Patent Description:
Refrigeration systems are utilized in many applications to condition an environment. The cooling or heating load of the environment may vary with ambient conditions, occupancy level, other changes in sensible and latent load demands, and with temperature and/or humidity changes.

Refrigeration systems typically include a compressor to deliver compressed refrigerant to a condenser. From the condenser, the refrigerant travels to an expansion valve and then to an evaporator. From the evaporator, the refrigerant returns to the compressor to be compressed.

A direct drive screw compressor in an HVAC chiller application has a driving (male) rotor and a driven (female) rotor. An electric motor drives the driving rotor to rotate. The driving rotor then drives the driven rotor by way of meshing. The meshing process requires direct contact of the rotors at contact locations. Lubrication is necessary to protect both rotors and decrease the friction during operation.

In addition, the rotors in a screw compressor in HVAC chiller applications are supported by rolling element bearings. These bearings may be lubricated using oil because of a high viscosity requirement of bearing lubricant. After passing through the bearings, oil is mixed with refrigerant in the compression process to be carried out of the compressor.

<CIT> discloses a screw refrigerating apparatus comprising a refrigerant circulating passage including a screw compressor, a condenser, an expansion valve, and an evaporator, which is constituted such that a bypass flow passage branching at a part of the refrigerant circulating passage between the condenser and the expansion valve, routing through throttle means, and communicating with a rotor cavity within the screw compressor, is provided.

<CIT> discloses a screw compressor employing sliding bearings. By employing the sliding bearings located in the rotors, the structure of the compressor is simplified. In addition, liquid return structures of the sliding bearings are simplified by means of channels formed in the male and female rotors, and meanwhile, the rotors can be cooled, so that the deformation quantity of the rotors caused by temperature is reduced, and the reliability and performance of the screw compressor are improved.

According to a first aspect of the invention, a direct-drive refrigerant screw compressor is provided. The direct-drive refrigerant screw compressor comprises: a housing; a compression chamber in the housing; a pair of rotors, each rotor of the pair of rotors being rotationally disposed in the compression chamber and including an outer surface with a screw-geared profile; a fluid being disposed in the compression chamber, the fluid consisting of a working fluid for providing lubrication to each rotor, wherein the working fluid is refrigerant; and a first port extending through the housing and configured for directing the fluid toward the compression chamber; wherein when the compressor is activated, each rotor rotates and the fluid is distributed about each rotor to lubricate each rotor; and for each rotor, the compressor includes a plurality of bearing packs disposed within a respective plurality of bearing chambers; the first port is fluidly connected to a passage in one rotor of the pair of rotors that directs the fluid to the compression chamber; the passage extends between an axial aft port in the one rotor and the outer surface of the one rotor, wherein the axial aft port is in one of the plurality of bearing chambers; and the passage includes an axial segment forming a blind hole and a radial segment fluidly connected between the axial segment and a surface port on the outer surface of the one rotor, whereby the compressor is configured to distribute fluid around the outer surface of the plurality of rotors.

Optionally, the passage includes a plurality of the radial segments fluidly connected to a respective plurality of the surface ports on the outer surface of the one rotor.

Optionally, the plurality of the surface ports are staggered at regular intervals along the outer surface of the one rotor.

Optionally, the plurality of the radial segments each include opposing radial portions extending to a respective plurality of the surface ports on the outer surface of the one rotor.

According to another aspect of the invention a refrigerant system is provided. The system includes: a condenser; a compressor according to the first aspect and optionally including any of the other features as described above; and a conduit fluidly connecting the condenser and the first port of the compressor, and configured to transport the fluid to the compressor to provide the working fluid to each rotor.

According to another aspect of the invention a method of directing fluid in a direct drive screw compressor is provided. The method comprises: receiving fluid at a first port of a housing of the compressor, wherein the fluid consists of a working fluid for providing lubrication to each rotor of a pair of rotors in the compressor, wherein the working fluid is refrigerant; and directing the fluid from the first port to a compression chamber in the compressor; wherein when the compressor is activated, each rotor rotates and the fluid is distributed about each rotor to lubricate each rotor, and wherein for each rotor, the compressor includes a plurality of bearing packs disposed within a respective plurality of bearing chambers; wherein directing the fluid to the compression chamber includes injecting the fluid from the first port, through a passage in one rotor of the pair of rotors, whereby the fluid is injected into the compression chamber; wherein injecting the fluid through the passage includes directing the fluid from the first port into an axial aft port in the passage and out an outer surface of the one rotor, wherein the axial aft port is in one of the plurality of bearing chambers; and wherein directing the fluid through the passage further includes directing the fluid through an axial segment forming a blind hole in the one rotor and a radial segment fluidly connected between the axial segment and a first surface port on the outer surface of the one rotor, to distribute the fluid about the plurality of rotors.

Optionally, directing the fluid through the passage further includes: directing the fluid though a plurality of the radial segments fluidly connected to a respective plurality of the surface ports on the outer surface of the one rotor.

Optionally, directing the fluid through the passage further includes: directing the fluid through opposing radial portions of each of the plurality of the radial segments, the opposing radial portions extending to a respective plurality of the surface ports on the outer surface of the one rotor.

Optionally, the method comprises receiving the fluid at the first port from a condenser in a refrigerant system in which the compressor is integrated, to provide the working fluid to each rotor.

Described herein are systems and methods for lubricating components of a compressor in a refrigeration system. <FIG> illustrates a refrigeration system <NUM> that is an oil lubricated system. The system <NUM> includes a condenser <NUM> that receives a high pressure gaseous form of the working fluid, ejects heat from the working fluid, for example to the environment, and outputs a high pressure liquid form of the working fluid. Downstream of the condenser <NUM> is an expansion valve <NUM> that receives the high pressure liquid form of the working fluid and outputs a low pressure liquid form of the working fluid. Downstream of the expansion valve <NUM> is an evaporator <NUM> that receives the low pressure liquid form of the working fluid, transfers heat to the working fluid, thereby conditioning warm air, and outputs a low pressure gaseous form of the working fluid. Downstream of the evaporator <NUM> is a compressor <NUM> that receives the low pressure gaseous form of the working fluid and outputs a high pressure gaseous form of the working fluid.

The compressor <NUM> is a screw compressor that includes suction bearings <NUM>, discharge bearings <NUM>, and a set of rotors <NUM> therebetween. Both sets of bearings <NUM>, <NUM> and the rotors <NUM> require some form of lubrication. Lubricating oil is provided by an oil separator <NUM>. The oil separator <NUM> transfers oil to an oil filter <NUM>. The oil filter <NUM> transfers oil a first portion of oil <NUM> to one orifice <NUM>, e.g. in the compressor housing, fluidly connected to the suction bearings <NUM>. A second portion of oil <NUM> is distributed in parallel to one orifice <NUM>, e.g., in the compressor housing, fluidly connected to the rotors <NUM> and another orifice <NUM>, e.g., in the compressor housing, fluidly connected to the discharged bearings <NUM>. The oil then mixes with the working fluid in the compressor <NUM>.

Output from the compressor <NUM> is directed to the oil separator <NUM>. The oil separator <NUM> separates the output from the compressor into a first portion <NUM> that is the working fluid directed the condenser <NUM>. The second portion <NUM> is the lubricant directed to the filter <NUM>. Unless otherwise indicated herein, for each embodiment all flows between the system components that are separately referred to are fluidly transferred in respective conduit lines. It is to be appreciated that fluid branches that are branched upstream or downstream of the orifices <NUM>, <NUM> in the housing of the compressor <NUM> may be branched in conduits exterior to the housing of the compressor <NUM>.

Viscosity of oil lubricant may be reduced when mixed with the working fluid. Both bearing load carrying capacity and oil sealing characteristics are dependent upon the oil viscosity. As such, due to lower viscosity, moving components, such as bearings and rotors, in some systems may experience increased wear during operation. In addition, separating lubricating oil from refrigerant requires the use and maintenance of additional equipment such as the oil separator and related filter. In addition, because the oil separation process cannot completely remove the oil from refrigerant, excessive oil may decrease heat transfer efficiency in the system and lower the overall system capacity. Oil may be saturated with refrigerant in the separator. The separation process is often unable to adequately lower the refrigerant content in the oil.

In view of the above challenges <FIG> disclose embodiments and examples in which an oil separator and oil filter may be avoided. More specifically, turning to <FIG>, disclosed is a refrigerant system <NUM> (a chiller) applicable to each of the embodiments and examples disclosed herein. The system <NUM> includes a condenser <NUM>, an expansion valve <NUM>, an evaporator <NUM>, and a dual rotor refrigerant screw compressor <NUM> (compressor <NUM>), which is a direct drive compressor. The compressor <NUM> includes two screw rotors <NUM>. The rotors <NUM> are configured in the compressor <NUM> with a suction side 140a and discharge side 140b (illustrated schematically in <FIG>). The compressor <NUM> includes bearing packs <NUM> including a suction side bearing pack 190a and a discharge side bearing pack 190b. The suction side bearing pack 190a may be referred to herein as a forward bearing pack and the discharge side bearing pack 190b may be referred to herein as an aft bearing pack.

The condenser feeds first portion <NUM> of a working fluid to the expansion valve <NUM> and, in parallel, a second portion <NUM> of the working fluid <NUM> to the compressor <NUM>. The working fluid consists of refrigerant from a condenser conduit <NUM> to the compressor <NUM> for providing lubrication to components of the compressor <NUM> as described below.

The second portion <NUM> of the working fluid is distributed in parallel to a first branch <NUM> and a second branch <NUM>. The first branch <NUM> is distributed in parallel to a third branch <NUM> and a fourth branch <NUM>. The third branch <NUM> delivers the working fluid through one or more orifices <NUM>, e.g. in the compressor housing <NUM>, to the suction side bearing pack 190a. The fourth branch <NUM> delivers the working fluid through another one or more orifices <NUM>, e.g. in the compressor housing <NUM>, to the rotors <NUM>. The second branch <NUM> delivers the working fluid to a further one or more orifices <NUM>, e.g. in the compressor housing <NUM>, to the branch side bearing pack 190b.

From the suction side bearing pack 190a, the working fluid flows directly into the rotors <NUM> with the working fluid from the evaporator <NUM>. This may occur within the compressor housing <NUM>. From the discharge side bearing pack 190b the working fluid flows to the evaporator <NUM> to mix with fluid therein and then be redirected to the rotors <NUM> of the compressor <NUM>. This may occur by the working fluid exiting the compressor housing <NUM> from the discharged side bearings 190b and being directed thereafter to the evaporator <NUM>. Unless otherwise indicated herein, for each embodiment all flows between the system components that are separately referred to are fluidly transferred in respective conduit lines. It is to be appreciated that fluid branches that are branched upstream or downstream of the orifices <NUM>, <NUM>, <NUM> in the compressor housing <NUM> may be branched in conduits exterior to the compressor housing <NUM>.

The features of the compressor are illustrated more specifically, for example, in <FIG>. Turning now to <FIG>, the compressor <NUM> includes the housing <NUM>. A compression chamber <NUM> is disposed in the housing <NUM>. The compression chamber <NUM> has a forward end 140a and an aft end 140b which are respective suction and discharge sides of the compression chamber <NUM>. For simplicity, inlet and outlet ports in the housing <NUM> for fluidly communicating working fluid <NUM> in the refrigeration system <NUM> are not illustrated in <FIG>.

The compressor <NUM> includes the plurality of rotors generally referred to as <NUM>, including the first rotor 150a and the second rotor 150b, rotationally disposed in the compression chamber <NUM>. Each rotor <NUM> includes an outer surface <NUM> with a screw-geared profile, for example, having an alternating plurality of peaks 160a and plurality of troughs 160b, for example, in cross sectional view. The plurality of rotors <NUM> intermesh and form compression volumes within the compression chamber <NUM>. The first rotor 150a is a driven rotor and the second rotor 150b is a drive rotor, driven by a motor <NUM>.

For each rotor <NUM>, the compressor <NUM> includes the plurality of bearing packs generally referred to as <NUM> including the forward bearing pack generally referred to as 190a and the aft bearing pack generally referred to as 190b. For each rotor <NUM>, the plurality of bearing packs <NUM> is disposed within a respective plurality of bearing chambers generally referred to as <NUM>. The bearing chambers <NUM> may be structural portions of the housing <NUM> in or proximate the compression chamber <NUM> configured to securely position the respective bearing packs <NUM>. The bearing chambers <NUM> may include a forward bearing chamber generally referred to as 200a and an aft bearing chamber generally referred to as 200b. The bearing chambers <NUM> may be fluidly connected with each other through the compression chamber <NUM>.

Turning now to <FIG>, an embodiment of the refrigeration system <NUM> is illustrated. The embodiment of <FIG> includes all of the features illustrated in the system <NUM> illustrated in <FIG>. In <FIG>, the fluid <NUM> is disposed within the compression chamber <NUM>. A first port <NUM>, extends through the housing <NUM>. In <FIG>, the first port <NUM> fluidly connects with a passage <NUM> within one rotor <NUM> (the first rotor 150a) for directing fluid toward the compression chamber <NUM>. Identifying the one rotor <NUM> as the first rotor 150a, and thus the other rotor <NUM> as the second rotor 150a, in the embodiment in <FIG> is for example only and not intended on limiting the scope of the embodiments. The first port <NUM> is connected by the condenser conduit <NUM> to the condenser <NUM>. According to an embodiment, the passage <NUM> includes a flow control orifice <NUM>, which may be the same as the above introduced flow control orifice <NUM>. This may be used to reduce a flow volume or rate from the condenser <NUM> as may be needed.

The passage <NUM> is an internal passage in the one rotor <NUM>. The passage <NUM> is fluidly connected between an axial aft port <NUM> in the one rotor <NUM> and the outer surface <NUM> of the one rotor <NUM>. The aft port <NUM> is in the respective aft bearing chamber 200b.

The passage <NUM> includes an axial segment <NUM> forming a blind hole in the one rotor <NUM> and a radial segment generally referred to as <NUM> fluidly connected between the axial segment <NUM> and a surface port generally referred to as <NUM> on the outer surface <NUM> of the one rotor <NUM>. In one embodiment, the passage <NUM> may include a plurality of the radial segments <NUM> fluidly connected to a respective plurality of the surface ports <NUM> on the outer surface <NUM> of the one rotor <NUM>. This configuration may provide a greater distribution of the fluid <NUM> about each rotor <NUM> as compared with, for example, a single fluid <NUM> port.

In one embodiment, the plurality of the surface ports <NUM> may be staggered at regular intervals along the outer surface <NUM>, for example, at or proximate the plurality of alternating peaks 160a or troughs 160b. This configuration may provide an even distribution of fluid <NUM> around the outer surface <NUM> of the each rotor <NUM>. In one embodiment the plurality of the radial segments <NUM> may each include a plurality of opposing radial portions 280a, 280b extending to a respective plurality of the radial ports 290a, 290b on the outer surface <NUM> of the one rotor <NUM>. This configuration may provide an ability to quickly distribute fluid <NUM> around the outer surface <NUM> of the rotors <NUM>.

Turning to <FIG>, a method is disclosed of directing fluid <NUM> in the compressor <NUM> for the embodiment illustrated in <FIG>. The method of <FIG> includes block <NUM> of receiving the fluid <NUM> at the first port <NUM> of the housing <NUM>. The method of <FIG> includes block <NUM> of directing the fluid <NUM>, from the first port <NUM>, to the compression chamber <NUM>. In an embodiment, block <NUM> further includes controlling flow in the passage <NUM> through a flow control orifice <NUM>. In an embodiment, block <NUM> further includes injecting the fluid <NUM> through the first port <NUM>, through a passage <NUM> in one rotor <NUM>, and into the compression chamber <NUM>. Then, at block <NUM> the compressor is activated to distribute the fluid about the rotors <NUM>.

Thus, in the above disclosed embodiments, the working fluid <NUM> is drawn from a chiller condenser and used to provide lubrication to the compressor and more specifically to the screw rotors. The liquid can be injected directly through a passage inside the driving rotor. The liquid flow can be adjusted by using flow restriction devices, such as a flow control orifice. The embodiments enable the utilization of pure refrigerant as the working fluid <NUM> in the components of the system <NUM>, including the condenser <NUM>, evaporator <NUM>, etc..

According to the above disclosure, for example in <FIG>, pure refrigerant lubricated (PRL) bearings are used in a screw compressor to support the loads on the rotors. The PRL bearings operate with a relatively low viscosity lubricant, such as liquid refrigerant as the working fluid. The liquid refrigerant as the working fluid is drawn from the chiller condenser and injected directly to each individual bearings or pack of bearings. The liquid flow can be adjusted by using flow restriction devices, such as an orifice.

With the above disclosed examples and embodiments, oil separation equipment on a chiller is no longer necessary. This configuration reduces the complexity of the chiller system. The chiller cost will be therefore reduced. The chiller heat transfer efficiency will therefore increase.

Accordingly, as indicated above, there are two kinds of fluids in a typical system: oil and a working fluid. Oil is typically used for lubricating bearings and rotors and for sealing. The working fluid, such as refrigerant, is typically used to transmit heat. According to the disclosed examples and embodiments, the working fluid, instead of oil, is used for lubricating bearings and rotors.

Claim 1:
A direct-drive refrigerant screw compressor (<NUM>), comprising:
a housing (<NUM>);
a compression chamber (<NUM>) in the housing (<NUM>);
a pair of rotors (<NUM>), each rotor of the pair of rotors (<NUM>) being rotationally disposed in the compression chamber (<NUM>) and including an outer surface (<NUM>) with a screw-geared profile;
a fluid being disposed in the compression chamber (<NUM>), the fluid consisting of a working fluid (<NUM>) for providing lubrication to each rotor, wherein the working fluid (<NUM>) is refrigerant; and
a first port (<NUM>) extending through the housing (<NUM>) and configured for directing the fluid toward the compression chamber (<NUM>);
wherein when the compressor (<NUM>) is activated, each rotor rotates and the fluid is distributed about each rotor to lubricate each rotor; and
for each rotor, the compressor (<NUM>) includes a plurality of bearing packs (<NUM>) disposed within a respective plurality of bearing chambers (<NUM>);
characterized in that:
the first port (<NUM>) is fluidly connected to a passage (<NUM>) in one rotor of the pair of rotors (<NUM>) that directs the fluid to the compression chamber (<NUM>);
the passage (<NUM>) extends between an axial aft port (<NUM>) in the one rotor and the outer surface (<NUM>) of the one rotor, wherein the axial aft port (<NUM>) is in one of the plurality of bearing chambers (<NUM>); and
the passage (<NUM>) includes an axial segment (<NUM>) forming a blind hole and a radial segment (<NUM>) fluidly connected between the axial segment (<NUM>) and a surface port on the outer surface (<NUM>) of the one rotor,
whereby the compressor (<NUM>) is configured to distribute fluid (<NUM>) around the outer surface (<NUM>) of the plurality of rotors (<NUM>).