the diverter valve  102  is not diverting any of the exhaust gas through the bypass path  107 . Pressure in the heat exchanger portion of the generator  104  may reach about 120-150 psig, resulting in ammonia gas travelling towards the evaporator  114  at a pressure of about 120-150 psig and a temperature of approximately 100 degrees Celsius. While specific examples and/or ranges of observed temperatures and/or pressures are provided here and further on in the description, these temperatures and pressures are dependent on the design and operating mode of the system  100  and may vary depending on the particular design criteria and operating mode of the system  100 . In other words, the examples of observed pressures and temperatures in the system  100  are provided as examples only and are not intended to be limiting. 
         [0050]    Next, at a block  304 , the ammonia gas passes into a first fluid passage (e.g., a first coil) of a heat exchanger, for example in the evaporator  114 , where the gas surrenders thermal energy and cools. In the process of cooling, the ammonia surrenders thermal energy through the heat exchanger portion of the evaporator  114  to the water/glycol mixture being circulated through a second fluid passage (e.g., a second coil) of the evaporator  114 , thereby heating the water/glycol mixture, which travels onwards to the thermal tank input coil and circuit  122 . The ammonia that enters the evaporator  114  may have a temperature of approximately 100 degrees Celsius and a pressure of approximately 120-250 psig. 
         [0051]    Next, at a block  306 , the ammonia gas passes through the evaporator pre-cooler  110 . In a heat storage mode the flow of ammoina may bypass not only the orifice  112  on its way to the evaporator  114  but also the pre-cooler  110  so almost no heat transfer occurs at this point. In the process  300 , the evaporator pre-cooler  110  may be used as a liquid to air heat exchanger, simply providing the function of cooling the ammonia gas to expel excess heat. The ammonia may leave the evaporator pre-cooler  110  at a temperature of about 10 degrees lower than upon entering the evaporator pre-cooler  110 , and the ammonia gas travels onwards through the system  100  towards the absorber  116 . The block  306  of the process  300  is optional, as is the direction of the ammonia through the evaporator pre-cooler shown in  FIG. 4 . Alternatively, the ammonia may proceed directly from the evaporator  114  to the absorber  116  when the system  100  operates in a heat storage mode. 
         [0052]    Next at a block  308 , the ammonia is absorbed back into the water of the ammonia/water solution. The water that the ammonia absorbs into may be the nearly ammonia free water produced at the block  302  when the ammonia is vaporized from the ammonia/water solution. The ammonia gas travels through the absorber  116  that includes a heat exchanger that allows the ammonia gas to dissolve back into the water by cooling both fluids (e.g., the ammonia and the water) to a suitable temperature where such can occur. The absorber  116  may include a spray bar at its lower end, which the ammonia is fed through where the ammonia bubbles through the water to the top and is largely absorbed in the water. 
         [0053]    Next at a block  310 , the water/ammonia solution passes through the absorber pre-cooler  118 . Block  310  that uses the absorber pre-cooler  118  may be an optional step in the process  300  that aims to increase the efficiency of the system  100  and the absorber pre-cooler  118  may be an optional feature of the system  100 . Hence, the block  310  and the absorber pre-cooler  118  may not be needed for the functioning of the system  100 . In embodiments that do use the pre-cooler  118 , the water/ammonia solution travelling towards the generator  104  through a first fluid passage (e.g., a first coil) of the pre-cooler  118  absorbs heat while the water travelling from the generator  104  to the absorber  116  (e.g., water that has had the ammonia vaporized out of solution) passes through a second fluid passage (e.g., a second coil) of the pre-cooler  118  is cooled to bring the water closer to the temperature where re-absorption of ammonia is best achieved at the absorber  116 . The water/ammonia solution arriving at the generator  104  completes the cycle of the process  300  and the process  300  returns to the block  302 . 
         [0054]    Reference is next made to  FIG. 4 , which illustrates in flow chart form a process  400  executed by the controller  128  in controlling the system  100 . In one example, the controller  128  may be implemented as an electronic control module (ECU) designed to facilitate the desired operation of the system  100 , also referred to as a Hybrid Auxiliary Power Unit (HAPU), by monitoring and controlling various aspects of the system  100  to achieve the function of providing heating and/or cooling to a vehicle and capturing and reusing what would otherwise be lost energy expelled as heat in the exhaust of the vehicle in an effort to reducing the overall carbon footprint of the vehicle. The controller  128  may be integral to the system  100  and may enable the system  100  to function according to the design criteria of the intended application. As shown in a first block  402 , the controller may monitor and/or collect data pertaining to operating parameters of the system  100  and/or the vehicle on which the system  100  is installed including but not limited to pressure, temperature, voltage, liquid level, flow, and/or vehicle operator inputs. Using data collected from these inputs and processing the information using control logic, the controller  128  directs the actions of the components of the system  100  to maintain proper functioning of the system  100 . The components of the system  100  that are either monitored or controlled by the controller  128  include but are not limited to valves, fans, actuators, relays, contactors, charge controllers, pumps and/or outputs. One possible use of the outputs maybe to illustrate aspects of the system operation to the user. 
         [0055]    In one example, the controller  128  monitors aspects of the system  100  operation and allows the thermal cycle (e.g., illustrated in connection with  FIGS. 2 and 3 ) and electrical system to function in harmony to provide conditioned air to the cab of the vehicle such as a truck. The controller  128  may be responsible for controlling several primary functions of the system  100 , as described below. Generally, as indicated by block  403 , the controller  128  controls a number of components of the system  100  coupled to outputs of the controller  128  to provide for proper functioning of the system  100 . 
         [0056]    The controller  128  may be electrically coupled to the exhaust diverter valve  102 , which may be a 3-way 2-position valve configured by the controller  128  to ensure that the thermal energy delivered to the generator  104  from the exhaust is appropriate for the system  100  and divert the exhaust away from the generator  104  if the system  100  becomes too hot or is in danger of becoming too hot. As illustrated in block  404 , the controller  128  controls the position of the exhaust diverter valve  102  according to relevant inputs received from, for example, transducers in the system  100 . In one example, the valve  102  may completely divert the exhaust to or away from the generator  104  or blend the exhaust flow between the generator  104  and bypass path  107  to achieve the suitable heat delivery to the generator  104 . In one example, the controller  128  monitors electrical signals from transducers indicating temperatures and/or pressures at various locations in the system  100  and generates a decision based on these signals according to control logic stored in the controller  128  and decides whether to increase or decrease the amount of thermal energy delivered to the generator  104  by comparing the signals the controller  128  receives from one or more of the input transducers against specific targets programmed into the control logic. The controller generates an output signal for the diverter valve  102  accordingly and operates the diverter valve  102  accordingly. If the controller  128  detects a fault based on one or more of the input signals, the controller  128  may generate an output signal to close the diverter valve  102  forcing all the thermal energy away from the generator  104  and through the bypass path  107  as part of a safety shutdown sequence. 
         [0057]    The controller  128  may further be electrically coupled to valve  106 , which may be a 3-way 2-position valve responsible for providing the system  100  with the ability to switch between a heating and cooling mode. As illustrated at block  406 , the controller  128  controls the position of the valve  106  thereby selecting the operating mode of the system  100  based on relevant inputs. When cooling is desired, the valve  106  directs the flow of ammonia through the condenser  108  and the system  100  functions as an absorption cycle, as described above in connection with  FIG. 2 . If heating is desired, the valve  106  directs the flow of ammonia through a secondary circuit bypassing the condenser  108  and spray orifice  112 , which eliminates the cooling portion of the system  100  and sends hot ammonia to the evaporator  114 , as described above in connection with  FIG. 3 . In one example, the controller  128  generates a decision as to which mode is appropriate, for example by receiving signals generated by manual inputs coupled to inputs of the controller  128  such as a button actuated by a user. In another example, the controller  128  generates a decision as to which mode is appropriate by automatically sensing the temperature, for example by receiving signals from an electrical temperature transducer coupled to an input of the controller  128  that may reside in the cab and/or outside of the vehicle. The controller  128  may read a signal generated by the temperature transducer coupled to an input and anticipate the proper action to maintain user comfort based on control logic stored in the controller  128  and the controller  128  may generate an output signal for the valve  106  causing the valve  106  to move to the desired position to place the system  100  in either cold storage mode or heat storage mode. 
         [0058]    The controller  128  may further be electrically coupled to any of the pumps (for example, pumps  128   a ,  128   b , and/or  128   c ) shown in  FIG. 1 . For example, the controller  128  may be electrically coupled to the pump  128   c , which may be an ammonia/water solution pump responsible for creating the return flow of the water/ammonia solution from the absorber  116  to the generator  104  in the final stages of the processes  200  or  300  described in connection with  FIGS. 2 and 3 . As indicated at block  408 , the controller  128  controls the pumps used to maintain the functioning of the system  100 . In one example, the controller  128  may control whether the pumps are on or off and at what speed the pumps are operating. In one example, the controller  128  controls operation of the pump, for example by generating an appropriate output signal to control a relay coupled to the pump  128   c , to maintain the suitable liquid level in both pressure vessels (e.g., the absorber  116  and the generator  104 ) by gathering information from a variety of sensors or transducers that provide signals indicating, for example, fluid flow at various stages of the system  100 , temperature in various sections of the system  100 , pressure at various sections of the system  100 , and/or liquid level indicators at various sections of the system  100 . The controller  128  may use one or more of these inputs to compare the readings the controller  128  obtains from the sensors or transducers against specific targets programmed in the control logic of the controller  128  and generate an appropriate output signal to control the pump  128   c  to satisfy the output conditions dictated by the control logic. 
         [0059]    The controller  128  may further be electrically coupled to the pump  128   a  and/or the pump  128   b , which may be responsible for circulating the solution (e.g., water/glycol) between two or more heat exchangers in order to transfer thermal energy from one component to the next in the system  100 . In one example, the controller  128  monitors the signals indicating temperatures supplied by temperature transducers coupled to heat exchangers (e.g., the evaporator  114  and/or the thermal storage tank fluid passages  122 ,  124 ) and determines through program logic stored in the controller  128  if the transfer of thermal energy is appropriate in order to meet the end thermal objectives of the system  100  by comparing the temperatures indicated by the temperature transducers against targets stored in the code. The controller  128  then operates the pumps accordingly. 
         [0060]    The controller  128  may further be electrically coupled to a number of cooling fans (not shown). Any of the components of the system  100  incorporating a heat exchanger may optionally include a cooling fan, for example the condenser  108 . A fan that blows air through the condenser  108  may be responsible for allowing such a liquid to air heat exchanger to function more efficiently and to reject the proper heat load to surrounding environment cooling the fluid media within (e.g., the ammonia, in the case of the condenser  108 ). As indicated by block  410 , the controller  128  controls any cooling fans installed in the system  100  based on the relevant input signals received by the controller  128 . In one example, the controller  128  may control operation of the fan to maintain the desired cooling effect on the heat exchanger, such as the condenser  108 , by monitoring input signals generated by temperature transducers and comparing these inputs to targets encoded in the control logic of the controller  128 . Fan operation may be adjusted accordingly. For example, the fan may either be turned completely on or off and, when on, the speed of the fan may be set accordingly. In one example, a fan coupled to the condenser  108  may operate when the system  100  is in cold storage mode, but not when the system  100  is in heat storage mode since the condenser  108  is not used in heat storage mode. Further, in one example, the speed of the fan may be suitably controlled by the controller  128  to achieve the desired cooling rate of fluid passing through the heat exchanger. 
         [0061]    The controller  128  may further be coupled to valve  130  that controls the flow of solution flowing through the thermal tank output fluid passage  124 . As indicated by block  412 , the controller  128  controls the position of the valve  130  based on relevant inputs, which controls use of the energy stored in the thermal storage tank  122 . The valve  130  may be a 3-way 3-position dual circuit type and may direct the flow of the solution (e.g., glycol/water) between the vehicle&#39;s HVAC  126 , the vehicle&#39;s engine, and thermal storage tank  120 . In one example, the controller  128  decides which flow path is appropriate by receiving input signals, for example generated by manual inputs of a user using a button, which indicates the desired operating mode of the system  100 . The controller may further receive inputs from temperature transducers indicating the temperatures in any of the previously mentioned components and the controller  128  may then decide the most appropriate action to achieve the goal of the system  100  and send the appropriate output signal to the valve  130 . As previously discussed in the exemplary context of the system  100  operating in heat storage mode, the valve  130  may have three possible positions. The valve  130  may be closed, for example when the vehicle is moving and the heat source from the thermal storage tank is currently not needed while the system  100  is heating the solution in the thermal storage tank  120  to store thermal energy for later use and therefore restoring conventional heating input from the engine to the HVAC  126 . Second, the valve may be in a first open position allowing the solution to pass to the HVAC unit  126 , thereby allowing the HVAC  126  to use the stored heat such as when the vehicle is parked with the engine off and a user of the system  100  desires the cabin of the vehicle to be heated. Third, the valve may be in a second open position directing the flow of solution to the vehicle engine. This may be useful during a cold start of the engine during cold conditions, allowing the user of the system  100  to pre-heat the engine before starting the engine, thereby reducing emissions emitted by the engine during a cold start and allowing the user to immediately use the vehicle heating system once the engine is started. 
         [0062]    The controller  128  may further be coupled to one or more charge controllers providing an electrical charge control function. The charge controller is responsible for but not limited to regulating the flow of electricity in and out of the batteries of the system  100  (not shown) contained within a number of optional components of the system  100 , such as an energy storage system, a plug-in battery charger, a photovoltaic array, and/or the bus of the vehicle or vehicle components. In one example, the controller  128  monitors the voltage coming in and out of the system  100  and regulates the flow of electricity while taking into account many different parameters for example, time of day, battery state of charge (SOC), vehicle operation, and the amount of power available to capture. The controller  128  receives signals indicating some or all of this information and decides a course of action for the charge controller based on the program logic programmed into the controller  128 . As indicated at block  414 , the controller  128  controls one or more charge controllers (not shown) based on relevant inputs. 
         [0063]    While the process or method  400  is shown as occurring in a particular order, any of the blocks  402 ,  404 ,  406 ,  408 ,  410 ,  412 , and  414  may be rearranged as the order of the blocks is not critical to the functioning of the system  100 . Further, it will be understood by those skilled in the relevant arts that the method  400  when executed by the controller  128  is cyclical and/or iterative, and the controller  128  typically executes the process  400  several times per second. Further, the functions illustrated by the blocks  402 ,  404 ,  406 ,  408 ,  410 ,  412 , and  414  are intended to be exemplary and one or more of the blocks may be optional, depending on the design criteria of a particular application. Further yet, the method  400  is intended to illustrate some of the major control aspects of the system  100 . It will be understood by those skilled in the relevant arts that the controller  128  performs more functions than what is illustrated by the method  400 . 
         [0064]    Reference is next made to  FIG. 5 , which shows a bottom view and a corresponding sectional view of the generator  104  for use with a thermal auxiliary power unit according to one aspect of the present description.  FIG. 5  illustrates one example of the generator  104  that may be suitable for use with the system  100  and is not intended to be limiting. Any generator may be used according to the design criteria of a particular application. The generator  104  generally comprises an outer tube or shell  502 , end plates  504 ,  506 , an inner tube  508 , an exhaust gas passage  509 , annular rings  510 , a separation ring  512 , a separation zone  514 , and an ammonia exit line  516 . 
         [0065]    The outer shell  502  portion of the generator  104  contains the pressurized and heated fluid, for example the ammonia and water solution. In one example, the solution may have a concentration that varies from a few percent of ammonia by weight to as high as 20% ammonia by weight. In one example, the generator  104  is designed as a pressure vessel to appropriate codes in the jurisdiction where the generator is used. Internal pressure of the generator  104  may rise to 250 psig while operating from 50 psig in a quiescent state. The temperature range of the generator may vary from −40 degrees Celsius while inoperative to 130 degrees Celsius or more internally during normal operation. During an overheat condition, the outer shell  502  may reach up to 250 degrees Celsius. The pressure vessel boundary includes the outer tube  502  as shown in  FIG. 5  and two endplates  504 ,  506  which are formed such that the end plates  504 ,  506  act as closures between the outer tube  502  and the concentric inner tube  508 . The outer shell  502  may be fabricated from carbon steel such as seamless tubing, having properties appropriate for the conditions and composition of the contained fluids such as, but not limited to, ASTM A516, and in some applications a grade of stainless steel such as SS304 may be used. 
         [0066]    The inner tube  508  may form part of the exhaust gas passage  509  from the engine to the atmosphere. The function of the inner tube may be to provide a passage for the hot exhaust gases that provide the energy harvested by the system  100  and also withstand on the outside of the inner tube  508  the high pressures generated by the pressurised working fluid (e.g., the solution) in the absorption circuit. The inner tube  508  may conduct heat from the flowing exhaust gases into the solution with the aid of the annular rings  510 , described below. In one example, the inner tube  508  may be manufactured from carbon steel such as seamless tubing and may have properties appropriate for the conditions and composition of the contained fluids such as, but not limited to, ASTM A516, and in some applications a grade of stainless steel such as SS304 may be used. 
         [0067]    These annular rings  510  surround the inner tube  508  and serve to increase the amount of heat conducted from the hot exhaust gas flowing through the inner tube  508  into the solution flowing through the outer tube  502  by increasing the amount of surface area available for heat transfer and helping to raise the temperature and pressure of the solution therefore increasing the effectiveness of the generator  104  and its ability to better vaporize the solute from the solution. In one example, the rings  510  have a tight fit to the inner tube  508 , but have a radial clearance relative to the outer tube  502  enabling fractionation of the solution while stabilizing the fluid column against violent bubbling and sloshing as the vehicle moves. The rings  510  may be fabricated of a material compatible with the inner tube  508  and the outer tube  502 . In one example, all the metallic components of the generator  104  may be made from the same materials for ease of fabrication. 
         [0068]    The separation ring  512  works to separate the lower space (e.g., to the left of the separation ring  512  as shown in  FIG. 5 ) which is a fluid heating and boiling zone whereby a wet gas (e.g., ammonia) with some entrained water from the separation zone is driven from the solution (e.g., water and ammonia) and an upper space (e.g., to the right of the separation ring  512  as shown in  FIG. 5 ) where fluid droplets are largely removed leaving a mostly dry gas (e.g., ammonia) to leave the vessel. In one example, the ring  512  may have a tight fit with both the inner tube  508  and the outer tube  502  and may be welded to the inner tube  508  for ease of assembly. The ring  512  may be fabricated from materials compatible with the tubes  502  and  508  as previously described. The ring  512  may include an annular plate penetrated by a series of holes which may be, in one example, approximately 25% in diameter of the annular gap. The open area of the plate created by the holes may be, but is not limited to, 10 to 20% of the total annular area. 
         [0069]    The separation zone  514  includes a volume. In one example, the volume may be packed with a droplet coalescence material such as stainless steel wool or other like material which provides a very high surface area. Droplets of solute (e.g., liquid water) form on these surfaces and drain back to the liquid space below the separation ring  512 . The gas (e.g., vaporized ammonia) that exits the vessel through the ammonia exit line  516  at the top is nearly all ammonia gas (e.g., as much as 99% ammonia gas with very little water vapour, for example 1% water vapour). 
         [0070]    The embodiments of the present disclosure described above are intended to be examples only. Those of skill in the art may effect alterations, modifications and variations to the particular embodiments without departing from the intended scope of the present disclosure. In particular, selected features from one or more of the above-described embodiments may be combined to create alternative embodiments not explicitly described, features suitable for such combinations being readily apparent to persons skilled in the art. The subject matter described herein in the recited claims intends to cover and embrace all suitable changes in technology.