GB2254135A

GB2254135A - A refrigeration system

Info

Publication number: GB2254135A
Application number: GB9206276A
Authority: GB
Inventors: Christopher Cook
Original assignee: IMI Cornelius Inc
Current assignee: Cornelius Inc
Priority date: 1991-03-23
Filing date: 1992-03-23
Publication date: 1992-09-30
Also published as: GB9106220D0; GB9206276D0

Abstract

A refrigeration system comprises by-passes (21, 23) that facilitate vapourisation of by-passed refrigerant condensate with the result that vapour temperature is reduced to improve compressor motor cooling in the by-pass mode. The by-pass (21) couples a liquid receiver (6) to the compressor (10) via valve (2) and throttle (5). Bypass (22) includes a valve (1) for the flow of vapour refrigerant. The system also includes a check valve (7) and a valve (3) stopping flow to the evaporator (11) when the evaporator is not required. <IMAGE>

Description

A Refrigeration System The present invention relates to a refrigeration system and more particularly, but not exclusively a by-pass loop for a hermetic compressor refrigeration system.

A refrigeration system normally includes a compressor, a condenser, a receiver or condensate reservoir and an evaporator in a usually closed circuit relationship. The evaporator provides the cooling action or refrigeration duty of the system on a stored article.

This action involves evaporation of a refrigerant condensate whereby heat energy is drawn from the stored article to provide the latent heat of vaporisation for the refrigerant condensate.

The vaporised refrigerant condensate is then passed to the compressor where it is compressed to form a condensate once again. The condenser with an associated cooling fan further propagates the formation of the refrigeration condensate. The condensate then flows to the receiver or condensate reservior. Typically, the condensate reservoir will be pressurised due to partial re-vaporisation of the condensate, this vapour acts on the liquid condensate to effectively "pump" the condensate to the evaporator.

It is desirable for the compressor to continuously operate to remove start up problems etc. These start-up problems result from the initial electrical current in rush on start-up and result in over heating. Typically, a compressor is rated for less than 15 start-ups per hour as the system and compressor are designed to cool on "run-through" that is to say the compressor cools once the system is in steady state. Thus, the compressor operates both when the evaporator has a high refrigeration duty and also when the evaporator has a low refrigeration duty. In order to reduce compressor motor power necessary in the low refrigeration duty phase a conventional by-pass loop is provided. This conventional by-pass loop couples the condenser and compressor through its suction port using a valve operable to open the by-pass loop when required.A check valve is also normally positioned in the condensate reservoir feed inlet to maintain pressure within the reservoir and prevent back flow of condensate vapour. These conventional by-pass loops effectively "short circuit" the refrigeration system so that condensate gas from the condenser is allowed to flow to the suction port under low pressure with the result that the compressive power required of the compressor is much reduced which in turn lowers the operating power requirements.

It will be appreciated, that it is a requirement that the condensate gas "by passed" to the suction port of the compressor should be cold to cool the motor windings of the compressor. In a conventional by-pass loop arrangement it will be appreciated that the condensate gas presented at the suction port is relatively warm. Thus, in a hermetic compressor, that is to say sealed, the suitability of a conventional by-pass loop arrangement is limited.

In accordance with the present invention there is provided a refrigeration system including by-pass means arranged to isolate in accordance with predetermined criteria an evaporator element of the refrigeration system, the by-pass means includes a liquid by-pass loop coupled to reservoir means arranged to accommodate liquid phase of a refrigerant and coupled to a compressor of the system whereby the liquid by-pass loop in operation, draws off refrigerant and facilitates vaporisation of that refrigerant liquid phase to substantially reduce the vapour temperature and so improve cooling of the compressor.

Preferably, the by-pass means also includes a vapour by-pass loop to pass refrigerant vapour phase from a condenser of the system to the compressor for mixing with the vaporised refrigerant liquid phase from the reservoir. Preferably, the liquid by-pass loop and the vapour by-pass loop include valve means to control flow of liquid and vapour respectively.

Preferably, the liquid by-pass loop includes a throttle.

Preferably, the valve means or other flow regulation mechanism is used to ensure vapour temperature is sufficiently low to maintain adequate cooling of the compressor. The valve means or other flow regulation mechanism can be controlled by vapour pressure monitoring, vapour temperature monitoring, timed operation or vapour flow monitoring.

Power consumption may be further reduced by switching off a cooling fan for the condensor of the refrigeration system.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing in which there is a schematic illustration of a refrigeration system.

Referring to the drawing, relatively cool condensate vapour is provided at a compressor suction port 12 when in by-pass mode by means of a condensate liquid by-pass loop 21 including a valve 2 and throttle 5 in association with a vapour by-pass loop 23. These loops 21, 23 are arranged to "short-circuit" a conventional refrigeration system comprising the compressor 10, a condenser 8 along with a fan 9, a receiver 6, an evaporator throttle 4 and an evaporator 11. The operation of this conventional refrigeration system with a refrigeration duty is as described previously. The subject of the present invention is with regard to the operation of the refrigeration system with by-pass loops 21, 23 as illustrated in the drawing when there is no or limited refrigeration duty on the evaporator 11.When the refrigeration duty is removed from the evaporator 11, that is to say when a stored product is adequately chilled, an evaporator valve 3 is closed preventing liquid refrigerant passing through the evaporator valve 4 to the evaporator 11. In co-operation with the closure of the evaporator valve 3 the condensate by-pass valve 2 and vapour by-pass valve 3 are opened to respectively allow liquid refrigerant and vapour refrigerant to flow to the suction port 12 of the compressor 10. The condensate by-pass loop 21 also includes a condensate by-pass throttle 5 to regulate condensate flow. In order to prevent back flow of refrigerant from the receiver 6 through the condenser 8 and to the compressor 10, a check value 7 is located in the receiver 6 inlet feed. The effect of the check valve 7 is to ensure a vapour pressure in the receiver 6 and also has the result of stimulating flow of the refrigerant liquid through the throttle 5.

With the refrigeration system in the by-pass mode described above, the compressor continues to operate but only pumps refrigerant vapour without changing its pressure with the result that little work energy is required that is to say there is a lower power requirement by the compressor 10. This pumped refrigerant vapour has a lower temperature than with conventional by-pass loops as the liquid refrigerant that passes through the throttle 5 vaporises within the suction piping and/or the suction port 12 resulting in a reduced vapour temperature. The motor windings of the compressor are thus more adequately cooled.

In order to further reduce power consumption by the refrigeration system it may be appropriate to switch off the fan 9 during the by-pass mode. This will reduce heat discipation from the condensor 8 but as there is no or limited refrigeration duty this should not be too detrimental.

It will be appreciated that the vapour pressure within the loops 21, 23 and suction port 12 will increase as there is no pressurisation of the vapour by the compressor and thus, only limited condensation in the condensor 8. This increase in vapour pressure results in a reciprical reduction in the cooling action due to vaporisation as the liquid refrigerant passing through the throttle 5 can not vaporise as easily and so consume heat energy. In order to prevent this detrimental effect, a cycling device such as a pressure sensor 14 is provided to ensure closure of the valves 1, 2 when the vapour pressure reaches a predetermined value. With the valves 1, 2 closed all the refrigerant vapour is pumped by the compressor 10 through its discharge port 13 under pressure so that the vapour condenses in the condensor 8 and passes through the check valve 7 for collection in the receiver 6.Once the vapour pressure at the suction port 12 has fallen to a suitable lower predetermined level the pressure switch 14 again stimulates opening of valves 1, 2. The cycle is then repeated to maintain the vapour temperature presented at the suction port is low enough to ensure adequate cooling of the compressor motor coils.

when more refrigeration duty is required of the evaporator 11, the valves 1, 2 are closed and the evaporator valve 3 opened in co-operation. The refrigeration system then resumes a conventional refrigeration operation.

It will be appreciated that control of the vapour temperature present in the by-pass mode could be achieved either as indicated by using a pressure sensor 14 or possibly with more advantage using a simple timer control or temperatue sensing of either the vapour and/or the motor windings or, simple sensing of vapour flow.

It will be understood that the valves used in the present invention could be solenoid valves.

It will be understood that an embodiment of the present invention could be constructed without a vapour by-pass loop 23 such that coolant vapour present at suction port 12 is derived solely from vaporisation of liquid phase coolant through by-pass loop 21.

Claims

CLAIMS:

1. A refrigeration system including by-pass means arranged to isolate in accordance with predetermined criteria an evaporator element of the refrigeration system, the by-pass means includes a liquid by-pass loop coupled to reservoir means arranged to accommodate liquid phase of a refrigerant and coupled to a compressor of the system whereby the liquid by-pass loop in operation, draws off refrigerant and facilitates vaporisation of that refrigerant liquid phase to substantially reduce the vapour temperature and so improve cooling of the compressor.

2. A refrigeration system as claimed in claim 1 wherein the by-pass means includes a vapour by-pass loop to pass refrigerant vapour phase from a condenser of the system to the compressor for mixing with a vaporised refrigerant liquid phase from the reservoir.

3. A refrigeration system as claimed in claim 1 or 2 wherein the liquid by-pass loop and the vapour by-pass loop include valve means to control flow of liquid and vapour respectively.

4. A refrigeration system as claimed in claim 1, 2 or 3 wherein the liquid by-pass loop includes a throttle.

5. A refrigeration system as claimed in claim 3 or 4 wherein the valve means or an other flow regulation mechanism is used to ensure vapour temperature is sufficiently low to maintain adequate cooling of the compressor.

6. A refrigeration system as claimed in claim 5 wherein the valve means or other flow regulation mechanism for temperature regulation is controlled by vapour pressure monitoring or vapour temperature monitoring or timed operation or vapour flow monitoring.

7. A refrigeration system as claimed in any proceeding claim wherein cooling fan means of the refrigeration sytem is arranged to be made inoperative during the by-pass mode.

8. A refrigeration system substantially as hereinbefore described with reference to the accompanying drawing.