GB2075649A

GB2075649A - Refrigeration system with defrost circuit

Info

Publication number: GB2075649A
Application number: GB8014621A
Authority: GB
Original assignee: Kenwood Manufacturing Co Ltd
Current assignee: Electrical and Musical Industries Ltd
Priority date: 1980-05-02
Filing date: 1980-05-02
Publication date: 1981-11-18
Also published as: GB2075649B

Abstract

A vapour compression refrigeration system has a two-way solenoid valve (19) for directing relatively hot vapour from the refrigeration circuit around a defrost circuit (26). The refrigerator circuit includes a heater (17), including a thermal store (20), for heating the vapour, located upstream of the valve. The valve may be de-energised should the temperature within the cold cabinet (13) of the refrigeration system become too high. <IMAGE>

Description

SPECIFICATION Refrigeration systems The present invention relates to refrigeration systems of the vapour compression type which include a hot vapour defrosting arrangement for periodically melting ice which builds up from atmospheric moisture on the cool parts of the system, particularly the evaporator and structure in thermal contact therewith.

Such refrigeration systems are known, for example from British Patent Specification No.

764736. In such systems, the evaporator'is periodically defrosted by diverting relatively hot vapour from the discharge side of the compressor to the evaporator along a defrosting path which by-passes the condenser and the restrictor forming an expansion device, access to the by-pass path being controlled at a diverter valve, the control for which may be manual or automatic for example involving a timer.

An object of the invention is to provide a refrigeration system having a hot vapour defrosting circuit, which is relatively simple and which can be used for example in a cabinet the interior of which is normally to be maintained at a temperature below the freezing point of water, while minimising the risk of thermal shock to the normally cold parts of the refrigeration system, including the evaporator.

Such cabinets may for example be used as domestic freezers for freezing and/or storing food at a temperature of for example - 20"C.

According to the present invention, there is provided a vapour-compression refrigeration system having a refrigeration circuit comprising a compressor for compressing the working vapour, a condenser for condensing the compressed vapour, a restrictor, and an evaporator, the system further including a hot-vapour defrost circuit comprising a diverter valve operable to divert hot compressed vapour to the evaporator along a path by-passing the restrictor, wherein the heating means comprise a thermal store arranged to be heated by the vapour into thermal equilibrium therewith when the diverter valve is inoperative and to return heat to the vapour when the diverter valve is operated and the temperature of the vapour reaching the heat means drops.

With this arrangement in which the heat is applied to the vapour from the compressor upstream of the diverter valve, the heated vapour can be arranged to have a sufficiently long path (preferably thermally insulated) to spread out the sudden rise in temperature which would otherwise occur when the diverter valve is operated to by-pass the condenser.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in Figs. 1 and 2 are circuit diagrams of two refrigeration systems in accordance with the invention.

The refrigeration system shown in Fig. 1 comprises the usual electric motor and compressor unit 1; the outlet 2 of which is connected through a pipe 3 to the inlet 4 of a condenser 5, the outlet 6 of which is connected through a drier 7, restrictor 8 and pipe 9 to the inlet 10 of an evaporator 11 formed by a net work of pipes distributed around the shelyes 1 2 of a freezer cabinet 1 3. The outlet 14 of the evaporator is returned by a pipe 1 5 to the inlet 1 6 of the compressor 1.

The compressor outlet 2 is connected to the pipe 3 through a heater 17, a pipe 1 8 and a solenoid-operated diverter valve 1 9. The heater 1 8 comprises a block of cementitious material 20 which is cast around a convoluted portion 21 of the pipe 18. An electrical heating wire 22 is disposed in intimate thermal contact with the pipe portion 21 and its ends are brought out at 23. The block 20 may be cast from a mixture Alag aggregate and Fondu Cement incorporating an accelerator, this material being available from Lafarge Aluminous Cement Company Limited. With aid of the accelerator, the setting time for the block may be of the order of five mintues. The block could also be made of cast silica material but would have to be protected against moisture.

This block could also be bonded with other materials including aluminum and/or silica and protecred against the ingress of moisture.

The diverter valve 1 9 is a two-way solenoid operated valve. In its unoperated condition, it connects the pipe 1 8 to the pipe 3. When energised, it isolates the pipe 1 8 from the pipe 3 and, instead connects the pipe 1 8 to the inlet 25 of a thermally insulated defrost line 26 leading directly to the evaporator inlet 10, by-passing the condenser 5 and restrictor 8.

In normal operation of the refrigeration circuit shown in Fig. 1, with the solenoid valve 1 9 de-energised, the block 20 is heated to an equilibrium condition relative to the compressed vapour leaving the compressor 1.

When it is required to defrost the cabinet 13, the solenoid valve 1 9 is energised, for example by a timer or manual control (not shown) and warm vapour is passed from the pipe 1 8 through the defrost line 26 towards the inlet 10 of the evaporator 11. It will be appreciated that prior to operation of the valve 1 8 there will be a thermal gradient along the line 26, at least at its portion near the evaporator inlet 10. Thus, upon initial energisation of the valve 19, the temperature of the vapour reaching the evaporator will rise gradualiy, thus avoiding thermal shocks.

As the vapour passes through the evaporator, it gives up heat to the ice within the cabinet 1 3 and accordingly cold vapour passes through the outlet 1 4 and pipe 1 5 to the inlet 1 6 of the compressor 1. The temper ature of the vapour leaving the compressor 2 thus drops but heat from the block 20 is transferred to this vapour as it passes through the pipe 21. Further heat is available by energising the electrical heater 22.

When the temperature within the cabinet 12 rises above 0 C, a thermostat (not shown) de-energises the solenoid valve 1 9 and heater 22 and the system reverts to normal operation.

The refrigeration apparatus shown in Fig. 2 is generally similar to that shown in Fig. 1 and corresponding parts are indicated by the same reference numerals. It differs however in that the condenser is divided into an upstream portion 51 and a downstream portion 52 the latter being situated between the diverter valve 1 9 and the drier 7. The inlet 53 of the upstream condenser portion 51 is connected to the outlet 2 of the compressor 1. The outlet 54 of the upstream condenser portion 51 is connected to the inlet of an oil cooler coil 55 for the lubricating oil within the compressor 1. The outlet of the coil 55 is connected to the heater 1 7 as in the case of Fig.

1.

The operation is in general similar to that of the system shown in Fig. 1 with the exception that under normal refrigeration operation the compressed vapour leaving the compressor is partially cooled in the upstream condenser portion 51 then serves to cool the lubricant of the compressor before passing to the remainder of the circuit. When the valve 1 9 is operated, the vapour continues to cool the oil within the compressor and the heat thus removed is used to assist in defrosting the cabinet 1 3.

Claims

1. A vapour-compression refrigeration system having a refrigeration circuit comprising a compressor for compressing the working vapour, a condenser for condensing the compressed vapour, a restrictor, and an evaporator, the system further including a hot-vapour defrost circuit comprising a diverter valve operable to divert hot compressed vapour to the evaporator along a path by-passing the restrictor, wherein the heating means comprise a thermal store arranged to be heated by the vapour into thermal equilibrium therewith when the diverter valve is inoperative and to return heat to the vapour when the diverter valve is operated and the temperature of the vapour reaching the heat means drops.

2. A refrigeration system according to claim 1, wherein the thermal store comprises a block of cementitious material cast around a conduit defining part of the refrigeration cir cuit.

3. A refrigeration system according to claim 1 wherein the thermal store comprises a block of aluminum cast around a conduit and suitably insulated against heat loss and protected against moisture ingress.

4. A refrigeration system according to claim 2 or 3, wherein the heating means also includes an electrical heater.

5. A refrigeration system according to any of the preceding claims wherein the diverter valve is located downstream of the compressor and upstream of the condenser.

6. A refrigeration system according to any of claims 1 to 4, wherein the condenser comprises an upstream portion and a downstream portion, and the refrigeration circuit includes a portion extending through the upstream condenser portion, a cooler for the compressor, the heating means, the diverter valve and the downstream condenser portion.

7. A refrigeration system according to claim 6, wherein the compressor is a liquidlubricated mechanical compressor and the compressor cooler is arranged to cool the compressor lubricant.

8. A refrigeration system substantially as herein before described with reference to Fig.

1 or Fig. 2 of the accompanying drawings.