Patent Application
20110126563
Currently, there are approximately one million ground source geothermal (GSG) systems installed in the U.S., which GSG systems are utilized in a range of government, commercial, and residential contexts. Further, approximately 50,000 residential GSG systems are added each year. The installation cost of GSG systems currently varies with geographic region, but can be as much as $10,000 per ton capacity or more. And, while energy savings are expected with the use of GSG systems as compared to more conventional heating and cooling systems, the payback period for typical GSG systems is estimated to range from 5 to 10 years. It may therefore be desirable to develop a less complex and/or more efficient GSG system, such that the cost of installation and/or the payback period can be reduced.
In a first aspect, a device, such as an absorption chiller sub-system, is provided. The absorption chiller sub-system can include an evaporator and an absorber. The evaporator can be configured to receive a liquid first working fluid and to produce first working fluid vapor. The absorber can be configured to receive and combine first working fluid vapor and a second working fluid, for example, so as to release thermal energy.
A divider having opposing first and second sides in respective fluid communication with the evaporator and the absorber can also be included. For example, the evaporator and the absorber can be respectively coupled to the first side and second sides of the divider. The divider can be configured to allow first working fluid vapor to pass therethrough between the first and second sides and to inhibit movement of liquid first working fluid therethrough between the first and second sides. For example, the divider may define holes therethrough having diameters, say, less than or equal to about 100 nm. In some embodiments, the divider can include a membrane.
The absorber can be configured to combine at least some first working fluid vapor passing through the divider and a second working fluid so as to cause at least some first working fluid vapor passing through the divider to become liquid. In some cases, the absorber can be configured to receive the second working fluid such that an equilibrium second partial pressure of first working fluid vapor at the second side of the divider is less than a first partial pressure of first working fluid vapor at the first side. For example, the evaporator can be configured to receive liquid NH3 as the liquid first working fluid, and the absorber is configured to receive water or a mixture of water and NH3 as the second working fluid.
In some embodiments, the evaporator can be configured such that a total pressure therein is at least twice a partial pressure of first working fluid vapor at the first side of the divider. The absorber can be configured such that a total pressure therein is at least twice a partial pressure of first working fluid vapor at the second side of the divider. Each of the evaporator and the absorber may be configured such that a respective total pressure therein is greater than or equal to about atmospheric pressure.
The evaporator can be configured to receive liquid water and to produce water vapor, and the absorber can be configured to combine water vapor passing through the divider and a relatively concentrated solution containing lithium bromide so to produce a relatively diluted solution containing lithium bromide. The divider can be formed at least partially of substantially hydrophobic material (e.g., polytetrafluoroethylene, polypropylene, or polyvinylidene fluoride) such that holes defined by the divider are defined by the substantially hydrophobic material.
A generator may be included and configured to receive the relatively diluted solution containing lithium bromide from the absorber and to produce separate outputs of water vapor and the relatively concentrated solution containing lithium bromide. A condenser can also be included and configured to receive water vapor from the generator and to provide liquid water to the evaporator. The generator and condenser can be in fluid communication with opposing sides of a second divider that is configured to allow water vapor to pass therethrough and to inhibit movement of liquid water therethrough, such that water vapor from the generator can pass through to the condenser while liquid water in the generator is substantially prevented from reaching the condenser.
A geothermal well, a heat exchanger, and a water heater can also be included. Each of the condenser, absorber, and evaporator can be configured to selectively thermally communicate with the geothermal well and the heat exchanger. In some embodiments, thermal energy may be transferred from the absorber and the condenser into a heated fluid stream, and thermal energy may be transferred from a cooled fluid stream into the liquid first working fluid, with the heated fluid stream being in selective fluid communication with each of the water heater, the heat exchanger, and the geothermal well, and the cooled fluid stream being in selective fluid communication with each of the heat exchanger and the geothermal well. The geothermal well and the heat exchanger may also be configured to selectively exchange thermal energy directly therebetween and to avoid exchanging thermal energy with each of the generator, condenser, evaporator, and absorber.
In another aspect, a method is provided, which includes providing a device including an evaporator, an absorber, and a divider having opposing first and second sides in fluid communication with the evaporator and the absorber, respectively. The divider can be configured to allow first working fluid vapor to pass therethrough between the first and second sides and to inhibit movement of liquid first working fluid therethrough between the first and second sides. Liquid first working fluid (e.g., liquid water) can be provided to the evaporator so as to produce first working fluid vapor (e.g., water vapor) that contacts the first side of the divider. First working fluid vapor passing through the divider from the first side to the second side and a second working fluid (e.g., a relatively concentrated solution containing lithium bromide) can be received at the absorber, and at least some first working fluid vapor passing through the divider can be combined in the absorber with the second working fluid, for example, so as to cause at least some of the first working fluid vapor passing through the divider to become liquid and/or release thermal energy (say, producing a relatively diluted solution containing lithium bromide).
In some embodiments, thermal energy can be supplied to the relatively diluted solution containing lithium bromide so as to cause water to evaporate out and thereby produce the relatively concentrated solution containing lithium bromide. Further, thermal energy can be removed from the water vapor produced from the relatively diluted solution containing lithium bromide so as to produce liquid water to be provided to the evaporator.
In some embodiments, the thermal energy removed from the water vapor produced from the relatively diluted solution containing lithium bromide can be selectively transferred to a heated fluid stream along with thermal energy from the absorber. Thermal energy can also be selectively transferred from a cooled fluid stream to the liquid water circulated to the evaporator. Further, thermal energy can be selectively transferred between the heated fluid stream and at least one of a heat exchanger or a geothermal well, and also between the cooled fluid stream and at least one of the heat exchanger and the geothermal well. In some cases, a target temperature can be selected, and, when the target temperature is higher than a ground temperature of the geothermal well, a geothermal fluid stream can be circulated between the geothermal well and the heat exchanger without receiving the thermal energy removed from the water vapor produced from the relatively diluted solution containing lithium bromide and without exchanging thermal energy with the absorber.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Example embodiments of the present invention are described below in detail with reference to the accompanying drawings, where the same reference numerals denote the same parts throughout the drawings. Some of these embodiments may address the above and other needs.
Referring to
The evaporator 102 can be configured to receive a liquid first working fluid 112a and to produce first working fluid vapor 112b. For example, in one embodiment, the first working fluid 112 may be water, and the evaporator 102 may receive liquid water (for example, through a liquid inlet port 114) and may produce water vapor. Other candidate first working fluids are discussed below. Liquid first working fluid 112a may circulate through the evaporator 102, such that unevaporated portions are outputted from the evaporator, say, at a liquid outlet port 116.
The absorber 104 can be configured to receive first working fluid vapor 112b and to combine at least some of that first working fluid vapor with a second working fluid 118. The second working fluid 118 may circulate through the absorber 104, such that the second working fluid is received, say, at an inlet port 120, travels through the absorber, and exits at an outlet port 122. Given that the second working fluid 118 enters the absorber 104 and then is combined therein with first working fluid vapor 112b, the second working fluid 118a entering the absorber has a relatively lesser concentration therein of first working fluid than does the second working fluid 118b inside and exiting the absorber. The second working fluid 118a entering the absorber 104 at the inlet port 120 is therefore referred to herein as “relatively concentrated second working fluid,” and the second working fluid 118b inside the absorber and exiting at the outlet port 122 is referred to herein as “relatively diluted second working fluid.”
The first and second working fluids 112, 118 may be chosen such that the act of combining first working fluid vapor 112b and the second working fluid causes a release of thermal energy. For example, the absorber 104 can be configured to combine first working fluid vapor 112b and the second working fluid 118 so as to cause at least some first working fluid vapor 112b to become liquid, thereby causing a release of the latent heat of evaporation associated with the vapor. In some embodiments, the second working fluid 118 may include at least one component (an “absorbent”) that tends to form a liquid solution with the first working fluid vapor 112b, such that when the first working fluid vapor comes into contact with the second working fluid, the first working fluid vapor tends to transform into a liquid component of the liquid solution with the absorbent, thereby causing a release of the heat of absorption. In other embodiments, a chemical reaction may occur between the first working fluid vapor 112b and a component of the second working fluid 118, which reaction may be exothermic and/or may induce a transformation of the first working fluid vapor 112b to a liquid, thereby releasing heat of reaction and/or latent heat.
Referring to
The membrane 106 may be configured to allow first working fluid vapor 112b to pass therethrough between the first and second sides 108, 110 and to inhibit movement of liquid first working fluid 112a, and the second working fluid 118, therethrough between said first and second sides. For example, the membrane 106 may define holes 124 therethrough. The holes 124 may be sized in accordance with the properties of the first and second working fluids 112, 118 and those of the material making up the membrane 106 in order to assure that the interfacial energies of liquid first and second working fluids and the membrane are such that the liquid first and second working fluids are energetically prevented from assuming a configuration necessary to pass through the holes in the membrane. Further details regarding the sizing of the holes 124, as well as the selection of the working fluids 112, 118 and material for the membrane 106, are provided below. A general discussion of the use of porous membranes in fluid separation applications is provided in Marcel Mulder, Basic Principles of Membrane Technology (Kluwer Academic Publishers, 1996), which is incorporated herein by reference in its entirety, and also in K. W. Lawson and D. R. Lloyd, “Review Membrane Distillation,” Journal of Membrane Science, 124 (1997), pp. 1-25, which is also incorporated herein by reference in its entirety.
The second working fluid 118 can be chosen such that, when received at the absorber 104 (under appropriate conditions), an equilibrium partial pressure P2 of first working fluid vapor 112b at the second side 110 (and possibly throughout the absorber) is less than a partial pressure P1 of first working fluid vapor at the first side 108 (and possibly throughout the evaporator 102). For example, the first and second working fluids 112, 118 can be chosen such that the second working fluid includes as a component thereof a liquid that has a strong affinity for the first working fluid. In such a case, the equilibrium partial pressure P2 of the first working fluid vapor 112b in the vicinity of the second working fluid 118 will tend to be low relative, say, to the partial pressure P1 expected in the vicinity of liquid first working fluid 112a. Examples of pairs of first and second working fluids 112, 118 that may be utilized in conjunction with embodiments of the above described absorption chiller sub-system 100 include, but are not limited to, water and lithium bromide; NH3 and water (or a mixture of water and NH3); water and LiClO3; water and CaCl2, water and ZnCl2; water and HnBr; water and H2SO4; and SO2 and organic solvents.
The difference in partial pressures P1 and P2 of first working fluid vapor 112b across the membrane 106 results in a driving force for diffusion of first working fluid vapor from the first side 108 to the second side 110. Once first working fluid vapor 112b reaches the second side 110, it can be combined in the absorber 104 with the second working fluid 118, with this combination being made more likely by the proper choice of a second working fluid having an affinity for first working fluid. Mass (i.e., first working fluid 112) will therefore be transferred from the evaporator 102 to the absorber 104. In addition, as mass is transferred from the evaporator 102 to the absorber 104, the balance in the evaporator between liquid first working fluid 112a and first working fluid vapor 112b will be disrupted, driving further evaporation of liquid first working fluid. It is noted that continued evaporation of liquid first working fluid 112a in the evaporator 102 does not necessarily require the input of energy, but instead may proceed simply due to the affinity of the second working fluid 118 for first working fluid.
As liquid first working fluid 112a evaporates in the evaporator 102 to form first working fluid vapor 112b, thermal energy is absorbed from the liquid first working fluid and used to overcome the latent heat of evaporation of the first working fluid 112. As the first working fluid vapor 112b moves through the membrane 106 and is combined in the absorber 104 with the second working fluid 118 to form a liquid, thermal energy in the form of latent heat of evaporation and/or absorption can be released (as well as heat produced by any exothermic chemical reactions that may take place between the first and second working fluids). The overall result is a thermal energy transfer, associated with the mass transfer, from the liquid first working fluid 112a in the evaporator 102 to the second working fluid 118 in the absorber 104. The membrane 106 can be configured such that the surface area presented to the first working fluid 112 at the first side 108 and to the second working fluid 118 at the second side 110 is sufficient to facilitate a desired level of thermal energy transfer.
With the evaporator 102 and the absorber 104 separated by the membrane 106 as discussed above, it may not be required that the total pressure within either of the evaporator or the absorber is approximately the same as the respective partial pressure therein of first working fluid vapor 112b, as may have been the case for previous absorption chiller sub-systems. Rather, the evaporator 102 may be configured such that the total pressure therein is at least twice the partial pressure P1 of first working fluid vapor 112b. Further, the absorber 104 may be configured such that the total pressure therein is at least twice the partial pressure P2 of first working fluid vapor 112b. As such, embodiments of the absorption chiller sub-system 100 may have a total size and weight that is significantly reduced with respect to previous absorption chiller sub-systems.
For the first working fluid vapor 112b to be driven from one side of the membrane 106 to the other, particular temperatures and pressures are needed. As mentioned above, the evaporation of liquid first working fluid 112a in the evaporator 102, the diffusion of first working fluid vapor 112b from the first side 108 of the membrane 106 to the second side 110, and the absorption of first working fluid vapor (or other energy-releasing event) in the absorber 104 can proceed spontaneously, acting to transfer thermal energy from the evaporator to the absorber. However, as thermal energy is transferred, the temperature of the liquid first working fluid 112a (in the absence of any other energy transfers) will drop, thereby reducing (and eventually eliminating) the tendency for further evaporation. At the same time, the temperature of the second working fluid 118 (again, in the absence of any other energy transfers) will rise, thereby decreasing (and eventually eliminating) the tendency of first working fluid vapor 112b therein to be absorbed. It is noted that, in some embodiments, the membrane 106 may include a thermally insulating material, thereby preventing the transfer of heat therethrough from the absorber 104 to the evaporator 102.
Referring to
Referring to
The first working fluid vapor 112b outputted from the generator 142 can be directed to a condenser 148. The condenser 148 can receive the first working fluid vapor 112b and to provide liquid first working fluid 112a to the evaporator 102. For example, thermal energy 150 can be removed at the condenser 148, say, through the use of a heat exchanger, in order to cause the first working fluid vapor 112b to condense.
Overall, the evaporator 102, absorber 104, generator 142, and condenser 148 may operate so as to form a continuous cycle in which the second working fluid 118 is combined with first working fluid 112 at the absorber and separated from first working fluid at the generator, and first working fluid is converted from gas to liquid at the condenser and from liquid to gas at the evaporator. The system 140 acts to affect the transfer of thermal energy from a source 126 to a sink 128. The only input of energy that may be required to sustain the operation of the system 140 is the thermal energy 146 that is directed to the generator 142 (and a small amount of energy required to circulate the second working fluid 118, for example, through the operation of the pump 144), which thermal energy may be supplied by, for example, the exhaust of an internal combustion engine, engine fluid such as water/glycol or oil, a burner, a solar collector, and/or the exhaust of a gas turbine.
Referring to
The membrane 206 can define holes 224 that extend between the evaporator 202 and the absorber 204. The membrane 206, or at least the portions through which the holes 224 are defined, may be formed of substantially hydrophobic material (e.g., polytetrafluoroethylene, polypropylene, and/or polyvinylidene fluoride). By forming the holes 224 with a maximum diameter of about 100 nm from a substantially hydrophobic material, the movement of liquid water 212a through the membrane 206 is substantially prevented, due to the surface energy effects discussed above, while water vapor 212b is permitted to pass through the holes between the evaporator 202 and absorber 204. As mentioned earlier, in some embodiments, the membrane 206 may be formed of thermally insulating material, with examples being the hydrophobic materials listed above.
The absorption chiller sub-system 200 can also employ a solution of lithium bromide and water 218 as the second working fluid. The absorber 204 can be configured to combine water vapor 212b passing through the membrane 206 with the lithium bromide-water solution 218a entering at an inlet port 220, thereby forming in the absorber a lithium bromide-water solution 218b that is relatively diluted with respect to lithium bromide content (the solution previously being relatively concentrated with respect to lithium bromide content prior to being combined with water vapor passing through the membrane 206). Lithium bromide tends to have a strong affinity for water, such that the partial pressure of water vapor in the vicinity of lithium bromide tends to be relatively low and the diffusion of water vapor through the membrane 206 is facilitated.
As mentioned above, the use of a membrane 206 between the evaporator 202 and absorber 204 may alleviate the need to maintain the total pressure in either of the evaporator or the absorber at a level that is about equal to the partial pressure of water vapor in either one. Specifically, each of the evaporator 202 and the absorber 204 may be configured such that a respective total pressure therein is greater than or equal to about atmospheric pressure. This may reduce the size, cost, and/or complexity of the evaporator 202 and absorber 204. In other embodiments either the evaporator 202 or the absorber 204 may be configured to operate either above or below atmospheric pressure.
The absorption refrigeration system 240 can also include a generator 242, which can receive the relatively diluted lithium bromide-water solution 218b from the absorber 204 (e.g., the relatively diluted lithium bromide-water solution exiting the absorber at the outlet port 222) and thermal energy 246 from an external source (not shown) to heat the diluted lithium bromide-water solution so as to produce separate outputs of water vapor 212b and the relatively concentrated containing lithium bromide-water solution 218a that is ultimately received at the inlet port 220. The lithium bromide-water solution 218 can be circulated between the absorber 204 and the generator 242, say, through the use of a pump 244.
As the absorption refrigeration system 240 operates, thermal energy can be transferred from the evaporator 202 to the absorber 204. The thermal energy deposited at the absorber 204 can then be rejected, say, to the ambient environment or some other energy sink. A cooled water stream 230 can be disposed in thermal contact with the evaporator 202, and thermal energy can be transferred from the cooled water stream to the evaporator (e.g., to the water 212a therein), thereby affecting (in the absence of other thermal transfers) a temperature decrease in the cooled water stream.
The water vapor 212b outputted by the generator 242 can be directed to a condenser 248, at which thermal energy can be removed from the water vapor in order to produce liquid water 212a. The liquid water 212b can then be directed to the evaporator 202 to repeat the cycle. A heated water stream 262 can be disposed in thermal contact with the condenser 248 such that the thermal energy extracted from the water vapor 212b is transferred (at least in part) to the heated water stream, thereby affecting (in the absence of other thermal transfers) a temperature increase in the heated water stream.
The heated water stream 262 can be circulated to each of a geothermal well 264, a water heater 266, and a heat exchanger 268 (the last of which may be used, for example, as a space heater/cooler) via manifolds 270. Thermal energy in the heated water stream 262 (received, for example, at the condenser 248) can then used to produce heat and hot water for residential or commercial use via the heat exchanger 268 and water heater 266, respectively, and/or can be rejected at the geothermal well 264. The heated water stream 262 can be connected to the geothermal well 264 and the heat exchanger 268 with valves 272 that allow the heated water stream to be selectively directed to or away from each of the geothermal well and the heat exchanger. In this way, heat can be provided via the heat exchanger only when desired (e.g., in the winter). In some embodiments, the heated water stream 262 may also be disposed in thermal communication with the absorber 204, such that thermal energy rejected at the absorber may be used to heat the heated water stream.
The cooled water stream 230 can be circulated to each of the geothermal well 264 and a heat exchanger 268 (the last of which may be used, for example, as a space heater/cooler) via manifolds 274. Thermal energy can then be transferred to the cooled water stream 230 at the heat exchanger 268 in order to provide ambient cooling or at the geothermal well 264 (with the thermal energy ultimately being rejected, for example, at the evaporator 202). The cooled water stream 230 can be connected to the geothermal well 264 and the heat exchanger 268 with valves 272 that allow the cooled water stream to be selectively directed to or away from each of the geothermal well and the heat exchanger. In this way, cooling can be provided via the heat exchanger only when desired (e.g., in the summer).
Valves 276 may be included that function so as to selectively create a geothermal fluid circulation loop 278 that allows fluid (a “geothermal fluid stream”) to circulate directly between the geothermal well 264 and the heat exchanger 268, this loop being otherwise isolated from the absorption refrigeration system 240. When the valves 276 are so positioned to isolate the fluid circulation loop 278 from the absorption refrigeration system 240, the geothermal well 264 and heat exchanger 268 may exchange thermal energy directly therebetween (via the geothermal fluid stream in the geothermal fluid circulation loop) without exchanging thermal energy with any of the generator 242, condenser 248, evaporator 202, and/or absorber 204.
The valves 276 may allow the heating and cooling system 260 to be operated more efficiently, under certain conditions, by foregoing the use of the absorption refrigeration system 240, the use of which requires some energy input at the generator 242. For example, considering the use of the heat exchanger 268 as a residential air conditioning unit for cooling a home, during summer months, the temperature of the ground surrounding the geothermal well 264 may be lower than a desired air temperature (a “target” temperature) for the home. In that case, the valves 276 can be adjusted to cause the geothermal fluid stream to circulate (say, with the help of a pump 279) directly between the geothermal well 264 and the heat exchanger 268, without interacting with the absorption refrigeration system 240. At these times, operation of the absorption refrigeration system 240 can be ceased entirely, avoiding the expenditure of energy otherwise required to operate that system. The heating and cooling system 260 can be configured to automatically switch between this “direct geothermal mode” of operation and the absorption refrigeration mode of operation in response to the ground temperature of the geothermal well 264 and a user-selected target temperature.
Referring to
The absorption refrigeration system 340 can also include a generator 342 and a condenser 348 each in fluid communication with opposing sides of a second membrane 306b. The second membrane 306b, like the first membrane 306a, can be configured to allow first working fluid vapor to pass therethrough and to inhibit movement of liquid first working fluid therethrough. The generator 342 can receive the relatively diluted second working fluid 318b being outputted from the absorber 304. Thermal energy 346 can be provided to the relatively diluted second working fluid 318b so as to cause first working fluid vapor 312b to be released from the second working fluid, thereby producing relatively concentrated second working fluid 318a that can be directed to the absorber 304. The first working fluid vapor 312b released from the second working fluid 318 can then pass through the second membrane 306b to the condenser 348, where thermal energy 350 can be removed to transform the vapor to liquid first working fluid 312a.
Referring to
The barrier 490 can be a relatively simple structure, such as a mesh, that is relatively permeable to liquids. Penetration of liquid first working fluid 412a from the evaporator 402 through the barrier 490 can be substantially prevented by configuring the absorption chiller sub-system 400 such that the liquid first working fluid entering the evaporator at the inlet port 414 has a relatively low hydrostatic pressure and a velocity V directed substantially parallel to the barrier. In this way, the liquid first working fluid 412a in the evaporator 402 would be expected to have a small (nearly zero) velocity component directed toward the barrier 490.
The vapor gap 494 may affect a decrease in the rate at which thermal energy is transmitted from the (potentially hotter) absorber 404 to the (potentially colder) evaporator 402. Conduction across the vapor gap 494 will be substantially limited to the energy transferred between colliding gaseous molecules, which process is expected to be substantially less efficient than conduction through a solid body. The vapor gap 494 may also result in a reduction in the mass transfer rate between the evaporator 402 and the absorber 404, causing a corresponding loss in thermal transfer efficiency from the evaporator to the absorber.
Referring to
As mentioned above, in order to assure that the liquid does not penetrate the barrier 490, 590, the hydrostatic pressure of the fluid contacting the barrier should be relatively small. Referring to
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. For example, while absorption refrigeration systems have been described that incorporate an evaporator and absorber coupled across a porous membrane and utilized in conjunction with either a conventional generator and condenser or a generator-condenser combination in which the generator and condenser are coupled across a porous membrane, it is also possible to utilize a generator-membrane-condenser combination with a conventional evaporator and absorber. Finally, while single stage or “single effect” absorption refrigeration systems have been described above, the concepts disclosed herein are also amenable to use in “multiple effect” or cascaded systems, in which the thermal energy that is outputted from one thermal cycling system (say, at the absorber and/or condenser) acts as the driving force for another thermal cycle (say, being the input to the generator). It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
