GB2468166A

GB2468166A - Cascade refrigeration system with aftercooler

Info

Publication number: GB2468166A
Application number: GB0903489A
Authority: GB
Inventors: Mark Anthony Lawson
Original assignee: Arctic Circle Ltd
Current assignee: Arctic Circle Ltd
Priority date: 2009-02-27
Filing date: 2009-02-27
Publication date: 2010-09-01
Also published as: GB0903489D0; GB2468166A9

Abstract

A multi-stage refrigeration system 24 has at least first and second stages 4, 6, each stage comprising a complete refrigeration circuit which includes a compressor 10, 18, a condenser 12, 20, an evaporator 8, 16, and an expansion valve 14, 22. The first stage also includes an aftercooler 26, for removing heat from refrigerant in the first stage before heat from the first stage is transferred to the second stage (6) for further cooling. The aftercooler may include a fan, and both the first and second stages may each have a different refrigerant. The multi-stage refrigeration system can include more than two stages, with each stage except the last stage including an aftercooler.

Description

A MULTI-STAGE REFRIGERATION SYSTEM

This invention relates to a refrigeration system and, more especially, this invention relates to a multi-stage refrigeration system.

Multi-stage refrigeration systems are known. The multi-stage refrigeration systems are sometimes referred to cascade refrigeration systems. They are used where refrigerant pressures or operating efficiencies make it impractical to operate with a large temperature difference between evaporating and condensing temperatures. In the known multi-stage refrigeration systems, there are two or more stages. Each stage is a complete refrigeration circuit. The condenser of the first stage is cooled by the evaporator of the second stage. If there are more than two stages, then the further stages operate in the same way. The cooling of the various stages requires a power input which can be significant and a waste of energy.

It is an aim of the present invention to obviate or reduce the above mentioned problem.

Accordingly, in one non-limiting embodiment of the present invention there is provided a multi-stage refrigeration system comprising at least first and second stages, the first stage and the second stage each comprising a complete refrigeration circuit, and the first stage including heat removing means for removing heat from refrigerant in the first stage before heat from the first stage is transferred to the second stage for further cooling.

In the multi-stage refrigeration system of the present invention, the transfer of the heat enables a substantial energy saving, which can be very significant over the entire operating life of the system.

The multi-stage refrigeration system may be one which includes more stages than the first and second stages, and in which each stage except the last stage has the heat removing means.

In the multi-stage refrigeration system of the present invention, each stage comprises an evaporator, a compressor, and a condenser.

Preferably, the heat removing means is a fan. Other types of heat removing means may be employed. Thus, for example, the heat removing means may alternatively be an arrangement of finned tubes through which refrigerant gas passes. The heat removing means may alternatively be an arrangement of finned tubes through which refrigerant gas passes, and a fan.

The heat removing means may alternatively be a water cooling circuit. The heat removing means may alternatively be a water cooling circuit and a fan.

The multi-stage refrigeration system may be one in which the first stage has a first refrigerant, the second stage has a second refrigerant, and the first and second refrigerants are different. One of the refrigerants is preferably carbon dioxide. With different refrigerants, the refrigerant for the second stage which is the higher temperature side may be a hydroflurocarbon (HFC), for example that known as 407A or 404A. In this case, the refrigerant on the first stage lower temperature side may be carbon dioxide. If desired, the first and the second refrigerants may be the same, and in this case the first and the second refrigerants may both be carbon dioxide.

An embodiment of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows schematically a known multi-stage refrigeration system comprising first and second stages; and Figure 2 shows a multi-stage refrigeration system of the present invention.

Referring to Figure 1, there is shown a multi-stage refrigeration system 2 comprising a first stage 4 and a second stage 6. The first and second stages 4, 6 each comprise a complete refrigeration circuit. Thus the first stage 4 has an evaporator 8, a compressor 10, a condenser 12 and an expansion device 14. The second stage 6 similarly has an evaporator 16, a compressor 18, a condenser 20 and an expansion device 22.

The multi-stage refrigeration system 2 operates such that heat QI is absorbed by the evaporator 8, and energy WI is added by the compressor 10. As a result of the heat input Qi and the energy input Wi, a transfer of heat Q2 occurs between the condenser 12 of the first stage 4, and the evaporator 16 of the second stage 6. In order to transfer the heat 02, a power input W2 is absorbed by the compressor 18 in the second stage 6. This power input W2 is appreciable and it would be an advantage if this power input W2 could be reduced.

Referring now to Figure 2, there is shown a multi-stage refrigeration system 24 of the present invention. Similar parts as in the multi-stage refrigeration system 2 have been given the same reference numbers for ease of comparison and understanding.

The multi-stage refrigeration system 24 is such that the first stage 4 includes heat removing means 26. The heat removing means 26 is fitted before the condenser 12. The heat removing means 26 removes heat Q4.

During operation of the multi-stage refrigeration system 24, energy in the form of heat Q4 is removed from the first stage 4 and is transferred to ambient surroundings of the multi-stage refrigeration system 24. This energy transfer occurs before the condenser 12, and it therefore reduces the load on the evaporator 16 of the second stage 6. This reduces the heat load on the second stage 6, which in turn reduces the power required by the compressor 18 in the second stage 6 to compress the refrigerant in the second stage 6.

By reducing the heat absorbed by the evaporator 16 in the second stage 6, the power input to the compressor 18 in the second stage 6 is also reduced, with a resultant saving in energy. More specifically, the refrigerant in the first stage 4 absorbs heat Qi in the evaporator 8, and energy Wi is added by the compressor 10. Heat Q4 is then rejected by the heat removing means 26 to give reduced heat at Q2 which is transferred between the condenser 12 in the first stage 4 and the evaporator 16 in the second stage 6. The power input W2 to the compressor 18 in the multi-stage refrigeration system 24 is lower than the power input W2 to the compressor 18 in the multi-stage refrigeration system 2 due to the transfer of the reduced heat at Q2 in the multi-stage refrigeration system 24.

The heat removing means 26 is preferably forced air. Other types of heat removing means 26 may alternatively be employed so that, for example the heat removing means 26 may be an arrangement of finned tubes or a water cooling circuit.

The saving in power afforded by the multi-stage refrigeration system 24 can be substantial, and this saving in power increases the number of stages employed in the multi-stage refrigeration system. The multi-stage refrigeration system 24 is able to make an appreciable energy saving, which can be very significant over the entire operating life of the multi-stage refrigeration system 24.

It is to be appreciated that the embodiment of the invention described above with reference to the accompanying drawings has been given by way of example only and that modifications may be effected, Thus, for example, as indicated above, the multi-stage refrigeration system 24 may comprise more than the illustrated two stages.

Claims

CLAIMS1. A multi-stage refrigeration system comprising at least first and second stages, the first stage and the second stage each comprising a complete refrigeration circuit, and the first stage including heat removing means for removing heat from refrigerant in the first stage before heat from the first stage is transferred to the second stage for further cooling.
2. A multi-stage refrigeration system according to claim I and including more stages than the first and second stages, and in which each stage except for the last stage has the heat removing means.
3. A multi-stage refrigeration system according to claim I or claim 2. in which the heat removing means is a fan. .
4. A multi-stage refrigeration system according to any one of the preceding claims in which the first stage has a first refrigerant, the second stage has a second refrigerant, and the first and second refrigerants are different.
5. A multi-stage refrigeration system substantially as herein described with reference to Figure 2 of the accompanying drawings.