HK1138361B - Methods and systems for controlling air conditioning systems having a cooling mode and a free-cooling mode - Google Patents

Description

Method and system for controlling air conditioning system having cooling mode and free cooling mode

Technical Field

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

During normal operation of the air conditioning system, the air conditioning system operates in a cooling mode in which energy is expended to compress and circulate a refrigerant by operating a compressor in a known manner to chill or condition a working fluid, such as air or other secondary loop fluid (e.g., water or glycol). The conditioned working fluid can then be used in refrigerators, freezers, buildings, automobiles, and other spaces with climate controlled environments.

However, when the outside ambient temperature is low, there is a possibility that the outside ambient air itself may be used to provide cooling to the working fluid without using a compressor. When the outside ambient air is used by the air conditioning system to condition the working fluid, the system is said to operate in a free-cooling mode. As described above, generally, the air conditioning system operates in the cooling mode even when the ambient outside air temperature is low. Operating in the cooling mode under such conditions provides an inefficient means of conditioning the working fluid. Conversely, it is more efficient to operate the air conditioning system in a free-cooling mode under such conditions. In the free-cooling mode, one or more ventilated heat exchangers and pumps are activated so that refrigerant circulating through the air conditioning system is cooled by outside ambient air, and the cooled refrigerant is then used to cool the working fluid.

Accordingly, the present invention identifies a need for a method and system for improving the efficiency of an air conditioning system having a free-cooling mode. Disclosure of Invention

A method of controlling an air conditioning system having a cooling mode and a free-cooling mode is provided.

The method includes starting the air conditioning system; measuring a first temperature of ambient air surrounding the condenser; measuring a second temperature of the working fluid; calculating a difference between the first temperature and the second temperature; and comparing the difference with a predetermined value, wherein the free-cooling mode is activated if the difference is greater than or equal to the predetermined value, and the cooling mode is activated if the difference is less than the predetermined value.

An air conditioning system having a cooling mode and a free-cooling mode is provided.

This air conditioning system includes: a condenser; a first temperature sensor for measuring a first temperature of ambient air surrounding the condenser; a working fluid; an evaporator for containing a portion of the working fluid; an expansion valve located in front of the evaporator; a second temperature sensor for measuring a second temperature of the working fluid; a controller for calculating a difference between the first temperature and the second temperature, the controller comparing the difference with a predetermined value, the controller activating the free-cooling mode when the difference is equal to or greater than the predetermined value, the apparatus activating the cooling mode when the difference is less than the predetermined value; a refrigerant pump that pumps refrigerant from the condenser to the evaporator through an expansion valve when the air conditioning system is in the free-cooling mode; a first valve for fluidly communicating the condenser to the expansion valve when the air conditioning system is in the cooling mode, the first valve for fluidly communicating the condenser to the refrigerant pump when the air conditioning system is in the free-cooling mode; a compressor for compressing the refrigerant when the air conditioning system is in the cooling mode; and a second valve for fluidly communicating the evaporator to the condenser when the air conditioning system is in the free-cooling mode, the second valve for fluidly communicating the evaporator to the condenser when the air conditioning system is in the cooling mode.

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. Drawings

Fig. 1 is an exemplary embodiment of an air conditioning system in a cooling mode according to the present invention.

Fig. 2 is an exemplary embodiment of an air conditioning system in a free-cooling mode according to the present invention.

Fig. 3 illustrates an exemplary embodiment of a method of operating an air conditioning system having a free-cooling mode and a cooling mode in accordance with the present invention.

Fig. 4 is a graph showing temperature versus time for an air conditioning system using only a cooling mode.

Fig. 5 is a graph showing temperature versus time for an air conditioning system using a free cooling determination step according to the present invention. Detailed Description

The present invention is directed to an air conditioning system having a cooling mode and a free-cooling mode. More specifically, the present invention is directed to a method and system for operating an air conditioning system having a free-cooling mode and a cooling mode.

Referring to the drawings, and more particularly to fig. 1 and 2, an exemplary embodiment of an air conditioning system 10 operating in a cooling mode and a free-cooling mode is shown and generally designated by reference numeral 10.

The air conditioning system 10 includes a compressor 12, a first valve 14, a first temperature sensor 16, a condenser 18, a refrigerant pump 20, a second valve 22, an expansion valve 24, a second temperature sensor 26, an evaporator 28, a controller 30, a third valve 32, a refrigerant 34, and a working fluid 36.

The air conditioning system 10 in the cooling mode uses the compressor 12 to pump refrigerant 34 from the evaporator 28 to the condenser 18. However, air conditioning system 10 in free-cooling mode uses refrigerant pump 20 to pump refrigerant through the entire system. Whereas the air conditioning system 10 in the cooling mode does not use the refrigerant pump 20 during operation, the air conditioning system 10 in the free-cooling mode does not use the compressor 12 during operation.

Referring to FIG. 1, air conditioning system 10 operates in a cooling mode in a known manner. Specifically, the controller 30 is electrically connected to the third valve 32 such that the third valve 32 is adjusted to a position such that refrigerant 34 can flow from the evaporator 28 to the compressor. The controller 30 turns on the compressor 12. The controller 30 turns on at least one fan in the condenser 18 so that ambient air flows through the condenser. If the air conditioning system 10 was previously operating in the free-cooling mode, the controller 30 turns off the refrigerant pump 20 and the refrigerant 34 flows from the condenser 18 to the expansion valve 24 through the second valve 22, thereby bypassing the refrigerant pump. The compressor 12 compresses the refrigerant 34 flowing through the first valve 14 to the condenser 18, wherein there is heat exchange between the refrigerant and the ambient outside air and the refrigerant begins to cool. In one embodiment of the present invention, the first valve 14 is a check valve. The first temperature sensor 16 measures the temperature of the ambient outside air. The condenser 18 includes a fan for contacting outside ambient air with the refrigerant 34 so that heat from the refrigerant is transferred to the ambient air. The refrigerant 34 then passes through the second valve 22, bypassing the refrigerant pump 20, to the expansion valve 24. In one embodiment of the present invention, second valve 22 is a check valve. When the expansion device 24 is opened, the compressed refrigerant 34 flows to the evaporator 28. The evaporator 28 is configured such that working fluid 36 flows through the evaporator, enabling 0 heat exchange between refrigerant 34 and the working fluid. The second temperature sensor 26 measures the temperature of the working fluid 36 exiting the evaporator 28. From the evaporator 28, the working fluid 36 flows through the third valve 32 to the compressor 12. In one embodiment of the present invention, the third valve 32 is a three-way valve. For purposes of the present invention, it is contemplated that working fluid 36 may be of any known type suitable for allowing heat exchange between refrigerant 34 and the working fluid. For example, the working fluid 36 may be water or air.

Referring now to FIG. 2, an air conditioning system 10 operating in a free-cooling mode is shown. When entering the free-cooling mode, controller 30 is electrically connected to the various elements of air conditioning system 10, placing each of the elements in an appropriate configuration so that the air conditioning system can operate in the free-cooling mode. For example, the controller 30 turns off the compressor 12 and adjusts the third valve 32 so that refrigerant 34 flows from the evaporator 28 to the condenser 18, thereby bypassing the compressor 12. In addition, the controller 30 turns on at least one fan in the condenser 18 so that ambient air flows through the condenser. The controller 30 also turns on the refrigerant pump 20 so that refrigerant 34 continuously flows from the condenser 18 to the refrigerant pump. Second valve 22 is a passive check valve. This valve allows fluid circulation from the condenser 18 to the expansion valve 24 and prohibits fluid circulation from the expansion valve 24 to the condenser 18 in other ways. The primary function of second valve 22 is to prevent refrigerant 34 from flowing back to the inlet of refrigerant pump 20 when air conditioning system 10 is operating in free-cooling mode. The refrigerant pump 20 pumps the refrigerant 34 from the condenser 18 through the expansion valve 24 to the evaporator 28, where there is heat exchange from the refrigerant to the working fluid 36, in the same manner as described above in the cooling mode. The second thermostat 26 measures the temperature of the working fluid 36 exiting the evaporator 28. Refrigerant 34, which is warmer than the outside ambient air, then flows through the third valve 32, bypassing the compressor 12, to the evaporator 28 due to natural refrigerant migration.

Referring to FIG. 3, an exemplary embodiment of a method of operating the air conditioning system 10 having a cooling mode and a free-cooling mode is illustrated and generally designated by reference numeral 50. Method 50 includes a free cooling condition determination step 54, a comparison of the difference to a predetermined value step 66, an available free cooling capacity step 68, and a free cooling condition check step 74.

The air conditioning unit 10 is either stopped or operated in a cooling mode at step 52. Advantageously, free-cooling condition determination step 54 determines whether the current conditions are sufficient to operate air conditioning system 10 in a free-cooling mode rather than a cooling mode, thereby optimizing the use of the free-cooling mode.

In a free cooling condition decision step 54, circulation of the working fluid is initiated at step 56 such that the working fluid flows in through the first opening and out through the second opening in the evaporator 28. Next, a device is used to measure a first temperature of the outside ambient air surrounding the exterior of the condenser 18. In one embodiment of the present invention, a first thermostat 16 is used. Next, a device is used to measure the temperature of the working fluid 36 exiting the evaporator 28. In one embodiment of the present invention, a second thermostat 26 is used. It should be appreciated that any device capable of measuring the temperature of both working fluid 36 and the outside ambient air may be used. For example, it is contemplated that suitable devices may include, but are not limited to, thermocouples or resistance temperature devices.

The difference between the first temperature and the second temperature is then calculated by the controller 30 at step 62. In one embodiment of the present invention, the controller 30 may use a software program to calculate the difference. The calculated difference is then compared to a predetermined value at step 64 and a determination is made at step 66 whether the difference is greater than or equal to the predetermined value or whether the difference is less than the predetermined value. If the difference is less than the predetermined value, the cooling mode remains on (if the air conditioning system 10 is already in cooling mode) or will be on if the air conditioning system has been stopped. In one embodiment of the invention, the predetermined value is about 6 degrees celsius. If, however, the difference is greater than or equal to the predetermined value, a system check is made at step 68 as to whether the available free cooling capacity is sufficient to operate the system in free-cooling mode. If there is sufficient cooling capacity, air conditioning system 10 switches to free-cooling mode 70. When air conditioning system 10 switches to free-cooling mode, the air conditioning system operates as shown in FIG. 2. When air conditioning system 10 is operating in free-cooling mode, step 72, then the system performs a continuous check to see if free-cooling conditions are maintained, step 74. The conditions that are continuously monitored include measuring a first temperature of the outside ambient air, measuring a second temperature of the working fluid 36 exiting the evaporator 28, calculating a difference between the first temperature and the second temperature, and comparing the difference to a predetermined value.

Air conditioning system 10 will remain in free-cooling mode until step 74 determines that the current conditions are no longer adequate. At this point, the air conditioning system 10 switches to cooling mode at step 76 and operates as shown in FIG. 1.

Referring now to fig. 4 and 5, graphs are shown in which time is plotted in hours on the X-axis and temperature is plotted in degrees celsius on the Y-axis. While fig. 5 illustrates an air conditioning system using a pre-free cooling step according to the present invention, the air conditioning system of fig. 4 does not use a pre-free cooling step. In both graphs, a water circuit with an initial temperature of 44 degrees celsius reaches a final temperature of 8 degrees celsius. In fig. 4, the air conditioning system was operated in cooling mode for 6 hours to bring the temperature of the water circuit to 8 degrees celsius. The energy required for this operation is 1080 kw/hr. However, in fig. 5, the air conditioning system having the pre-free cooling step is operated in the free cooling mode for 6 hours. Subsequently, the system was run in cooling mode for two more hours. The energy required to operate the air conditioning system of fig. 5 is 468 kw/hr. Advantageously, it can be seen that the energy usage associated with a cooling system equipped with a pre-free cooling step is substantially reduced by 57%, as contemplated by the present invention.

It should also 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 invention without departing from its scope. Therefore, it is intended that the disclosure 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 free-cooling mode and a cooling mode, comprising:

a condenser;

a first temperature sensor for measuring a first temperature of ambient outside air;

an evaporator in separate fluid communication with a working fluid and a refrigerant;

an expansion valve located in front of the evaporator;

a second temperature sensor for measuring a second temperature of the working fluid as it exits the evaporator;

a refrigerant pump for pumping refrigerant from the condenser to the evaporator through an expansion valve when the air conditioning system is in the free-cooling mode;

a second valve for fluidly communicating the condenser to the expansion valve when the air conditioning system is in the cooling mode, the second valve for fluidly communicating the condenser to the refrigerant pump when the air conditioning system is in the free-cooling mode;

a compressor for compressing the refrigerant when the air conditioning system is in the cooling mode;

a first valve for fluidly communicating the condenser to the expansion valve when the air conditioning system is in the cooling mode, the first valve for fluidly communicating the condenser to the refrigerant pump when the air conditioning system is in the free-cooling mode;

a third valve for fluidly communicating the evaporator to the condenser when the air conditioning system is in the free-cooling mode, the third valve for fluidly communicating the evaporator to the condenser when the air conditioning system is in the cooling mode; and

a controller for calculating a difference between the first temperature and the second temperature, the controller comparing the difference with a predetermined value, the controller adjusting positions of the first valve and the second valve, opening the compressor, and closing the refrigerant pump when the difference is equal to or greater than the predetermined value, and the controller closing the compressor, opening the refrigerant pump, and adjusting positions of the second valve and the third valve when the difference is less than the predetermined value.

2. The air conditioning system of claim 1, wherein the third valve is a three-way valve.

3. The air conditioning system of claim 1, wherein the second valve is a check valve.

4. The air conditioning system of claim 1, wherein the working fluid is water.

5. The air conditioning system of claim 1, wherein the working fluid is air.

6. A method of controlling the air conditioning system having a cooling mode and a free-cooling mode according to claim 1, comprising: circulating a working fluid through an evaporator of the air conditioning system;

measuring a first temperature of ambient outside air;

measuring a second temperature of the working fluid exiting the evaporator;

calculating a difference between the first temperature and the second temperature;

comparing the difference value with a predetermined value;

operating the air conditioning system in the free-cooling mode if the difference is greater than or equal to the predetermined value; and

operating the air conditioning system in the cooling mode if the difference is less than the predetermined value.

7. The method of claim 6, wherein the first temperature of ambient outside air is measured proximate a condenser of the air conditioning system.

8. The method of claim 6, wherein measuring the first temperature comprises controlling a first temperature sensor to determine the first temperature and measuring the second temperature comprises controlling a second temperature sensor to determine the second temperature.

9. The method of claim 6, wherein the calculating step is performed by a software program.

10. The method of claim 6, wherein the predetermined value is approximately 6 degrees Celsius.

11. The method of claim 6, wherein the comparing step is performed during the cooling mode operation of the air conditioning system.

12. The method of claim 6, wherein the comparing step is performed when the air conditioning system is not operating in the cooling mode or the free-cooling mode.