JPH0435661B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a heat pump type air conditioner that uses air as a heat source, and more specifically to defrosting control that melts frost that adheres to an outdoor heat exchanger when the outside air temperature is low. It is.

Conventional technology The defrosting method of the outdoor heat exchanger of conventional air source heat pump air conditioners is mostly a cooling cycle by switching the four-way valve, and a reverse cycle in which the outdoor heat exchanger serves as the condenser and the indoor heat exchanger serves as the evaporator. Due to the defrosting method, the indoor fan was stopped at this time to prevent cold drafts.

With this method, there is basically little refrigerant circulation and it is not possible to expect much increase in compressor input, so the defrosting time becomes longer, and the indoor fan stops for several minutes during defrosting operation, so there is a lack of heating sensation and comfort. Moreover, even after the four-way valve is switched and the heating operation is resumed after the defrosting operation is completed, it takes time for the temperature of the indoor heat exchanger to rise, which is not satisfactory from the user's point of view. It wasn't.

In recent years, in place of the reverse cycle defrosting system, which has these drawbacks, the four-way valve is left in the same position as in heating operation during defrosting operation, and a portion of the gas discharged from the compressor is passed through the indoor heat exchanger to A hot gas bypass defrosting method has been proposed that defrosts the remaining discharged gas by guiding it to the inlet of the outdoor heat exchanger while maintaining the heating capacity (for example, "Japan Refrigeration Association Lecture Proceedings",
S59−11, P53).

An example of the above-mentioned conventional heat pump type air conditioner will be described below with reference to the drawings.

FIG. 4 shows a refrigeration cycle diagram of a conventional heat pump type air conditioner.

In the figure, 1 is a variable frequency compressor whose capacity can be controlled, 2 is a four-way valve, 3 is an indoor heat exchanger, 4 is an electric expansion valve whose valve opening can be varied, 5 is an outdoor heat exchanger,
6 is a hot gas bypass circuit, and 7 is a two-way valve.

The hot gas bypass circuit 6 connects the discharge side of the variable frequency compressor 1 to a pipe that becomes the inlet side during heating operation of the outdoor heat exchanger 5, and includes a two-way valve 7 in the middle. During normal heating operation, the two-way valve 7 is closed to form a heating cycle, but when frost forms on the outdoor heat exchanger 5 when the outside air temperature is low, the heating capacity decreases and a defrosting operation becomes necessary. The two-way valve 7 is opened to direct most of the high temperature discharged gas to the inlet side of the outdoor heat exchanger 5 via the hot gas bypass circuit 6. At the same time, the remainder of the high-temperature discharged gas is transferred to the four-way valve 2, indoor heat exchanger 3, and electric expansion valve 4 in the same way as during heating operation.
Then, a slight heating operation is continued, and at point C, which is the inlet side of the outdoor heat exchanger 5, the refrigerant is merged with most of the refrigerant branched on the high pressure side. After this combined refrigerant defrosts the outdoor heat exchanger 5 with its own condensation heat, it returns to the variable frequency compressor 1 via the four-way valve 2 and completes the defrosting cycle.

Problems to be Solved by the Invention However, the above configuration has the following problems. FIG. 5 shows the cycle of the conventional heat pump air conditioner shown in FIG. 4 during defrosting operation on a Mollier diagram.

Symbols a to e shown in the figure correspond to those shown in FIG. That is, during defrosting operation, the refrigerant branched at point a on the compressor discharge side joins at point C on the inlet side of the outdoor heat exchanger 5, and this point C exists in the superheating region. Here, the refrigerant has an enthalpy of i _c . After condensation, that is, after defrosting, the refrigerant state changes to a point d with a high liquid content in the two-phase region and reaches a point _e after pressure loss. 1, so a considerable amount of liquid compression is being performed. This poses a major problem in terms of compressor reliability when considering the number of defrosting operations during the annual heat pump season. Furthermore, from the usage status of refrigerant during defrosting (point c → point d), the sensible heat (superheat region) and latent heat (two-phase region) of the refrigerant are used, and as the frost melts, drain water begins to drip. In the later stages of defrosting, a temperature distribution occurs on the surface of the outdoor heat exchanger 5, so that convective heat is radiated from the high temperature portion of the surface of the outdoor heat exchanger 5 to the surrounding atmosphere, reducing the defrosting performance.

Further, FIG. 6 shows the change in the heating capacity of the conventional heat pump type air conditioner during defrosting operation, and FIG. 7 similarly shows the change in high pressure side pressure and low pressure side pressure during defrosting operation. In FIG. 7, A indicates the high pressure side pressure, and B indicates the low pressure side pressure.

As is clear from the figure, as defrosting progresses, the ratio of the high pressure side pressure A and the low pressure side pressure B, that is, the compression ratio, decreases, and the low pressure side pressure B increases, so that the suction side of the frequency variable compressor 1 decreases. As the specific volume of the refrigerant decreases, the amount of refrigerant circulated within the refrigeration cycle increases, and therefore the heating capacity decreases significantly at the start of defrosting and then gradually increases. For this reason, when defrosting begins, the heating capacity may drop significantly, causing discomfort to the occupants, and conversely, near the end of defrosting, the heating capacity becomes too large compared to when defrosting begins, and the defrosting increases. The hours were getting long.

In view of the above-mentioned problems, the present invention allows a portion of the high temperature discharged gas to flow through the indoor heat exchanger during defrosting operation to allow continued heating operation, thereby reducing a large amount of liquid returning to the compressor and liquid compression. It improves the temperature distribution on the surface of the outdoor heat exchanger to achieve uniform defrosting with a uniform temperature, and also makes the ratio of the refrigerant flow rate flowing through the indoor heat exchanger and the refrigerant flow rate flowing through the bypass circuit variable, so that it can be used for a long period of time. To provide a heat pump air conditioner that is highly reliable and has improved defrosting efficiency without causing discomfort to residents.

Means for Solving the Problems In order to solve the above problems, the heat pump air conditioner of the present invention includes a compressor, a four-way valve, an indoor heat exchanger,
A first throttling device with a variable throttling amount, an outdoor heat exchanger, etc. are sequentially connected in an annular manner by piping to constitute a refrigeration cycle, and piping leads from the compressor, which is at high pressure during heating operation, to the indoor heat exchanger. and a bypass circuit connecting the outdoor heat exchanger to the compressor, which also has a low pressure during heating operation, and a second throttle that has a variable throttle amount and can block the flow path. a heating capacity detection means capable of detecting a change in heating capacity during a defrosting operation for defrosting the outdoor heat exchanger; is controlled to a predetermined value smaller than the throttling amount during the heating operation, and the throttling amount of the second throttling device is controlled to be a predetermined value that opens the flow path of the bypass circuit, and the defrosting operation is performed. A throttle amount control means is provided therein for controlling the throttle amount of the second throttle device in accordance with the value detected by the heating capacity detection means.

Effects With the above configuration, the present invention allows part of the high temperature discharged gas to flow to the indoor heat exchanger even during defrosting operation to continue the heating operation, and reduces the aperture of the first throttle device to discharge the high temperature discharged gas. Since the remainder of the gas is returned directly to the outdoor heat exchanger outlet, which is the compressor suction side, the refrigerant circulation is good, and while the compressor input is maintained, the dryness of the compressor suction refrigerant can be increased, even though it is two-phase. It can reduce backflow and liquid compression. In addition, the refrigerant flowing into the outdoor heat exchanger becomes two-phase, and the temperature on the surface of the outdoor heat exchanger rises uniformly and uniformly from the early and middle stages of defrosting, as well as from the latter stages of dripping water after melting to the drying stage. This prevents the temperature of a portion from rising rapidly before returning to heating operation, which reduces convective heat radiation loss to the surroundings and improves defrosting efficiency. Furthermore, by making the ratio of the refrigerant flow rate flowing through the indoor heat exchanger and the refrigerant flow rate flowing through the bypass circuit variable according to changes in heating capacity during defrosting operation,
Defrosting efficiency can be further improved without causing discomfort to residents during defrosting and without causing an extreme increase in heating capacity.

Embodiment A heat pump air conditioner according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a refrigeration cycle diagram of a heat pump air conditioner according to an embodiment of the present invention.

In the figure, 11 is a compressor, 12 is a four-way valve,
13 is an indoor heat exchanger, 14 is a first electric expansion valve whose opening degree can be varied by electromagnetic force, 15 is an outdoor heat exchanger,
16 is a bypass circuit, and 17 is a second electric expansion valve that is provided in the bypass circuit and whose valve opening degree can be varied by electromagnetic force. Further, 18 is an indoor temperature detection element that detects the temperature of the indoor heat exchanger 13, and 19 is an outdoor temperature detection element that detects the temperature of the outdoor heat exchanger 15.
20 receives the temperature signals from the indoor temperature detection element 18 and the outdoor temperature detection element 19, and operates the first electric expansion valve 1.
4. A control circuit that controls the valve opening degree of the second electric expansion valve 17. Then, the compressor 11, the four-way valve 12, the indoor heat exchanger 13, the first electric expansion valve 14, and the outdoor heat exchanger 15 are sequentially connected in an annular manner.
The outlet side of the outdoor heat exchanger 15 during heating operation is connected to the outlet side of the outdoor heat exchanger 15 during heating operation, and a bypass circuit 16 including a second electric expansion valve 17 is provided in the middle.

Next, the operation of the heat pump air conditioner configured as described above will be explained. During normal heating operation, the second electric expansion valve 17 is in a fully closed state, and the refrigerant is supplied to the compressor 11, four-way valve 12, indoor heat exchanger 13, first electric expansion valve 14, outdoor heat exchanger 15, The refrigerant flows through the four-way valve 12 and returns to the compressor 11 to form a heating cycle, and no refrigerant flows into the bypass circuit 16.

However, when the outside temperature is low, frost forms on the outdoor heat exchanger 15, and when the temperature signal of the outdoor temperature detection element 19 drops to the set value, the control circuit 20 issues a command to start defrosting, and the four-way valve 12 remains in the same state. The second electric expansion valve is opened to a predetermined valve opening that is set to reduce the heating capacity to an extent that does not cause discomfort to the occupants, and the high temperature discharged gas is branched off at point a', with some remaining as it is. It flows into the indoor heat exchanger 13, and the rest is guided to the outlet side of the outdoor heat exchanger 15, and defrosting is started by setting the valve opening of the first electric expansion valve 14 to a slightly fully open position to reduce the throttling amount to almost zero. .

FIG. 2 is a Mollier diagram showing a cycle during defrosting operation of one embodiment of the heat pump type air conditioner shown in FIG.

Symbols a' to e' shown in the figure correspond to those shown in FIG. In other words, the high temperature discharged gas that flows directly from point a' to the indoor heat exchanger 13 during defrosting operation is:
Since the valve opening degree of the first electric expansion valve 14 is almost fully open, the heat is condensed and radiated at a relatively low temperature of about 30 to 40 degrees Celsius, and then moving to point b', heating operation can be continued by the N of the indoor fan (not shown). . The pressure is reduced through the pipes along the way and a slight restriction in the first electric expansion valve 14, and the temperature reaches point c', where it flows into the outdoor heat exchanger 15, where it is further condensed at about 0°C, which is the melting temperature of frost, and radiated heat to defrost it. It reaches point d′. The enthalpy difference of the refrigerant used for defrosting at this time is Δidef=ic'-id', and the state of the refrigerant flowing into the outdoor heat exchanger 15 is already two-phase as shown at point c'. By the way, the enthalpy difference of the refrigerant used for indoor heating is ia'-ib' if we ignore the heat loss along the way.

On the other hand, the discharged gas at the remaining temperature is transferred to the outdoor heat exchanger 15.
Since the refrigerant is guided to the outlet side of the refrigerant, after changing its enthalpy, it joins and mixes with the liquid-rich refrigerant that has flowed through the main circuit, reaches point e', and is sucked into the compressor 11.
This point e′ is the dryness of the refrigerant even though it is in a two-phase state.
Since xe′ is large and the liquid content is small, liquid return and liquid compression can be reduced or substantially avoided. Furthermore, since the refrigerant flowing into the outdoor heat exchanger 15 during defrosting operation is basically in a two-phase state, the refrigerant temperature, that is, the surface temperature of the outdoor heat exchanger 15, is also constant, and there is no unevenness in the surface temperature. Uniform defrosting can be achieved.

Furthermore, when the defrosting operation starts, by setting the valve opening of the second electric expansion valve 17 to a predetermined valve opening rather than fully opening, the drop in high pressure side pressure is small, and therefore the heating capacity is sharply reduced. without causing any discomfort to residents. Furthermore, as defrosting progresses, the high pressure side pressure gradually increases and the heating capacity increases as shown in the conventional example, but the indoor temperature detection element 1
When the temperature signal of 8 rises to the set value, the control circuit 2
0 issues a signal to increase the valve opening of the second electric expansion valve 17, thereby suppressing the increase in high pressure side pressure and heating capacity, and increasing the flow rate of refrigerant flowing through the bypass circuit 16, further defrosting. Efficiency can be improved.

The solid line in FIG. 3 shows the change in heating capacity during defrosting operation of the heat pump type air conditioner in one embodiment of the present invention.
By changing the opening degree of the valve 7, defrosting can be completed without causing discomfort to residents at the start of defrosting compared to the change in heating capacity during snow removal of the conventional heat pump air conditioner shown by the broken line. There is no need for unnecessary heating near the time of day.

Note that the present invention has been described using the first and second electric expansion valves 14 and 17 whose valve opening degree is variable using electromagnetic force as a driving source as the best form of the first and second throttle devices. Each throttle device may be configured using a plurality of throttles such as capillaries, and may be controlled by appropriate switching, and bimetal, shape memory alloy, or the like may be used as a means for varying the valve opening degree. In addition, increasing heating capacity can be achieved by using indoor heat exchanger 13.
Although the present invention is not limited to this, the position of the pressure, temperature, etc. to be detected and the means thereof are arbitrary as long as an increase in heating capacity can be detected. The same applies to the determination of the time to start defrosting.

Effects of the Invention As described above, the heat pump air conditioner of the present invention has a compressor, a four-way valve, an indoor heat exchanger, a first throttling device with a variable throttling amount, and an outdoor heat exchanger that are connected via piping. A bypass circuit is formed that forms a cycle and connects piping from the compressor to the indoor heat exchanger, which is at high pressure during heating operation, and piping from the outdoor heat exchanger to the compressor, which is also at low pressure during heating operation. A second throttling device is provided in the bypass circuit with a variable throttling amount and can shut off the flow path, and a change in heating capacity can be detected during a defrosting operation to defrost the outdoor heat exchanger. heating capacity detection means is provided, and when the defrosting operation is started, the first
The throttling amount of the second throttling device is set to a predetermined value smaller than the throttling amount during heating operation, and the throttling amount of the second throttling device is set to a predetermined value that opens the flow path of the bypass circuit. and a throttling amount control means for controlling the throttling amount of the second throttling device according to the value detected by the heating capacity detecting means during defrosting operation. By allowing a portion of the high temperature discharged gas to flow through the heat exchanger to continue heating operation, it reduces the amount of liquid returning to the compressor and liquid compression, and improves the temperature distribution on the surface of the outdoor heat exchanger to maintain a uniform temperature. It achieves uniform defrosting, and also changes the ratio of the refrigerant flow rate through the indoor heat exchanger to the refrigerant flow rate through the bypass circuit in response to changes in heating capacity during defrosting operation, ensuring long-term reliability. It has various effects such as being able to improve defrosting efficiency without causing discomfort to residents.

[Brief explanation of drawings]

Fig. 1 is a refrigeration cycle diagram of a heat pump air conditioner according to an embodiment of the present invention, Fig. 2 is a diagram showing the cycle during defrosting operation of the heat pump air conditioner on a Mollier diagram, and Fig. 3 is a diagram showing the cycle during defrosting operation of the heat pump air conditioner. An explanatory diagram showing changes in heating capacity during defrosting operation of the heat pump air conditioner, Figure 4 is a refrigeration cycle diagram of a conventional heat pump air conditioner, and Figure 5 is a diagram of the conventional heat pump air conditioner shown in Figure 4. Figure 6 is an explanatory diagram showing the change in heating capacity during defrosting operation of a conventional heat pump air conditioner, and Figure 7 is a diagram showing the cycle during defrosting operation of a conventional heat pump air conditioner on a Mollier diagram. FIG. 2 is an explanatory diagram showing changes in high-pressure side pressure and low-pressure side pressure during defrosting operation of the heat pump air conditioner. 11... Compressor, 12... Four-way valve, 13... Indoor heat exchanger, 14... First electric expansion valve (first throttling device), 15... Outdoor heat exchanger, 16... Bypass circuit, 17...Second electric expansion valve (second throttle device), 18...Indoor temperature detection element (heating capacity detection means), 20...Control circuit (throttling amount control means).

Claims (1)

[Scope of Claims] 1 A compressor, a four-way valve, an indoor heat exchanger, a first throttling device with a variable throttling amount, and an outdoor heat exchanger are sequentially connected via piping to constitute a refrigeration cycle, and during heating operation A bypass circuit is formed that bypasses piping from the compressor to the indoor heat exchanger, which is at high pressure, and piping from the outdoor heat exchanger to the compressor, which is at low pressure during heating operation. A second throttling device is provided that is variable and capable of blocking the flow path, and heating capacity detection means is provided that is capable of detecting a change in heating capacity during a defrosting operation to defrost the outdoor heat exchanger. , at the start of the defrosting operation, the throttle amount of the first throttle device is smaller than the throttle amount during the heating operation, and the throttle amount of the second throttle device is set such that the flow path of the bypass circuit is opened. The heat pump air conditioner is provided with a throttling amount control means for controlling the throttling amount of the second throttling device according to the value detected by the heating capacity detecting means during defrosting operation. 2 During defrosting operation, when the value detected by the heating capacity detection means exceeds a predetermined value, the throttling amount control means sets the throttling amount of the second throttling device to a value smaller than the predetermined value at the start of the defrosting operation. The heat pump type air conditioner according to claim 1, wherein the heat pump type air conditioner is controlled so that the following is achieved.