Patent Publication Number: US-11022122-B2

Title: Intermediate discharge port for a compressor

Description:
FIELD 
     This disclosure relates generally to fluid discharge in a vapor compression system. More specifically, this disclosure relates to an intermediate discharge port of a compressor in a vapor compression system such as, but not limited to, a heating, ventilation, and air conditioning (HVAC) system. 
     BACKGROUND 
     One type of compressor for a vapor compression system is generally referred to as a screw compressor. A screw compressor generally includes one or more rotors (e.g., one or more rotary screws). Typically, a screw compressor includes a pair of rotors (e.g., two rotary screws) which rotate relative to each other to compress a working fluid such as, but not limited to, a refrigerant or the like. 
     SUMMARY 
     This disclosure relates generally to fluid discharge in a vapor compression system. More specifically, this disclosure relates to an intermediate discharge port of a compressor in a vapor compression system such as, but not limited to, a heating, ventilation, and air conditioning (HVAC) system. 
     In an embodiment, the compressor is a screw compressor. In an embodiment, the screw compressor can be used in an HVAC system (sometimes referred to alternatively as a refrigeration system) to compress a heat transfer fluid. The heat transfer fluid can be, for example, a refrigerant. 
     In an embodiment, the intermediate discharge port for the screw compressor can be included when the screw compressor is manufactured. In an embodiment, the intermediate discharge port for the screw compressor can be retrofit into the screw compressor that was manufactured without the intermediate discharge port. In an embodiment, the intermediate discharge port for the screw compressor can be retrofit into the screw compressor even after the screw compressor has been operated. 
     In an embodiment, the intermediate discharge port can be added to the screw compressor at a location that is in fluid communication with a compression chamber of the screw compressor. In an embodiment, the intermediate discharge port can be added to the screw compressor at a location that is disposed in fluid communication with a compression chamber of the screw compressor and is at a location between the inlet port and the outlet port of the compressor. 
     In an embodiment, a fluid flow state (e.g., flow-permitted, flow-blocked) of the intermediate discharge port of the screw compressor can be controlled based on a pressure differential. In an embodiment, the fluid flow state of the intermediate discharge port can be controlled by a biasing mechanism actuated in response to a signal from a controller. 
     A screw compressor is disclosed. In an embodiment, the screw compressor includes a compressor housing defining a working chamber, the housing including a plurality of bores; a first rotor having helical threads, the first rotor being housed in a first of the plurality of bores; a second rotor having helical threads intermeshing with the helical threads of the first rotor, the second rotor being housed in a second of the plurality of bores; an inlet port that receives a fluid to be compressed; an outlet port that receives a compressed fluid; and an intermediate discharge port disposed between the compression chamber and the outlet port, the intermediate discharge port including a sealing member and a biasing mechanism, fluid flow being prevented between the compression chamber and the intermediate discharge port when in a flow-blocked state, and fluid flow being enabled from the compression chamber through the intermediate discharge port when in a flow-permitted state. 
     An HVAC system is disclosed. In an embodiment, the HVAC system includes a condenser, an expansion device, and an evaporator, and a screw compressor fluidly connected and forming a heat transfer circuit. The screw compressor includes a compressor housing defining a working chamber, the housing including two bores; a first rotor having helical threads, the first rotor being housed in a first of the two bores; a second rotor having helical threads intermeshing with the helical threads of the first rotor, the second rotor being housed in a second of the two bores; a suction port that receives a fluid to be compressed; an outlet port that receives a compressed fluid; and an intermediate discharge port disposed between the compression chamber and the outlet port, the intermediate discharge port including a sealing member and a biasing mechanism, fluid flow being prevented between the compression chamber and the intermediate discharge port when in a flow-blocked state, and fluid flow being enabled from the compression chamber through the intermediate discharge port when in a flow-permitted state. 
     A method is disclosed. In an embodiment, the method includes providing an intermediate discharge port at a location in fluid communication with a compression chamber of a screw compressor, the intermediate discharge port being disposed between an inlet port and an outlet port of the screw compressor, wherein when operating the screw compressor at part-load, discharging a portion of a working fluid being compressed from the compression chamber toward a discharge of the screw compressor, the working fluid being at a pressure that is lower than a discharge pressure of the screw compressor, and when operating the screw compressor at full-load, discharging the working fluid being compressed from the outlet port of the screw compressor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       References are made to the accompanying drawings that form a part of this disclosure and which illustrate embodiments in which the systems and methods described in this specification can be practiced. 
         FIG. 1  is a schematic diagram of a heat transfer circuit with which embodiments of this disclosure can be practiced, according to an embodiment. 
         FIG. 2  illustrates a partial view of a screw compressor with which embodiments of this disclosure can be practiced, according to an embodiment. 
         FIG. 3  illustrates a screw compressor including an intermediate discharge port in a flow-blocked state, according to an embodiment. 
         FIG. 4  illustrates the screw compressor including the intermediate discharge port of  FIG. 3  in a flow-permitted state, according to an embodiment. 
         FIG. 5  illustrates a screw compressor including an intermediate discharge port in a flow-blocked state, according to another embodiment. 
         FIG. 6  illustrates the screw compressor including the intermediate discharge port of  FIG. 5  in a flow-permitted state, according to another embodiment. 
         FIG. 7  illustrates another view of the screw compressor including the intermediate discharge port of  FIG. 5  in the flow-blocked state, according to another embodiment. 
     
    
    
     Like reference numbers represent like parts throughout. 
     DETAILED DESCRIPTION 
     This disclosure relates generally to fluid discharge in a vapor compression system. More specifically, this disclosure relates to an intermediate discharge port of a compressor in a vapor compression system such as, but not limited to, a heating, ventilation, and air conditioning (HVAC) system. 
     Generally, when a compressor is running at a part load operation, the compressor may over pressurize the working fluid. In an embodiment, an intermediate discharge port can be added to the compressor to allow the working fluid to leave the compression chamber prior to reaching the discharge port. In such an embodiment, the intermediate discharge port can increase an efficiency of the compressor by reducing the over pressurization of the working fluid. In an embodiment, an increase in efficiency can be at or about 12%. In an embodiment, an increase in efficiency can be up to 12% or up to about 12%. Unlike a slide valve, the intermediate discharge port is not determinative of a capacity of the screw compressor. Further, slide valves generally move in a direction that is parallel to the rotors of the screw compressor, while the intermediate discharge port generally moves in a direction that is about perpendicular to the rotors of the screw compressor. 
       FIG. 1  is a schematic diagram of a heat transfer circuit  10 , according to an embodiment. The heat transfer circuit  10  generally includes a compressor  12 , a condenser  14 , an expansion device  16 , and an evaporator  18 . The compressor  12  can be powered by an electric motor (not shown). The heat transfer circuit  10  is an example and can be modified to include additional components. For example, in an embodiment, the heat transfer circuit  10  can include an economizer heat exchanger, one or more flow control devices, a receiver tank, a dryer, a suction-liquid heat exchanger, or the like. 
     The heat transfer circuit  10  can generally be applied in a variety of systems (e.g., vapor compression systems) used to control an environmental condition (e.g., temperature, humidity, air quality, or the like) in a space (generally referred to as a conditioned space). Examples of systems include, but are not limited to HVAC systems, transport refrigeration systems, or the like. 
     The components of the heat transfer circuit  10  are fluidly connected. The heat transfer circuit  10  can be specifically configured to be a cooling system (e.g., a fluid chiller of an HVAC system and/or an air conditioning system) capable of operating in a cooling mode. Alternatively, the heat transfer circuit  10  can be specifically configured to be a heat pump system which can operate in both a cooling mode and a heating/defrost mode. 
     Heat transfer circuit  10  operates according to generally known principles. The heat transfer circuit  10  can be configured to heat or cool a process fluid. In an embodiment, the process fluid can be, for example, a fluid such as, but not limited to, water or the like, in which case the heat transfer circuit  10  may be generally representative of a chiller system. In an embodiment, the process fluid can be, for example, a fluid such as, but not limited to, air or the like, in which case the heat transfer circuit  10  may be generally representative of an air conditioner or heat pump. 
     The compressor  12  is generally representative of a screw compressor. In operation, the compressor  12  compresses a working fluid (e.g., a heat transfer fluid such as refrigerant or the like) from a relatively lower pressure gas to a relatively higher-pressure gas. The relatively higher-pressure and higher temperature gas is discharged from the compressor  12  and flows through the condenser  14 . In accordance with generally known principles, the working fluid flows through the condenser  14  and rejects heat to the process fluid (e.g., a heat transfer fluid or medium such as, but not limited to, water, air, etc.), thereby cooling the working fluid. The cooled working fluid, which is now in a liquid form, flows to the expansion device  16 . The expansion device  16  reduces the pressure of the working fluid. As a result, a portion of the working fluid is converted to a gaseous form. The working fluid, which is now in a mixed liquid and gaseous form flows to the evaporator  18 . The working fluid flows through the evaporator  18  and absorbs heat from the process fluid (e.g., a heat transfer fluid or medium such as, but not limited to, water, air, etc.), heating the working fluid, and converting it to a gaseous form. The gaseous working fluid then returns to the compressor  12 . The above-described process continues while the heat transfer circuit is operating, for example, in a cooling mode (e.g., while the compressor  12  is enabled). 
     In an embodiment, the compressor  12  can be controlled by, for example, a controller  20 . The controller  20  can, in an embodiment, control one or more of the other components of the heat transfer circuit  10  or the HVAC system corresponding to the heat transfer circuit  10 . 
       FIG. 2  illustrates a screw compressor  100  with which embodiments as disclosed in this specification can be practiced, according to an embodiment. The screw compressor  100  can be used in the heat transfer circuit  10  of  FIG. 1  (e.g., as the compressor  12 ). It is to be appreciated that the screw compressor  100  can be used for purposes other than in the heat transfer circuit  10 . For example, the screw compressor  100  can be used to compress air or gases other than a heat transfer fluid (e.g., natural gas, etc.). It is to be appreciated that the screw compressor  100  includes additional features that are not described in detail in this specification. For example, the screw compressor  100  can include a lubricant sump for storing lubricant to be introduced to the moving features of the screw compressor  100 . 
     The screw compressor  100  includes a first helical rotor  105  and a second helical rotor  110  disposed in a rotor housing  115 . The rotor housing  115  includes a plurality of bores  120 A and  120 B. The plurality of bores  120 A and  120 B are configured to accept the first helical rotor  105  and the second helical rotor  110 . 
     The first helical rotor  105 , generally referred to as the male rotor, has a plurality of spiral lobes  125 . The plurality of spiral lobes  125  of the first helical rotor  105  can be received by a plurality of spiral grooves  130  of the second helical rotor  110 , generally referred to as the female rotor. In an embodiment, the spiral lobes  125  and the spiral grooves  130  can alternatively be referred to as the threads  125 ,  130 . The first helical rotor  105  and the second helical rotor  110  are arranged within the housing  115  such that the spiral grooves  130  intermesh with the spiral lobes  125  of the first helical rotor  105 . 
     During operation, the first and second helical rotors  105 ,  110  rotate counter to each other. That is, the first helical rotor  105  rotates about an axis A in a first direction while the second helical rotor  110  rotates about an axis B in a second direction that is opposite the first direction. Relative to an axial direction that is defined by the axis A of the first helical rotor  105 , the screw compressor  100  includes an inlet port  135  and an outlet port  140 . 
     The rotating first and second helical rotors  105 ,  110  can receive a working fluid (e.g., heat transfer fluid such as refrigerant or the like) at the inlet port  135 . The working fluid can be compressed between the spiral lobes  125  and the spiral grooves  130  (in a pocket  145  formed therebetween) and discharged at the outlet port  140 . The pocket is generally referred to as the compression chamber  145  and is defined between the spiral lobes  125  and the spiral grooves  130  and an interior surface of the housing  115 . In an embodiment, the compression chamber  145  may move from the inlet port  135  to the outlet port  140  when the first and second helical rotors  105 ,  110  rotate. In an embodiment, the compression chamber  145  may continuously reduce in volume while moving from the inlet port  135  to the discharge port  145 . This continuous reduction in volume can compress the working fluid (e.g., heat transfer fluid such as refrigerant or the like) in the compression chamber  145 . 
     The screw compressor  100  can include an intermediate discharge port  175 . The intermediate discharge port  175  can, for example, provide an exit flow path for the working fluid being compressed (e.g., heat transfer fluid such as refrigerant or the like). The intermediate discharge port  175  may alternatively be referred to as the radial discharge port  175 , the radial intermediate discharge port  175 , or the like. The intermediate discharge port  175  can, for example, enable the fluid being compressed to radially exit the compression chamber  145  prior to being discharged from the axial outlet port  140 . The intermediate discharge port  175  can be oriented such that the fluid being compressed exits in a direction that is about perpendicular to the axial direction that is defined by the axis A of the first helical rotor  105  and the axis B of the second axial rotor  110 . 
     Advantageously, according to an embodiment, the intermediate discharge port  175  can prevent overcompression of the working fluid by radially discharging the fluid from the compression chamber  145  prior to the outlet port  140 . In an embodiment, preventing overcompression of the fluid can increase an efficiency of the screw compressor  100 . In an embodiment, an increase in efficiency of the screw compressor  100  can be at or about 12%. In an embodiment, an increase in efficiency of the screw compressor  100  can be up to 12% or up to about 12%. The intermediate discharge port  175  is shown and described in additional detail according to various embodiments in accordance with  FIGS. 3-6  below. 
     In an embodiment, the intermediate discharge port  175  can be included in the screw compressor  100  at a time of manufacturing. In an embodiment, the intermediate discharge port  175  can be retrofitted into the screw compressor  100  after manufacturing. In an embodiment, the intermediate discharge port  175  can be retrofitted into the screw compressor  100  even after the screw compressor  100  has been in use. 
       FIG. 3  illustrates the screw compressor  100  including an intermediate discharge port  175 A, according to an embodiment. In  FIG. 3 , the intermediate discharge port  175 A is in a flow-blocked (e.g., closed) state.  FIG. 4  illustrates the screw compressor  100  including the intermediate discharge port  175 A, according to an embodiment. In  FIG. 4 , the intermediate discharge port  175 A is in a flow-permitted (e.g., opened) state.  FIGS. 3-4  will be described generally, unless specific reference is made to the contrary. 
     In an embodiment, the screw compressor  100  can include a plurality of intermediate discharge ports  175 A. For example, the screw compressor  100  can include a first intermediate discharge port at a first intermediate location and a second intermediate discharge port at a second intermediate location, with the first and second intermediate locations being selected to provide an intermediate discharge at a particular compressor load. 
     The intermediate discharge port  175 A includes a biasing mechanism  180 ; a sealing member  185  connected to the biasing mechanism  180  and disposed within a chamber  190  of the intermediate discharge port  175 A; and a plurality of apertures  195 . 
     The biasing mechanism  180  can be an actively controlled mechanism, according to an embodiment. For example, the biasing mechanism  180  can be a biasing mechanism electrically connected to a controller (e.g., the controller  20  in  FIG. 1 ). In such an embodiment, the controller can be connected to a sensor (e.g., a pressure sensor, etc.). The controller can provide an electric signal to the biasing mechanism  180  to control whether the biasing mechanism  180  is in the flow-blocked state ( FIG. 3 ) or in the flow-permitted state ( FIG. 4 ). For example, the controller might identify that the screw compressor  100  is operating at full capacity, in which case the controller might send a signal to the biasing mechanism  180  to place/maintain the biasing mechanism  180  in the flow-blocked state of  FIG. 3 . Alternatively, the controller might identify that the screw compressor  100  is operating at a capacity less than full capacity, in which case the controller might send a signal to the biasing mechanism  180  to place/maintain the biasing mechanism  180  in the flow-permitted state of  FIG. 4 . 
     In an embodiment, the biasing mechanism  180  can be a passively controlled mechanism. For example, the biasing mechanism  180  can be a biasing mechanism that is controllable between the flow-blocked ( FIG. 3 ) and the flow-permitted ( FIG. 4 ) states based on a pressure differential between the compression chamber  145  and the discharge. In such an embodiment, the intermediate discharge port  175 A can alternate between the flow-blocked state ( FIG. 3 ) and the flow-permitted state ( FIG. 4 ) based on, for example, pressure differential of the discharge and the compression chamber  145 . In such an embodiment, the intermediate discharge port  175 A may be disposed at a top portion of the housing  115  such that the biasing mechanism moves vertically upward (e.g. with respect to the ground) or downward to transition between the flow-blocked state ( FIG. 3 ) and the flow-permitted state ( FIG. 4 ). It is to be appreciated that a passively controlled biasing mechanism may be placed in a different orientation, according to an embodiment, but for simplicity of the design, the vertical orientation may be preferred. In a vertical orientation, the intermediate discharge port  175 A can move radially (e.g., about perpendicular to the rotors  105 ,  110 ) from or toward the compression chamber  145 . 
     When the screw compressor  100  is operating at a lower pressure ratio than designed (e.g., a part-load operation), the intermediate discharge port  175 A can be in the flow-permitted state ( FIG. 4 ). In such an operating condition, the pressure of the discharge is lower than the pressure in the compression chamber  145 . Accordingly, the pressurized fluid can force the sealing member  185  in the d 1  direction (vertically upward), enabling flow of the working fluid from the compression chamber  145  through the intermediate discharge port  175 A. When the compressor is operating at its designed pressure ratio (e.g., full-load operation) the pressure of the working fluid at the discharge may be higher than the pressure of the working fluid in the compression chamber  145 . As a result, the sealing member  185  may be forced in the d 2  direction (vertically downward), thereby causing the sealing member  185  to be in sealing contact with the surface  190 A, thereby preventing flow through the intermediate discharge port  175 A. In such an operating condition, the fluid being compressed can be discharged through the outlet port  140 . 
     The biasing mechanism  180  is connected to the sealing member  185  such that the biasing mechanism  180  can move the sealing member  185  in either a direction d 1  (vertically up with respect to the page in the figures) or a direction d 2  (vertically down with respect to the page in the figures). The sealing member  185  can include a surface  185 A which can serve as a sealing surface in a flow-blocked state. That is, the surface  185 A can form a sealing engagement with a sealing surface  190 A of the chamber  190  when in the flow-blocked state ( FIG. 3 ). In the flow-blocked state ( FIG. 3 ), the surface  185 A of the sealing member  185  can prevent a fluid (e.g., working fluid such as a heat transfer fluid, etc.) from radially exiting the compression chamber  145 . 
     The chamber  190  can be sized to permit the sealing member  185  to translate in the d 1  and d 2  directions. The chamber  190  can be in fluid communication with a discharge of the screw compressor  100  when the intermediate discharge port  175 A is in the flow-permitted state ( FIG. 4 ). The plurality of apertures  195  is disposed within the housing  115 . In an embodiment, the plurality of apertures  195  is bored into the housing  115 . When in the flow-permitted state ( FIG. 4 ), the plurality of apertures  195  is fluidly connected with the chamber  190 , and accordingly with the discharge of the screw compressor  100 . When in the flow-blocked state ( FIG. 3 ), the plurality of apertures  195  is fluidly sealed from the chamber  190  by a sealing engagement between the surface  185 A of the sealing member  185  and the sealing surface  190 A of the chamber  190 . 
     In the illustrated embodiment, three apertures  195  are shown. It will be appreciated that the number of apertures  195  is an example. The intermediate discharge port  175 A can include more than three apertures  195 , according to an embodiment, or fewer than three apertures  195 , according to an embodiment. For example, in an embodiment, the intermediate discharge port  175 A can include four apertures  195 , with two apertures being disposed in each bore  120 A,  120 B of the screw compressor  100  such that symmetry is maintained between each of the bores  120 A,  120 B. The apertures  195  can be based on a size of the bore  120 A,  120 B. Generally, a number of apertures  195  may be limited based on, for example, manufacturing limitations. 
     The size and geometry of the plurality of apertures  195  can be determined based on, for example, simplicity of manufacturing, flow rate of the working fluid, or the like. In an embodiment, a distance L 1  from an inlet of the plurality of apertures  195  to an outlet of the plurality of apertures into the chamber  190  can be determined by, for example, manufacturing tolerances or the like. Additionally, the distance L 1  can be selected to minimize an amount of the working fluid which may enter the plurality of apertures  195  when the intermediate discharge port  175  is in the flow-blocked state ( FIG. 3 ). 
       FIG. 5  illustrates the screw compressor  100  including an intermediate discharge port  175 B, according to an embodiment. In  FIG. 5 , the intermediate discharge port  175 B is in the flow-blocked state.  FIG. 6  illustrates the screw compressor  100  including the intermediate discharge port  175 B of  FIG. 5 , according to an embodiment. In  FIG. 6 , the intermediate discharge port  175 B is in the flow-permitted state.  FIG. 7  illustrates an alternative view of the screw compressor  100  including the intermediate discharge port  175 B of  FIG. 5  in the flow-blocked state.  FIGS. 5-7  will be described generally, unless specific reference is made to the contrary. 
     Aspects of the intermediate discharge port  175 B in  FIGS. 5-7  are the same as or similar to aspects of the intermediate discharge port  175 A in  FIGS. 3-4 . To simplify this specification, aspects of  FIGS. 5-7  which are different from aspects of  FIGS. 3-4  will be discussed, while aspects which are the same or substantially similar will not be described in additional detail. 
     The intermediate discharge port  175 B includes a single aperture  200 , according to an embodiment. The single aperture  200  functions similarly to the plurality of apertures  195  in the embodiment shown and described above with respect to  FIGS. 3-4 . The aperture  200  can follow a contour of the bores  120 A and  120 B of the housing  115  (see  FIG. 7 ). A portion of the aperture  200  is in the bore  120 A and another portion of the aperture  200  is in the second bore  120 B. Accordingly, the aperture  200  can be approximately shaped to match a rotor-helix angle of the screw compressor  100 . In an embodiment, the aperture  200  can be approximately v-shaped. A sealing member  205  is configured to include a surface  205 A which follows a contour of the bores  120 A,  120 B as well ( FIG. 7 ). Accordingly, the sealing member  205  can be approximately v-shaped to correspond to the aperture  200 , according to an embodiment. 
     When the intermediate discharge port  175 B is in the flow-blocked state ( FIG. 5 ), the surface  205 A approximately follows the contour of the bores  120 A,  120 B of the housing  115 . Accordingly, when the intermediate discharge port  175 B is in the flow-blocked state ( FIG. 5 ), the bores  120 A,  120 B and the housing  115  may be substantially smooth. The intermediate discharge port  175 B and corresponding shape can, for example, prevent portions of the working fluid being compressed from entering the aperture  200  when in the flow-blocked state ( FIG. 5 ). That is, relative to the embodiment in  FIGS. 3-4 , which includes a distance L 1  between the bores  120 A,  120 B and the sealing member  185  in a flow-blocked state ( FIG. 3 ), the embodiment in  FIGS. 5-6  does not include (or reduces) an area in which the working fluid being compressed can be directed when in the flow-blocked state. When the intermediate discharge port  175 B is in the flow-permitted state ( FIG. 6 ), the compression chamber  145 , the aperture  200 , and the discharge are fluidly connected such that the working fluid can be discharged from the intermediate discharge port  175 B. 
     Aspects: 
     It is to be appreciated that any one of aspects 1-8 can be combined with any one of aspects 9-18 or any one of aspects 19-20. Any one of aspects 9-18 can be combined with any one of aspects 19-20. 
     Aspect 1. A screw compressor, comprising: 
     a compressor housing defining a working chamber, the housing including a plurality of bores; 
     a first rotor having helical threads, the first rotor being housed in a first of the plurality of bores; 
     a second rotor having helical threads intermeshing with the helical threads of the first rotor, the second rotor being housed in a second of the plurality of bores; 
     an inlet port that receives a fluid to be compressed; 
     an outlet port that receives a compressed fluid; and 
     an intermediate discharge port disposed between the compression chamber and the outlet port, the intermediate discharge port including a sealing member and a biasing mechanism, fluid flow being prevented between the compression chamber and the intermediate discharge port when in a flow-blocked state, and fluid flow being enabled from the compression chamber through the intermediate discharge port when in a flow-permitted state. 
     Aspect 2. The screw compressor according to aspect 1, wherein the intermediate discharge port is disposed at a location of the compression chamber at which a fluid being compressed is partially compressed. 
     Aspect 3. The screw compressor according to any one of aspects 1-2, wherein the screw compressor includes a plurality of intermediate discharge ports disposed between the inlet port and the outlet port. 
     Aspect 4. The screw compressor according to any one of aspects 1-3, wherein the biasing mechanism is electrically connected to a controller for selectively placing the intermediate discharge port in the flow-blocked state or the flow-permitted state. 
     Aspect 5. The screw compressor according to any one of aspects 1-3, wherein the biasing mechanism is passively controlled based on a pressure ratio between the fluid in the working chamber and the compressed fluid at the outlet port. 
     Aspect 6. The screw compressor according to any one of aspects 1-5, wherein the compressor housing includes a plurality of apertures configured to fluidly connect the compression chamber and the intermediate discharge port when in the flow-permitted state. 
     Aspect 7. The screw compressor according to any one of aspects 1-5, wherein the compressor housing includes a single aperture configured to fluidly connect the compression chamber and the intermediate discharge port when in the flow-permitted state. 
     Aspect 8. The screw compressor according to aspect 7, wherein the single aperture is formed in a wall of the housing, a portion of the aperture being in the first of the plurality of bores and another portion of the aperture being in the second of the plurality of bores. 
     Aspect 9. A heating, ventilation, and air conditioning (HVAC) system, comprising: 
     a condenser, an expansion device, and an evaporator, and a screw compressor fluidly connected and forming a heat transfer circuit, wherein the screw compressor includes:
         a compressor housing defining a working chamber, the housing including two bores;   a first rotor having helical threads, the first rotor being housed in a first of the two bores;   a second rotor having helical threads intermeshing with the helical threads of the first rotor, the second rotor being housed in a second of the two bores;   a suction port that receives a fluid to be compressed;   an outlet port that receives a compressed fluid; and   an intermediate discharge port disposed between the compression chamber and the outlet port, the intermediate discharge port including a sealing member and a biasing mechanism, fluid flow being prevented between the compression chamber and the intermediate discharge port when in a flow-blocked state, and fluid flow being enabled from the compression chamber through the intermediate discharge port when in a flow-permitted state.       

     Aspect 10. The HVAC system according to aspect 9, further comprising a controller electrically connected to the biasing mechanism that selectively controls the intermediate discharge port such that the intermediate discharge port is placed in the flow-blocked or the flow-permitted state. 
     Aspect 11. The HVAC system according to aspect 9, wherein the biasing mechanism is passively controlled based on a pressure ratio between the fluid in the working chamber and the compressed fluid at the discharge port. 
     Aspect 12. The HVAC system according to any one of aspects 9-11, wherein the intermediate discharge port is in the flow-blocked state when the screw compressor is operating at a full-load. 
     Aspect 13. The HVAC system according to any one of aspects 9-12, wherein the intermediate discharge port is in the flow-permitted state when the screw compressor is operating at a partial load. 
     Aspect 14. The HVAC system according to any one of aspects 9-12, wherein the intermediate discharge port is disposed at a location of the compression chamber at which a fluid being compressed is partially compressed. 
     Aspect 15. The HVAC system according to any one of aspects 9-14, wherein the screw compressor includes a plurality of intermediate discharge ports disposed between the inlet port and the outlet port. 
     Aspect 16. The HVAC system according to any one of aspects 9-15, wherein the compressor housing includes a plurality of apertures configured to fluidly connect the compression chamber and the intermediate discharge port when in the flow-permitted state. 
     Aspect 17. The HVAC system according to any one of aspects 9-16, wherein the compressor housing includes a single aperture configured to fluidly connect the compression chamber and the intermediate discharge port when in the flow-permitted state. 
     Aspect 18. The HVAC system according to aspect 17, wherein the single aperture is formed in a wall of the housing, a portion of the aperture being in the first of the plurality of bores and another portion of the aperture being in the second of the plurality of bores. 
     Aspect 19. A method, comprising: 
     providing an intermediate discharge port at a location in fluid communication with a compression chamber of a screw compressor, the intermediate discharge port being disposed between an inlet port and an outlet port of the screw compressor, 
     wherein when operating the screw compressor at part-load,
         discharging a portion of a working fluid being compressed from the compression chamber toward a discharge of the screw compressor, the working fluid being at a pressure that is lower than a discharge pressure of the screw compressor, and when operating the screw compressor at full-load,   discharging the working fluid being compressed from the outlet port of the screw compressor.       

     Aspect 20. The method according to aspect 19, wherein the providing includes retrofitting the intermediate discharge port into the screw compressor following manufacturing. 
     The terminology used in this specification is intended to describe particular embodiments and is not intended to be limiting. The terms “a,” “an,” and “the” include the plural forms as well, unless clearly indicated otherwise. The terms “comprises” and/or “comprising,” when used in this specification, indicate the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or components. 
     With regard to the preceding description, it is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size, and arrangement of parts, without departing from the scope of the present disclosure. The word “embodiment” as used within this specification may, but does not necessarily, refer to the same embodiment. This specification and the embodiments described are examples only. Other and further embodiments may be devised without departing from the basic scope thereof, with the true scope and spirit of the disclosure being indicated by the claims that follow.