Patent Description:
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.

<CIT> describes a system and method for controlling the volume ratio of a compressor.

<CIT> describes a compressor including a housing having a suction inlet and a discharge outlet.

<CIT> describes a compressor having a movable trapped volume such as a screw or scroll type of compressor.

<CIT> describes a device for controlling a screw rotor machine for compression or expansion of gaseous media with at least two intermeshing ridges and grooves of male and female screw rotors in a working space.

<CIT> describes a rotary pump comprising a number of intermeshing screws.

The invention is defined in the attached independent claims to which reference should now be made. Further, optional features may be found in the sub-claims appended thereto.

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 is controlled based on a pressure differential. In an embodiment, the fluid flow state of the intermediate discharge port is 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.

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.

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 <NUM>%. In an embodiment, an increase in efficiency can be up to <NUM>% or up to about <NUM>%. 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> is a schematic diagram of a heat transfer circuit <NUM>, according to an embodiment. The heat transfer circuit <NUM> generally includes a compressor <NUM>, a condenser <NUM>, an expansion device <NUM>, and an evaporator <NUM>. The compressor <NUM> can be powered by an electric motor (not shown). The heat transfer circuit <NUM> is an example and can be modified to include additional components. For example, in an embodiment, the heat transfer circuit <NUM> 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 <NUM> 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 <NUM> are fluidly connected. The heat transfer circuit <NUM> 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 <NUM> 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 <NUM> operates according to generally known principles. The heat transfer circuit <NUM> 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 <NUM> 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 <NUM> may be generally representative of an air conditioner or heat pump.

The compressor <NUM> is generally representative of a screw compressor. In operation, the compressor <NUM> 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 <NUM> and flows through the condenser <NUM>. In accordance with generally known principles, the working fluid flows through the condenser <NUM> 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 <NUM>. The expansion device <NUM> 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 <NUM>. The working fluid flows through the evaporator <NUM> 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 <NUM>. The above-described process continues while the heat transfer circuit is operating, for example, in a cooling mode (e.g., while the compressor <NUM> is enabled).

In an embodiment, the compressor <NUM> can be controlled by, for example, a controller <NUM>. The controller <NUM> can, in an embodiment, control one or more of the other components of the heat transfer circuit <NUM> or the HVAC system corresponding to the heat transfer circuit <NUM>.

<FIG> illustrates a screw compressor <NUM> with which embodiments as disclosed in this specification can be practiced, according to an embodiment. The screw compressor <NUM> can be used in the heat transfer circuit <NUM> of <FIG> (e.g., as the compressor <NUM>). It is to be appreciated that the screw compressor <NUM> can be used for purposes other than in the heat transfer circuit <NUM>. For example, the screw compressor <NUM> 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 <NUM> includes additional features that are not described in detail in this specification. For example, the screw compressor <NUM> can include a lubricant sump for storing lubricant to be introduced to the moving features of the screw compressor <NUM>.

The screw compressor <NUM> includes a first helical rotor <NUM> and a second helical rotor <NUM> disposed in a rotor housing <NUM>. The rotor housing <NUM> includes a plurality of bores 120A and 120B. The plurality of bores 120A and 120B are configured to accept the first helical rotor <NUM> and the second helical rotor <NUM>.

The first helical rotor <NUM>, generally referred to as the male rotor, has a plurality of spiral lobes <NUM>. The plurality of spiral lobes <NUM> of the first helical rotor <NUM> can be received by a plurality of spiral grooves <NUM> of the second helical rotor <NUM>, generally referred to as the female rotor. In an embodiment, the spiral lobes <NUM> and the spiral grooves <NUM> can alternatively be referred to as the threads <NUM>, <NUM>. The first helical rotor <NUM> and the second helical rotor <NUM> are arranged within the housing <NUM> such that the spiral grooves <NUM> intermesh with the spiral lobes <NUM> of the first helical rotor <NUM>.

During operation, the first and second helical rotors <NUM>, <NUM> rotate counter to each other. That is, the first helical rotor <NUM> rotates about an axis A in a first direction while the second helical rotor <NUM> 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 <NUM>, the screw compressor <NUM> includes an inlet port <NUM> and an outlet port <NUM>.

The rotating first and second helical rotors <NUM>, <NUM> can receive a working fluid (e.g., heat transfer fluid such as refrigerant or the like) at the inlet port <NUM>. The working fluid can be compressed between the spiral lobes <NUM> and the spiral grooves <NUM> (in a pocket <NUM> formed therebetween) and discharged at the outlet port <NUM>. The pocket is generally referred to as the compression chamber <NUM> and is defined between the spiral lobes <NUM> and the spiral grooves <NUM> and an interior surface of the housing <NUM>. In an embodiment, the compression chamber <NUM> may move from the inlet port <NUM> to the outlet port <NUM> when the first and second helical rotors <NUM>, <NUM> rotate. In an embodiment, the compression chamber <NUM> may continuously reduce in volume while moving from the inlet port <NUM> to the discharge port <NUM>. 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 <NUM>.

The screw compressor <NUM> can include an intermediate discharge port <NUM>. The intermediate discharge port <NUM> 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 <NUM> may alternatively be referred to as the radial discharge port <NUM>, the radial intermediate discharge port <NUM>, or the like. The intermediate discharge port <NUM> can, for example, enable the fluid being compressed to radially exit the compression chamber <NUM> prior to being discharged from the axial outlet port <NUM>. The intermediate discharge port <NUM> 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 <NUM> and the axis B of the second axial rotor <NUM>.

Advantageously, according to an embodiment, the intermediate discharge port <NUM> can prevent overcompression of the working fluid by radially discharging the fluid from the compression chamber <NUM> prior to the outlet port <NUM>. In an embodiment, preventing overcompression of the fluid can increase an efficiency of the screw compressor <NUM>. In an embodiment, an increase in efficiency of the screw compressor <NUM> can be at or about <NUM>%. In an embodiment, an increase in efficiency of the screw compressor <NUM> can be up to <NUM>% or up to about <NUM>%. The intermediate discharge port <NUM> is shown and described in additional detail according to various embodiments in accordance with <FIG> below.

In an embodiment, the intermediate discharge port <NUM> can be included in the screw compressor <NUM> at a time of manufacturing. In an embodiment, the intermediate discharge port <NUM> can be retrofitted into the screw compressor <NUM> after manufacturing. In an embodiment, the intermediate discharge port <NUM> can be retrofitted into the screw compressor <NUM> even after the screw compressor <NUM> has been in use.

<FIG> illustrates the screw compressor <NUM> including an intermediate discharge port 175A, according to an embodiment. In <FIG>, the intermediate discharge port 175A is in a flow-blocked (e.g., closed) state. <FIG> illustrates the screw compressor <NUM> including the intermediate discharge port 175A, according to an embodiment. In <FIG>, the intermediate discharge port 175A is in a flow-permitted (e.g., opened) state. <FIG> will be described generally, unless specific reference is made to the contrary.

In an embodiment, the screw compressor <NUM> can include a plurality of intermediate discharge ports 175A. For example, the screw compressor <NUM> 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 175A includes a biasing mechanism <NUM>; a sealing member <NUM> connected to the biasing mechanism <NUM> and disposed within a chamber <NUM> of the intermediate discharge port 175A; and a plurality of apertures <NUM>.

The biasing mechanism <NUM> can be an actively controlled mechanism. For example, the biasing mechanism <NUM> can be a biasing mechanism electrically connected to a controller (e.g., the controller <NUM> in <FIG>). 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 <NUM> to control whether the biasing mechanism <NUM> is in the flow-blocked state (<FIG>) or in the flow-permitted state (<FIG>). For example, the controller might identify that the screw compressor <NUM> is operating at full capacity, in which case the controller might send a signal to the biasing mechanism <NUM> to place / maintain the biasing mechanism <NUM> in the flow-blocked state of <FIG>. Alternatively, the controller might identify that the screw compressor <NUM> is operating at a capacity less than full capacity, in which case the controller might send a signal to the biasing mechanism <NUM> to place / maintain the biasing mechanism <NUM> in the flow-permitted state of <FIG>.

In an embodiment, the biasing mechanism <NUM> is a passively controlled mechanism. The biasing mechanism <NUM> is a biasing mechanism that is controllable between the flow-blocked (<FIG>) and the flow-permitted (<FIG>) states based on a pressure differential between the compression chamber <NUM> and the discharge. In such an embodiment, the intermediate discharge port 175A alternates between the flow-blocked state (<FIG>) and the flow-permitted state (<FIG>) based on pressure differential of the discharge and the compression chamber <NUM>. In such an embodiment, the intermediate discharge port 175A may be disposed at a top portion of the housing <NUM> 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>) and the flow-permitted state (<FIG>). 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 175A can move radially (e.g., about perpendicular to the rotors <NUM>, <NUM>) from or toward the compression chamber <NUM>.

When the screw compressor <NUM> is operating at a lower pressure ratio than designed (e.g., a part-load operation), the intermediate discharge port 175A can be in the flow-permitted state (<FIG>). In such an operating condition, the pressure of the discharge is lower than the pressure in the compression chamber <NUM>. Accordingly, the pressurized fluid can force the sealing member <NUM> in the d1 direction (vertically upward), enabling flow of the working fluid from the compression chamber <NUM> through the intermediate discharge port 175A. 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 <NUM>. As a result, the sealing member <NUM> may be forced in the d2 direction (vertically downward), thereby causing the sealing member <NUM> to be in sealing contact with the surface 190A, thereby preventing flow through the intermediate discharge port 175A. In such an operating condition, the fluid being compressed can be discharged through the outlet port <NUM>.

The biasing mechanism <NUM> is connected to the sealing member <NUM> such that the biasing mechanism <NUM> can move the sealing member <NUM> in either a direction d1 (vertically up with respect to the page in the figures) or a direction d2 (vertically down with respect to the page in the figures). The sealing member <NUM> can include a surface 185A which can serve as a sealing surface in a flow-blocked state. That is, the surface 185A can form a sealing engagement with a sealing surface 190A of the chamber <NUM> when in the flow-blocked state (<FIG>). In the flow-blocked state (<FIG>), the surface 185A of the sealing member <NUM> can prevent a fluid (e.g., working fluid such as a heat transfer fluid, etc.) from radially exiting the compression chamber <NUM>.

The chamber <NUM> can be sized to permit the sealing member <NUM> to translate in the d1 and d2 directions. The chamber <NUM> can be in fluid communication with a discharge of the screw compressor <NUM> when the intermediate discharge port 175A is in the flow-permitted state (<FIG>). The plurality of apertures <NUM> is disposed within the housing <NUM>. In an embodiment, the plurality of apertures <NUM> is bored into the housing <NUM>. When in the flow-permitted state (<FIG>), the plurality of apertures <NUM> is fluidly connected with the chamber <NUM>, and accordingly with the discharge of the screw compressor <NUM>. When in the flow-blocked state (<FIG>), the plurality of apertures <NUM> is fluidly sealed from the chamber <NUM> by a sealing engagement between the surface 185A of the sealing member <NUM> and the sealing surface 190A of the chamber <NUM>.

In the illustrated embodiment, three apertures <NUM> are shown. It will be appreciated that the number of apertures <NUM> is an example. The intermediate discharge port 175A can include more than three apertures <NUM>, according to an embodiment, or fewer than three apertures <NUM>, according to an embodiment. For example, in an embodiment, the intermediate discharge port 175A can include four apertures <NUM>, with two apertures being disposed in each bore 120A, 120B of the screw compressor <NUM> such that symmetry is maintained between each of the bores 120A, 120B. The apertures <NUM> can be based on a size of the bore 120A, 120B. Generally, a number of apertures <NUM> may be limited based on, for example, manufacturing limitations.

The size and geometry of the plurality of apertures <NUM> can be determined based on, for example, simplicity of manufacturing, flow rate of the working fluid, or the like. In an embodiment, a distance L1 from an inlet of the plurality of apertures <NUM> to an outlet of the plurality of apertures into the chamber <NUM> can be determined by, for example, manufacturing tolerances or the like. Additionally, the distance L1 can be selected to minimize an amount of the working fluid which may enter the plurality of apertures <NUM> when the intermediate discharge port <NUM> is in the flow-blocked state (<FIG>).

<FIG> illustrates the screw compressor <NUM> including an intermediate discharge port 175B, according to an embodiment. In <FIG>, the intermediate discharge port 175B is in the flow-blocked state. <FIG> illustrates the screw compressor <NUM> including the intermediate discharge port 175B of <FIG>, according to an embodiment. In <FIG>, the intermediate discharge port 175B is in the flow-permitted state. <FIG> illustrates an alternative view of the screw compressor <NUM> including the intermediate discharge port 175B of <FIG> in the flow-blocked state. <FIG> will be described generally, unless specific reference is made to the contrary.

Aspects of the intermediate discharge port 175B in <FIG> are the same as or similar to aspects of the intermediate discharge port 175A in <FIG>. To simplify this specification, aspects of <FIG> which are different from aspects of <FIG> will be discussed, while aspects which are the same or substantially similar will not be described in additional detail.

The intermediate discharge port 175B includes a single aperture <NUM>, according to an embodiment. The single aperture <NUM> functions similarly to the plurality of apertures <NUM> in the embodiment shown and described above with respect to <FIG>. The aperture <NUM> can follow a contour of the bores 120A and 120B of the housing <NUM> (see <FIG>). A portion of the aperture <NUM> is in the bore 120A and another portion of the aperture <NUM> is in the second bore 120B. Accordingly, the aperture <NUM> can be approximately shaped to match a rotor-helix angle of the screw compressor <NUM>. In an embodiment, the aperture <NUM> can be approximately v-shaped. A sealing member <NUM> is configured to include a surface 205A which follows a contour of the bores 120A, 120B as well (<FIG>). Accordingly, the sealing member <NUM> can be approximately v-shaped to correspond to the aperture <NUM>, according to an embodiment.

When the intermediate discharge port 175B is in the flow-blocked state (<FIG>), the surface 205A approximately follows the contour of the bores 120A, 120B of the housing <NUM>. Accordingly, when the intermediate discharge port 175B is in the flow-blocked state (<FIG>), the bores 120A, 120B and the housing <NUM> may be substantially smooth. The intermediate discharge port 175B and corresponding shape can, for example, prevent portions of the working fluid being compressed from entering the aperture <NUM> when in the flow-blocked state (<FIG>). That is, relative to the embodiment in <FIG>, which includes a distance L1 between the bores 120A, 120B and the sealing member <NUM> in a flow-blocked state (<FIG>), the embodiment in <FIG> 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 175B is in the flow-permitted state (<FIG>), the compression chamber <NUM>, the aperture <NUM>, and the discharge are fluidly connected such that the working fluid can be discharged from the intermediate discharge port 175B.

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.

Claim 1:
A screw compressor (<NUM>), comprising:
a compressor housing (<NUM>) defining a working chamber, the housing including a plurality of bores (120A, 120B);
a first rotor (<NUM>) having helical threads, the first rotor being housed in a first of the plurality of bores (120A, 120B);
a second rotor (<NUM>) 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 (120A, 120B);
an inlet suction port (<NUM>) that receives a fluid to be compressed;
an outlet discharge port (<NUM>) that receives a compressed fluid;
a compression chamber (<NUM>) formed by the intermeshing of the helical threads of the first rotor (<NUM>) and the helical threads of the second rotor (<NUM>) between the inlet suction port (<NUM>) and the outlet discharge port (<NUM>); and
an intermediate discharge port (<NUM>) fluidly connectable to the compression chamber (<NUM>) and disposed between the inlet suction port (<NUM>) and the outlet discharge port (<NUM>) to allow a working fluid to leave the compression chamber prior to reaching the outlet discharge port, the screw compressor being characterised in that
the intermediate discharge port (<NUM>) being disposed at a portion of the compressor housing (<NUM>) so that a biasing mechanism (<NUM>) included in the intermediate discharge port is passively controlled based on a pressure differential between the compression chamber (<NUM>) and a discharge of the screw compressor (<NUM>) at the outlet discharge port (<NUM>) to selectively transition the intermediate discharge port between a flow-blocked state and a flow-permitted state,
the intermediate discharge port (<NUM>) including a sealing member (<NUM>) having a sealing surface (185A) and forms a sealing engagement with a surface within the intermediate discharge port when biased by the biasing mechanism (<NUM>) to be in the flow-blocked state so that fluid flow is prevented between the compression chamber and the intermediate discharge port when in the flow-blocked state, and fluid flow being enabled from the compression chamber through the intermediate discharge port when biased by the biasing mechanism to be in the flow-permitted state in which the sealing surface is disengaged from sealing engagement with the surface within the intermediate discharge port.