CA3038013A1 - Modulated co2 refrigeration for display case - Google Patents

Description

ABSTRACT
A refrigerated display case with a cooling compartment that includes a base assembly.
The base assembly includes evaporator(s) and PWM (Pulse width modulated) valve(s) that allow for the circulation of CO2 refrigerant. Air is circulated from the cooling compartment through the evaporators. The CO2 refrigerant is supplied by a CO2 refrigeration system that includes a receiver having a liquid outlet connected to the PWM
valves, which are connected to evaporators, which are connected to the suction line leading to the compressor. Refrigerated display cases are arranged in rows on the supermarket floor. CO2 refrigerant is supplied for each row of refrigerated display case through a receiver line and connected to the PWM valve which controls the flow of CO2 refrigerant and its pressure.

The present invention pertains to a PULSE WIDTH MODULATED VALVE FOR
REFRIGERATED DISPLAY CASES USING CO2 REFRIGERANT. More particularly, the present invention relates to a method and apparatus for safely and accurately controlling the mass flow of CO2 refrigerant to the evaporators located in the refrigerated display cases.
BACKGROUND
Numerous solenoid valves and diaphragm valves are used to control refrigerant pressure reduction from the receiver to the evaporator. Such valve applications are not generally as accurate as PWM (pulse width modulated) valves. Controls on the PWM valve use longitudinal valve opening and rotary valve opening. To achieve accurate motion of the valve, a stepper motor actuator is used to rotate the valve and open or close the orifice, and a pulse width actuation is used to pull the valve metering section in and out the valve longitudinally.

The industry went from thermostatic valves to solenoid valves to activate a metering plunger that allows more or less refrigerant into the evaporators depending on its temperature. These valve systems are obsolete for large scale refrigeration such as supermarket. Systems must meet energy standards and policies that comply with ARI, ASHRAE, DOE and programs such as ENERGYSTAR and LEED.
The use of a PWM valve has numerous advantages. One of the advantages of the invention pertains to the accurate control of the metering valve element allowing the proper mass of refrigerant to enter the evaporator. Another advantage relates to the method of actuation to control the flow of refrigerant to the evaporator. The precision of the mass of refrigerant processed through the PWM valve is much more accurate than traditional solenoid valves and expansion valves.
Therefore, a PWM valve can be used to control high pressure CO2 refrigerant, reducing pressure and flow to lower parameters by means of angular and longitudinal valve positioning and releasing the refrigerant to the evaporator(s).
Such solenoid valves and diaphragm valves are presented is US patents 8596552, 10082219. Further information, concepts and patents related to refrigerated display case and CO2 refrigeration can be found in the following patents;
Prior intellectual property;
Patent No. Date Inventor 10082219 September 25, 2018 Birkelund 10194757 February 5, 2019 Re sch 9933194 April 3, 2018 Pendlebury, Hull 9377236 June 28, 2016, Christensen 8966934 March 3rd 2015, Christensen 8596552 December 3, 2013 Nicolaisen et Al

2 SUMMARY OF THE INVENTION
The invention provides a PWM valve for accurately controlling the mass flow of CO2 refrigerant entering the refrigerated display cases.
The preferred embodiment of the invention provides an ECU (electronic computer unit), a power supply, pressure and temperature sensors and the PWM valve. The ECU is set with parameters that provide optimal performance of the display case.
Such parameters include but is not limited to pressure of the refrigerant as it exits the PWM valve and temperature of the evaporator. The PWM valve interact with the supplied CO2 refrigerant to supply the proper mass of refrigerant to the evaporator(s) according to the ECU computed parameters.
The CO2 refrigerant system brings the liquid refrigerant to the supermarket floor where the display cases are installed through a series of pipes. The refrigerant lines are connected to the PWM valves located in the refrigerated display case. The PWM valve controls the mass flow of refrigerant as dictated by the ECU pulse width signal. The ECU is assisted by a temperature sensor and a pressure sensor to better compute the parameters and output the PWM signal. The PWM signal sets the PWM valve position, creating a precise opening of the metering plunger.
The refrigerant passes through the PWM valve and enters the evaporator located at the bottom of the display case. Heat is absorbed by the refrigerant through the evaporator and returns to the CO2 refrigeration system via the refrigerant suction line. The later form a cycle that is repeated until the proper temperature into the display case is reached.
The metering section of the PWM valve is controlled by the ECU through a voltage signal ranging from 0 (closed) to 24 volts (fully open) moving the metered plunger in and out of the electromagnetic coil. Such method provides very high accuracy.

3 The metering plunger is conceived to let a certain mass of CO2 refrigerant through the valve and to the evaporator.
Those well acquainted with CO2 refrigeration will appreciate the performance of such innovations and also appreciate its inherent safety for users. It is well known that CO2 systems absorbing heat can reach very high pressures and burst. The necessity of controlling temperature and pressure is essential to achieving proper refrigeration capacity. Considering the expansion capacity of CO2, a major gain of performance is reached by controlling mass. The measurement of temperature and pressure at specific locations in the display case allows the ECU to determine the exact mass of refrigerant needed to reach the necessary heat absorption through the evaporator(s).
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated by way of example in the figures of the accompanying drawings.
FIG. 1 is a schematic view of the refrigerated display case refrigeration system embodying the invention.
FIG. 2 is a schematic sectional view of the (PWM) Pulse Width Modulated valve assembly and its main components.
FIG. 3 is a typical refrigerated display case embodying the invention and its connection to evaporators, ECU and sensors.
FIG. 4, is a schematic view of the electronic control unit (ECU) with a pictorial view of its output waveform, its components and subsystems, pressure sensor (Px), temperature sensor (Tx), power supply unit (PSU).
FIG. 5, is a pictorial view of the thermodynamic process shown on the CO2 refrigerant psychrometric chart.

4 DETAILED DESCRIPTION OF THE DRAWINGS
While referring to figure 1, a schematic view of the PWM valve and apparatus is presented, describing the modulated CO2 refrigeration for refrigerated display cases. The system and apparatus presented consist of an electronic control unit (ECU) 50 that outputs a waveform 55 to the pulse width modulated valve PWM
valve 30 allowing CO2 refrigerant from receiver 10 to enter the evaporator 120 for the purpose of cooling the refrigerated display case 1. Parameters used by ECU

to calculate the variables of the output waveform 55 are measured by temperature sensor (Tx) 90, pressure sensor (Px) 80 and programmed limits 140. Power needed to operate the system and apparatus is provided by power supply unit (PSU) 110 that is powered through 120 AC connection 100. Upon absorbing the heat of refrigerated display case 1, the CO2 refrigerant contained in the evaporator enters the suction header 20 and returns to compressor room 15. The later describes the entire cycle which is repeated while maintaining pressure Px and temperature Tx within set parameters.
While referring to figure 2, a sectional view of the PWM valve 30 and its components is presented. The PWM valve 30 consist of an electromagnetic coil 31, yoke 42 attached to a metering plunger 33 and valve cylinder 34. The metering plunger 33 posses a metering valve profile 39 that allows the refrigerant from inlet 36 to be metered from 0% to 100%. In its 0% position the metering plunger 33 is push completely by spring 43 and the metering valve profile 39 is closed. In any position above 0%, the metered refrigerant exits the valve through outlet 37 and enters the evaporator 120. The metering plunger 33 has a seal 35 and internal ring 38 and external ring 44 adjusted to cylinder 34. The PWM valve is activated by an electrical waveform 55 inputted into the electromagnetic coil though connection 32. The electromagnetic coil 31 is isolated by shield 40 and sealed by cap 41.

While referring to figure 3, there is described a sectional view of the refrigerated display case 1 and one typical system and apparatus embodiment. There is displayed, the PWM valve 30 installed in the base assembly 2 which is connected in a configuration of two evaporators 120. There is shown, ECU 50 and connections to pressure sensor (Px) 80 and temperature sensor (Tx) 90. The ECU 50 can communicate through wifi and RFID using antenna 60.
While referring to figure 4, there is described a schematic view of the ECU 50 system and apparatus with output waveform 55 details. The ECU 50 receives measured data from pressure sensor (Px) 80 and temperature sensor (Tx) 90 to compute output waveform 55. The ECU 50 is powered by power supply unit (PSU) 110. The power supply unit (PSU)110 outputs 0-5 volts dc, 0-12 volts dc at 1A.

Typical Electronic Control Units similar to described ECU 50 and its application are found from OEM (original equipment manufacturers) like Texas Instruments (Dallas, Tx) and National Semiconductors (Santa Clara, Ca). Newly developed prototyping products by Arduino provide ECUs capable of providing the described output waveform 55. OEM software is provided that can easily be adapted to provide control of the limits 140 set by the pressure-temperature envelope 143. OEM software 51 can be accessed via wifi antenna 60 provided onboard. All data measured and computed by ECU 50 is stored for access via wifi antenna 60. Data on ECU 50 is kept for limited time but can be transmitted to larger computer platforms such as store management systems. Numerous operations can be performed remotely from store management systems by accessing ECU 50 of each refrigerated display case 1 to set or modify limits of pressure-temperature envelope 143.

Still referring to figure 4, There is described the parameters of output waveform 55. The ECU 50 calculates the output waveform 55 based on continuous measurements of pressure and temperature. The output waveform 55 contains three parameters that form the envelope of the waveform, which are;
a Pulse width 0-100 milliseconds Duty cycle 0-100%
Amplitude 0-12 volts dc The pulse width a 57 determines the amount of time the voltage amplitude c 58 is applied to the electromagnetic coil 31 in a full cycle. The duty cycle b 56 determines the level of energy that is applied to the electromagnetic coil 31. When duty cycle b 56 becomes 0%, the metering plunger 33 is released completely to shut metering valve profile 39. The ECU 50 computes duty cycle b56 consisting of dividing a57/b56 and stores the latest data. Limits 140 are programmable into the ECU

to adapt the system and apparatus to various refrigerated display case 1 configurations.
A multitude of parameters and limits can be set to satisfy different types of refrigerated display case. Typically, refrigerated display case are found for dairy products, meat and frozen foods. The refrigeration needs for each display case is different and set to maintain the quality of food products. Thus, while referring to figure 5, a psychrometric chart 140 of r-744 (CO2) refrigerant shows the typical pressure-temperature envelope 143 of the refrigeration cycle which can be set through the ECU 50 to control the action of the PWM valve 30. A typical envelope of pressure-temperature point P1,T1 141 is the lower limit and the point P2,T2 is the higher limit. Higher range pressure-temperature envelopes are feasible as that indicated by envelope 145.

The values of parameters shown by figure 5 pressure-temperature envelope 143 are exemplary;
P1 15 bar ti -30C
P2 35 bar t2 0 C
It must be noted that as temperature of CO2 refrigerants approach -70C the risk of phase change increases which may cause damage to the systems. Solid CO2 occurs at temperature of -78.5 C and pressure of 1 bar.