EP1892489A2 - Method for monitoring a compression refrigerating system - Google Patents

Abstract

The method involves measuring a boiling temperature on a high pressure side as a function of a pressure (pH) on the high pressure side and a refrigerant. A temperature (TH) is measured between a condenser (2) and a throttle (3), and the temperature difference is formed between the boiling temperature and the temperature between the condenser and the throttle. An error status is activated if the temperature difference exceeds a given limit value for a first time. A compression refrigerating system is disconnected if the temperature difference exceeds the given limit value repeatedly.

Description

The invention relates to a method for monitoring a compression refrigeration cycle with at least one compressor, a condenser, a throttle and an evaporator.

For compression refrigeration circuits, the refrigerant must be liquid between the compressor and the throttle in the high pressure range. Between the throttle and the compressor, the refrigerant must be gaseous in the low pressure range. If this is not the case, it will cause interference.

For the maintenance, diagnosis and assessment of the performance of the refrigeration circuit, various measured variables are recorded. In addition, it is of interest whether overheating or hypothermia is present.

The overheating ΔT _L is defined as the difference between the temperature of the superheated gas (inlet temperature in the compressor) T _L and the evaporation temperature T " _L on the dew line at the low pressure associated with T _L Temperature difference between the measured temperature of the gas from the dew line.

The supercooling .DELTA.T _H is defined as the difference between the high pressure present at T _H associated boiling temperature T ' _H on the boiling line and the temperature of the supercooled liquid (inlet temperature in the throttle) T _H. It thus indicates the distance or the temperature difference of the measured liquid temperature from the boiling line.

The causes of a too low overheating ΔT _L are, for example, an incorrectly set throttle (Thermostatic Expansion Valve (TEV)), insufficient contact of the temperature sensor of the TEV or a defective or incorrectly adjusted TEV. Cause of fault for too high overheating ΔT _L could also be a leak in the refrigerant circuit with the loss of refrigerant.

Due to the continuous operation of a compressor with too little overheating of the refrigerant in the suction line, it may come to suction liquid refrigerant droplets. These evaporate in the compressor and can irreparably damage the compressor.

A permanent operation with too little refrigerant and thus an operation with too high overheating can lead to an excessive compressor end temperature and thus also permanently damage the compressor thermally.

Cause of too low supercooling ΔT _H may indicate that there is a leak in the refrigerant circuit and the loss of refrigerant. In addition, in an operation due to a low or negative supercooling can lead to unstable operating conditions in the refrigerant circuit.

According to the state of the art, a refrigeration engineer must approach the plant to determine the operating state and pressure and temperature measuring means at the refrigeration circuit connect. Then the overheating and subcooling must be calculated from the measured values.

The object of the invention is an automatic monitoring by an automatic calculation of overheating and subcooling, which is based on the measurement of integrated in the refrigerant circuit temperature and pressure sensors and corresponding stored algorithms.

This object is achieved according to the features of the independent claims 1 and 4 characterized in that from measured variables, the superheating .DELTA.T _L and / or subcooling .DELTA.T _H determined and compared with setpoints. If the values deviate significantly, there is presumably an error. The compression refrigeration cycle is switched off to prevent damage.

This automatic comparison of overheating and super-cooling with critical values protects the refrigeration circuit from erroneous operation. In addition, the data in the display of the device and online can be read. Furthermore, eliminates the need for the installation of measuring equipment during maintenance. The monitoring can be done very easily via the display or online in the form of a remote diagnosis / remote monitoring. In addition, active refrigerant leakage monitoring can be ensured.

Figure 1 shows a compression refrigeration cycle with a compressor 1, a condenser 2, an internal heat exchanger 5, a throttle 3 and an evaporator 4. A gaseous refrigerant is compressed in a compressor 1 to high pressure; In this case, the refrigerant is heated. Subsequently, the refrigerant in a condenser 2 gives off heat. This heat can be used for heating purposes. The refrigerant is then introduced into the internal heat exchanger 5. Subsequently, the then liquid refrigerant reaches the throttle 3, in which it is relaxed and partially gaseous. In which subsequent evaporator 4, the refrigerant absorbs heat; This happens with heat pumps by environmental heat. The refrigerant becomes completely gaseous. Subsequently, the refrigerant enters the internal heat exchanger 5, in which a heat exchange with the refrigerant flow between the condenser 2 and throttle 3 takes place. After the internal heat exchanger 5, the gaseous refrigerant flows back to the compressor. 1

To monitor the pressure on the high pressure side p _H between the compressor 1 and throttle 3 is detected. Subsequently, the boiling temperature T ' _H on the high pressure side is calculated as a function of the pressure on the high pressure side p _H and the refrigerant. $${\mathrm{T}}^{{\text{'}}_{\mathrm{H}}}=\mathrm{f}\left({\mathrm{p}}_{\mathrm{H}}.\mathrm{refrigerant}\right)$$

In parallel, the temperature T _H between the condenser 2 and throttle 3 is detected. The temperature difference ΔT _H results from the difference between T ' _H and T _H. In the case where the temperature difference .DELTA.T _H falls below a predetermined threshold for the first time, an error status is activated. This can be displayed on an ad. Furthermore, the error status can be retrieved via a remote data connection. In the case where the temperature difference .DELTA.T _H falls below the predetermined limit repeatedly by a predetermined number (for example, 5 times), the compression refrigeration cycle is turned off to prevent damage.

An equivalent monitoring is carried out in the low pressure range. Here, too, a fault condition is activated when the temperature difference .DELTA.T _L falls below a critical limit, as well as an error status activated when the temperature difference .DELTA.T _L exceeds a critical limit.

FIG. 2 shows the wet steam area N of a cooling process in the pressure-enthalpy diagram (log p-h) in which the operating points A to D are shown in FIG. In the wet steam area N, the refrigerant is in two phases. To the left of the wet steam area N is subcooled liquid SL, to the right of the wet steam area N is superheated gas SG. The wet steam area N is separated from the supercooled liquid area by the boiling line BL. The dew line DL separates the wet steam area N from the area of the superheated gas SG. The critical point K at maximum pressure of the wet steam area N separates the boiling line BL from the dew line DL. The numbers 1 to 5 in FIG. 2 clarify which operating states in units 1 to 5 are traversed with respect to their position in the wet steam zone N or in the gaseous SG and liquid zone SL.

Downstream of the compressor 1, the refrigerant is present as a superheated gas at a pressure p _H at point B. In the condenser 2, the refrigerant is cooled and in this case passes through the wet steam area N. In the subsequent internal heat exchanger 5, the refrigerant releases further heat. It adjusts a temperature T _H at the point C in the region of the supercooled liquid SL. In the throttle 3, the refrigerant is expanded to a pressure p _L at the point D. In the evaporator 4, the refrigerant is heated along the line 4 through the wet steam area N. In the internal heat exchanger 5, the refrigerant absorbs the heat which emits the refrigerant between the condenser 2 and the throttle 3.

Both the overheating ΔT _L and the subcooling ΔT _H are setpoints or nominal ranges. If the values for the overheating ΔT _L and / or supercooling ΔT _H determined from the measured values T _H , T _L , p _H and p _L differ significantly from the desired value, this is an indication of the presence of an error.

Claims (6)

Method for monitoring a compression refrigeration cycle with at least one compressor (1), a condenser (2), a throttle (3) and an evaporator (4), characterized in that the pressure p _H on the high pressure side between compressor (1) and throttle ( 3), the boiling temperature T ' _H on the high pressure side is calculated as a function of the pressure on the high pressure side p _H and the refrigerant, the temperature T _H between the condenser (2) and the throttle (3) is detected, the temperature difference ΔT _H between T ' _H and T _{H is} formed and in the case in which the temperature difference .DELTA.T _H a predetermined threshold first falls below an error status is activated and in the case in which the temperature difference .DELTA.T _H falls below the predetermined limit once or repeatedly with a predetermined number The compression refrigeration circuit is turned off. Method for monitoring a compression refrigeration cycle according to claim 1, characterized in that between the condenser (2) and the throttle (3) the primary side of an internal heat exchanger (5) and between the evaporator (4) and the compressor (1) the secondary side of the internal Heat exchanger (5) are arranged. Method for monitoring a compression refrigeration cycle according to claim 2, characterized in that the temperature T _H between the condenser (2) and the internal heat exchanger (5) or between the internal heat exchanger (5) and the throttle (3) can be measured. Method for monitoring a compression refrigeration cycle with at least one compressor (1), a condenser (2), a throttle (3) and an evaporator (4), characterized in that the pressure on the low pressure side p _{L is} detected, the dew point temperature T " _L is calculated on the low pressure side between throttle (3) and compressor (1) as a function of the pressure on the low pressure side p _L and the refrigerant, the temperature T _L between evaporator (4) and compressor (1) is detected, the temperature difference .DELTA.T _L between T _L and T " _{L is} formed and in the case where the temperature difference .DELTA.T _L falls below a predetermined threshold for the first time or exceeds an error status is activated and in the case in which the temperature difference .DELTA.T _L the predetermined limit once or repeatedly with a predetermined Number falls below or exceeds the compression refrigeration cycle is switched off. Method for monitoring a compression refrigeration cycle according to claim 4, characterized in that between the condenser (2) and the throttle (3) the primary side of an internal heat exchanger (5) and between the evaporator (4) and the compressor (1) the secondary side of the internal Heat exchanger (5) are arranged. Method for monitoring a compression refrigeration cycle according to claim 2, characterized in that the temperature T _L between the internal heat exchanger (5) and the compressor (1) or between the evaporator (4) and the internal heat exchanger (5) can be measured.

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