HK1138360B - Free-cooling limitation control for air conditioning systems - Google Patents

Description

Free cooling limit control for air conditioning systems

[ technical field ] A method for producing a semiconductor device

The present invention relates to an air conditioning system. More particularly, the present invention relates to a method and system for controlling an air conditioning system having a free-cooling mode and a cooling mode.

[ background of the invention ]

Air conditioning systems operate by consuming energy to cool a specific volume of air. Typically, air conditioning systems operate in a chiller or cooling mode (chiller or cooling mode) that includes circulating a refrigerant through a thermodynamic cycle. During the cycle, heat and work are transferred to the refrigerant. The refrigerant enters the heat exchanger and cools the working fluid (e.g., water), which in turn may be used to cool the conditioned space. Work is typically transferred to the refrigerant using a compressor.

However, when the temperature of the outside ambient air is low, the outside air may be used to cool the refrigerant without the participation of the compressor. When the outside ambient air is used by the air conditioning system to cool the refrigerant, the system is said to operate in a free-cooling mode. Operating the air conditioning system in the free-cooling mode is more efficient than operating the air conditioning system in the cooling mode because less work is required to be expended to operate the air conditioning system in the free-cooling mode.

Traditionally, air conditioning systems have been operated in cooling mode even when the temperature of the outside ambient air is low. Under such conditions, operating in the cooling mode provides an inefficient means of conditioning the refrigerant. In contrast, it is more efficient to run the air conditioning system in free cooling mode under such conditions. In the free-cooling mode, one or more ventilated heat exchangers and pumps are activated and the refrigerant circulating throughout the air conditioning system is cooled by the outside ambient air without the need for a compressor.

The air conditioning unit may be configured to operate using a cooling mode and a free-cooling mode. Accordingly, there is a need for methods and systems that improve the efficiency and control of air conditioning systems having a free-cooling mode.

[ summary of the invention ]

An air conditioning system and a control method are provided: when operating in the free-cooling mode, including the free-cooling limitation and sequence, the opening of the expansion device is varied based at least on a temperature difference between the working fluid exiting the air conditioning system and the outside ambient air.

An air conditioning system having a cooling mode and a free-cooling mode is provided. The system includes a refrigeration circuit having a compressor, a pump, an expansion device having a variable opening, and a controller. The controller selectively operates the system in the cooling mode by circulating and compressing a refrigerant through the refrigeration circuit via the compressor or operates the system in the free-cooling mode by circulating the refrigerant through the refrigeration circuit via the pump. The free cooling limit and the change program are stored in the controller and the variable opening is changed based at least on the temperature difference.

A method of controlling an air conditioning system having a cooling mode and a free-cooling mode is also provided. The method includes determining a temperature differential between the outside ambient air and the conditioned working fluid, operating the system in a cooling mode when the temperature differential is below a first predetermined level, operating the system in a free-cooling mode with the refrigerant expansion device fully open when the temperature differential exceeds a second predetermined level, and partially opening the refrigerant expansion device to operate the system in the free-cooling mode based on the temperature differential when the temperature differential is between the first and second predetermined levels.

The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.

[ description of the drawings ]

FIG. 1 is an exemplary embodiment of an air conditioning system in a free-cooling mode according to the present invention;

FIG. 2 is an exemplary embodiment of an air conditioning system according to the present invention in a cooling mode;

FIG. 3 illustrates an exemplary embodiment of a method of operating the air conditioning system of FIGS. 1 and 2; and

fig. 4 is a graph illustrating an exemplary free-cooling operating range of the air conditioning system of fig. 1 and 2.

[ detailed description ] embodiments

Referring now to the drawings, and more particularly to FIGS. 1 and 2, there is shown an exemplary embodiment of an air conditioning system, generally designated by the reference numeral 10. System 10 is configured to operate in a free-cooling mode 12 (fig. 1) and a cooling mode 14 (fig. 2).

The system 10 includes a controller 16 for selecting switching between the free-cooling and cooling modes 12, 14. Advantageously, controller 16 includes a limit and change control routine 18 that monitors one or more conditions within system 10, and adjusts the size of the opening of the expansion device when operating in free-cooling mode 12 to maintain sufficient pressure within system 10 and prevent damage to the pump. In this manner, limiting and altering control program 18 improves the performance of system 10 during free-cooling mode 12 as compared to prior art systems.

The system 10 includes a refrigeration circuit 20, the refrigeration circuit 20 having a condenser 22, a pump 24, an expansion device 26, an evaporator 28, and a compressor 30. Controller 16 is configured to selectively control pump 24 (when in free-cooling mode 12) or compressor 30 (when in cooling mode 14) to circulate refrigerant through system 10 in a flow direction (D). Therefore, when in free-cooling mode 12, system 10 controls pump 24 to circulate the refrigerant in flow direction D. However, when in cooling mode 14, system 10 controls compressor 30 to compress and circulate the refrigerant in flow direction D. Free-cooling mode 12 uses less energy than cooling mode 14 because free-cooling mode 12 does not require additional work input to operate compressor 30.

The system 10 includes a compressor bypass loop 32 and a pump bypass loop 34. The system 10 includes one or more valves 36 controlled by the controller 16, enabling the controller to selectively position the valves 36 to selectively open and close the bypass circuits 32, 34 as desired.

In cooling mode 14, controller 16 controls valve 36 such that compressor bypass loop 32 is closed and pump bypass loop 34 is open. In this configuration, the system 10 allows the compressor 30 to compress and circulate refrigerant in the flow direction D by flowing through the pump bypass loop 34.

In contrast, when in free-cooling mode 12, controller 16 controls valve 36 such that compressor bypass loop 32 is open and pump bypass loop 34 is closed. In this configuration, system 10 allows pump 24 to circulate refrigerant in flow direction D by flowing through compressor bypass loop 32.

Thus, system 10 provides heat transfer between refrigerant 44 and working fluid 46 in evaporator 28. Heat is transferred from the working fluid 46 to the refrigerant 44, cooling the working fluid 46. The cooled working fluid 46 exits the evaporator 28 at an outlet 48, circulates throughout the area requiring reduced temperature, and returns to the evaporator through an inlet 50. This process occurs in both free-cooling mode 12 and cooling mode. Refrigerant 44 may be R22, R410A, or any other known refrigerant. The working fluid 46 may be air, water, glycol, or any other fluid known in the art.

In cooling mode 14, system 10 operates like a standard vapor-compression (vapor-compression) air conditioning system known in the art, and the compression and expansion of the refrigerant via expansion device 26 is used to condition working fluid 46. Expansion device 26 may be any known expansion device such as, but not limited to, a controllable expansion device (e.g., a thermostatic expansion valve). In a preferred embodiment, expansion device 26 is an electronically controllable expansion valve. In another preferred embodiment, the expansion device 26 is a two-way valve. In the example where expansion device 26 is a controllable expansion device, the expansion device is preferably controlled by controller 16.

In free-cooling mode 12, system 10 utilizes the heat removal capability of outside ambient air 40 in heat exchange relationship with condenser 22 via one or more fans 42. The efficacy of free-cooling mode 12 depends on the difference or temperature differential (delta T or Δ T) between the temperature 52 of the outside ambient air 40 and the temperature of the working fluid 46 as it exits evaporator 28 through outlet 48 (exit temperature 54). That is, Δ T is (leaving temperature 54) - (outside air temperature 52). In general, free-cooling mode 12 is more efficient at higher Δ T values.

In an exemplary embodiment, Δ T is determined using first temperature sensor 56 and second temperature sensor 58. A first temperature sensor 56 is positioned to measure the outside air temperature 52 and a second temperature sensor 58 is positioned to measure the leaving temperature 54. Preferably, the controller 16 interfaces with the first and second temperature sensors 56, 58 to calculate Δ T. The first and second temperature sensors 56, 58 may be any temperature sensitive element known in the art including, but not limited to, thermocouples and thermistors.

When system 10 is operating in free-cooling mode 12, refrigerant 44 naturally migrates toward the coldest point of circuit 20. In an exemplary embodiment, condenser 22 is the coldest point of circuit 20, and refrigerant 44 moves from evaporator 28 to condenser 22, creating a first flow rate Q1. Working fluid 44 exiting condenser 22 is pumped by pump 24 to produce a second flow rate Q2 toward expansion device 26. The manufacturer of pump 24 sets a low restriction speed Q3, which is a lower limit at which pump 24 can safely operate without causing damage to the pump.

When the difference Δ Τ between the outside air temperature 52 and the leaving temperature 54 is small, the first flow rate Q1 will decrease and may become lower than the second flow rate Q2. When this occurs, the amount of refrigerant 44 present in condenser 28 will be depleted, and operating system 10 in free-cooling mode 12 may cause damage to pump 24. The low restriction speed Q3 sets a lower limit at which the pump 24 can operate. To avoid damage to the pump 24, the second flow rate Q2 must be maintained at a value that is higher than the low restriction rate Q3 and lower than the first flow rate Q1.

It has been determined by the present disclosure that the refrigerant exiting the condenser 22 may be in one of several different states, namely a gas phase, a liquid-gas phase, or a liquid phase. After controller 16 initiates free-cooling mode 14, and during the time it takes system 10 to reach equilibrium, pump 24 is supplied with refrigerant in a different state. Unfortunately, when pump 24 is supplied with refrigerant in the gas or liquid-gas phase, the pump does not operate optimally. Moreover, the vapor and/or liquid-vapor phase refrigerant can cause cavitation (cavitation) and/or flooding (diffusion) of the pump 24, which can damage the pump and/or the pump motor (not shown).

Advantageously, the controller 16 includes a limit and change control routine 18, and the limit and change control routine 18 monitors and changes one or more conditions within the circuit 20 to mitigate and/or prevent damage to the pump 24.

Free-cooling mode 12 is enabled only when there is a sufficient pressure drop in system 10. The prior art systems fail to provide adequate pressure drop within the system 10 for low delta T values. Advantageously, the present invention allows system 10 to operate in free-cooling mode 12 when Δ T is small. By varying the size of opening 25 of expansion device 26, controller 16 is able to maintain a desired pressure drop within system 10 even for small values of Δ T. Controller 16 controls the size of opening 25 via pressure limiting and varying program 18.

Fig. 3 and 4 describe the operation of the restriction and change program 18 in more detail. Fig. 3 illustrates an exemplary embodiment of a method 60 for operating the system 10. Fig. 4 is a graph illustrating an exemplary range in which system 10 can operate in free-cooling mode 12.

When system 10 is operating in cooling mode 14, method 60 includes a first temperature comparison step 62. During first temperature comparison step 62, method 60 determines whether the difference Δ T between temperature 52 of outside ambient air 40 and leaving temperature 54 of working fluid 46 is sufficient for system 10 to switch to free-cooling mode 12. System 10 continues to operate in cooling mode 14 if at is less than a first predetermined temperature, shown as approximately 6 degrees celsius (c). However, if Δ T is equal to or greater than the first predetermined temperature, method 60 performs a switching step 64 to operate system 10 in free-cooling mode 12. After the switching step 64, the method 60 performs a second temperature comparison step 66 to determine if Δ T is less than a second predetermined temperature (shown as about 10℃.). If Δ T is equal to or greater than the second predetermined temperature, system 10 continues to operate in free-cooling mode 12. If Δ T is less than the second predetermined temperature, controller 16 initiates sequence 18 to vary the size of opening 25 of expansion device 26 to maintain a sufficient pressure drop and flow rate from system 10 to pump 24.

Thus, as a result of the initiation of sequence 18, method 60 controls system 10 to selectively restrict flow through expansion device 26 based at least on Δ T to maintain a predetermined pressure drop through pump 24. Below the first predetermined temperature, method 60 operates in cooling mode 14. Above the second predetermined temperature, method 60 operates system 10 in unrestricted free-cooling mode 12, i.e., expansion device 26 is in a fully open position. However, between the first and second predetermined temperatures, method 60 operates in limited or limited free-cooling mode 12 such that method 60 varies expansion device 26 anywhere between the fully open position and the substantially closed position, and any subranges therebetween.

Method 60 continues to operate in free-cooling mode 12 after start-up sequence 18 and, in certain embodiments, includes a third temperature comparison step 68. Much like first comparison step 80 discussed above, third comparison step 80 determines that if Δ T is greater than or equal to the first predetermined temperature, system 10 continues to operate in free-cooling mode 12. However, if Δ T is less than the first predetermined temperature, routine 18 switches pump 24 to the "off" state at a pump shut-down step 70 and switches system 10 back to cooling mode 14 at a cooling mode switching step 90.

Fig. 6 is a graph illustrating an operating range 74 in which system 10 can operate in free-cooling mode 12. Here, the operating range 74 includes a plot of the unrestricted portion 74-1 and the restricted portion 74-2. The x-axis of the graph shows Δ T in degrees Celsius; the y-axis of the graph shows the opening size R of the expansion device 26 as a percentage of the opening size of the expansion device in its fully open state R _ full.

In the illustrated embodiment, opening size R is fully open (e.g., 100) during unrestricted portion 74-1 of free-cooling mode 12. However, the opening size R is altered by program 18 between being partially closed (e.g., 45) and fully open (e.g., 100). As shown, the change in percent opening of the expansion device 26 is linear with respect to the change in Δ T. However, it is contemplated by the present disclosure for sequence 18 to control expansion device 26 in a manner with respect to changes in Δ T, i.e., linear, non-linear, and any combination thereof.

The present inventors have determined that for low values of deltat, in particular between the first and second predetermined temperatures, the pump 24 does not work optimally without controlling the opening 25 of the expansion device 26. In some embodiments, the lowest value of R (R _ min) may be about 45, that is, the minimum size of opening 25 of expansion device 26 is about 45% of R _ full to allow sufficient flow rate.

Sequence 18 is configured to continuously adjust the size of opening 25 of expansion device 26 to maintain a desired pressure drop and flow rate within system 10 such that Q3 < Q2 < Q1. When the appropriate pressure drop and/or flow rate cannot be maintained by adjusting the expansion device opening, controller 16 switches system 10 from free-cooling mode 12 to cooling mode 14.

It should be noted that the terms "first," "second," "third," "upper," "lower," and the like may be used herein to modify various elements. These modifiers do not imply a spatial, sequential, or hierarchical order to the modified elements unless specifically stated.

While the invention has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated, but that the disclosure will include all embodiments falling within the scope of the appended claims.

Claims (12)

1. An air conditioning system having a cooling mode and a free-cooling mode, the system comprising:

a refrigeration circuit having a compressor, a pump, and an expansion device with a variable opening;

a controller for selectively operating in the cooling mode by circulating and compressing a refrigerant through the refrigeration circuit via the compressor or in the free-cooling mode by circulating the refrigerant through the refrigeration circuit via the pump; and

a free-cooling limiting and varying program stored in the controller that varies the variable opening based at least on a temperature differential between the outside ambient air and the conditioned working fluid to maintain sufficient pressure within the system and prevent damage to the pump.

2. The system of claim 1, wherein the free cooling limit and change program changes the variable opening linearly with respect to the temperature differential.

3. The system of claim 1, wherein the free cooling limitation and change procedure varies the variable opening non-linearly with respect to the temperature differential.

4. The system of claim 1, further comprising:

a heat exchanger in which heat is transferred between the refrigerant and a working fluid; and

a first temperature sensor and a second temperature sensor, the first temperature sensor and the second temperature sensor interfaced with the controller,

wherein the first temperature sensor measures a first temperature of the outside ambient air and the second temperature sensor measures a second temperature of the working fluid exiting the heat exchanger, an

Wherein the controller determines the temperature difference based on the first temperature and the second temperature.

5. The system of claim 1, wherein the free cooling limiting and varying program partially opens the variable opening when the temperature differential is within a predetermined range.

6. The system of claim 5, wherein the free-cooling limiting and varying procedure fully opens the variable opening when the temperature differential is above the predetermined range.

7. The system of claim 6, wherein said free-cooling limiting and altering routine switches the system from said free-cooling mode to said cooling mode when said temperature differential is below said predetermined range.

8. A method of controlling an air conditioning system having a cooling mode and a free-cooling mode, the method comprising:

determining a temperature difference between the outside ambient air and the conditioned working fluid;

operating the system in the cooling mode when the temperature difference is below a first predetermined level;

operating the system in the free-cooling mode with the refrigerant expansion device fully opened when the temperature differential is above a second predetermined level; and

partially opening the refrigerant expansion device in accordance with the temperature differential to operate the system in the free-cooling mode when the temperature differential is between the first and second predetermined levels.

9. The method as set forth in claim 8, wherein the step of partially opening said refrigerant expansion device as a function of said temperature differential is accomplished by varying an opening of said refrigerant expansion device in a linear manner with respect to said temperature differential.

10. The method of claim 9, wherein the first predetermined level is about 6 degrees celsius.

11. The method of claim 9, wherein the second predetermined level is about 10 degrees celsius.

12. The method as set forth in claim 8, wherein the step of partially opening said refrigerant expansion device as a function of said temperature differential is accomplished by varying an opening of said refrigerant expansion device in a non-linear manner with respect to said temperature differential.