Counter-current flow in both ac and hp modes for part load optimization

Abstract

A HVAC system having an indoor heat exchanger having a first refrigerant passage extending in a first direction and a second refrigerant extending in a second direction opposite from the first direction, a first refrigerant circuit comprising a first compressor, a first expansion valve, a first outdoor heat exchanger, the first refrigerant passage, and a first reversing valve operable to control a direction of first refrigerant in the first refrigerant circuit, and a second refrigerant circuit comprising a second compressor, a second expansion valve, a second outdoor heat exchanger, the second refrigerant passage, and a second reversing valve operable to control a direction of second refrigerant in the second refrigerant circuit.

What is claimed is: 
     
         1 . A heating, ventilation, and air conditioning (HVAC) system operable in a cooling (AC) mode and a heat pump (HP) mode, the HVAC system comprising:
 an indoor heat exchanger having a first refrigerant passage extending in a first direction and a second refrigerant passage extending in a second direction opposite from the first direction;   a first refrigerant circuit comprising a first compressor, a first expansion valve, a first outdoor heat exchanger, the first refrigerant passage, and a first reversing valve operable to control a direction of first refrigerant in the first refrigerant circuit; and   a second refrigerant circuit comprising a second compressor, a second expansion valve, a second outdoor heat exchanger, the second refrigerant passage, and a second reversing valve operable to control a direction of second refrigerant in the second refrigerant circuit.   
     
     
         2 . The HVAC system of  claim 1 , wherein the first compressor comprises one or more first compressors and the second compressor comprises one or more second compressors. 
     
     
         3 . The HVAC system of  claim 1 , wherein in the AC mode the first direction is a counter-current flow relative to an intended direction of air flow across the indoor heat exchanger. 
     
     
         4 . The HVAC system of  claim 1 , wherein the first refrigerant circuit is configured to be AC mode optimized and the second refrigerant circuit is configured to be HP mode optimized. 
     
     
         5 . The HVAC system of  claim 1 , wherein in the AC mode:
 the first refrigerant circuit is configured with the first refrigerant passage in counter-current flow; and   the second refrigerant circuit is configured with the second refrigerant passage in co-current flow.   
     
     
         6 . The HVAC system of  claim 1 , wherein in the AC mode the first refrigerant circuit is configured with the first refrigerant passage in counter-current flow and the second refrigerant circuit is configured with the second refrigerant passage in co-current flow; and
 in the HP mode the first refrigerant circuit is configured with the first refrigerant passage in co-current flow and the second refrigerant circuit is configured with the second refrigerant passage in counter-current flow.   
     
     
         7 . The HVAC system of  claim 1 , wherein in the AC mode:
 the first refrigerant circuit is configured with the first outdoor heat exchanger and the first refrigerant passage in counter-current flow; and   the second refrigerant circuit is configured with the second outdoor heat exchanger and the second refrigerant passage in co-current flow.   
     
     
         8 . The HVAC system of  claim 1 , wherein the HVAC system a rooftop unit. 
     
     
         9 . The HVAC system of  claim 8 , wherein the first refrigerant circuit is AC mode optimized whereby the first outdoor heat exchanger and the first refrigerant passage are counter-current flow in the AC mode and co-current flow in the HP mode; and
 the second refrigerant circuit is HP mode optimized whereby the second outdoor heat exchanger and the second refrigerant passage are counter-current flow in the HP mode and co-current flow in the AC mode.   
     
     
         10 . A heating and/or cooling method, the method comprising:
 operating a heating, ventilation, and air conditioning (HVAC) system in a cooling (AC) mode or a heating (HP) mode, the HVAC system comprising:   an indoor heat exchanger having a first refrigerant passage extending in a first direction and a second refrigerant passage extending in a second direction opposite from the first direction, wherein fresh air flows generally in the second direction across the indoor heat exchanger;   a first refrigerant circuit comprising a first refrigerant, a first compressor, a first outdoor heat exchanger, and the first refrigerant passage; and   a second refrigerant circuit comprising a second refrigerant, a second compressor, a second outdoor heat exchanger, and the second refrigerant passage.   
     
     
         11 . The method of  claim 10 , wherein operating in the AC mode comprises directing the first refrigerant in a direction from the first compressor through the first outdoor heat exchanger and then the first refrigerant passage, wherein the first refrigerant is in counter-current flow through the first outdoor heat exchanger and the first refrigerant passage. 
     
     
         12 . The method of  claim 11 , further comprising only operating the first refrigeration circuit. 
     
     
         13 . The method of  claim 10 , wherein operating in the AC mode comprises:
 directing the first refrigerant in a direction from the first compressor through the first outdoor heat exchanger and then the first refrigerant passage, wherein the first refrigerant is in counter-current flow through the first outdoor heat exchanger and the first refrigerant passage; and   directing the second refrigerant in a direction from the second compressor through the second outdoor heat exchanger and then the second refrigerant passage, wherein the second refrigerant is in co-current flow in the second outdoor heat exchanger and in the second refrigerant passage.   
     
     
         14 . The method of  claim 10 , wherein operating in the HP mode comprises:
 directing the second refrigerant in a direction from the second compressor through the second refrigerant passage and then the second outdoor heat exchanger, wherein the second refrigerant is in counter-current flow in the second outdoor heat exchanger and in the second refrigerant passage.   
     
     
         15 . The method of  claim 14 , further comprising only operating the second refrigeration circuit. 
     
     
         16 . The method of  claim 10 , wherein operating in the HP mode comprises:
 directing the second refrigerant in a direction from the second compressor through the second refrigerant passage and then the second outdoor heat exchanger, wherein the second refrigerant is in counter-current flow in the second outdoor heat exchanger and in the second refrigerant passage; and   directing the first refrigerant in a direction from the first compressor through the first refrigerant passage and then the first outdoor heat exchanger, wherein the first refrigerant is in co-current flow in the first outdoor heat exchanger and in the first refrigerant passage.   
     
     
         17 . The method of  claim 10 , wherein the first compressor comprises one or more first compressors and the second compressor comprises one or more second compressors. 
     
     
         18 . The method of  claim 17 , wherein the HVAC system is a rooftop unit. 
     
     
         19 . A heating and/or cooling method, the method comprising:
 operating a heating, ventilation, and air conditioning (HVAC) system in a cooling (AC) mode part load, an AC mode full load, a heating (HP) mode part load, or a HP mode full load, the HVAC system comprising:
 an indoor heat exchanger having a first refrigerant passage extending in a first direction and a second refrigerant passage extending in a second direction opposite from the first direction, wherein fresh air flows generally in the second direction across the indoor heat exchanger; 
 a first refrigerant circuit comprising a first refrigerant, a first compressor, a first outdoor heat exchanger, and the first refrigerant passage; and 
 a second refrigerant circuit comprising a second refrigerant, a second compressor, a second outdoor heat exchanger, and the second refrigerant passage; 
   wherein operating in the AC mode part load comprises:
 operating only the first refrigerant circuit; and 
 directing the first refrigerant in a direction from the first compressor through the first outdoor heat exchanger and then the first refrigerant passage, wherein the first refrigerant is in counter-current flow through the first outdoor heat exchanger and the first refrigerant passage; 
   wherein operating in the AC mode full load comprises:
 directing the first refrigerant in a direction from the first compressor through the first outdoor heat exchanger and then the first refrigerant passage, wherein the first refrigerant is in counter-current flow through the first outdoor heat exchanger and the first refrigerant passage; and 
 directing the second refrigerant in a direction from the second compressor through the second outdoor heat exchanger and then the second refrigerant passage, wherein the second refrigerant is in co-current flow in the second outdoor heat exchanger and in the second refrigerant passage; 
   wherein operating in the HP mode part load comprises:
 operating only the second refrigerant circuit; and 
 directing the second refrigerant in a direction from the second compressor through the second refrigerant passage and then the second outdoor heat exchanger, wherein the second refrigerant is in counter-current flow in the second outdoor heat exchanger and in the second refrigerant passage; and 
   wherein operating in the HP mode full load comprises:
 directing the second refrigerant in a direction from the second compressor through the second refrigerant passage and then the second outdoor heat exchanger, wherein the second refrigerant is in counter-current flow in the second outdoor heat exchanger and in the second refrigerant passage; and 
 directing the first refrigerant in a direction from the first compressor through the first refrigerant passage and then the first outdoor heat exchanger, wherein the first refrigerant is in co-current flow in the first outdoor heat exchanger and in the first refrigerant passage. 
   
     
     
         20 . The method of  claim 19 , wherein the first compressor comprises one or more first compressors and the second compressor comprises one or more second compressors; and
 the HVAC system is a rooftop unit.