Systems and methods for controlling refrigerant concentration

Abstract

A refrigeration control system includes: a refrigerant including a blend of a first refrigerant and a second refrigerant; an accumulator; a compressor that receives the refrigerant from the accumulator and compresses the refrigerant; a first heat exchanger disposed downstream of the compressor; a receiver disposed downstream of the first heat exchanger; a first valve disposed between a liquid-to-suction heat exchanger and the receiver; a second valve disposed between the receiver and a second heat exchanger, wherein the second heat exchanger receives the refrigerant from the second valve and at least partially vaporizes the refrigerant and outputs the at least partially vaporized refrigerant to the liquid-to-suction heat exchanger; and a control module configured to selectively adjust a speed of the compressor based on adjusting (a) a temperature of air output from the second heat exchanger and into a space toward (b) a setpoint temperature within the space.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional of U.S. application Ser. No. 19 / 079,420 filed Mar. 13, 2025, titled “Systems And Methods For Controlling Refrigerant Concentration,” the entirety of which is incorporated herein by reference.FIELD

[0002] The field of the present disclosure relates to climate control systems for use with working fluids having refrigerant blends exhibiting high glide and methods for operating the same, and more specifically to systems and methods for controlling refrigerant concentration.BACKGROUND

[0003] The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0004] A thermodynamic climate control system such as, a heat-pump system, a refrigeration system, or an air conditioning system may include a fluid circuit having a first heat exchanger (e.g., a condenser that facilitates a phase change of refrigerant from gas / vapor to a liquid) that is typically located outdoors, a second heat exchanger (e.g., an evaporator that facilitates a phase change of refrigerant from liquid to gas / vapor) that is typically located indoors or within the environment to be cooled, a receiver that operates to store liquid refrigerant between the first and second heat exchangers, an accumulator that operates to store liquid phase refrigerant upstream of the second heat exchangers, a liquid pump disposed between the first and second heat exchangers, expansion devices disposed between the first heat exchanger and the receiver and between the receiver and the second heat exchanger, and a compressor disposed between the first and second heat exchangers that operates to pressurize gas / vapor phase refrigerant.

[0005] These types of systems can be fixed, such as at a building or residence, or can be mobile, such as in, or as part of a vehicle. For example, vehicles include land based vehicles (e.g., trucks, cars, trains, etc.), water based vehicles (e.g., boats, sea containers), air based vehicles (e.g., airplanes), and vehicles that operate over a combination of more than one of land, water, and air.

[0006] There is growing pressure to adopt refrigerants with lower global warming potential (GWP) due to environmental concerns. Traditional synthetic refrigerants are being reconsidered in favor of natural refrigerants, which can offer a more eco-friendly alternative. The shift towards these natural refrigerants introduces new challenges which include device applicability, environmental acceptability and safety. While natural refrigerants present a promising solution to reduce environmental impact, their adoption requires careful management of these associated challenges.

[0007] Synthetic refrigerants may be replaced by natural refrigerants in some climate control applications. Lower global warming potential refrigerants may be used.

[0008] Several refrigerants have been developed that are considered low global warming potential options, and they have an ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) classification as A2 (relatively lower flammability than A3 refrigerants), A2L (mildly flammable / lower flammable than A2 and A3 refrigerants and lower toxicity), or A1 (no flame propagation / lower toxicity levels). Examples of an A2 refrigerant include 1,1-difluorethane (R-152A—as used herein, the refrigerants may be interchangeably described by the conventional nomenclature of “R” for refrigerants or their specific chemical class code, like HFC-152A) with a global warming potential of about 124, while examples of A2L refrigerants include difluoromethane (CH2F2 or R-32—as used herein, the refrigerants may be interchangeably described by the conventional nomenclature of “R” for refrigerants or their specific chemical class code, like HFC-32) with a global warming potential of about 677, and hydrofluorolefins (HFOs), like 2,3,3,3,-tetrafluoroprop-1-ene (HFO-1234yf or R-1234yf), trans-1,3,3,3,-tetrafluoroprop-1-ene (HFO-1234ze or R-1234ze). A1 refrigerants include carbon dioxide (CO2 or R-744), which has a desirably low global warming potential of 1,1-chloro-3,3,3-trifluoropropene (cis- and trans-HFO-1233zd(Z) or R-1233zd (Z) and HCFO-1233zd(E) or R-1233zd (E)), chlorodifluoromethane (R-22 or CHClF2), R-410A that is a near-azeotropic mixture of difluoromethane (HFC-32) and pentafluoroethane (HFC-125), and other hydrocarbon refrigerants, such as hexane, heptane, octane, nonane, and decane.

[0009] It would be desirable to employ climate control systems that can successfully employ such environmentally friendly refrigerants with low global warming potential.SUMMARY

[0010] In a feature, a refrigeration control system includes: a refrigerant including a blend of a first refrigerant and a second refrigerant; an accumulator; a compressor that receives the refrigerant from the accumulator and compresses the refrigerant; a first heat exchanger disposed downstream of the compressor; a receiver disposed downstream of the first heat exchanger; a first valve disposed between a liquid-to-suction heat exchanger and the receiver; a second valve disposed between the receiver and a second heat exchanger, wherein the second heat exchanger receives the refrigerant from the second valve and at least partially vaporizes the refrigerant and outputs the at least partially vaporized refrigerant to the liquid-to-suction heat exchanger; and a control module configured to selectively adjust a speed of the compressor based on adjusting (a) a temperature of air output from the second heat exchanger and into a space toward (b) a setpoint temperature within the space.

[0011] In further features, the control module is configured to adjust the speed of the compressor only every predetermined compressor period.

[0012] In further features, the control module is configured to: determine a speed adjustment based on a difference between (a) the temperature of the air output from the second heat exchanger and (b) the setpoint temperature; and adjust the speed of the compressor based on the speed adjustment.

[0013] In further features, the control module is configured to one of (a) increase the speed of the compressor by the speed adjustment and (b) decrease the speed of the compressor by the speed adjustment.

[0014] In further features, the control module is further configured to selectively adjust an opening of the first valve based on adjusting (a) a temperature of refrigerant output from the first heat exchanger toward (b) an outlet setpoint temperature for the refrigerant output from the first heat exchanger.

[0015] In further features, the control module is configured to determine the outlet setpoint temperature based on a subcooling target.

[0016] In further features, the control module is configured to adjust the opening of the first valve only every predetermined first valve period.

[0017] In further features, the control module is configured to: determine a first valve adjustment based on a difference between (a) the temperature of refrigerant output from the first heat exchanger and (b) the outlet setpoint temperature for the refrigerant output from the first heat exchanger; and adjust the opening of the first valve based on the first valve adjustment.

[0018] In further features, the control module is configured to determine the outlet setpoint temperature based on an ambient air temperature.

[0019] In further features, the control module is further configured to selectively adjust an opening of the second valve based on adjusting (a) a concentration of the refrigerant toward (b) a target concentration.

[0020] In further features, the control module is configured to determine the target concentration based on an ambient air temperature.

[0021] In further features, the control module is configured to adjust the opening of the second valve only every predetermined second valve period.

[0022] In further features, the control module is configured to: determine a second valve adjustment based on a difference between (a) the concentration of the refrigerant and (b) the target concentration; and adjust the opening of the second valve based on the second valve adjustment.

[0023] In further features, the control module is further configured to selectively adjust an opening of the first valve based on adjusting (a) a temperature of refrigerant output from the first heat exchanger toward (b) an outlet setpoint temperature for the refrigerant output from the first heat exchanger.

[0024] In further features, the concentration is a mass concentration of a component of the blend.

[0025] In further features, the first refrigerant is carbon dioxide (CO2) and the second refrigerant is R1233zde refrigerant.

[0026] In further features, the accumulator includes both liquid form refrigerant and vapor form refrigerant.

[0027] In further features, the compressor receives vapor form refrigerant from the accumulator.

[0028] In further features, the receiver includes both liquid form refrigerant and vapor form refrigerant.

[0029] In a feature, a refrigeration control method includes: circulating a refrigerant including a blend of a first refrigerant and a second refrigerant in a refrigeration system, the refrigeration system including: an accumulator; a compressor that receives the refrigerant from the accumulator and compresses the refrigerant; a first heat exchanger disposed downstream of the compressor; a receiver disposed downstream of the first heat exchanger; a first valve disposed between a liquid-to-suction heat exchanger and the receiver; a second valve disposed between the receiver and a second heat exchanger, wherein the second heat exchanger receives the refrigerant from the second valve and at least partially vaporizes the refrigerant and outputs the at least partially vaporized refrigerant to the liquid-to-suction heat exchanger; and selectively adjusting a speed of the compressor based on adjusting (a) a temperature of air output from the second heat exchanger and into a space toward (b) a setpoint temperature within the space.

[0030] In a feature, a refrigeration control system includes: a refrigerant including a blend of a first refrigerant and a second refrigerant; an accumulator; a compressor that receives the refrigerant from the accumulator and compresses the refrigerant; a first heat exchanger disposed downstream of the compressor; a receiver disposed downstream of the first heat exchanger; a first valve disposed between a liquid-to-suction heat exchanger and the receiver; a second valve disposed between the receiver and a second heat exchanger, wherein the second heat exchanger receives the refrigerant from the second valve and at least partially vaporizes the refrigerant and outputs the at least partially vaporized refrigerant to the liquid-to-suction heat exchanger; and a control module configured to: selectively operate the compressor at a fixed speed; and selectively adjust an opening of the second valve based on (a) a concentration of the refrigerant at a point in the refrigeration control system and (b) a concentration setpoint.

[0031] In further features, the control module is further configured to turn off the compressor when the concentration is greater than an upper limit of a predetermined range around the concentration setpoint.

[0032] In further features, the control module is further configured to turn on the compressor when the concentration is less than a lower limit of a predetermined range around the concentration setpoint.

[0033] In further features, the control module is configured to set the concentration setpoint based on an ambient temperature.

[0034] In further features, the control module is configured to determine the concentration setpoint using an equation that relates ambient temperatures to concentration setpoints.

[0035] In further features, the control module is configured to determine the concentration setpoint using a lookup table that relates ambient temperatures to concentration setpoints.

[0036] In further features, the control module is configured to determine the concentration based on at least one of (a) a temperature of the refrigerant and (b) a pressure of the refrigerant.

[0037] In further features, the control module is configured to determine the concentration based on a differential pressure of the receiver.

[0038] In further features, the control module is configured to decrease the opening of the second valve by a predetermined amount when (a) the concentration of the refrigerant at the point in the refrigeration control system is less than (b) the concentration setpoint.

[0039] In further features, the control module is configured to decrease the opening of the second valve by the predetermined amount when (a) the concentration of the refrigerant at the point in the refrigeration control system is less than (b) the concentration setpoint and greater than a lower limit of a range around the concentration setpoint.

[0040] In further features, the control module is configured to increase the opening of the second valve by a predetermined amount when (a) the concentration of the refrigerant at the point in the refrigeration control system is greater than (b) the concentration setpoint.

[0041] In further features, the control module is configured to close the opening of the second valve by the predetermined amount when (a) the concentration of the refrigerant at the point in the refrigeration control system is less than (b) the concentration setpoint and greater than a lower limit of a range around the concentration setpoint.

[0042] In further features, the concentration is a mass concentration a component of the blend.

[0043] In further features, the first refrigerant is carbon dioxide (CO2) and the second refrigerant is R1233zde refrigerant.

[0044] In further features, the accumulator includes both liquid form refrigerant and vapor form refrigerant.

[0045] In further features, the compressor receives vapor form refrigerant from the accumulator.

[0046] In further features, the receiver includes both liquid form refrigerant and vapor form refrigerant.

[0047] In further features, the control module is further configured to selectively adjust an opening of the first valve.

[0048] In further features, the control module is configured to selectively adjust the opening of the first valve based on adjusting (a) a temperature of refrigerant output from the first heat exchanger toward (b) an outlet setpoint temperature for the refrigerant output from the first heat exchanger.

[0049] In a feature, a refrigeration control method includes: circulating a refrigerant including a blend of a first refrigerant and a second refrigerant in a refrigeration system, the refrigeration system including: an accumulator; a compressor that receives the refrigerant from the accumulator and compresses the refrigerant; a first heat exchanger disposed downstream of the compressor; a receiver disposed downstream of the first heat exchanger; a first valve disposed between a liquid-to-suction heat exchanger and the receiver; a second valve disposed between the receiver and a second heat exchanger, wherein the second heat exchanger receives the refrigerant from the second valve and at least partially vaporizes the refrigerant and outputs the at least partially vaporized refrigerant to the liquid-to-suction heat exchanger; selectively operating the compressor at a fixed speed; and selectively adjusting an opening of the second valve based on (a) a concentration of the refrigerant at a point in the refrigeration control system and (b) a concentration setpoint.

[0050] Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0052] FIG. 1 is a functional block diagram of an example refrigeration system;

[0053] FIG. 2 is a functional block diagram of an example control system;

[0054] FIG. 3 is a flowchart depicting an example method of controlling refrigerant concentration and capacity of the refrigeration system;

[0055] FIG. 4 includes a graph of example concentration setpoints as a function of temperature; and

[0056] FIG. 5 is a flowchart depicting an example method of controlling refrigerant concentration and capacity of the refrigeration system.

[0057] In the drawings, reference numbers may be reused to identify similar and / or identical elements.DETAILED DESCRIPTION

[0058] FIG. 1 is a functional block diagram of an example of a refrigeration system. Refrigeration system as used herein includes systems that cool a (temperature conditioned) space 104, such as a refrigeration system, a heat pump system, a chiller system, a freezer system, a heating ventilation and air conditioning (HVAC) system, and other types of systems. Some refrigeration systems may also be configured to heat the space, such as by reversing operation of the condenser and evaporator.

[0059] A refrigerant is circulated in the refrigeration system, and the refrigerant includes a blend of a first refrigerant (A) and a second refrigerant (B) that together exhibit glide. The blended refrigerant may include, for example, carbon dioxide (CO2) and R1233zde refrigerant. The capacity of the refrigeration system may be adjusted by changing relative proportions of the first refrigerant (A) and the second refrigerant (B) at different locations in the system. A control module 108 may control relative proportions of the first refrigerant (A) and the second refrigerant (B) as discussed further below to adjust capacity and increase efficiency.

[0060] As discussed above, two or more refrigerants may be present, but for simplicity, two refrigerants are used in this example. The difference in boiling points between the first refrigerant (A) and the second refrigerant (B) may be greater than or equal to approximately 25° R at atmospheric pressure. The refrigerant may also include lubricating oil(s) at certain locations in the system. Refrigerant as used herein may encompass liquid, gas, and any combination thereof, including vapor (e.g., a gas phase having aerosolized liquid droplets). The term gas or gas phase as used herein may encompass both vapor and pure gas phases.

[0061] The refrigeration system has a fluid flow path within a series of fluid conduits (e.g., 112) that establishes fluid communication between the various components, so that the refrigerant circulates in a loop. As shown in FIG. 1, the refrigeration system includes an evaporator 116 (a heat exchanger). While one evaporator 116 is shown, two or more evaporators may be connected in parallel, for example, such that refrigerant flows into each evaporator are approximately equal. In the example of multiple evaporators, one or more valves may be implemented to allow / block refrigerant flow to / from specific evaporators.

[0062] The first refrigerant (A) and / or the second refrigerant (B) transform from a liquid phase to a gas or vapor phase within the evaporator 116 as it exchanges heat with air passing through the evaporator 116 to thereby cool air entering the space 104. One or more blowers, such as blower 204, blow the air through the evaporator 116 and into the space 104. Multiple blowers may be used in the example of multiple evaporators, such as one blower per evaporator.

[0063] Refrigerant output from the evaporator 116 flows through a first flow path within heat exchanger 124, which may be referred to as a liquid to suction heat exchanger (liq-suc-htx), where heat is exchanged with a refrigerant output from a condenser 128 that is flowing through a second flow path within heat exchanger 124.

[0064] Refrigerant output from the first flow path within heat exchanger 124 flows to an accumulator 132. Within the accumulator 132, refrigerant in both liquid and vapor phases may be present, with the liquid refrigerant settling vertically lower than the refrigerant vapor. As shown in FIG. 1, the concentration of liquid refrigerant in the accumulator 132 is represented by c2l, while the concentration of vapor refrigerant in the accumulator 132 is represented by c2v. The concentration as discussed herein may refer to a mass concentration of the high critical temperature component of the refrigerant blend (e.g., R1233zd in the example discussed herein), as a percentage.

[0065] Refrigerant vapor is drawn from the accumulator 132 by a compressor 136, which compresses the refrigerant and outputs compressed refrigerant to the condenser 128. While the example of one compressor and one condenser is shown, the present application is also applicable to multiple compressors and / or multiple condensers. The condenser 128 transfers heat from refrigerant flowing through the condenser 128 to air. A fan or blower 208 may blow air through the condenser 128. In the example of multiple condensers, one fan or blower may be provided per condenser. In the example of two or more condensers, the condensers may be connected in parallel, for example, such that refrigerant flow into each condenser is approximately equal. In the example of multiple condensers, one or more valves may be implemented to allow / block refrigerant flow to / from specific condensers. As discussed above, refrigerant output from the condenser flows through the second flow path within heat exchanger 124. A first valve (e.g., a control valve, CV1) 140 controls refrigerant flow from the second flow path of the heat exchanger 124 to a receiver 144. Flow rate may be controlled by the amount that the first valve 140 is open (e.g., the flow rate increases when the amount the valve is open increases and the flow rate decreases when the amount the valve is open decreases).

[0066] Within the receiver 144, refrigerant in both liquid and vapor phases may be present, with the liquid refrigerant may settling vertically lower than the refrigerant vapor. The concentration of liquid refrigerant (in this case the higher critical temperature refrigerant) in the receiver 144 is represented by c1l, while the concentration of vapor refrigerant in the receiver 144 is represented by c1v (in this case the higher critical temperature refrigerant).

[0067] A second valve (e.g., an expansion valve EXV1) 148 controls refrigerant (e.g., liquid) flow from the receiver 144 to the evaporator 116. Flow rate may be controlled by the amount that the second valve 148 is open (e.g., the flow rate increases when the amount the valve is open increases and the flow rate decreases when the amount the valve is open decreases).

[0068] A thermostat 152 or another suitable type of temperature sensor measures a temperature of air within the conditioned space 104. A control module 108 controls operation of the compressor 136 (e.g., ON / OFF and speed), opening and closing of the first valve 140, and opening and closing of the second valve 148. The control module 108 also controls operation of the fans / blowers of the evaporator 116 and the condenser 128. For example, the control module 108 may open the first and second valves 140 and 148, operate the compressor 136, and operate the fans and / or blowers when the temperature within the conditioned space 104 is greater than a setpoint temperature to cool the conditioned space 104. During cooling, the control module 108 may control operation of the compressor 136 and / or actuate the first and second valves 140 and 148 as discussed further below to adjust refrigerant concentration and capacity of the refrigeration system. In various implementations, while not shown, the system may also include one or more other sensors, such as flow rate sensors, pressure sensors, or temperature sensors.

[0069] DP1 is a differential pressure sensor in the example of FIG. 1 and may be omitted. A correlation between refrigerant temperature, and concentration can be used to determine liquid level in the receiver 144. Opening and closing of the first valve 140 is used to control the temperature of the liquid refrigerant leaving the receiver 144. By varying the temperature of the liquid refrigerant leaving the receiver, the critical point of the refrigerant can be changed, which thereby changes the concentration of the blend. This can be used to optimize performance as the ambient temperature changes. By decreasing the receiver pressure, for a given temperature, the concentration of both the liquid and vapor phase concentration will increase because more liquid will be driven to the receiver which in turn increases concentration of the high critical temperature refrigerant circulating in the system.

[0070] As the ambient temperature increases, R1233zd concentration should increase for improving performance. Adjusting the first valve 140 may involve a slow response rate. This prevents too much hunting as the first and second valves 140 and 148 may be trying to react to each other's changes.

[0071] The second valve 148 may be used to control the receiver liquid level. The differential pressure may be used as an input to control the second valve 148. As the receiver liquid level rises, the control module 108 may open the second valve 148 more. As the receiver liquid level lowers, the control module 108 may close the second valve 148 more. Receiver level may be maintained by the control module 108 adjusting the first valve 140 to maintain a constant liquid level. The level may be controlled between 5% and 99% to avoid vapor entrenchment and to ensure the receiver remains at a saturated state. This will enable the control of the temperature of the refrigerant leaving the receiver to control the concentration of refrigerant. In various implementations, the pressure in the receiver 144 may be measured to use correlations between pressure and temperature to calculate the concentration in circulation directly.

[0072] FIG. 2 is a functional block diagram of an example control system. The blower 204 for the evaporator 116, and the fan 208 for the condenser 128 are discussed above. An air control module 212 controls operation of the blower 204 and the fan 208. For example, the air control module 212 turns on the blower 204 and the fan 208 during cooling of the conditioned space 104.

[0073] A compressor control module 216 controls operation of the compressor 136. The compressor 136 may be a fixed speed compressor (e.g., FIGS. 3-4) or a variable speed compressor (e.g., FIG. 5). The compressor control module 216 may control a speed of the compressor 136 by controlling power applied to the compressor 136, such as by controlling pulse width modulation (PWM) signals applied to the compressor 136.

[0074] A valve control module 220 controls opening of the first and second valves 140 and 148. A concentration determination module 224 determines a concentration of the refrigerant at a point in the system (e.g., input to the evaporator 116 or in the receiver 144). The concentration determination module 224 may determine the concentration based on one or more temperatures of the refrigerant (e.g., at that point) and / or one or more pressures of the refrigerant (e.g., at that point). The concentration determination module 224 determines the concentration using one or more lookup tables and / or equations that relate temperature and / or pressure to refrigerant concentration.

[0075] A setpoint module 228 determines a setpoint for the concentration at the point (concentration setpoint) based on a temperature, such as an outdoor ambient temperature (OAT). The OAT may be measured by a temperature sensor, such as at a condenser unit outside of the conditioned space (e.g., outside of a building). The condenser unit includes the condenser 128 and the compressor 136. The setpoint module 228 may determine the setpoint using a lookup table or an equation that relates temperature to concentration setpoint. FIG. 4 includes a graph of example concentration setpoints as a function of temperature.

[0076] Control of the first and second valves 140 and 148 and the compressor 136 to the concentration and thereby control capacity of the refrigeration system is discussed further below. Increasing compressor speed and / or number of compressors on will lower the concentration of refrigerant input to the evaporator 116. This, however, is a relatively coarse adjustment. Controlling opening of the first and / or second valves 140 and 148 provides a relatively fine adjustment relative to the compressor control.

[0077] FIG. 3 is a flowchart depicting an example method of controlling refrigerant concentration and capacity of the refrigeration system, such as where the compressor 136 is a fixed speed compressor. Control begins with 304 where one or more of the modules of the control module 108 determine whether cooling of the conditioned space 104 is being performed. Cooling may be performed, for example, when the temperature within the conditioned space 104 (space temperature) is greater than a setpoint temperature for the air within the conditioned space 104. The setpoint temperature may be adjusted, for example, via the thermostat 152.

[0078] If 304 is true, control may continue with 308. If 304 is false, control may remain at 304. In various implementations, 304 may be omitted.

[0079] At 308, the concentration determination module 224 determines the concentration of the refrigerant. The setpoint module 228 determines the concentration setpoint based on the ambient temperature. For example, FIG. 4 includes an example graph of refrigerant (R1233zd) concentration setpoint as a function of ambient temperature (e.g., OAT). As an example, the setpoint module 228 may determine the concentration setpoint using a lookup table or equation generated based on the trace (solid line) of concentration setpoint of FIG. 4. The concentration determination module 224 may determine the concentration at two or more different times and set the concentration to be used at 308 based on an average of the two or more different concentrations from the two or more times.

[0080] At 312, the compressor control module 216 may determine whether the concentration determined is greater than an upper limit of a predetermined range around the concentration setpoint. An example of the predetermined range is illustrated by concentration deadband in FIG. 4. The predetermined range is defined by the upper limit (concentration) that is greater than the concentration setpoint and a lower limit that is lower than the concentration setpoint. The upper and lower limits are illustrated by dashed lines in FIG. 4. If 312 is true, the compressor control module 216 may turn off a compressor (e.g., the compressor 136) at 316, and control may return to 304. Turning off a compressor decreases the concentration toward the concentration setpoint. This may provide a relatively coarse adjustment of the concentration to adjust the concentration toward the concentration setpoint. If 312 is false, control may continue to 320.

[0081] At 320, the compressor control module 216 may determine whether the concentration determined is greater than the lower limit of the predetermined range around the concentration setpoint. If 320 is true, the compressor control module 216 may turn on a compressor (e.g., the compressor 136) at 324, and control may return to 304. Turning on a compressor increases the concentration toward the concentration setpoint. Turning on a compressor provides a relatively larger concentration adjustment than opening the second valve 148. If 320 is false, control may continue with 328. The compressor control module 216 may turn on and operate the compressor at a predetermined fixed speed. The compressor control module 216 may record the present time each time operation of a compressor is adjusted.

[0082] At 328, the concentration is within the predetermined range, and the valve control module 220 may determine whether the concentration determined is less than the concentration setpoint. If 328 is true, the valve control module 220 may open the second valve 148 by a first predetermined amount (e.g., percentage open) at 332. This increases the concentration toward the concentration setpoint, but by a lesser amount than the turning on of a compressor. If 328 is false, control may continue with 336.

[0083] At 336, the valve control module 220 may determine whether the concentration determined is greater than the concentration setpoint. If 336 is true, the valve control module 220 may close the second valve 148 by a second predetermined amount (e.g., percentage open) at 340. The second predetermined amount may be less than, equal to, or greater than the first predetermined amount. This decreases the concentration toward the concentration setpoint, but by a lesser amount than the turning off of a compressor. If 336 is false, control may return to 304. The valve control module 220 may record the present time each time the opening of the first control valve 140 is adjusted. The valve control module 220 may record the present time each time the opening of the second control valve 148 is adjusted.

[0084] FIG. 5 is a flowchart depicting an example method of controlling refrigerant concentration and capacity of the refrigeration system, such as where the compressor 136 is a variable speed compressor. Control begins with 504 where one or more of the modules of the control module 108 determine whether cooling of the conditioned space 104 is being performed. Cooling may be performed, for example, when the temperature within the conditioned space 104 (space temperature) is greater than a setpoint temperature for the air within the conditioned space 104. If 504 is true, control may continue with 508. If 504 is false, control may remain at 504.

[0085] At 508, the valve control module 220 may determine whether the period since the last time when the opening of the first valve 140 was determined and set (e.g., last instance of 508-512) is greater than a predetermined first valve period. The predetermined first valve period is greater than zero and may be, for example, approximately 1 second or another suitable period. If 508 is false, the valve control module 220 maintains the present opening of the first valve 140 at 516, and control continues with 520. If 508 is true, control continues with 512.

[0086] At 512, the valve control module 220 may determine an adjustment for the opening of the first valve 140 based on adjusting a temperature of the refrigerant at an output of the condenser (condenser output temperature) toward or to a target saturated condenser liquid (refrigerant) temperature. The valve control module 220 may determine the target saturated condenser liquid temperature, for example, based on a predetermined subcooling target for the refrigeration system, such as using one of an equation and a lookup table that relates subcooling targets to target saturated condenser liquid temperatures.

[0087] In various implementations, the valve control module 220 may instead determine the adjustment based on adjusting the condenser output temperature toward or to a target temperature set based on the outdoor ambient temperature. The valve control module 220 may determine the target temperature, for example, using one of an equation and a lookup table that relates OATs to target temperatures.

[0088] The valve control module 220 may determine the adjustment, for example, using proportional control, proportional integral control, proportional integral derivative control, fuzzy logic, or another suitable type of closed loop control based on a difference between the inputs (e.g., condenser output temperature and target temperature). The valve control module 220 may set a target opening of the first valve 140 based on the present opening of the first valve 140 and the adjustment, such as the present opening plus the adjustment. The valve control module 220 actuates the first valve 140 to the target opening at 512, and control continues with 520.

[0089] At 520, the valve control module 220 may determine whether the period since the last time when the opening of the second valve 140 was determined and set (e.g., last instance of 520-524) is greater than a predetermined second valve period. The predetermined second valve period is greater than zero and may be, for example, approximately 1 second or another suitable period. The predetermined first valve period may be the same as or different than the predetermined second valve period. If 520 is false, the valve control module 220 maintains the present opening of the second valve 148 at 528, and control continues with 532. If 520 is true, control continues with 524.

[0090] At 524, the valve control module 220 may determine an adjustment for the opening of the second valve 148 based on adjusting the concentration toward or to a target concentration. The valve control module 220 may determine the adjustment using one of an equation and a lookup table that relates differences between concentration and target concentration to adjustment.

[0091] In various implementations, the valve control module 220 may instead determine the adjustment based on adjusting a temperature of refrigerant input to the accumulator 132 toward or to a target temperature, such as set based on the OAT. The valve control module 220 may determine the target temperature, for example, using one of an equation and a lookup table that relates OATs to target temperatures.

[0092] The valve control module 220 may determine the adjustment, for example, using proportional control, proportional integral control, proportional integral derivative control, fuzzy logic, or another suitable type of closed loop control based on a difference between the inputs. The valve control module 220 may set a target opening of the second valve 148 based on the present opening of the second valve 148 and the adjustment, such as the present opening plus the adjustment. The valve control module 220 actuates the second valve 148 to the target opening at 524, and control continues with 532.

[0093] At 532, the compressor control module 216 may determine whether the period since the last time when the speed of the compressor 136 was determined and set (e.g., last instance of 532-536) is greater than a predetermined compressor period. The predetermined compressor period is greater than zero and may be, for example, approximately 1 second or another suitable period. The predetermined compressor period may be the same as or different than the predetermined second valve period, and the predetermined compressor period may be the same as or different than the predetermined first valve period. If 532 is false, the compressor control module 216 maintains the present speed of the compressor 136 at 540, and control returns to 504. If 532 is true, control continues with 536.

[0094] At 536, the compressor control module 216 may determine an adjustment for the compressor speed based on adjusting the temperature of air output from the evaporator 116 into the conditioned space 104 toward or to the temperature setpoint within the conditioned space 104. The compressor control module 216 may determine the adjustment using one of an equation and a lookup table that relates differences between temperature and temperature setpoint to adjustment.

[0095] The compressor control module 216 may determine the adjustment, for example, using proportional control, proportional integral control, proportional integral derivative control, fuzzy logic, or another suitable type of closed loop control based on the difference. The compressor control module 216 may set a target speed of the compressor 136 based on the present speed of the compressor 136 and the adjustment, such as the present speed plus the adjustment. The compressor control module 216 adjusts the speed of the compressor 136 to the target speed at 536, and control continues with 504.

[0096] The above adjusts the concentration and therefore the capacity of the refrigeration system.

[0097] The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and / or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.

[0098] Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,”“engaged,”“coupled,”“adjacent,”“next to,”“on top of,”“above,”“below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

[0099] In the figures, the direction of an arrow, as indicated by the arrowhead, generally demonstrates the flow of information (such as data or instructions) that is of interest to the illustration. For example, when element A and element B exchange a variety of information but information transmitted from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B may send requests for, or receipt acknowledgements of, the information to element A.

[0100] In this application, including the definitions below, the term “module” or the term “controller” may be replaced with the term “circuit.” The term “module” may refer to, be part of, or include: an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog / digital discrete circuit; a digital, analog, or mixed analog / digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.

[0101] The module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces that are connected to a local area network (LAN), the Internet, a wide area network (WAN), or combinations thereof. The functionality of any given module of the present disclosure may be distributed among multiple modules that are connected via interface circuits. For example, multiple modules may allow load balancing. In a further example, a server (also known as remote, or cloud) module may accomplish some functionality on behalf of a client module.

[0102] The term code, as used above, may include software, firmware, and / or microcode, and may refer to programs, routines, functions, classes, data structures, and / or objects. The term shared processor circuit encompasses a single processor circuit that executes some or all code from multiple modules. The term group processor circuit encompasses a processor circuit that, in combination with additional processor circuits, executes some or all code from one or more modules. References to multiple processor circuits encompass multiple processor circuits on discrete dies, multiple processor circuits on a single die, multiple cores of a single processor circuit, multiple threads of a single processor circuit, or a combination of the above. The term shared memory circuit encompasses a single memory circuit that stores some or all code from multiple modules. The term group memory circuit encompasses a memory circuit that, in combination with additional memories, stores some or all code from one or more modules.

[0103] The term memory circuit is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory, tangible computer-readable medium are nonvolatile memory circuits (such as a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), volatile memory circuits (such as a static random access memory circuit or a dynamic random access memory circuit), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc).

[0104] The apparatuses and methods described in this application may be partially or fully implemented by a special purpose computer created by configuring a general purpose computer to execute one or more particular functions embodied in computer programs. The functional blocks, flowchart components, and other elements described above serve as software specifications, which can be translated into the computer programs by the routine work of a skilled technician or programmer.

[0105] The computer programs include processor-executable instructions that are stored on at least one non-transitory, tangible computer-readable medium. The computer programs may also include or rely on stored data. The computer programs may encompass a basic input / output system (BIOS) that interacts with hardware of the special purpose computer, device drivers that interact with particular devices of the special purpose computer, one or more operating systems, user applications, background services, background applications, etc.

[0106] The computer programs may include: (i) descriptive text to be parsed, such as HTML (hypertext markup language), XML (extensible markup language), or JSON (JavaScript Object Notation) (ii) assembly code, (iii) object code generated from source code by a compiler, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. As examples only, source code may be written using syntax from languages including C, C++, C#, Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5 (Hypertext Markup Language 5th revision), Ada, ASP (Active Server Pages), PHP (PHP: Hypertext Preprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, MATLAB, SIMULINK, and Python®.

Claims

1. In a system for compressing a blended refrigerant from a first refrigerant and a second refrigerant, a compressor that receives and compresses the blended refrigerant from an accumulator and discharges the blended refrigerant to a first heat exchanger and a receiver disposed downstream of the compressor, a first valve between the first heat exchanger and the receiver, a second heat exchanger that at least partially vaporizes and outputs the blended refrigerant to a liquid-to-suction heat exchanger, and a second valve positioned between the receiver and the second heat exchanger, a refrigeration control system comprising a control module configured to selectively operate the compressor at a fixed speed and selectively adjust an opening of the second valve based on (a) a concentration of the blended refrigerant at a point in the refrigeration control system and (b) a concentration setpoint.

2. The refrigeration control system of claim 1 wherein the control module is further configured to turn off the compressor when the concentration is greater than an upper limit of a predetermined range around the concentration setpoint.

3. The refrigeration control system of claim 1 wherein the control module is further configured to turn on the compressor when the concentration is less than a lower limit of a predetermined range around the concentration setpoint.

4. The refrigeration control system of claim 1 wherein the control module is configured to set the concentration setpoint based on an ambient temperature.

5. The refrigeration control system of claim 4 wherein the control module is configured to determine the concentration setpoint using an equation that relates ambient temperatures to concentration setpoints.

6. The refrigeration control system of claim 4 wherein the control module is configured to determine the concentration setpoint using a lookup table that relates ambient temperatures to concentration setpoints.

7. The refrigeration control system of claim 1 wherein the control module is configured to determine the concentration based on at least one of (a) a temperature of the blended refrigerant and (b) a pressure of the blended refrigerant.

8. The refrigeration control system of claim 1 wherein the control module is configured to determine the concentration based on a differential pressure of the receiver.

9. The refrigeration control system of claim 1 wherein the control module is configured to decrease the opening of the second valve by a predetermined amount when (a) the concentration of the blended refrigerant at the point in the refrigeration control system is less than (b) the concentration setpoint.

10. The refrigeration control system of claim 9 wherein the control module is configured to decrease the opening of the second valve by the predetermined amount when (a) the concentration of the blended refrigerant at the point in the refrigeration control system is less than (b) the concentration setpoint and greater than a lower limit of a range around the concentration setpoint.

11. The refrigeration control system of claim 1 wherein the control module is configured to increase the opening of the second valve by a predetermined amount when (a) the concentration of the blended refrigerant at the point in the refrigeration control system is greater than (b) the concentration setpoint.

12. The refrigeration control system of claim 11 wherein the control module is configured to close the opening of the second valve by the predetermined amount when (a) the concentration of the blended refrigerant at the point in the refrigeration control system is less than (b) the concentration setpoint and greater than a lower limit of a range around the concentration setpoint.

13. The refrigeration control system of claim 1 wherein the concentration is a mass concentration a component of the blended refrigerant.

14. The refrigeration control system of claim 1 wherein the first refrigerant is carbon dioxide (CO2) and the second refrigerant is R1233zde refrigerant.

15. The refrigeration control system of claim 1 wherein the accumulator includes the blended refrigerant in both liquid form and vapor form.

16. The refrigeration control system of claim 1 wherein the compressor receives the blended refrigerant in vapor form from the accumulator.

17. The refrigeration control system of claim 1 wherein both liquid form and vapor form refrigerant form the blended refrigerant in the receiver.

18. The refrigeration control system of claim 1 wherein the control module is further configured to selectively adjust an opening of the first valve.

19. The refrigeration control system of claim 2 wherein the control module is configured to selectively adjust the opening of the first valve based on adjusting (a) a temperature of the blended refrigerant output from the first heat exchanger toward (b) an outlet setpoint temperature for the blended refrigerant output from the first heat exchanger.

20. In a system including a control module selectively operating a compressor that compresses a blended refrigerant including a first refrigerant and a second refrigerant from an accumulator and discharges the blended refrigerant to a first heat exchanger and a receiver disposed downstream of the compressor, a first valve between the first heat exchanger and the receiver, a second heat exchanger that at least partially vaporizes and outputs the blended refrigerant to a liquid-to-suction heat exchanger, and a second valve positioned between the receiver and the second heat exchanger, a refrigeration control method comprising selectively operating the compressor at a fixed speed and selectively adjusting an opening of the second valve based on (a) a concentration of the blended refrigerant at a point in the refrigeration control system and (b) a concentration setpoint.

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