GB2550921A

GB2550921A - Cooling system

Info

Publication number: GB2550921A
Application number: GB1609498.9A
Authority: GB
Inventors: Oliver Hoffmann Bruno; Richard Hilgert Andreas; Kreutz Marlene
Original assignee: Eaton Industrial IP GmbH and Co KG
Current assignee: Eaton Industrial IP GmbH and Co KG
Priority date: 2016-05-31
Filing date: 2016-05-31
Publication date: 2017-12-06
Also published as: WO2017207526A1; US20200318869A1; CN109477674A; GB201609498D0; EP3465028A1

Abstract

A cooling system 1 comprises a compressor 2, condenser 3, expansion valve 4 and evaporator 5 connected in a loop. An internal heat exchanger 6 has a first conduit 7 in thermal contact with a second conduit 10, wherein the first conduit is part of a first (high) pressure fluid line 8 & 9 and the second conduit is part of a second pressure fluid line 11 & 12 that is at a pressure that is lower than the first. A bypass line 13 connects the first pressure fluid line with the second pressure fluid line for injecting an amount of liquid fluid from one to the other and a valve 14 is arranged to open or close the bypass line. A temperature 15 and / or pressure sensor monitors the load point of the compressor and a controller controls the valve. The bypass line is preferably arranged in the internal heat exchanger (figure 2). The bypass valve may be a back pressure or thermostatic valve.

Description

Cooling system

The invention relates to a cooling system comprising, connected in a bop by fluid lines and in succession, a compressor, a condenser, an expansion valve and an evaporator, further comprising an internal heat exchanger having a first conduit in heat exchanging contact with a second conduit, wherein the first conduit is part of the high pressure fluid line between the condenser and the expansion valve and wherein the second conduit is part of the tow pressure fluid line between the evaporator and the compressor.

Such a cooling system is for example known from EP 1043550. This publication describes a cooling system in which a fluid in particular CO2 is used which is made super-critical in the high pressure line between the compressor and the expansion valve. The internal heat exchanger cools the fluid in the high pressure line, such that the COP (coefficient of performance) of the cooling system is improved

During high load points, typically at high condensation temperature with a low pressure on the suction side of the compressor, the vapor in the low pressure fluid line could be superheated too much. This effect is partially contributed to the internal heat exchanger, which transfers heat from the high pressure fluid line to the low pressure fluid line.

So, although the internal heat exchanger has the advantage of improving the COP during most of the operation conditions of the cooling system, in high load point conditions, the internal heat exchanger result in a disadvantage, because the fluid in the low pressure fluid line could get too much superheated This results in a decrease of the volumetric efficiency of the compressor, which in turn results in a decreased COP. It also results in a too high compressor outlet temperature, which has negative effects on for example the oil, and it could lead to overheating of the compressor it self.

It is an object of the invention to reduce the above mentioned disadvantages.

This object is achieved with a cooling system according to the preamble, which is characterized by a bypass line connecting the high pressure fluid line with the low pressure fluid line for injecting small amounts of liquid fluid from the high pressure fluid line into the bw pressure fluid line; and - a valve arranged in the bypass line for opening or cbsing the bypass line; and - control means for monitoring the bad point of the compressor and for controlling the valve to an open position when the bad point exceeds a threshold

With the cooling system according to the invention, the bad point of the compressor is monitored and when the bad point becomes too high, which would result in too much superheated vapor in the bw pressure fluid line, the valve is controlbd open for a short time, such that a small amount of fluid from the high pressure fluid line is injected into the bw pressure fluid line. The fluid in the high pressure fluid line is liquid and upon injection in the bw pressure fluid line, the liquid fluid will evaporate resulting in a cool down of the superheated vapor in the low pressure fluid line.

As soon as the vapor is cooled down and the bad point is bebw the threshold, the valve is controlbd to cbse the bypass line, such that the cooling system can operate in the common way.

In a preferred embodiment of the cooling system according to the invention the bypass line is arranged in the internal heat exchanger between the first conduit and the second conduit.

By arranging the bypass line in the internal heat exchanger, it is more easy to convert existing layouts to a cooling system according to the invention. It would only require to exchange the internal heat exchanger of an existing cooling system with an internal heat exchanger incorporating a bypass line to convert an existing cooling system to a cooling system according to the invention.

The position of the bypass line in the internal heat exchanger could be chosen depending on the conditions, for exampb at the beginning, the middb or the end of the internal heat exchanger in view of the liquid side. A further embodiment of the cooling system according to the invention further comprises a temperature sensor and/or a pressure sensor connected to the control means and arranged in the bw pressure fluid line, preferably near the compressor.

Whether the vapor in the bw pressure fluid line is too much superheated can be derived from the temperature of the fluid in the low pressure fluid line or the pressure thereof. Also a combination of temperature and pressure can be used to determine whether the vapor is too much superheated and the valve needs to be controlled open to cool the vapor down.

In another embodiment of the cooling system according to the invention the valve is a back pressure valve or a thermostat valve having the respective sensor in fluid connection with the low pressure fluid line. These valves provide mechanical control means, wherein the superheated condition is mechanically detected and the valve is opened when the pressure exceeds a threshold or the temperature causes a bi-metal to open the valve.

Depending on the general conditions in the internal heat exchanger, the valve and control means could also be embodied as a small hole. The flow through this hole will only be considerate, when the pressure difference between the first and second conduit. So, by designing the dimensions of this hole, the same effect as a back pressure valve could be obtained

The invention also relates to a method for controlling a cooling system according to the invention, which method comprises the steps: - while having the bypass line closed, monitoring the toad point of the compressor; - when the monitored toad point exceeds a threshold, shortly opening the bypass line by controlling the valve, to inject an amount of liquid from the high pressure fluid line into the tow pressure fluid line.

In a preferred embodiment of the method according to the invention the toad point of the compressor is monitored by the temperature of the fluid entering the compressor.

This temperature is measured for example in the tow pressure fluid line just before the fluid enters the compressor. This provides a reliable value to determine whether the overheated vapor should be cooled down by injection of liquid fluid from the high pressure fluid line.

In yet another embodiment of the method according to the invention the toad point of the compressor is monitored by the pressure of the fluid entering the compressor.

These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows a schematic view of a first embodiment of a cooling system according to the invention.

Figure 2 shows a schematic view of a second embodiment of a cooling system according to the invention.

Figure 1 shows a first embodiment of a cooling system 1 according to the invention. The cooling system 1 has connected in a loop by fluid lines and in succession, a compressor 2, a condenser 3, an expansion valve 4 and an evaporator 5. To further improve the efficiency of the cooling system 1 an internal heat exchanger 6 is provided with a first conduit 7 arranged in the high pressure fluid line 8,9 between the condenser 3 and the expansion valve 4. The internal heat exchanger 6 has a second conduit 10 in heat exchanging contact with the first conduit 7, and arranged in the tow pressure fluid line 11,12 between the evaporator 5 and the compressor 2. A bypass line 13 with a valve 14 is provided between the high pressure line 8 and the tow pressure line 12. A temperature sensor 15 is furthermore provided in the tow pressure fluid line 12 to detect the temperature of the vapor. The temperature sensor 15 is connected to the controller 16, which can control the valve 14 open or closed

The controller 16 thus checks whether the temperature measured by the temperature sensor 15 exceeds a threshold and then controls the valve 14 to an open state, such that liquid fluid can flow from the high pressure line 8 via the bypass line 13 to the tow pressure line 12 to cool down the vapor in the low pressure line.

Figure 2 shows schematically a second embodiment 20 of a cooling system according to the invention. The cooling system 20 has schematically, a compressor 21, a condenser 22, a restriction 23 and an evaporator 24.

An internal heat exchanger 25 is provided having an internal channel 26 and an concentrically arranged external channel 27. The external channel provides the high pressure fluid line and connects the condenser 22 with the restriction 23, while the internal channel 26 connects the evaporator 24 with the compressor 21 and provides the low pressure fluid line.

Due to the concentric arrangement of the internal channel 26 and the external channel 27 heat can be exchanged between the high pressure fluid line and the low pressure fluid line.

Furthermore, a valve 28 is provided between the wall of the internal channel 26 and the external channel 27. This valve 28 is operated by an actuator 29, which can be triggered by the temperature or the pressure in the bw pressure fluid line.

When the valve 28 is opened liquid fluid can flow from the high pressure fluid line to the low pressure fluid line to cool the vapor in the bw pressure fluid line.

Claims

1. Cooling system comprising, connected in a bop by fluid lines and in succession, a compressor, a condenser, an expansion valve and an evaporator, further comprising an internal heat exchanger having a first conduit in heat exchanging contact with a second conduit, wherein the first conduit is part of the high pressure fluid line between the condenser and the expansion valve and wherein the second conduit is part of the bw pressure fluid line between the evaporator and the compressor, characterized by - a bypass line connecting the high pressure fluid line with the bw pressure fluid line for injecting small amounts of liquid fluid from the high pressure fluid line into the bw pressure fluid line; and - a valve arranged in the bypass line for opening or cbsing the bypass line; and - control means for monitoring the load point of the compressor and for controlling the valve to an open position when the bad point exceeds a threshold

2. Cooling system according to claim 1, wherein the bypass line is arranged in the internal heat exchanger between the first conduit and the second conduit.

3. Cooling system according to claim 1 or 2, further comprising a temperature sensor and/or a pressure sensor connected to the control means and arranged in the bw pressure fluid line, preferably near the compressor.

4. Cooling system according to the preceding claims, wherein the valve is a back pressure valve or a thermostat valve having the respective sensor in fluid connection with the low pressure fluid line.

5. Method for controlling a cooling system according to the preceding claims, which method comprises the steps: - while having the bypass line dosed, monitoring the bad point of the compressor; - when the monitored bad point exceeds a threshold shortly opening the bypass line by controlling the valve, to inject an amount of liquid from the high pressure fluid line into the bw pressure fluid line.

6. Method according to claim 5, wherein the load point of the compressor is monitored by the temperature of the fluid entering the compressor.

7. Method according to claim 5 or 6, wherein the load point of the compressor is monitored by the pressure of the fluid entering the compressor.