JPH0689949B2 - Air conditioner - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to control of an expansion valve of an air-cooled heat pump type air conditioner.

[Conventional technology]

In the conventional device, as described in JP-A-62-213655, the expansion valve is controlled to open and close so that the difference between the discharge gas temperature of the compressor and the condensation temperature on the high-pressure side becomes constant, and at the outlet of the evaporator. The above-mentioned temperature difference is set so that the wet state can be always maintained, and the optimum value of the superheat degree is determined for each condensation temperature. Further, in Japanese Patent Laid-Open No. 62-213655, the set value of the superheat degree with respect to the operating frequency was separately determined, but no particular consideration was given to the setting method in which both are considered at the same time.

[Problems to be Solved by the Invention]

In the above-mentioned conventional technology, since the compressor frequency is variable, when the speed at which the frequency changes and the speed at which the expansion valve is controlled to the target degree of superheat are compared, the speed at which the frequency changes is greater than the frequency. If the set values are set, it is difficult to stabilize the refrigeration cycle, and if set to the high temperature side condensation temperature, the low pressure side is high when the frequency is low, The refrigerant at the outlet of the heat exchanger may overheat even if it is a set value that makes the refrigerant at the outlet wet, and if the frequency is high, the refrigerant at the outlet of the heat exchanger may become excessively wet. There was a problem with that.

An object of the present invention is to provide a control device capable of controlling an expansion valve so as to form a stable refrigeration cycle with high efficiency even when the temperature condition of the heat exchanger or the rotation speed of the compressor changes. is there.

[Means for Solving the Problems]

The purpose is to set the set superheat degree in relation to both the stable discharge side condensation temperature of the refrigeration cycle and the compressor operating frequency with high efficiency on the refrigeration cycle, and to open the expansion valve in order to approach the set value. Achieved by controlling the degree.

[Action]

First, set the superheat degree on the compressor discharge side for the condensation temperature,
The target superheat degree is determined by correcting the set superheat degree according to the compressor operating frequency at that time, and the expansion valve is operated so that the detected superheat degree approaches the target superheat degree. As a result, the degree of superheat is controlled to be in a wet state at the outlet of the heat exchanger under all conditions, and the refrigeration cycle can be stably and efficiently operated.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a refrigeration cycle system diagram for implementing the present invention. The refrigeration cycle is configured by sequentially connecting the compressor 1, the condenser 2, the expansion valve 3, and the evaporator 4, and the refrigerant circulates through the above-mentioned path to repeat the state change. The expansion valve 3 is opened and closed by detecting the discharge gas temperature Td of the compressor 1 by the detector 7 and the discharge gas condensing temperature Tc by the detector 8, and electrically controlling the opening degree by the controller 6. In addition, the power supply for driving the compressor 1 is controlled by the control device 6 to determine the operating frequency. 2 and 3 are Mollier diagrams showing changes in the state of the refrigeration cycle, which will be described below with reference to these diagrams. The high temperature gas refrigerant (B) compressed and compressed by the compressor 1 is cooled and liquefied by the condenser 2 and the refrigerant (D) is decompressed by the expansion valve 3 and flows into the evaporator 4 (E), The evaporator 4 evaporates and vaporizes while absorbing heat from the outside air, and is again sucked into the compressor 1 (A). Here, the operation of the expansion valve will be described.

The discharge gas temperature Td and the condensation temperature Tc of the compressor 1 are detected by the respective temperature detectors 7 and 8 and input to the control device 6. The control device 6 includes the detected condensation temperatures (Tc ₁ , Tc ₂ ... T
against c _n), the target value of the degree of superheat is _{(SH 1, SH 2 ... SH} n) are set. For the compressor frequencies (Hz ₁ , Hz ₂ , Hz _n ), correction values (ΔSH ₁ , ΔSH ₂ ...
ΔSH _n ) is set, and the control device 6 sets the superheat degree (Td−Tc) = ΔT derived from the detected temperature to the target value (SH _n + ΔSH _n ) of the superheat degree corresponding to the condensation temperature. ), The opening of the expansion valve 3 is controlled. The target value of the degree of superheat is set so that the refrigerant at the outlet of the evaporator is in a wet state even when the operating conditions such as the temperature condition of the heat exchanger and the frequency of the compressor are changed. That is, in the Mollier diagram shown in FIG. 3, when the rotation speed of the compressor decreases from the rated frequency shown by the solid line, if the superheat degree SHn is set based only on the condensation temperature, the suction pressure of the compressor will be In addition, the refrigerant at the outlet of the evaporator is overheated, and the capacity of the evaporator is not fully utilized. Conversely, when the rotation speed of the compressor increases,
At the evaporator outlet, the refrigerant becomes excessively wet and damages the compressor bearings. Therefore, if the rotation frequency of the compressor is lower than the rated frequency, lower the degree of superheat below the target value,
When the frequency is high, the correction amount ΔSHn that makes the degree of superheat higher than the target value is added or subtracted from the target value.

In a steady operation state, the heat absorption amount in the evaporator 4 is small, and the refrigeration cycle is operated as shown by the solid line in FIG. 2, the superheat degree ΔT on the discharge side of the compressor 1 in this case is
It is smaller than the set value SH _{2 of the} degree of superheat for the condensation temperature Tc ₂ . At this time, the temperatures detected by the discharge gas temperature detector 7 and the condensation temperature detector 8 are input to the control device 6, and the control device 6 adds a correction ΔSH ₂ for the frequency and adds a new target value (SH ₂ ) Operate the expansion valve in the throttle direction so that it approaches ₂ + △ SH ₂ ). On the contrary, when the degree of superheat is larger than the target value, the expansion valve 3 is opened and control is performed so as to approach the target value.

〔The invention's effect〕

According to the present invention, it is possible to finely control the superheat degree on the discharge side of the compressor in response to changes in the load condition of the heat exchanger and the rotation speed of the compressor, and to increase the efficiency of the compressor and the heat exchanger efficiently. Since it can be maintained, the performance of the air conditioner can be improved.

In addition, the inverter-driven compressor is liable to have a high load when the number of rotations is increased, and the temperature is likely to increase. Therefore, in order to lower the temperature of the discharged gas, the wetness on the suction side is increased, the temperature rise of the motor coil is reduced, and the reliability of the compressor is improved.

[Brief description of drawings]

FIG. 1 is a refrigeration cycle diagram of one embodiment of the present invention, FIG. 2 is a refrigeration Mollier diagram of one embodiment of the present invention, and FIG. 3 is a Mollier diagram corresponding to the operating frequency of the compressor of the present invention. is there. 1 ... Compressor, 2 ... Condenser, 3 ... Expansion valve, 4 ... Evaporator, 6 ... Control device, 7 ... Discharge gas detector, 8 ...
Condensation temperature detector.

Claims (1)

[Claims] 1. A refrigeration cycle is formed by connecting a compressor whose operating frequency is variable, a four-way valve, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger, and a discharge gas temperature and a condensation temperature of the compressor. In an air conditioner equipped with a means for detecting, the superheat degree of the discharge gas detected by the discharge gas temperature and the condensation temperature, each superheat degree corresponding to the condensation temperature of a plurality of preset discharge gas is compressed. With respect to the operating frequency of the machine, it is small when the operating frequency of the compressor is lower than the rated operating frequency, and is set to be larger when the operating frequency of the compressor is higher than the rated operating frequency, and the superheat is set. An air conditioner characterized by controlling the opening of an expansion valve so as to maintain a set superheat degree.