High pressure ratio multi-stage centrifugal compressor

Abstract

A heat pump system includes a refrigerant circuit. First and second heat exchangers are arranged in the refrigerant circuit. A flow reversing device selectively changes a direction of flow in the refrigerant circuit between the first and second heat exchangers. A centrifugal compressor is arranged in the fluid circuit and has first and second impellers arranged in series relative to one another to provide a desired compressor pressure ratio. In one example, the centrifugal compressor mounts the first and second impellers on opposing ends of a shaft. The first and second impellers respectively include first and second stage inlets and outlets. One example desired compressor pressure ratio of at least 10:1 corresponds to a second stage outlet pressure to a first stage inlet pressure. A first diffuser is arranged at the first stage outlet, and the first diffuser is a variable geometry diffuser.

What is claimed is: 
     
         1 . A heat pump system comprising:
 a refrigerant circuit;   first and second heat exchangers arranged in the refrigerant circuit;   a flow reversing device selectively changing a direction of flow in the refrigerant circuit between the first and second heat exchangers; and   a centrifugal compressor arranged in the fluid circuit and having first and second impellers arranged in series relative to one another and providing a desired compressor pressure ratio.   
     
     
         2 . The heat pump system according to  claim 1 , wherein the first and second impellers respectively include first and second stage inlets and outlets, and the desired compressor pressure ratio corresponds to a second stage outlet pressure to a first stage inlet pressure. 
     
     
         3 . The heat pump system according to  claim 2 , wherein the desired compressor pressure ratio is about 10:1. 
     
     
         4 . The heat pump system according to  claim 2 , wherein the compressor includes first and second diffusers respectively arranged at the first and second stage outlets. 
     
     
         5 . The heat pump system according to  claim 4 , wherein the first and second diffusers are variable geometry diffusers, and the compressor includes first and second actuators configured to respectively move the first and second variable geometry diffusers between first and second positions. 
     
     
         6 . The heat pump system according to  claim 2 , comprising an economizer arranged fluidly between the first stage outlet and the second stage inlet. 
     
     
         7 . The heat pump system according to  claim 1 , wherein the compressor includes a variable speed motor configured to rotationally drive the first and second impellers. 
     
     
         8 . The heat pump system according to  claim 1 , wherein compressor includes a shaft supporting the first and second impellers, and magnetic bearings support the shaft. 
     
     
         9 . A refrigerant centrifugal compressor comprising:
 first and second impellers mounted on opposing ends of a shaft, the first and second impellers respectively include first and second stage inlets and outlets, and a desired compressor pressure ratio of at least 10:1 corresponding to a second stage outlet pressure to a first stage inlet pressure; and   a first diffuser arranged at the first stage outlet, wherein the first diffuser is a variable geometry diffuser.   
     
     
         10 . The refrigerant centrifugal compressor according to  claim 9 , comprising a second diffuser arranged at the second stage outlet. 
     
     
         11 . The refrigerant centrifugal compressor according to  claim 10 , wherein the second diffuser is a variable geometry diffuser. 
     
     
         12 . The refrigerant centrifugal compressor according to  claim 11 , comprising first and second actuators configured to respectively move the first and second variable geometry diffusers between first and second positions. 
     
     
         13 . The refrigerant centrifugal compressor according to  claim 9 , comprising an economizer mounted on the compressor and arranged fluidly between the first stage outlet and the second stage inlet. 
     
     
         14 . The refrigerant centrifugal compressor according to  claim 9 , comprising a variable speed motor configured to rotationally drive the first and second impellers. 
     
     
         15 . The refrigerant centrifugal compressor according to  claim 9 , comprising magnetic bearings supporting the shaft.