Refrigerator

Details Refrigerator Refrigerator

2001-03-28

2002-06-18

Tapolcai, William E. (Department: 3744)

Refrigeration

Plural paired different function refrigeration producing...

C062S175000

Reexamination Certificate

active

06405554

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a refrigerating system, and particularly relates to a binary refrigerating system including a low stage side refrigerant circuit and a high stage side refrigerant circuit.
BACKGROUND ART
A binary refrigerating system has been conventionally used as a refrigerating system for a cold storage, a thermal-shock testing system or the like. The binary refrigerating system is constituted by a low stage side refrigerant circuit and a high stage side refrigerant circuit which are connected to each other through a cascade condenser as disclosed in Japanese Unexamined Patent Publication Gazette No. 9-210515.
With reference to
FIG. 13
, the conventional binary refrigerating system (
200
) will be now described. The low stage side refrigerant circuit (
202
) is formed by connecting a low stage side compressor (
207
), a cascade condenser (
206
), a low stage side receiver (
208
), a low stage side expansion valve (
204
) and an evaporator (
209
) in this order, while the high stage side refrigerant circuit (
203
) is formed by connecting a high stage side compressor (
210
), a condenser (
212
), a high stage side receiver (
211
), a high stage side expansion valve (
205
) and the cascade condenser (
206
) in this order. Further, in the conventional binary refrigerating system (
200
), the expansion valves (
204
) and (
205
) of the high stage side refrigerant circuit (
203
) and the low stage side refrigerant circuit (
202
) are each constituted by a temperature-sensitive thermostatic expansion valve (hereinafter, referred to as a temperature-sensitive expansion valve) Furthermore, the cascade condenser (
206
) is constituted by a double-pipe heat exchanger.
In the high stage side refrigerant circuit (
203
), a high stage side refrigerant discharged from the high stage side compressor (
210
) develops such circulation as to condense in the condenser (
212
), reduce its pressure in the high stage side expansion valve (
205
), evaporate in the cascade condenser (
206
) and return to the high stage side compressor (
210
). On the other hand, in the low stage side refrigerant circuit (
202
), a low stage side refrigerant discharged from the low stage side compressor (
207
) develops such circulation as to condense in the cascade condenser (
206
) to recover cold heat from the high stage side refrigerant, reduce its pressure in the low stage side expansion valve (
204
), evaporate in the evaporator (
209
) to cool substance to be cooled (ex., air), and return to the low stage side compressor (
207
).
Meanwhile, at the time of start-up of the system (
200
), the temperature in the cascade condenser (
206
) may not be decreased down to a predetermined condensation temperature for the low stage side refrigerant. For example, if the system (
200
) has been shut down for a long time, the temperature in the cascade condenser (
206
) rises up to around ordinary temperatures. Therefore, if the high stage side compressor (
210
) and the low stage side compressor (
207
) are started up at the same time, the low stage side refrigerant circuit (
202
) may be excessively raised in its high pressure, resulting in operation of a protective device such as a high-pressure switch in spite of the system (
202
) being in normal conditions. To cope with this and prevent such unintended behavior of the protective device, the system is generally arranged so that the high stage side compressor (
210
) is started up ahead of start-up of the low stage side compressor (
207
) and after the expiration of a certain period the low stage side compressor (
207
) is started up.
For the binary refrigerating systems, it is important to stabilize the high pressure in the low stage side refrigerant circuit (
202
) since their performance is determined mainly depending upon operating conditions of the low stage side refrigerant circuit (
202
). In the conventional binary refrigerating system, however, the temperature-sensitive expansion valve (
205
) is used for the high stage side refrigerant circuit (
203
) and therefore it takes a considerably long time (for example, about 5 minutes) to stabilize the superheating degree of the high stage side refrigerant at the outlet of the cascade condenser (
206
) after the start-up of the high stage side compressor (
210
). Accordingly, there has been a problem in the conventional binary refrigerating system in that even if the low stage side compressor (
207
) is started up behind a certain period, the temperature-sensitive expansion valve (
205
) cannot response to an abrupt increase in load resulting in operation of the protective device of the low stage side refrigerant circuit (
202
).
Particularly for a so-called multi-system equipped with low stage side refrigerant circuitry constituted by a plurality of pipelines including a plurality of low stage side compressors, respectively, if the number of low stage side compressors started up is changed, the temperature-sensitive expansion valve (
205
) of the high stage side refrigerant circuit (
203
) cannot response to load variations of the low stage side refrigerant circuit so that the protective device of the low stage side refrigerant circuit easily operates.
The present invention has been made in view of this problem and therefore its object is to improve operational responsiveness of the high stage side refrigerant circuit to the low stage side refrigerant circuit.
DISCLOSURE OF INVENTION
To attain the above object, the present invention employs a motor-operated expansion valve as an expansion mechanism in the high stage side refrigerant circuit and provides for controlling the motor-operated expansion valve so that the high pressure in the low stage side refrigerant circuit reaches a target high pressure. In other words, the present invention provides for controlling the expansion mechanism of the high stage side refrigerant circuit based on the conditions of the low stage side refrigerant circuit.
More specifically, a first invention is directed to a refrigerating system, which comprises: a high stage side refrigerant circuit (
3
,
120
) formed by connecting a high stage side compressor (
9
,
18
,
121
), a condenser (
10
,
122
), a motor-operated expansion valve (
12
, EVL
1
, EVL
2
) and a refrigerant heat exchanger (
5
,
111
A,
111
B) in this order; a low stage side refrigerant circuit (
2
,
103
A,
103
B) formed by connecting a low stage side compressor (
4
,
31
A,
31
B,
131
A,
131
B), the refrigerant heat exchanger (
5
,
111
A,
111
B), an expansion mechanism (
7
, EV
21
) and an evaporator (
8
,
50
) in this order; a high-pressure sensing means (SPH
2
), provided in the low stage side refrigerant circuit (
2
,
103
A,
103
B), for sensing the high pressure in the low stage side refrigerant circuit (
2
,
103
A,
103
B); and an expansion valve control means (
16
) for controlling the motor-operated expansion valve (
12
, EVL
1
, EVL
2
) of the high stage side refrigerant circuit (
2
,
120
) so that the pressure sensed by the high-pressure sensing means (SPH
2
) reaches a predetermined target high pressure.
With this arrangement, in the high stage side refrigerant circuit (
3
,
120
), a high stage side refrigerant develops such circulation as to be discharged from the high stage side compressor (
9
,
18
,
121
), condense in the condenser (
10
,
122
), reduce its pressure in the motor-operated expansion valve (
12
, EVL
1
, EVL
2
), evaporate in the refrigerant heat exchanger (
5
,
111
A,
111
B) and return to the high stage side compressor (
9
,
18
,
121
). On the other hand, in the low stage side refrigerant circuit (
2
,
103
A,
103
B), a low stage side refrigerant develops such circulation as to be discharged from the low stage side compressor (
4
,
31
A,
31
B,
131
A,
131
B), exchange heat with the high stage side refrigerant in the refrigerant heat exchanger (
5
,
111
A,
111
B) to condense, reduce its pressure in the expansion mechanism (
7
, EV
21
), evaporate in the evaporator (
8
,
50
) for cooling substance to be cooled, and return to the low s

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