JP4692002B2 - Air conditioner - Google Patents

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JP4692002B2
JP4692002B2 JP2005034000A JP2005034000A JP4692002B2 JP 4692002 B2 JP4692002 B2 JP 4692002B2 JP 2005034000 A JP2005034000 A JP 2005034000A JP 2005034000 A JP2005034000 A JP 2005034000A JP 4692002 B2 JP4692002 B2 JP 4692002B2
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refrigerant
heat exchanger
temperature
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優芽 井ノ口
道雄 森脇
克己 鉾谷
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ダイキン工業株式会社
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本発明は、冷媒として二酸化炭素を用いる空気調和装置に関するものである。   The present invention relates to an air conditioner using carbon dioxide as a refrigerant.

従来より、空気調和装置としては、冷媒回路内で冷媒を循環させて冷凍サイクルを行うものが知られている。例えば、特許文献1には、冷媒として二酸化炭素(CO)を用いて冷凍サイクルを行う装置が開示されている。この特許文献1にも記載されているように、二酸化炭素を冷媒として冷凍サイクルを行う空気調和装置では、冷房能力を確保するために冷凍サイクルの高圧を二酸化炭素の臨界圧よりも高く設定するのが通常である。つまり、冷媒として二酸化炭素を採用する空気調和装置では、圧縮機の吐出圧力が冷媒の臨界圧よりも高くなる超臨界サイクルを行うのが一般的であった。
特開2000−329416号公報
Conventionally, as an air conditioner, one that performs a refrigeration cycle by circulating a refrigerant in a refrigerant circuit is known. For example, Patent Document 1 discloses an apparatus that performs a refrigeration cycle using carbon dioxide (CO 2 ) as a refrigerant. As described in Patent Document 1, in an air conditioner that performs a refrigeration cycle using carbon dioxide as a refrigerant, the high pressure of the refrigeration cycle is set higher than the critical pressure of carbon dioxide in order to ensure cooling capacity. Is normal. That is, in an air conditioner that uses carbon dioxide as a refrigerant, a supercritical cycle in which the discharge pressure of the compressor is higher than the critical pressure of the refrigerant is generally performed.
JP 2000-329416 A

しかしながら、冷媒として二酸化炭素を採用する空気調和装置において、暖房運転中に超臨界サイクルを行うと、運転状態によっては充分な暖房能力を確保できない場合があった。この問題点について説明する。   However, in an air conditioner that uses carbon dioxide as a refrigerant, if a supercritical cycle is performed during heating operation, sufficient heating capacity may not be ensured depending on the operating state. This problem will be described.

圧縮機と膨張機が設けられた冷媒回路で冷凍サイクルを行う場合には、冷媒回路が閉回路であることから、膨張機を通過する冷媒の質量流量が圧縮機を通過する冷媒の質量流量と常に等しくなる。そして、例えば冷媒の蒸発圧力が低くなって圧縮機の吸入冷媒の密度が小さくなる運転状態では、膨張機へ流入する冷媒の密度が小さくならなければ圧縮機での冷媒流量と膨張機での冷媒流量とがバランスしない。   When performing a refrigeration cycle in a refrigerant circuit provided with a compressor and an expander, since the refrigerant circuit is a closed circuit, the mass flow rate of the refrigerant passing through the expander is equal to the mass flow rate of the refrigerant passing through the compressor. Always equal. For example, in an operating state in which the refrigerant evaporating pressure is low and the density of refrigerant sucked into the compressor is low, the refrigerant flow rate in the compressor and the refrigerant in the expander are not reduced unless the density of refrigerant flowing into the expander is low. The flow rate is not balanced.

ここで、超臨界状態では、蒸発や凝縮といった相変化がおこらない。そして、冷媒の密度が同じだけ低くなっても、それに伴う比エンタルピの増大幅は、超臨界状態の方が気液二相状態に比べて大きくなる。このため、超臨界サイクル中に膨張機へ流入する冷媒の密度が小さくなるような運転条件では、膨張機の入口における冷媒のエンタルピが高くなり過ぎてしまう。その結果、このような運転条件では、放熱器の出入口における冷媒のエンタルピ差を確保できなくなり、充分な暖房能力を得られなくなっていた。   Here, phase change such as evaporation and condensation does not occur in the supercritical state. And even if the density of a refrigerant | coolant becomes the same low, the increase width of the specific enthalpy accompanying it becomes large compared with a gas-liquid two-phase state in the supercritical state. For this reason, the enthalpy of the refrigerant at the inlet of the expander becomes too high under operating conditions in which the density of the refrigerant flowing into the expander becomes small during the supercritical cycle. As a result, under such operating conditions, it is impossible to secure a difference in the enthalpy of the refrigerant at the entrance and exit of the radiator, and a sufficient heating capacity cannot be obtained.

本発明は、かかる点に鑑みてなされたものであり、その目的は、二酸化炭素を冷媒として用いる空気調和装置において、運転条件に拘わらず充分な暖房能力を得られるようにすることにある。   This invention is made | formed in view of this point, The objective is to make it possible to obtain sufficient heating capability irrespective of an operating condition in the air conditioning apparatus which uses a carbon dioxide as a refrigerant | coolant.

第1の発明は、圧縮機(32)及び膨張機(33)が接続されると共に冷媒としての二酸化炭素を循環させて冷凍サイクルを行う冷媒回路(20)を備え、上記冷媒回路(20)の利用側熱交換器(24)で加熱した空気を室内へ供給する暖房運転を少なくとも行う空気調和装置を対象としている。そして、上記圧縮機(32)と上記膨張機(33)のそれぞれが容積形流体機械であり、上記圧縮機(32)と上記膨張機(33)がシャフト(35)によって互いに連結される一方、上記利用側熱交換器(24)へ室内空気を供給する室内ファン(14)と、暖房運転中に上記圧縮機(32)及び膨張機(33)の回転速度と上記室内ファン(14)の回転速度とを調節するコントローラ(90)とを更に備えるものである。更に、この第1の発明において、上記コントローラ(90)は、暖房運転中の制御動作として、上記利用側熱交換器(24)の出口における冷媒温度の目標値を二酸化炭素の臨界温度よりも低い値に設定する動作と、上記利用側熱交換器(24)の出口における冷媒温度の実測値がその目標値以上の場合において、室内空気温度の実測値がその設定値を下回るときには上記室内ファン(14)の回転速度を上昇させ、室内空気温度の実測値がその設定値以上のときには上記圧縮機(32)及び膨張機(33)の回転速度を低下させる動作と、上記利用側熱交換器(24)の出口における冷媒温度の実測値がその目標値未満の場合において、室内空気温度の実測値がその設定値を下回るときには上記圧縮機(32)及び膨張機(33)の回転速度を上昇させ、室内空気温度の実測値がその設定値以上のときには上記室内ファン(14)の回転速度を低下させる動作とを行う。 The first invention includes a refrigerant circuit (20) that is connected to the compressor (32) and the expander (33) and circulates carbon dioxide as a refrigerant to perform a refrigeration cycle, and includes the refrigerant circuit (20). It is intended for an air conditioner that performs at least a heating operation for supplying air heated by a use side heat exchanger (24) into a room. Each of the compressor (32) and the expander (33) is a positive displacement fluid machine, while the compressor (32) and the expander (33) are connected to each other by a shaft (35), The indoor fan (14) for supplying room air to the use side heat exchanger (24), the rotation speed of the compressor (32) and the expander (33) during the heating operation, and the rotation of the indoor fan (14) And a controller (90) for adjusting the speed. Furthermore, in this 1st invention, the said controller (90) makes the target value of the refrigerant | coolant temperature in the exit of the said use side heat exchanger (24) lower than the critical temperature of a carbon dioxide as control operation during heating operation. When the measured value of the refrigerant temperature at the outlet of the use side heat exchanger (24) is equal to or higher than the target value and the measured value of the indoor air temperature falls below the set value, the indoor fan ( 14) when the rotational speed of the compressor (32) and the expander (33) is decreased when the measured value of the indoor air temperature is equal to or higher than the set value, and the use side heat exchanger ( 24) When the measured value of the refrigerant temperature at the outlet of the outlet is less than the target value, when the measured value of the indoor air temperature falls below the set value, the rotational speeds of the compressor (32) and the expander (33) are increased. , Indoor air temperature It performs an operation and to reduce the rotational speed of the indoor fan (14) when the measured value is greater than the set value of.

第1の発明では、空気調和装置(10)が暖房運転を少なくとも行う。暖房運転中には、圧縮機(32)から吐出された高圧冷媒が利用側熱交換器(24)で空気と熱交換し、利用側熱交換器(24)で放熱した冷媒が膨張機(33)へ流入する。この発明の空気調和装置(10)では、暖房運転中の利用側熱交換器(24)の出口における冷媒温度の目標値が、二酸化炭素の臨界温度よりも低い値に設定される。このため、暖房運転中の利用側熱交換器(24)の出口では、冷媒が気液二相状態となり得ることになる。気液二相状態では相変化がおこるため、冷媒の密度が同じだけ低くなっても、それに伴う比エンタルピの増大幅は、気液二相状態の方が超臨界状態に比べて小さくなる。そして、圧縮機(32)の吸入冷媒の密度低下に伴って膨張機(33)へ流入する冷媒の密度が低くならざるを得ない運転状態でも、利用側熱交換器(24)の出口における冷媒のエンタルピが比較的低く保たれる。 In the first invention, the air conditioner (10) performs at least the heating operation. During the heating operation, the high-pressure refrigerant discharged from the compressor (32) exchanges heat with air in the usage-side heat exchanger (24), and the refrigerant radiated by the usage-side heat exchanger (24) becomes the expander (33 ). In the air conditioner (10) of the present invention, the target value of the refrigerant temperature at the outlet of the use side heat exchanger (24) during the heating operation is set to a value lower than the critical temperature of carbon dioxide. For this reason, a refrigerant | coolant can be in a gas-liquid two-phase state in the exit of the utilization side heat exchanger (24) during heating operation . Since the phase change occurs in the gas-liquid two-phase state, even if the refrigerant density is reduced by the same amount, the increase in the specific enthalpy associated therewith is smaller in the gas-liquid two-phase state than in the supercritical state. The refrigerant at the outlet of the use-side heat exchanger (24) even in an operating state in which the density of the refrigerant flowing into the expander (33) is inevitably reduced as the density of the refrigerant sucked into the compressor (32) decreases. The enthalpy of is kept relatively low.

本発明に係る空気調和装置(10)では、暖房運転中の利用側熱交換器(24)の出口における冷媒温度の目標値が、二酸化炭素の臨界温度よりも低い値に設定される。ここで、二酸化炭素の臨界温度は31.05℃であるのに対し、暖房中の室内気温は20℃〜25℃程度であるため、暖房運転中に利用側熱交換器(24)の出口における冷媒温度を二酸化炭素の臨界温度よりも低くすることは可能である。 In the air conditioner (10) according to the present invention, the target value of the refrigerant temperature at the outlet of the use side heat exchanger (24) during the heating operation is set to a value lower than the critical temperature of carbon dioxide. Here, while the critical temperature of carbon dioxide is 31.05 ° C., the indoor air temperature during heating is about 20 ° C. to 25 ° C., and therefore, at the outlet of the use side heat exchanger (24) during heating operation. It is possible to make the refrigerant temperature lower than the critical temperature of carbon dioxide.

本発明に係る空気調和装置(10)において、暖房運転中には、利用側熱交換器(24)の出口における冷媒温度が二酸化炭素の臨界温度よりも低くなり且つ冷凍サイクルの高圧が二酸化炭素の臨界圧よりも低くなる運転状態となり得る。そして、圧縮機(32)の吸入冷媒密度の低下に伴って膨張機(33)へ流入する冷媒の密度が低くならざるを得ない運転条件でこの運転状態になると、暖房運転時に利用側熱交換器(24)から膨張機(33)へ流入する冷媒を気液二相状態とすることが可能となり、このような運転条件でも、利用側熱交換器(24)の出口における冷媒のエンタルピが比較的低く保つことが可能となる。従って、本発明によれば、冷凍サイクルの高圧が二酸化炭素の臨界圧よりも高くなる運転では暖房能力が低下してしまうような運転条件でも、上述した運転動作を行うことによって利用側熱交換器(24)の出入口における冷媒のエンタルピ差を確保することが可能となり、暖房能力の低下を抑えることが可能となる。 In the air conditioner (10) according to the present invention, during the heating operation, the refrigerant temperature at the outlet of the use side heat exchanger (24) is lower than the critical temperature of carbon dioxide, and the high pressure of the refrigeration cycle is that of carbon dioxide. There may be operating conditions that are lower than the critical pressure . When the refrigerant density flowing into the expander (33) is inevitably lowered as the refrigerant density sucked by the compressor (32) decreases, the use side heat exchange is performed during the heating operation. The refrigerant flowing into the expander (33) from the compressor (24) can be in a gas-liquid two-phase state, and even under these operating conditions , the refrigerant enthalpy at the outlet of the use side heat exchanger (24) is compared. Can be kept low. Therefore, according to the present invention, the use-side heat exchanger can be obtained by performing the above-described operation even in an operation condition in which the heating capacity is reduced in the operation in which the high pressure of the refrigeration cycle is higher than the critical pressure of carbon dioxide. It becomes possible to ensure the enthalpy difference of the refrigerant | coolant in the entrance / exit of (24), and it becomes possible to suppress the fall of heating capability.

以下、本発明の実施形態を図面に基づいて詳細に説明する。   Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

図1に示すように、本実施形態の空気調和装置(10)は、いわゆるセパレート型のものであって、室外機(11)と室内機(13)とを備えている。室外機(11)には、室外ファン(12)、室外熱交換器(23)、第1四路切換弁(21)、第2四路切換弁(22)、及び圧縮・膨張ユニット(30)が収納されている。室内機(13)には、室内ファン(14)及び室内熱交換器(24)が収納されている。室外機(11)は屋外に設置され、室内機(13)は屋内に設置されている。   As shown in FIG. 1, the air conditioner (10) of the present embodiment is a so-called separate type, and includes an outdoor unit (11) and an indoor unit (13). The outdoor unit (11) includes an outdoor fan (12), an outdoor heat exchanger (23), a first four-way switching valve (21), a second four-way switching valve (22), and a compression / expansion unit (30). Is stored. The indoor unit (13) houses an indoor fan (14) and an indoor heat exchanger (24). The outdoor unit (11) is installed outdoors, and the indoor unit (13) is installed indoors.

上記空気調和装置(10)では、室外機(11)と室内機(13)とを一対の連絡配管(15,16)で接続することによって冷媒回路(20)が形成されている。圧縮・膨張ユニット(30)や室内熱交換器(24)などは、この冷媒回路(20)に設けられている。また、この冷媒回路(20)には、冷媒として二酸化炭素(CO)が充填されている。なお、二酸化炭素の臨界点(CP)における圧力と温度(即ち臨界圧と臨界温度)は、それぞれ7.34MPaと31.05℃である。 In the air conditioner (10), the refrigerant circuit (20) is formed by connecting the outdoor unit (11) and the indoor unit (13) with a pair of connecting pipes (15, 16). The compression / expansion unit (30), the indoor heat exchanger (24), and the like are provided in the refrigerant circuit (20). The refrigerant circuit (20) is filled with carbon dioxide (CO 2 ) as a refrigerant. The pressure and temperature at the critical point (CP) of carbon dioxide (that is, the critical pressure and the critical temperature) are 7.34 MPa and 31.05 ° C., respectively.

上記圧縮・膨張ユニット(30)は、縦長円筒形の密閉容器状に形成されたケーシング(31)を備えている。このケーシング(31)内には、圧縮機としての圧縮機構(32)と、膨張機としての膨張機構(33)と、電動機(34)とが収納されている。ケーシング(31)内では、圧縮機構(32)と電動機(34)と膨張機構(33)とが下から上へ向かって順に配置されている。圧縮機構(32)と電動機(34)と膨張機構(33)とは、互いに1本のシャフト(35)で連結されている。圧縮機構(32)および膨張機構(33)は、それぞれがロータリ型流体機械やスクロール型流体機械などの容積型流体機械によって構成されている。1本のシャフト(35)で連結された圧縮機構(32)と電動機(34)と膨張機構(33)とは、それぞれの回転速度が常に等しくなる。   The compression / expansion unit (30) includes a casing (31) formed in a vertically long cylindrical sealed container shape. The casing (31) accommodates a compression mechanism (32) as a compressor, an expansion mechanism (33) as an expander, and an electric motor (34). In the casing (31), the compression mechanism (32), the electric motor (34), and the expansion mechanism (33) are sequentially arranged from the bottom to the top. The compression mechanism (32), the electric motor (34), and the expansion mechanism (33) are connected to each other by a single shaft (35). Each of the compression mechanism (32) and the expansion mechanism (33) is constituted by a positive displacement fluid machine such as a rotary fluid machine or a scroll fluid machine. The compression mechanism (32), the electric motor (34), and the expansion mechanism (33) connected by one shaft (35) always have the same rotation speed.

上記冷媒回路(20)において、圧縮機構(32)は、その吐出側が第1四路切換弁(21)の第1のポートに、その吸入側が第1四路切換弁(21)の第4のポートにそれぞれ接続されている。一方、膨張機構(33)は、その流出側が第2四路切換弁(22)の第1のポートに、その流入側が第2四路切換弁(22)の第4のポートにそれぞれ接続されている。   In the refrigerant circuit (20), the compression mechanism (32) has a discharge side at the first port of the first four-way switching valve (21) and an inlet side at the fourth port of the first four-way switching valve (21). Each is connected to a port. On the other hand, the outflow side of the expansion mechanism (33) is connected to the first port of the second four-way switching valve (22), and the inflow side thereof is connected to the fourth port of the second four-way switching valve (22). Yes.

また、上記冷媒回路(20)において、室外熱交換器(23)は、その一端が第2四路切換弁(22)の第2のポートに、その他端が第1四路切換弁(21)の第3のポートにそれぞれ接続されている。この室外熱交換器(23)は、熱源側熱交換器を構成しており、冷媒回路(20)内の冷媒を室外ファン(12)により送り込まれた室外空気と熱交換させる。一方、室内熱交換器(24)は、その一端が第1四路切換弁(21)の第2のポートに、その他端が第2四路切換弁(22)の第3のポートにそれぞれ接続されている。この室内熱交換器(24)は、利用側熱交換器を構成しており、冷媒回路(20)内の冷媒を室内ファン(14)により送り込まれた室内空気と熱交換させる。   In the refrigerant circuit (20), the outdoor heat exchanger (23) has one end connected to the second port of the second four-way switching valve (22) and the other end connected to the first four-way switching valve (21). Are connected to the third ports. The outdoor heat exchanger (23) constitutes a heat source side heat exchanger, and exchanges heat between the refrigerant in the refrigerant circuit (20) and the outdoor air sent by the outdoor fan (12). On the other hand, the indoor heat exchanger (24) has one end connected to the second port of the first four-way selector valve (21) and the other end connected to the third port of the second four-way selector valve (22). Has been. The indoor heat exchanger (24) constitutes a use side heat exchanger, and exchanges heat between the refrigerant in the refrigerant circuit (20) and the indoor air fed by the indoor fan (14).

上記第1四路切換弁(21)と第2四路切換弁(22)は、それぞれ、第1のポートと第2のポートとが連通し且つ第3のポートと第4のポートとが連通する状態(図1に実線で示す状態)と、第1のポートと第3のポートとが連通し且つ第2のポートと第4のポートとが連通する状態(図1に破線で示す状態)とに切り換わるように構成されている。   In the first four-way switching valve (21) and the second four-way switching valve (22), the first port and the second port communicate with each other, and the third port and the fourth port communicate with each other. A state in which the first port and the third port communicate with each other and a state in which the second port communicates with the fourth port (a state indicated by a broken line in FIG. 1). It is comprised so that it may switch to.

上記空気調和装置(10)には、コントローラ(90)が設けられている。また、図示しないが、空気調和装置(10)には、冷媒温度や空気温度などを計測するための各種のセンサが設けられており、これらセンサの出力値がコントローラ(90)へ入力されている。そして、コントローラ(90)は、センサからの入力などを利用して、空気調和装置(10)の運転制御を行う。   The air conditioner (10) is provided with a controller (90). Although not shown, the air conditioner (10) is provided with various sensors for measuring the refrigerant temperature, the air temperature, etc., and the output values of these sensors are input to the controller (90). . And a controller (90) performs operation control of an air harmony device (10) using an input from a sensor.

−空気調和装置の冷房運転−
上記空気調和装置(10)の冷房運転時の動作について説明する。冷房運転時には、第1四路切換弁(21)及び第2四路切換弁(22)が図1に破線で示す状態に設定される。この状態で電動機(34)へ通電すると、冷媒回路(20)内で冷媒が循環する。
-Cooling operation of air conditioner-
The operation of the air conditioner (10) during the cooling operation will be described. During the cooling operation, the first four-way switching valve (21) and the second four-way switching valve (22) are set in a state indicated by broken lines in FIG. When the electric motor (34) is energized in this state, the refrigerant circulates in the refrigerant circuit (20).

具体的に、圧縮機構(32)から吐出された超臨界状態の高圧冷媒は、室外熱交換器(23)へ流入し、室外空気へ放熱した後に膨張機構(33)へ流入する。膨張機構(33)では流入した高圧冷媒から動力が回収され、この回収された動力がシャフト(35)によって圧縮機構(32)へ伝えられる。膨張機構(33)で膨張した冷媒は、室内熱交換器(24)へ流入する。室内熱交換器(24)では、流入した低圧冷媒が室内空気から吸熱して蒸発し、これによって室内空気が冷却される。室内熱交換器(24)で蒸発した低圧冷媒は、圧縮機構(32)へ吸入されて圧縮される。   Specifically, the supercritical high-pressure refrigerant discharged from the compression mechanism (32) flows into the outdoor heat exchanger (23), dissipates heat to the outdoor air, and then flows into the expansion mechanism (33). In the expansion mechanism (33), power is recovered from the high-pressure refrigerant that has flowed in, and the recovered power is transmitted to the compression mechanism (32) by the shaft (35). The refrigerant expanded by the expansion mechanism (33) flows into the indoor heat exchanger (24). In the indoor heat exchanger (24), the low-pressure refrigerant that has flowed in absorbs heat from the indoor air and evaporates, thereby cooling the indoor air. The low-pressure refrigerant evaporated in the indoor heat exchanger (24) is sucked into the compression mechanism (32) and compressed.

ここで、通常、冷房運転中は、室内熱交換器(24)での冷媒蒸発温度を10℃程度に設定され、このことから冷凍サイクルの低圧は4.5MPa前後となる。そして、室内熱交換器(24)の出口における冷媒の過熱度が概ね一定であれば、冷凍サイクルの低圧が決まれば圧縮機構(32)へ吸入される冷媒の密度も決まる。一方、冷房運転が行われる夏季の外気温が30℃〜35℃程度であることを考慮すると、室外熱交換器(23)の出口における冷媒温度は40℃程度になる。また、膨張機構(33)を通過する冷媒の質量流量は、圧縮機構(32)を通過する冷媒の質量流量と等しくなければならない。このため、冷凍サイクルの高圧は、膨張機構(33)へ流入する冷媒の温度が40℃程度で、しかもその密度が圧縮機構(32)と膨張機構(33)における冷媒流量がバランスするという条件の下で、室内熱交換器(24)の入口での冷媒のエンタルピがある程度低い値になるような所定の値(例えば10MPa前後)となる。   Here, normally, during the cooling operation, the refrigerant evaporation temperature in the indoor heat exchanger (24) is set to about 10 ° C., and the low pressure of the refrigeration cycle is about 4.5 MPa. And if the superheat degree of the refrigerant | coolant in the exit of an indoor heat exchanger (24) is substantially constant, if the low pressure of a refrigerating cycle is decided, the density of the refrigerant | coolant suck | inhaled to a compression mechanism (32) will also be decided. On the other hand, considering that the outdoor temperature in the summer in which the cooling operation is performed is about 30 ° C. to 35 ° C., the refrigerant temperature at the outlet of the outdoor heat exchanger (23) is about 40 ° C. The mass flow rate of the refrigerant passing through the expansion mechanism (33) must be equal to the mass flow rate of the refrigerant passing through the compression mechanism (32). For this reason, the high pressure of the refrigeration cycle is such that the temperature of the refrigerant flowing into the expansion mechanism (33) is about 40 ° C., and the density of the refrigerant flows in the compression mechanism (32) and the expansion mechanism (33) is balanced. Below, it becomes a predetermined value (for example, around 10 MPa) such that the enthalpy of the refrigerant at the inlet of the indoor heat exchanger (24) becomes a low value to some extent.

−空気調和装置の暖房運転−
上記空気調和装置(10)の暖房運転時の動作について説明する。暖房運転時には、第1四路切換弁(21)及び第2四路切換弁(22)が図1に実線で示す状態に設定される。この状態で電動機(34)へ通電すると、冷媒回路(20)内で冷媒が循環する。
-Heating operation of air conditioner-
The operation of the air conditioner (10) during the heating operation will be described. During the heating operation, the first four-way switching valve (21) and the second four-way switching valve (22) are set to a state indicated by a solid line in FIG. When the electric motor (34) is energized in this state, the refrigerant circulates in the refrigerant circuit (20).

具体的に、圧縮機構(32)から吐出された超臨界状態の高圧冷媒は、室内熱交換器(24)へ流入する。室内熱交換器(24)では、流入した高圧冷媒が室内空気へ放熱し、これによって室内空気が加熱される。室内熱交換器(24)で放熱した高圧冷媒は、続いて膨張機構(33)へ流入する。膨張機構(33)では流入した高圧冷媒から動力が回収され、この回収された動力がシャフト(35)によって圧縮機構(32)へ伝えられる。膨張機構(33)で膨張した冷媒は、室外熱交換器(23)で室外空気から吸熱して蒸発し、その後に圧縮機構(32)へ吸入されて圧縮される。   Specifically, the supercritical high-pressure refrigerant discharged from the compression mechanism (32) flows into the indoor heat exchanger (24). In the indoor heat exchanger (24), the high-pressure refrigerant that has flowed in dissipates heat to the indoor air, thereby heating the indoor air. The high-pressure refrigerant radiated by the indoor heat exchanger (24) then flows into the expansion mechanism (33). In the expansion mechanism (33), power is recovered from the high-pressure refrigerant that has flowed in, and the recovered power is transmitted to the compression mechanism (32) by the shaft (35). The refrigerant expanded in the expansion mechanism (33) absorbs heat from the outdoor air and evaporates in the outdoor heat exchanger (23), and then is sucked into the compression mechanism (32) and compressed.

暖房運転時には、室内熱交換器(24)の出口における冷媒温度が二酸化炭素の臨界温度(31.05℃)よりも低く設定される。暖房運転中における室内空気の温度(内気温)は、20℃程度である。従って、室内熱交換器(24)の出口における冷媒温度を二酸化炭素の臨界温度より低くすることは、充分に可能である。コントローラ(90)は、室内熱交換器(24)の出口における冷媒温度の目標値を設定し、その実測値が目標値となるように空気調和装置(10)の運転制御を行う。このコントローラ(90)の動作については、後述する。   During the heating operation, the refrigerant temperature at the outlet of the indoor heat exchanger (24) is set lower than the critical temperature of carbon dioxide (31.05 ° C.). The temperature of the indoor air (internal temperature) during the heating operation is about 20 ° C. Therefore, it is sufficiently possible to make the refrigerant temperature at the outlet of the indoor heat exchanger (24) lower than the critical temperature of carbon dioxide. The controller (90) sets a target value of the refrigerant temperature at the outlet of the indoor heat exchanger (24) and controls the operation of the air conditioner (10) so that the actually measured value becomes the target value. The operation of this controller (90) will be described later.

ここでは、暖房運転中に冷媒回路(20)で行われる冷凍サイクルについて、室内熱交換器(24)の出口における冷媒温度が25℃に設定された場合を例に、図2のモリエル線図(圧力−エンタルピ線図)を参照しながら説明する。なお、同図において、細い実線で示されているのは等密度線であり、細い破線で示されているのは等温線である。   Here, for the refrigeration cycle performed in the refrigerant circuit (20) during the heating operation, the case where the refrigerant temperature at the outlet of the indoor heat exchanger (24) is set to 25 ° C. is taken as an example. This will be described with reference to the pressure-enthalpy diagram. In the figure, a thin solid line indicates an isodensity line, and a thin broken line indicates an isotherm.

例えば、外気温が10℃程度の場合は、室外熱交換器(23)における冷媒の蒸発温度が0℃となった冷凍サイクル、即ち図2に太い実線で表された冷凍サイクルが行われる。具体的に、冷媒回路(20)内を循環する冷媒は、点Aの状態で圧縮機構(32)へ吸入され、圧縮機構(32)で圧縮されて点Bの状態となり、室内熱交換器(24)で放熱して点Cの状態となり、膨張機構(33)で膨張して点Dの状態となり、室外熱交換器(23)で吸熱して点Aの状態に戻る。この冷凍サイクルの高圧(即ち点Bや点Cにおける冷媒圧力)は、8.3Mpa前後になる。室内熱交換器(24)の出口(即ち膨張機構(33)の入口)における冷媒状態(点C)は、温度が25℃で、密度が圧縮機構(32)と膨張機構(33)の流量がバランスするような値となる状態である。   For example, when the outside air temperature is about 10 ° C., a refrigeration cycle in which the evaporation temperature of the refrigerant in the outdoor heat exchanger (23) becomes 0 ° C., that is, a refrigeration cycle represented by a thick solid line in FIG. Specifically, the refrigerant circulating in the refrigerant circuit (20) is sucked into the compression mechanism (32) in the state of point A, and is compressed by the compression mechanism (32) to be in the state of point B. The heat is dissipated in 24) to be in the state of point C, expanded by the expansion mechanism (33) to be in the state of point D, absorbed by the outdoor heat exchanger (23), and returned to the state of point A. The high pressure of the refrigeration cycle (that is, the refrigerant pressure at points B and C) is around 8.3 Mpa. The refrigerant state (point C) at the outlet of the indoor heat exchanger (24) (that is, the inlet of the expansion mechanism (33)) has a temperature of 25 ° C. and a density of the compression mechanism (32) and the flow rate of the expansion mechanism (33). This is a state where the values are balanced.

外気温が0℃程度にまで下がると、室外熱交換器(23)における冷媒の蒸発温度が−10℃となった冷凍サイクル、即ち図2に太い破線で表された冷凍サイクルが行われる。具体的には、外気温が10℃程度の場合に比べて冷凍サイクルの高圧と低圧が共に低下し、圧縮機構(32)の入口における冷媒状態が点Aから点A'となり、膨張機構(33)の入口における冷媒状態が点Cから点C'となる。   When the outside air temperature falls to about 0 ° C., a refrigeration cycle in which the evaporation temperature of the refrigerant in the outdoor heat exchanger (23) reaches −10 ° C., that is, a refrigeration cycle represented by a thick broken line in FIG. Specifically, both the high pressure and low pressure of the refrigeration cycle are reduced compared to the case where the outside air temperature is about 10 ° C., the refrigerant state at the inlet of the compression mechanism (32) is changed from the point A to the point A ′, and the expansion mechanism (33 ) From the point C to the point C ′.

この冷媒蒸発温度が−10℃となる冷凍サイクルでは、冷凍サイクルの高圧が6.5MPa前後となる。つまり、冷凍サイクルの高圧が、二酸化炭素の臨界圧よりも低くなる。そして、膨張機構(33)の入口では、冷媒が気液二相状態となっている、
本実施形態の空気調和装置(10)において、膨張機構(33)の入口における冷媒状態は、圧縮機構(32)の入口における冷媒状態に応じて決まる。この点について説明する。本実施形態では、圧縮機構(32)と膨張機構(33)が共に容積型の流体機械で構成されており、しかも圧縮機構(32)と膨張機構(33)が1本のシャフト(35)で連結されて常に同じ回転速度で回転する。このため、圧縮機構(32)と膨張機構(33)とで通過する冷媒の質量流量が一致するには、圧縮機構(32)の入口における冷媒密度と膨張機構(33)の入口における冷媒密度の比が常に一定でなければならない。従って、冷媒蒸発温度が−10℃となる冷凍サイクルでの膨張機構(33)の入口における冷媒状態(点C')は、点C'と点A'の冷媒密度の比が点Cと点Aの冷媒密度の比と等しくなる密度で、且つ温度が25℃となるような状態となる。
In the refrigeration cycle in which the refrigerant evaporation temperature is −10 ° C., the high pressure of the refrigeration cycle is around 6.5 MPa. That is, the high pressure of the refrigeration cycle is lower than the critical pressure of carbon dioxide. And, at the inlet of the expansion mechanism (33), the refrigerant is in a gas-liquid two-phase state.
In the air conditioner (10) of the present embodiment, the refrigerant state at the inlet of the expansion mechanism (33) is determined according to the refrigerant state at the inlet of the compression mechanism (32). This point will be described. In the present embodiment, the compression mechanism (32) and the expansion mechanism (33) are both constituted by a displacement type fluid machine, and the compression mechanism (32) and the expansion mechanism (33) are formed by a single shaft (35). Connected and always rotates at the same rotational speed. Therefore, in order for the mass flow rates of the refrigerant passing through the compression mechanism (32) and the expansion mechanism (33) to coincide, the refrigerant density at the inlet of the compression mechanism (32) and the refrigerant density at the inlet of the expansion mechanism (33) The ratio must always be constant. Therefore, the refrigerant state (point C ′) at the inlet of the expansion mechanism (33) in the refrigeration cycle where the refrigerant evaporation temperature is −10 ° C. is that the ratio of the refrigerant density between point C ′ and point A ′ is point C and point A. The refrigerant density is equal to the refrigerant density ratio, and the temperature is 25 ° C.

外気温が更に−10℃程度にまで下がると、室外熱交換器(23)における冷媒の蒸発温度が−20℃となった冷凍サイクル、即ち図2に太い一点鎖線で表された冷凍サイクルが行われる。具体的には、冷媒蒸発温度が−10℃となる場合に比べて冷凍サイクルの低圧だけが低下し、圧縮機構(32)の入口における冷媒状態が点A'から点A''となり、膨張機構(33)の入口における冷媒状態が点C'から点C''となる。上述したように点C'の状態では冷媒が気液二相状態になっており、点C''の状態と点C'の状態とで冷媒温度が同じであるため、冷凍サイクルの高圧は変化しない。膨張機構(33)の入口における冷媒状態(点C'')は、点C''と点A''の冷媒密度の比が点C'と点A'の冷媒密度の比と等しくなる密度で、且つ温度が25℃となるような状態となる。   When the outside air temperature further drops to about −10 ° C., a refrigeration cycle in which the evaporation temperature of the refrigerant in the outdoor heat exchanger (23) reaches −20 ° C., that is, a refrigeration cycle represented by a thick dashed line in FIG. Is called. Specifically, only the low pressure of the refrigeration cycle is lowered as compared with the case where the refrigerant evaporation temperature is −10 ° C., the refrigerant state at the inlet of the compression mechanism (32) is changed from the point A ′ to the point A ″, and the expansion mechanism The refrigerant state at the inlet of (33) changes from point C ′ to point C ″. As described above, the refrigerant is in a gas-liquid two-phase state at the point C ′, and the refrigerant temperature is the same at the point C ″ and the point C ′. do not do. The refrigerant state (point C ″) at the inlet of the expansion mechanism (33) is a density at which the ratio of the refrigerant density at points C ″ and A ″ is equal to the ratio of the refrigerant density at points C ′ and A ′. And the temperature is 25 ° C.

ここで、比較例として、暖房運転中の室内熱交換器(24)の出口における冷媒温度が二酸化炭素の臨界温度よりも高く設定される場合の冷凍サイクルについて、図4のモリエル線図を参照しながら説明する。なお、ここでは、室内熱交換器(24)の出口における冷媒温度が35℃である場合について説明する。   Here, as a comparative example, refer to the Mollier diagram of FIG. 4 for the refrigeration cycle when the refrigerant temperature at the outlet of the indoor heat exchanger (24) during heating operation is set higher than the critical temperature of carbon dioxide. While explaining. Here, the case where the refrigerant temperature at the outlet of the indoor heat exchanger (24) is 35 ° C. will be described.

室外熱交換器(23)での冷媒蒸発温度が0℃となる運転条件では、図4に太い実線で表された冷凍サイクル(a−b−c−dで示されるサイクル)が行われる。一方、室外熱交換器(23)での冷媒蒸発温度が−10℃となる運転条件では、図4に太い破線で表された冷凍サイクル(a'−b'−c'−d'で示されるサイクル)が行われる。また、室外熱交換器(23)での冷媒蒸発温度が−20℃となる運転条件では、図4に太い破線で表された冷凍サイクル(a''−b''−c''−d''で示されるサイクル)が行われる。   Under operating conditions where the refrigerant evaporation temperature in the outdoor heat exchanger (23) is 0 ° C., a refrigeration cycle (a cycle indicated by abcd) represented by a thick solid line in FIG. 4 is performed. On the other hand, under the operating condition where the refrigerant evaporation temperature in the outdoor heat exchanger (23) is -10 ° C, it is indicated by a refrigeration cycle (a'-b'-c'-d ') represented by a thick broken line in FIG. Cycle). Further, under operating conditions where the refrigerant evaporation temperature in the outdoor heat exchanger (23) is -20 ° C., the refrigeration cycle (a ″ −b ″ −c ″ −d ′) represented by the thick broken line in FIG. The cycle indicated by 'is performed.

この場合も、膨張機構(33)の入口における冷媒密度は、圧縮機構(32)の入口における冷媒密度が低下するのにつれて低下してゆく。具体的に、膨張機構(33)の入口における冷媒状態は、温度35℃の等温線上を密度が低くなる方向(点cから点c''へ向かう方向)へ変化してゆく。一方、これら点c,点c',点c''では何れの状態においても冷媒が超臨界状態となっており、冷媒の密度が下がるのにつれてそのエンタルピが比較的大幅に低下してしまう。従って、この比較例では、膨張機構(33)の入口における冷媒状態が点cから点c'へ、あるいは点c'から点c''へ変化するのに伴い、各点における冷媒のエンタルピが大きく増大してしまう。   Also in this case, the refrigerant density at the inlet of the expansion mechanism (33) decreases as the refrigerant density at the inlet of the compression mechanism (32) decreases. Specifically, the refrigerant state at the inlet of the expansion mechanism (33) changes on the isotherm at a temperature of 35 ° C. in the direction of decreasing density (the direction from the point c toward the point c ″). On the other hand, at these points c, c ′, and c ″, the refrigerant is in a supercritical state in any state, and the enthalpy is relatively lowered as the density of the refrigerant decreases. Therefore, in this comparative example, as the refrigerant state at the inlet of the expansion mechanism (33) changes from the point c to the point c ′ or from the point c ′ to the point c ″, the refrigerant enthalpy increases at each point. It will increase.

これに対し、本実施形態では膨張機構(33)の入口における冷媒温度が二酸化炭素の臨界温度よりも低くなっており、室外熱交換器(23)での冷媒蒸発温度が−10℃や−20℃となる運転条件では、膨張機構(33)の入口では冷媒が気液二相状態となる(図2を参照)。このため、圧縮機構(32)の入口における冷媒密度が低下するのに伴って膨張機構(33)の入口における冷媒密度が低下しても、それに伴う冷媒のエンタルピの増加量は、超臨界状態で冷媒の密度が低下した場合に比べて大幅に小さくなる。そして、膨張機構(33)の入口における冷媒のエンタルピがさほど増加しなければ、放熱器である室内熱交換器(24)の出入口におけるエンタルピ差もさほど小さくならず、室内熱交換器(24)で冷媒から室内空気へ放熱される熱量もそれほど少なくならない。   On the other hand, in this embodiment, the refrigerant temperature at the inlet of the expansion mechanism (33) is lower than the critical temperature of carbon dioxide, and the refrigerant evaporation temperature in the outdoor heat exchanger (23) is -10 ° C or -20. Under the operating condition of ° C., the refrigerant is in a gas-liquid two-phase state at the inlet of the expansion mechanism (33) (see FIG. 2). For this reason, even if the refrigerant density at the inlet of the expansion mechanism (33) decreases as the refrigerant density at the inlet of the compression mechanism (32) decreases, the amount of increase in the enthalpy of the refrigerant accompanying this decreases in the supercritical state. Compared to the case where the density of the refrigerant is lowered, the density is significantly reduced. If the enthalpy of the refrigerant at the inlet of the expansion mechanism (33) does not increase so much, the enthalpy difference at the inlet / outlet of the indoor heat exchanger (24), which is a radiator, does not become so small. The amount of heat radiated from the refrigerant to the indoor air is not so small.

図5は、本実施形態と上記比較例のそれぞれについて、暖房運転中に冷媒蒸発温度が低くなるにつれて暖房能力やCOP(成績係数)がどの程度低下してゆくかを示ししたものである。   FIG. 5 shows how much the heating capacity and COP (coefficient of performance) decrease as the refrigerant evaporation temperature decreases during the heating operation for each of the present embodiment and the comparative example.

室内熱交換器(24)の出口における冷媒温度が35℃の場合、冷媒蒸発温度が−20℃となる運転条件で得られる暖房能力は、冷媒蒸発温度が0℃となる運転条件で得られる暖房能力の82%程度にまで下がってしまう。また、この場合、冷媒蒸発温度が−20℃となる運転条件におけるCOPは、冷媒蒸発温度が0℃となる運転条件におけるCOPの60%程度にまで下がってしまう。   When the refrigerant temperature at the outlet of the indoor heat exchanger (24) is 35 ° C., the heating capacity obtained under the operating condition where the refrigerant evaporation temperature is −20 ° C. is the heating capacity obtained under the operating condition where the refrigerant evaporation temperature is 0 ° C. It will drop to about 82% of capacity. In this case, the COP under the operating condition where the refrigerant evaporation temperature is −20 ° C. is reduced to about 60% of the COP under the operating condition where the refrigerant evaporation temperature is 0 ° C.

一方、室内熱交換器(24)の出口における冷媒温度が25℃の場合、冷媒蒸発温度が−20℃となる運転条件で得られる暖房能力は、冷媒蒸発温度が0℃となる運転条件で得られる暖房能力の96%程度にまでしか下がらない。また、この場合、冷媒蒸発温度が−20℃となる運転条件におけるCOPは、冷媒蒸発温度が0℃となる運転条件におけるCOPの73%程度にまでしか下がらない。   On the other hand, when the refrigerant temperature at the outlet of the indoor heat exchanger (24) is 25 ° C., the heating capacity obtained under the operation condition where the refrigerant evaporation temperature is −20 ° C. is obtained under the operation condition where the refrigerant evaporation temperature is 0 ° C. It can only be reduced to about 96% of the available heating capacity. In this case, the COP under the operating condition where the refrigerant evaporation temperature is −20 ° C. is only reduced to about 73% of the COP under the operating condition where the refrigerant evaporation temperature is 0 ° C.

このように、外気温が極端に低い条件で暖房運転を行う場合には、冷凍サイクルの高圧を二酸化炭素の臨界圧よりも低く設定し、更には室内熱交換器(24)の出口における冷媒温度を二酸化炭素の臨界温度よりも低く設定するほうが、暖房能力やCOPの点で有利となる。   Thus, when heating operation is performed under conditions where the outside air temperature is extremely low, the high pressure of the refrigeration cycle is set lower than the critical pressure of carbon dioxide, and the refrigerant temperature at the outlet of the indoor heat exchanger (24) It is advantageous in terms of heating capacity and COP to set the temperature lower than the critical temperature of carbon dioxide.

−コントローラの制御動作−
上述したように、コントローラ(90)は、暖房運転中に室内熱交換器(24)の出口における冷媒温度が所定の値に保たれるように、空気調和装置(10)の運転制御を行う。このコントローラ(90)の制御動作について、図3のフロー図を参照しながら説明する。
-Controller control action-
As described above, the controller (90) controls the operation of the air conditioner (10) so that the refrigerant temperature at the outlet of the indoor heat exchanger (24) is maintained at a predetermined value during the heating operation. The control operation of the controller (90) will be described with reference to the flowchart of FIG.

先ず、ステップST1において、コントローラ(90)は、空気調和装置(10)の各部に設けられたセンサからの出力信号を取得する。例えば、室内熱交換器(24)の出口における冷媒温度、室外熱交換器(23)での冷媒蒸発温度、冷凍サイクルの高圧の値などのデータをコントローラ(90)が取得する。続くステップST2では、室内熱交換器(24)の出口における冷媒温度の目標値Tgc,objを設定する。その際、コントローラ(90)は、予め記憶していた関係式や数値表とステップST1で取得したデータを利用して演算を行い、その時点での運転条件に適した目標値Tgc,objを設定する。   First, in step ST1, the controller (90) acquires output signals from sensors provided in each part of the air conditioner (10). For example, the controller (90) acquires data such as the refrigerant temperature at the outlet of the indoor heat exchanger (24), the refrigerant evaporation temperature in the outdoor heat exchanger (23), and the high pressure value of the refrigeration cycle. In the subsequent step ST2, the target value Tgc, obj of the refrigerant temperature at the outlet of the indoor heat exchanger (24) is set. At that time, the controller (90) performs calculations using the relational expressions and numerical tables stored in advance and the data acquired in step ST1, and sets target values Tgc and obj suitable for the operating conditions at that time. To do.

次に、ステップST3では、室内熱交換器(24)の出口における冷媒温度の実測値Tgcと、ステップST2で設定した目標値Tgc,objとが比較される。そして、実測値Tgcが目標値Tgc,obj以上であればステップST4へ移り、実測値Tgcが目標値Tgc,obj未満であればステップST7へ移る。 ステップST4やステップST7では、室内空気温度の実測値Traと、ユーザーにより設定された室内空気温度の目標値Tra,objとが比較される。   Next, in step ST3, the measured value Tgc of the refrigerant temperature at the outlet of the indoor heat exchanger (24) is compared with the target value Tgc, obj set in step ST2. If the measured value Tgc is greater than or equal to the target value Tgc, obj, the process proceeds to step ST4. If the measured value Tgc is less than the target value Tgc, obj, the process proceeds to step ST7. In step ST4 and step ST7, the measured value Tra of the room air temperature is compared with the target value Tra, obj of the room air temperature set by the user.

ステップST4において、実測値Traが目標値Tra,objを下回っていれば、ステップST5へ移り、室内ファン(14)の回転速度を上げることによって室内機(11)の吹出風量を増やす。つまり、この状態では、Tra<Tra,objとなっていて暖房能力を増やす必要があるため、コントローラ(90)は室内熱交換器(24)を通過する風量を増やすことによって室内熱交換器(24)の出口における冷媒温度を引き下げる。一方、実測値Traが目標値Tra,obj以上となっていれば、ステップST6へ移り、圧縮・膨張ユニット(30)の電動機(34)の回転速度を下げることによって圧縮機構(32)の容量を減らす。つまり、この状態では、Tra≧Tra,objとなっていて暖房能力を増やす必要が無いため、コントローラ(90)は室内熱交換器(24)を通過する冷媒流量を減らすことによって室内熱交換器(24)の出口における冷媒温度を引き下げる。   In step ST4, if the measured value Tra is lower than the target value Tra, obj, the process proceeds to step ST5, and the blowing air volume of the indoor unit (11) is increased by increasing the rotational speed of the indoor fan (14). That is, in this state, since Tra <Tra, obj, and it is necessary to increase the heating capacity, the controller (90) increases the amount of air passing through the indoor heat exchanger (24) to increase the indoor heat exchanger (24 ) Lower the refrigerant temperature at the outlet. On the other hand, if the measured value Tra is equal to or greater than the target value Tra, obj, the process proceeds to step ST6, and the capacity of the compression mechanism (32) is reduced by reducing the rotational speed of the motor (34) of the compression / expansion unit (30). cut back. That is, in this state, since Tra ≧ Tra, obj, it is not necessary to increase the heating capacity, the controller (90) reduces the flow rate of the refrigerant passing through the indoor heat exchanger (24), thereby reducing the indoor heat exchanger ( 24) Reduce the refrigerant temperature at the outlet.

ステップST7において、実測値Traが目標値Tra,objを下回っていれば、ステップST8へ移り、圧縮・膨張ユニット(30)の電動機(34)の回転速度を上げることによって圧縮機構(32)の容量を増やす。つまり、この状態では、Tra<Tra,objとなっていて暖房能力を増やす必要があるため、コントローラ(90)は室内熱交換器(24)を通過する冷媒流量を増やすことによって室内熱交換器(24)の出口における冷媒温度を引き上げる。一方、実測値Traが目標値Tra,obj以上となっていれば、ステップST9へ移り、室内ファン(14)の回転速度を下げることによって室内機(11)の吹出風量を減らす。つまり、この状態では、Tra≧Tra,objとなっていて暖房能力を増やす必要が無いため、コントローラ(90)は室内熱交換器(24)を通過する風量を減らすことによって室内熱交換器(24)の出口における冷媒温度を引き下げる。   In step ST7, if the actual value Tra is below the target value Tra, obj, the process proceeds to step ST8, where the capacity of the compression mechanism (32) is increased by increasing the rotational speed of the motor (34) of the compression / expansion unit (30). Increase. That is, in this state, since Tra <Tra, obj, and it is necessary to increase the heating capacity, the controller (90) increases the flow rate of the refrigerant passing through the indoor heat exchanger (24) to increase the indoor heat exchanger ( 24) Increase the refrigerant temperature at the outlet. On the other hand, if the actual measurement value Tra is equal to or greater than the target value Tra, obj, the process proceeds to step ST9, and the blowout air volume of the indoor unit (11) is reduced by reducing the rotation speed of the indoor fan (14). That is, in this state, since Tra ≧ Tra, obj, there is no need to increase the heating capacity, the controller (90) reduces the air volume passing through the indoor heat exchanger (24), thereby reducing the indoor heat exchanger (24 ) Lower the refrigerant temperature at the outlet.

−実施形態の効果−
本実施形態の空気調和装置(10)では、外気温が比較的低い運転条件での暖房運転において、冷凍サイクルの高圧が二酸化炭素の臨界圧よりも低く、室内熱交換器(24)の出口における冷媒温度が二酸化炭素の臨界温度よりも低くなる動作を行っている。このため、冬季の寒冷地で暖房運転を行うような運転条件においても、室内熱交換器(24)の出口における冷媒のエンタルピを比較的低く保つことができ、室内熱交換器(24)の出入口におけるエンタルピ差を確保して暖房能力の低下を可能な限り抑制することができる。また、冷媒蒸発温度の低下に伴って圧縮・膨張ユニット(30)の電動機(34)の消費電力は増大するが、室内熱交換器(24)で得られる暖房能力の低下を少なくできるため、冬季の寒冷地で暖房運転を行うような運転条件においても比較的高いCOPを得ることが可能となる。
-Effect of the embodiment-
In the air conditioner (10) of the present embodiment, in the heating operation under an operation condition where the outside air temperature is relatively low, the high pressure of the refrigeration cycle is lower than the critical pressure of carbon dioxide, and at the outlet of the indoor heat exchanger (24) The refrigerant temperature is lower than the critical temperature of carbon dioxide. For this reason, the enthalpy of the refrigerant at the outlet of the indoor heat exchanger (24) can be kept relatively low even under operating conditions in which heating operation is performed in a cold region in winter, and the entrance and exit of the indoor heat exchanger (24) The enthalpy difference in can be ensured and the reduction in heating capacity can be suppressed as much as possible. In addition, although the power consumption of the motor (34) of the compression / expansion unit (30) increases as the refrigerant evaporation temperature decreases, the decrease in heating capacity obtained by the indoor heat exchanger (24) can be reduced. It is possible to obtain a relatively high COP even under operating conditions in which heating operation is performed in a cold region.

なお、以上の実施形態は、本質的に好ましい例示であって、本発明、その適用物、あるいはその用途の範囲を制限することを意図するものではない。   In addition, the above embodiment is an essentially preferable illustration, Comprising: It does not intend restrict | limiting the range of this invention, its application thing, or its use.

以上説明したように、本発明は、冷媒として二酸化炭素を用いた空気調和装置について有用である。   As described above, the present invention is useful for an air conditioner using carbon dioxide as a refrigerant.

実施形態における冷媒回路の構成図である。It is a block diagram of the refrigerant circuit in embodiment. 実施形態の空気調和装置における暖房運転時の冷凍サイクルを示すモリエル線図である。It is a Mollier diagram which shows the refrigerating cycle at the time of the heating operation in the air conditioning apparatus of embodiment. 暖房運転時にコントローラが行う制御動作を示すフロー図である。It is a flowchart which shows the control operation which a controller performs at the time of heating operation. 比較例の暖房運転における冷凍サイクルを示すモリエル線図である。It is a Mollier diagram which shows the refrigerating cycle in the heating operation of a comparative example. 実施形態の空気調和装置と比較例との暖房運転時の性能を示す冷媒蒸発温度と暖房能力比及びCOP比との関係図である。It is a related figure of the refrigerant | coolant evaporation temperature which shows the performance at the time of heating operation with the air conditioning apparatus of embodiment, and a comparative example, a heating capability ratio, and a COP ratio.

10 空気調和装置
20 冷媒回路
24 室内熱交換器(利用側熱交換器)
32 圧縮機構(圧縮機)
33 膨張機構(膨張機)
10 Air conditioner
20 Refrigerant circuit
24 Indoor heat exchanger (use side heat exchanger)
32 Compression mechanism (compressor)
33 Expansion mechanism (expander)

Claims (1)

  1. 圧縮機(32)及び膨張機(33)が接続されると共に冷媒としての二酸化炭素を循環させて冷凍サイクルを行う冷媒回路(20)を備え、上記冷媒回路(20)の利用側熱交換器(24)で加熱した空気を室内へ供給する暖房運転を少なくとも行う空気調和装置であって、
    上記圧縮機(32)と上記膨張機(33)のそれぞれが容積形流体機械であり、
    上記圧縮機(32)と上記膨張機(33)がシャフト(35)によって互いに連結される一方、
    上記利用側熱交換器(24)へ室内空気を供給する室内ファン(14)と、
    暖房運転中に上記圧縮機(32)及び膨張機(33)の回転速度と上記室内ファン(14)の回転速度とを調節するコントローラ(90)とを更に備え、
    上記コントローラ(90)は、暖房運転中の制御動作として、
    上記利用側熱交換器(24)の出口における冷媒温度の目標値を二酸化炭素の臨界温度よりも低い値に設定する動作と、
    上記利用側熱交換器(24)の出口における冷媒温度の実測値がその目標値以上の場合において、室内空気温度の実測値がその設定値を下回るときには上記室内ファン(14)の回転速度を上昇させ、室内空気温度の実測値がその設定値以上のときには上記圧縮機(32)及び膨張機(33)の回転速度を低下させる動作と、
    上記利用側熱交換器(24)の出口における冷媒温度の実測値がその目標値未満の場合において、室内空気温度の実測値がその設定値を下回るときには上記圧縮機(32)及び膨張機(33)の回転速度を上昇させ、室内空気温度の実測値がその設定値以上のときには上記室内ファン(14)の回転速度を低下させる動作とを行う
    ことを特徴とする空気調和装置。
    A compressor (32) and an expander (33) are connected, and a refrigerant circuit (20) that performs a refrigeration cycle by circulating carbon dioxide as a refrigerant is provided, and a use side heat exchanger ( 24) an air conditioner that performs at least a heating operation for supplying the air heated in the room to a room;
    Each of the compressor (32) and the expander (33) is a positive displacement fluid machine,
    While the compressor (32) and the expander (33) are connected to each other by a shaft (35),
    An indoor fan (14) for supplying room air to the use side heat exchanger (24);
    A controller (90) for adjusting the rotational speed of the compressor (32) and the expander (33) and the rotational speed of the indoor fan (14) during heating operation;
    The controller (90) is a control operation during heating operation.
    An operation for setting the target value of the refrigerant temperature at the outlet of the use side heat exchanger (24) to a value lower than the critical temperature of carbon dioxide;
    When the measured value of the refrigerant temperature at the outlet of the use side heat exchanger (24) is equal to or higher than the target value, the rotational speed of the indoor fan (14) is increased when the measured value of the indoor air temperature falls below the set value. When the measured value of the indoor air temperature is equal to or higher than the set value, the operation of reducing the rotational speed of the compressor (32) and the expander (33),
    When the measured value of the refrigerant temperature at the outlet of the use side heat exchanger (24) is less than the target value, when the measured value of the indoor air temperature falls below the set value, the compressor (32) and the expander (33 ), And when the measured value of the indoor air temperature is equal to or higher than the set value, the operation of decreasing the rotational speed of the indoor fan (14) is performed.
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JP2001108314A (en) * 1999-10-05 2001-04-20 Zexel Valeo Climate Control Corp Refrigerating cycle controller
JP2002130770A (en) * 2000-10-30 2002-05-09 Mitsubishi Electric Corp Refrigerating cycle device and its control method
JP2003240366A (en) * 2002-02-21 2003-08-27 Mitsubishi Electric Corp Refrigerating air conditioner
JP2004138333A (en) * 2002-10-18 2004-05-13 Matsushita Electric Ind Co Ltd Refrigeration cycle device

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Publication number Priority date Publication date Assignee Title
JP2001108314A (en) * 1999-10-05 2001-04-20 Zexel Valeo Climate Control Corp Refrigerating cycle controller
JP2002130770A (en) * 2000-10-30 2002-05-09 Mitsubishi Electric Corp Refrigerating cycle device and its control method
JP2003240366A (en) * 2002-02-21 2003-08-27 Mitsubishi Electric Corp Refrigerating air conditioner
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