JPS6048452A - Refrigerator capacity control method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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]

Conventionally, capacity control of a turbo chiller has been performed by adjusting the opening degree of a suction valve of a turbo compressor. Such a method has the disadvantage that it is not possible to fully demonstrate the power saving effect and that the efficiency at low loads also decreases.

[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 completely improve the power saving effect and the 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 these rainwater temperatures. The present invention is characterized in that the electric motor of the turbo compressor is controlled at variable speed by using the square root of the difference between the detected values as a rotational speed command value.

[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 is N.

Assuming that the heat insulating head is eH, the increase in enthalpy is Δi, the condensation pressure is Pc, and the steam pressure is Pt, the following relationship exists.

HcI:N2 ・・・・・・・・・(1) HσΔi ・
(2) However, R: Gas constant T: Absolute temperature of inlet gas: Specific heat ratio The following equation (4) can be changed from the above equations (1) and (2).

and NLxΔ! (4) On the other hand, if the condensation temperature is Tc and the total evaporation temperature is Tz, both Tc and T
There is the following relationship between I and the Δheat.

Δlσ(Tc Tg) (5) The above TC and TI are the cooling water outlet temperatures t, respectively. .

and cold water outlet temperature t,. approximately equal to (Tc'-t6
0, Tffi'-ttao) to f4)(5
), the following equation (6) “Z, jD)jL9・ , Nσ(t6o t-o)2---(6) From this equation (6), the cooling water and cold water outlet temperature of the refrigerator, that is, the refrigeration load If all the information indicating the condition is used to command the rotation speed of the motor of the compressor, it is possible to appropriately control the motor at variable speed.This control method is more efficient than other control methods described below. This control method uses the total temperature information as described above, so the problem of poor responsiveness is taken into account. Since this is related to a refrigerator, strict responsiveness is not required, so there is no problem.

On the other hand, based on the above equation (3), the condensation pressure Pc of the condenser and the vapor pressure Pt of the evaporator are detected, and these detected values are used to calculate the rotation speed index of the compressor motor. Separate control methods are also conceivable. However, this separate control method has the drawback of requiring complicated calculations as shown in equation (3), 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 discharge side of the turbo compressor 1, respectively, and 5
, 6 are a cooling water system and a cold water system that pass through the condenser 4 and the evaporator 3, respectively.

Reference numeral 7 denotes an inverter connected to the electric motor 2, and the inverter 7 comprises a subtraction circuit 10 and a function generator 11, as shown in FIG. One subtraction 10 is each outlet temperature t of the cooling water system 5 and the cold water system 6. . 1 Input the detection value 8.9 of jaQ, perform subtraction, and
is the output from the subtraction circuit 10 (difference of detected value 8.9)
, that is, manually calculate the temperature difference (t..-t,.) and calculate the square root of the temperature difference 12, that is, (jeo t, o)2
Then, the rotation speed N of the electric motor 20 is controlled based on the relationship of equation (6) above.

In this embodiment as described above, if the required power Pe is 100% when the refrigeration capacity Q (refrigeration load) 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 refrigerator, there is a relationship between the refrigeration load Q and the rotation speed N, and the required power P and the rotation speed N as shown in the following equation (8).

Qcf, N ・Old...(7) PO:N3 ・・・・・・(8) Therefore, by variable speed control of the electric motor of the centrifugal chiller, the required power P can be reduced to 3 of the rotation speed N. It is possible to reduce it by multiplicative property.

〔Effect of the invention〕

As explained above, according to the present invention, by variable speed controlling one engine of the centrifugal chiller according to the state of the refrigeration load, the required power is reduced, and the effect of saving on drilling power is greatly increased. Efficiency at low loads can be improved.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment of the refrigerator capacity control method of the present invention, FIG. 2 is an inverter control circuit diagram of the same embodiment,
FIG. 3 is a graph showing the relationship between refrigeration capacity and required power in the same example. DESCRIPTION OF SYMBOLS 1...Turbo compressor, 2...Electric motor, 5...Cooling water system, 6...Cold water system, 7...Inverter, 8,9.
...Detected value. Agent: Patent Attorney Akio Takahashi ? Diagram ``Zv-ff1-m- 111 11 1 (1 q -11111 mountain ・-1・ 1

Claims (1)

[Claims] In a refrigerator consisting of a turbo compressor, an evaporator with a cold water system, and a condenser with a cooling water system, the dynamic water outlet temperature and the cooling water outlet temperature are respectively detected, and the square root of the difference between these rain detection values is rotated. A capacity control method for a refrigerator, characterized in that a variable speed control of an electric motor of the turbo compressor is performed as a numerical command value.