JPH0360032B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for controlling the capacity of a refrigerator, and in particular to a method for variable speed control of a turbo refrigerator depending on the refrigerating load state.

[Background of the invention]

Capacity control of conventional turbo chillers has been performed by adjusting the opening degree of the intake valve of the turbo compressor. Such a method has the disadvantage that it cannot fully exhibit the power saving effect and also that the efficiency at low loads is reduced.

In addition, as an example of this kind, for example, Japanese Patent Application Laid-Open No. 1983-
No. 115656 is mentioned.

[Purpose of the invention]

In view of the above points, it is an object of the present invention to provide a method for controlling the capacity of a refrigerator that can improve power saving effects and efficiency at low loads.

[Summary of the invention]

In order to achieve the above object, the present invention detects the chilled water outlet temperature and the chilled water temperature in a refrigerator including a turbo compressor, an evaporator with a chilled water system, and a condenser with a chilled water system, and detects both of these temperatures. The square root of the difference between the detected values is used as the rotation speed command value,
The present invention is characterized in that the electric motor of the turbo compressor is variable speed controlled.

[Embodiments of the invention]

Before explaining one embodiment of the present invention with reference to the drawings, the principle thereof will be described below.

In a compressor for a centrifugal refrigerator, the rotation speed N,
Assuming that the adiabatic head is H, the increase in enthalpy is Δi, the condensation pressure is P _C , and the steam pressure is P _l , the following relationship exists.

H∝N ² …(1) H∝Δi …(2) However, R: Gas constant T: Absolute temperature of inlet gas K: Specific heat ratio From the above equations (1) and (2), the following equation (4) can be obtained.

N∝Δi ^1/2 ...(4) On the other hand, if the condensation temperature is T _C and the evaporation temperature is T _E , then
The following relationship exists between both T _C and T _E and the above-mentioned Δi.

Δi∝(T _C −T _E ) ...(5) The above T _C and T _E are approximately equal to the cooling water outlet temperature t _c0 and the cooling water outlet temperature t _e0 , respectively (T _C ≒ t _c0 , T _E
≒t _e0 ), the following equation (6) can be obtained from the above equations (4) and (5).

N∝(t _c0 −t _e0 ) ^1/2 ...(6) From equation (6), the rotation of the compressor motor is determined by using information indicating the chiller cooling water and chilled water outlet temperatures, that is, the refrigeration load state. With several commands, it is possible to appropriately control the motor at variable speed. This control method allows the rotational speed index to be obtained through simpler processing than other control methods described below.
This control method uses temperature as the amount of information as described above, so the problem of poor responsiveness is taken into consideration.
Since this control method is related to a centrifugal refrigerator, it does not require strict responsiveness, so there is no problem.

On the other hand, based on equation (3) above, the condensing pressure of the condenser is
Detect P _C and vapor pressure P _l of the evaporator, respectively,
A separate control method may also be considered in which these detected values are used as the rotation speed index of the motor of the compressor. However, this separate control method has the drawback of requiring complicated calculations as in equation (3) above, and is therefore unsuitable as a capacity control method for refrigerators.

Next, a specific example based on the principle of the present invention described above will be explained with reference to FIG.

In FIG. 1, 1 is a turbo compressor, 2 is an electric motor directly connected to the turbo compressor, 3 and 4 are evaporators and condensers connected to the suction side and the discharge side of the turbo compressor 1, respectively, 5 and 6 is condenser 4 and evaporator 3
A cooling water system and a cold water system each passing through the

7 is an inverter connected to the electric motor 2;
This inverter 7 consists of a subtraction circuit 10 and a function generator 11, as shown in FIG. One of them, subtraction 10, is performed by inputting the detected values 8 and 9 of the respective outlet temperatures t _c0 and t _e0 of the cooling water system 5 and the cold water system 6,
The other function generator 11 inputs the output from the subtraction circuit 10 (the difference between the detected values 8 and 9, that is, the temperature difference (t _c0 - t _e0 ), and calculates the square root 12 of the temperature difference, that is, (t _c0 - t _e0 ) ^1/2 is determined, and the rotational speed N of the electric motor 2 is controlled based on the relationship in equation (6) above.

In this embodiment as described above, assuming that the required power P when the refrigeration capacity Q (refrigeration load) is 100% is 100%, the relationship between both Q and P is as shown in FIG. From this figure, it can be seen that when the refrigeration load Q is 80%, the required power is approximately 50%.

On the other hand, in a centrifugal chiller, regarding the refrigeration load Q and rotational speed N, and the required power P and rotational speed N, the following (7)
There is a relationship as shown in equation (8).

Q∝N ...(7) P∝N ³ ...(8) Therefore, by variable speed control of the electric motor of the centrifugal chiller, it is possible to reduce the required power P according to the cube characteristic of the rotation speed N. It is possible.

〔Effect of the invention〕

As explained above, according to the present invention, by controlling the electric motor of the centrifugal chiller at variable speed according to the state of the refrigeration load, the required power is reduced and the power saving effect is greatly improved. can improve time efficiency.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing an embodiment of the chiller capacity control method of the present invention, Fig. 2 is an inverter control circuit diagram of the embodiment, and Fig. 3 shows the refrigeration capacity and required power of the embodiment. This is a graph showing the relationship between 1...Turbo compressor, 2...Electric motor, 5...Cooling water system, 6...Cold water system, 7...Inverter, 8,
9...Detection value.

Claims (1)

[Claims] 1. In a refrigerator consisting of a turbo compressor, an evaporator with a cold water system, and a condenser with a cooling water system, the cold water outlet temperature of the evaporator and the cooling water outlet temperature of the condenser are respectively detected, and both detected values are calculated. A capacity control method for a refrigerator, characterized in that the electric motor of the turbo compressor is controlled at variable speed using the square root of the difference between the two as a rotational speed command value.