JP4239256B2

JP4239256B2 - Heat pump cycle

Info

Publication number: JP4239256B2
Application number: JP30876698A
Authority: JP
Inventors: 幸克尾崎; 成秀木村; 伸西田
Original assignee: Denso Corp; Nippon Soken Inc
Current assignee: Denso Corp; Soken Inc
Priority date: 1998-10-29
Filing date: 1998-10-29
Publication date: 2009-03-18
Anticipated expiration: 2018-10-29
Also published as: JP2000130878A

Description

【０００１】
【発明の属する技術分野】
本発明は、高圧冷媒の圧力（圧縮機の吐出圧）が、冷媒の臨界圧力以上となる超臨界冷凍サイクルを用いたヒートポンプサイクルに関するもので、空調装置に適用して有効である。
【０００２】
【従来の技術】
近年、冷凍サイクルの脱フロン対策の１つとして、例えば特公平７−１８６０２号公報に記載のごとく、二酸化炭素（ＣＯ₂）を使用した冷凍サイクル（以下、ＣＯ₂サイクルと呼ぶ。）が提案されている。
このＣＯ₂サイクルは、ＣＯ₂の臨界温度が約３１℃とフロンの臨界温度と比べて低いため、夏等の大きな冷凍能力を必要とするときには、放熱器側の冷媒圧力（吐出圧）を臨界圧力以上まで高めて（圧縮して）冷凍サイクルを運転する必要がある。
【０００３】
そこで、上記公報に記載の発明では、冷凍サイクルの効率及び冷凍能力の向上を図るとともに、圧縮機に液相冷媒が吸入されることを防止すべく、放熱器を出た高圧冷媒と圧縮機に吸入される低圧冷媒との間で熱交換を行う内部熱交換器を設けている。
【０００４】
【発明が解決しようとする課題】
しかし、内部熱交換器を設けて高圧冷媒と低圧冷媒との間で熱交換を行うと、圧縮機に吸入される低圧冷媒の温度が高くなるため、圧縮機から吐出する高圧冷媒の温度も上昇してしまう。このため、上記公報に記載のＣＯ₂サイクルを単純に冷暖房可能なヒートポンプサイクルに適用すると、以下に述べるような問題が発生する。
【０００５】
すなわち、内部熱交換器にて低圧冷媒が加熱されることに加えて、冬等の外気温度が低いときに暖房運転を行うと、低圧冷媒の圧力が冷房運転時より低くなって、圧縮比（吸入圧と吐出圧との比）が冷房運転時より大きくなるので、圧縮機から吐出する高圧冷媒の温度が冷房運転時より高くなる。
このため、高圧冷媒の温度が、冷媒中に混合された潤滑油（冷凍機油）の耐熱温度を越えてしまうので、冷媒中に混合された潤滑油が分解又は変性してしまい、圧縮機が損傷してしまうという問題が発生する。
【０００６】
因みに、図１２は、ＨＦＣ１３４ａ（フロン）は高圧冷媒の圧力を１５ｋｇｆ／ｃｍ²ａｂｓとし、ＣＯ₂は高圧冷媒の圧力を９０ｋｇｆ／ｃｍ²ａｂｓとした場合において、圧縮機の効率を１としたときの蒸発器の飽和温度に対するＨＦＣ１３４ａを冷媒とする冷凍サイクルの吐出冷媒温度（高圧冷媒の温度）と、ＣＯ₂サイクル吐出温度の吐出冷媒温度（高圧冷媒の温度）とを示すグラフである。
【０００７】
そして、図１２から明らかなように、蒸発器の飽和温度、すなわち低圧冷媒の圧力が低下するほど高圧冷媒の温度が上昇するので、暖房運転時に内部熱交換器を設けると、吐出冷媒の温度がさらに上昇してしまうことが判る。
本発明は、上記点に鑑み、圧縮機の吐出圧が冷媒の臨界圧力以上となるヒートポンプサイクルにおいて、暖房運転時に圧縮機が損傷することを防止することを目的とする。
【０００８】
【課題を解決するための手段】
上記目的を達成するために、請求項１に記載の発明では、冷媒として二酸化炭素を用いる冷暖房切換可能なヒートポンプサイクルであって、
前記冷媒を吸入し、その吸入した冷媒を冷媒の臨界圧力以上まで圧縮する圧縮機（１）と、
室外空気と冷媒との間で熱交換を行う室外熱交換器（２）と、
室内に吹き出す室内空気と冷媒との間で熱交換を行う室内熱交換器（３）と、
前記室内熱交換器（３）と前記室外熱交換器（２）とを結ぶ冷媒通路に設けられ、冷媒を減圧する減圧器（４）と、
前記圧縮機（１）の吸入側に設けられ、冷媒を気相冷媒と液相冷媒とに分離するとともに、気相冷媒を前記圧縮機（１）の吸入側に向けて流出させるアキュムレータ（５）と、
前記アキュムレータ（５）から前記圧縮機（１）の吸入側に向かって流通する冷媒が流通する第１冷媒通路（６ａ）、及び前記第１冷媒通路（６ａ）に隣接する第２冷媒通路（６ｂ）を有し、前記両冷媒通路（６ａ、６ｂ）間で熱交換を行う内部熱交換器（６）と、
冷房運転時には前記室外熱交換器（２）が高圧冷媒の放熱側となるとともに前記室内熱交換器（３）が低圧冷媒の吸熱側となり、これに対し、暖房運転時には前記室内熱交換器（３）が高圧冷媒の放熱側となるとともに前記室外熱交換器（２）が低圧冷媒の吸熱側となるように冷媒流れを切り換える切換弁（７）とを備え、
前記暖房運転を外気温が低いときに行うと、前記暖房運転時の低圧冷媒の圧力が前記冷房運転時よりも低くなって、前記暖房運転時の圧縮比が前記冷房運転時よりも大きくなり、これにより、前記暖房運転時に前記圧縮機（１）から吐出する高圧冷媒の温度が前記冷房運転時よりも高くなる超臨界冷凍サイクルであり、
前記冷房運転時には、前記第２冷媒通路（６ｂ）に前記減圧器（４）にて減圧される前の高圧冷媒を流通させ、前記暖房運転時には、前記第２冷媒通路（６ｂ）に前記減圧器（４）にて減圧された後の低圧冷媒を流通させることにより、前記内部熱交換器（６）にて前記高圧冷媒と前記低圧冷媒とを熱交換させないようになっており、
前記暖房運転時には、前記高圧冷媒の温度が冷媒中に混合される潤滑油の耐熱温度を越えない温度範囲に維持されることを特徴とする。
【０００９】
これにより、冷媒として二酸化炭素を用いる超臨界冷凍サイクルからなるヒートポンプサイクルにおいて、暖房運転時には、両冷媒通路（６ａ、６ｂ）を流通する冷媒の温度及び圧力が等しくなるので、高圧冷媒と低圧冷媒とが熱交換されない。したがって、低外気温時における暖房運転時に圧縮機（１）から吐出する高圧冷媒の温度が過度に上昇することを防止できるので、高圧冷媒の温度が冷媒中に混合された潤滑油の耐熱温度を越えてしまうことを防止できる。したがって、冷媒中に混合された潤滑油が分解又は変性してしまうことを防止でき、圧縮機（１）が損傷することを防止できる。
【００１１】
因みに、上記各手段の括弧内の符号は、後述する実施形態に記載の具体的手段との対応関係を示す一例である。
【００１２】
【発明の実施の形態】
（第１実施形態）
本実施形態は、本発明に係るヒートポンプサイクルを二酸化炭素を冷媒とするヒートポンプサイクルを用いた空調装置に適用したものであって、図１は本実施形態に係るヒートポンプサイクルの模式図である。
【００１３】
図１中、１は冷媒（ＣＯ₂）を吸入し、その吸入した冷媒を冷媒の臨界圧力以上にまで圧縮する圧縮機であり、この圧縮機１は冷媒と共に潤滑油を吸入することにより、圧縮機１内の潤滑を図っている。２は室外空気と冷媒との間で熱交換を行う室外熱交換器であり、３は室内に吹き出す室内空気と冷媒との間で熱交換を行う室内熱交換器である。
【００１４】
そして、この室内熱交換器３と室外熱交換器２との間には、冷媒を減圧する減圧器４が設けられている。なお、減圧器４は、特願平８−３３９６２号出願に記載されている圧力制御弁と同様なものであるので、本明細書では、減圧器４の詳細説明は省略する。
また、圧縮機１の吸入側には、冷媒を気相冷媒と液相冷媒とに分離するとともに、気相冷媒を圧縮機１の吸入側に向けて流出させるアキュムレータ（気液分離手段）５が設けられている。そして、６は、アキュムレータ５と圧縮機１との間に存在する冷媒と、室外熱交換器２と減圧器４との間に存在する冷媒とを熱交換する内部熱交換器であり、７は、圧縮機１から吐出する冷媒を室外熱交換器２に向けて流通させる場合と、室内熱交換器３に向けて流通させる場合とを切り換える切換弁（四方弁）である。
【００１５】
なお、内部熱交換器６は、アキュムレータ５から圧縮機１の吸入側に向かって流通する冷媒が流通する第１冷媒通路６ａ、及び第１冷媒通路６ａに隣接する冷媒通路６ｂを有するように二重円筒状に構成されている。このため、第１冷媒通路６ａを流通する冷媒（アキュムレータ５と圧縮機１との間に存在する冷媒）と、第２冷媒通路６ｂを流通する冷媒との間で熱交換が行われる。
【００１６】
因みに、８は室内熱交換器に向けて空気を送風する室内送風機であり、９は室外熱交換器２に向けて空気を送風する室外送風機であり、両送風機８、９及び切換弁７は、電子制御装置（図示せず）により制御される。
次に、本実施形態に係るヒートポンプサイクルの作動について述べる。
１．冷房運転時（図１参照）
圧縮機１から吐出する冷媒が室外熱交換器２に向けて流通するように、切換弁７を作動させる。
【００１７】
これにより、圧縮機１から吐出した冷媒は、切換弁７、室外熱交換器２、内部熱交換器６、減圧器４、室内熱交換器３、切換弁７、アキュムレータ５及び内部熱交換器６の順にこれらの機器を経由して圧縮機１に吸入されて、再び室外熱交換器２に向けて吐出される。したがって、室内熱交換器３にて室内空気から蒸発潜熱を奪って冷媒が蒸発して室内空気を冷却し、その室内空気から奪った熱は、室外熱交換器２にて室外空気中に放熱される。
【００１８】
このとき、内部熱交換器６にて減圧器４で減圧される前の高圧冷媒と、圧縮機１に吸入される低圧冷媒とが熱交換されるため、図２のＡ−Ｂ−Ｃ−Ｄに示すように、室内熱交換器３の入口側における冷媒の比エンタルピが、内部熱交換器６にて熱交換を行わない場合に比べて、δＱだけ小さくなる。したがって、室内熱交換器３の入口と出口との比エンタルピ差が、内部熱交換器６にて熱交換を行わない場合に比べて、δＱだけ大きくなるので、冷凍能力及び効率（成績係数）が向上する。因みに、図２のａ−ｂ−ｃ−ｄは、内部熱交換器６を有していない場合のサイクルの挙動を示す線図である。
【００１９】
また、圧縮機１の吸入側にアキュムレータ５が設けられているため、圧縮機１に液相冷媒が吸入されることが防止される。
なお、減圧器４の開度は、特願平８−３３９６２号出願に記載のごとく、ヒートポンプサイクル（冷凍サイクル）の成績係数が最大となるように、室外熱交換器２の出口側の冷媒温度に基づいて調節される。
【００２０】
２．暖房運転時（図３参照）
圧縮機１から吐出する冷媒が室内熱交換器３に向けて流通するように、切換弁７を作動させる。
これにより、圧縮機１から吐出した冷媒は、切換弁７、室内熱交換器３、減圧器４、内部熱交換器６、室外室内熱交換器２、切換弁７、アキュムレータ５及び内部熱交換器６の順にこれらの機器を経由して圧縮機１に吸入されて、再び室内熱交換器３に向けて吐出される。したがって、室外熱交換器２にて室外空気から蒸発潜熱を吸熱して冷媒が蒸発し、その室外空気から吸熱した熱は、室内熱交換器３にて室内空気中に放熱される。
【００２１】
このとき、減圧器４で減圧された後の冷媒は、図４のｄ−ａに示すように、温度及び圧力が一定で相変化するので、内部熱交換器６の両冷媒通路６ａ、６ｂを流通する冷媒の温度及び圧力が等しくなる。したがって、減圧器４から流出した冷媒とアキュムレータ５から流出した冷媒との間で実質的に熱交換が行われないので、減圧器４で減圧される前の高圧冷媒と、圧縮機１に吸入される低圧冷媒との間で熱交換が行われない。
【００２２】
なお、減圧器４の開度は、冷房運転時と同様に、ヒートポンプサイクルの成績係数が最大となるように、室内熱交換器３の出口側の冷媒温度に基づいて調節される。
次に、本実施形態の特徴を述べる。
本実施形態によれば、暖房運転時には、内部熱交換器６で熱交換が行われず、減圧器４で減圧される前の高圧冷媒と、圧縮機１に吸入される低圧冷媒とが熱交換されないので、圧縮機１から吐出する高圧冷媒の温度が過度に上昇することを防止できる。
【００２３】
したがって、高圧冷媒の温度が冷媒中に混合された潤滑油の耐熱温度を越えてしまうことを防止できるので、冷媒中に混合された潤滑油が分解又は変性してしまうことを防止でき、圧縮機１が損傷することを防止できる。
（第２実施形態）
本実施形態は、冷房運転及び暖房運転に加えて、除湿運転ができるようにしたものである。
【００２４】
すなわち、本実施形態では、図５に示すように、室内熱交換器３（以下、この室内熱交換器を第１室内熱交換器３と呼ぶ。）より空気流れ下流側に、室内に吹き出す室内空気と冷媒との間で熱交換を行う第２室内熱交換器１０を設けるとともに、第２室内熱交換器１０と室外熱交換器２とを結ぶ冷媒通路に冷媒を減圧する第２減圧器１１を設ける。なお、以下、減圧器４を第１減圧器４と呼ぶ。
【００２５】
因みに、１２は冷媒が一方向にのみ流通する（本実施形態では、室外熱交換器２に向けてのみ流通する）ことを許容する逆止弁であり、１３は冷媒通路を開閉する電磁弁である。
また、本実施形態に係る切換弁７は、圧縮機１から吐出する冷媒を室外熱交換器２に向けて流通させる場合と、第２室内熱交換器１０に向けて流通させる場合とを切り換える。
【００２６】
次に、本実施形態の作動を述べる。
１．冷房運転時（図５参照）
圧縮機１から吐出する冷媒が室外熱交換器２に向けて流通するように、切換弁７を作動させるとともに、電磁弁１３を閉じる。
これにより、圧縮機１から吐出した冷媒は、切換弁７、室外熱交換器２、内部熱交換器６、第１減圧器４、第１室内室内熱交換器３、アキュムレータ５及び内部熱交換器６の順にこれらの機器を経由して圧縮機１に吸入されて、再び室外熱交換器２に向けて吐出される。したがって、第１室内熱交換器３にて室内空気から蒸発潜熱を奪って冷媒が蒸発して室内空気を冷却し、その室内空気から奪った熱は、室外熱交換器２にて室外空気中に放熱されるとともに、内部熱交換器６で高圧冷媒と低圧冷媒が熱交換される。
【００２７】
２．暖房運転時（図６参照）
圧縮機１から吐出する冷媒が第２室内熱交換器１０に向けて流通するように、切換弁７を作動させ、かつ、第１減圧器４を全閉とするとともに、電磁弁１０を開く。
これにより、圧縮機１から吐出した冷媒は、切換弁７、第２室内熱交換器１０、第２減圧器１１、室外熱交換器２、内部熱交換器６、アキュムレータ５及び内部熱交換器６の順にこれらの機器を経由して圧縮機１に吸入されて、再び第２室内熱交換器１０に向けて吐出される。なお、冷媒の減圧は、第２減圧器１１にて行う。
【００２８】
したがって、室外熱交換器２にて室外空気から蒸発潜熱を吸熱して冷媒が蒸発し、その室外空気から吸熱した熱は、第２室内熱交換器１０にて室内空気中に放熱される。
また、内部熱交換器６には、第２減圧器１１にて減圧された冷媒が流入するので、内部熱交換器６では、実質的に熱交換は行われない。
【００２９】
３．第１除湿運転時（図７参照）
圧縮機１から吐出する冷媒が第２室内熱交換器１０に向けて流通するように、切換弁７を作動させ、かつ、第２減圧弁１１を全開とするとともに、電磁弁１３を閉じる。
これにより、圧縮機１から吐出した冷媒は、切換弁７、第２室内熱交換器１０、第２減圧器１１、室外熱交換器２、内部熱交換器６、第１減圧器４、第１室内熱交換器３、アキュムレータ５及び内部熱交換器６の順にこれらの機器を経由して圧縮機１に吸入されて、再び第２室内熱交換器１０に向けて吐出される。なお、冷媒の減圧は、第１減圧器４にて行う。
【００３０】
したがって、第１室内熱交換器３にて室内空気から蒸発潜熱を奪って冷媒が蒸発して室内空気を冷却する。そして、その室内空気から奪った熱の一部は、第２室内熱交換器１０にて室内空気中に放熱され、その他の熱は室外熱交換器２にて室外空気中に放熱される。
なお、この第１除湿運転では、内部熱交換器６にて高圧冷媒と低圧冷媒との間で熱交換が行われ、圧縮機１に吸入される冷媒が加熱されるが、高圧冷媒は、既に２つに熱交換器（第２室内熱交換器１０及び室外熱交換器２）で放熱していることに加えて、第１除湿運転では大きな暖房能力を必要とせず、高圧冷媒の圧力が暖房運転時ほど高くないので、圧縮機１に吸入される冷媒の温度は大きく上昇しない。したがって、高圧冷媒の温度が、潤滑油の耐熱温度以上まで上昇することはない。
【００３１】
４．第２除湿運転時（図８参照）
圧縮機１から吐出する冷媒が第２室内熱交換器１０に向けて流通するように、切換弁７を作動させ、かつ、第１減圧器４を全開とするとともに、電磁弁１３を閉じる。
これにより、圧縮機１から吐出した冷媒は、切換弁７、第２室内熱交換器１０、第２減圧器１１、室外熱交換器２、内部熱交換器６、第１減圧器４、第１室内熱交換器３、アキュムレータ５及び内部熱交換器６の順にこれらの機器を経由して圧縮機１に吸入されて、再び第２室内熱交換器１０に向けて吐出される。なお、冷媒の減圧は、第２減圧器１１にて行う。
【００３２】
したがって、第１室内熱交換器３にて室内空気から蒸発潜熱を奪って冷媒が蒸発して室内空気を冷却する。さらに、室外熱交換器２にて室外空気から熱を吸熱し、第２室内熱交換器１０にてその吸熱した熱が室内空気に向けて放熱される。また、内部熱交換器６には、第２減圧器１１にて減圧された冷媒が流入するので、内部熱交換器６では、実質的に熱交換は行われない。
【００３３】
（第３実施形態）
第２実施形態では、第１、２除湿運転時のみ両室内熱交換器３、１０を利用したが、本実施形態は、図９に示すように、第２減圧器１１を第１、２室内熱交換器３、１０を結ぶ冷媒通路に設けて冷房運転時及び暖房運転時においても両室内熱交換器３、１０を利用するようにしたものである。
【００３４】
以下、本実施形態の作動を述べる。
１．冷房運転時（図９参照）
圧縮機１から吐出する冷媒が室外熱交換器２に向けて流通するように、切換弁７を作動させるとともに、第２減圧器１１を全開とする。
これにより、圧縮機１から吐出した冷媒は、切換弁７、室外熱交換器２、内部熱交換器６、第１減圧器４、第１室内熱交換器３、第２減圧器１１、第２室内熱交換器１０、切換弁７、アキュムレータ５及び内部熱交換器６の順にこれらの機器を経由して圧縮機１に吸入されて、再び室外熱交換器２に向けて吐出される。なお、冷媒の減圧は、第１減圧器４にて行われる。
【００３５】
したがって、第１、２室内熱交換器３、１０にて室内空気から蒸発潜熱を奪って冷媒が蒸発して室内空気を冷却し、その室内空気から奪った熱は、室外熱交換器２にて室外空気中に放熱されるとともに、内部熱交換器６で高圧冷媒と低圧冷媒とが熱交換される。
２．暖房運転時（図１０参照）
圧縮機１から吐出する冷媒が第２室内熱交換器１０に向けて流通するように、切換弁７を作動させ、かつ、第２減圧器１１を全閉とする。
【００３６】
これにより、圧縮機１から吐出した冷媒は、切換弁７、第２室内熱交換器１０、第２減圧器１１、第１室内熱交換器３、第１減圧器４、内部熱交換器６、室外熱交換器２、切換弁７、アキュムレータ５及び内部熱交換器６の順にこれらの機器を経由して圧縮機１に吸入されて、再び第２室内熱交換器１０に向けて吐出される。なお、冷媒の減圧は、第１減圧器４にて行う。
【００３７】
したがって、室外熱交換器２にて室外空気から蒸発潜熱を吸熱して冷媒が蒸発し、その室外空気から吸熱した熱は、第１、２室内熱交換器３、１０にて室内空気中に放熱される。
また、内部熱交換器６には、第１減圧器４にて減圧された冷媒が流入するので、内部熱交換器６では、実質的に熱交換は行われない。
【００３８】
３．除湿運転時（図１１参照）
圧縮機１から吐出する冷媒が第２室内熱交換器１０に向けて流通するように、切換弁７を作動させ、かつ、第１減圧器４を全開とする。
これにより、圧縮機１から吐出した冷媒は、切換弁７、第２室内熱交換器１０、第２減圧器１１、第１室内熱交換器３、第１減圧器４、内部熱交換器６、室外熱交換器２、切換弁７、アキュムレータ５及び内部熱交換器６の順にこれらの機器を経由して圧縮機１に吸入されて、再び室内熱交換器３に向けて吐出される。なお、冷媒の減圧は、第２減圧器１１にて行う。
【００３９】
したがって、第１室内熱交換器３及び室外熱交換器２にて空気から蒸発潜熱を吸熱して冷媒が蒸発するとともに、その吸熱された熱は、第２室内熱交換器１０にて室内空気中に放熱される。
因みに、室外空気の温度が冷媒温度より低い場合には、室外熱交換器２では吸熱は行われず、冷媒の熱は外気中に放熱される。
【００４０】
ところで、上述の実施形態では、空調装置を例に本発明に係るヒートポンプサイクルを説明したが、本発明はこれに限定されるものではなく、その他のヒートポンプサイクルにも適用することができる。
また、上述の実施形態では、二酸化炭素を冷媒とするヒートポンプサイクルであったが、本発明はこれに限定されるものではなく、例えば、エチレン、エタン、酸化窒素等の超臨界域で使用する冷媒を用いるヒートポンプサイクルにも適用することができる。
【図面の簡単な説明】
【図１】第１実施形態に係るヒートポンプサイクルの模式図である。
【図２】冷房運転時におけるヒートポンプサイクルのサイクル線図である。
【図３】第１実施形態に係るヒートポンプサイクルの模式図である。
【図４】暖房運転時におけるヒートポンプサイクルのサイクル線図である。
【図５】冷房運転時における第２実施形態に係るヒートポンプサイクルの模式図である。
【図６】暖房運転時における第２実施形態に係るヒートポンプサイクルの模式図である。
【図７】第１除湿運転時における第２実施形態に係るヒートポンプサイクルの模式図である。
【図８】第２除湿運転時における第２実施形態に係るヒートポンプサイクルの模式図である。
【図９】冷房運転時における第３実施形態に係るヒートポンプサイクルの模式図である。
【図１０】暖房運転時における第２実施形態に係るヒートポンプサイクルの模式図である。
【図１１】除湿運転時における第２実施形態に係るヒートポンプサイクルの模式図である。
【図１２】蒸発器内飽和温度と吐出温度との関係を示すグラフである。
【符号の説明】
１…圧縮機、２…室外熱交換器、３…室内熱交換器、４…減圧器、
５…アキュムレータ、６…内部熱交換器、７…切換弁。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat pump cycle using a supercritical refrigeration cycle in which the pressure of the high-pressure refrigerant (compressor discharge pressure) is equal to or higher than the critical pressure of the refrigerant, and is effective when applied to an air conditioner.
[0002]
[Prior art]
In recent years, a refrigeration cycle using carbon dioxide (CO ₂ ) (hereinafter, referred to as a CO ₂ cycle) has been proposed as one of countermeasures against de-fluorocarbons in the refrigeration cycle, for example, as described in Japanese Patent Publication No. 7-18602. ing.
In this CO ₂ cycle, the critical temperature of CO ₂ is about 31 ° C, which is lower than the critical temperature of Freon, so the refrigerant pressure (discharge pressure) on the radiator side is critical when large refrigeration capacity is required such as in summer. It is necessary to operate the refrigeration cycle at a pressure higher than the pressure (compressed).
[0003]
Therefore, in the invention described in the above publication, in order to improve the efficiency and refrigeration capacity of the refrigeration cycle, and to prevent the liquid-phase refrigerant from being sucked into the compressor, the high-pressure refrigerant and the compressor that have come out of the radiator are used. An internal heat exchanger that exchanges heat with the low-pressure refrigerant that is sucked is provided.
[0004]
[Problems to be solved by the invention]
However, if an internal heat exchanger is installed to exchange heat between the high-pressure refrigerant and the low-pressure refrigerant, the temperature of the low-pressure refrigerant sucked into the compressor increases, so the temperature of the high-pressure refrigerant discharged from the compressor also increases. Resulting in. For this reason, when the CO ₂ cycle described in the above publication is applied to a heat pump cycle capable of simply cooling and heating, the following problems occur.
[0005]
That is, in addition to heating the low-pressure refrigerant in the internal heat exchanger, when the heating operation is performed when the outside air temperature is low such as in winter, the pressure of the low-pressure refrigerant becomes lower than that in the cooling operation, and the compression ratio ( Since the ratio between the suction pressure and the discharge pressure becomes larger than that during the cooling operation, the temperature of the high-pressure refrigerant discharged from the compressor becomes higher than that during the cooling operation.
For this reason, since the temperature of the high-pressure refrigerant exceeds the heat resistance temperature of the lubricating oil (refrigeration machine oil) mixed in the refrigerant, the lubricating oil mixed in the refrigerant is decomposed or denatured, and the compressor is damaged. The problem of end up occurs.
[0006]
Incidentally, FIG. 12 shows that HFC134a (Freon) has a high-pressure refrigerant pressure of 15 kgf / cm ² abs, and CO ₂ has a compressor efficiency of 1 when the pressure of the high-pressure refrigerant is 90 kgf / cm ² abs. 6 is a graph showing a refrigerant temperature discharged from a refrigeration cycle using HFC134a as a refrigerant (temperature of a high-pressure refrigerant) and a refrigerant temperature discharged from CO ₂ cycle discharge temperature (temperature of a high-pressure refrigerant) with respect to the saturation temperature of the evaporator.
[0007]
As is clear from FIG. 12, the saturation temperature of the evaporator, that is, the temperature of the high-pressure refrigerant increases as the pressure of the low-pressure refrigerant decreases. Therefore, when the internal heat exchanger is provided during heating operation, the temperature of the discharged refrigerant is increased. It turns out that it rises further.
In view of the above points, an object of the present invention is to prevent the compressor from being damaged during heating operation in a heat pump cycle in which the discharge pressure of the compressor is equal to or higher than the critical pressure of the refrigerant.
[0008]
[Means for Solving the Problems]
To achieve the above object, the invention described in claim 1, a cooling and heating switchable heat pump cycle using carbon dioxide as a refrigerant,
A compressor (1) that sucks the refrigerant and compresses the sucked refrigerant to a critical pressure or higher;
An outdoor heat exchanger (2) for exchanging heat between the outdoor air and the refrigerant;
An indoor heat exchanger (3) for exchanging heat between the indoor air blown into the room and the refrigerant;
A decompressor (4) that is provided in a refrigerant passage connecting the indoor heat exchanger (3) and the outdoor heat exchanger (2), and depressurizes the refrigerant;
An accumulator (5) that is provided on the suction side of the compressor (1), separates the refrigerant into a gas phase refrigerant and a liquid phase refrigerant, and causes the gas phase refrigerant to flow out toward the suction side of the compressor (1). When,
A first refrigerant passage (6a) through which refrigerant flows from the accumulator (5) toward the suction side of the compressor (1), and a second refrigerant passage (6b) adjacent to the first refrigerant passage (6a). And an internal heat exchanger (6) for exchanging heat between the refrigerant passages (6a, 6b),
During the cooling operation, the outdoor heat exchanger (2) is on the heat radiation side of the high-pressure refrigerant and the indoor heat exchanger (3) is on the heat absorption side of the low-pressure refrigerant. On the other hand, during the heating operation, the indoor heat exchanger (3 And a switching valve (7) for switching the refrigerant flow so that the outdoor heat exchanger (2) is on the heat absorption side of the low pressure refrigerant
When the heating operation is performed when the outside air temperature is low, the pressure of the low-pressure refrigerant during the heating operation is lower than during the cooling operation, and the compression ratio during the heating operation is greater than during the cooling operation, This is a supercritical refrigeration cycle in which the temperature of the high-pressure refrigerant discharged from the compressor (1) during the heating operation is higher than during the cooling operation,
During the cooling operation, the high-pressure refrigerant before being decompressed by the decompressor (4) is circulated through the second refrigerant passage (6b), and during the heating operation, the decompressor is disposed in the second refrigerant passage (6b). by circulating a low-pressure refrigerant after being decompressed by (4), and so as not to heat exchange with said low-pressure refrigerant and the high-pressure refrigerant in the internal heat exchanger (6),
During the heating operation, the temperature of the high-pressure refrigerant is maintained in a temperature range that does not exceed the heat resistance temperature of the lubricating oil mixed in the refrigerant .
[0009]
As a result, in the heat pump cycle composed of a supercritical refrigeration cycle using carbon dioxide as the refrigerant, the temperature and pressure of the refrigerant flowing through both refrigerant passages (6a, 6b) are equal during heating operation. Is not heat exchanged. Accordingly, it is possible to prevent the temperature of the high-pressure refrigerant discharged from the compressor (1) from excessively rising during the heating operation at the low outside air temperature, so that the temperature of the high-pressure refrigerant is set to the heat resistant temperature of the lubricating oil mixed in the refrigerant. It can be prevented from exceeding. Accordingly, it is possible to prevent the lubricating oil mixed in the refrigerant from being decomposed or denatured and to prevent the compressor (1) from being damaged .
[0011]
Incidentally, the reference numerals in parentheses of each means described above are an example showing the correspondence with the specific means described in the embodiments described later.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
In the present embodiment, the heat pump cycle according to the present invention is applied to an air conditioner using a heat pump cycle using carbon dioxide as a refrigerant, and FIG. 1 is a schematic diagram of the heat pump cycle according to the present embodiment.
[0013]
In FIG. 1, reference numeral 1 denotes a compressor that sucks refrigerant (CO ₂ ) and compresses the sucked refrigerant to a critical pressure or higher of the refrigerant. The compressor 1 compresses by sucking lubricating oil together with the refrigerant. Lubrication inside the machine 1 is intended. 2 is an outdoor heat exchanger that exchanges heat between the outdoor air and the refrigerant, and 3 is an indoor heat exchanger that exchanges heat between the indoor air blown into the room and the refrigerant.
[0014]
And between this indoor heat exchanger 3 and the outdoor heat exchanger 2, the decompressor 4 which decompresses a refrigerant | coolant is provided. The decompressor 4 is the same as the pressure control valve described in Japanese Patent Application No. 8-33962, and therefore, detailed description of the decompressor 4 is omitted in this specification.
On the suction side of the compressor 1, an accumulator (gas-liquid separation means) 5 that separates the refrigerant into a gas phase refrigerant and a liquid phase refrigerant and causes the gas phase refrigerant to flow out toward the suction side of the compressor 1. Is provided. Reference numeral 6 denotes an internal heat exchanger for exchanging heat between the refrigerant existing between the accumulator 5 and the compressor 1 and the refrigerant existing between the outdoor heat exchanger 2 and the decompressor 4. The switching valve (four-way valve) switches between a case where the refrigerant discharged from the compressor 1 is circulated toward the outdoor heat exchanger 2 and a case where the refrigerant is circulated toward the indoor heat exchanger 3.
[0015]
The internal heat exchanger 6 includes a first refrigerant passage 6a through which refrigerant flowing from the accumulator 5 toward the suction side of the compressor 1 flows, and a refrigerant passage 6b adjacent to the first refrigerant passage 6a. It is composed of a heavy cylinder. For this reason, heat exchange is performed between the refrigerant flowing through the first refrigerant passage 6a (the refrigerant existing between the accumulator 5 and the compressor 1) and the refrigerant flowing through the second refrigerant passage 6b.
[0016]
Incidentally, 8 is an indoor blower that blows air toward the indoor heat exchanger, 9 is an outdoor blower that blows air toward the outdoor heat exchanger 2, and both the blowers 8, 9 and the switching valve 7 are: It is controlled by an electronic control device (not shown).
Next, the operation of the heat pump cycle according to this embodiment will be described.
1. During cooling operation (see Fig. 1)
The switching valve 7 is operated so that the refrigerant discharged from the compressor 1 flows toward the outdoor heat exchanger 2.
[0017]
Thereby, the refrigerant discharged from the compressor 1 is changed over to the switching valve 7, the outdoor heat exchanger 2, the internal heat exchanger 6, the decompressor 4, the indoor heat exchanger 3, the switching valve 7, the accumulator 5, and the internal heat exchanger 6. In this order, the air is sucked into the compressor 1 through these devices and discharged again toward the outdoor heat exchanger 2. Accordingly, the indoor heat exchanger 3 takes away latent heat of evaporation from the indoor air, the refrigerant evaporates to cool the indoor air, and the heat taken away from the indoor air is radiated into the outdoor air by the outdoor heat exchanger 2. The
[0018]
At this time, since the high-pressure refrigerant before being decompressed by the decompressor 4 in the internal heat exchanger 6 and the low-pressure refrigerant sucked into the compressor 1 are heat-exchanged, ABCD in FIG. As shown in FIG. 5, the specific enthalpy of the refrigerant on the inlet side of the indoor heat exchanger 3 is reduced by δQ as compared with the case where heat exchange is not performed in the internal heat exchanger 6. Therefore, the specific enthalpy difference between the inlet and outlet of the indoor heat exchanger 3 is increased by δQ compared to the case where heat exchange is not performed in the internal heat exchanger 6, so that the refrigerating capacity and efficiency (coefficient of performance) are increased. improves. Incidentally, abcd in FIG. 2 is a diagram showing the cycle behavior when the internal heat exchanger 6 is not provided.
[0019]
Further, since the accumulator 5 is provided on the suction side of the compressor 1, the liquid phase refrigerant is prevented from being sucked into the compressor 1.
In addition, the opening degree of the decompressor 4 is the refrigerant temperature at the outlet side of the outdoor heat exchanger 2 so that the coefficient of performance of the heat pump cycle (refrigeration cycle) is maximized as described in Japanese Patent Application No. 8-33962. Adjusted based on.
[0020]
2. During heating operation (see Fig. 3)
The switching valve 7 is operated so that the refrigerant discharged from the compressor 1 flows toward the indoor heat exchanger 3.
Thereby, the refrigerant discharged from the compressor 1 is changed over to the switching valve 7, the indoor heat exchanger 3, the decompressor 4, the internal heat exchanger 6, the outdoor indoor heat exchanger 2, the switching valve 7, the accumulator 5, and the internal heat exchanger. The air is sucked into the compressor 1 via these devices in the order of 6 and discharged again toward the indoor heat exchanger 3. Therefore, the refrigerant evaporates by absorbing the latent heat of evaporation from the outdoor air in the outdoor heat exchanger 2, and the heat absorbed from the outdoor air is radiated into the indoor air by the indoor heat exchanger 3.
[0021]
At this time, the refrigerant after being decompressed by the decompressor 4 changes its phase at a constant temperature and pressure, as shown by da in FIG. 4, so that both the refrigerant passages 6 a and 6 b of the internal heat exchanger 6 are passed through. The temperature and pressure of the circulating refrigerant become equal. Therefore, heat exchange is not substantially performed between the refrigerant flowing out from the decompressor 4 and the refrigerant flowing out from the accumulator 5, so that the high-pressure refrigerant before being decompressed by the decompressor 4 and the compressor 1 are sucked into the compressor 1. Heat exchange with the low-pressure refrigerant is not performed.
[0022]
Note that the opening of the decompressor 4 is adjusted based on the refrigerant temperature on the outlet side of the indoor heat exchanger 3 so that the coefficient of performance of the heat pump cycle is maximized, as in the cooling operation.
Next, features of the present embodiment will be described.
According to the present embodiment, during the heating operation, heat exchange is not performed in the internal heat exchanger 6, and heat exchange between the high-pressure refrigerant before being decompressed by the decompressor 4 and the low-pressure refrigerant sucked into the compressor 1 is not performed. Therefore, it is possible to prevent the temperature of the high-pressure refrigerant discharged from the compressor 1 from rising excessively.
[0023]
Therefore, the temperature of the high-pressure refrigerant can be prevented from exceeding the heat resistance temperature of the lubricating oil mixed in the refrigerant, so that the lubricating oil mixed in the refrigerant can be prevented from being decomposed or denatured. 1 can be prevented from being damaged.
(Second Embodiment)
In this embodiment, in addition to the cooling operation and the heating operation, a dehumidifying operation can be performed.
[0024]
That is, in this embodiment, as shown in FIG. 5, the indoor air blown into the room on the downstream side of the air flow from the indoor heat exchanger 3 (hereinafter, this indoor heat exchanger is referred to as the first indoor heat exchanger 3). The second indoor heat exchanger 10 that exchanges heat between the air and the refrigerant is provided, and the second decompressor 11 that decompresses the refrigerant in the refrigerant passage that connects the second indoor heat exchanger 10 and the outdoor heat exchanger 2. Is provided. Hereinafter, the decompressor 4 is referred to as a first decompressor 4.
[0025]
Incidentally, 12 is a check valve that allows the refrigerant to flow only in one direction (in this embodiment, only flows toward the outdoor heat exchanger 2), and 13 is an electromagnetic valve that opens and closes the refrigerant passage. is there.
Further, the switching valve 7 according to the present embodiment switches between a case where the refrigerant discharged from the compressor 1 is circulated toward the outdoor heat exchanger 2 and a case where the refrigerant is circulated toward the second indoor heat exchanger 10.
[0026]
Next, the operation of this embodiment will be described.
1. During cooling operation (see Fig. 5)
The switching valve 7 is operated and the electromagnetic valve 13 is closed so that the refrigerant discharged from the compressor 1 flows toward the outdoor heat exchanger 2.
Thereby, the refrigerant discharged from the compressor 1 is changed over to the switching valve 7, the outdoor heat exchanger 2, the internal heat exchanger 6, the first decompressor 4, the first indoor indoor heat exchanger 3, the accumulator 5, and the internal heat exchanger. The air is sucked into the compressor 1 via these devices in the order of 6 and discharged again toward the outdoor heat exchanger 2. Therefore, the first indoor heat exchanger 3 takes away latent heat of evaporation from the indoor air, the refrigerant evaporates to cool the indoor air, and the heat taken from the indoor air is transferred into the outdoor air by the outdoor heat exchanger 2. While radiating heat, the internal heat exchanger 6 exchanges heat between the high-pressure refrigerant and the low-pressure refrigerant.
[0027]
2. During heating operation (see Fig. 6)
The switching valve 7 is operated so that the refrigerant discharged from the compressor 1 flows toward the second indoor heat exchanger 10, the first decompressor 4 is fully closed, and the electromagnetic valve 10 is opened.
Thereby, the refrigerant discharged from the compressor 1 is changed over to the switching valve 7, the second indoor heat exchanger 10, the second decompressor 11, the outdoor heat exchanger 2, the internal heat exchanger 6, the accumulator 5, and the internal heat exchanger 6. In this order, the air is sucked into the compressor 1 via these devices and discharged again toward the second indoor heat exchanger 10. The refrigerant is decompressed by the second decompressor 11.
[0028]
Therefore, the refrigerant evaporates by absorbing the latent heat of evaporation from the outdoor air in the outdoor heat exchanger 2, and the heat absorbed from the outdoor air is radiated into the indoor air by the second indoor heat exchanger 10.
Moreover, since the refrigerant decompressed by the second decompressor 11 flows into the internal heat exchanger 6, the internal heat exchanger 6 does not substantially perform heat exchange.
[0029]
3. During the first dehumidifying operation (see FIG. 7)
The switching valve 7 is operated so that the refrigerant discharged from the compressor 1 flows toward the second indoor heat exchanger 10, the second pressure reducing valve 11 is fully opened, and the electromagnetic valve 13 is closed.
Thereby, the refrigerant discharged from the compressor 1 is changed over to the switching valve 7, the second indoor heat exchanger 10, the second decompressor 11, the outdoor heat exchanger 2, the internal heat exchanger 6, the first decompressor 4, and the first. The indoor heat exchanger 3, the accumulator 5, and the internal heat exchanger 6 are sucked into the compressor 1 through these devices in this order, and discharged again toward the second indoor heat exchanger 10. Note that the decompression of the refrigerant is performed by the first decompressor 4.
[0030]
Therefore, the first indoor heat exchanger 3 takes away latent heat of evaporation from the room air, and the refrigerant evaporates to cool the room air. A part of the heat taken from the indoor air is radiated into the indoor air by the second indoor heat exchanger 10, and the other heat is radiated into the outdoor air by the outdoor heat exchanger 2.
In the first dehumidifying operation, heat exchange is performed between the high-pressure refrigerant and the low-pressure refrigerant in the internal heat exchanger 6 and the refrigerant sucked into the compressor 1 is heated. In addition to radiating heat to the two heat exchangers (the second indoor heat exchanger 10 and the outdoor heat exchanger 2), the first dehumidifying operation does not require a large heating capacity, and the pressure of the high-pressure refrigerant is heated. Since the temperature is not as high as during operation, the temperature of the refrigerant sucked into the compressor 1 does not increase greatly. Therefore, the temperature of the high-pressure refrigerant does not rise above the heat resistance temperature of the lubricating oil.
[0031]
4). During the second dehumidifying operation (see FIG. 8)
The switching valve 7 is operated so that the refrigerant discharged from the compressor 1 flows toward the second indoor heat exchanger 10, the first decompressor 4 is fully opened, and the electromagnetic valve 13 is closed.
Thereby, the refrigerant discharged from the compressor 1 is changed over to the switching valve 7, the second indoor heat exchanger 10, the second decompressor 11, the outdoor heat exchanger 2, the internal heat exchanger 6, the first decompressor 4, and the first. The indoor heat exchanger 3, the accumulator 5, and the internal heat exchanger 6 are sucked into the compressor 1 through these devices in this order, and discharged again toward the second indoor heat exchanger 10. The refrigerant is decompressed by the second decompressor 11.
[0032]
Therefore, the first indoor heat exchanger 3 takes away latent heat of evaporation from the room air, and the refrigerant evaporates to cool the room air. Furthermore, the outdoor heat exchanger 2 absorbs heat from the outdoor air, and the heat absorbed by the second indoor heat exchanger 10 is radiated toward the indoor air. Moreover, since the refrigerant decompressed by the second decompressor 11 flows into the internal heat exchanger 6, the internal heat exchanger 6 does not substantially perform heat exchange.
[0033]
(Third embodiment)
In the second embodiment, the two indoor heat exchangers 3 and 10 are used only during the first and second dehumidifying operations. However, in the present embodiment, as shown in FIG. The heat exchangers 3 and 10 are provided in a refrigerant passage connecting the heat exchangers 3 and 10 so that the indoor heat exchangers 3 and 10 are used even during the cooling operation and the heating operation.
[0034]
The operation of this embodiment will be described below.
1. During cooling operation (see Fig. 9)
The switching valve 7 is operated so that the refrigerant discharged from the compressor 1 flows toward the outdoor heat exchanger 2, and the second decompressor 11 is fully opened.
Thereby, the refrigerant discharged from the compressor 1 is changed over to the switching valve 7, the outdoor heat exchanger 2, the internal heat exchanger 6, the first decompressor 4, the first indoor heat exchanger 3, the second decompressor 11, and the second. The indoor heat exchanger 10, the switching valve 7, the accumulator 5, and the internal heat exchanger 6 are sequentially sucked into the compressor 1 through these devices, and discharged again toward the outdoor heat exchanger 2. Note that the decompression of the refrigerant is performed by the first decompressor 4.
[0035]
Accordingly, the first and second indoor heat exchangers 3 and 10 take away the latent heat of evaporation from the indoor air, the refrigerant evaporates to cool the indoor air, and the heat taken from the indoor air is transferred to the outdoor heat exchanger 2. While being radiated into the outdoor air, the internal heat exchanger 6 exchanges heat between the high-pressure refrigerant and the low-pressure refrigerant.
2. During heating operation (see Fig. 10)
The switching valve 7 is operated so that the refrigerant discharged from the compressor 1 flows toward the second indoor heat exchanger 10, and the second decompressor 11 is fully closed.
[0036]
Thereby, the refrigerant discharged from the compressor 1 is changed over to the switching valve 7, the second indoor heat exchanger 10, the second decompressor 11, the first indoor heat exchanger 3, the first decompressor 4, the internal heat exchanger 6, The outdoor heat exchanger 2, the switching valve 7, the accumulator 5, and the internal heat exchanger 6 are sucked into the compressor 1 through these devices in this order, and discharged again toward the second indoor heat exchanger 10. Note that the decompression of the refrigerant is performed by the first decompressor 4.
[0037]
Therefore, the refrigerant evaporates by absorbing the latent heat of evaporation from the outdoor air in the outdoor heat exchanger 2, and the heat absorbed from the outdoor air is radiated into the indoor air by the first and second indoor heat exchangers 3 and 10. Is done.
Further, since the refrigerant depressurized by the first pressure reducer 4 flows into the internal heat exchanger 6, the internal heat exchanger 6 does not substantially perform heat exchange.
[0038]
3. During dehumidifying operation (see Fig. 11)
The switching valve 7 is operated and the first decompressor 4 is fully opened so that the refrigerant discharged from the compressor 1 flows toward the second indoor heat exchanger 10.
Thereby, the refrigerant discharged from the compressor 1 is changed over to the switching valve 7, the second indoor heat exchanger 10, the second decompressor 11, the first indoor heat exchanger 3, the first decompressor 4, the internal heat exchanger 6, The outdoor heat exchanger 2, the switching valve 7, the accumulator 5, and the internal heat exchanger 6 are sucked into the compressor 1 via these devices in this order, and discharged again toward the indoor heat exchanger 3. The refrigerant is decompressed by the second decompressor 11.
[0039]
Therefore, the first indoor heat exchanger 3 and the outdoor heat exchanger 2 absorb the latent heat of vaporization from the air to evaporate the refrigerant, and the absorbed heat is absorbed in the indoor air by the second indoor heat exchanger 10. Heat is dissipated.
Incidentally, when the temperature of the outdoor air is lower than the refrigerant temperature, the outdoor heat exchanger 2 does not absorb heat and the heat of the refrigerant is radiated into the outside air.
[0040]
By the way, in the above-mentioned embodiment, although the heat pump cycle which concerns on this invention was demonstrated to the example of the air conditioner, this invention is not limited to this, It can apply also to another heat pump cycle.
In the above-described embodiment, the heat pump cycle uses carbon dioxide as a refrigerant. However, the present invention is not limited to this. For example, a refrigerant used in a supercritical region such as ethylene, ethane, or nitrogen oxide. It can also be applied to a heat pump cycle using
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a heat pump cycle according to a first embodiment.
FIG. 2 is a cycle diagram of a heat pump cycle during cooling operation.
FIG. 3 is a schematic diagram of a heat pump cycle according to the first embodiment.
FIG. 4 is a cycle diagram of a heat pump cycle during heating operation.
FIG. 5 is a schematic diagram of a heat pump cycle according to a second embodiment during cooling operation.
FIG. 6 is a schematic diagram of a heat pump cycle according to a second embodiment during a heating operation.
FIG. 7 is a schematic diagram of a heat pump cycle according to a second embodiment during a first dehumidifying operation.
FIG. 8 is a schematic diagram of a heat pump cycle according to a second embodiment during a second dehumidifying operation.
FIG. 9 is a schematic diagram of a heat pump cycle according to a third embodiment during cooling operation.
FIG. 10 is a schematic diagram of a heat pump cycle according to a second embodiment during heating operation.
FIG. 11 is a schematic diagram of a heat pump cycle according to a second embodiment during a dehumidifying operation.
FIG. 12 is a graph showing the relationship between the saturation temperature in the evaporator and the discharge temperature.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Compressor, 2 ... Outdoor heat exchanger, 3 ... Indoor heat exchanger, 4 ... Decompressor,
5 ... Accumulator, 6 ... Internal heat exchanger, 7 ... Switching valve.

Claims

A heat pump cycle capable of switching between heating and cooling using carbon dioxide as a refrigerant ,
Sucks the refrigerant, the compressor compresses the sucked refrigerant to a critical pressure or higher of the refrigerant (1),
An outdoor heat exchanger (2) for exchanging heat between the outdoor air and the refrigerant;
An indoor heat exchanger (3) for exchanging heat between indoor air blown into the room and the refrigerant;
A decompressor (4) provided in a refrigerant passage connecting the indoor heat exchanger (3) and the outdoor heat exchanger (2), and decompressing the refrigerant;
An accumulator (5) that is provided on the suction side of the compressor (1) and separates the refrigerant into a gas phase refrigerant and a liquid phase refrigerant, and causes the gas phase refrigerant to flow out toward the suction side of the compressor (1). When,
A first refrigerant passage (6a) through which refrigerant flows from the accumulator (5) toward the suction side of the compressor (1), and a second refrigerant passage (6b) adjacent to the first refrigerant passage (6a) ) has said the two refrigerant passage (6a, 6b) internal heat exchanger for exchanging heat between (6),
In the cooling operation, the outdoor heat exchanger (2) is on the heat dissipation side of the high-pressure refrigerant and the indoor heat exchanger (3) is on the heat absorption side of the low-pressure refrigerant, whereas in the heating operation, the indoor heat exchanger (3 And a switching valve (7) for switching the refrigerant flow so that the outdoor heat exchanger (2) is on the heat absorption side of the low pressure refrigerant
When the heating operation is performed when the outside air temperature is low, the pressure of the low-pressure refrigerant during the heating operation is lower than during the cooling operation, and the compression ratio during the heating operation is greater than during the cooling operation, This is a supercritical refrigeration cycle in which the temperature of the high-pressure refrigerant discharged from the compressor (1) during the heating operation is higher than during the cooling operation,
The cooling In operation, the said pressure reducer in the second refrigerant passage (6b) (4) is passed through the high-pressure refrigerant before being decompressed by the during the heating operation, the pressure reducer in the second refrigerant passage (6b) By circulating the low-pressure refrigerant after being depressurized in (4), the high-pressure refrigerant and the low-pressure refrigerant are not exchanged in the internal heat exchanger (6),
During the heating operation , the heat pump cycle is characterized in that the temperature of the high-pressure refrigerant is maintained in a temperature range that does not exceed the heat resistance temperature of the lubricating oil mixed in the refrigerant .