JPH0519724Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a refrigeration system that prevents liquid hammer caused by pump down.

[Conventional technology]

In order to prevent liquid from returning to the compressor, performing pump-down operation at startup is a well-known operating technique, as seen in Utility Model Publication No. 57-21003 and Japanese Patent Application Laid-Open No. 59-138863. Usually, a low-pressure pressure switch is installed in the suction pipe of the compressor, and a solenoid valve installed in the high-pressure liquid pipe downstream of the liquid receiver operates the low-pressure pressure switch.
It is designed to repeat opening and closing only for a certain period of time at the time of startup based on ON and OFF.

However, in a refrigeration system equipped with such a pump-down mechanism, an impact called a liquid hammer occurs upstream of the expansion mechanism as the solenoid valve opens during the pump-down period. This liquid hammer is a major cause of piping cracks and failure of the expansion mechanism in heat pump refrigeration equipment equipped with a reverse cycle defrost mechanism, especially when the pump is down after defrosting, or when heating operation is restarted. It's summery. The details of this liquid hammer are as follows.

[Problem that the invention attempts to solve]

When pumping down a heat pump type refrigeration system that has a reverse cycle defrost mechanism, pumping down is performed not only at the start of each cooling operation and heating operation, but also when defrosting is started during heating operation and when heating operation is restarted. has become the norm.

Liquid hammer is a phenomenon that occurs when the liquid refrigerant downstream of the solenoid valve is accelerated when the low pressure drops during the pump-down period and the solenoid valve is used. This is especially noticeable on the pumpdown at the start.

The reason for this will be explained with reference to FIG. 3. The energy of the liquid hammer is expressed by the following formula, and the energy increases as the flow velocity increases.

u ² /2gr However, u: flow velocity g: gravitational acceleration r: specific weight In Fig. 3, if 9 is a pump-down solenoid valve and 6 is an expansion mechanism, then when solenoid valve 9 is closed, the upstream of solenoid valve 9 The high pressure liquid pipe 8″ becomes high pressure P ₁ ,
The high pressure liquid pipe 8' from the solenoid valve 9 to the expansion mechanism 6 is at low pressure _P2 .

If the high-pressure liquid pipe 8' from the electromagnetic valve 9 to the expansion mechanism 6 is filled with liquid refrigerant, or if there is no liquid refrigerant at all, liquid hammer will not occur even if the electromagnetic valve 9 is opened. In the former case, this is because the flow velocity u is clearly small. Furthermore, since liquid hammer does not occur in the latter case, it can be said that liquid hammer is unlikely to occur under the pressure difference ΔP (P ₁ -P ₂ ) due to normal pump down. Liquid hammer occurs mainly when a small amount of liquid refrigerant remains in the high-pressure liquid pipe 8' from the solenoid valve 9 to the expansion mechanism 6.

This is because the liquid refrigerant remaining in the high-pressure liquid pipe 8' evaporates when the solenoid valve is closed during the pump-down period and cools the high-pressure liquid pipe 8', and when the solenoid valve 9 is opened, the liquid refrigerant passes through the solenoid valve 9. It is thought that this is because the liquid expands adiabatically, changes from a liquid state to a gas-liquid two-phase state, and flows into the high-pressure liquid pipe 8'.

That is, when the solenoid valve 9 is opened, the refrigerant gas that flows into the high-pressure liquid pipe 8' exchanges heat with the high-pressure liquid pipe 8' that has been cooled to a low temperature, and is accelerated while rapidly decreasing its volume. This accelerates the small amount of liquid refrigerant remaining in the refrigerant, causing a noticeable liquid hammer.

When the solenoid valve is closed during the pump-down period, a large pressure difference generally occurs between the upstream and downstream sides of the solenoid valve, and depending on the refrigerant situation in the high-pressure liquid pipe 8', there is a risk of liquid hammer, but there is a particularly high risk. What is shown is the pump down after defrosting when a small amount of liquid refrigerant remains in the high pressure liquid pipe 8'.

The purpose of the present invention is to prevent such liquid hammering and eliminate the disadvantages such as split pipe cracking and expansion mechanism failure caused by liquid hammering.

[Means for solving problems]

As shown in FIGS. 1 and 2 of the embodiment drawings, the refrigeration system of the present invention has a low-pressure pressure switch 11 provided in the suction pipe 10 of the compressor 1 and a high-pressure liquid pipe 8 downstream of the liquid receiver 5. An interposed electromagnetic valve 9, a time limit means A that outputs a signal only for a certain period of time at the start of each heating operation and cooling operation,
and a pump-down mechanism consisting of a solenoid valve control means B that opens and closes the solenoid valve 9 based on the output signal from the low pressure switch 11 while the time limit means A is outputting a signal, and Heat pump refrigeration equipped with a reverse cycle defrost mechanism that temporarily switches the four-way switching valve 2 to the cooling operation side during heating operation based on the output signal of defrost command means D that determines whether defrost is necessary and outputs a defrost command signal. In the device, a bypass circuit 12 provided between the upper part of the liquid receiver 5 and the high pressure liquid pipe 8' downstream of the electromagnetic valve 9, and a second electromagnetic valve 13 interposed in the bypass circuit 12.
Then, while the time limit means A is outputting the signal after the defrost command means D has stopped outputting the signal, the second solenoid valve 13
The present invention is characterized in that it is equipped with a second electromagnetic valve control means C that outputs an opening command signal.

[Effect]

When defrosting is finished and heating operation is resumed,
At the time of starting, a signal is output from the timer means A.
Then, the solenoid valve control means B opens and closes the solenoid valve 9 based on the signal from the low pressure switch 11, liquid refrigerant is stored in the liquid receiver 5 upstream of the solenoid valve 9, and pump-down is performed.

At the same time, during this pump-down period, an open command signal is input from the second solenoid valve control means C to the second solenoid valve 13, and the second solenoid valve 13 opens.

As a result, even when the solenoid valve 9 is closed during the pump-down period at the start of heating operation after defrosting, high-pressure gas flows from the upper part of the liquid receiver 5 through the bypass circuit 12 into the high-pressure liquid pipe 8' downstream of the solenoid valve 9. , remove the liquid refrigerant that accumulates here. As a result, even if the accelerated refrigerant should flow from the liquid receiver 5 through the solenoid valve 9 into the high-pressure liquid pipe 8' when the solenoid valve 9 is opened, there will be no liquid refrigerant in the high-pressure liquid pipe 8'. Therefore, liquid hammer does not occur.

In addition, only the refrigerant gas flows into the high-pressure liquid pipe 8' through the bypass circuit 12, and the liquid refrigerant is effectively retained in the lower part of the liquid receiver 5 by closing the solenoid valve 9, so that the pump down function is achieved. It is unlikely to have any negative impact on.

〔Example〕

Hereinafter, a case in which the present invention is applied to a heat pump chiller, which is a type of heat pump type refrigeration device, will be described in detail. This refrigeration system is equipped with a reverse cycle defrost mechanism, and the liquid hammer prevention mechanism is designed to function only during the pump-down period after the completion of significant defrost of the liquid hammer (when heating operation is restarted).

According to the refrigerant circuit diagram in FIG. 1, the main refrigerant circuit includes a compressor 1, a four-way switching valve 2, an air-to-air type heat source side heat exchanger 3, one-way valves 4a to 4d, a liquid receiver 5, and a cooling expansion mechanism. 6a, a heating expansion mechanism 6b, and a water-type usage-side heat exchanger 7, and a pump-down solenoid valve 9 is interposed in the high-pressure liquid pipe 8 downstream of the liquid receiver 5. Further, a thermistor Th of a dewatering sensor 18, which will be described later, is provided in the downstream piping of the heat source side exchanger 3, and a low pressure switch 11 is further provided in the suction pipe 10 of the compressor 1.

By operating the four-way switching valve 2, during cooling operation (including defrost), the refrigerant flows in the direction indicated by the solid line arrow, converting the heat source side exchanger 3 into a condenser and the user side heat exchanger 7 into an evaporator. During heating operation, the refrigerant flows in the direction indicated by the dashed line, causing the heat source side heat exchanger 3 to function as an evaporator and the user side heat exchanger 7 to function as a condenser.

The bypass circuit 12 is provided between the upper part of the liquid receiver 5 and the high pressure liquid pipe 8' downstream of the solenoid valve 9, and a second solenoid valve 1 is provided to open the bypass circuit 12.
It has 3.

The connection position of the bypass circuit 12 in the liquid receiver 5 is such that the bypass circuit 12 is connected when the second solenoid valve 13 is opened.
It is desirable to select a position as high as possible in the liquid receiver 5 to prevent liquid refrigerant from flowing into the liquid refrigerant. Furthermore, the connection position of the bypass circuit 12 in the high pressure liquid pipe 8' downstream of the solenoid valve 9 allows the liquid refrigerant remaining in the high pressure liquid pipe 8' to be efficiently removed by the high pressure gas flowing into the high pressure liquid pipe 8' through the bypass circuit 12. From the viewpoint of eliminating the gas, it is desirable to select a position close to the solenoid valve 9.

FIG. 2 shows the main parts of the operation control circuit for the refrigerant circuit described above, in which 14 represents a relay that controls the start and stop of the compressor 1, and 15 represents its control contact.

16 is a cooling/heating changeover switch, to which a relay 17 is connected in series, and 18 is a de-cooler serving as defrost command means D, to which a relay 19 (defrost relay) is connected in series. The normally open contact 17a of the relay 17 and the normally closed contact 19b of the defrost relay 19 are connected in series to the electromagnetic coil 2S (heating side selected by energization) of the four-way switching valve 2. The flow path of the four-way switching valve 2 is switched depending on when the machine is in operation. The above is the reverse cycle defrost mechanism.

The de-Iiser 18 has a well-known structure, and consists of a combination of a timer T and a thermistor Th installed in the refrigerant pipe near the heat source side exchanger 3, and is controlled by the operating cycle of the timer T and frost formation from the thermistor Th. When the signals match, the switch 18' is activated to output a defrost command signal.

_T1 is a timer as the time limit means A, 9S
indicates the electromagnetic coil of the electromagnetic valve 9, and 21 indicates a contact point of the low pressure switch 11. The timer T ₁ keeps its normally open contacts T ₁ a and T ₁ a' closed for a certain period of time after a signal is input, and the defrost relay is activated when the relay 14 is activated (14 a is closed) or when the defrost relay is activated while the relay 14 is activated. 19 is activated (closed 19a) or deactivated (closed 19b). The activation time determines the pump-down period and is set to about 3 minutes, for example. Further, the low pressure switch 11 has a predetermined differential and ^is activated (contact 21
(closed), and the operation is stopped (contact 21 is opened) when the lower limit value (for example, 2.5 Kg/cm ² ) is reached. Then, only when both the timer T ₁ and the low pressure switch 11 are operating, the electromagnetic coil 9S is energized and the electromagnetic valve 9 is activated.
is now closed. The above is the control means B for the solenoid valve 9.

Like T ₁ , T ₂ keeps its normally open contact T ₂ a closed for a certain period of time after a signal is input, and starts operating when the normally open contact 19a' of the defrost relay 19 is closed. There is. Timer T ₂
The operating time is set to cover at least the period from the start of defrost to the end of pump down when heating operation is restarted, and the operation is completed by the start of the next defrost. Normally open contact T ₂ of timer T ₂
a is connected in series to the electromagnetic coil 13S of the second electromagnetic valve 13, together with the normally open contact 17a' of the relay 17, the normally closed contact _19b ' of the defrost relay, and the normally open contact _T1a ' of the timer T1. . The above is the second solenoid valve control mechanism C.

The operation of heating operation and defrosting in the above-mentioned refrigeration system will be explained below. Regarding the cooling operation, no measures are taken to prevent liquid hammer during the pump down period, and normal operation is performed, so a description thereof will be omitted.

In the heating operation, the changeover switch 16 is selected to the heating side. As a result, the relay 17 is energized, its normally open contact 17a is closed, the electromagnetic coil 2S is energized, and the flow path of the four-way switching valve 2 selects the heating side.

When the control contact 15 is closed in this state, the relay 14 is energized and starts the compressor 1. At the same time, the normally open contact 14a of the relay 14 is closed in the solenoid valve control means B, and the timer _T1 is activated. Its normally open contact T ₁ a closes. In this state, when the low pressure in the suction pipe 10 of the compressor 1 exceeds the upper limit set in the low pressure switch 11, the contact 21 closes, the electromagnetic coil 9S is energized, and the electromagnetic valve 9 is closed. do. When the liquid refrigerant accumulates in the receiver 5 due to the closure of the solenoid valve 9 and the low pressure drops to the lower limit value set in the low pressure switch 11, its contact 21 opens to open the solenoid valve 9.
This opening and closing of the solenoid valve 9 is repeated during the set time of the timer T ₁ (during the period when the contact T ₁ a is closed). The above is the pump down at the start of heating operation.

After pump down, frosting progresses in the heat source side exchanger 3 as the heating operation progresses, and when the timer T cycle of the de-icer 18 and the frost detection signal from the thermistor Th match, the contact 1 of the de-icer 18
The defrost relay 19 is energized by the operation of the defrost relay 19, and the opening of the normally closed contact 19b causes the electromagnetic coil 2S to become de-energized, thereby switching the flow path of the four-way switching valve 2 to the cooling operation side. At the same time, normally open contact 1 of defrost relay 19 is connected to solenoid valve control means B.
9a is closed, the timer _T1 is activated, and the same pump-down as described above is performed. This is the pump down at the start of defrost.

In this pump down, the normally open contact 19 of the defrost relay 19 is connected to the second solenoid valve control means C.
a' closes, actuating timer T ₂ to close its normally open contact T ₂ a, and normally open contacts 17a', T ₁
a' is also closed, but since the normally closed contact 19b' of the defrost relay 19 is open, the electromagnetic coil 13S is not excited, and the second electromagnetic valve 13
remains closed.

After the pump down is completed, normal defrost is performed, and when the defrost is completed, that is, when the defrost relay 19 is de-energized, its normally closed contact 19b is closed, the electromagnetic coil 2S is de-energized, and the four-way switching valve 2 is closed. The flow path returns to the heating operation side. At the same time, in the solenoid valve control means B, the normally closed contact 1
Closing 9b' activates timer _T1 and starts pumping down.

At this time, in the second electromagnetic valve control means C, the contact T ₂ a of the timer T ₂ that started operating at the time of the start of defrosting continues to be closed even after the heating operation is restarted, and is normally opened at the same time as the heating operation is restarted. Contact 17
a', the normally closed contact 19b' and the relay contact T ₁ a' are closed, and the electromagnetic coil 13S is energized.

As a result, the second solenoid valve 13 opens at the same time as the start of pump down, liquid refrigerant is stored in the liquid receiver 5, and high-pressure gas is passed from the upper part of the liquid receiver 5 to the high-pressure liquid downstream of the solenoid valve 9 through the bypass circuit 12. The liquid refrigerant flowing into the pipe 8' and staying there is removed.
Therefore, during this pump down period, the solenoid valve 9
Liquid hammer will not occur even if the is opened. In this way, the second solenoid valve 13 opens after the defrost is finished, that is, during the pump-down period when the heating operation is restarted, and liquid hammer is prevented during this period.

This state remains until the pump-down period ends.
That is, until the normally open contact T ₁ a' opens, thus preventing liquid hammer from occurring throughout this pump-down period.

The normally open contact T ₂ of the timer T ₂ is opened during the heating operation. Further, when the relay 17 is de-energized, its normally open contact 17a' is opened, so the second solenoid valve 13 is not opened during the cooling operation.

As described above, the second
The second solenoid valve 13 opens to prevent liquid hammering, but in all pump downs the second solenoid valve 1
It is also possible to configure so that 3 is open.

Further, in this embodiment, the operation control circuit is configured with a relay, but it is of course possible to configure it with a circuit using a microcomputer.

[Effect of idea]

As is clear from the above description, the present invention bypasses high-pressure gas to the downstream side of the solenoid valve of the pump-down mechanism during the pump-down period when restarting the heating operation after defrosting, and the liquid remaining there By eliminating the refrigerant, it reliably prevents the liquid hammer that occurs when the pump is down, thereby preventing pipe cracking and expansion mechanism failure, and is highly effective in improving the durability of refrigeration equipment. . Further, in order to implement the present invention, it is only necessary to slightly change the refrigerant circuit and the operation control circuit, and therefore the implementation cost can be kept low. Furthermore, since the liquid refrigerant is reliably stored in the liquid receiver during pump-down, there is little influence on the pump-down effect.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention,
FIG. 1 is a refrigerant circuit diagram, and FIG. 2 is an operation control circuit. FIG. 3 is an explanatory diagram of the cause of occurrence of liquid hammer. In the figure, 1...Compressor, 5...Liquid receiver, 9...Solenoid valve, 8...High pressure liquid pipe downstream of liquid receiver 5, 8'...
High pressure liquid pipe downstream of solenoid valve 9, 10... Suction pipe, 11
...Low pressure switch, 12...Bypass circuit,
13...Second solenoid valve, A...Time limit means, B...
Solenoid valve control means, C... second solenoid valve control means,
D...Defrost command means.

Claims (1)

[Scope of Claim for Utility Model Registration] The low pressure switch 11 provided in the suction pipe 10 of the compressor 1, the solenoid valve 9 provided in the high pressure liquid pipe 8 downstream of the liquid receiver 5, and each of the heating and cooling operations. a time limit means A that outputs a signal only for a certain period of time at the time of starting;
The pump-down mechanism includes a solenoid valve control means B that opens and closes the solenoid valve 9 based on the output signal from the low pressure switch 11 while the timer A is outputting the signal, and Heat pump refrigeration equipped with a reverse cycle defrost mechanism that temporarily switches the four-way switching valve 2 to the cooling operation side during heating operation based on the output signal of defrost command means D that determines whether defrost is necessary and outputs a defrost command signal. In the device, a bypass circuit 12 provided between the upper part of the liquid receiver 5 and the high pressure liquid pipe 8' downstream of the electromagnetic valve 9, and a second electromagnetic valve 13 interposed in the bypass circuit 12.
Then, while the time limit means A is outputting the signal after the defrost command means D has stopped outputting the signal, the second solenoid valve 13
1. A refrigeration system comprising: second electromagnetic valve control means C for outputting an opening command signal to the refrigeration system.