Patent Publication Number: US-8117855-B2

Title: Refrigeration system with consecutive expansions and method

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to refrigeration climate control systems, the systems that either absorb heat from indoor air and reject it to ambient or deliver heat absorbed from ambient to indoor air. Those systems include residential and commercial heat pumps and air conditioners. Invention also relates to refrigeration systems with air circulating in an enclosed volume. Those systems include, for example, dehumidifiers and heat pumps for clothing dryers. 
     Air conditioners/heat pumps, and dehumidifiers operate conventional refrigeration cycle ( FIG. 2 ) and in a cooling mode extract heat from indoor air and condense moisture from this air, delivering extracted heat along with heat from the compressor to ambient. For air conditioners and heat pumps, ambient is normally outdoor air or other outdoor media. For dehumidifiers ambient is same indoor air. In cooling mode heat pumps and air conditioners reduce temperature and humidity of the indoor air to a comfortable level while dehumidifiers reduce humidity increasing indoor air temperature. For air conditioners and heat pumps, a set of indoor air temperature and airflow rate through the evaporator together with a given indoor air exchange rate and conditions of outdoor air will also define indoor air humidity. When air conditioner/heat pump operates in the cooling mode, average indoor air relative humidity (RH) can stay in comfortable level of around 35-50%. However, even with average indoor air humidity of 50% or below RH of chilled air leaving evaporator may reach 90-95%. Air with such high humidity carries small water drops that accumulate on air duct surfaces or even on the walls inside of a building that may result in mold and allergies. Reduction in airflow through the indoor heat exchanger (evaporator), or reduction in the evaporator dimensions, or heating air after the evaporator with an additional heater or with a condensing coil may reduce indoor air humidity, but with considerable up to 15-20% reduction in cooling capacity and efficiency of air conditioning. Besides, during summer time in many places with high outside air temperature and humidity and with increased indoor air exchange (i.e. old buildings, open windows or doors) average indoor air relative humidity may rise far above 50% and even 70%. Thus, the danger of water accumulations in air ducts and on the walls can be even higher and will require adding to leaving evaporator air considerable heat. 
     Climate controlling heat pumps operating in a heating mode extract heat from outside air and deliver this heat together with heat from compressor to the indoor heat exchanger while heat pumps in dryers reheat circulating air. A fan blowing air through the warm heat exchanger coil transfers heat to air. Concerning climate control systems in warm regions such as, for example, Florida, most of the time heat pumps provide sufficient indoor air temperatures through wintertime. However, in colder regions, heat pumps often require additional gas or resistance heaters, and generally are not efficient with low outdoor temperatures. 
     One solution to improve heat pump operations in the heating and cooling modes, also as air conditioner in cooling mode has been presented in U.S. Pat. No. 5,689,962. The patent offers schematics in which an indoor heat exchanger is divided in two parts. In the heating mode the first part becomes a condenser the second is a subcooler. In the cooling mode the first part of the heat exchanger is a subcooler and the second is an evaporator. The design problems are how to properly operate “subcooler” and what way to split indoor heat exchanger into two parts. If the parts are equal or approximately equal, the heat pump will operate inefficiently in both modes. If one part is much larger than another, heat pump is extremely inefficient in a mode where subcooler is larger than the evaporator or condenser. Concerning the method for dehumidifying and cooling air, there is only one refrigerant expansion before the subcooler, thus the subcooler works as a part of the evaporator. Lack of any expansion in the method for heating air makes the system not operable. 
     More specifically, U.S. Pat. Nos. 6,212,892 and 6,595,012 offer a refrigeration cycle with two expansions (see  FIG. 3 ) for a heat pump. The cycle first has been introduced by the author of the present invention in an application for U.S. Pat. No. 5,755,104 to improve efficiency of refrigeration system with a thermal storage. Further, the cycle with cascade expansions was used in U.S. Pat. Nos. 6,212,892 and 6,595,012. As in the initial patent in these patents the cycle with two consecutive expansions has been offered exclusively for air conditioner or heat pump in cooling indoor air modes but not for the heating mode of a heat pump. Both patents specify two different cooling modes: conventional and with enhanced dehumidification. In dehumidification mode that operates the cycle of  FIG. 3  both patents consider that auxiliary coil works as a subcooler. It implies that independently on expansion in the first expansion device the system would operate with efficient subcooling. This is an incorrect assumption. Insufficient subcooling may greatly affect efficiency of the system. For proper subcooling, refrigerant charge of the system is supposed to be higher than without subcooling. However, increased refrigerant charge will be collected in an accumulator or, in a worse case, excessive liquid refrigerant may reach the compressor, causing liquid slugs. Thus, practically it&#39;s very difficult to get condensing and deep subcooling in a heat transfer coil with a conventional geometry. As a consequence, offered in these patents design may increase condensing temperature and considerably reduce efficiency of the system. Also, as in U.S. Pat. No. 5,689,962, U.S. Pat. Nos. 6,212,892 and 6,595,012 don&#39;t specify dimensions of the auxiliary coil. Besides, U.S. Pat. Nos. 6,212,892 and 6,595,012 offer a second reversing valve turning on and off to alternate the conventional cooling mode with the mode with enhanced dehumidification. This brings additional installation, operating, and maintenance expenses. 
     SUMMARY OF THE INVENTION 
     In this invention, as opposed to conventional refrigeration systems including air conditioners, heat pumps, dehumidifiers, etc., refrigeration cycle is modernized and includes two consecutive expansions with two expansion devices and two condensers, wherein the first condenser liquefies refrigerant after compressor and the second condenser liquefies refrigerant after the first expansion device. The cooling medium for the second condenser is either air to be conditioned in the refrigeration system or other available medium. First embodiment of the present invention describes this refrigeration cycle. 
     Other embodiments include schematics and sequence of operations of sealed systems of air conditioners, dehumidifiers, and heat pumps in either cooling and/or heating modes working according to aforementioned refrigeration cycle. Included in the embodiments second condenser&#39;s dimensions limitations and general design requirements are based on the results of math modeling of an air conditioner and/or heat pump operating with cascade expansions. That allows enhanced dehumidification with efficiency improvement in cooling mode and capacity and efficiency increase in heating mode. 
     Yet another embodiment includes a valve to bypass second expansion device that allows air conditioner operations according to conventional refrigeration cycle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a P-H diagram of a modernized refrigeration cycle for conditioning air with two cascade expansions and two condensers. 
         FIG. 2  (previous arts) is a P-H diagram of a conventional refrigeration cycle. 
         FIG. 3  (previous arts) is a P-H diagram of a refrigeration cycle with cascade expansions and an auxiliary subcooler. 
         FIG. 4  is a schematic of an air conditioner according to one embodiment of the invention. 
         FIG. 5  is a schematic of a heat pump operating in cooling mode per refrigeration cycle of  FIG. 1 . 
         FIG. 6  is a schematic of the heat pump of  FIG. 5  operating in heating mode. 
         FIG. 7  presents results of math modeling of efficiency and relative humidity of air conditioner of  FIG. 4  and heat pump of  FIG. 5 . 
         FIG. 8  is an arrangement of tubes in an indoor heat exchanger of an air conditioner of  FIG. 4  and heat pump of  FIGS. 5 ,  6 . 
         FIG. 9  is a schematic of a heat pump according to another embodiment of the invention operating in heating mode per refrigeration cycle of  FIG. 1 . 
         FIG. 10  is a schematic of the heat pump of  FIG. 9  operating conventional refrigeration cycle in cooling mode. 
         FIG. 11  presents results of math modeling of efficiency and heating capacity of the heat pump of  FIG. 9 . 
         FIG. 12  is an arrangement of tubes in an indoor heat exchanger of the heat pump of FIGS.  9 , 10 . 
         FIG. 13  is a schematic of a heat pump according to yet another embodiment of the invention operating in cooling mode per refrigeration cycle of  FIG. 1 . 
         FIG. 14  is a schematic of the heat pump of  FIG. 13  operating refrigeration cycle of  FIG. 1  in heating mode. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a P-H diagram of a refrigeration cycle with two consecutive expansions and two consecutive condensers. 
     Line  1 - 2 - 3 - 4 - 5 - 6 - 1  depicts the cycle where line  1 - 2  represents vaporized refrigerant compression in a compressor, line  2 - 3  represents desuperheating and condensing refrigerant in a first condenser, line  3 - 4  represents expansion in a first expansion device, line  4 - 5  condensing in a second condenser, line  5 - 6  shows expansion in a second expansion device, and line  6 - 1  shows evaporating in an evaporator. Evaporator capacity increase compared to the conventional cycle without any subcooling is shown by section  6 - 4 ′. In heating mode it also translates to an increase in heat delivered to the indoor coil. 
     In all-air systems a heat sink for the cooling mode is ambient air where the first or main condenser rejects heat. The second condenser requires a heat sink with lower temperature. It may be cold air after the evaporator that is delivered to the second condenser to condense refrigerant partly expanded in the first expansion device. Thus, for cooling mode it is most convenient to have the second condenser as a section of the indoor heat exchanger with air flowing first against the evaporator and then against the second condenser. 
     To use extra heat that the evaporator gets from ambient in the heating mode, the second condenser also has to be installed inside heating area to be a part of the indoor heat exchanger. Unlike the cooling mode, here cold air in the indoor heat exchanger first flows through the second condenser, and then air flows through the first condenser. In another arrangement cold air initially flows in parallel through the second condenser and part of the first condenser. 
     Line  1 - 2 - 3 - 4 - 1  in  FIG. 2  demonstrates a conventional refrigeration cycle. Conventional cycle with subcooling after condenser is shown by line  1 - 2 - 5 - 6 - 1 . Theoretically cycle  1 - 2 - 5 - 6 - 1  achieves the same effect as a modernized cycle of  FIG. 1 . Still, it&#39;s practically impossible to get deep subcooling in a condenser operating according to the conventional cycle. Normally, subcooling in the condenser rarely exceeds 1-3 deg. F. There are literature sources suggesting that deep subcooling may be reached with extra refrigerant charge. Condenser is supposed to liquefy refrigerant vapor in the first part of the heat transfer coil, leaving considerable part of the coil filled with liquid that may be subcooled by incoming cold air. However, increased refrigerant charge may be collected in an accumulator or, in a worse case, excessive liquid refrigerant may reach the compressor, thus causing a liquid slug. 
     In refrigeration cycle of  FIG. 3  line  1 - 2  represents refrigerant vapor compression, line  2 - 3  shows desuperheating and condensing in a condenser, line  3 - 4  expansion in a first expansion device, line  4 - 5  condensing and subcooling in a subcooler, line  5 - 6  shows expansion in a second expansion device, and line  6 - 1  liquid refrigerant evaporation in an evaporator. Same as in the conventional refrigeration cycle, to achieve deep subcooling in the subcooler additional refrigerant charge is required. 
     Advantage of the cycle of  FIG. 1  compared to the conventional cycle of  FIG. 2  (with subcooling) and cycle of  FIG. 3  is stability of condensing process. First expansion device controls the first (main) condenser. The second expansion device controls additional heat rejected in the second (auxiliary) condenser. This arrangement doesn&#39;t require refrigerant overcharge, providing considerable capacity and efficiency increase in the heating mode, and improved dehumidification together with efficiency in the cooling mode. 
       FIG. 4  depicts schematics of a sealed system of an air conditioner operating according to  FIG. 1 . Hot compressed refrigerant vapor after compressor  110  through line  112  flows to outdoor heat exchanger  116  that operates as a first condenser desuperheating and condensing refrigerant vapor. After the first condenser  116  liquid refrigerant through line  122  flows to the first expansion device  120 . The device  120  can be an orifice, valve, thermostatic expansion valve, capillary tube, piston type short tube restrictor or any other device that expands refrigerant flowing in the direction of indoor heat exchanger  150 . Indoor heat exchanger  150  consists of 2 sections: an auxiliary section  138  that operates as a second condenser and a main section  146  that operates as an evaporator. A mixture of vapor and liquid refrigerant expanded in device  120  reaches second condenser  138  wherein it liquefies, rejecting heat to indoor air that left the evaporator. After second condenser  138  liquid refrigerant reaches a second expansion device  130  which, like the first expansion device can be an orifice, valve, thermostatic expansion valve, capillary tube, piston type short tube restrictor or any other device that expands refrigerant flowing in the direction of main section  146  of the indoor heat exchanger  150 . Expansion device  130  may also be combined with a distributor (not shown), if evaporator includes several parallel refrigerant passes. Mostly liquid refrigerant evaporates in evaporator  146 , absorbing heat and condensing moisture from incoming indoor air  144 . After evaporator  146 , vaporized refrigerant through line  142  flows to suction of compressor  110 . Optional solenoid valve  152  to bypass second expansion device  130  can be installed. When solenoid valve  152  is in an open position, an auxiliary section  138  of indoor heat exchanger  150  will work as a first part of the evaporator, evaporating refrigerant after the first expansion device  120 . 
     In some applications heat exchanger  116  could be also located indoors. If air from same enclosed volume passes in series through both heat exchanger  150  and heat exchanger  116 , the sealed system of  FIG. 4  can be used in dehumidifiers for dehumidifying indoor air or in heat pumps for cloth dryers to provide air with additional heat needed to dry clothing. In a cloth dryer, auxiliary section of heat exchanger  150  may be located either after the first condenser or in a separate loop to reject extra heat from the system. Besides articles shown in the schematics, sealed system of  FIG. 4  also may include filter, dryer, accumulator, and other common sealed system parts. 
       FIG. 5  depicts a sealed system of a heat pump operating in cooling mode. Excluding 4-way reversing valve  248 , the heat pump operations are mostly identical to operations of air conditioner of  FIG. 4 . Hot compressed vapor refrigerant after compressor  210  flows through line  212  to port a of 4-way reversing valve  248 . In the cooling mode, refrigerant from port a flows to port b and further through line  214  to outdoor heat exchanger  216  that in this mode operates as a first condenser, desuperheating and condensing refrigerant vapor. After the first condenser  216 , liquid refrigerant flows through a third expansion device  254  to line  222  and further to the first expansion device  220 . In this mode, the third expansion device allows refrigerant to flow to line  222  without expansion. On the contrary, first expansion device  220  expands refrigerant flowing in this direction so that partly vapor and partly liquid refrigerant reaches an indoor heat exchanger  250 . Indoor heat exchanger  250  consists of 2 sections: a first (auxiliary) section  238  that operates as a second condenser and a second (main) section  246  that operates in this mode as an evaporator. First, refrigerant expanded in device  220  reaches second condenser  238  wherein it liquefies, rejecting heat to indoor air that left the evaporator. After condenser  238  liquid refrigerant reaches a second expansion device  230  that expands refrigerant flowing in the direction of main section  246  of the indoor heat exchanger  250 . Then, mostly liquid refrigerant evaporates in evaporator  246  absorbing heat and condensing moisture from incoming indoor air  244 . After evaporator  246 , vaporized refrigerant flows to port d of 4-way reversing valve  248  through line  240 . In this mode port d is connected to port c that, in turn, delivers vaporized refrigerant to the suction of compressor  210  through line  242 . The design of any of three expansion devices may include a cap tube, an orifice, or thermostatic expansion valve with an additional check valve allowing free refrigerant movement in one direction. It could also be a short tube restrictor or any other expansion device that expands refrigerant in one direction and allows free flow in an opposite direction. Optional solenoid valve  252  to bypass the second expansion device  230  also can be installed. When solenoid valve  252  is in an open position, an auxiliary section  238  of indoor heat exchanger  250  will work as a first part of evaporator, evaporating liquid refrigerant after the first expansion device  220 . In some heat pumps, where, for example, indoor and outdoor heat exchangers are in proximity, the third and the first expansion devices could be combined in one apparatus that expands refrigerant in cooling mode in one direction and in heating mode in the opposite direction. The second expansion device  230  may be combined with a distributor (not shown), if the evaporator includes several parallel refrigerant passes. In addition, sealed system of this heat pump as others described in the present invention may include filter, dryer, accumulator, and other sealed system parts. 
       FIG. 6  shows refrigerant path in the sealed system of heat pump of  FIG. 5  operating in heating mode. Hot refrigerant vapor flows from discharge port of compressor  210  through line  212  to port a of 4-way valve  248 . In this mode refrigerant after port a flows to port d and further through line  240  to the main section  246  of the indoor heat exchanger  250 . After main section  246 , refrigerant moves to auxiliary section  238  of heat exchanger  250  through a second expansion device  230 . In this direction expansion device  230  allows refrigerant flowing without expansion. Both sections  246  and  238  of heat exchanger  250  work as a single condenser, condensing refrigerant vapor and rejecting heat to indoor airflow  244 . After condensing, liquid refrigerant passes the first expansion device  220  also without expansion and through line  222  reaches the third expansion device  254 . After expansion in device  254 , mostly liquid refrigerant flows to outdoor heat exchanger  216 , which in this mode operates as an evaporator. After evaporator, vaporized refrigerant through line  214  and port b of reversing valve  248  moves through port c and line  242  to suction port of compressor  210 . Thus, in this mode heat pump operates according to the conventional refrigeration cycle depicted in  FIG. 2 . 
       FIG. 7  represents results of math modeling of operations of air conditioner of  FIG. 4  and heat pump of  FIG. 5  in cooling mode. An important design parameter is what portion of indoor heat exchanger shall be used as an auxiliary section or as the second condenser. The rest of the indoor heat exchanger is the main section or in this mode, the evaporator. The assumptions include: average indoor air temperature is 75 deg. F. with relative humidity of 50%, refrigerant is R410A, evaporating temperature is 50 deg. F. As it can be seen from  FIG. 7  when operating in conventional refrigeration cycle (percentage of the second condenser surface equals 0%) air relative humidity RH at the exit is around 95%, which is extremely high and will cause water drops in air after the evaporator. Analysis of the chart of  FIG. 7  helps in finding proper range of ratio between the auxiliary section and main section of the indoor heat exchanger. The chart demonstrates that, if the second condenser takes only 5%-6% of the total indoor heat exchanger surface, relative humidity of air leaving indoor heat exchanger drops by 15-16% and reaches a safe level of 80% or below. Large drop in air RH can be explained by 2 factors. First is an additional load on the evaporator (see  FIG. 1 , section  6 - 4 ′ of line  6 - 1 ). This extra load forces lowering of evaporating temperature, which, in turn, increases moisture condensation. Model shows that even small (5%-6% of total indoor heat exchanger) second condenser will increase evaporator capacity by 12% and moisture condensation by more than 30%. Second factor is that the second condenser warms up outgoing air, further reducing RH. 
     However, reduction in evaporating temperature causes some reduction in efficiency. With the second condenser surface of 5-6% from total indoor heat exchanger surface efficiency drop is around 2-2.5%. Compared to other means for air humidity reduction, such as aforementioned reduction in airflow, or in the evaporator surface, or heating air after the evaporator with an additional heater or a part of condensing coil, it&#39;s still relatively low price. In most applications, the second condenser occupying 5-6% of indoor heat exchanger will be enough. However, the tubes of the second condenser shall be located in a way that at least most of the air leaving the evaporator has to be reheated in a second condenser. 
       FIGS. 8   a ,  8   b ,  8   c  demonstrate ways to arrange main and auxiliary sections in an indoor heat exchanger. In the schematics, tubes of the main section are not filled and tubes of the auxiliary section are filled with black color. The arrangement in  FIG. 8   a  includes 3 rows of the main (evaporating) section of the indoor coil and one extra row occupied by the auxiliary coil. In this arrangement auxiliary coil takes 25% of total indoor heat exchanger surface. If the main section consisted of 2 rows and auxiliary heat exchanger still occupied one row, the second condenser would take one third of the total indoor heat exchanger tubing. As shown in  FIG. 7 , further increase in auxiliary heat exchanger dimensions is irrational: COP sharply going down while reduction in leaving evaporator air relative humidity below 70% is not necessary. The arrangement of tubes in  FIG. 8   b  again includes 3 rows of the evaporator and a half row of the second condenser that here occupies around 14% of indoor heat exchanger. What&#39;s important is that tube distribution in the row occupied by the auxiliary section has to be as even as possible. This provides an opportunity to reheat most of the air leaving the evaporator. Finally, in arrangement of  FIG. 8   c , second condenser takes only 5.2% of the indoor heat exchanger. If air is well mixed in the indoor heat exchanger before the auxiliary coil, this will be enough to reduce relative humidity of air after evaporator. 
       FIG. 9  depicts a sealed system of a heat pump operating in heating mode. Compared to a conventional heat pump, in this mode the system provides extra capacity and efficiency. Hot compressed refrigerant vapor after compressor  310  through line  312  flows to port a of 4-way reversing valve  348 . In the heating mode, refrigerant from port a flows to port d and further through line  340  to main section  346  of indoor heat exchanger  350  that in this mode operates as a first condenser, desuperheating and condensing refrigerant vapor and rejecting heat to indoor air stream. After the first condenser  346  liquid refrigerant flows through a second expansion device  330 , expands in this device and reaches an auxiliary section  338  that operates as a second condenser, condensing refrigerant vapor after the second expansion device  330  and rejecting heat to incoming air  344 . Further refrigerant flows to a first expansion device  320 . In this mode the first expansion device allows refrigerant to flow to line  322  without expansion. Then a third expansion device  354  expands refrigerant. After expansion mostly liquid refrigerant reaches an outdoor heat exchanger  316 , which in this mode operates as an evaporator. After evaporator  316 , refrigerant vapor through line  314  reaches port b of reversing valve  348 . Then, through port c and line  342 , vaporized refrigerant comes to the compressor suction. The design of anyone of the expansion devices maybe a cap tube, an orifice, or a thermostatic expansion valve with an additional check valve allowing free refrigerant movement in one direction. It could be also a short tube restrictor or any other expansion device expanding refrigerant in one direction and allowing free flow in the opposite direction. In some heat pumps where, for example, indoor and outdoor heat exchangers are in proximity, the third and the first expansion devices could be combined in one apparatus that expands refrigerant in cooling mode in one direction and in heating mode in the opposite direction. The second expansion device  330  may be combined with a distributor (not shown) if main section  346  of the indoor heat exchanger consists of several parallel passes. In addition, sealed system of this heat pump also, as others described in the present invention, may include filter, dryer, accumulator, and other sealed system parts. 
       FIG. 10  shows refrigerant path in the sealed system of heat pump of  FIG. 9  operating in cooling mode. Hot refrigerant vapor flows from compressor  310  discharge to port a of 4-way valve  348  through line  312 . In this mode, refrigerant after port a flows to port b and further through line  314  to outdoor heat exchanger  316 , that operates as a condenser, desuperheating and condensing refrigerant and rejecting heat to ambient. After condenser  316 , refrigerant moves to the first expansion device  320  through the third expansion device  354  and line  322 . In this direction, expansion device  354  allows refrigerant flowing without expansion, while expansion device  320  expands refrigerant before auxiliary section  338  of the indoor heat exchanger  350  that operates as a first part of the evaporator. After auxiliary heat exchanger  338 , refrigerant reaches the second expansion device  330  and further, the main section  346 . In this mode, expansion device  330  allows refrigerant flowing through without expansion while the section  346  operates as a second part of the evaporator. Thus, both sections  346  and  338  of heat exchanger  350  work as a single evaporator, evaporating liquid refrigerant and absorbing heat from indoor airflow  344 . After evaporator vaporized refrigerant flows through line  340  and reaches port d of reversing valve  348 , then through port c and line  342  refrigerant goes to suction port of compressor  310 . Thus, in this mode, heat pump operates according to the conventional refrigeration cycle depicted in  FIG. 2 . 
       FIG. 11  shows results of math modeling of heat pump of  FIG. 9  in heating mode. Again, as for air conditioner of  FIG. 4  an important design parameter is what portion of indoor heat exchanger shall be used as an auxiliary section or as a second condenser. The rest of the indoor heat exchanger is the main section that in this mode works as a first condenser. The assumptions include: refrigerant is R410A, indoor air temperature is 68 deg. F., when operating in conventional refrigeration cycle condensing temperature is 110 deg. F. and evaporating temperature is 40 F. As it can be seen from  FIG. 11 , the schematics may provide around 12% in capacity increase and almost 3% increase in efficiency. Best efficiency is achieved when auxiliary coil takes 10-15% of total indoor heat exchanger surface while largest capacity is achieved if auxiliary coil is around one forth of the indoor heat exchanger. Thus, the best range for auxiliary section of indoor heat exchanger is between 5% and 25%. The chart demonstrates that if the auxiliary section exceeds one third of total indoor heat exchanger surface, the efficiency drops by more than 4% while heating capacity also starts decreasing. 
       FIGS. 12   a ,  12   b ,  12   c , and  12   d  represent different tube arrangements in the heat pump of  FIGS. 9 and 10 . In all four arrangements, the number of tubes in the auxiliary section (tubes filled with black color) of indoor heat exchanger is 4 that is 10% of 40 tubes in  FIGS. 12   a  and 11% of 36 tubes in  FIGS. 12   b ,  12   c ,  12   d . Here, unlike the arrangement in  FIG. 8 , the auxiliary section of the indoor heat exchanger has to be at the air inlet. The best solution is to spread tubes of auxiliary heat exchanger evenly before the main section of the indoor heat exchanger ( FIG. 12   a ). However, there are no such strict requirements as for arrangement in  FIG. 8  and auxiliary heat exchanger tubes can be located between tubes of main heat exchanger ( FIG. 12   b ), in one end ( FIG. 12   c ), or even partly occupy a couple of first (in the direction of air) rows ( FIG. 12   d ). Still, efficiency will gradually worsen from arrangement of  FIG. 12   a  through arrangement of  FIG. 12   d.    
       FIGS. 13 and 14  show a heat pump operating with cascade expansions in both cooling and heating modes. 
       FIG. 13  shows schematics in cooling mode operations. Hot refrigerant vapor after compressor  410  through line  412  flows to port a of an 8-way reversing valve  448 . Then, through port b and line  414 , refrigerant reaches outdoor heat exchanger  416 . In this mode, heat exchanger  416  operates as a first condenser rejecting heat to ambient, desuperheating refrigerant vapor and condensing this vapor. Liquid refrigerant after condenser  416  flows through a third expansion device  454  that in this direction allows refrigerant flow without expansion. Then, through line  422 , refrigerant reaches port e of reversing valve  448 . Further, refrigerant flows through port f and line  424  to a first expansion device  420 , expanding refrigerant in both directions. Expanded refrigerant flows to a first auxiliary section  438  of indoor heat exchanger  450 , which operates as a second condenser, recondensing vapor after the first expansion device  420  and rejecting heat to cold air leaving indoor heat exchanger. After the second condenser  438 , liquid refrigerant expands again, now in a second expansion device  430 . Expanded refrigerant flows to a main section  446  of indoor heat exchanger  450 , which operates as a first part of evaporator, evaporating liquid refrigerant and absorbing heat and condensing moisture from indoor air. After heat exchanger  446 , refrigerant flows to port h of reversing valve  448  through line  434 . Then, through port g and line  436 , refrigerant flows to a second auxiliary section  456  of indoor heat exchanger  450 , which operates as the last part of the evaporator, vaporizing the rest of liquid refrigerant and absorbing heat and condensing moisture from incoming air  444 . After evaporator  456 , vaporized refrigerant flows to port d of 8-way reversing valve  448  through line  440  and through port c and line  442  reaches compressor suction. In this schematics the first expansion device  420  is an apparatus that expands refrigerant in cooling mode in one direction and in heating mode in the opposite direction. The design of second and third expansion devices may include cap tubes, orifices, or thermostatic expansion valves with additional check valves allowing free refrigerant movement in one direction. It could also be short tube restrictors or any other expansion devices expanding refrigerant in one direction and allowing free flow in the opposite direction. The second expansion device  430  may be combined with a distributor (not shown), if main section  446  of indoor heat exchanger consists of several parallel passes. In addition, sealed system of this heat pump also, as others described in the present invention, may include filter, dryer, accumulator, and other sealed system parts. 
       FIG. 14  is a schematic of heat pump of  FIG. 13  operating in heating mode. Hot refrigerant vapor after compressor  410  flows to port a of 8-way reversing valve  448  through line  412 . Then, through port h and line  434 , refrigerant reaches main section  446  of indoor heat exchanger  450 . In this mode, section  446  operates as a first part of a first condenser, desuperheating and partly condensing refrigerant vapor and rejecting heat to indoor airflow. After heat exchanger  446 , refrigerant freely flows through second expansion device  430  to reach a first auxiliary section  438  that now operates as a second part of the first condenser, condensing the rest of refrigerant vapor and rejecting heat to outgoing airflow. Liquid refrigerant after section  438  expands in first expansion device  420  and, through line  424  flows to port f, then to port g and through line  436  to the second auxiliary section  456  of indoor heat exchanger  450  that now operates as a second condenser. In section  456 , refrigerant recondenses, rejecting heat to incoming indoor airflow  444 . After section  456 , liquid refrigerant through line  440 , ports d and e flows to third expansion device  454  wherein it expands. After expansion, liquid refrigerant evaporates in outside heat exchanger  416 , absorbing heat from ambient. After evaporator  416 , vaporized refrigerant reaches compressor suction through ports b, c, and line  442 . 
     Design of  FIGS. 13 ,  14  could be different. For example, first expansion device  420  could be designed a way to expand refrigerant only in one direction and an additional device expanding refrigerant in the opposite direction is to be installed in line  436 . However, relative to airflow to be conditioned the second condenser in the cooling mode has always to be downstream of the evaporator and in the heating mode, the second condenser has to be upstream of the first condenser. 
     While preferred embodiments of the invention have been describe above in details, it will be understood that many modifications can be made to the illustrated systems without departing from the spirit and scope of the invention.