KR20120100620A - Method for controlling a water circulation system using heat pump - Google Patents

Abstract

PURPOSE: A method for controlling a hot water circulator using a heat pump is provided to enough hot water capacity with reducing energy consumption even when using the heat pump with small capacity. CONSTITUTION: A method for controlling a hot water circulator using a heat pump is as follows. Target suction superheating predetermined according to the outdoor air temperature of an evaporator is set(S01). The opening degree of an expansion valve is controlled according to the target suction superheating. The target suction superheating is changed when the outdoor air temperature is changed(S03). When the temperature of water inflow increases and the temperature of water outflow is less than a target value, the target suction superheating is lowered(S06). [Reference numerals] (AA) Start; (BB,DD,GG,JJ) No; (CC,EE,FF,HH,II) Yes; (KK) Finish; (S01) Setting the target suction superheating after measuring the temperature of external air; (S02) Checking whether or not the temperature of external air changes; (S03) Re-setting the target suction superheating according to the changed temperature of external air; (S04.S07) Checking whether or not the temperature of water outflow is below the target temperature; (S05) Checking whether the temperature of water inflow increases, and a compressor is restrictively operated; (S06) The target suction overheating is lowered at a predetermined value; (S08) Checking whetehr or not the compressor is restrictively operated; (S09) Decreasing the amount of water

Description

Control method of hot water circulator using heat pump {METHOD FOR CONTROLLING A WATER CIRCULATION SYSTEM USING HEAT PUMP}

The present invention relates to a control method of a hot water circulator using a heat pump, and more particularly, to a control method of a hot water circulator for supplying hot water using a heat pump as a heat source.

The hot water circulation system is a device for providing hot water by heating low temperature water supplied from a water supply source such as a water supply source, and various types of heat sources have been conventionally used to heat water. Among them, the hot water circulator using a heat pump using a refrigerant compression cycle utilizes the heat of the high temperature refrigerant passing through the condenser as a heat source, and is a device for producing hot water by heat-exchanging low temperature water radiated from the condenser.

The hot water circulator must supply the required amount of hot water above the set temperature. Unlike the case of using a heat source such as a boiler, the heat pump is supplied through the condenser because the cycle is affected by the external environment such as the outdoor temperature. You may not be able to supply enough heat.

For example, when the refrigerant discharged from the evaporator flows into the compressor in a liquid state, there is a problem of damaging the compressor or generating noise. Therefore, the refrigerant should be introduced into the compressor in a gaseous state. To this end, the refrigerant passing through the evaporator has a certain degree of superheat to prevent the introduction of the liquid refrigerant. However, when the temperature of the external air to exchange heat with the evaporator is low, a sufficient amount of heat cannot be obtained. It can be lowered, causing problems with liquid refrigerant inflow.

In this case, conventionally, by controlling the opening of the expansion valve to reduce the flow rate of the refrigerant passing through the evaporator to allow the refrigerant to sufficiently evaporate even with a small amount of heat to solve the problem caused by the liquid refrigerant inflow, as described above In the hot water circulation system, when the temperature of the refrigerant is lowered, there is a problem that the temperature of the supplied hot water is lowered.

The present invention has been made to overcome the disadvantages of the prior art as described above, the technical problem to provide a hot water circulator that can supply hot water above the target temperature while operating the heat pump system stably even if the external environment changes. It is.

According to an aspect of the present invention for achieving the above technical problem, a control method of a hot water circulator including a heat pump including a compressor, a condenser, an expansion valve and an evaporator, and supplies hot water using the condenser as a heat source. Setting a predetermined suction superheat degree according to the outside air temperature (Tea) around the evaporator; Adjusting the opening degree of the expansion valve according to a set target suction superheat degree; Changing a target suction superheat according to a change in the outside temperature if the outside temperature is changed; And lowering the changed target suction superheat when the water extraction temperature Twi is lower than the target value while the water temperature Twi rises.

That is, in the present invention, in determining the superheat degree (hereinafter referred to as "suction superheat") of the refrigerant flowing into the compressor, the suction superheat degree to be maintained in consideration of the ambient air temperature around the evaporator (hereinafter referred to as "target suction superheat degree") After setting, the target suction superheat is additionally adjusted in consideration of the operating state of the compressor and the outlet temperature.

Here, the target suction superheat degree is set differently according to the outside air temperature of the evaporator. If the outside air temperature is low, the amount of heat that the refrigerant passing through the evaporator does not have is sufficient, so the target suction superheat degree is set high. As a result, since the temperature of the refrigerant discharged from the compressor is increased, the temperature of the hot water supplied from the hot water circulation system (hereinafter, referred to as "water extraction temperature") can be maintained at or above a target value even when the outside temperature is low.

In this process, the target suction superheat can be set to change continuously in accordance with the evaporator ambient temperature change. Since the stability of the cycle apparatus is sensitively affected by the slight suction superheat change when the target suction superheat fluctuates, it is possible to continuously change the target suction superheat rather than step by step.

On the other hand, when the temperature of the water supplied to the hot water circulator (hereinafter, “water inlet temperature”) increases while the target suction superheat is set, heat is accumulated in the cycle due to insufficient heat radiation from the condenser. If the inlet temperature further increases, the temperature of the refrigerant flowing into the compressor rises and the discharge pressure of the compressor exceeds the allowable value. In this case, the compressor may be shut down or the discharge pressure intentionally lowered to protect the compressor. Limited operation will be carried out.

In this state in which the compressor is operated in a limited operation, when the discharge water temperature is lower than the target value, it is impossible to secure the discharge water temperature by increasing the target suction superheat. This is because the temperature and pressure of the refrigerant discharged from the pressurizer are limited even if the target suction superheat is increased. In this case, in one aspect of the present invention, the target suction superheat is lowered. When the target suction overheating is lowered, the temperature of the refrigerant sucked into the compressor is lowered, thereby limiting the limited operation of the compressor, thereby increasing the operating time of the compressor, thereby increasing the amount of heat delivered to the water supplied.

In this case, as the intake temperature increases, the target suction superheat may be continuously decreased, or may be decreased by a predetermined value. Even if the operation is performed by lowering the target suction superheat, the target suction superheat may be further lowered if the discharge water temperature is not restored and the limited operation of the compressor is not eliminated.

In this case, if the target suction superheat is excessively lowered, liquid refrigerant may flow into the compressor, and the temperature and pressure of the refrigerant discharged from the compressor may be too low to reduce the water exit temperature. It can be set to control the target suction superheat in the range above the minimum value.

In this case, the minimum value of the target suction superheat may be determined according to the outside air temperature of the evaporator.

According to another aspect of the present invention, a control method of a hot water circulation system including a heat pump including a compressor, a condenser, an expansion valve, and an evaporator, and supplies hot water using the condenser as a heat source, the evaporator outside temperature (Tea) Differently setting the target suction superheat according to the method; Measuring the exit temperature (Two); Detecting an operating state of the compressor when the water outlet temperature Two is lower than a target value; And reducing the target suction superheat when the discharge water temperature Two is less than the target value even though the discharge pressure of the compressor reaches the maximum value and the operation of the compressor is limited. The control method of the hot water circulation system is provided. .

According to the aspects of the present invention having the configuration as described above, it is possible to ensure a water supply temperature stably and to ensure a sufficient hot water supply capacity even when using a heat pump device of a small capacity. In addition, energy consumption can be reduced.

1 is a configuration diagram schematically showing the configuration of a hot water circulation system to which an embodiment of a control method according to the present invention is applied.
2 is a Moliere diagram showing an operating state of the hot water circulator shown in FIG.
3 is a flowchart illustrating an operation process of the hot water circulator shown in FIG. 1.
FIG. 4 is a graph schematically showing a change in target suction superheat according to an outdoor temperature change in the hot water circulator shown in FIG. 1.

Hereinafter, with reference to the accompanying drawings, it will be described in detail an embodiment of a control method of the hot water circulation device according to the present invention.

1 is a block diagram showing a part of a hot water circulation system to which an embodiment of the control method according to the present invention is applied, Figure 2 is a Moliere diagram showing the operating principle of the heat pump system applied to the hot water circulation system. 1 and 2, the hot water circulator includes a compressor 10 for compressing a refrigerant in a P1 state to a P2 state, a condenser 20 in which heat of the refrigerant discharged from the compressor and water supplied to the hot water circulator are heat-exchanged. It includes. Here, the water having a water acquisition temperature of Twi is heated by the condenser 20 and supplied as hot water having a water discharge temperature of Two, and the refrigerant introduced into the P2 state is cooled to the P3 state while releasing heat.

The refrigerant passing through the condenser 20 flows into the expansion valve 30. The expansion valve 30 is known as a so-called linear expansion valve (LEV), and a type that can freely adjust its opening degree within a predetermined range is used. The refrigerant introduced into the expansion valve 30 is reduced to P3 while passing through the expansion valve, and the flow rate and the discharge pressure of the refrigerant are adjusted according to the opening degree of the expansion valve, thereby adjusting the target suction superheat and the outlet water temperature. Will be.

The refrigerant passing through the expansion valve 30 is introduced into the evaporator 40 in the P3 state, vaporized by receiving heat from the outside air in the evaporator 40, and returned to the P4 state and then recompressed by the compression (group 10). Supplied. At this time, the state of P4 is changed according to the amount of heat supplied to the evaporator 40. For example, when sufficient temperature is not supplied to the evaporator due to a low temperature (Tea) of the air around the evaporator 40, the P4 is supplied to the wet steam region. The liquid refrigerant is introduced into the compressor 10. In order to prevent this, the accumulator 50 is added between the compressor and the evaporator to prevent the liquid refrigerant from flowing directly into the compressor, but the flow rate of the refrigerant is reduced by the amount of the liquid refrigerant remaining in the accumulator 50. The performance of the entire cycle is reduced by that much.

Thus, the embodiment is configured to have a suction superheat degree SH1 such that the refrigerant passing through the evaporator is at least in the region of the superheated steam. Specifically, the control of the expansion valve 30 to control the point P4 to be in the region of the superheated steam as shown, so the system intended suction superheat is referred to as the target suction superheat.

With reference to FIG. 3, the control method of the said embodiment is demonstrated concretely.

First, the outside air temperature of the evaporator is measured in step S01, and the target suction superheat degree SH1 is set accordingly. The target suction superheat degree SH1 may use a value obtained through a preliminary test or the like, and has a different value depending on the outside temperature. 4 shows the relationship between the outdoor temperature and the target suction superheat. As shown in FIG. 4, the solid line disposed in the upper portion represents the target suction superheat degree, and as the outdoor temperature increases, the target suction superheat degree decreases. As shown, both may have a linear relationship, but this may be set differently according to the specifications and requirements of each system.

Such a relationship can be formulated based on the obtained data after securing the target water output temperature and the maximum target suction superheat values for the maximum water supply possible for each outdoor temperature through a test or the like.

On the other hand, the temperature of the outside air in which the evaporator is located during the operation of the heat pump system cannot be kept constant, such a change in the outside air temperature will affect the performance of the heat pump system. In addition, when the performance of the heat pump system becomes unstable, the hot water supply temperature of the hot water supplied by the hot water circulator also changes, so it is necessary to control in consideration of this.

For example, when the outside air temperature (Tea) is lowered, the amount of heat flowing through the evaporator is also lowered, so that the actual suction superheat is lower than the target suction superheat. In addition, since the temperature of the refrigerant flowing into the compressor is lowered, the amount of heat transferred through the condenser is also lowered. Therefore, in this case, if the flow rate of the refrigerant is reduced by controlling the expansion valve, the suction superheat can be maintained to have the value of SH1 in FIG. 2 even though the same amount of heat is supplied through the evaporator. However, this is advantageous for the introduction of liquid refrigerant into the compressor, but the flow rate of the refrigerant is reduced, resulting in a decrease in the amount of heat supplied through the condenser. Therefore, when the outside air temperature decreases, if the target suction superheat is increased to a value larger than SH1, which is a value for preventing liquid refrigerant inflow, the pressure and temperature of the refrigerant discharged from the compressor increase, so that the hot water outlet temperature even with a small flow rate refrigerant. And water supply capacity can be obtained.

If the ambient temperature rises, there is no need to change the target suction superheat because sufficient heat flows through the evaporator. However, since the suction superheat actually obtained is smaller than the target suction superheat SH1, the expansion valve is opened to increase the flow rate of the refrigerant or increase the amount of water supplied to the condenser so that a greater amount of heat is transferred from the condenser. Prevents the superheat from lowering.

Therefore, in step S02, the outside air temperature Te is continuously checked to confirm the change, and when the outside air temperature decreases, the target suction superheat degree SH2 is lower than the SH1 in step S01 when the outside air temperature decreases in step S03. By setting it large, it controls so that the water outlet temperature can be maintained even if the outside temperature falls.

Here, the water extraction temperature is continuously checked (step S04). If the target water extraction temperature is not obtained despite the same control as in step S03, the inlet temperature and the operation state of the compressor are checked (step S05). When the inlet temperature is increased at the same outside temperature, the amount of heat dissipation through the condenser is reduced, which is accumulated in heat in the heat pump apparatus, thereby increasing the temperature of the refrigerant flowing into the compressor and the discharge pressure of the compressor. When the discharge pressure continuously rises and exceeds the limit pressure that the compressor can operate stably, the protection algorithm built into the hot water circulation system is activated to stop the operation of the compressor or to limit the operation of the compressor, so the discharge pressure is normal. Controlled to stay within range.

When the compressor is limited in this way, the water to be supplied is not heated continuously, but the heating and stopping are repeated, so that the water discharge temperature becomes irregular, and the heat pump device also becomes unstable. To solve this, in step S06, the target suction superheat degree SH2 set in step S03 is reset to a lower value. In this way, when the target suction superheat degree SH2 is set to a lower value, the expansion valve is opened to increase the flow rate of the refrigerant, thereby lowering the temperature of the refrigerant flowing into the compressor. Therefore, the discharge pressure of the compressor is lowered to escape the limited operation, and as the operation time of the compressor is longer, the amount of heat dissipation through the condenser is also increased. As a result, the withdrawal temperature may increase and cycle stability may also increase.

At this time, in step S06 SH2 is reduced by a predetermined value. That is, instead of decreasing SH2 continuously as the acquisition temperature rises, SH2 is lowered by a predetermined interval as indicated by a plurality of 'c'-shaped arrows in FIG. 4. Through this, it is possible to escape from the limited operation state more quickly. And, the SH2 is reduced only to the minimum value of the target suction superheat.

That is, if the target suction superheat is excessively lowered, liquid refrigerant may be introduced into the compressor, and the temperature and pressure of the refrigerant discharged from the compressor may be too low to reduce the discharge water temperature. And control the target suction superheat in the range above the minimum value. In FIG. 4, the line indicated by the dotted line corresponds to the minimum value of the target suction superheat. In this case, the minimum value of the target suction superheat may be determined according to the outside air temperature of the evaporator.

After resetting the SH2 value in step S06, it is again checked in step S07 whether the water discharge temperature is recovered. If the outlet temperature is higher than the target value, the control is terminated. Otherwise, it is checked in step S08 whether the compressor is out of the limited operation state. If the limited operation of the compressor has not been eliminated, the process returns to step S06 to lower the target suction superheat once again and repeat steps S07 and S08.

If the compressor is not in the limited operation state in step S08, even though the heat pump is operated to the maximum limit, the water discharge temperature is not obtained. Therefore, the water supply is reduced (step S09) to control the water output temperature. . If the water supply amount is more important than the water exit temperature, step S09 may be omitted.

Claims (9)

A control method of a hot water circulator including a heat pump including a compressor, a condenser, an expansion valve, and an evaporator, and supplying hot water using the condenser as a heat source.
Setting a predetermined target suction superheat degree according to the outdoor air temperature (Tea) around the evaporator;
Adjusting the opening degree of the expansion valve according to a set target suction superheat degree;
Changing a target suction superheat according to a change in the outside temperature if the outside temperature is changed; And
And lowering the altered target suction superheat when the water extraction temperature Twi is lower than the target value while the water temperature Twi rises. The method of claim 1,
The control method of the hot water circulation system, characterized in that the target suction superheat is continuously changed in accordance with the change of the evaporator outdoor temperature (Tea). The method of claim 2,
If the evaporator outdoor temperature (Tea) is lowered, the set target suction superheat is set to increase the control method of the hot water circulation system. The method of claim 1,
The target suction superheat degree is set as low as a predetermined value when the inlet temperature (Twi) increases, the control method of the hot water circulation system. The method of claim 1,
And further lowering the target suction superheat even when the discharge pressure of the compressor is not lowered below the limit even after the target suction superheat is lowered and the discharge water temperature is lower than the target value. The method of claim 5,
And setting a minimum value of the target suction superheat degree according to the evaporator outdoor temperature (Tea) in advance and lowering the target suction superheat degree only until the target suction superheat degree reaches the minimum value. A control method of a hot water circulator including a heat pump including a compressor, a condenser, an expansion valve, and an evaporator, and supplying hot water using the condenser as a heat source.
Setting a target suction superheat differently according to an evaporator outdoor temperature (Tea);
Measuring the exit temperature (Two);
Detecting an operating state of the compressor when the water outlet temperature Two is lower than a target value; And
Reducing the target suction superheat when the discharge water temperature (Two) is less than the target value despite the discharge pressure of the compressor reaches the maximum value is less than the target value. The method of claim 7, wherein
And the target suction superheat is reduced by a predetermined value. The method of claim 7, wherein
If the evaporator outdoor temperature (Tea) is lowered, the set target suction superheat is set to increase the control method of the hot water circulation system.

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