JP2013508662A - Refrigeration plant and method for controlling the same - Google Patents

Abstract

The refrigeration plant has a refrigerator circuit having a compressor, a condensing coil, an expansion valve, and an evaporator. Heat is absorbed in the evaporator and exhausted at the condenser. The pressure is measured at the compressor inlet, and a blower system that blows cool air onto the heat transfer surface of the condenser is controlled in response to the pressure measurement.

Description

  The present invention relates to a refrigeration plant and a method for controlling the same.

  A conventional refrigeration plant has a refrigeration circuit including a compressor, a condensing coil, an expansion valve, and an evaporator, and the expansion valve and the evaporator are usually arranged in a refrigerator cabinet or a freezer cabinet. Heat is absorbed in the evaporator and exhausted at the condenser.

  The refrigeration capacity demand in typical installations can fluctuate significantly. In large installations with refrigeration capacities typically found in supermarkets and warehouses, typically tens to hundreds of kilowatts, there are basically multiple (eg, 3-10) compressors connected in parallel. In some cases, one or more compressors can be selectively driven depending on the load to accommodate fluctuations in compressor demand. However, facilities with multiple compressors are costly, complex to control, large, and therefore impractical for smaller facilities such as small stores that may have only a few refrigerator cabinets Traditionally, refrigeration facilities are usually configured for average demand, and generally the operating situation becomes inefficient when the demand is on either side of the expected demand and the ambient conditions Is different from the expected maximum design point.

  It is known to provide one or more fans to increase the air flow over the condenser and / or evaporator. In some configurations, the fan combined with the condenser operates only at a temperature higher than a certain temperature, or higher than a certain pressure on the high pressure side of the circuit combined with the condenser, so the fan is Operates only at a temperature or pressure higher than a certain temperature or pressure, reduces fan noise and protects the system against insufficient discharge pressure to allow the expansion valve to operate normally As such, it is known to control this fan.

  An object of the present invention is to provide a medium-sized refrigeration facility typically having a capacity of about 1 kW to 20 kW, more typically 2.5 kW to about 10 kW. Such a capacity is typical of a hermetic compressor having neither a variable capacity drive nor a mechanical capacity changer.

  In accordance with a first aspect, the present invention is coupled to receive a high pressure refrigerant and a compressor coupled to receive and compress low pressure refrigerant from a low pressure circuit at a compressor inlet to produce high pressure refrigerant. A condenser having at least one heat transfer surface for releasing heat from the condenser and supplying cooled high-pressure refrigerant to the expansion valve; and a blower system for blowing cooling air onto the at least one heat transfer surface; And a refrigeration plant characterized by a blower control device configured to control the blower according to the pressure in the low-pressure circuit.

  According to one embodiment, the present invention receives a high pressure refrigerant and a compressor coupled to receive and compress low pressure refrigerant gas from a low pressure circuit at the compressor inlet to produce high pressure refrigerant gas. A condenser having at least one heat transfer surface coupled to release heat from the condenser and supplying cooled high-pressure liquid refrigerant to the expansion valve; and a blower for blowing cooling air onto the at least one heat transfer surface And a refrigeration plant characterized by a blower controller configured to control the blower in response to pressure in the low pressure circuit.

  According to the present invention, by controlling the blower / fan according to the pressure in the low pressure circuit, the demand fluctuation and advantageous ambient dispersion compared to the conventional configuration which simply switches on the fan at a given pressure or temperature. The efficiency can be improved surprisingly in typical installations employing the scheme. In particular, the output capacity of a typical plant can be significantly increased during normal operation, i.e., the compressor typically operates at a lower duty cycle, reducing energy consumption.

  The blower controller is coupled to a sensor configured to provide a variable output indicative of the pressure in the low pressure circuit, and the blower controller is configured to control the fan in accordance with an algorithm receiving pressure. It is preferable to have a processor.

  Typically, the blower control device is operable to determine a discharge pressure in accordance with the fluid pressure at the compressor inlet and to control the blower based on the determined discharge pressure. It is preferable that the blower control device controls the blower based on a difference between the obtained discharge pressure and the measured discharge pressure. In one possibility, the blower controller is operable to control the blower in response to the measured ambient temperature. In one possibility, a refrigeration plant with a fixed steam displacement compressor is provided.

  In one embodiment, the refrigeration plant has a fixed steam displacement compressor.

  In one aspect, a method of controlling a refrigeration plant having a compressor and a blower that cools a condenser, measuring pressure at the compressor inlet and controlling the blower in response to the measured pressure Is provided.

  Typically, the fans and / or blowers are controlled according to an algorithm that takes compressor inlet pressure as input. Optionally, the method according to the invention includes determining a discharge pressure in response to the fluid pressure at the compressor inlet and controlling the blower based on the determined discharge pressure. Such a method preferably includes receiving a measured value of the discharge pressure at the compressor outlet and controlling the blower based on the difference between the determined discharge pressure and the measured value of the discharge pressure. .

  In one possibility, the method according to the invention receives an ambient temperature measurement and controls the blower in response to the ambient temperature measurement.

  In one embodiment, the controller receives pressure voltage measurements from the transducer corresponding to the pressure-temperature relationship of the vapor form refrigerant. The compressor switches on and off depending on the measured suction pressure, which is inflated by the evaporator controller when the predetermined control value for the desired space temperature is met and the mechanical solenoid valve is closed. Reduced by exhaustion of refrigerant by impeding liquid flow to the valve. The compressor removes the remaining steam in the evaporator to reduce the pressure, and then switches off when the set LP point is reached. This unit is activated again when the suction pressure rises by the evaporator controller opening the solenoid valve to allow liquid refrigerant to flow into the evaporator space and consequently increasing the pressure to the required value that requires compression. Be made. When the compressor is switched on, the blower is initially operated at a preset minimum value, and then the desired HP read by the second pressure-voltage transducer for the measured LP value. Operated to meet the value. The blower operates in the control band on either side of the desired discharge point according to an algorithm that automatically adjusts to achieve the required hp value. The control parameters are preset in a computer program / algorithm that always receives and interprets variable input voltage signals from the two transducers and supplies output signals to the compressor (fixed) and blower (variable). The blower output provides a voltage output that increases or decreases between the lowest allowable blower speed and the highest blower speed, and the blower accelerates / decelerates to maintain the lowest condensation temperature (HP) associated with the measured LP value.

  Each example of the present invention provides a refrigerator unit, a freezer unit, a chest freezer, a storage container, and a warehouse having a refrigeration plant operated in accordance with each example of the present invention.

  The present invention provides a computer program and a computer program product for performing any of the methods described herein and / or embodying any of the features of the apparatus described herein, Provided is a computer readable medium having stored thereon a program for performing any of the methods described herein and / or embodying any of the apparatus features described herein.

  The present invention provides a signal embodying a computer program for performing any of the methods described herein and / or embodying any of the features of the apparatus described herein. A computer program that performs at least one of a method for transmitting such a signal, implementing any of the methods described herein, and embodying any of the features of the apparatus described herein. A computer product having a supported operating system is provided.

  The present invention extends at least one of the methods and apparatus substantially as herein described with reference to the accompanying drawings.

  Any feature in one aspect of the invention may be applied in any appropriate combination with other aspects of the invention. In particular, method aspects may be applied to apparatus aspects, and conversely apparatus aspects may be applied to method aspects.

  In addition, a feature generally realized by hardware may be realized by software, and conversely, a feature realized by software may be realized by hardware. Any reference to software and hardware features herein should be construed as such.

  Preferred embodiments of the present invention will now be described in detail by way of example only with reference to the accompanying drawings.

FIG. 2 is a very schematic diagram of a refrigeration unit and control system according to an example of the present invention. 4 is a plot of the high-pressure and low-pressure temperatures of a refrigeration unit according to the present invention.

  The example of FIG. 1 has a compressor 10 coupled to compress a refrigerant fluid (usually vapor) into a condenser 14 where the fluid is condensed into a liquid and releases heat. Then, the refrigeration unit having a refrigeration circuit 22 that is passed through the expansion valve 20 and fed into the evaporator 18 where the fluid absorbs heat and is evaporated and then returned to the compressor 10. 1 shows a control system. Fluid flow to the expansion valve 20 is controlled by a solenoid valve 8 coupled between the condenser 14 and the expansion valve 20.

  The controller 16 is coupled to control a cooling fan or blower 12 that forces air onto the condenser 14 to cool the condenser 14. The controller 16 is coupled to the condenser 14 and the evaporator 18 and monitors at least one of temperature and pressure in these parts of the refrigeration unit. In other words, the controller 16 is coupled to pressure sensors 16a and 16b which are positioned to measure pressure at the compressor inlet (suction point) and compressor outlet (discharge point), respectively. The condenser pressure (hereinafter referred to as HP) and the evaporator pressure (hereinafter referred to as LP) are compared by the controller 16 and are based on the compressor operating envelope and the optimal condensing pressure at the measurement suction point (compressor input). Used to guide optimal operating conditions. The fan speed is controlled according to these parameters to achieve a desired operating state. The evaporator sensor 6 has a temperature sensor such as a thermocouple coupled to the evaporator 18 side of the system (eg, in a refrigeration space or refrigerator cabinet) and controls the solenoid valve 8 based on the measured space temperature. It is possible to operate.

  The transducer 16a supplies the controller 16 with a voltage based on the pressure-temperature relationship, for example, the pressure and / or temperature of the vapor form refrigerant. In operation, the evaporator controller 6 controls the solenoid valve 8 to close when it detects that the desired space (or cabinet) temperature has been achieved. This prevents liquid from flowing into the expansion valve. The compressor is configured to switch on and off in response to the measured suction pressure, i.e., the pressure at the compressor inlet. When the suction pressure exceeds the selected value, the compressor is switched on to remove the refrigerant from the evaporator, thereby reducing the pressure. When the selected low pressure value is reached, the compressor switches off.

  When the evaporator controller 6 detects that the threshold space (or cabinet) temperature has been exceeded, it controls the solenoid valve 8 to open. Thereby, the liquid can flow to the expansion valve and flow into the evaporator. When the evaporator controller 6 detects that the desired space (or cabinet) temperature has been achieved, it controls the solenoid valve 8 to close, and this cycle is repeated.

  When the compressor is switched on, the blower 12 is initially operated at a preset minimum speed. The blower speed is then adjusted based on the difference between the pressure measurements obtained by transducer 16a and transducer 16b. Accordingly, the blower 16 operates to control the pressure at the discharge point (compressor output) so as to maintain the HP value within an allowable range. The controller 16 controls the blower speed and switches the compressor on and off based on preset control parameters and voltage signals from the two transducers 16a and 16b. The control device 16 converts the voltage signals input from the two transducers to generate an output signal, and controls the compressor (fixed speed) and the blower (variable speed). The blower is controlled using an increasing or decreasing voltage output that changes the speed between the lowest allowable blower speed and the highest blower speed. Thus, the blower is controlled to accelerate or decelerate to maintain a minimum condensation temperature (HP) associated with the measured LP value.

  In another example, the controller 16 receives a compressor inlet pressure measurement from the sensor 16a. The controller 16 compares the measured compressor inlet pressure with the selected switch-on pressure. When the measured pressure exceeds this switch-on pressure, the fan controller 16 generates a control signal that switches on the blower 12 to operate at the first fan speed. While the measured compressor inlet pressure is higher than this selected threshold level, the fan speed is controlled in proportion to the measured pressure. The proportionality factor for this control is selected depending on the characteristics of the particular system, such as the size and shape of the condenser and the operating power of the compressor.

  Normally, in the example of the present invention, the suction point (compressor input) changes according to the refrigeration demand. In general, a compressor does not have a capacity for variable speed operation, whether it operates or not, and a low pressure so that the compressor has hysteresis so that it does not switch on and off excessively. The pressure switch turns on the compressor when the internal pressure rises above the turn-on threshold, and the compressor operates until the pressure falls below a turn-off threshold that is slightly less than the normal turn-on threshold . The controller 16 uses the sensor 16a to monitor the suction pressure and controls the blower 12 to cool the condenser. As a result, a more optimal (lowest) corresponding discharge pressure can be realized. In some examples, the optimal discharge pressure is calculated taking into account the ambient temperature, but this is not essential.

  In the low noise mode of operation, the effect of measurements taken from the low pressure portion of the system (eg, the evaporator) can be mitigated, and the operation of the blower 12 can be set to high pressure measurements to maintain a high pressure above the minimum value. Based on weakened and controlled. Using the HP measurements, the fan / blower is adjusted to maintain low noise and high pressure conditions. In general, this is selected as the lowest condensation point at the maximum evaporation pressure set point. For efficiency reasons, the “average” state is generally the highest minimum condensation temperature of the compressor, for example 30 ° C. To further reduce fan noise at the expense of increased power consumption, this value can be increased. In other words, this condition is generally the highest of the minimum condensation temperature of the compressor, for example 30 ° C., so that a pre-configured package unit capable of operating at various LP conditions can operate normally and efficiently. , Set in advance.

  The minimum condensation temperature is determined by the suction of the compressor. Usually, when reducing the condensation temperature, the compressor can operate with a lower total differential pressure to improve the coefficient of performance (COP—the ratio of cooling capacity to input power). Therefore, the required compressor input power is reduced. Such an advantageous improvement of COP cannot be achieved with standard settings that adjust the system to maintain the desired high pressure value.

  Advantageously, in the present example, low and high pressures are measured, thereby allowing operation at temperatures closer to the optimum known minimum condensation temperature. In one example, only the low pressure value is measured.

  In the plot shown in FIG. 2, the function of an example of the present invention is illustrated by a plot of high pressure values versus low pressure values. These values correspond to the condenser and evaporator temperatures, respectively. Typically, in an “economic” setting, the condenser pressure (HP setting) is adjusted to the suction pressure measurement (ie, the pressure measured at the suction point). This realizes a refrigeration plant with improved regulation function and efficiency.

  As shown in FIG. 2, each value varies most significantly at two points. Data corresponding to these two points (Point 1 and Point 2) are listed in Table 1. The HP maximum set value and the HP minimum set value may be related to a difference value larger than the required HP average value and a difference value smaller than the HP average value (selected according to these difference values). These values are defined as target pressures for points 1 and 2.

  As shown in FIG. 2, which relates to a pressure difference of 2 bar, the fan speed is within ambient temperature constraints to maintain the lowest condensation temperature so that the unit can operate in its most efficient mode. It is adjusted with.

Claims (19)

  A compressor coupled to receive and compress low pressure refrigerant from a low pressure circuit at a compressor inlet to generate high pressure refrigerant; and a condenser coupled to receive said high pressure refrigerant, wherein the condenser A condenser having at least one heat transfer surface for releasing heat from and supplying a cooled high-pressure refrigerant to the expansion valve; and a blower system for blowing cooling air onto the at least one heat transfer surface; A refrigeration plant comprising a blower control device configured to control the blower according to a pressure in the low-pressure circuit.   The refrigeration plant of claim 1, wherein the blower controller is coupled to a sensor configured to provide a variable output indicative of a pressure in the low pressure circuit.   The refrigeration plant according to claim 2, wherein the blower control device includes a processor configured to control a fan in accordance with an algorithm having the pressure as an input.   The control device according to claim 3, wherein the control device is operable to determine a discharge pressure according to the fluid pressure at the compressor inlet, and to control the blower based on the determined discharge pressure. Refrigeration plant.   The refrigeration plant according to claim 4, wherein the blower control device is operable to control the blower based on a difference between the determined discharge pressure and the measured discharge pressure.   The refrigeration plant according to any one of claims 1 to 5, wherein the blower control device is operable to control the blower according to a measured ambient temperature.   The refrigeration plant according to any one of claims 1 to 6, having a cooling capacity between 1 kW and 20 kW.   The refrigeration plant according to any one of claims 1 to 7, comprising a single compressor.   The refrigeration plant according to any one of claims 1 to 8, comprising a constant speed compressor.   A method for controlling a refrigeration plant having a compressor and a blower for cooling a condenser, measuring pressure at a compressor inlet and controlling the blower according to the measured pressure And a method comprising.   The method of claim 10, further comprising controlling the fan in response to an algorithm that takes the inlet pressure of the compressor as an input.   The method of claim 11, further comprising determining a discharge pressure in response to a fluid pressure at the compressor inlet and controlling the blower based on the determined discharge pressure.   Receiving the measured value of the discharge pressure at the outlet of the compressor and controlling the blower based on the difference between the determined discharge pressure and the measured value of the discharge pressure. The method according to 8 or 9.   14. A method according to any one of the preceding claims, comprising receiving an ambient temperature measurement and controlling the blower in response to the ambient temperature measurement.   A method of controlling a refrigeration plant substantially as herein described with reference to the accompanying drawings.   A computer program product comprising instructions capable of programing a processor to perform the method of any one of claims 10 to 15.   A processor programmed to perform the method of any one of claims 10 to 15.   A refrigerator having the refrigeration plant according to any one of claims 1 to 9 or the processor according to claim 17.   A refrigeration plant substantially as herein described with reference to the accompanying drawings.

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