JPH0593547A - Control device for electric expansion valve - Google Patents

Abstract

(57) [Abstract] [Purpose] The opening of the electric expansion valve to keep the refrigerant at the evaporator outlet overheated in the refrigeration circuit that circulates the refrigerant in the order of compressor, condenser, electric expansion valve, and evaporator. In this case, the decrease in the coefficient of performance due to the adjustment of the opening degree of the electric expansion valve against the increase in the pressure loss in the evaporator due to the influence of the compressor capacity control is suppressed. A temperature detecting means for detecting the refrigerant outlet temperature to of the refrigerant and a pressure detecting means for detecting the refrigerant outlet pressure po of the refrigerant are provided, and the refrigerant is detected based on the detection information of the temperature detecting means and the pressure detecting means. The superheat degree S (= to-tso), which is the difference between the saturation temperature tso and the evaporator outlet temperature to of the evaporator outlet pressure po, is calculated, and the calculated superheat degree S is electrically driven so as to be a predetermined target value Sm. Valve control means for adjusting the opening degree of the expansion valve is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric expansion valve, and more particularly, to the opening degree of the electric expansion valve in a refrigeration circuit for circulating a refrigerant in the order of a compressor, a condenser, an electric expansion valve and an evaporator. The present invention relates to a control device that keeps the refrigerant at the outlet of an evaporator in an overheated state by adjustment.

[0002]

2. Description of the Related Art Conventionally, as a superheat index of the refrigerant at the outlet of the evaporator, the above-mentioned control device determines from the evaporator outlet temperature to of the refrigerant detected by the temperature detecting means at the outlet and the inlet of the evaporator to the evaporator inlet. The inlet / outlet temperature difference dt (= to-ti) is calculated by subtracting the temperature ti, and the inlet / outlet temperature difference dt as the superheat degree index is a predetermined target value dt.
The configuration is such that the opening degree of the electric expansion valve is adjusted so as to be m.

[0003]

However, in the conventional control device, when a large pressure loss dp is generated in the evaporator due to the capacity control of the compressor or the like, the inlet as a superheat index for the increase in the pressure loss is generated. The outlet temperature difference dt is set to a constant target value d
There has been a problem that the coefficient of performance is greatly reduced with the adjustment of the opening degree of the electric expansion valve so as to be tm.

That is, the cycle state shown by the solid line in the Mollier diagram of FIG. 3 is when the pressure loss dp in the evaporator is negligible (that is, when the compressor output is small in terms of compressor capacity control). ) Shows a state close to the ideal cycle, but the inlet / outlet temperature difference dt as a superheat index
As a result of adjusting the opening degree of the electric expansion valve so that (= to-ti) becomes the predetermined target value dtm, the evaporator inlet point is a (evaporator inlet temperature ti), but the evaporator outlet point is b1
(Evaporator outlet temperature to = to1, to1-ti = dt
m), and in this cycle state, the refrigerating effect is Q1 (= hb1-ha) and the compression work is W1 (= hc1).
-Hb1) and the coefficient of performance becomes Q1 / W1.

However, when the pressure loss dp in the evaporator increases from the cycle state shown by the solid line due to the influence of the compressor capacity control, etc., with respect to the increase in pressure loss,
The inlet / outlet temperature difference dt as a superheat degree index is maintained at the predetermined target value dtm (that is, the evaporator inlet temperature ti).
On the other hand, when the opening degree of the electric expansion valve is adjusted so that the evaporator outlet temperature to is maintained at to1, the cycle changes to the state indicated by the broken line (evaporator inlet point a, evaporator outlet point b2).

When the evaporator outlet point shifts from b1 to b2 in this cycle change, the refrigerating effect is slightly increased from Q1 to Q2 (= hb2-ha), but the compression work amount is from W1 to W2 (= hc2). -Hb2), the coefficient of performance greatly decreases from Q1 / W1 to Q2 / W2.

An object of the present invention is to adjust the opening degree of the electric expansion valve with a rational control mode so as to reduce the coefficient of performance associated with the opening adjustment of the electric expansion valve against the increase in pressure loss in the evaporator. The point is to effectively suppress.

[0008]

A first characteristic configuration of a control device for an electric expansion valve according to the present invention is a refrigeration circuit for circulating a refrigerant in the order of a compressor, a condenser, an electric expansion valve, and an evaporator. A temperature detecting means for detecting the refrigerant outlet temperature of the refrigerant and a pressure detecting means for detecting the refrigerant outlet pressure of the refrigerant are provided, and the refrigerant outlet pressure of the refrigerant is based on the detection information of the temperature detecting means and the pressure detecting means. And a valve control means for calculating the degree of superheat, which is the difference between the saturation temperature and the outlet temperature of the evaporator, and adjusting the opening degree of the electric expansion valve so that the calculated degree of superheat reaches a predetermined target value. The action and effect are as follows.

[0009]

That is, when the conventional control device described above is further considered, as shown in FIG. 3, in the conventional control device, the inlet-outlet temperature difference dt (to-ti) of the evaporator is the predetermined target value d.
As a result of adjusting the opening degree of the electric expansion valve to be tm,
In the cycle state (evaporator outlet point b1) indicated by the solid line when the pressure loss in the evaporator is negligible, the actual superheat degree S of the refrigerant at the evaporator outlet (saturation temperature tso of the refrigerant with respect to the evaporator outlet pressure po) is And the evaporator outlet temperature to) are S1 (= to1-tso1), the cycle state shown by the broken line (evaporator outlet point) changed from the state shown by the solid line due to the increase in pressure loss dp in the evaporator. In b2), the superheat degree S is from S1 to S2 (= to2-tso).
It is increasing to 2).

That is, when the degree of superheat S at the evaporator outlet increases as described above, compared to the isentropic line from point b1 to point c1 in the compression process in the cycle state shown by the solid line, the cycle state shown by the broken line B in the compression process
The average slope of the isentropic line from the 2nd point to the 2nd point becomes small, which causes an increasing tendency of the compression work W. In the conventional control device, the increase in the pressure loss in the evaporator is the direct cause. In addition to the increasing tendency of the compression work W, the increasing tendency of the compression work W due to the decrease of the slope of the isentropic line in the compression process due to the increase of the superheat degree S as described above is added. , The increase of the compression work amount W accompanying the cycle change from the state shown by the solid line to the state shown by the broken line is promoted, and the increase width (W2-W1) of the compression work amount W becomes large, and therefore the coefficient of performance is large. Causing a decline.

In view of this, if the evaporator outlet temperature of the refrigerant and the evaporator outlet pressure are detected, the true degree of superheat of the refrigerant at the evaporator outlet can be calculated from the detected information,
According to the first characteristic configuration of the present invention in which the opening degree of the electric expansion valve is adjusted in a state where the calculated superheat degree is used as an adjustment index, the predetermined target value Sm of the superheat degree S in FIG. Refrigerant superheat S1 at the evaporator outlet in the solid line cycle state
Assuming that a value equal to (= to1-tso1) is set, when the pressure loss in the evaporator is negligible,
As a result of adjusting the opening degree of the electric expansion valve so that the superheat degree S reaches the above-mentioned predetermined target value Sm (= S1), as shown by the solid line in FIG. 2, the end point d of the condensation process and the evaporator inlet point are shown. While a is equal to the cycle shown in FIG. 3, the evaporator outlet point is also b1 (evaporator outlet temperature to = to1), and the cycle state is exactly the same as the solid line cycle state in FIG. Q1 (= hb1-ha),
The compression work is W1 (= hc1-hb1) and the coefficient of performance is Q
It becomes 1 / W1.

If the increase in the pressure loss dp, which is similar to the state in which the cycle changes from the state indicated by the solid line to the state indicated by the broken line in FIG. 3, occurs in the evaporator due to the influence of the compressor capacity control, etc., this pressure loss. With respect to the increase, the opening degree of the electric expansion valve is adjusted so as to maintain the superheat degree S at the predetermined target value dtm (= S1). As a result, the cycle is in the state shown by the broken line in FIG. 2 (evaporator outlet point b3 , To3-ts
o3 = Sm), and due to this cycle change, the refrigeration effect changes from Q1 to Q3 (= hb3-ha), and the compression work amount changes from W1 to W3 (= hc3-hb3). The coefficient of performance is from Q1 / W1 to Q3 / W above
Change to 3.

That is, as is apparent from a comparison between FIG. 3 showing a cycle change in the case of the conventional control device and FIG. 2 showing a cycle change in the case of the first feature structure of the present invention, the first feature structure of the present invention. In the case of, due to the decrease in the slope of the isentropic line in the compression process, the opening degree of the electric expansion valve is adjusted so as to maintain the superheat degree S at a constant value Sm against the increase in pressure loss in the evaporator. It is possible to suppress the increase tendency of the compression work amount W which has become worse, and to suppress the increase of the compression work amount W due to the cycle change (W3 <W2), thereby effectively suppressing the decrease of the coefficient of performance (Q3 / W3
> Q2 / W2).

By the way, the state value (refrigerant R22) at each point when the pressure loss in the evaporator is negligible is point 115.0 kcal / kg, 5.0 kgf / cm ² (ti = 0 ° C.) b1 point 150. 6 kcal / kg, 5.0 kgf / cm ² (to1 = 10 ° C.) c1 point 159.0 kcal / kg, 20.0 kgf / cm ² d point 115.0 kcal / kg, 20.0 kgf / cm ² , and S1 = 10 ° C. deg (= dt) Q1 = hb1-ha = 35.6 kcal / kg W1 = hc1-hb1 = 8.4 kcal / kg The standard cycle state (the cycle state shown by the solid line in each of FIGS. 2 and 3) is Assuming

From this standard cycle state, an increase in pressure loss occurs in the evaporator. In response to this increase in pressure loss, the conventional controller controls the inlet / outlet temperature difference dt to 10.0 ° C. deg.
As a result of adjusting the opening of the electric expansion valve to maintain
As shown by the broken line in FIG. 3, the cycle changes and the evaporator outlet point shifts from b1 to b2, and along with the shift of the outlet point, the c1 point shifts to the c2 point, and these b2 point and c2 point State value is b2 point 151.6 kcal / kg, 3.0 kgf / cm ² (to2 = 10.0 ° C., dt = to2-ti = 10.0 ° C. deg) c2 point 164.6 kcal / kg, 20.0 kgf / If it becomes cm ² , due to this cycle change, S2 = 25 ° C. deg Q2 = hb2-ha = 36.6 kcal / kg W2 = hc2-hb2 = 13.0 kcal / kg and the coefficient of performance Q2 / W2 = 2.81. ..

On the other hand, with respect to the same increase in pressure loss in the evaporator, the first characteristic configuration of the present invention allows the electric expansion valve to maintain the superheat degree S at a predetermined target value Sm (= S1 = 10 ° C. deg). When the opening degree of is adjusted, the cycle state changes from the above reference cycle state as shown by the broken line in FIG. 2, the evaporator outlet point shifts from b1 to b3, and the c1 point shifts to c3 as the outlet point shifts. Point, these b3 points,
And the state value of c3 point is b3 point 149.5 kcal / kg, 3.2 kgf / cm ² (to3 = −3.0 ° C., dt = to3-ti = −3.0 ° C. deg) c3 point 161.1 kcal / Kg, 20.0 kgf / cm ² . Then, due to this cycle change, Q3 = hb3-ha = 34.5 kcal / kg W3 = hc3-hb3 = 11.6 kcal / kg (<W2) Performance coefficient Q3 / W3 = 2.97 (> Q2 / W2) ..

[0017]

That is, according to the first characteristic configuration of the present invention, as described above, in adjusting the opening degree of the electric expansion valve so as to keep the refrigerant at the outlet of the evaporator in an overheated state,
By effectively suppressing the decrease in the coefficient of performance associated with the adjustment of the opening of the electric expansion valve against the increase in pressure loss in the evaporator due to the influence of the compressor capacity control, etc. The operating cost can be reduced.

[Second Characteristic Configuration of the Present Invention] In a second characteristic configuration of the control device for an electric expansion valve according to the present invention, the valve control means is approximated by an equation that indicates the correlation between the refrigerant pressure and the saturation temperature. Based on this, the saturation temperature for the outlet pressure is calculated from the evaporator outlet pressure detected by the pressure detecting means.

That is, in the process of calculating the degree of superheat of the refrigerant at the outlet of the evaporator, in order to obtain the saturation temperature corresponding to the outlet pressure from the evaporator outlet pressure detected by the pressure detecting means, It is conceivable to store the correlation table in the storage means, but in this case, the necessary storage capacity becomes large because the numerical data in the table is extremely large, and the numerical values in the table when using different types of refrigerant All of the data needs to be re-entered.

In this respect, according to the above-mentioned second characteristic configuration, since the approximate expression is stored, the required storage capacity can be made small, and the coefficient of the approximate expression can be reduced even when different kinds of refrigerants are used. You can easily deal with it only by changing it.

[0021]

EXAMPLES Next, examples will be described.

FIG. 1 shows a basic refrigerating circuit used in a package type air conditioner and a home air conditioner.
The condenser 2, the electric expansion valve 3, and the evaporator 4 are connected by a refrigerant pipe 5 so that the refrigerant circulates in that order.

The evaporator 4 is composed of a fin-tube type heat exchanger, and the return air RA returning from the room to be cooled is cooled in the evaporator 4 by the heat of vaporization accompanying the vaporization of the circulating refrigerant, and the cooled air is cooled. The supply air SA is supplied to the cooling target room.

The condenser 2 is also constituted by a fin-tube type heat exchanger, and the outside air OA ventilating to the condenser 2 is used as a heat dissipation target to dissipate the condensation heat generated by the condensation of the circulating refrigerant. I am doing it.

Reference numeral 6 denotes a return air / air supply fan which ventilates the evaporator 4, and 7 denotes an outside air fan which ventilates the outside air OA to the condenser 2.

Reference numeral 8 denotes a controller. In the controller 8, the return air temperature tr is set based on the detection information of the return air temperature sensor 9 for detecting the temperature tr of the return air RA returning to the evaporator 4. Capacity adjusting unit for controlling the capacity of the compressor 1 and adjusting the cooling output of the evaporator 4 so that the room temperature of the room to be cooled is kept constant regardless of the change of the cooling load. 10 is provided.

In the evaporator 4, when the output of the compressor 1 is adjusted to the increasing side by the above-mentioned compressor capacity control with respect to the increase of the cooling load, the refrigerant circulation amount increases accordingly, and the pressure loss dp in the evaporator 4 is increased. And the refrigeration cycle changes from the state shown by the solid line in FIG. 2 to the state shown by the broken line by the increase of this pressure loss dp. , The opening of the electric expansion valve 3 is adjusted so as to keep the refrigerant at the evaporator outlet in a superheated state irrespective of such changes in the pressure loss dp in the evaporator 4, and liquid compression in the compressor 1 is prevented. A valve control unit 11 is provided.

Further, the valve control unit 11 controls the electric expansion valve 3
In automatically adjusting the opening degree of, the temperature sensor 12 for detecting the evaporator outlet temperature to of the refrigerant is provided in the evaporator 4, and
A pressure sensor 13 for detecting the refrigerant outlet pressure po of the refrigerant is provided.

The valve control section 11 has a specific control configuration that correlates the pressure p (kgf / cm ² , G) of the refrigerant used (R22 in this example) with the saturation temperature ts (° C). The following approximate expression shown, that is, an approximate expression indicating the saturated vapor line of the used refrigerant ts = k ₄ · ln {k ₃ (p + k ₁ ) ² + k ₂ (p + k ₁ )} + k ₀ k ₄ = 33.4165 k ₃ = _{0.003968 k 2 = 0.144907 k 1 =} 2.09636 k 0 = -1.58064 storing memory unit 11a,

Based on the above memory approximation formula, the pressure sensor 1
The saturation temperature tso for the outlet pressure po is calculated from the evaporator outlet pressure po detected by No. 3, and the calculated saturation temperature tso is subtracted from the evaporator outlet temperature to detected by the temperature sensor 12 to obtain the value at the evaporator outlet. Calculation unit 11 for calculating the degree of superheat S (= to-tso) of the refrigerant
b,

Calculated superheat degree S and preset target value Sm
And the above calculation unit 1 based on the comparison result.
The opening degree of the electrically driven expansion valve 3 is adjusted so that the calculated superheat degree S by 1b becomes the target value Sm, that is, the calculated superheat degree S.
Is larger than the target value Sm, the opening of the electric expansion valve 3 is adjusted to the open side, and when the calculated superheat degree S is smaller than the target value Sm, the opening of the electric expansion valve 3 is closed. The adjustment unit 11c for adjusting the calculated superheat degree S to match the target value Sm and maintaining the matching state by adjusting the calculated superheat degree S.

That is, in the cycle state (a, b1, c1, d) shown by the solid line in FIG. 2, that is, when the pressure loss in the evaporator 4 is negligible (speaking of the capacity control of the compressor 1, the compressor). In the cycle state (when the output is small), as a result of adjusting the opening degree of the electric expansion valve 3 so that the superheat degree S of the refrigerant at the evaporator outlet becomes the target value Sm as described above, the evaporator outlet point becomes b1. At the same time, the end point of the compression process is c1 correspondingly, and the pressure loss dp in the evaporator 4 is greatly increased (in the capacity control of the compressor 1, the compressor output is greatly increased). The cycle state (a,
b3, c3, d), as a result of adjusting the opening degree of the electric expansion valve 3 so as to maintain the superheat degree S of the refrigerant at the evaporator outlet at the target value Sm against the increase in pressure loss in the evaporator 4, The outlet point of the vessel is b3, and the end point of the compression process is c3 correspondingly.

The pressure loss change in the evaporator 4 is adjusted by adjusting the opening degree of the electric expansion valve 3 so as to maintain the superheat degree S of the refrigerant at the evaporator outlet at a constant target value Sm. Irrespective of the above, it surely achieves the intended purpose of preventing liquid compression in the compressor 1.
Further, adjustment of the opening degree of the electric expansion valve 3 with respect to the increase of the pressure loss dp in the evaporator 4 is accompanied by a decrease in the coefficient of performance, and this decrease in the coefficient of performance causes the opening of the electric expansion valve 3 with respect to the increase in the pressure loss dp. It is intended to avoid the situation that the degree adjustment is accompanied by an unnecessary increase in the degree of superheat, which is further promoted.

Another Embodiment Next, another embodiment will be described.

The target value Sm of the superheat degree S may be appropriately determined according to the design conditions of the refrigeration circuit, and in some cases Sm.
= 0 may be set.

The specific circuit configuration of the refrigeration circuit can be changed in various ways, for example, by switching the cooling cycle and the heating cycle by a four-way valve, and the purpose of the circuit operation is cooling, heating, etc. It is not limited to air conditioning.

It should be noted that reference numerals are given in the claims for convenience of comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a block diagram of a refrigeration circuit

FIG. 2 is a refrigeration cycle diagram for explaining an adjustment mode of an electric expansion valve.

FIG. 3 is a refrigeration cycle diagram for explaining a conventional adjustment mode of an electric expansion valve.

[Explanation of symbols]

 1 Compressor 2 Condenser 3 Motorized expansion valve 4 Evaporator 11 Valve control means 12 Temperature detection means 13 Pressure detection means S Superheat degree Sm Target value to Evaporator outlet temperature ts Saturation temperature tso Saturation temperature to evaporator outlet pressure p Pressure po evaporator outlet pressure

Claims (2)

[Claims] 1. In a refrigeration circuit in which a refrigerant is circulated through a compressor (1), a condenser (2), an electric expansion valve (3), and an evaporator (4) in this order, the evaporator outlet temperature (to) of the refrigerant is adjusted. A temperature detecting means (12) for detecting and a pressure detecting means (13) for detecting the evaporator outlet pressure (po) of the refrigerant are provided, and the temperature detecting means (12) and the pressure detecting means (13) detect information. Based on the calculated superheat degree (S), which is the difference between the saturation temperature (tso) and the evaporator outlet temperature (to) with respect to the evaporator outlet pressure (po) of the refrigerant, the calculated superheat degree (S) is a predetermined target. A control device for an electric expansion valve, comprising valve control means (11) for adjusting the opening of the electric expansion valve (3) so as to obtain a value (Sm). 2. The evaporator outlet detected by the pressure detecting means (13) based on an approximate expression showing a correlation between the pressure (p) of the refrigerant and the saturation temperature (ts) of the valve control means (11). 2. The control device for an electrically driven expansion valve according to claim 1, wherein the saturation temperature (tso) for the outlet pressure (po) is calculated from the pressure (po).