BACKGROUND

[0001] Cooling is a process that may be employed to lower a temperature of a space. Air conditioning systems, such as those based on vapour compression refrigeration process, are used in cooling of spaces and are able to transfer heat from a heat source at lower temperature to a heat sink at higher temperature. Generally, such air conditioning systems consume significant amount of energy to be able to cool a certain space.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The features, aspects, and advantages of the subject matter will be better understood with regard to the following descriptions and accompanying figures. In the figures, the left-most digit of a reference number identifies the figure in which the reference number first appears. Use of the same reference number in different figures indicates similar or identical features and components.

[0003] Fig 1 illustrates a schematic of a heating, ventilation, and air conditioning (HVAC) system illustrating a heat source, a refrigeration system, and a heat sink, in accordance with an example implementation of the present subject matter.

[0004] Fig 2 illustrates a schematic of the HVAC system illustrating a first configuration as a cooling system, in accordance with an example implementation of the present subject matter.

[0005] Fig 3 illustrates a schematic of the HVAC system illustrating a second configuration as a cooling system, in accordance with an example implementation of the present subject matter.

[0006] Fig 4 illustrates a schematic of the HVAC system illustrating the second configuration as a cooling system, in accordance with another example implementation of the present subject matter. [0007] Fig 5 illustrates a schematic of the HVAC system illustrating a third configuration as a cooling system, in accordance with an example implementation of the present subject matter.

[0008] Fig 6 illustrates a schematic of the HVAC system illustrating a configuration as a heating system, in accordance with an example implementation of the present subject matter.

[0009] Fig 7 illustrates a method for operating the HVAC system, in accordance with an example implementation of the present subject matter.

DETAILED DESCRIPTION

[0010] Air conditioning systems use a variety of heat transfer loops and techniques to transfer heat from the heat source (for example, the space to be cooled) to the heat sink where the heat is dissipated (for example, the ambient atmosphere). The air conditioning systems may have different configurations based on various factors, such as the amount of cooling required, size and desired temperature of the space to be cooled, temperature of the heat sink etc. For example, in certain cases, the air conditioning system may not include any intermediate heat transfer fluids. In such cases, for instance, the refrigerant in the air conditioning system may take heat directly from the air in the space to be cooled and dissipate the heat directly to the air in the ambient environment. Such system may employ air-cooled heat exchangers at both ends, one in the space to be cooled to absorb the heat from the space, and the other in the ambient environment to dissipate heat to the environment. A common approach is to use a fan coupled with a finned-tube heat exchanger to transfer heat between the air from the heat source or the heat sink, and the refrigerant in the air conditioning system.

[0011] In another case, the air conditioning system may employ one or more intermediate heat transfer fluids, and loops or circuits in addition to the refrigerant in the refrigeration system. For example, a liquid working fluid may be used as the heat transfer fluid to transfer heat from the heat source to the refrigeration system, i.e., the working fluid may absorb heat from the space to be cooled and transfer the heat to the refrigerant in the refrigeration system. In such a case, the heat is first transferred from the heat source to the liquid working fluid and then from the liquid working fluid to the refrigerant in the refrigeration system. In another example, some air conditioning systems may use a liquid working fluid to transfer heat from the refrigeration system to the heat sink, such that heat is first transferred from the refrigerant in the refrigeration system to the liquid working fluid and then from the liquid working fluid to the heat sink. In certain other cases, the air conditioning systems may use liquid working fluids on both the heat source side and the heat sink side such that on the heat source side of the air conditioning system, the heat can be first transferred from the heat source to a liquid working fluid, then from this liquid working fluid to the refrigerant in the refrigeration system, then from the refrigerant to a liquid working fluid on the heat sink side of the air conditioning system and then to the heat sink. In such air conditioning applications, the liquid working fluids at the heat source side and at the heat sink side are typically maintained in separate loops or circuits. It is also possible to use two or more liquid working fluids on the same side of the air conditioning system. As an example, in an air conditioning system, heat can be transferred from the refrigerant on the heat sink side to the first liquid working fluid, and then from the first liquid working fluid to the second liquid working fluid before being transferred to the heat sink.

[0012] Therefore, various such designs of the air conditioning systems are conventionally used in different configurations, based on the specific application where they are to be implemented. These conventional air conditioning systems usually have fixed coolant flow paths. However, in many applications it may be required that the air conditioning systems are able to change coolant flow paths to increase energy efficiency, such as by lowering power consumption, or improve other performance parameters. For instance, an air conditioning system with fixed coolant flow paths designed to be used with liquid working fluids in separate loops on both the heat source side and the heat sink side necessarily involves transferring heat through the refrigeration system, which consumes significant amount of power. However, in some cases the temperature of the heat sink may be low enough to provide cooling to the space without the need of the refrigeration system. In this scenario it might be appropriate and beneficial to bypass the refrigeration system, and transfer the heat directly between the liquid working fluids on the heat source side and the heat sink side. It might be even more beneficial to connect the coolant flow paths on the heat source side and the heat sink side which can directly transfer heat between the heat source and the heat sink using a liquid working fluid. This can save significantly on the power consumption of the whole air conditioning system.

[0013] To this end, a heating, ventilation, and air conditioning (HVAC) system and techniques for cooling a heat source, such as a space, are disclosed. According to an aspect, the HVAC system is designed to work in varying configurations, depending on suitability to the given situation such as the ambient environment in which the HVAC system is to operate.

[0014] According to an example, the HVAC system based on the present subject matter includes a refrigeration system, a first heat exchanger in a heat exchange configuration with the heat source, a second heat exchanger in a heat exchange configuration with the heat sink, and a plurality of cooling circuits that thermally couple the first heat exchanger, the second heat exchangers and the refrigeration system in various configurations. In one example, the thermal coupling between the first heat exchanger, the second heat exchanger, and the refrigeration system may be achieved by fluidically coupling the various components. In the said example, the working fluid is configured to circulate through the various components in a plurality of circuits, where the various components can exchange the thermal energy or heat with each other through the working fluid thereby achieving thermal coupling therebetween. Further, the plurality of cooling circuits may be dynamically configurable to allow a working fluid to flow between the refrigeration system, the first and the second heat exchangers. For instance, the plurality of cooling circuits can include a plurality of circuit elements, such as pumps, valves etc., which are appropriately positioned in the cooling circuits and can be controlled to connect or disconnect the cooling circuits, the refrigeration system, the first and the second heat exchangers, or combinations thereof.

[0015] According to an example, each of the plurality of the cooling circuits may have a defined flow path that can fluidically and thermally couple the heat exchangers, and/or the refrigeration system. Further, the HVAC system may dynamically route the working fluid in one of the plurality of cooling circuits based on a temperature of the working fluid exiting the first and/or the second heat exchanger, or entering the first heat exchanger. Accordingly, in one example, the HVAC system can include a plurality of sensors positioned appropriately at various positions in the HVAC system to provide the feedback regarding the temperature so that the valves and pumps of the HVAC system can be, accordingly, regulated to achieve a predefined configuration of the air conditioning system. Accordingly, the HVAC system can also include a control unit which can be operably coupled to the various components of the HVAC system, such as the valves, the pumps and the sensors, to be able to control the valves and the pumps based on the feedback mechanism from the sensors, and to bring the HVAC system to operate into different configurations, for example, based on the feedback.

[0016] For example, the control unit can regulate the components of the HVAC system to allow a portion of the volume of the working fluid to flow in a cooling circuit from amongst the plurality of cooling circuits that fluidically couple the first heat exchanger and the refrigeration system, while the remaining volume of the working fluid is made to flow through another cooling circuit that fluidically couple the first heat exchanger and the second heat exchanger.

[0017] In one case, the control unit can control the components of the HVAC system to re-route the working fluid in the cooling circuit based on the temperatures of the working fluids exiting the first and the second heat exchangers. For instance, if the temperature of the working fluid exiting the second heat exchanger is higher than a temperature of the working fluid exiting the first heat exchanger, the control unit can control the components of the HVAC system to route the working fluid in the cooling circuit such that the working fluid exiting the first heat exchanger may be directed to the refrigeration system at the heat source side and the working fluid exiting the second heat exchanger may be directed to the refrigeration system at the heat sink side.

[0018] In another case, the control unit can control the components of the HVAC system to re-route the working fluid in the cooling circuit based on the temperatures of the working fluids exiting the first heat exchanger, entering the first heat exchanger and exiting the second heat exchanger. For instance, if the temperature of the working fluid exiting the second heat exchanger is higher than a temperature of the working fluid entering the first heat exchanger but lower than the temperature of the working fluid exiting the first heat exchanger, the control unit can control the components of the HVAC system to route the working fluid in the cooling circuit such that a portion of the working fluid coming from the second heat exchanger may be directed to the refrigeration system at the heat source side, and another portion may be directed to the refrigeration system at the heat sink side. As a result, the refrigeration system needs to cool the working fluid by a lower temperature difference. As a result, the total amount of power consumed by the HVAC system to cool the heat source may be reduced.

[0019] In the case where the temperature of the working fluid exiting the second heat exchanger is higher than a temperature of the working fluid entering the first heat exchanger but lower than the temperature of the working fluid exiting the first heat exchanger, the control unit can alternatively control the components of the HVAC system to route the working fluid in the cooling circuit such that the working fluid coming from the second heat exchanger may be directed to the refrigeration system at the heat source side, and the working fluid coming from the first heat exchanger may be directed at the refrigeration system at the heat sink side. As a result of such configuration, the total amount of power consumed by the HVAC system to cool the heat source may be reduced.

[0020] According to an example, the HVAC system may, based on a very low temperature of the working fluid exiting the second heat exchanger, route the working fluid in a cooling circuit such that it may completely bypass the air conditioning system such that the working fluid may directly flow between the first and the second heat exchanger. In such a case, the refrigeration system can be switched off and the consumption of power by the HVAC system may be substantially reduced. In one example, the amount of power consumed by the HVAC system may be reduced by up to 80%.

[0021] According to an aspect, the techniques of the present subject matter are agnostic to the type of heat source or the heat sink, type of the heat exchanger at the heat source and the heat sink, type of the refrigeration system, the mechanism of heat transfer, or the liquid working fluid used therewith. For example, the technique is agnostic to the manner of heat being discharged to the heat sink and the heat can be discharged to the heat sink using a dry cooler, a direct evaporative cooler, an indirect evaporative cooler, a dew point evaporative cooler, a geothermal cooler or the like, or can be discharged directly from the liquid working fluid to the heat sink or it can be transferred to another medium before being discharged to the heat sink. In another example, the heat source can be hot air from a space cooling application, hot water from an industrial process cooling application, or the like.

[0022] These and other advantages of the present subject matter would be described in greater detail in conjunction with the following figures. While aspects of an apparatus for providing cooling can be implemented in any number of different configurations, the embodiments are described in the context of the following devices and methods.

[0023] Fig. 1 illustrates a schematic of a Heating, Ventilation, and Air Conditioning (HVAC) system 100, in accordance with one implementation of the present subject matter. The HVAC system 100 may be configured to extract heat from a heat source, such as a space to be cooled and may dissipate the heat to a heat sink such as the ambient environment. According to an aspect, the HVAC system 100 of the present subject matter may dynamically route the working fluid in the circuit amongst various components to reduce the amount of work done by the HVAC system 100 to transfer heat from the heat source to the heat sink. This may reduce the power consumption and may increase the overall efficiency of the HVAC system 100. Accordingly, the HVAC system may selectively route some or all heat from one component to another, by-passing few other components in between, to reduce consumption of power while removing heat from the heat source and transferring heat to the heat sink.

[0024] The HVAC system 100 may include a refrigeration system 102, a heat source coupled with a first heat exchanger 104, and a heat sink coupled with a second heat exchanger 106. Refrigeration system 102, heat source coupled with a first heat exchanger 104, and a heat sink coupled with a second heat exchanger 106 may be in a heat exchange configuration with each other. Although the present illustration shows single heat source coupled with a first heat exchanger 104 and a single heat sink coupled with a second heat exchanger 106, the HVAC system 100 may include multiple heat sources coupled with first heat exchangers 104 and multiple heat sinks coupled with second heat exchangers 106. In the illustrated example, the term heat source coupled with a first heat exchanger 104 may be interchangeably used with the heat source (HSO) 104 while the term heat sink coupled with a second heat exchanger 106 is used interchangeably with the heat sink (HSI) 106. The HSO 104, the HSI 106, and the refrigeration system 102 are thermally coupled to each other. In one example, the thermal coupling between the HSO 104, the HSI 106, and the refrigeration system 102 may be achieved through fluidic coupling. In said example, the working fluid transfers thermal energy or heat between the HSO 104, the HSI 106, and the refrigeration system 102. Further, the HSO 104 may include a HSO outlet 108 and a HSO inlet 110 while the HSI 106 may include a HSI inlet 112 and a HSI outlet 114. Furthermore, the refrigeration system 102 may include a source end which includes a source-end inlet 116 and a source-end outlet 118 and a sink end which includes a sink-end outlet 120 and a sink-end inlet 122.

[0025] Further, as illustrated in Fig. 1, arrows indicate the direction of flow of a working fluid to and from the refrigeration system 102, the HSO 104 and the HSI 106. [0026] According to an example, the various inlets and outlets of the HSO 104, the HSI 106 and the refrigeration system 102 of the HVAC system 100 may be connected to each other using a plurality of conduits (not shown) that can fluidically connect the inlets and outlets of the HSO 104, the HSI 106 and the refrigeration system 102. Further, the HVAC system 100 may include a plurality of valves (not shown) that can selectively open and close the various conduits in the HVAC system 100 to form a plurality of cooling circuits to route the working fluid among the refrigeration system 102, the HSO 104 and the HSI 106. Further, the HVAC system 100 may include a plurality of pumps (not shown) that can pump the working fluid in a plurality of cooling circuits to route the working fluid flowing between the refrigeration system 102, the HSO 104 and the HSI 106.

[0027] According to an example, the HVAC system 100 may include a plurality of sensors (not shown), such as temperature sensors (not shown) and humidity sensors (not shown). The HSO inlet 110 may include a HSO inlet temperature sensor (not shown) to monitor a temperature at the HSO inlet 110. The HSO outlet 108 may include a HSO outlet temperature sensor (not shown) to monitor a temperature at the HSO outlet 108. The HSI inlet 112 may include a HSI inlet temperature sensor (not shown) to monitor a temperature at the HSI inlet 112. The HSI outlet 114 may include a HSI outlet temperature sensor (not shown) to monitor a temperature at the HSI outlet 114. The source-end inlet 116 may include a source-end inlet temperature sensor (not shown) to monitor a temperature at the source-end inlet 116. The source-end outlet 118 may include a source-end outlet temperature sensor (not shown) to monitor a temperature at the source-end outlet 118. The sink-end inlet 122 may include a sink-end inlet temperature sensor (not shown) to monitor a temperature at the sink-end inlet 122. The sink-end outlet 120 may include a sink-end outlet temperature sensor (not shown) to monitor a temperature at the sink-end outlet 120. The heat sink 606 may include a heat sink temperature sensor (not shown) and a heat sink humidity sensor (not shown) to monitor a temperature and humidity of the heat sink. [0028] In the illustrated example, the HVAC system 100 may also include a control unit 124 that may control the plurality of valves to form the plurality of cooling circuits and route the working fluid in one of the formed plurality of cooling circuits. According to the illustrated aspect, the control unit 124 includes processors which may be implemented as microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, and/or any devices that manipulate signals based on operational instructions. Among other capabilities, the processors may fetch and execute computer-readable instructions stored in a memory not shown coupled to the processors of the controller. The memory may include any non-transitory computer-readable storage medium including, for example, volatile memory e.g., ram, and/or non-volatile memory e.g., EPROM, flash memory, NVRAM, memristor, etc. The memory may be internal or external to the control unit 124. The functions of the control unit 124 may be provided through the use of dedicated hardware as well as hardware capable of executing computer-readable instructions.

[0029] In operation, the control unit 124 may receive temperature signals from the different temperature sensors and may perform various calculations to determine how the different valves and pumps are to be operated to route the working fluid. For example, the control unit 124 may obtain temperature readings from a HSO inlet temperature sensor, a HSO outlet temperature sensor, a HSI inlet temperature sensor, a HSI outlet temperature sensor, a source-end inlet temperature sensor, a source-end outlet temperature sensor, a sink-end inlet temperature sensor and a sink-end outlet. The HSO inlet temperature sensor obtains a temperature (TV) of the HSO inlet 110 and the HSO outlet temperature sensor obtains a temperature (Ti) of the HSO outlet 108. The HSI inlet temperature sensor obtains a temperature (T ₃ ) of the HSI inlet 112 and the HSI outlet temperature sensor obtains a temperature (TV) of the HSI outlet 114. The source-end inlet temperature sensor obtains a temperature (TA) of the source-end inlet 116 and the source-end outlet temperature sensor obtains a temperature (TB) of the source-end outlet 118. The sink-end inlet temperature sensor obtains a temperature (TD) of the sink-end inlet 122 and the sink-end outlet temperature sensor obtains a temperature (Tc) of the sink-end outlet 120. Based on the obtained temperatures, the control unit 124 controls the thermal coupling between the HSO inlet 110, the HSO outlet 108, the HSI inlet 112, the HSI outlet 114, the source-end inlet 116, the source-end outlet 118, the sink-end inlet 122, and the sink end outlet 120. Various examples of the cooling circuits formed by the control unit are explained with respect to Fig. 2 to 5. In said examples, the control unit 124 may be configured to operate the HVAC system 100 as the cooling system 100.

[0030] For example, in one aspect of the present subject matter, the control unit 124 may be configured to turn off the refrigeration system 102, when the operation of the refrigeration system 102 is not required. Further, the HSO 104 is a space to be cooled and the HSI 106 may be either a heat exchanger coupled to the ambient environment, a dry cooler coupled to the ambient environment, a direct evaporative cooler coupled to the ambient environment, an indirect evaporative cooler coupled to the ambient environment, a dew point evaporative cooler coupled to the ambient environment or a heat exchanger coupled to the geothermal ground source.

[0031] Fig. 2 illustrates the cooling circuit depicting a first configuration, in accordance with one implementation of the present subject matter. In the illustrated example, the control unit 124 receives the temperature signals from the temperature sensors. The control unit 124 may check if the temperature of the working fluid coming out from HSI 106, T ₄ , is higher than the temperature of the working fluid coming out from HSO 104, 7 . In case T ₄ > Ti, the control unit 124 may operate valves such that the HSO outlet 108 can be thermally coupled to the source-end inlet 116 and HSO inlet 110 can be thermally coupled to the source-end outlet 118 to form a cooling circuit. In addition, the HSI inlet 112 can be thermally coupled to the sink-end outlet 120 and the HSI outlet 114 can be thermally coupled to the sink- end inlet 122 to form another cooling circuit. In the illustrated example, the first and the second cooling circuit are separate and are fluidically isolated. For instance, in the first cooling circuit, the working fluid circulates between the HSO 104 and the HSO side of the refrigeration system 102. Further, in the second cooling circuit, the working fluid circulates between the HSI 106 and the HSI side of the refrigeration system 102. Here, all the heat from the working fluid on the HSO side is first transferred to the refrigerant in the refrigeration system 102 and then to the working fluid on the HSI side of the refrigeration system 102 before being discharged to the HSI 106. The control unit 124 may maintain this configuration until the relation between temperatures T4 and Ti is T ₄ > Ti.

[0032] Fig. 3 illustrates the cooling circuit depicting a second configuration, in accordance with one example implementation of the present subject matter. During the operation, there may be an instance when the temperature T ₄ at the HSI 106 changes with respect to temperature Ti and T ₂ . For instance, when the temperature T ₄ is lower than the temperature of the working fluid coming out from HSO 7 , but higher than the required temperature of the working fluid going to HSO T ₂ , the control unit 124 may operate the valves, such that connections can be such: the HSO outlet 108 and sink-end outlet 120 can be both thermally coupled to the HSI inlet 112, the HSO inlet 110 can be thermally coupled to the source-end outlet 118, and HSI outlet 114 can be thermally coupled to both the sink-end inlet 122 and source-end inlet 116. In this scenario, two interconnected cooling circuits are formed that are fluidically coupled to each other. In one of two cooling circuit illustrated in Fig. 3, the working fluid circulates between the HSO 104, the HSI 106 and the HSO side of the refrigeration system 102. In the other cooling circuit, the working fluid circulates between the HSI 106 and the HSI side of the refrigeration system 102. Note that HSI 106 is a common part of both the working fluid loops, and all of the working fluid passes through the HSI 106. Here, only a part of the heat from the HSO 104 passes through the refrigeration system 102, rest of the heat bypasses the refrigeration system 102 and is directly discharged by the HSI 106. As a result, the amount of energy required by the refrigeration system 102 may be reduced because the working fluid is now partly directly cooled by the HSI 106. The control unit 124 may maintain this configuration until the temperature T ₄ , T ₂ , and Ti satisfy the condition: T ₂ < T ₄ <Ti. [0033] Fig. 4 illustrates the cooling circuit depicting the second configuration, in accordance with another example implementation of the present subject matter. In the second configuration where the temperatures Ti, T2 and T ₄ satisfy the condition T2 < T4 < Ti, the control unit 124 may operate the valves in an alternate manner such that HSO outlet 108 can be thermally coupled to the sink-end inlet 122, the HSI outlet 114 can be thermally coupled to the source-end inlet 116, the source-end outlet 118 is thermally coupled to the HSO inlet 110, and the sink-end outlet 120 can be thermally coupled to the HSI inlet 112. In the illustrated example, one cooling circuit is formed which connects the refrigeration system 102, HSO 104 and HSI 106.

[0034] Fig. 5 illustrates the cooling circuit depicting a third configuration, in accordance with one implementation of the present subject matter. During the operation, there may be an instance when the temperature T4 at HSI 106 becomes equal to or less than the temperature T2. The control unit 124 may then operate the valves such that the HSO outlet 108 can be connected to HSI inlet 112, and HSO inlet 110 is connected to HSI outlet 114 to form a cooling circuit. In this configuration, the working fluid circulates directly between the HSO 104 and the HSI 106 in a single cooling circuit. Further, the refrigeration system 102 is completely bypassed and the heat from the HSO 104 is directly discharged by the HSI 106. In this configuration, the control unit may be configured to turn off the refrigeration system 102 to save energy.

[0035] Generally, when the refrigeration system 102 is operational and at least some of the heat is transferred through it, the refrigeration system 102 creates an additional thermal load, which also needs to be dissipated to the HSI 106. This additional thermal load can increase the temperature of the working fluid coming out from refrigeration system 102 on HSI side, T _c and can subsequently increase the temperature of the working fluid coming out from HSI 106, T _4. This consideration can be used to enable switching from one configuration to another and can further decrease the amount of heat passing through the refrigeration system 102. For example, when the temperature 74 is higher than the required temperature T ₂ of the working fluid going to the HSO 104, and it is estimated that if the additional heat load from the air conditioning system is removed, G ₄ would be lower than or equal to T ₂ , then the configuration of connections can be changed from those in Fig. 3 or Fig. 4 to those in Fig. 5. This would bypass the refrigeration system 102 which can be turned off.

[0036] According to an example, the above-mentioned system can also be used to provide heating instead of providing cooling. Accordingly, an example of a heating system 600 is provided with respect to Fig. 6. In this example, the HVAC system 100 may be configured to act as a heating system 600. Further, the heating system 600 may have similar components, such as the HSO 606 and the HSI 604. In use as a heating system 600, the direction of heat flow is reversed such that what was originally the HSO 104 is now the heat sink 604 and vice versa. For example, in use as a heating system 600, the HSO 606 can be a heat exchanger coupled to the ambient atmosphere or a heat exchanger coupled to the geothermal heat source and the HSI 604 can be a space that is to be heated. This can be especially useful in space heating applications, as the same equipment can be used for both space cooling and space heating.

[0037] In said example, where the HVAC system 100 is to be operated as the heating system 600, the control unit 124 can operate the valves such that the HSO outlet 608 can be thermally coupled to the sink-end inlet 622, the source-end outlet 618 can be thermally coupled to the HSI inlet 612, the HSI outlet 614 can be thermally coupled to the source-end inlet 616, and the sink-end outlet 620 can be thermally coupled to the HSO inlet 610.

[0038] In the scenario shown in Fig. 6, all of the heat passes through the heat pump 602. But as in the case of the HVAC system 100, depending on various parameters, other connection configurations can be used to partially or completely bypass the heat pump 602. [0039] In another embodiment of the present subject matter, the HVAC system 100 can include, along with the refrigeration system 102 and the HSI 106, the plurality of sensors, such as temperature sensors, which are present at specific positions and not at all the outlets and inlets. In the present embodiment, the HSO inlet 110 may include the HSO inlet temperature sensor to monitor a temperature at the HSO inlet 110 and the HSO outlet 108 may include the HSO outlet temperature sensor to monitor a temperature at the HSO outlet 108. Similarly, the HSI outlet 114 may include the HSI outlet temperature sensor to monitor a temperature at the HSI outlet 114. The control unit 124 is coupled to the HSO 104, the refrigeration system 102, and the HSI 106 to obtain the temperature readings from the HSO inlet temperature sensor, HSO outlet temperature sensor, and the HSI outlet temperature sensor. Further, the control unit 124 is configured to control the thermal coupling between the HSO outlet 108, the HSO inlet 110, the HSI outlet 114, the HSI inlet 112, the source-end inlet 116, the source-end outlet 118, the sink-end inlet 122 and the sink-end outlet 120 based on the obtained temperature readings. The operations and functions of the components in the present embodiment remain similar to those described with reference to the previous embodiment and have not been repeated for the sake of brevity.

[0040] According to one embodiment of the present subject matter, the control unit 124 is configured to control the thermal coupling between the HSO inlet 110, the HSO outlet 108, the HSI inlet 112, the HSI outlet 114, the source-end inlet 116, the source-end outlet 118, the sink-end inlet 122, and the sink end outlet 120, based on ambient conditions. In an example, the ambient conditions can be one of the ambient temperature, the ambient temperature and a measure of humidity (either absolute or relative humidity), the dew point temperature, the wet-bulb temperature, or a combination thereof.

[0041] The ambient temperature can be monitored or measured by using an appropriately positioned temperature sensor. Further, the humidity values can be measured using a humidity sensor which are appropriately positioned. The humidity sensors may even provide, both, temperature and humidity values. Further, the control unit 124, in an example, may use the ambient temperature and humidity values to calculate the wet-bulb temperature and the dew point temperature. In addition, the control unit 124 can be preconfigured to, based on the ambient conditions, determine the different modes of operation in which the HVAC system 100 can be operated. For instance, the control unit 124 may obtain a HSI ambient temperature, a HSI ambient environment wet-bulb temperature and a HSI ambient environment dew point temperature from the temperature sensor positioned at the HSI 106. The control unit 124 may also obtain a HSI ambient environment absolute humidity and a HSI ambient environment relative humidity from the humidity sensor positioned at the HSI 106. The control unit 124 may be configured to form a plurality of cooling circuits, as depicted in Figs. 2 to 5, based on one of the HSI ambient environment temperature, the HSI ambient environment absolute humidity, the HSI ambient environment relative humidity, the HSI ambient environment wet-bulb temperature and the HSI ambient environment dew point temperature. In an example, the control unit 124 may compare the various temperature and humidity values to a first pre-set or a second pre-set value to switch the HVAC system 100 from one mode to another. All such conditions and modes are envisaged as part of the present subject matter. The first pre-set value may be a default set of values for temperature and humidity, such as a first ambient environment temperature, a first ambient environment absolute humidity, a first ambient environment relative humidity, a first ambient environment wet-bulb temperature and a first ambient environment dew point temperature. Similarly, the second pre-set value may be another default set of values for temperature and humidity, such as a second ambient environment temperature, a second ambient environment absolute humidity, a second ambient environment relative humidity, a second ambient environment wet-bulb temperature and a second ambient environment dew point temperature. In one example, the temperature values at the HSO inlet 110, HSO outlet 108, HSI inlet 112 and HSI outlet 114 may be dependent on ambient conditions.

[0042] In an example of the present subject matter, where one of the HSI ambient environment temperature, the HSI ambient environment absolute humidity, the HSI ambient environment relative humidity, the HSI ambient environment wet- bulb temperature and the HSI ambient environment dew point temperature is lower than or equal to a first pre-set value, the control unit 124 may be configured to operate the valves such that the HSO outlet 108 can be connected to HSI inlet 112, and HSO inlet 110 is connected to HSI outlet 114 to form a cooling circuit. In this configuration, the working fluid circulates directly between the HSO 104 and the HSI 106 in a single cooling circuit. Further, the refrigeration system 102 is completely bypassed and the heat from the HSO 104 is directly discharged by the HSI 106. In this configuration, the control unit 124 may be configured to turn off the refrigeration system 102 to save energy.

[0043] In an example of the present subject matter, where one of the HSI ambient environment temperature, the HSI ambient environment absolute humidity, the HSI ambient environment relative humidity, the HSI ambient environment wet- bulb temperature and the HSI ambient environment dew point temperature is higher than a first pre-set value but lower than a second pre-set value, the control unit may be configured to operate the valves such that the HSO outlet 108 and sink-end outlet 120 can be both thermally coupled to the HSI inlet 112, the HSO inlet 110 can be thermally coupled to the source-end outlet 118, and HSI outlet 114 can be thermally coupled to both the sink-end inlet 122 and source-end inlet 116. In another aspect of said example, the control unit 124 may operate the valves in an alternate manner such that HSO outlet 108 can be thermally coupled to the sink-end inlet 122, the HSI outlet 114 can be thermally coupled to the source-end inlet 116, the source-end outlet 118 is thermally coupled to the HSO inlet 110, and the sink-end outlet 120 can be thermally coupled to the HSI inlet 112.

[0044] In an example of the present subject matter, where one of the HSI ambient environment temperature, the HSI ambient environment absolute humidity, the HSI ambient environment relative humidity, the HSI ambient environment wet- bulb temperature and the HSI ambient environment dew point temperature is higher than a second pre-set value, the control unit 124 may be configured to operate the valves such that the HSO outlet 108 can be thermally coupled to the source-end inlet 116 and HSO inlet 110 can be thermally coupled to the source-end outlet 118 to form a cooling circuit. In addition, the HSI inlet 112 can be thermally coupled to the sink-end outlet 120 and the HSI outlet 114 can be thermally coupled to the sink- end inlet 122 to form another cooling circuit.

[0045] According to an example, Fig 7 illustrates a method of operating a Heating, Ventilation, and Air Conditioning (HVAC) system 100. The process is aimed at thermally coupling a refrigeration system 102, a heat source 104 and a heat sink 106 of the HVAC system 100. At block 702, first different temperatures of the refrigeration system 102, the heat source 104 and the heat sink 106 are detected. For example, a heat source inlet temperature sensor and a heat source outlet temperature sensor may be configured to detect temperatures at a heat source (HSO) inlet 110 and a heat source (HSO) outlet 108, respectively, of the heat source 104. Further, a heat sink inlet temperature sensor and a heat sink outlet temperature sensor may be configured to detect temperatures of a heat sink (HSI) inlet 112 and a heat sink (HSI) outlet 114 of the heat sink 106. A source-end inlet temperature sensor and a source-end outlet temperature sensor may be configured to detect temperatures of a source-end inlet 116 and a source-end outlet 118 of a source end of the refrigeration system 102. A sink-end inlet temperature sensor and a sink-end outlet temperature sensor may be configured to detect temperatures of a sink-end inlet 122 and a sink-end outlet 120 of a sink end of the refrigeration system 102. At block 704, based on the detected or obtained temperatures, a control unit 124 performs the controlling of thermal coupling between the HSO inlet 110, the HSO outlet 108, the HSI inlet 112, the HSI outlet 114, the source-end inlet 116, the source-end outlet 118, the sink-end inlet 122, and the sink-end outlet 120 based on selected temperatures. The selected temperatures may be, for example, the temperature at the HSO outlet 108 obtained by the heat source outlet temperature sensor, the temperature at the HSO inlet 110 obtained by the heat source inlet temperature sensor and the temperature at the HSI outlet 114 obtained by the heat sink outlet temperature sensor. In said example, the control unit is configured to control the thermal coupling between the HSO outlet 108, the HSO inlet 110, the HSI outlet 114, the HSI inlet 112, the source-end inlet 116, the source-end outlet 118, the sink-end inlet 122 and the sink-end outlet 120 based on the obtained temperature readings. The control unit 124 may be configured to control the thermal coupling between the HSO outlet 108, the HSO inlet 110, the HSI outlet 114, the HSI inlet 112, the source-end inlet 116, the source-end outlet 118, the sink-end inlet 122 and the sink-end outlet 120 based on ambient conditions. The ambient conditions may be, for example, a HSI ambient environment temperature, a HSI ambient environment absolute humidity, a HSI ambient environment relative humidity, a HSI ambient environment wet-bulb temperature and a HSI ambient environment dew point temperature. In an example, the above-mentioned method or process can also be used to provide heating instead of providing cooling by controlling the thermal coupling.

[0046] The HVAC system 100, as described in various embodiments of the present subject matter, can lead to significantly higher energy efficiency than the traditional approaches. In the traditional air conditioning approach, all of the heat to be discharged passes through the refrigeration system. The new approach enables all or a part of the heat to bypass the refrigeration system. The heat that bypasses the refrigeration system can be directly discharged to a heat sink. In many typical air conditioning setups, the power consumption of the refrigeration system is typically much higher than that of all the other components combined. Hence, enabling some or all of the heat to bypass the refrigeration system would significantly lower the overall energy consumption of the air conditioning system.

[0047] The new approach also allows use of the air conditioning equipment as a heat pump for heating applications without any significant changes to the equipment. This enables the use of same equipment for both heating and cooling applications, for example the same equipment can be used for space cooling in summer and for space heating in winter.

[0048] The invention has been described using liquid working fluid as an example. Other types of working fluids can be used, for example a mixture where one of the constituents is a liquid can also be used. [0049] Various modifications of the disclosed embodiments, as well as alternate embodiments of the subject matter, will become apparent to persons skilled in the art upon reference to the description of the subject matter. It is therefore contemplated that such modifications can be made without departing from the scope of the present subject matter as defined.