Patent Publication Number: US-2022235974-A1

Title: Thermodynamic heat recovery without an additional thermodynamic circuit

Description:
TECHNICAL FIELD 
     This application relates generally to heating, ventilation, and air conditioning (HVAC) systems and more particularly, but not by way of limitation, to implementing thermodynamic heat recovery without utilizing a thermodynamic circuit in addition to the main cooling and heating thermodynamic circuit(s). 
     BACKGROUND 
     This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. 
     Thermodynamic vapor-compression systems are used to regulate environmental conditions within an enclosed space. Typically, such systems have a circulation fan that pulls air from the enclosed space through ducts and pushes the air back into the enclosed space through additional ducts after conditioning the air (e.g., heating or cooling). A refrigerant may flow in a circuit between two heat exchangers, typically coils. One heat exchanger may be “inside” the structure (the “indoor heat exchanger” or “indoor coil”) and the other heat exchanger may be outside the structure (the “outdoor heat exchanger” or “outdoor coil”). For heating, the refrigerant may absorb heat as it passes through the outdoor heat exchanger and release heat as it passes through the indoor heat exchanger. For air conditioning, the refrigerant may absorb heat as it passes through the indoor heat exchanger and release heat as it passes through the outdoor heat exchanger. Heat pumps can reverse the direction of refrigerant flow, to change between heating and air conditioning. A reversing valve typically controls the direction of refrigerant flow. 
     Heat recovery can be implemented by recirculating conditioned air from the structure and/or by operation of a thermodynamic circuit in addition to the heat pump&#39;s refrigerant circuit. For example, a system may include a heat pump to cool or heat the conditioned space and an additional thermodynamic circuit for heat recovery. The additional thermodynamic circuit including an independent compressor and refrigerant circuit from the heat pump. The main interest of the thermodynamic heat recovery circuit is to reach a high efficiency with all the air going in the conditioned space taken from the external environment and is considered as “cleaner” than the air taken from the conditioned space. By “cleaner” is considered air with a lower CO2 concentration, less particles and/or virus for instance. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not necessarily intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of claimed subject matter. 
     An exemplary refrigerant circuit includes a compressor operable to compress a refrigerant, an expansion valve, an outdoor heat exchanger, an indoor heat exchanger in a fresh air inlet to a conditioned space, a recovery heat exchanger in an extracted air outlet from the conditioned space, and a reversing valve operable to direct a direction of refrigerant flow between a cooling mode and a heating mode. 
     An exemplary method includes operating a refrigerant circuit in a cooling mode or a heating mode to condition an indoor air in a conditioned space, the refrigerant circuit comprising a compressor operable to compress a refrigerant, an expansion valve, an outdoor heat exchanger, an indoor heat exchanger in a fresh air inlet to the conditioned space, and a recovery heat exchanger in an extracted air outlet from the conditioned space, and recovering energy from the indoor air via the recovery heat exchanger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a block diagram of an exemplary HVAC system that can implement thermodynamic heat recovery in the cooling mode and the heating mode; 
         FIG. 2  is a block diagram of an exemplary HVAC system in a cooling mode with thermodynamic heat recovery; 
         FIG. 2A  illustrates an exemplary vapor-compression cycle of the refrigeration circuit of  FIG. 2 ; 
         FIG. 3  is a block diagram of an exemplary HVAC system in cooling mode with total air recirculation; 
         FIG. 4  is a block diagram of an exemplary HVAC system in heating mode with thermodynamic heat recovery: 
         FIG. 4A  illustrates an exemplary vapor-compression cycle of the refrigeration circuit of  FIG. 4 ; 
         FIG. 5  is a block diagram of an exemplary HVAC system in cooling mode with total air recirculation; 
         FIG. 6  is a block diagram of an exemplary HVAC system in cooling mode with thermodynamic heat recovery; 
         FIG. 6A  illustrates an exemplary vapor-compression cycle of the refrigeration circuit of  FIG. 6 ; 
         FIG. 7  is a block diagram of an exemplary HVAC system in heating mode with thermodynamic heat recovery and a recovery heat exchanger superheating the refrigerant; 
         FIG. 7A  illustrates an exemplary vapor-compression cycle of the refrigeration circuit of  FIG. 7 ; 
         FIG. 8  is a block diagram of an exemplary HVAC system in cooling mode with thermodynamic heat recovery; 
         FIG. 9  is a block diagram of an exemplary HVAC system in heating mode with thermodynamic heat recovery and a recovery heat exchanger superheating the refrigerant; 
         FIG. 10  is a block diagram of an exemplary HVAC system in heating mode without using an outdoor heat exchanger: 
         FIG. 10A  illustrates an exemplary vapor-compression cycle of the refrigeration circuit of  FIG. 10 ; and 
         FIG. 11  is a block diagram of an exemplary HVAC system in a deicing mode. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will now be described more fully with reference to the accompanying drawings. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
       FIG. 1  is a schematic illustration of an exemplary HVAC system  100 . HVAC system  100  is a vapor-compression system comprising a refrigerant circuit  102  that can implement a thermodynamic heat recovery process in the cooling mode and the heating mode. HVAC system  100  may be implemented for example as a rooftop unit. 
     Refrigerant circuit  102  includes a compressor  104 , an expansion valve  106 , an outdoor heat exchanger  108 , an indoor heat exchanger  110 , a recovery heat exchanger  112 , and a reversing valve  114  (e.g., 4-way valve), operable between a cooling mode to direct the refrigerant  116  from the compressor in a direction from the outdoor heat exchanger to the indoor heat exchanger and a heating mode to direct the refrigerant from the compressor in the direction from the indoor heat exchanger to the outdoor heat exchanger. Recovery heat exchanger  112  utilizes the same compressor  104  as the outdoor and indoor heat exchangers. 
     Indoor heat exchanger  110  is positioned in a fresh air inlet  118  (e.g., duct) to the conditioned space  120  (e.g., enclosure). Recovery heat exchanger  112  is located in an extracted air outlet  122  (e.g., duct) from conditioned space  120 . Dampers  118   a  control flow of fresh air  124  into the fresh air inlet  118  and conditioned space  120 . Dampers  122   a  selectively allow all or a portion of the indoor air  126 , shown as exhausted air  126   a , to be exhausted from the condition space through extracted air outlet  122 . Cross-dampers  128  selectively allow indoor air  126  to recirculate into fresh air inlet  118 . 
     An electronic controller  130  comprising computer-readable storage medium may be in communication for example with compressor  104 , reversing valve  114 , dampers  118   a ,  122   a , and  128 , and various valves to operate the HVAC system in various modes including without limitation, a cooling mode, a heating mode, thermodynamic heat recovery mode, and deicing mode. 
     In an exemplary embodiment, a first refrigerant line  132  and a second refrigerant line  134  extends from outdoor heat exchanger  108  to recovery heat exchanger  112 . A first valve  132   a  is positioned in the first refrigerant line  132  with expansion valve  106  in communication with first refrigerant line  132  between first valve  132   a  and recovery heat exchanger  112 . In an exemplary embodiment, second refrigerant line  134  includes a valve  134   a.    
       FIG. 2  schematically illustrates an exemplary HVAC system  100  in the cooling mode with thermodynamic heat recovery.  FIG. 2A  illustrates an exemplary vapor-compression cycle of refrigeration circuit  102  of  FIG. 2 . Refrigerant  116  is compressed by compressor  104  and directed through reversing valve  114  to outdoor heat exchanger  108  where it releases heat and is cooled. First valve  132   a  is closed directing the refrigerant from the outdoor heat exchanger through second refrigerant line  134  to recovery heat exchanger  112 . Indoor air  126  passes across recovery heat exchanger  112  subcooling the refrigerant as illustrated in  FIG. 2A  at portion  212 . The refrigerant flows from recovery heat exchanger  112  through expansion valve  106  to indoor heat exchanger  110  and then returns to the suction side of compressor  104 . Fresh air  124  passes across indoor heat exchanger  110 , wherein the refrigerant absorbs heat, resulting in cooler conditioned air  124   a  that passes into the conditioned space. 
       FIG. 3  illustrates an exemplary HVAC system  100  in the cooling mode with total air recirculation. In this example, dampers  118   a .  122   a  are closed and cross-dampers  128  are open resulting in substantially zero percent fresh air and 100% recirculation of indoor air  126 . The refrigerant is directed from compressor  104  to outdoor heat exchanger  108 . First valve  132   a  is open and the refrigerant is directed through first refrigerant line  132  and expansion valve  106  to indoor heat exchanger  110 . If second refrigerant line  134  does not include a valve, e.g., valve  134   a  shown in  FIG. 3 , substantially all of the refrigerant will be directed through first line  132  due to the lower pressure drop and a very low flow rate of refrigerant may pass through second refrigerant line  134  and recovery heat exchanger  112 . If second refrigerant line  134  has a valve  134   a  ( FIG. 1 ) it may be closed to eliminate the low flow rate through the recovery heat exchanger and prevent heat pickup through the recover heat exchanger. 
       FIG. 4  schematically illustrates an exemplary HVAC system  100  in the heating mode with thermodynamic heat recovery.  FIG. 4A  illustrates an exemplary vapor-compression cycle of refrigeration circuit  102  of  FIG. 4 . Refrigerant  116  is compressed by compressor  104  and directed through reversing valve  114  to indoor heat exchanger  110  where the refrigerant releases heat to conditioned air  124   a . First valve  132   a  is closed directing the refrigerant from the indoor heat exchanger to recovery heat exchanger  112  where the refrigerant absorbs heat from indoor air  126 . The refrigerant flows from recovery heat exchanger  112  to outdoor heat exchanger  108 . 
       FIG. 5  illustrates an exemplary an exemplary HVAC system  100  in the heating mode with total air recirculation. In this example, dampers  118   a ,  122   a  are closed and cross-dampers  128  are open resulting in substantially zero percent fresh air  124  and 100% recirculation of indoor air  126 . The refrigerant is directed from compressor  104  through reversing valve  114  to indoor heat exchanger  110 . First valve  132   a  is open and the refrigerant is directed through expansion valve  106  to outdoor heat exchanger  108 . If second refrigerant line  134  does not include a valve, a very low flow rate of refrigerant may pass through recovery heat exchanger  112  as the refrigerant will primarily be directed through first line  132  due to the lower pressure drop. If second refrigeration line  134  has a valve  134   a  ( FIG. 1 ) it may be closed to eliminate the low flow rate through the recovery heat exchanger and prevent a liquid refrigerant trap if inside temperature is colder than outside temperature in the condensing unit. 
       FIGS. 6-11  illustrate an exemplary HVAC system  100  with additional piping to facilitate position the heat recovery heat exchanger in the vapor-compression cycle for subcooling and for superheating heat transfer, where the temperature pinch is higher, in particular in heating mode. In some embodiments, the external and indoor heat exchangers may be maintained in counter-current flow. 
       FIG. 6  schematically illustrates an exemplary HVAC system  100  in the cooling mode with the recovery heat exchanger  112  utilized to subcool the refrigerant.  FIG. 6A  illustrates an exemplary vapor-compression cycle of refrigeration circuit  102  of  FIG. 6 . Refrigerant  116  is compressed by compressor  104  and directed through reversing valve  114  to outdoor heat exchanger  108  where it releases heat and is cooled. Outdoor heat exchanger  108  and recovery heat exchanger  112  may be in counter-current flow. First valve  132   a  is closed, directing the refrigerant from the outdoor heat exchanger through second refrigerant line  134  to recovery heat exchanger  112 . Indoor air  126  passes across recovery heat exchanger  112  subcooling the refrigerant as illustrated in  FIG. 6A  at portion  612 . The refrigerant flows from recovery heat exchanger  112  through expansion valve  106  to indoor heat exchanger  110  and then returns to the suction side of compressor  104 . Fresh air  124  passes across indoor heat exchanger  110 , wherein the refrigerant absorbs heat, resulting in cooler conditioned air  124   a  introduced into the conditioned space. In  FIG. 6 , the refrigerant enters the bottom of outdoor heat exchanger  108  and exits the top of heat exchanger  108 . 
       FIG. 7  schematically illustrates an exemplary HVAC system  100  in the heating mode with thermodynamic heat recovery and recovery heat exchanger  112  superheating the refrigerant.  FIG. 7A  illustrates an exemplary vapor-compression cycle of refrigeration circuit  102  of  FIG. 7 . Refrigerant  116  is compressed by compressor  104  and directed through reversing valve  114  to indoor heat exchanger  110  where the refrigerant releases heat to the conditioned air  124   a . First valve  132   a  is closed directing the refrigerant from the indoor heat exchanger  110  to outdoor heat exchanger  108  where it absorbs heat from the cool outdoor air. The refrigerant is directed from the outdoor heat exchanger  108  to the recovery heat exchanger  112 , where indoor air  126 , which is already heated, is utilized as the hot source to superheat the refrigerant as illustrated in  FIG. 7A  at portion  712 . With reference to the system in  FIG. 4 , the system in  FIG. 7  reverses the order of the outdoor heat exchanger and the recovery heat exchanger in the refrigerant circuit and the vapor-compression cycle, producing a more efficient system. Using the heated indoor air as the hot source for superheating is more efficient than using the outdoor air as the hot source for superheating. In the heating mode illustrated in  FIG. 7 , the refrigerant flows in the same direction through outdoor heat exchanger  108  as in the cooling mode illustrated in  FIG. 6 . For example, the outdoor heat exchanger is in counter-current flow in the heating mode ( FIG. 7 ) and the cooling mode ( FIG. 6 ). 
       FIG. 8  schematically illustrates an exemplary HVAC system  100  in the cooling mode with the recovery heat exchanger  112  utilized to subcool the refrigerant. Refrigerant  116  is compressed by compressor  104  and directed through reversing valve  114  to outdoor heat exchanger  108  where it releases heat and is cooled. Outdoor heat exchanger  108  may be co-current flow or counter-current flow. First valve  132   a  is closed, directing the refrigerant from the outdoor heat exchanger through second refrigerant line  134  to recovery heat exchanger  112 . Indoor air  126  passes across recovery heat exchanger  112  subcooling the refrigerant, see e.g., portion  612  in  FIG. 6A . The refrigerant flows from recovery heat exchanger  112  through expansion valve  106  to indoor heat exchanger  110  and then returns to the suction side of compressor  104 . Fresh air  124  passes across indoor heat exchanger  110 , wherein the refrigerant absorbs heat, resulting in cooler conditioned air  124   a  introduced into the conditioned space. 
       FIG. 9  schematically illustrates an exemplary HVAC system  100  in the heating mode with thermodynamic heat recovery and recovery heat exchanger  112  superheating the refrigerant. Refrigerant  116  is compressed by compressor  104  and directed through reversing valve  114  to indoor heat exchanger  110  where the refrigerant releases heat to the conditioned air  124   a . First valve  132   a  is opened directing the refrigerant from indoor heat exchanger  110  to outdoor heat exchanger  108  where it absorbs heat from the cool outdoor air. First valve  132   a  is opened, as opposed to closed in  FIG. 7 , directing the refrigerant into the top of outdoor heat exchanger  108 , as opposed to the bottom in  FIG. 7 . The refrigerant is directed from the outdoor heat exchanger  108  to recovery heat exchanger  112  where indoor air  126 , which is already heated, is utilized as the hot source to superheat the refrigerant as illustrated in  FIG. 7A  at portion  712 . 
       FIG. 10  schematically illustrates an exemplary HVAC system  100  in the heating mode without using outdoor heat exchanger  108 . This mode may be suited for cold environments, for example about 0 C or lower and inside air  126  has been heated.  FIG. 10A  illustrates an exemplary vapor-compression cycle of refrigeration circuit  102  of  FIG. 10 . 
     Refrigerant  116  is directed from compressor  104  through reversing valve  114  to indoor heat exchanger  110  where the fresh air  124  absorbs heat from the refrigerant and is pushed into the conditioned space as heated conditioned air  124   a . The refrigerant flows from the indoor heat exchanger through the expansion valve  106  to recovery heat exchanger  112  where the indoor air  126  heats the refrigerant which is directed to the compressor.  FIG. 10A  illustrates that it is possible to fit the compressor operating map even with fresh air at low ambient temperature. 
       FIG. 11  schematically illustrates an HVAC system  100  in a deicing mode at low ambient temperature without any, or limited, impact on thermal comfort. A first portion  136  of indoor air  126 , which is warm, is recirculated from the extracted air outlet  122  through cross-dampers  128  to fresh air inlet  18  upstream of indoor heat exchanger  110 . The second portion  138  of indoor air  126  is directed across recovery heat exchanger  112  melting ice that may have accumulated. The refrigerant is directed from compressor  104  to indoor heat exchanger  110 , where the mixture of fresh air  124  and first indoor air portion  136  absorbs heat from the refrigerant. The refrigerant is directed from indoor heat exchanger through expansion valve  106  to outdoor heat exchanger  108  and back to compressor  104 , bypassing recovery heat exchanger  12 . 
     The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially.” “approximately.” “generally.” and “about” may be substituted with “within 10% of” what is specified. 
     For purposes of this disclosure, the term computer-readable storage medium encompasses one or more tangible computer-readable storage media possessing structures. As an example and not by way of limitation, a computer-readable storage medium may include a semiconductor-based or other integrated circuit (IC) (such as, for example, a field-programmable gate array (FPGA) or an application-specific IC (ASIC), a hard disk, an HDD, a hybrid hard drive (HHD), an optical disc, an optical disc drive (ODD), a magneto-optical disc, a magneto-optical drive, a floppy disk, a floppy disk drive (FDD), magnetic tape, a holographic storage medium, a solid-state drive (SSD), a RAM-drive, a SECURE DIGITAL card, a SECURE DIGITAL drive, a flash memory card, a flash memory drive, or any other suitable tangible computer-readable storage medium or a combination of two or more of these, where appropriate. 
     Particular embodiments may include one or more computer-readable storage media implementing any suitable storage. In particular embodiments, a computer-readable storage medium implements one or more portions of a controller as appropriate. In particular embodiments, a computer-readable storage medium implements RAM or ROM. In particular embodiments, a computer-readable storage medium implements volatile or persistent memory. In particular embodiments, one or more computer-readable storage media embody encoded software. 
     In this patent application, reference to encoded software may encompass one or more applications, bytecode, one or more computer programs, one or more executables, one or more instructions, logic, machine code, one or more scripts, or source code, and vice versa, where appropriate, that have been stored or encoded in a computer-readable storage medium. In particular embodiments, encoded software includes one or more application programming interfaces (APIs) stored or encoded in a computer-readable storage medium. Particular embodiments may use any suitable encoded software written or otherwise expressed in any suitable programming language or combination of programming languages stored or encoded in any suitable type or number of computer-readable storage media. In particular embodiments, encoded software may be expressed as source code or object code. In particular embodiments, encoded software is expressed in a higher-level programming language, such as, for example, C, Python, Java, or a suitable extension thereof. In particular embodiments, encoded software is expressed in a lower-level programming language, such as assembly language (or machine code). In particular embodiments, encoded software is expressed in JAVA. In particular embodiments, encoded software is expressed in Hyper Text Markup Language (HTML), Extensible Markup Language (XML), or other suitable markup language. 
     Depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. Although certain computer-implemented tasks are described as being performed by a particular entity, other embodiments are possible in which these tasks are performed by a different entity. 
     Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices or algorithms illustrated can be made without departing from the spirit of the disclosure. As will be recognized, the processes described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. The scope of protection is defined by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.