GB2528213A

GB2528213A - Heat pump device and air-conditioning system

Info

Publication number: GB2528213A
Application number: GB1519215.6A
Authority: GB
Inventors: Mamoru Hamada; Fumitake Unezaki
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2013-04-18
Filing date: 2013-04-18
Publication date: 2016-01-13
Anticipated expiration: 2033-04-18
Also published as: GB2528213B; JPWO2014170982A1; GB201519215D0; JP6072901B2; WO2014170982A1

Abstract

In this heat pump device, a refrigerant circuit is constructed by connecting, by piping, a compressor (1), a condenser (2), an expansion device (3), and an evaporator (4), and the heat pump device comprises: a condensation temperature detection means (11) that detects the saturation temperature of the condenser (2) as the condensation temperature; an evaporation temperature detection means (12) that detects the saturation temperature of the evaporator (4) as the evaporation temperature; and a control device (50) that performs a process for calculating, on the basis of the condensation temperature and the evaporation temperature, at least an average operation efficiency from the start of operation to the end of defrosting on the assumption that defrosting is performed at the present moment, and determining the start of defrosting of the evaporator on the basis of the calculated average operation efficiency.

Description

DESCRIPTION

Title of Invention

HEAT PUMP APPARATUS AND AIR CONDITIONING SYSTEM

Technical Field

[0001] The present invention relates to a heat pump apparatus capable of defrosting operation, and more particularly relates to determining a start of defrosting operation.

Background Art

[0002] Typically, with an evaporator in a heat pump apparatus, a frosting phenomenon in which frost grows on the evaporator surface occurs when the evaporating temperature is less than or equal to 0 degrees C and also less than or equal to the dew-point temperature of the air The occurrence of such a frosting phenomenon leads to increases in ventilation resistance and increases in heat resistance in the evaporator, and operating efficiency in the evaporator falls.

Accordingly, a heat pump apparatus requires a defrosting operation to guide discharge refrigerant from the compressor to the evaporator, and remove frost buildup on the evaporator surface.

[0003] In the related art, there exist heat pump apparatuses able to execute defrosting operation that melts frost adhering to the evaporator One such device, a "heat pump apparatus determining a start timing of a defrosting operation so as to maximize the one-cycle average COP (coefficient of performance, operating efficiency) from the start of heating operation to the end of defrosting operation", has been proposed (for example, see Patent Literature 1). The heat pump apparatus computes the current COP and the one-cycle COP on the basis of the refrigerant condensing temperature and the refrigerant evaporating temperature, and upon judging that the current COP has become smaller than the one-cycle COP, issues a command to start defrosting operation.

Citation List Patent Literature [0004] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 201 0-060150

Summary of Invention

Technical Problem [0005] In the heat pump apparatus according to Patent Literature 1, the refrigerant condensing temperature and the refrigerant evaporating temperature are used to computationally estimate the COP However, if factors such as the compressor frequency or the air temperature change, for example, at least one of the condensing temperature and the evaporating temperature of the refrigerant changes, and the COP also changes correspondingly. For this reason, if the computed COP falls even though frost is not adhering to the evaporator, for example, the situation may be inappropriately determined to be the start timing of the defrosting operation.

[0006] The present invention has been devised in order to solve the above problem and an objective thereof is to provide a heat pump apparatus capable of determining the start of defrosting more accurately.

Solution to Problem [0007] In order to solve the problems discussed above, a heat pump apparatus according to the invention is a heat pump apparatus connecting a compressor, a condenser, an expansion device, and an evaporator with pipes to constitute a refrigerant circuit, and includes a condensing temperature detector configured to detect a saturation temperature of the condenser as a condensing temperature, an evaporating temperature detector configured to detect a saturation temperature of the evaporator as an evaporating temperature, and a controller configured to conduct a process of computing, if defrosting were conducted at a present time, at least an average operating efficiency from a start of operation until an end of defrosting based on the condensing temperature and the evaporating temperature, and determining, based on the computed average operating efficiency, a start of defrosting of the evaporator.

Advantageous Effects of Invention [0008] According to the invention, a condensing temperature and an evaporating temperature are corrected, and factors such as the operating efficiency are computed on the basis of the corrected condensing temperature and the corrected evaporating temperature, thereby enabling a more correct determination of the start of defrosting, even when the compressor frequency or the air temperature changes, for example.

Brief Description of Drawings

[0009] [FIG. 1] FIG. 1 is a diagram illustrating a schematic configuration of a heat pump apparatus 100 according to Embodiment 1 of the present invention.

[FIG. 2] FIG. 2 is a block diagram illustrating a summary of signal input/output relationships related to control in the heat pump apparatus 100 according to Embodiment 1 of the present invention.

[FIG. 3] FIG. 3 is a diagram illustrating a graph of the relationship between time and COP according to Embodiment 1 of the present invention.

[FIG. 4] FIG. 4 is a diagram illustrating a graph of the relationship between time and COP in one cycle according to Embodiment 1 of the present invention.

[FIG. 5] FIG. 5 is a diagram illustrating a flowchart of one example of the flow of a process related to defrosting start determination control of the heat pump apparatus 100.

[FIG. 6] FIG. 6 is a diagram illustrating a graph of the relationship between instantaneous COP and average COP according to Embodiment 1 of the present invention.

[FIG. 7] FIG. 7 is a diagram illustrating a graph of the relationship between instantaneous COP and one-cycle average COP according to Embodiment 1 of the present invention.

[FIG. 8] FIG. 8 is a diagram illustrating a graph of the relationship between instantaneous COP and average COP according to Embodiment 1 of the present invention.

[FIG. 9] FIG. 9 is a diagram illustrating the relationship between compressor frequency F, evaporating temperature Te, and condensing temperature Tc according to Embodiment 1 of the present invention.

[FIG. 10] FIG. 10 is a diagram illustrating the relationship between evaporator intake air temperature Tae and evaporating temperature Te according to Embodiment 1 of the present invention.

[FIG. 11] FIG. 11 is a diagram illustrating the relationship between condenser intake air temperature Tac and condensing temperature Tc according to Embodiment 1 of the present invention.

[FIG. 12] FIG. 12 is a diagram illustrating a flowchart of one example of the flow of a process related to defrosting start determination control of the heat pump apparatus 100 according to Embodiment 1 of the present invention.

[FIG. 13] FIG. 13 is a diagram illustrating the relationship between instantaneous heating capacity and one-cycle average heating capacity according to Embodiment 2 of the present invention.

[FIG. 14] FIG. 14 is a diagram illustrating change overtime in instantaneous COP and heating capacity according to Embodiment 2 of the present invention.

[FIG. 15] FIG. 15 is a diagram illustrating a change in instantaneous COP and heating capacity when the condenser intake air temperature Tac changes according to Embodiment 2 of the present invention.

[FIG. 16] FIG. 16 is a diagram illustrating a change in instantaneous COP and heating capacity when the evaporator intake air temperature Tae changes according to Embodiment 2 of the present invention.

[FIG. 17] FIG. 17 is a diagram illustrating a flowchart of one example of the flow of a process related to defrosting start determination control of the heat pump apparatus 100 according to Embodiment 2 of the present invention.

[FIG. 18] FIG. 18 is a diagram illustrating change overtime in instantaneous COP and heating capacity according to Embodiment 3 of the present invention.

[FIG. 19] FIG. 19 is a diagram illustrating change overtime in instantaneous COP and heating capacity according to Embodiment 3 of the present invention.

Description of Embodiments

[0010] Embodiment 1.

FIG. 1 is a diagram illustrating a schematic configuration of a heat pump apparatus 100 according to Embodiment 1 of the present invention. A refrigerant circuit configuration and operation of the heat pump apparatus 100 will be described on the basis of FIG. 1. The heat pump apparatus 100 is a device such as a refrigeration device that causes refrigerant to circulate and thereby conducts cooling operation with respect to a space or object to be refrigerated, or an air conditioning system that executes cooling operation to cool an air-conditioned space or heating operation to heat an air-conditioned space.

Herein, an air conditioning system will be described as a representative example.

Herein, in the drawings hereinafter, including FIG. 1, the relative sizes of respective structural members may differ from actual sizes in some cases. Also, in the drawings hereinafter, including FIG. 1, elements denoted with the same sign are the same or corresponding elements, and this holds true similarly throughout the text of the embodiments described hereinafter. Additionally, the aspect of the structural elements expressed throughout the text of this specification is merely illustrative, and such structural elements are not limited to

the aspect described in the specification.

[0011] As illustrated in FIG. 1, in the heat pump apparatus 100, a compressor 1, a condenser 2, an expansion device 3, and an evaporator 4 are successively connected in series with refrigerant pipes to constitute a heat pump circuit.

Also, a condenser fan 5 and a condensing temperature detector 11 are provided near the condenser 2. An evaporator fan 6 and an evaporating temperature detector 12 are provided near the evaporator 4. The condensing temperature detector 11 and the evaporating temperature detector 12 respectively detect a temperature, and transmit a signal including a value of the detected temperature (detection value) to a controller 50 that centrally controls the heat pump apparatus 100 overall.

[0012] The compressor 1 suctions refrigerant flowing through the refrigerant pipes, and compresses and discharges the refrigerant in a high temperature and high pressure state. The condenser 2 exchanges heat between the refrigerant and a fluid, causing the refrigerant to condense. In the present embodiment, air is used as the fluid. The expansion device 3 decompresses the refrigerant passing through the refrigerant pipes, causing the refrigerant to expand. The expansion device 3 may be configured using an expansion device such as an electronic expansion valve, for example. The evaporator 4 exchanges heat between the refrigerant and air, causing the refrigerant to evaporate. The condenser fan 5 supplies air to the condenser 2. Also, the evaporator fan 6 supplies air to the evaporator 4.

[0013] The condensing temperature detector 11 is a detecting device such as a temperature sensor that detects a saturation temperature of the condenser 2 (condensing temperature). The evaporating temperature detector 12 is a detecting device such as a temperature sensor that detects a saturation temperature of the evaporator 4 (evaporating temperature). In addition, an evaporator intake air temperature detector 13 that acts as an evaporator intake temperature detector is a detecting device such as a temperature sensor that detects the temperature of air flowing into the evaporator 4 (evaporator intake air temperature). Additionally, a condenser intake air temperature detector 14 that acts as a condenser intake temperature detector is a detecting device such as a temperature sensor that detects the temperature of fluid (air) flowing into the condenser 2 (condenser intake air temperature). Compressor frequency detector 15 is a device that detects the rotational frequency of the compressor (hereinafter designated the corn pressor frequency).

[0014] The controller 50 is made up of a microcontroller or the like, for example.

The controller 50 decides and controls the rotational frequency of the compressor 1 as well as the rotational speeds of the condenser fan 5 and the evaporator fan 6, on the basis of detection values from each above-mentioned detector (such as the condensing temperature detected by the condensing temperature detector 11 and the evaporating temperature detected by the evaporating temperature detector 12), for example. The controller 50 also controls the opening degree of the expansion device 3, for example. Also, in a case of changing the refrigerant flow channel or the like depending on operation, like in an air conditioning system or the like, the controller 50 includes a function of controlling the switching of a four-way valve (not illustrated), which is a refrigerant flow switching device. The operation and the like of the controller 50 according to the present embodiment will be described in detail later on the basis of FIG. 2.

[0015] Operation of the heat pump apparatus 100 will now be described briefly on the basis of the flow of refrigerant. When the heat pump apparatus 100 starts an operation, the heat pump apparatus 100 first drives the compressor 1. High temperature and high pressure gas refrigerant compressed by the compressor 1 is discharged from the compressor 1, and flows into the condenser 2. In the condenser 2, inflowing gas refrigerant condenses while transferring heat to the fluid used for heat exchange, and becomes low temperature and high pressure refrigerant. The refrigerant flows out from the condenser 2, and is depressurized by the expansion device 3 to become two-phase gas-liquid refrigerant. The two-phase gas-liquid refrigerant flows into the evaporator 4.

The refrigerant flowing into the evaporator 4 removes heat from the air, and thereby evaporates and gasifies. The refrigerant flows out from the evaporator 4, and flows into the compressor 1 again. At this point, while the heat pump apparatus 100 is running, the condensing temperature detector 11 and the evaporating temperature detector 12 are respectively detecting temperature and transmitting signals according to the detection values to the controller 50.

[0016] FIG. 2 is a block diagram illustrating a summary of signal input/output relationships related to control in the heat pump apparatus 100 according to Embodiment 1 of the present invention. The function of the controller 50 will be described in detail on the basis of FIG. 2. As illustrated in FIG. 2, the controller includes memory 51 that acts as a storage device, and a computational unit 52 that conducts computational processing based on detection values and the like. The memory 51 stores, as data, detection values detected by the condensing temperature detector 11, the evaporating temperature detector 12, the evaporator intake air temperature detector 13, the condenser intake air temperature detector 14, and the compressor frequency detector 15, for example. In addition, the computational unit 52 conducts computational processing on the basis of detection values stored by the memory 51. As above, the controller 50, on the basis of computational results from the computational unit 52, performs control by sending signals to each of the compressor 1, the four-way valve (not illustrated), the expansion device 3, the condenser fan 5, and the evaporator fan 6.

[0017] For example, when the controller 50 controls heating operation of the heat pump apparatus 100, the instantaneous COP (=COP) expressing the operating efficiency at the present time is computationally estimated (hereinafter, computed) from Expression (1), on the basis of the condensing temperature Tc and the evaporating temperature Te. Herein, Expression (1) is a definitional equation of the Carnot efficiency. Also, the power consumption is the result of computing the condensing temperature Ic minus the evaporating temperature Te.

[0018] [Math. 1] COP =(Tc+273.15)/(TcTe)...(1) [0019] FIG. 3 is a diagram illustrating a graph of the relationship between time and COP according to Embodiment 1 of the present invention. The relationship between time and instantaneous COP in the heat pump apparatus 100 will be described on the basis of FIG. 3. In FIG. 3, the horizontal axis represents time, while the vertical axis represents COP. In the heat exchange between the refrigerant and air in the evaporator 4, if the temperature of the refrigerant is less than or equal to 0 degrees C and also less than or equal to the dew-point temperature of the air, a frosting phenomenon occurs in which moisture included in the air adheres to the evaporator 4 and builds up into frost. If frosting of the evaporator 4 proceeds, the increase in ventilation resistance and the increase in heat resistance cause the amount of heat exchange in the evaporator 4 to decrease, and the instantaneous COP falls as illustrated in FIG. 3. Accordingly, defrosting becomes necessary. Herein, a defrosting operation that defrosts by passing high temperature refrigerant through the evaporator 4 will be described, but the defrosting method is not limited thereto, and may also involve superheating with a heater or the like, for example.

[0020] The instantaneous COP (=COP) illustrated in Expression (1) may accurately capture how the decrease in the evaporating temperature Te is greater than the condensing temperature Tc in conjunction with frosting, and the decrease in instantaneous COP due to frosting. For example, for the condensing temperature Tc, whereas Tc = 49 degrees C at the start of operation, Ic = 47 degrees C immediately before defrosting is started, decreasing by approximately 2 degrees C. Meanwhile, for the evaporating temperature Te, whereas Te = -2 degrees C at the start of operation, Te = -6 degrees C immediately before defrosting is started, decreasing by approximately 4 degrees C, and thus the instantaneous COP falls in conjunction with frosting.

[0021] FIG. 4 is a diagram illustrating a graph of the relationship between time and COP in one cycle according to Embodiment 1 of the present invention. The one-cycle average COP of the heat pump apparatus 100 will be described on the basis of FIG. 4. The operating efficiency when running with defrosting operation is rated according to a one-cycle average COP, in which one cycle is treated as being from the start of normal operation to the end of defrosting operation as illustrated in FIG. 4. Herein, since defrosting operation does not contribute to operation, the instantaneous COP becomes 0. Consequently, if defrosting operation is started at a timing when the one-cycle average COP reaches a maximum, energy savings may be realized effectively, and thus the start timing becomes important.

[0022] FIG. 5 is a diagram illustrating a flowchart of one example of the flow of a process related to defrosting start determination control of the heat pump apparatus 100. Also, FIG. 6 is a diagram illustrating a graph of the relationship between instantaneous COP and average COP according to Embodiment 1 of the present invention. FIG. 7 is a diagram illustrating a graph of the relationship between instantaneous COP and one-cycle average COP according to Embodiment 1 of the present invention. FIG. 8 is a diagram illustrating a graph of the relationship between instantaneous COP and average COP according to Embodiment 1 of the present invention. A flow of a process related to defrosting start determination control of the heat pump apparatus 100 will be described on the basis of FIGS. 5 to 8. Herein, in FIGS. 6 to 8, the horizontal axis represents time, while the vertical axis represents COP.

[0023] A process related to a start of defrosting conducted by the controller 50 will be described on the basis of FIG. 5. When the heat pump apparatus 100 starts an operation, the controller 50 stores, in the memory 51, the condensing temperature Tc which is the detection value detected by the condensing temperature detector 11, and the evaporating temperature Te which is the detection value detected by the evaporating temperature detector 12 (step SlOl). Subsequently, the computational unit 52 computes the instantaneous COP (=COP) expressed in Expression (1) above (step S102). Afterthat, as illustrated in FIG. 6, the computational unit 52 computes the average COP (=COP_AVE) from the start of normal operation (heating operation) to the present time (step S103).

[0024] As illustrated in FIG. 7, the defrosting start timing at which the one-cycle COP (=COP_CYCLE) reaches a maximum is when the instantaneous COP (=COP) falls to the one-cycle average COP (=COP_CYCLE) due to frosting.

[0025] The one-cycle average COP (=COP_CYCLE) when starting defrosting operation at the present time is expressed using the average COP (=COP_AVE) from the start of normal operation to the present time, as in Expression (2) below.

[0026] [Math. 2] COP_CYCLE = Ci x COP_AVE... (2) [0027] Herein, the term Cl on the right side of Expression (2) above accounts for the drop in the average COP due to defrosting operation, as illustrated in FIG. 7.

The term Ci may be a preset constant. For example, if defrosting operation causes the one-cycle average COP to become 96% of the average COP during heating operation (=COP_AVE), Cl = 0.96. Also, since the optimal value differs depending on factors such as the defrosting method and the device specifications, Cl may not be a constant, but set to a value that yields the optimal value as appropriate.

[0028] The one-cycle average COP when starting defrosting operation at the present time is computed from Expression (2) above, and compared to the instantaneous COP (=COP) at the present time (step Si 04). As a result of the comparison, in a case of determining that a relationship as indicated in Expression (3) below holds (step S 104; Yes), defrosting operation is started (step SlOb). On the other hand, in a case of determining that Expression (3) below does not hold (step S104; No), the process returns to step SlOi, and the process steps are repeated.

[0029] [Math. 3] COP «= COP_CYCLE... (3) [0030] However, the above description holds when the frequency of the compressor 1 is constant, the temperature of air flowing into the evaporator 4 (evaporator intake temperature) is constant, and the temperature of air flowing i3 into the condenser 2 (condenser intake temperature) is constant. In actual practice, the frequency of the compressor 1, the temperature of the intake air of the evaporator 4, and the temperature of the intake air of the condenser 2 change over time in many cases.

[0031] If the frequency of the compressor 1 the temperature of the intake air of the evaporator 4, and the temperature of the intake air of the condenser 2 change, the condensing temperature Tc and the evaporating temperature Te change. For example, if the frequency of the compressor 1 rises, the difference between the condensing temperature Tc and the evaporating temperature Te becomes larger, and the instantaneous COP in Expression (1) faIls. Also, if the temperature of the intake air of the condenser 2 rises, the condensing temperature Tc rises, and the instantaneous COP in Expression (1) falls. Also, if the temperature of the intake air of the evaporator 4 falls, the evaporating temperature Te, falls, and the instantaneous COP in Expression (1)falls.

[0032] In this way, if the frequency of the compressor 1, the temperature of the intake air of the evaporator 4, or the temperature of the intake air of the condenser 2 changes, the instantaneous COP falls, and Expression (3) above is satisfied, defrosting operation will be started by an incorrect determination, even though frosting has not occurred.

[0033] Accordingly, to avoid an incorrect determination, in the present embodiment, a corrected evaporating temperature and a corrected condensing temperature are computed as follows. First, let a reference evaporating temperature TeO and a reference condensing temperature TcO be the evaporating temperature and the condensing temperature when operating at a predetermined reference compressor frequency FO, reference evaporator intake air temperature TaeO, and reference condenser intake air temperature TacO.

[0034] Next, the compressor frequency detector 15 detects the actual compressor frequency F Also, the evaporator intake air temperature detector 13 detects the actual evaporator intake air temperature Tae. The condenser intake air temperature detector 14 detects the actual condenser intake air temperature Tac.

The evaporating temperature detector 12 detects the actual evaporating temperature Te. The condensing temperature detector 11 detects the actual condensing temperature Tc. Subsequently, on the basis of the above detection values, in the current frosting state, the evaporating temperature and the condensing temperature are corrected to an evaporating temperature (corrected evaporating temperature Te_mod) and a condensing temperature (corrected condensing temperature Tc_mod) when operating (performing heating operation) at the reference compressor frequency FO, the reference evaporator intake air temperature TaeO, and the reference condenser intake air temperature TacO.

[0035] FIG. 9 is a diagram illustrating the relationship between compressor frequency F, evaporating temperature Te, and condensing temperature Tc according to Embodiment 1 of the present invention. Specifically, the evaporating temperature Te and the condensing temperature Tc are corrected according to the difference AF between the actual compressor frequency F and the reference compressor frequency FO. As illustrated in FIG. 9, when AF is positive, the condensing temperature Tc is corrected downward and the evaporating temperature Te is corrected upward, according to the absolute value of AF Conversely, when AF is negative, the condensing temperature Tc is corrected upward and the evaporating temperature Te is corrected downward, according to the absolute value of AF In so doing, it becomes possible to compute the corrected evaporating temperature Te_mod and the corrected condensing temperature Tc_mod if the compressor 1, which is currently being driven at the compressor frequency F at the present time, were driven at the reference compressor frequency EQ. At this point, if control is applied so that the condensing temperature Tc does not change even if the compressor frequency F changes, the condensing temperature Tc and the corrected condensing temperature Tc_mod become the same. Also, if control is applied so that the evaporating temperature Te does not change even if the compressor frequency F changes, the evaporating temperature Te and the corrected evaporating temperature Te_mod become the same. For this reason, although correction is not particularly necessary, the above case will be described as being similar to the case of conducting correction so that the condensing temperature Ic equals the corrected condensing temperature Tc_mod, and the evaporating temperature Te equals the corrected evaporating temperature Te_mod (this applies similarly hereinafter).

[0036] FIG. 10 is a diagram illustrating the relationship between evaporator intake air temperature Tae and evaporating temperature Te according to Embodiment 1 of the present invention. The evaporating temperature Te is also corrected according to the difference ATae between the actual evaporator intake air temperature Tae and the reference evaporator intake air temperature TaeO. As illustrated in FIG. 10, when ATae is positive, the evaporating temperature Te is corrected downward, according to the absolute value of ATae. Conversely, when ATae is negative, the evaporating temperature Te is corrected upward, according to the absolute value of ATae. In so doing, it becomes possible to compute the corrected evaporating temperature Te_mod when the evaporator intake air temperature Tae at the present time is the reference evaporator intake air temperature TaeO.

[0037] FIG. 11 is a diagram illustrating the relationship between condenser intake air temperature Tac and condensing temperature Tc according to Embodiment 1 of the present invention. The condensing temperature Tc is also corrected according to the difference ATac between the actual condenser intake air temperature Tac and the reference condenser intake air temperature TacO. As illustrated in FIG. 11, when ATac is positive, the condensing temperature Tc is corrected downward, according to the absolute value of ATac. Conversely, when ATac is negative, the condensing temperature Ic is corrected upward, according to the absolute value of ATac. In so doing, it becomes possible to compute the corrected condensing temperature Tc_mod when the condenser intake air temperature Tac at the present time is the reference condenser intake air temperature TacO.

[0038] As above, the actual condensing temperature Tc and evaporating temperature Te are corrected on the basis of the compressor frequency F, the evaporator intake air temperature Tae, and the condenser intake air temperature Tac. Herein, the condensing temperature Tc may be subjected to a correction based on the compressor frequency F and a correction based on the condenser intake air temperature Tac, but in the present embodiment, the condensing temperature Tc is subjected to a correction reflecting both the compressor frequency F and the condenser intake air temperature Tac. At this point, the correction based on the condenser intake air temperature Tac may also be conducted after conducting the correction based on the compressor frequency F, or the corrections may be conducted in the reverse order. Similarly, the evaporating temperature Te may also be subjected to a correction based on the compressor frequency F and a correction based on the evaporator intake air temperature Tae, but in the present embodiment, the evaporating temperature Te is subjected to a correction reflecting both the compressor frequency F and the evaporator intake air temperature Tae. At this point, the correction based on the evaporator intake air temperature Tae may also be conducted after conducting the correction based on the compressor frequency F, or the corrections may be conducted in the reverse order. By conducting the corrections, the instantaneous COP when operating at the reference compressor frequency FO, the reference evaporator intake air temperature TaeO, and the reference condenser intake air temperature TacO may be computed in the present frosted state on the basis of Expression (4).

[0039] [Math. 4] Instantaneous COP = (Tc_mod +273.15)I(Tc_mod -Te_mod) ... (4) [0040] FIG. 12 is a diagram illustrating a flowchart of one example of the flow of a process related to defrosting start determination control of the heat pump apparatus 100 according to Embodiment 1 of the present invention. A process related to control of a defrosting start determination using Expression (4) will now be described.

[0041] When the heat pump apparatus 100 starts an operation, the controller 50 detects the condensing temperature Ic with the condensing temperature detector 11, the evaporating temperature Te with the evaporating temperature detector 12, Iae with the evaporator intake air temperature detector 13, and Tac with the condenser intake air temperature detector 14 (step 5301). Subsequently, on the basis of the detection values, the controller 50 computes the corrected evaporating temperature Te_mod and the corrected condensing temperature Ic_mod (step S302). Furthermore, on the basis of the corrected evaporating temperature Te_mod and the corrected condensing temperature Tc_mod, the controller 50 computes the instantaneous COP (=COP) expressed by Expression (4) above (step S303). Furthermore, the controller 50 calculates the average COP (=COP_AVE) from the start of normal operation to the present time as illustrated in FIG. 6 (step S304).

[0042] As illustrated in FIG. 7, the defrosting start timing at which the one-cycle COP (=COP_CYCLE) reaches a maximum is when the instantaneous COP (=COP) falls to the one-cycle average COP (=COP_CYCLE) due to frosting.

Accordingly, the one-cycle average COP is computed on the basis of Expression (2) above, and compared to the instantaneous COP (=COP) at the present time (step S305). As a result of the comparison, in a case of determining that a relationship as indicated in Expression (3) holds (step 305; Yes), defrosting operation is started (step 306). On the other hand, in a case of judging that the relationship indicated in Expression (3) does not hold (step 5305; No), the process returns to step S301, and the process steps are repeated.

[0043] Since the instantaneous COP illustrated in Expression (4) does not change according to the compressor frequency F, the evaporator intake air temperature Iae, and the condenser intake air temperature Tac, and falls only because of frosting, the timing of the start of defrosting is determined from values computed on the basis of Expressions (2) to (4), and thus defrosting operation may be started at an optimal timing without making an incorrect determination. For this reason, the one-cycle average COP rises, which may lead to energy savings.

[0044] Embodiment 2.

In Embodiment 1 discussed above, in order to avoid an incorrect determination of the start timing for defrosting operation, the evaporating temperature Te or the condensing temperature Tc is subjected to a correction.

The present embodiment avoids an incorrect determination without correcting the evaporating temperature Te or the condensing temperature Tc.

[0045] For this reason, in the present embodiment, the controller 50 conducts a defrosting start determination process on the basis of Expressions (1)to (3), and also makes a determination based on an instantaneous heating capacity (instantaneous capacity) Oh expressed in Expression (5) below in terms of the compressor frequency F and the condensing temperature Tc.

[0046] [Math. 5] Oh =(Tc+273.15) F... (5) [0047] FIG. 13 is a diagram illustrating a graph of the relationship between instantaneous heating capacity and one-cycle average heating capacity according to Embodiment 2 of the present invention. The relationship between time and capacity (heating capacity) in the heat pump apparatus 100 will be described on the basis of FIG. 13. In FIG. 13, the horizontal axis represents time, while the vertical axis represents capacity. If frosting of the evaporator 4 proceeds, the increase in ventilation resistance and the increase in heat resistance cause the amount of heat exchange in the evaporator 4 to decrease, and the instantaneous heating capacity Oh falls as illustrated in FIG. 13. By adding the drop in the instantaneous heating capacity Qh to the defrosting start determination condition, it becomes possible to avoid an incorrect determination even if the compressor frequency F, the evaporator intake air temperature Tae, and the condenser intake air temperature Tac change.

[0048] The determination is made on the basis of a comparison between the one-cycle average heating capacity (average capacity) Oh_CYCLE when starting defrosting operation at the present time, and the instantaneous heating capacity Oh. Herein, the one-cycle average heating capacity Oh_CYCLE is expressed using the average heating capacity Oh_AVE from the start of normal operation to the present time, as in Expression (6).

[0049] [Math. 6] Oh_CYCLE = C2 x Oh_AVE... (6) [0050] Herein, the term C2 on the right side of Expression (6) above accounts for the drop in the average heating capacity Oh_AVE due to defrosting operation, as illustrated in FIG. 13. The term C2 may be a preset constant. For example, if defrosting operation causes the one-cycle average heating capacity Oh_CYCLE to become 96% of the average heating capacity Oh_AVE during heating operation, C2 = 0.96. Also, since the optimal value differs depending on the defrosting method and the device specifications, C2 may not be a constant, but set to a value that yields the optimal value as appropriate.

[0051] FIG. 14 is a diagram illustrating change over time in instantaneous COP and heating capacity according to Embodiment 2 of the present invention. In FIG. 14, the horizontal axis represents time, while the vertical axis represents COP and capacity. If frosting of the evaporator 4 proceeds, the increase in ventilation resistance and the increase in heat resistance cause both the instantaneous COP and the instantaneous heating capacity to fall. At this point, if the compressor frequency F rises, the condensing temperature Tc rises and the evaporating temperature Te falls, and thus the instantaneous COP expressed in Expression (1) falls, but since the condensing temperature Tc and the compressor frequency F both rise, the instantaneous heating capacity Oh expressed in Expression (5) rises.

[0052] FIG. 15 is a diagram illustrating a change in instantaneous COP and heating capacity when the condenser intake air temperature Tac changes according to Embodiment 2 of the present invention. In FIG. 15, the horizontal axis represents time, while the vertical axis represents COP and capacity. If frosting of the evaporator 4 proceeds, the increase in ventilation resistance and the increase in heat resistance cause both the instantaneous COP and the instantaneous heating capacity Oh to fall. At this point, if the condenser intake air temperature Tac rises, the condensing temperature Tc rises, and for the instantaneous COP expressed by Expression (1), the increase of the denominator becomes greater than the increase of the numerator, and thus the instantaneous COP falls. On the other hand, the rise of the condensing temperature Tc causes the instantaneous heating capacity Qh expressed by Expression (5) to rise.

[0053] FIG. 16 is a diagram illustrating a change in instantaneous COP and heating capacity when the evaporator intake air temperature Tae changes according to Embodiment 2 of the present invention. In FIG. 16, the horizontal axis represents time, while the vertical axis represents COP and capacity. If frosting of the evaporator 4 proceeds, the increase in ventilation resistance and the increase in heat resistance cause both the instantaneous COP and the instantaneous heating capacity to fall. At this point, if the evaporator intake air temperature Tae falls, the evaporating temperature Te lowers, and for the instantaneous COP expressed by Expression (1), the denominator increases, and thus the instantaneous COP falls. On the other hand, the instantaneous heating capacity Oh, which is expressed by Expression (4) not including the evaporating temperature Te, does not change.

[0054] In this way, when there is a change in the compressor frequency, a change in the evaporator intake air temperature, ora change in the condenser intake air temperature, even if the instantaneous COP expressed by Expression (1) falls below the average COP as in Expression (3), the instantaneous heating capacity Oh does not fall below the one-cycle average heating capacity Oh_CYCLE, thereby demonstrating that the drop in the COP is not due to defrosting, but rather due to a change in the compressor frequency, a change in the evaporator intake air temperature, or a change in the condenser intake air temperature.

[0055] Conversely, when the instantaneous COP (=COP) and the instantaneous heating capacity Oh fall at the same time, the fall may be judged to be the result of frosting, and thus the controller 50 starts defrosting operation after judging that Expression (3) and Expression (7) below both hold true.

[0056] [Math. 7] Oh «= Oh_CYCLE... (7) [0057] FIG. 17 is a diagram illustrating a flowchart of one example of the flow of a process related to defrosting start determination control of the heat pump apparatus 100 according to Embodiment 2 of the present invention. When the heat pump apparatus 100 starts an operation, the controller 50 stores, in the memory 51, each value of the compressor frequency F detected by the compressor frequency detector 15, the condensing temperature Ic detected by the condensing temperature detector 11, and the evaporating temperature Te detected by the evaporating temperature detector 12 (step S401).

Subsequently, the computational unit 52 computes the instantaneous COP (COP) expressed in Expression (1) and the instantaneous heating capacity Oh expressed in Expression (5) above (step S402).

[0058] After that, the average COP (=COP_AVE) and the average heating capacity Oh_AVE are calculated from the start of normal operation to the present time as illustrated in FIG. 6 (step S403).

[0059] Next, the one-cycle average COP when starting defrosting operation at the present time is computed from Expression (2) above, the one-cycle average heating capacity is computed from Expression (6) above, and the above are compared to the instantaneous COP (=COP) and the instantaneous heating capacity (=Qh) at the present time, respectively (step S404). As a result of the comparison, in a case of determining that the relationships of Expression (3) and Expression (7) above hold (step S404; Yes), defrosting operation is started (step S405). On the other hand, in a case of determining that the relationship of either Expression (3) above or Expression (7) above does not hold (step S403; No), the process returns to step S401, and the process steps are repeated.

[0060] The cause by which the relationships of both Expression (3) and Expression (7) above hold at the same time can only be the defrosting phenomenon. Thus, according to the heat pump apparatus 100 of the present embodiment, by using Expression (3) and Expression (7) above in the defrosting start determination, it becomes possible to start defrosting operation at an optimal timing without making an incorrect determination even when the compressor frequency F, the evaporator intake air temperature Tae, or the condenser intake air temperature Tac changes, and energy savings may be realized.

[0061] Embodiment 3.

In Embodiment 1 and Embodiment 2 above, a correction that varies Cl and C2 according to the previous defrosting operation may also be conducted.

For example, a reference defrosting operation time may be decided in advance, and when the previous defrosting operation time is longer than the reference defrosting operation time, Cl in Expression (2) or C2 in Expression (6) is corrected to be larger. Conversely, when the previous defrosting operation time is shorter than the reference defrosting operation time, Cl in Expression (2) or C2 in Expression (6) is corrected to be smaller.

[0062] FIG. 18 is a diagram illustrating change over time in instantaneous COP and heating capacity according to Embodiment 3 of the present invention. As illustrated in FIG. 18, a long defrosting time means that the drop in COP and heating capacity due to defrosting operation was too large, and the heating operating time was too long, and thus it is good to increase Cl in Expression (2) or C2 in Expression (6).

[0063] FIG. 19 is a diagram illustrating change over time in instantaneous COP and heating capacity according to Embodiment 3 of the present invention. As illustrated in FIG. 19, a short defrosting time means that the drop in COP and heating capacity due to defrosting operation was too small, and the heating operating time was too short, and thus it is good to decrease Cl in Expression (2) or C2 in Expression (6).

[0064] By correcting Cl in Expression (2) or C2 in Expression (6) as above, the computational accuracy of the one-cycle average COP and the one-cycle average heating capacity may be improved. For this reason, it becomes possible to start defrosting operation at a more optimal timing, which leads to energy savings.

[0065] Embodiment 4.

In Embodiment 1 and Embodiment 2 above, the evaporator intake air temperature Tae may also use the evaporator intake air wet-bulb temperature.

[0066] Also, in Embodiment 1 and Embodiment 2 above, the condenser 2 exchanges heat between air and the refrigerant, but may also exchange heat between water or the like and the refrigerant, for example. In this case, the condenser intake air temperature Tac becomes the condenser inflow water temperature.

[0067] In Embodiment 1 above, the condensing temperature and the evaporating temperature are corrected on the basis of detection values from all of the evaporator intake air temperature detector 13, the condenser intake air temperature detector 14, and the compressor frequency detector 15, but the configuration is not limited thereto. The invention may be realized in the case of using any of the above detectors.

[0068] Furthermore, in Embodiment 2 above, correction of the condensing temperature and the evaporating temperature is not conducted, but like Embodiment 1, a corrected condensing temperature or a corrected evaporating temperature may be computed, and the instantaneous heating capacity Oh or the like may be computed on the basis of the corrected condensing temperature or the corrected evaporating temperature.

Reference Signs List [0069] 1 compressor, 2 condenser, 3 expansion device, 4 evaporator, condenser fan, 6 evaporator fan, 11 condensing temperature detector, 12 evaporating temperature detector, 13 evaporator intake air temperature detector, 14 condenser intake air temperature detector, 15 compressor frequency detector, 50 controller, 51 memory, 52 computational unit, 100 heat pump apparatus