US20140109612A1

US20140109612A1 - Phase Transition Air Cooling System Utilizing a Water Sub-Cooler for Chilling Liquid Refrigerant

Info

Publication number: US20140109612A1
Application number: US14/061,343
Authority: US
Inventors: Drew Philip LaMarca; Thomas Zich
Original assignee: ECEnergy LLC
Current assignee: ECEnergy LLC
Priority date: 2012-10-23
Filing date: 2013-10-23
Publication date: 2014-04-24

Abstract

A traditional refrigeration system including a compressor, condenser and evaporator and expansion valve that utilizes an additional sub-cooler downstream of the condenser for cooling liquid refrigerant prior to the refrigerant being provided to the evaporator for increased system efficiency. The sub-cooler can utilize existing groundwater, particularly water with a large amount of dissolved materials such as naturally occurring sea water, to provide for the sub-cooling effect with only a modicum of additional energy use.

Description

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/717,453, filed Oct. 23, 2012, the entire disclosure of which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention.
This disclosure is related to the field of air cooling or refrigeration systems, particularly to systems which improve efficiency by cooling liquid refrigerant prior to evaporation.
2. Description of Related Art.
The cooling of structures is an expensive and energy intensive operation. Most commonly, cooling of structures relates to the use of “air conditioners” which serve to absorb heat from the air in a building and effectively move that heat external to the building, but it also relates to refrigerators and other cooling devices. The US Department of Energy has estimated that the average home can spend 43% of their monthly utility bill on the costs of cooling the home in summer months. This expense not only comes with a significant dollar cost, but with a loss of the availability of that energy for other tasks (and with occasional brownouts and similar problems), and the environmental impact of generating the electricity used for the cooling.
Most of the cost of traditional cooling arises from the manner of operation of a traditional air conditioner. Effectively, a traditional air conditioner, which is more accurately called a phase transition direct exchange system, actually generates both cold air and heated air. The reason why it is effective at cooling a structure is because the cold air is released within the structure, while the hot air is released external to the structure. A heat pump, which is effectively such a system simply operating in reverse, does precisely the opposite to heat a structure.
Since its first commercial applications, the operation of an air cooler has generally relied on a common principle. The principle is to pass warmer air over a structure which absorbs heat through one of the well-known laws of thermodynamics and supply air which is cooled by the thermal connectivity to the area that is to be cooled. In effect, it is precisely the same principle being applied to the air in the structure as is used to cool a drink by placing ice in it. Heat is transferred from the air in the structure through the a material (such as piping) holding a substance that can absorb heat. Once the heat is taken into the material from the air, the chilled air is circulated within the structure while the warmed material is sent back outside where heat is released to external air and the process is repeated.
In traditional air conditioning systems, the material inside the pipes is a refrigerant, which is a material having a phase transition temperature that is generally below the temperature of warm air. Traditionally, these were hydrochlorofluorocarbons such as R-22, but those have been substituted out in favor of materials that do not include chlorine. The primary refrigerant used today is R-410A, a mixture of difluoromethane (CH₂F₂or R-32) and pentafluoroethane (CHF₂CF₃or R-125) which is sold under a number of brand names including Forane™, Puron™, EcoFluor™, and Genetron™. Regardless of the materials used, refrigerants used in these systems provide cooling by utilizing the refrigerants phase transition to absorb heat from the air. Specifically, the refrigerant is converted from a gas to a liquid state via compression and the conversion from liquid to gas is used to absorb heat from the air.
The compressor in the air conditioner performs compression of the refrigerant external to the structure as this process gives off waste heat which is vented to the external atmosphere. The liquid refrigerant is then carried via pipes to evaporator coils which are within the structure, passing through an expansion valve on the way there. Air (or in some cases water) from the structure is passed over the evaporator coils where heat is absorbed by the refrigerant so that it converts back to its gaseous form. The gaseous refrigerant is then passed from the evaporator back to the compressor and the process is repeated. Meanwhile, the cooled air (or water) is circulated throughout the structure to provide for air within the structure which is cooler.
Energy use in these systems is generally dependent on a variety of factors. The primary energy drain is the act of the compressor to compress the refrigerant. Further, fans and related components also use energy to move air over the evaporator and to remove waste heat from the condenser coils (where the refrigerant goes from gas to liquid state). These, however, are generally very minor consumers of energy compared to the compressor. There also can be losses in the system from undesired heat absorption of the refrigerant as it moves from the condenser to the evaporator, which is why certain systems transfer heat from circulating water to the evaporator and then from the water to air where the cooling is actually desired.
Systems using circulating water generally are larger systems and are used in larger structures. The chilled water can generally be circulated more easily throughout the structure and air can be passed over it where needed dealing with some of the inefficiencies of transferring the compressed refrigerant to the target location. These systems are commonly called chilled water systems and while the actual cooling of the air takes place using a slightly modified process, the operation of the refrigerant aspects of the system are essentially the same.
It has been recognized that the distribution water in a chilled water (or the similar cooling tower) system can be used to improve efficiency of the system. In effect, the water can be used to “store cool” at times when it is more readily available. For example, it is generally cooler during the night (and is often quite comfortable if not cold). Thus, some systems can utilize this phenomenon to cool water in the system by exposing the water in the system to chilled outside air during the night. This can allow the water to cool during the night without any use of external energy. The water can then be brought internal to the structure prior to the sun rising allowing it to be used to cool the internal environment of the structure without need to use the refrigerant's phase transition. In a more extreme example, energy can be used to freeze the water overnight (specifically to cool it more than would naturally occur) and it can then be stored as ice, which can then have air passed over it to melt the ice and cool the air the next day. These latter kind of systems don't so much save energy, as utilize energy during the night when demand (and thus cost) is generally less.
While the use of nighttime cooling can be helpful, it is dependent on sufficient cooling via exposure to night air being available, which may not always be the case. Thus, some systems take advantage of cooler areas which exist more constantly and are not dependent on the earth's rotation. Specifically, it can be possible to utilize the insulative properties of the earth itself to provide cooling and or heating. Specifically, it is known that at a distance of about 6 feet or more under the surface of the earth, the temperature is maintained at generally a range of 45-75 degrees Fahrenheit. This is why the air in caves and mines is generally a constant temperature regardless of the external temperature. It is fortunate that the temperature inside the earth is generally a suitable temperature for cooling (and sometimes heating, depending on the outside temperature) a structure. Specifically, most humans prefer a temperature of around 68-72degrees Fahrenheit, which is within the natural range of air, water and soil within the structure of the earth.
Geothermal systems utilize the temperature within the earth for cooling and sometimes heating by providing closed loop systems which comprise pipes filled with liquid that are buried at a distance underneath the earth. The liquid in the pipes is allowed to adjust to the ambient temperature within the earth, and the liquid is then brought back to the structure and air is circulated over it to provide for cooling or heating depending on the outside temperature and the temperature of the liquid in the pipes. The water is then returned under the earth where heat is exchanged with the earth cooling, or heating, the water again. While such systems do technically heat up (or cool down) the earth surrounding them, the amount of earth is enormous compared to the amount of water and the “heat sink” properties generally allow the system to work regardless of the amount of heat being transferred.
While these types of geothermal solutions can provide dramatic energy savings, they still have a number of problems. The most noticeable is that they require a rather large amount of piping underground in order to have enough water (that can circulate quickly enough) to provide for sufficient cooling throughout a hot day. Further, the systems are generally limited by the amount of water and the temperature of it to provide cooling. Thus, the systems can only cool air so much depending on the water temperature available and how much there is. Transfer with the earth surrounding the system is often relatively slow, and thus these systems are often backed up by more traditional air conditioning systems for use on particularly hot days.

SUMMARY OF THE INVENTION

Because of these and other problems in the art, described herein, among other things, is a traditional refrigeration system that includes a compressor, condenser, evaporator, and expansion valve that additionally utilizes a sub-cooler downstream of the condenser but upstream of the evaporator for providing cooling to the liquid refrigerant prior to the refrigerant being provided to the evaporator. This provides increased system efficiency. In an embodiment, the sub-cooler utilizes geothermal cooling of liquid to provide the cooling and may utilize existing groundwater eliminating the need for larger closed loop water sources. Placement of the sub-cooler to the refrigerant's liquid phase can allow the operating pressure and temperature of the refrigeration system to be reduced and the refrigerant in the system to provide the greatest cooling effect in the evaporator. This can both provide a more energy efficient cool, and potentially a faster one.
In order to provide for effective heat transfer between the refrigerant and what is likely highly corrosive groundwater (as it may be salt water or sea water or have significant dissolved minerals), the exchanger is formed from a polymer coated marine grade steel tube which is resistant to the corrosion and galvanic reaction caused by water that can contain a significant concentration of dissolved salts. The exchanger is placed directly in a buried water bath to provide for a maximum cooling effect.
Because of the high thermal conductivity of the water bath, design wireless sensors can accurately monitor the refrigerant cooler operation providing for more efficient thermostat control.
There is provided herein, among other things, an air cooling system comprising: a compressor; a condenser; a refrigerant, the compressor compressing the refrigerant in the condenser from a gas to a liquid state; an evaporator, the refrigerant in the evaporator absorbing heat to phase transition from a liquid to a gas; and a sub cooler, the sub cooler comprising: an exchanger; and a container including a liquid bath which is in thermal contact with the exchanger; wherein, when the refrigerant is in the liquid state, the refrigerant is fed into the exchanger within the liquid bath, the liquid bath cooling the refrigerant; and wherein, after the refrigerant leaves the exchanger, it is provided to the evaporator.
In an embodiment of the cooling system, the liquid bath is corrosive.
In an embodiment of the cooling system, the liquid bath comprises salt water.
In an embodiment of the cooling system, the exchanger is comprised of marine grade stainless steel.
In an embodiment of the cooling system, the marine grade stainless steel is coated with a polymer.
In an embodiment of the cooling system, the container is placed underground.
In an embodiment, the cooling system further comprises a sensor attached to the exchanger.
In an embodiment, the cooling system further comprises a thermostat for controlling the cooling system.
In an embodiment of the cooling system, the thermostat is connected to the Internet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an embodiment of a cooling system which utilizes an underground water bath where the water bath includes a significant concentration of dissolved salts.

FIG. 2 depicts an embodiment of a thermostat control system for a cooling system such as that shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 1 depicts an embodiment of a phase transition refrigerant cooling system which utilizes water which may include a significant concentration of dissolved salts (such as sea water) to provide additional cooling capacity of the refrigerant and reduces the A/C compressor power, leading to higher overall system efficiency. As indicated in FIG. 2, wireless sensors and connected thermostats may be used to monitor the operation and notify users of the product operation and savings through various devices as well as controlling cooling provided by the system.
The embodiment of FIG. 1 provides for an addition to what is otherwise essentially a traditional air cooling system. Specifically, the system includes known parts of a phase transition air cooling system (200) including a compressor (201), condenser (203), expansion valve (207), and evaporator (205). These may be of traditional style and operation as is well known to those of ordinary skill. The system of FIG. 1, however, includes an additional system in the form of a sub-cooler (100) which is used to improve the efficiency of the existing phase transition system (200). As should be apparent, as the sub-cooler (100) is its own self-contained cooler, it can be added to existing air chilling systems in any application including, without limitation, residential and commercial air cooling and refrigerators, or can be built into such traditional systems (200) when they are built.
The sub-cooler (100) generally utilizes a heat exchanger (101) which is placed in a container (103) including a bath (105) of cooled fluid. This bath (105) can be comprised of any cooled fluid but is preferably fluid obtained from underground. It, thus, may be fluid obtained from a traditional closed loop geothermal cooling system or may be from a naturally occurring or man-made underground water source (119) such as, but not limited to, an aquifer, underground lake, cenote, underground reservoir, well, sea cave, or a flooded mine. The fluid used is preferably water and is more preferably water including a significant concentration of dissolved materials such as salts.
Waters with high concentrations of absorbed salts have a higher boiling point than standard water and can generally absorb more heat than clear water which can make them particularly useful in the system of FIG. 1. Further, water sources which include dissolved minerals (such as sea water) are generally unusable as drinking water sources and have relatively few other uses. In fact, most currently have no particularly valuable use and are generally considered undesirable.
Liquid refrigerant is circulated through the exchanger (101) to lower the refrigerant's temperature and absorb heat in the liquid refrigerant into the water of the bath (105). Specifically, the water of the bath (105) will naturally be at a temperature generally below that of the liquid refrigerant which is traditionally around it's phase transition temperature. The container (103) is preferably located at least partially underground which also allows the water of the bath (105) to dissipate heat absorbed through the container and into the surrounding soil (301) and to better avoid heat absorption into the bath (105), except from the exchanger (101). The water of the bath (105) is preferably circulated with the bath (105) and an open loop system flowing from the water source (119) to the bath (105) via a suction line (111) and pump (113).
While it is generally preferred that the system utilize an open loop system with the water source (119), it should be recognized that the system can be a closed loop utilizing a traditional geothermal piping system. Further, the system may end up being a closed loop even with a naturally occurring water source (119) as the source (119) may be self-contained depending on how it is selected.
In an embodiment, the water source (119) comprises sea water or brackish water which is in fluid communication with a naturally occurring large body of water such as an ocean. This system can utilize not only the temperature control of soil (301), but can also utilize the temperature control of the large body of water itself. Thus, the temperature of the water source (119) can generally be considered a constant or near constant temperature regardless of the amount of heat it absorbs via the evaporator. The system can be particularly beneficial near coasts where salty or brackish water is often common at a relatively low depth below ground level and can be readily obtained. Further, the temperature of such water is generally below that of the refrigerant's phase transition allowing heat transfer to cool the refrigerant. In an embodiment, the source (119) may not actually be underground, but may instead be water pulled from the deep sea (e.g. significantly below sea level).
Traditionally, copper pipe and tubing has been used for refrigerant transfer in air conditioning installations. Copper, however, has a high corrosion and galvanic reaction rate and failure when exposed or submerged in water that contains a significant concentration of dissolved salts (as would be expected of sea water). Thus, while copper tubes can be desirable for exchange with air, they are generally undesirable for applications where the piping is directly submerged in water. Thus, in the embodiment of FIG. 1, the exchanger (101) utilizes a polymer coated marine grade steel tube which resolves corrosion and galvanic reaction due to water that contains a significant concentration of dissolved salts.
This material is resistant to the corrosive and galvanic effects of the water. In an embodiment, the steel piping of the exchanger (101) comprises type 316 stainless steel which is already known to be resistant to many corrosive effects although other materials may be used in alternative embodiments. The steel may then be externally coated with a synthetic insulating enamel such as that used on electrical equipment and/or a polyester powder coat to provide for galvanic insulation as is known to those of ordinary skill in the art. In alternative embodiments, other materials may be used in place of stainless steel including, but not limited to, titanium, cupronickel and/or thermoplastic.
In the embodiment of FIG. 1, the system (100) will generally be arranged in the following manner. The exchanger (101) is generally placed within a container (103) which is generally placed at least partially underground. It may be originally formed when the air conditioner (200) is installed, or may be added retroactively at a later date. While it is not necessary for the container (103) to be at least partially underground, this is generally preferred to allow for the earth (301) to act as an additional insulator and preserve the temperature of the bath (105) close to that of the water source (119). The container (103) then has a water bath (105) placed therein which is in thermal connection with the exchanger (101).
A standard air conditioning unit (200) with a condenser coil (203) and compressor unit (201) is installed upstream of the exchanger (101). This will generally be a standard direct-expansion vapor-compression refrigerant system utilizing phase transition. This unit (200) will operate in the standard fashion and the compressor (201) will be used to compress the refrigerant into a liquid state within the condenser (203). The liquid refrigerant is then sent down piping (251) and fed into the exchanger (101) where it flows through the piping of the exchanger (101). The container (103) is generally filled with a fluid bath (105) comprising water from the water source (119) which is in thermal connection to the material of the exterior of the exchanger (101). As the refrigerant passes through the exchanger (101), the liquid refrigerant is cooled by heat exchange with the bath (105) as the bath (105) will be at or near the temperature of the source (119) which is below that of the phase transition point of the refrigerant.
After it has passed through the exchanger (101), the liquid refrigerant is fed back through piping (253) to the evaporator (205) via an expansion valve (207) and air (215) is allowed to pass over the evaporator (205) with the refrigerant absorbing heat from the air (215). While it is presumed that in many applications the evaporator (205) will be used to cool air (215) directly, it should be recognized that in the system of FIG. 1 the air (215) could be replaced by water or any other fluid which heat is absorbed from and is usable in all forms of air cooling including, but not limited to, chilled water systems and cooling towers.
As the refrigerant has been cooled by its time in the exchanger (101), air (215) passing over the evaporator (205) will first serve to heat the refrigerant to the point of phase transition. This heat transfer will result in a first amount of heat being drawn from the air (215) to the refrigerant. Once the refrigerant has heated to its phase transition temperature, it will absorb an additional second amount of heat in order to change phase to a gas and will further cool the air (215). The refrigerant, thus, provides two types of cooling. Specifically, heat is absorbed to raise the temperature of the refrigerant to its phase transition point from the temperature it was cooled to in the exchanger (101), and the phase transition of the refrigerant further absorbs heat. While the two forms are technically a continuation of the same thermodynamic process, they are called out here as separate for clarity.
As discussed above, in order to feed water into the container (103) to provide the bath (105), there generally will be a source (119) of water nearby. In an embodiment, this may be a standard geothermal closed loop cooling system or may be a naturally occurring or manmade source of underground water. In the later type of system as depicted in FIG. 1, a suction line (111) is provided which is connected to the water source (119). Water is moved from the source (119) into the suction line (111) via a pump (113). The pump (113) serves to pull cold water into the bath (105) and, as the bath (105) warms, the pump (113) serves to remove the warmer water from the bath (105) and then pump it back through the suction line (111) returning it to the water source (119).
An advantage of an open loop system, particularly one with a large water source (119), is that the pump (113) can be used to circulate water within the bath (105) in addition to supplying it. Having moving water in the bath (105) can provide for improved thermal transfer between the refrigerant and the bath (105) compared to if the bath (105) is stagnant or mostly stagnant. The large water source (119) allows for the bath (105) to have access to water which has not recently been circulated through the bath (which can be the case in a closed loop system) and therefore the temperature of the bath (105) is generally maintained more consistently at the temperature of the source (119).
As should be apparent from the above description and FIG. 1, if the water source (119) is of sufficient size, even with a relatively strong cooling load, the water source (119) will rarely suffer any significant temperature increase from being part of the system (100). It also should be recognized that while the above specifically contemplates use of salt water, this is not required. Salt water is often preferred as it is more readily available from natural sources, particularly in coastal areas, and is generally unusable as drinking water. However, the system (100) is capable of using any kind of water including fresh, stagnant, acidic, alkaline, polluted and de-aerated waters for cooling. The only requirement is that the source be underground or otherwise at a naturally occurring temperature below the phase transition point of the refrigerant. This can include, and is not limited to, above ground water sources (particularly when water is sourced from deeper depths) or from other types of water sources that may include water at a sufficiently low temperature. In an embodiment, a swimming pool, fountain, decorative pool, or similar man-made water structure can be used as a source of water.
As there is no direct contact (only thermal contact) between the water and the refrigerant, there is no possibility of material in the water being released into the refrigerant or the structure (501) and thus polluted water sources may be used. Further, having the bath (105) be in an underground (301) container (103) can further protect occupants of the structure (501) by shielding them from contact to the bath (105). Further, as the exchanger (101) is designed to work in the corrosive environment of salty water, it generally will be useable in less corrosive environments and with other dissolved compounds in water such as pollutants.
In an embodiment, it can be desirable to monitor and control the additional cooling provided by the system (100). In an embodiment, a sensor (121) is provided which is connected directly to the exchanger (101) at the point when the refrigerant is provided to the exchanger (101) and/or removed from the exchanger (101). This can provide indications of the refrigerant temperature and/or temperature differential to monitor the cooling provided by the system (100).
Should the structure (501) need less cooling (such as on a cooler day) the compressor can be slowed and refrigerant can be circulated through the exchanger (100) as a primary source of cooling. This can greatly relieve demand on the compressor and allow the system to provide sufficient cooling with relatively little energy input. On a particularly warm day, the speed of the pump (113) can be accelerated and/or refrigerant can remain in the exchanger a longer time to provide for greater cooling effect on the refrigerant and attempt to provide relatively more cooling via the cooled refrigerant than the phase transition can alone. A sensor (121) can assist with these alterations by monitoring the temperature of the refrigerant. If the temperature is insufficiently cool to meet demand, the system can then alter its operating parameters to try and more greatly cool the refrigerant and vice versa.
There also can be provided a thermostat (123) which can be used to control the system and make sure temperature in the structure (501) is maintained. In an embodiment, the thermostat (123) is connected to a computer network such as, but not limited to, the Internet, and can provide for data on energy usage and energy savings to the user as well as providing for remote temperature management. This may be done in conjunction with feedback from the sensor (121) as contemplated in FIG. 2. One interconnected thermostat (123) which may be used with the system (100) is sold under the brand name Nest™ and functionality of such a device can be used to augment the system (100) by increasing user control and feedback. User control may be provided, as shown in FIG. 2, by providing sensor data via a cloud based web service (401) or similar data transfer service, which can provide data to a variety of user devices (403).
Further, the thermostat (123) can monitor system (100) performance to determine if changes in operation need to be made to obtain appropriate cooling. Thus, if the thermostat (123) determines that the air (215) is not being cooled enough, the thermostat (123) can increase the pump (113) speed to get more colder water in the bath (105). Alternatively, it could slow down the flow of refrigerant through pipe (253) to increase the amount of time that the refrigerant spends in the bath (105).
While the invention has been disclosed in conjunction with a description of certain embodiments, including those that are currently believed to be the preferred embodiments, the detailed description is intended to be illustrative and should not be understood to limit the scope of the present disclosure. As would be understood by one of ordinary skill in the art, embodiments other than those described in detail herein are encompassed by the present invention. Modifications and variations of the described embodiments may be made without departing from the spirit and scope of the invention.

Claims

1. An air cooling system comprising:

a compressor;

a condenser;

a refrigerant, said compressor compressing said refrigerant in said condenser from a gas to a liquid state;

an evaporator, said refrigerant in said evaporator absorbing heat to phase transition from a liquid to a gas; and

a sub cooler, said sub cooler comprising:

an exchanger; and

a container including a liquid bath which is in thermal contact with said exchanger;

wherein, when said refrigerant is in said liquid state, said refrigerant is fed into said exchanger within said liquid bath, said liquid bath cooling said refrigerant; and

wherein, after said refrigerant leaves said exchanger, it is provided to said evaporator.

2. The cooling system of claim 1 wherein said liquid bath is corrosive.

3. The cooling system of claim 1 wherein said liquid bath comprises salt water.

4. The cooling system of claim 1 wherein said exchanger is comprised of marine grade stainless steel.

5. The cooling system of claim 4 wherein said marine grade stainless steel is coated with a polymer.

6. The cooling system of claim 1 wherein said container is placed underground.

7. The cooling system of claim 1 further comprising a sensor attached to said exchanger.

8. The cooling system of claim 1 further comprising a thermostat for controlling said cooling system.

9. The cooling system of claim 8 wherein said thermostat is connected to the Internet.