JP2007178042A - Supercritical vapor compression type refrigerating cycle and cooling and heating air conditioning facility and heat pump hot-water supply machine using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a supercritical vapor compression type refrigerating cycle provided with a two-stage compressor reducing suction heating loss and having high efficiency with a heat radiation side of carbon dioxide refrigerant operating in a supercritical zone. <P>SOLUTION: In this supercritical vapor compression type refrigerating cycle having the two-stage compressor having an intermediate connection circuit to compress the refrigerant in two stages, a first expansion device for reducing the pressure of the refrigerant to an intermediate pressure, a gas-liquid separator for separating the refrigerant into gas and liquid, an injection circuit for injecting the gas phase side refrigerant after separating into gas and liquid into the intermediate connection circuit, and a second expansion device, an expulsion volume ratio of expulsion volume on a high stage side to expulsion volume on a low stage side is higher than the adiabatic index root of a ratio of a suction pressure of the two-stage compressor to a refrigerant saturated liquid pressure in the first expansion device. Opening or degree of suction heating of the first and second expansion devices is controlled to keep the refrigerant injected into the intermediate connection circuit in a gas phase state. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a supercritical vapor compression refrigeration cycle including a two-stage compressor that compresses a refrigerant in two stages and injects the refrigerant to an intermediate pressure, an air conditioning and air conditioning facility using the same, and a heat pump water heater.

Specified chlorofluorocarbons used in air conditioning and air conditioning facilities are regulated due to problems such as ozone layer destruction and global warming. Also, newly developed alternative refrigerants do not destroy the ozone layer, but have a global warming potential that is several hundred to several thousand times that of carbon dioxide refrigerants. Against this background, carbon dioxide is attracting attention as a refrigerant that is friendly to the global environment.
However, the critical temperature of carbon dioxide is about 31 ° C, and when used as a working fluid in an air-conditioning refrigeration cycle, the normal heat radiation side environmental temperature (outside of cooling room: about 25 ° C to 35 ° C, indoor of heating time: 15 ° C) The refrigerant compressed at about ˜25 ° C. exceeds the critical temperature of carbon dioxide and the critical pressure of 7.38 MPa, and forms a supercritical vapor compression refrigeration cycle. In the heat dissipation process of the supercritical vapor compression refrigeration cycle, the carbon dioxide refrigerant is in a supercritical pressure state, so heat is released in the form of sensible heat instead of latent heat like conventional refrigerants, compared to conventional refrigeration cycles. There was a problem that the cycle efficiency was lowered.

Therefore, in order to improve the efficiency of a supercritical vapor compression refrigeration cycle using carbon dioxide as a refrigerant, a cycle using an internal heat exchanger and gas injection has been proposed (see, for example, Patent Document 1).
Further, an exclusion volume ratio suitable for a refrigeration cycle in which gas is injected into an intermediate pressure of a two-stage compressor is examined for the HFC refrigerant (R410A) and the HCFC refrigerant (R22) (see, for example, Patent Document 2).
Also, in the internal intermediate pressure type carbon dioxide refrigerant two-stage rotary compressor, the excluded volume ratio of the second stage to the first stage is set in the range of 0.56 to 0.8 (especially 0.65 is recommended), It is disclosed that oil forming can be suppressed by reducing the pressure fluctuation (see, for example, Patent Document 3).

JP 2001-116376 A JP 2000-87892 A JP 2001-73976 A

However, in the conventional proposal, although it is a refrigeration cycle in which gas is injected to an intermediate pressure, the case where carbon dioxide refrigerant whose critical operation is performed on the high pressure side is not taken into consideration. Another conventional proposal is a refrigeration cycle using a carbon dioxide refrigerant in an internal intermediate pressure type two-stage rotary compressor, but an excluded volume ratio suitable for gas injection to an intermediate pressure has not been studied.
In the supercritical vapor compression refrigeration cycle using carbon dioxide as the refrigerant, the supercritical state is reached with a high-pressure radiator, so gas-liquid separation is not possible even if the excluded volume ratio of the two-stage compressor is determined according to the conventional proposal. There is a problem that the performance improvement effect and the reliability improvement effect due to the intermediate injection cannot be obtained sufficiently because the intermediate injection cannot be performed properly.

  An object of the present invention is to provide a supercritical vapor compression refrigeration cycle that includes a high-efficiency high-pressure shell-type two-stage compressor that has a small suction heating loss and that operates on the heat dissipation side of carbon dioxide refrigerant in the supercritical region. .

  In the supercritical vapor compression refrigeration cycle according to the present invention, the refrigerant in which the low-pressure refrigerant is compressed to the intermediate pressure by the low-stage side rotary compression element is sucked into the high-stage side rotary compression element via the intermediate connection circuit. A two-stage compressor that is compressed to a high pressure by a high-stage rotary compression element, a first expansion device that decompresses the refrigerant that is compressed to a high pressure to a saturation liquid pressure or less, and a wet gas state that is below the saturation liquid pressure A gas-liquid separator that gas-liquid separates the refrigerant; an injection circuit that injects the gas-phase refrigerant after gas-liquid separation into the intermediate connection circuit; and a second that depressurizes the liquid-phase refrigerant after gas-liquid separation to a low pressure In a supercritical vapor compression refrigeration cycle having an expansion device and an evaporator for evaporating a refrigerant whose pressure is reduced to a low pressure, an exclusion volume of the high-stage rotary compression element is smaller than an exclusion volume of the low-stage rotary compression element Excluded volume ratio is It is equal to or higher than the root of the isentropic exponent of the ratio of the suction pressure of the two-stage compressor to the refrigerant saturated liquid pressure in the first expansion device, and the opening degree of the first expansion device or the second expansion device The degree of suction heating is controlled so that the refrigerant injected into the intermediate coupling circuit is kept in a gas phase state.

  The effect of the supercritical vapor compression refrigeration cycle according to the present invention is that the refrigerant main component that is intermediately injected into the two-stage compressor can be maintained in the gas phase, and the compressor efficiency that can occur by injecting a large amount of liquid phase refrigerant. And reliability can be prevented.

Embodiment 1 FIG.
1 is a circuit diagram of a supercritical vapor compression refrigeration cycle using a gas-liquid separator according to Embodiment 1 of the present invention.
A supercritical vapor compression refrigeration cycle according to Embodiment 1 of the present invention includes a two-stage compressor 1 that compresses refrigerant in two stages, a first expansion device 3 that expands refrigerant in two stages, and a second expansion device. 7 is adopted. Carbon dioxide is used as the refrigerant.
In the two-stage compressor 1 according to the first embodiment, the refrigerant is sequentially compressed by the low-stage side rotary compression element 11 and the high-stage side rotary compression element 12 contained in the hermetic container 13, and the pressure is increased to a supercritical state. It discharges into the sealed container 13 from the discharge port d ₂ of the stage side rotary compressing element 12. Thereafter, the refrigerant discharged from the hermetic container 13 to the external circuit is radiated and cooled by the high-pressure radiator 2, and then depressurized to a saturation pressure or less by the first expansion device 3. Gas-liquid separation is performed by the separator 4. The discharge port d _{1 of the} low-stage side rotary compression element 11 and the suction port S _{2 of the} high-stage side rotary compression element 12 are connected by an intermediate connection circuit 15.

The refrigerant mainly composed of the gas phase in the gas-liquid separator 4 is intermediately injected from the injection circuit 5 to the refrigerant mixer 14 in the middle of the intermediate connection circuit 15 of the two-stage compressor 1, and the low-stage side rotary compression element. After being mixed with the refrigerant discharged from 11, the refrigerant is sucked into the high-stage rotary compression element 12.
The injection circuit 5 is provided with a flow rate adjusting valve 16 for adjusting the injection amount.
On the other hand, the liquid-phase refrigerant in the gas-liquid separator 4 is further depressurized by the second expansion device 7, endothermically heated by the evaporator 8, evaporated to a gas phase state, and again on the lower stage side of the two-stage compressor 1. It is sucked from the suction port S ₁ rotary compression element 11.

  In the two-stage compressor 1, the ratio of the excluded volume of the high-stage rotary compression element 12 to the excluded volume of the low-stage rotary compression element 11 (hereinafter referred to as the excluded volume) so that the intermediate pressure is equal to or lower than the critical pressure of the refrigerant. (Referred to as a ratio) is equal to or higher than the isentropic exponent root of the quotient obtained by dividing the suction pressure of the two-stage compressor 1 by the refrigerant saturated liquid pressure in the first expansion device 3.

Further, in the supercritical vapor compression refrigeration cycle according to the first embodiment, the thermometers 20 and 21 are on the upstream side and the downstream side of the first expansion device 3, and the thermometer 22 is connected to the gas-liquid separator 4. The side pipe 23, the thermometer 24 is connected to the injection circuit 5 connected to the gas-liquid separator 4, and the thermometers 25 and 26 are connected from the discharge port d _{1 of the} low stage side rotary compression element 11 to the suction port of the high stage side rotary compression element 12. before and after the position where the injection circuit 5 of the intermediate connecting circuit 15 for coupling the S ₂ is connected, in the longitudinal thermometer 27 and 28 of the high-pressure radiator 2, thermometer 29 and 30 respectively before and after the evaporator 8 The state of the refrigerant is estimated from the temperature measured. Then, in order to make the refrigerant before suction of the gas-liquid separator 4 less than the saturated liquid pressure and the wet gas state, the temperature of the thermometer 21 before suction of the gas-liquid separator 4 is less than the saturated liquid temperature, that is, the wet gas. It is determined whether or not the refrigerant is in a state, and if the temperature of the refrigerant immediately before being sucked into the gas-liquid separator 4 is a liquid temperature range, the first expansion device 3 is throttled to adjust the intermediate pressure to be lowered.

FIG. 2 is a Ph diagram of the supercritical vapor compression refrigeration cycle according to Embodiment 1 of the present invention.
Next, the effect of performing the intermediate injection will be described with reference to FIG. The low-stage suction pressure of the two-stage compressor 1 is P _S1 (equal to the suction pressure P _SS of the two-stage compressor 1), and the intermediate pressure is P _m (low-stage discharge pressure P _d1 and high-stage suction pressure). equal to the P _S2), representative of the high-stage discharge pressure _{P d2} (equal to the discharge pressure _{P d} of the two-stage compressor 1). Further, the circulation amount circulating through the evaporator 8 is represented by G _eV , the intermediate injection amount is represented by G _inj , and the gas cooler side circulation flow rate is represented by G _gC . Here, the gas cooler-side circulation flow rate G _gC is obtained from G _gC = G _eV + G _inj, and the ratio α of the intermediate injection amount is defined as α = G _inj / G _eV .

The improvement in the coefficient of performance (referred to as COP for Coefficient of Performance) by intermediate injection in the two-stage compression improves the compressor efficiency and the cycle efficiency.
First, the effect of improving cycle efficiency will be described.
(1) In air conditioning and cooling applications, the difference in enthalpy on the condenser side is increased by two-stage compression injection, and the cooling capacity and the cooling performance coefficient are improved.
(2) In air-conditioning / heating applications, the gas cooler-side refrigerant circulation rate is increased and the heating capacity and coefficient of performance are improved, but the effect is small compared to air-conditioning / cooling applications.
(3) The hot water supply application has the same effect as the air conditioning heating application, but the injection amount is restricted because the discharge temperature is lowered.
(4) When the high pressure shell compressor is operated at a high compression ratio, the high stage discharge temperature becomes abnormally high and the reliability of the two stage compressor 1 is impaired. By performing intermediate injection as a countermeasure, it is possible to suppress an abnormal increase in the high-stage discharge temperature without reducing the coefficient of performance.

Figure 3 illustrates a P-h diagram of the suction port S ₂ of the high-stage rotary compression element 12 of the embodiment two-stage compressor 1 according to the first embodiment of the present invention. In FIG. 3, A ₀ is an ideal state without injection, that is, volumetric efficiency is 1, and when there is no suction heating loss, A ₁ is an ideal state with injection, that is, volumetric efficiency is 1, When there is no heating loss, B ₀ is volume efficiency with actual volume efficiency without injection and there is no suction heating loss, B ₁ is with C ₀ when volume efficiency is actual volume efficiency and there is no suction heating loss, C ₀ the real state without injection, i.e., the volumetric efficiency is the actual volumetric efficiency, if there is a suction heat loss, C ₁ is the actual state of there injection, i.e., the volumetric efficiency is the actual volumetric efficiency, in the case where there is a suction heat loss shows the enthalpy and pressure at the suction port S ₂ of each of the high-stage side rotary compressing element 12.
Also, the intermediate pressure is greater with and without injection. Further, the intermediate pressure in the actual state is larger than the intermediate pressure in the ideal state.

Next, the condition of the excluded volume ratio necessary for establishing the two-stage compression injection cycle will be described.
1) An ideal state when no injection is performed, that is, a case where volumetric efficiency is 1 and intermediate heating is not performed will be described. (It is the state of _{A 0} in FIG. 3.)
At this time, the ideal intermediate pressure P _{m ad} is equal to the low-stage discharge pressure P _{d1 ad} when the isentropic compression is performed in the low-stage rotary compression element 11, and is obtained by Expression (1). Where V _St1 is the low-stage excluded volume, V _St2 is the high-stage excluded volume, ρ _S1 is the low-stage suction refrigerant density, ρ _d1ad is the low-stage discharge refrigerant density when _isentropic compression, and P _S1 the low-stage suction pressure of the two-stage compressor 1, P _m is the intermediate pressure of the two-stage compressor 1, n is an isentropic exponent.

P _{m ad} = P _{d1 ad} = P _S1 × (ρ _d1ad / ρ _S1 ) ⁿ
= P _S1 × (V _St1 / V _St2 ) ⁿ (1)

The isentropic index n is obtained by calculating from the REFPROP 7th edition database using n = LN (P _m / P _S1 ) ÷ LN (ρ _m / ρ _S1 ), and the isentropic index n is about 1 .3.
Further, the high-stage suction pressure _{P S2} of the two-stage compressor 1 is equal to the ideal intermediate pressure _{P m ad.}

2) Next, the case where injection is performed, volumetric efficiency is actual volumetric efficiency, and intermediate heating is not performed will be described. (It is the state of _{B 1} in FIG.)
At this time, the mass conservation formula is represented by the formula (2). However, eta _V1 is low-stage volumetric efficiency, eta _V2 is higher stage volumetric efficiency, the [rho _S2 is suction refrigerant density of the high-stage side.

V _St1 × η _V1 × ρ _S1 × (1 + α) = V _St2 × η _V2 × ρ _S2 (2)

When the injected refrigerant changes at the same pressure from the low-stage discharge port d ₁ to the high-stage suction port S ₂ , the energy of the mixed refrigerant is stored, and Equation (3) is established. Then, the excluded volume ratio V _St2 / V _St1 is obtained by Expression (4) obtained by substituting Expression (3) into Expression (2).

ρ _S2 = {(1 + α) × ρ _d1 × ρ _inj } / (ρ _d1 × α + ρ _inj ) (3)
V _St2 / V _St1 = (η _V1 / η _V2 ) × (1 + α) × (ρ _S1 / ρ _S2 )
= (Η _V1 / η _V2 ) × (1 + α × ρ _d1 / ρ _inj ) × (ρ _S1 / ρ _d1 ) (4)

The prerequisite for that can be gas injection after a gas-liquid separation is that the intermediate pressure P _{m ad} of the ideal state is less than the saturated liquid pressure P _liq the first expansion device 3. When this necessary condition is rewritten, Equation (5) and Equation (6) are obtained. Here, the when the low-stage discharge port d ₁ is equal to the ideal low-stage discharge port d _{1 ad,} requirement formula (7).

P _S1 × (ρ _{d1 ad} / ρ _S1 ) ⁿ <P _liq <P _crt (5)
ρ _S1 / ρd _{1 ad} > (P _s1 / P _liq ) ^{1 / n} > (P _s1 / P _crt ) ^{1 / n} (6)
ρ _S1 / ρd ₁ > (P _s1 / P _liq ) ^{1 / n} > (P _s1 / P _crt ) ^{1 / n} (7)

Therefore, the necessary condition for the excluded volume ratio V _St2 / V _St1 is expressed by Equation (4) and Equation (7) to Equation (8).

V _St2 / V _St1 > (η _V1 / η _V2 ) × (1 + α × ρ _d1 / ρ _inj ) × (P _s1 / P _liq ) ^{1 / n}
> (Η _V1 / η _V2 ) × (1 + α × ρ _d1 / ρ _inj ) × (P _s1 / P _crt ) ^{1 / n} (8)

Normally, it is known that when the rotary type rotary compression element is configured using the same cylinder (with the same inner diameter and thickness), the leakage sensitivity (= leakage area / exclusion volume) increases as the rejection volume decreases. Usually, since the low-stage excluded volume V _St1 is larger than the high-stage excluded volume V _St2 (that is, here, _assuming that V _St2 / V _St1 <1), the low-stage side volume efficiency η _V1 is the high-stage side volume. The relationship of the formula (9) is established when the efficiency is larger than η _V2 . Further, since the relationship of the equation (10) is established with respect to (1 + α × ρ _d1 / ρ _inj ) of the equation (4), the necessary condition for the excluded volume ratio V _St2 / V _St1 is the equation (11).

η _V1 / η _V2 > 1 (9)
(1 + α × ρ _d1 / ρ _inj )> 1 (10)
V _St2 / V _St1 > (P _s1 / P _liq ) ^{1 / n} > (P _s1 / P _crt ) ^{1 / n} (11)

3) Next, the case where injection is performed, volumetric efficiency is actual volumetric efficiency, and intermediate heating is performed will be described. (It is the state of _{C 1} in FIG.)
Due to the occurrence of various compressor losses, when the intermediate pressure refrigerant is heated to a constant pressure and the temperature rises, the refrigerant density ρ _{d1 r} of the discharged intermediate pressure is isentropically compressed by the low-stage rotary compression element 11. The lower-stage-side discharged refrigerant density ρ _{d1 ad in FIG} . Also, substituting [rho _{d1 r} in [rho _d1 of formula (4), equation (13) is obtained. By replacing ρ _{d1 r} in this equation (13) with ρ _{d1 ad} , equation (14) is obtained from relational equation (12).

ρ _{d1 ad} <ρ _{d1 r} (12)
V _St2 / V _St1 = (η _V1 / η _V2 ) × (1 + α × ρ _d1 / ρ _inj ) × (ρ _S1 / ρ _{d1 r} ) (13)
V _St2 / V _St1 > (η _V1 / η _V2 ) × (1 + α × ρ _d1 / ρ _inj ) × (ρ _S1 / ρ _{d1 ad} )
= (Η _V1 / η _V2 ) × (1 + α × ρ _d1 / ρ _inj ) × (P _S1 / P _{m ad} ) (14)

  In addition, the necessary condition regarding the excluded volume ratio for performing gas injection after gas-liquid separation is Expression (8), and further Expression (11).

4) In the state of A ₀ in FIG. 3, α in the equation (8) is set to zero and η _V1 = η _V2 may be set. In the state of B ₀ in FIG. 3, α in Expression (8) may be set to zero and ρ _{d1 ad} = ρ _{d1 r} . In the state of C ₀ in FIG. 3, α in Expression (8) may be zero and ρ _{d1 ad} <ρ _{d1 r} .
Further, when the state of the _{A 1} in FIG. 3, and alpha> 0 of the formula (8) may be set to η _V1 = η _V2.
Moreover, the necessary condition regarding the excluded volume ratio for performing gas injection after gas-liquid separation is Expression (8), and further Expression (11).

Next, the effect of the supercritical vapor compression refrigeration cycle according to Embodiment 1 will be described.
Table 1 shows typical environmental conditions and operating conditions used for residential carbon dioxide refrigerant heat pump water heaters. This environmental condition is quoted from the temperature conditions described in the Japan Refrigeration and Air Conditioning Industry Association Standard “JRA4050-2005” and the values specified in the Better Living Enacted Good Housing Parts Performance Test Method (BLT EH: 2003). did. SH is an abbreviation for Super-Heat and represents the degree of suction heating. Here, about 10 ° C. was assumed. The subscript S means suction, d means discharge, and exp means before the expansion valve. The temperatures and pressures before the suction, discharge, and expansion valve shown in the operating conditions are determined almost uniformly within the practical range from the environmental condition temperature.

  Table 2 shows the basic specifications of the rotary type two-stage compressor 1 used for comparing the effects of the first embodiment.

また、表３には、二段圧縮機１の性能特性のうち、中間圧の予測値と実験値を示す。なお、予測方法は、技術文献１（福田充宏、他３名、「Ｒ４１０Ａ用２段ロータリ圧縮機の性能予測」、平成１０年度日本冷凍空調学会学術講演会講演論文集、日本冷凍空調学会、平成１０年１０月、ｐ．４１−４４）や技術文献２（角田昌之、他１名、「回転式容積形圧縮機の内部漏れの解析と評価」、第１９回空気調和・冷凍連合講演会講演論文集、日本冷凍空調学会、１９８５年４月、ｐ．１７−１９）に記載されている解析手段を適用する。

Table 3 shows predicted values and experimental values of the intermediate pressure among the performance characteristics of the two-stage compressor 1. The prediction method is described in Technical Document 1 (Fukuda Mitsuhiro and three others, “Performance Prediction of R410A Two-Stage Rotary Compressor”, 1998 Proc. October 2010, p.41-44) and Technical Document 2 (Masayuki Tsunoda and one other, "Analysis and Evaluation of Internal Leakage of Rotary Displacement Type Compressor", 19th Air Conditioning and Refrigeration Union Lecture Lecture The analysis means described in the paper collection, Japan Society of Refrigerating and Air Conditioning, April 1985, p.17-19) is applied.

Table 3 shows the intermediate pressure predicted when the injection rate is 10% when the ratio (α) of the injection amount is 10% in the hot water supply rating and JRAIA winter (high temperature heating in winter). In addition, the intermediate pressure prediction value in the state (B ₁ ) considering the actual volume efficiency is larger than the intermediate pressure prediction value in the ideal state (A ₁ ), and the intermediate pressure in the state (C ₁ ) in consideration of the suction heating loss. The predicted value was larger and it was confirmed that it was in good agreement with the measured value.

  Next, in the gas-liquid separation type two-stage compressed gas injection cycle, the performance improvement effect by the intermediate injection when the excluded volume ratio of the two-stage compressor 1 is 0.65 and 0.85 is predicted and compared. explain. As calculation conditions for prediction, operating conditions of hot water supply ratings shown in Table 1 are used. Moreover, the ratio of the injection amount assumed that the gas phase gas after gas-liquid separation was gas-injected to the maximum.

FIG. 4 is a graph showing the relationship of the compressor efficiency with respect to the total compression ratio P _d2 / P _S1 with the excluded volume ratio and the presence or absence of injection as parameters. FIG. 5 is a graph showing the relationship of the hot water supply heating coefficient of performance (COP) with respect to the total compression ratio P _d2 / P _S1 with the excluded volume ratio and the presence or absence of injection as parameters.
As can be seen from FIG. 4 and FIG. 5, in the case of no injection, the two-stage compressor 1 with a rejection volume ratio of 0.85 has a total compression ratio of 2.5 or less and performance such as compressor efficiency and hot water heating performance coefficient. The two-stage compressor 1 having an excluded volume ratio of 0.65 is excellent, and the performance is excellent in a region where the total compression ratio is larger than 2.5. On the other hand, when there is injection, the performance of the two-stage compressor 1 having an overall compression ratio in the range of about 2 to about 4 and an excluded volume ratio of 0.85 is excellent.

FIG. 6 is a graph showing the relationship of the ratio of the gas injection amount to the total compression ratio with the excluded volume ratio as a parameter.
In order to perform gas-liquid separation type gas injection, it is a necessary condition that the refrigerant decompressed by the first expansion device 3 is not higher than the saturated liquid pressure P _liq and becomes a wet gas state, and the higher the dryness β, the more the injection is performed. The amount ratio α increases. However, when the rejection volume ratio is 0.65, the intermediate pressure is relatively high, so that gas-liquid separation cannot be performed at a total compression ratio of 2.5 or less. Even if the total compression ratio exceeds 2.5, the dryness β is small, so that a large injection amount cannot be obtained.

  FIG. 7 is a graph showing the relationship between the low-stage compression ratio and the high-stage compression ratio with respect to the total compression ratio with the presence or absence of injection in the two-stage compressor 1 having an excluded volume ratio of 0.85 as a parameter. FIG. 8 is a graph showing the relationship between the low-stage compression ratio and the high-stage compression ratio with respect to the total compression ratio with the presence or absence of injection in the two-stage compressor 1 having an excluded volume ratio of 0.65 as a parameter. 7 and 8 also show the optimum value of the compression ratio with respect to the total compression ratio. In general, in the two-stage compressor 1, the low-stage compression ratio and the high-stage compression ratio are the square roots of the total compression ratio, respectively, and the intermediate pressure is the suction pressure and discharge pressure of the two-stage compressor 1. Since it is known that the compressor efficiency is best when the square root of the product of, the square root of this total compression ratio is used as the optimum value of the low-stage compression ratio and the high-stage compression ratio. .

In the case of the two-stage compressor 1 with an excluded volume ratio of 0.85, as shown in FIG. 7, when injection is performed, the intermediate pressure increases, and the low-stage compression ratio P _d1 / _PS1 and the high-stage compression ratio Both P _d2 / P _S2 are close to the optimum values, and the compressor efficiency can be improved.
On the other hand, in the case of the two-stage compressor 1 having an excluded volume ratio of 0.65, the compressor efficiency cannot be improved because the low-stage compression ratio and the high-stage compression ratio do not change even if injection is performed.

In a two-stage compression injection cycle using such a gas-liquid separator, the excluded volume ratio 0.65 disclosed in Japanese Patent Laid-Open No. 2001-73976 is not an optimum value. In order to obtain the performance improvement effect by gas injection, first, it is necessary that the refrigerant decompressed by the first expansion device 3 be in a wet gas state at a saturated fluid pressure P _liq or less, and also regarding the excluded volume ratio. Relational expression (8) or relational expression (11) is a necessary condition.

  By doing so, the pressure of the refrigerant depressurized by the first expansion device 3 becomes equal to or lower than the saturated hydraulic pressure, and the isosteric volume ratio is the isentropy of the ratio of the suction pressure of the two-stage compressor 1 to the saturated hydraulic pressure. Since it is more than the root of the index, the compressor efficiency and reliability can be improved.

Further, if the intermediate pressure is smaller than the square root of the product of the suction pressure and the discharge pressure of the two-stage compressor 1, the intermediate pressure is compressed by two-stage compression by intermediately injecting the refrigerant into the intermediate pressure of the two-stage compressor 1. Asymptotically approaches the square root of the product of the suction pressure and the discharge pressure of the machine 1, the compressor efficiency is improved and the reliability is improved. Here, if the saturated hydraulic pressure P _liq in the equation (8) is replaced with the square root of the product of the suction pressure and the discharge pressure of the two-stage compressor 1, the equations (15) and (16) are necessary conditions. It becomes.

V _St2 / V _St1 > (η _V1 / η _V2 ) × (1 + α × ρ _d1 / ρ _inj ) × (P _s1 / P _d2 ) ^{1 / 2n} (15)
V _St2 / V _St1 > (P _s1 / P _d2 ) ^{1 / 2n} (16)

Next, the effect of injecting the refrigerant into the intermediate pressure according to the first embodiment will be described from another viewpoint.
Table 4 shows general operating conditions of an air conditioning heating / cooling facility using a carbon dioxide refrigerant. FIG. 9 shows the dryness as a parameter, and under the conditions of the cooling rating shown in Table 4, the volume efficiency is 1, ideal condition without intermediate heating, and the intermediate pressure of the two-stage compressor 1 is the optimum value (P _S / P _d ) It is a graph showing an excluded volume ratio corresponding to ^1/2 . FIG. 10 shows the optimum value of the intermediate pressure of the two-stage compressor 1 under the conditions of the cooling rating shown in Table 4 under the conditions of the cooling rating shown in Table 4 under the actual conditions taking into account the effects of the actual volumetric efficiency and intermediate heating. it is a graph showing the displacement volume ratio that matches _{P S} / P ^{d) 1/2.}

  When the ratio (α) of the refrigerant injection amount is 0%, the excluded volume ratio calculated backward is 0.79, and the optimum excluded volume ratio increases as the ratio of the refrigerant injection amount increases. When the ratio of the refrigerant injection amount is increased to 60%, the rejection volume ratio is predicted to change in the range of 0.79 to 1.12 in the ideal condition and in the range of 0.84 to 1.15 in the actual condition. . The larger the lower-stage suction superheat (SH), the smaller the excluded volume ratio, and the smaller the dryness of the intermediate injection refrigerant, the smaller the excluded volume ratio tends to be.

The ratio of injecting the refrigerant with the gas main component needs to be not too small and not too large considering the stability of the refrigeration cycle, and is usually in the range of 10% to 50%. The optimum excluded volume ratio varies depending on α, but a range of (P _S / P _d ) ^{1 / 2n} or more is a necessary condition, and is a value of 0.8 or more in a normally considered cooling rated condition.
Moreover, since this time ^{_{(P S / P crt) 1}} / 2n <(P S / P d) 1 / 2n of the equation is satisfied, satisfying requirement equation for gas-liquid separation injection is established (16). If the excluded volume ratio is appropriately set as described above, the intermediate pressure approaches the optimum value by the intermediate injection, and the effect of improving the compressor efficiency can be obtained.

Embodiment 2. FIG.
FIG. 11 is a circuit diagram of a two-stage compression / two-stage expansion supercritical vapor compression refrigeration cycle using a gas-liquid separator according to Embodiment 2 of the present invention.
The supercritical vapor compression refrigeration cycle according to the second embodiment of the present invention includes a check valve 19 provided in the intermediate coupling circuit 15 in the supercritical vapor compression refrigeration cycle according to the first embodiment and a low-stage side. The difference is that a return circuit 18 for returning the discharged refrigerant gas to the gas-liquid separator 4 is added, and the rest is the same, so the same reference numerals are given to the same parts and the description is omitted.
In the supercritical vapor compression refrigeration cycle according to the second embodiment, the refrigerant gas discharged from the low-stage side rotary compression element 11 is discharged from the intermediate coupling circuit 15 when the gas-liquid separator 4 is in a liquid phase state and cannot be injected. A check valve 19 that branches and a return circuit 18 that returns the branched refrigerant gas to the gas-liquid separator 4 are provided.

The refrigerant gas discharging this way from the low-stage side rotary compressing element 11 without transmitting the high-stage suction port S _2, when via the return circuit 18 back to the gas-liquid separator 4, the gas-liquid separator 4 to increase the degree of dryness by mixing and heat exchange with the liquid phase refrigerant in the inner, it is possible to inject the gas-phase refrigerant from the injection circuit 5 to the high-stage suction port S _2.
By doing so, the refrigerant main component that is intermediately injected into the two-stage compressor 1 can be kept in a gas phase, and the compressor efficiency and reliability are reduced by injecting a large amount of liquid phase refrigerant. Can be prevented.

Embodiment 3 FIG.
FIG. 12 is a circuit diagram of a supercritical vapor compression refrigeration cycle of a two-stage compression / one-stage expansion system using an internal heat recovery heat exchanger according to Embodiment 3 of the present invention.
The supercritical vapor compression refrigeration cycle according to Embodiment 3 of the present invention uses an internal heat recovery heat exchanger 10 instead of the supercritical vapor compression refrigeration cycle and gas-liquid separator 4 according to Embodiment 1. This is different from that of the high-pressure radiator 2 by the second expansion device 7 to the suction pressure to the low-stage side rotary compression element 11, and the rest is the same. Additional description will be omitted.

  Further, the supercritical vapor compression refrigeration cycle according to the third embodiment includes a refrigerant mixer 14 at the junction of the injection circuit 5 and the intermediate connection circuit 15. In the refrigerant mixer 14, the main component of the gas phase supplied from the injection circuit 5 is mixed with the refrigerant discharged from the low-stage rotary compression element 11 and gasified, and then the high-stage rotary compression element 12 is supplied to the refrigerant mixer 14. Inhale.

FIG. 13 is a configuration diagram of an example of the refrigerant mixer 14.
As shown in FIG. 13, the refrigerant mixer 14 includes a torsion tube type refrigerant-refrigerant heat exchanger 14 a wound around the intermediate coupling circuit 15. One end of the refrigerant-refrigerant heat exchanger 14 a is connected to the injection circuit 5, and the other end is connected in the middle of the intermediate coupling circuit 15.
In this refrigerant mixer 14, heat exchange is performed between the liquid-mixed injection refrigerant sent from the injection circuit 5 and the gas refrigerant discharged from the low-stage rotary compression element 11, and the injection refrigerant whose dryness is increased is intermediately connected. It is joined to the circuit 15 and sent to the high stage side rotary compression element 12.

FIG. 14 is a configuration diagram of another example of the refrigerant mixer 14.
Further, as shown in FIG. 14, another refrigerant mixer 14 includes a buffer tank 14b, and connects the injection circuit 5 to the buffer tank 14b so that the refrigerant injected into the buffer tank 14b is swirled. Since the refrigerant injected from the injection circuit 5 is swirled and mixed in this way, it is sufficiently mixed.
It is also possible to make the two-stage compressor 1 compact by configuring this refrigerant mixing function inside the shell.

By doing so, it is possible to avoid liquid injection into the high-stage rotary compression element 12 even in an operation state in which a large amount of liquid-phase refrigerant flows from the injection circuit 5, thereby preventing a decrease in reliability.
Also in the third embodiment, by appropriately setting the excluded volume ratio in the same manner as in the first embodiment, as in the first embodiment, the refrigerant main component that is intermediately injected into the two-stage compressor 1 is used as the gas phase. The state can be maintained, and the reduction in the compressor efficiency and the reliability caused by injecting a large amount of the liquid phase refrigerant can be prevented.

Next, the effect of the supercritical vapor compression refrigeration cycle according to Embodiment 3 will be described.
FIG. 15 is a graph showing the relationship between the coefficient of heating performance and the ratio of the injection amount in the supercritical vapor compression refrigeration cycle according to the third embodiment.
The calculation method is the cycle of Technical Document 3 (Fumitake Amagasaki, “Simulation Technology in Refrigeration and Air Conditioning Equipment”, Refrigeration, Japan Society of Refrigeration and Air Conditioning, July 2003, Vol. 78, No. 909, p. 573-578). Using simulation, calculation was performed under the heating rated operating conditions in Table 4. When the ratio (α) of the refrigerant injection amount is in the range of about 20% to 50%, the heating performance coefficient (COP _H ) is the best and can be improved by 6% to 7%. When α is 10% or less and 60% or more, the performance deteriorates.
FIG. 16 is a graph showing the relationship of the rejection volume ratio to the ratio of the injection amount with the superheat degree (SH) as a parameter in the supercritical vapor compression refrigeration cycle according to the third embodiment.
16 is calculated under the conditions of the heating ratings shown in Table 4 by calculating the appropriate ratio of injection amount, dryness, and intermediate pressure, respectively. _V1 = η _V2 , without intermediate heating).
As can be seen from FIG. 16, the excluded volume ratio increases as the ratio of the injection amount increases. Standard low-stage side superheat of the suction port S ₁ is about 10 ° C., displacement volume ratio to reduce the degree of superheat is increased.
Further, as can be seen from FIGS. 15 and 16, a high heating coefficient of performance (COP _H ) is obtained when the ratio of the injection amount is in the range of 20% to 50%, which is an excluded volume ratio of 0.8. It corresponds to the range of -1.1.
Normally, the excluded volume ratio is in the range of 1 or less. However, when a large amount of refrigerant is injected in the middle, it is also effective when the excluded volume ratio is 1 or more.

Embodiment 4 FIG.
FIG. 17 is a cross-sectional view of a rotary compression element of a two-stage compressor according to Embodiment 4 of the present invention.
As shown in FIG. 17, the low-stage side rotary compression element 11 and the high-stage side rotary compression element 12 are arranged around the main shaft 30a of the common crankshaft 30, respectively, a pin shaft 30b, a cylinder 31, a roller 32, and a vane 33. The vane support spring 34. Usually, these part dimensions are determined according to the value of the excluded volume.

In the present invention, since the injection amount is adjusted so that the excluded volume ratio becomes 1, these component dimensions can be made common and the manufacturing cost can be reduced.
However, since the volume flow rate is higher on the lower stage side than on the higher stage side, the inner diameter dimensions of the suction port 35 and the discharge port 36 may be larger in the low stage side rotary compression element 11 than in the higher stage side rotary compression element 12. preferable. Further, the gap size of the roller 32 is different between the low-stage side rotary compression element 11 and the high-stage side rotary compression element 12.

Embodiment 5 FIG.
FIG. 18 is a circuit diagram of a supercritical vapor compression refrigeration cycle according to Embodiment 5 of the present invention.
The supercritical vapor compression refrigeration cycle according to the fifth embodiment of the present invention has an internal heat between the gas-liquid separator 4 and the second expansion device 7 of the supercritical vapor compression refrigeration cycle according to the first embodiment. The difference is that the exchanger 6 has been added, and the rest is the same, so the same reference numerals are given to the same parts, and the description will be omitted.

  In the supercritical vapor compression refrigeration cycle according to the fifth embodiment, the liquid-phase refrigerant separated by the gas-liquid separator 4 is endothermically heated by the evaporator 8 in the internal heat exchanger 6 and evaporated to the gas phase state. Since heat exchange is performed with the gas-phase refrigerant separated by the second gas-liquid separator 9, the coefficient of performance is improved as compared with the case of the first embodiment.

In any of the first to fifth embodiments, each stage (low stage and high stage) excluded volume of the rotary type two-stage compressor is defined as a theoretical excluded volume (theoretical displacement) V _{St th.} Seeking from. However, R is a cylinder radius, r is a roller radius, and L is a cylinder length.

V _{St th} = π (R ² −r ² ) L (17)

Usually, since V _St1 > V _St2 , the lower stage cylinder length (L ₁ )> the higher stage cylinder length (L ₂ ), or the lower stage roller radius (r ₁ ) <high. If the step-side roller radius (r ₂ ) is used, it is configured using two types of rotary compression elements.
Further, normally, the suction phase is delayed so that the suction port overlaps the vane position, and the suction angle (θ _S : see FIG. 17, the unit is expressed in degrees = degree) is set. Although the actual excluded volume taking into consideration the suction angle θ _{S of} less than 30 degrees is smaller than the theoretical excluded capacity, the difference is within 1%. Therefore, the numerical values specifying the range of the excluded volume ratio in the first to fifth embodiments include an error of 1% or less.
In addition, when the suction angle θ _S is delayed by about 50 degrees, the actual excluded volume becomes 2-3% smaller than the theoretical excluded capacity. Therefore, by delaying the suction angle θ _S , the excluded volume ratio becomes 0.8 to 1.0. Variable in range.

From the calculation results obtained in Embodiments 1 to 5, it was predicted that the compressor efficiency and the reliability could be improved if the excluded volume ratio was 0.8 or more and 1 or less. Therefore, the supercritical vapor compression cycle according to Embodiments 1 to 5 is applied to a cooling / heating air conditioning facility of carbon dioxide refrigerant that operates supercritically. For example, the indoor temperature during cooling is 25 ° C. (ET is 15 ° C.), the outdoor temperature during cooling is 30 ° C. (T _exp is 35 ° C.), the indoor temperature during heating is 20 ° C. (T _exp is 25 ° C.), and the outdoor temperature during heating is 1.2 Assuming ℃ (ET is 10 ° C), the compression ratio during cooling is approximately 1.8 to 1.9, and the compression ratio during heating is approximately 1.9 to 2.1. As described above, since the carbon dioxide refrigerant operates under a relatively low compression ratio condition as compared with the chlorofluorocarbon refrigerant, the excluded volume ratio can be set larger than that of the chlorofluorocarbon refrigerant. When the carbon dioxide refrigerant is operated under a low compression ratio, the compressor efficiency can be improved and the reliability can be improved by selecting the excluded volume ratio as a design condition from the range of 0.8 to 1. It is done.

  Further, the supercritical vapor compression cycle according to Embodiments 1 to 5 is applied to a carbon dioxide refrigerant heat pump water heater operating in a supercritical state. Under the condition of the hot water supply rating of the Japan Refrigeration and Air Conditioning Industry Association Standard, the compression ratio is about 2.5. As described above, since the carbon dioxide refrigerant operates under a relatively low compression ratio condition as compared with the chlorofluorocarbon refrigerant, the excluded volume ratio can be set larger than that of the chlorofluorocarbon refrigerant.

  In addition, the calculation results and experimental results obtained in Embodiments 1 to 5 have been described assuming a high-pressure shell type compressor, but similar calculation results and incident results are also obtained in the low-pressure shell type and the intermediate pressure shell type. As a result, if the excluded volume ratio is set by the same method, it is possible to provide an air-conditioning / air-conditioning facility or a heat pump water heater in which the intermediate pressure is appropriately set, the compressor efficiency is high, and the reliability is excellent.

  The calculation results and experimental results obtained in Embodiments 1 to 5 have been described assuming a rotary type two-stage compressor. However, in the case of a scroll type, a swing type, a reciprocating type, and other compression types, a rotary type compressor is used. Calculation results and experimental results similar to the equation are obtained, and if the volume ratio is set in the same way, the intermediate pressure is set appropriately, the compressor efficiency is high, and the air conditioning and air conditioning equipment and heat pump hot water supply that are highly reliable Machine can be provided.

In the first to fifth embodiments, carbon dioxide is used as a refrigerant in a cycle in which the high pressure side operates in a supercritical state. However, ethane, acetylene, Nitrogen dioxide, chlorotrifluoromethane (R13), trifluoromethane (R23), or fluoromethane (R41) can be used.
A mixed refrigerant in which difluoromethane (R32) is mixed in carbon dioxide within 20 w% can also be used. Even in the supercritical vapor compression refrigeration cycle using these refrigerants, the intermediate pressure can be set appropriately, the compressor efficiency is high, and the reliability can be achieved by setting the excluded volume ratio in the same manner as in the first to fifth embodiments. Excellent in properties. However, the numerical range of the excluded volume ratio differs somewhat depending on the refrigerant.

1 is a circuit diagram of a supercritical vapor compression refrigeration cycle using a gas-liquid separator according to Embodiment 1 of the present invention. 1 is a Ph diagram of a supercritical vapor compression refrigeration cycle according to Embodiment 1 of the present invention. FIG. It is a Ph diagram at the inlet of the high stage side rotary compression element of the two stage compressor concerning Embodiment 1 of this invention. It is a graph which shows the relationship of the compressor efficiency with respect to the total compression ratio which makes an exclusion volume ratio and the presence or absence of injection a parameter. It is a graph which shows the relationship of the hot_water | molten_metal heating performance coefficient with respect to the total compression ratio which uses the exclusion volume ratio and the presence or absence of injection as a parameter. It is a graph which shows the relationship of the ratio of the gas injection quantity with respect to the total compression ratio which makes an exclusion volume ratio a parameter. It is a graph which shows the relationship between the low stage side compression ratio and the high stage side compression ratio with respect to the total compression ratio which makes the parameter the presence or absence of the injection in the two-stage compressor of exclusion volume ratio 0.85. It is a graph which shows the relationship of the low stage side compression ratio and the high stage side compression ratio with respect to the total compression ratio which makes the parameter the presence or absence of injection in the two-stage compressor of exclusion volume ratio 0.65. It is a graph which shows the excluded volume ratio which uses dryness as a parameter and the intermediate pressure of a two-stage compressor corresponds to an optimal value on ideal conditions. It is a graph which shows the excluded volume ratio which uses dryness as a parameter and the intermediate pressure of a two-stage compressor corresponds to an optimal value on real conditions. It is a circuit diagram of the supercritical vapor compression refrigerating cycle of the two-stage compression two-stage expansion system using the gas-liquid separator concerning Embodiment 2 of this invention. It is a circuit diagram of the supercritical vapor compression refrigerating cycle of the two-stage compression one-stage expansion system using the internal heat recovery type heat exchanger concerning Embodiment 3 of this invention. It is a block diagram of an example of a refrigerant mixer. It is a block diagram of the other example of a refrigerant mixer. 6 is a graph showing a relationship of a heating performance coefficient with respect to a ratio of an injection amount in a supercritical vapor compression refrigeration cycle according to Embodiment 3. 7 is a graph showing a relationship of an excluded volume ratio with respect to a ratio of an injection amount having a superheat degree as a parameter in a supercritical vapor compression refrigeration cycle according to Embodiment 3. It is sectional drawing of the rotary compression element of the two-stage compressor concerning Embodiment 4 of this invention. It is a circuit diagram of the supercritical vapor compression refrigeration cycle concerning Embodiment 5 of this invention.

Explanation of symbols

  1 Two-stage compressor, 2 High pressure radiator, 3, 7 Expansion device, 4, 9 Gas-liquid separator, 5 Injection circuit, 6 Internal heat exchanger, 8 Evaporator, 10 Internal heat recovery type heat exchanger, 11 Low Stage side rotary compression element, 12 High stage side rotary compression element, 13 Airtight container, 14 Refrigerant mixer, 14a Refrigerant-refrigerant heat exchanger, 14b Buffer tank, 15 Intermediate connection circuit, 16 Flow rate adjusting valve, 18 Return circuit, 19 Check valve, 20, 21, 22, 24, 25 Thermometer, 23 Liquid phase side piping, 30a Main shaft, 30b Pin shaft, 31 Cylinder, 32 Roller, 33 vane, 34 Vane support spring, 35 Suction port, 36 Discharge port .

Claims (8)

The low-pressure refrigerant is compressed to the intermediate pressure by the low-stage side rotary compression element, and is sucked into the high-stage side rotary compression element via the intermediate connection circuit, and is compressed to the high pressure by the high-stage side rotary compression element. A first stage compressor, a first expansion device that depressurizes the refrigerant compressed to a high pressure to a saturation liquid pressure or less, a gas-liquid separator that gas-liquid separates the refrigerant in a wet gas state below the saturation liquid pressure, An injection circuit that injects the gas-phase refrigerant after liquid separation into the intermediate coupling circuit, a second expansion device that depressurizes the liquid-phase refrigerant after gas-liquid separation to a low pressure, and a refrigerant that is depressurized to a low pressure. In a supercritical vapor compression refrigeration cycle having an evaporator,
The rejection volume ratio of the displacement volume of the high-stage rotational compression element to the displacement volume of the low-stage rotation compression element is the ratio of the suction pressure of the two-stage compressor to the refrigerant saturation fluid pressure in the first expansion device. Greater than or equal to the isentropic exponent
The supercritical vapor compression system, wherein the opening degree or the suction heating degree of the first expansion device or the second expansion device is controlled so as to keep the refrigerant injected into the intermediate connection circuit in a gas phase state. Refrigeration cycle. The low-pressure refrigerant is compressed to the intermediate pressure by the low-stage rotary compression element, and the refrigerant is sucked into the high-stage rotary compression element via the intermediate connection circuit and compressed to the high pressure by the high-stage rotary compression element. A stage compressor, a high-pressure radiator that cools a refrigerant compressed to a high pressure and divides the refrigerant into two systems, a first expansion device that decompresses one of the divided refrigerants to an intermediate pressure, and the first expansion device A heat exchanger that recovers the internal heat of the refrigerant that has been reduced to an intermediate pressure, an injection circuit that injects the refrigerant that has recovered the internal heat into the intermediate connection circuit, and a second that reduces the other divided refrigerant to a low pressure. In a supercritical vapor compression refrigeration cycle having an expansion device and an evaporator for evaporating the refrigerant decompressed to a low pressure,
The rejection volume ratio of the displacement volume of the high-stage rotational compression element to the displacement volume of the low-stage rotation compression element is the ratio of the suction pressure of the two-stage compressor to the refrigerant saturation fluid pressure in the first expansion device. Greater than or equal to the isentropic exponent
A supercritical vapor compression refrigeration cycle characterized in that the opening degree or the suction heating degree of the first expansion device is controlled so as to keep the dryness of the refrigerant injected into the intermediate coupling circuit at a high level. The low-pressure refrigerant is compressed to the intermediate pressure by the low-stage rotary compression element, and the refrigerant is sucked into the high-stage rotary compression element via the intermediate connection circuit and compressed to the high pressure by the high-stage rotary compression element. A first stage compressor, a first expansion device that depressurizes the refrigerant compressed to a high pressure to a saturation liquid pressure or less, a gas-liquid separator that gas-liquid separates the refrigerant in a wet gas state below the saturation liquid pressure, An injection circuit that injects the gas-phase refrigerant after liquid separation into the intermediate connection circuit, a second expansion device that depressurizes the liquid-phase refrigerant after gas-liquid separation to a low pressure, and evaporates the refrigerant depressurized to a low pressure. A supercritical vapor compression refrigeration cycle comprising:
The ratio of the excluded volume of the high-stage rotary compression element to the excluded volume of the low-stage rotary compression element is the isentropic index of the ratio of the suction pressure of the two-stage compressor to the discharge pressure of the two-stage compressor More than twice the root of
Controlling the opening of the first expansion device or the second expansion device so that the pressure of the refrigerant injected into the intermediate connection circuit approaches the square root of the product of the suction pressure and the discharge pressure. Supercritical vapor compression refrigeration cycle. The low-pressure refrigerant is compressed to the intermediate pressure by the low-stage rotary compression element, and the refrigerant is sucked into the high-stage rotary compression element via the intermediate connection circuit and compressed to the high pressure by the high-stage rotary compression element. A stage compressor, a high-pressure radiator that cools a refrigerant compressed to a high pressure and divides the refrigerant into two systems, a first expansion device that decompresses one of the divided refrigerants to an intermediate pressure, and the first expansion device A heat exchanger for exchanging heat from the refrigerant output from the high-pressure radiator to the refrigerant decompressed to an intermediate pressure and recovering internal heat, and an injection circuit for injecting the refrigerant recovered from the internal heat into the intermediate connection circuit; In a supercritical vapor compression refrigeration cycle having a second expansion device that depressurizes the other divided refrigerant to a low pressure, and an evaporator that evaporates the refrigerant depressurized to a low pressure.
The ratio of the excluded volume of the high-stage rotary compression element to the excluded volume of the low-stage rotary compression element is the isentropic index of the ratio of the suction pressure of the two-stage compressor to the discharge pressure of the two-stage compressor More than twice the root of
Supercritical steam, characterized in that the opening degree of the first expansion device is controlled so that the pressure of the refrigerant injected into the intermediate connection circuit approaches the square root of the product of the suction pressure and the discharge pressure. Compression refrigeration cycle. The refrigerant consists of carbon dioxide,
The supercritical vapor compression refrigeration cycle according to any one of claims 1 to 4, wherein the excluded volume ratio is 0.8 or more and 1.1 or less.   The supercritical vapor compression refrigeration cycle according to any one of claims 1 to 4, wherein the excluded volume ratio is 1.   A cooling / heating air-conditioning system using the supercritical vapor compression refrigeration cycle according to any one of claims 1 to 6, wherein the refrigerant is carbon dioxide.   A heat pump type water heater using the supercritical vapor compression refrigeration cycle according to any one of claims 1 to 6, wherein the refrigerant is carbon dioxide.

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