Patent Application
20050193758
1. Field of the Invention
The subject invention relates to a system and method for selective heating and cooling. In particular, the present invention directs itself to a system utilizing a refrigerant and absorbant mixture composition held within an absorption tank. More particularly, a boiler is provided for heating the mixture composition such that the boiler vaporizes the refrigerant and the liquid absorbant is delivered back into the absorption tank for reuse. Further, the vaporized refrigerant is delivered to a closed-loop thermal exchange system for selectively heating and cooling ambient air.
The present invention system and method further directs itself to providing a novel mixture of refrigerants and an absorbant composition allowing the system to act as both a heating and cooling system. More particularly, the mixture of refrigerants and the absorbant provide an environmentally friendly composition, which further allows the system to be hermetically sealed. Additionally, the heating and cooling system may further be utilized as a power generation system.
Furthermore, the inventive mixture of refrigerants have pressure and corrosion characteristics that advantageously allow the utilization of lower-cost aluminum heat exchangers. The aluminum heat exchangers may also be surface-treated, such as by anodization or passivation, particularly on those surfaces exposed to the refrigerant mixture to further protect the heat exchanger and thereby extend the usable lifetime thereof. The use of aluminum components in the boiler fluid circuit of the present invention is a clear advantage of the present invention over existing high-pressure ammonia-water absorption systems.
The system and method of the present invention is further directed to the use of a refrigerant consisting of substantially pure 1, 1, 1, 3, 3 pentafluoropropane (HFC-245fa) and an absorption material consisting of substantially pure n-methyl, 2-pyrrolidone (NMP) with small amounts (ranging within 0.1-1% by volume) of one or more stabilizers selected from the group of nitroalkanes such as nitromethane, phosphates such as tributyl phosphate, zinc dithiophosphate, or other stabilizers. Furthermore, the present system employs the additional steps 1) passivation and 2) silicone sealing of the aluminum system components to make these stabilizers even more effective.
2. Brief Description of the Prior Art
Heating and cooling systems are well-known in the art. In general, such prior art systems generally utilize two different sets of heating and cooling sub-systems. The system of the subject patent application, however, provides for a single closed-loop thermal exchange system allowing selection of a heating cycle or a cooling cycle, where both cycles involve common system components in their respective executions. The system is sealed and utilizes heating/cooling solution mixtures which may be reused in the heating and cooling cycles.
Given present thermal exchange systems, a need exists in the market for a system that produces a heat pump or cooling effect, or producing both electric power and a cooling effect utilizing heat input. The system should be both efficient and inexpensive. Such a system would preferably use substantially “off-the-shelf” components. For example, stock automotive fuel pumps might act as a system liquid pump. Stock air conditioning electric refrigeration compressors, particularly of the scroll type, might act as the system expander/power producing element if the scroll compressor were modified by simply removing the check valve that is installed in typical air conditioning service. The present inventive system concept is directed to utilizing such “off-the-shelf” components and, in particular, is directed at a novel and unique selection of working fluid and absorption materials which are compatible with the system components.
Systems utilizing isoparaffins as absorption materials for use with butane refrigerants are well-known in the art. The present system provides an improvement over prior art systems in that it employs working fluid refrigerants, which are both non-flammable and non-toxic, and absorption materials which have an advantageously high boiling point. The refrigerant and absorption materials are chemically non-reactive with lower-cost construction materials designed for medium-pressure systems, such as lightweight aluminum heat exchangers. The ability to incorporate lower-cost materials such as aluminum into the boiler fluid circuit of the present invention is a significant advancement over similar systems of the prior art. Moreover, as the refrigerants utilized by the present system are non-flammable and operate at only moderate pressure, operational safety is enhanced.
Systems implementing scroll compressors which are run in reverse as expansion engines are known. Among the many advantageous features of the present system is the use of such an expansion engine to drive an electric power generation system. Thus, some of the energy dissipated to the surrounding environment during expansion by prior art systems is converted by the inventive system into electric power.
The present invention provides for a combined heating/cooling system. The heating/cooling system utilizes a refrigerant and absorbant mixture composition held, initially, in an absorption tank. A pump in fluid communication with the absorption tank pressurizes the mixture composition and delivers it to a first heat exchanger. A boiler is provided for receiving the high pressure mixture composition, with the boiler vaporizing the refrigerant and delivering the liquid absorbant back into the absorption tank for later reuse. The vaporized refrigerant is delivered to a closed-loop thermal exchange system for selective heating and cooling of ambient air.
It is a principal objective of the subject heating/cooling system to provide an optimized refrigerant and absorbant mixture composition.
It is a further objective of the subject heating/cooling system to provide a boiler for heating a high pressure mixture composition in order to vaporize the refrigerant component of the mixture.
It is a further objective of the subject invention to provide means for retrieving the liquid absorbant from the boiler in order to reuse the absorbant in the absorbant/refrigerant mixture.
It is yet a further objective of the present invention to provide a closed-loop thermal exchange system for selectively heating and cooling ambient air.
It is a further objective of the present invention to provide a closed-loop thermal exchange system utilizing HFC-245fa as a refrigerant.
It is another objective of the present invention system to provide NMP as an absorption material.
It is yet a further objective of the present invention system to provide improved compatibility of the working fluid mixtures to aluminum component parts, such as aluminum heat exchangers, by providing relatively low corrosion characteristics and lower operating pressure. It is a further objective of the present invention to subject the aluminum components to surface treatments to extend system lifetime over that of untreated aluminum components alone.
I. Overview
Referring to
The vaporized refrigerant may pass into a power generation sub-system 70. In power generation sub-system 70, the vaporized refrigerant flows into a scroll expander 80, causing the scroll expander 80 to rotate and drive generator 90 via the rotation of shaft 100. The power generation sub-system 70 is optional and may be bypassed, with the vaporized refrigerant passing directly into a closed-loop thermal exchange system for selectively heating or cooling ambient air. The closed-loop thermal exchange system will be discussed, for both a heating cycle and a cooling cycle, in greater detail below.
II. Exemplary Embodiment for Hybrid Organic Absorption/Rankine Scroll Electric System Based on HFC-245fa and NMP
The thermal exchange system 500 shown in
The absorption material and refrigerant mixture, in certain beneficial embodiments, consists substantially of pure n-methyl, 2-pyrrolidone (NMP) with small amounts (in the range of 0.1-1% by volume) of one or more stabilizers selected from the group of nitroalkanes, such as nitromethane, phosphates such as tributyl phosphite, zinc dithiophosphate, or other suitable stabilizer.
As an alternative, a polyglycol dibutyl ether, such as Genosorb® 1843, may be utilized as the absorbant. An advantageous characteristic of Genosorb®1843 is that it physically absorbs non-polar compounds, such as aromatics and hydrocarbons. The specific compositions for the absorbant and refrigerant are further discussed in Section V of the application, related to the specific compositions.
Referring to
The mixture is delivered to a counter-flow liquid-liquid heat exchanger 530, where the mixture is pre-heated. When the mixture exits heat exchanger 530, the mixture has a temperature of approximately 90° C.
The mixture is delivered to boiler 540, which boils the mixture of refrigerant and absorbant at a pressure of approximately 30-70 psia. Because the HFC-245fa is dissolved in the NMP, it is maintained at a pressure lower than that of pure HFC-245fa at the same temperature. As HFC-245fa is removed from the mixture by evaporation, the solution must be heated to a higher temperature in order to continue to drive the HFC-245fa out. Optimally, the liquid mixture exiting the boiler contains HFC-245fa in a concentration of approximately 10-20%. As shown in
Superheated dry HFC-245fa vapor exits the boiler 540 and is delivered to the scroll expander 550. The superheated HFC-245fa enters the scroll expander and expands with a volumetric expansion ratio of approximately 3. Due to the properties of HFC-245fa, the pressure ratio achieved is approximately 3.0.
The HFC-245fa temperature upon exit from the scroll expander 550 has dropped, at this point in the cycle, to approximately 70° C. The lower temperature HFC-245fa vapor may be used, in certain embodiments of the invention, to cool the windings of electric generator 560, which is coupled to scroll expander 550 by shaft 570. The shaft-driven generator 560 may be used to generate electrical power. The generator 560 is, in certain embodiments, cooled by the ambient air in which it is operated.
In order to improve the lifetime of system 500, a portion of the cooled NMP absorption composition, which has exited boiler 540 and re-entered heat exchanger 530, is routed through a regulator valve 580 so as to meter out a small portion of the composition material into scroll expander 550, thereby providing lubrication thereto.
NMP is chosen as a preferred absorbant in certain embodiments because NMP compositions exhibit exceptional thermally stability. However, NMP also has a relatively high electrical conductivity. As a result, scroll expander 550 is preferably coupled to electrical generator while separated from the system working fluids via a hermetic shaft seal. The shaft seal may be constructed of either silicone rubber or butyl rubber, both of which show excellent resistance to both the NMP and the HFC-245fa.
The thermal stability of the absorbant/refrigerant mixture can be substantially improved by adding certain well-known chemical additives. For example, the additive may be a phosphate, a phosphite, a borate, or a zinc dialkyldithiophosphate (ZDDP) compound, such as OLOA 262, manufactured by the Chevron Corporation. The additives may also be any of the many well-known oil anti-oxidants. These oil additives act to coat surfaces of metal and reduce the tendency of the metal surfaces to catalyze the reaction of the decomposition of the adsorption material and the refrigerant.
The performance of such additives described above, particularly when aluminum is employed, is dramatically enhanced by first pre-treating the aluminum surfaces, such as by chromate conversion with, for example, well-known Alodine® treatment, by anodization, or by passivation techniques including, but not limited to: fluorine treatment, ozone treatment, nitric acid treatment, vanadate treatment, or sol-gel surface treatment. Surface treatment of system components is discussed further below in Section VIII.
Returning to the system 500 of
Returning to the scroll expander 550, HFC-245fa vapor exits the scroll expander 550 at approximately 2-6 atmospheres of pressure. This relatively moderate pressure allows the main condenser 600 to be compact. The condenser may be cooled by air or water, shown by arrow 650. The refrigerant vapor exits the scroll expander 550 and enters condenser 600, where the refrigerant is converted to a liquid by the cooling action of condenser 600. The cooled and condensed liquid HFC-245fa exits the condenser and is directed to a refrigeration expansion valve 610, where the liquid steps down in pressure to approximately 0.5-2.5 atmospheres. The depressurized liquid exits the expansion valve 610 and enters evaporator 620. Evaporator 620 converts the liquid refrigerant to a vaporized refrigerant. The vaporization process is endothermic thereby effecting a cooling of the air or water flowing through evaporator 620, as illustrated by the arrows 640. The cooled air or liquid 640 exiting evaporator 620 can be routed through a home, building, or other edifice, thus providing a cooling effect.
The absorption tank 510 may be provided with an air-cooled contactor to allow intimate mixing of the HFC-245fa vapor and the cool, concentrated NMP absorption solution. The vaporized refrigerant is drawn from evaporator 620 back into the absorption tank 510, containing the air-cooled contactor. The absorption tank 510 further holds the liquid absorbant drawn from the boiler 540 and through valve 590.
The adsorption process of the vaporized refrigerant mixing with the liquid absorbant produces heat, and a fluid material such as air or water flows through the contactor, illustrated by the arrows 630, in order to remove this excess thermal energy. Typically, the contactor performance is improved by operating at as low a temperature as possible. Thus, the air or other fluid 630 entering the contactor within absorption tank 510 is preferably cooled first by, for example, a wick-type water evaporation cooler.
After entering the contactor, the NMP material and HFC-245fa have formed the original mixture, which began the cooling cycle, and the mixture, once again, exits the contactor to enter pump 520, thus restarting the cycle.
Due to the fact that the HFC-245fa is superheated and expanded at a pressure ratio of approximately 3, the thermodynamic efficiency of the scroll Rankine cycle is expected to be between 7 and 10%. Higher efficiency results if the condenser 600 is operated on a cool day.
As an absorption system, the expected coefficient of performance of system 500 is similar to any other efficient single-effect absorption unit, i.e., approximately 0.6-0.9.
If the electric power produced by generator 560 is produced at an efficiency of approximately 7 to 9%, and is coupled to an electric compressor and used with conventional equipment with an electrical-to-cooling coefficient of performance (COP) of approximately 3.0, the net effect of the overall system in terms of COP is the sum of the absorption unit, 0.6, and the Rankine/electric unit, 0.4, thus giving a net system COP of approximately 1.0.
It should be noted that the boiler temperature of system 500 is substantially higher than would be required of the system operating with only pure HFC-245fa as the working fluid.
Pump 520 may be a chemically compatible centrifugal pump, such as a polypropylene magnetically-coupled pump. Furthermore, the centrifugal pump may be operated in an intermittent mode by providing a check valve after the pump, and a hydraulic accumulator on the high-pressure side of the system.
III. Cooling Cycle
The liquid refrigerant is passed through a second expansion valve 140 where the pressure of the liquid refrigerant is dropped to slightly below atmospheric pressure. The depressurized liquid refrigerant passes from the second expansion valve 140 into a second liquid-vapor converter 150. The second liquid-vapor converter 150 re-vaporizes the liquid refrigerant and passes the vaporized refrigerant through a second selector valve 120, which in the cooling cycle, passes the vaporized refrigerant back into absorption tank 20 to form the refrigerant and absorbant mixture composition.
A salt or brine solution is provided with the brine solution passing through liquid-vapor converter 130. When the vaporized refrigerant condenses into the liquid refrigerant within liquid-vapor converter 130, the heat of the vaporized refrigerant is released. This heat is used to heat the brine solution. This heated brine solution then passes into a first air-to-liquid contactor member 170.
When the cooling/heating system 10 is installed in a home or other edifice, the first air-to-liquid contactor member 170 is positioned external to the edifice. Ambient or environmental air is drawn into the first air-to-liquid contactor member 170 and the heated brine solution causes the ambient air to be heated, with the air-to-liquid contactor member 170 expelling heated air into the environment. A fan or blower (not shown) may be used to force air through air-to-liquid contact member 170.
The now-cooled brine solution is driven through second heat exchanger 160 by fluid pump 180. The second heat exchanger 160 further cools the brine solution as it is being drawn therethrough by pump 180. The cooled brine solution is then passed into second liquid-vapor converter 150.
The second liquid-vapor converter 150 vaporizes the liquid refrigerant, thus requiring thermal energy to be added thereto. This thermal energy comes from the brine solution driven by pump 180, the transfer of which causes the brine solution to be further cooled as it passes through second liquid-vapor converter 150.
This cooled brine solution is then driven through second air-to-liquid contactor 190. When the cooling/heating system 10 is installed in a home or other edifice, the second air-to-liquid contactor 190 is installed within the home or edifice and draws in ambient air. The ambient air is cooled by the now-cooled brine solution passing through contactor 190, thus allowing the second air-to-liquid contactor 190 to provide cooled air to home or edifice. Again, as was indicated for air-to-liquid contactor member 170, a fan or blower (not shown) may be installed adjacent to contactor 190 to force air therethrough.
The brine solution passes from the second air-to-liquid contactor 190 through absorption tank 20, thus heating the brine solution, where it can then be passed through second heat exchanger 160 in order to start the cycle over again.
The heat of condensation of the vapor is transferred to the brine solution passing through condenser 130. As the brine enters the condenser 130, the brine is somewhat water-saturated, and that water-saturated brine is heated by the action of the condenser. When the brine exits condenser 130, it is heated and enters the liquid contactor 170. The air-to-liquid contactor 170 may be constructed of a honeycomb absorptive paper or other similar kind of pad material. Since the brine, at this point, is heated, the brine loses water to the ambient air such that the air exiting the contactor 170 is saturated with water vapor and is further heated. Thus, brine solution exiting contactor 170 is substantially depleted of water and has a far higher concentration of salt. Upon entering the heat exchanger 160, the brine solution transfers its remaining thermal energy to the incoming water-rich brine solution, thus pre-heating the water-rich brine within heat exchanger 160.
When the water is depleted, brine solution exits heat exchanger 160 in a near ambient-temperature state, where upon it enters brine pump 180. Brine pump 180 directs the brine solution into liquid-vapor converter 150 and as the refrigerant is evaporated, the brine is cooled well below room temperature so that the brine exits on the right-hand side of 150 (in
When the brine solution enters contactor 190, which is located within the building or edifice, the air from the building is blown over the high concentration salt water brine and the air from the building gives up its moisture to the cold brine solution, thus effecting both dehumidification and cooling on the air going through the contactor 190.
Upon exiting contactor 190, the brine solution is slightly cooled and water-rich, where it is then directed to the absorption tank 20. The heat of absorption is removed by the brine solution in the absorption tank 20, and the brine solution exits absorption tank 20 at a temperature of approximately 100° F. The brine solution then flows back into heat exchanger 160 to start the cycle over again.
IV. Heating Cycle
An exemplary heating cycle of certain embodiments of cooling/heating system 10 is shown diagrammatically in
The second selector valve 120 directs the vaporized refrigerant through liquid-vapor converter 150. The second liquid-vapor converter 150 acts, essentially, as a condenser and converts the vaporized refrigerant to a liquid refrigerant. The liquid refrigerant is then passed through the second expansion valve 140 where it is depressurized.
The newly-depressurized liquid refrigerant is then driven through the first liquid-vapor converter 130 where the refrigerant is re-vaporized. The re-vaporized refrigerant then passes back through first selector valve 110 where it is directed to second selector valve 120. Second selector valve 120 passes the vaporized refrigerant back into absorption tank 20, where it mixes with the absorbant to form the refrigerant and absorbant mixture composition.
When the liquid refrigerant passes through the first liquid-vapor converter 130, thereby vaporizing the liquid refrigerant, an addition of thermal energy is required. This energy is provided by the brine solution as it passes through the liquid-vapor converter 130.
The now-cooled brine solution passes through the first air-to-liquid contactor member 170. When the cooling/heating system 10 is installed in a home or other edifice, the first air-to-liquid contactor member 170 is positioned external to the home or edifice. Ambient air is drawn through the first air-to-liquid contactor member 170 and the cooled brine solution causes the air-to-liquid contactor member 170 to expel cooled air, thereby heating the brine solution.
The now-heated brine solution is passed through second heat exchanger 160, which heats the brine solution. The heated brine solution is driven by pump 14 into second liquid-vapor converter 150. As the vaporized refrigerant passes through second liquid-vapor converter 150, converting the vaporized refrigerant into a liquid, thermal energy is transferred to the brine solution, which is then driven into second air-to-liquid contactor member 190.
When the cooling/heating system 10 is installed in a home or other edifice, the second air-to-liquid contactor member 190 may be installed therein. The heated brine solution in the second air-to-liquid contactor 190 heats the air drawn therethrough. The heated air is then provided to the home or edifice.
From the contactor member 190, the brine solution passes back through absorption tank 20, where it is further cooled. The brine solution is transferred back to heat exchanger 160 whereupon a new cycle may begin.
In the heating cycle, the condensing vapor in liquid-vapor converter 150 gives up its heat to the water-rich brine entering the converter 150. The water-rich brine is heated at this point. Similarly, the evaporator 130 of the heating cycle chills the concentrated brine solution. The concentrated brine at this point is quite cold and exits the liquid-vapor converter 130, flowing into the ambient air-to-liquid contactor 170 (similar to the flow of the cooling cycle) in its cold state and, further, depleted of water. Ambient air in the air contactor 170 flows over the cold and water-depleted brine solution, allowing the brine solution to absorb heat and absorb water vapor from the ambient air, thus resulting in a heated brine solution with an increased water content.
The brine solution exits the contactor 170 and enters heat exchanger 160, which acts to pre-heat the brine solution as it is pumped from the upper left-hand side (referring to
V. Specific Compositions of Absorbant and Refrigerant
The absorbant, in certain embodiments, consists substantially of pure NMP with small amounts (ranging from 0.1-1% by volume) of one or more stabilizers selected from the group of nitroalkanes, such as nitromethane, phosphates such as tributyl phosphate, zinc dithiophosphate, or other stabilizers. The absorbant may, in the alternative, be a liquid polymer containing triethylene glycol dibutyl ether. A polyglycol dibutyl ether, such as Genosorb® 1843 may also be utilized. Genosorb® 1843 is hydrophobic and contains a stabilizer and is used to physically absorb nonpolar compounds, such as aromatics and hydrocarbons. Genosorb® 1843 is a product of the Clariant Corporation of Mount Holly, N.C.
The refrigerant may be a hydrofluorocarbon or a hydrochlorofluorocarbon refrigerant composition. The refrigerant may consist of HFC134a, HFC245fa, or a combination of the two. In certain embodiments, the refrigerant is substantially pure HFC-245fa. Further, the refrigerant may be any of the following compounds: trichlorofluoromethane, dichlorodifluoromethane, chlorodifluoro-methane, difluoromethane, 1,1,2-trichlorotrifluoroethane, 1,2-dichlorotetra-fluoroethane, chloropentafluoroethane, 1,1,1,2-tetrafluoroethane, 1,1-dichloro-1-fluoroethane, 1,1-difluoroethane, and methylene chloride.
When the absorbent is not NMP, the refrigerant may be selected from the above group based upon the refrigerant's affinity for the selected absorbant. For example, the substances chlorodifluoromethane, difluoromethane, and methylene chloride are non-NMP refrigerants having the highest affinities for Genosorb® 1843.
The refrigerant may further be a mixture of 10% 1,1-difluoroethane (R152a) and 90% 1, 1, 1, 3, 3-pentafluoropropane (R245fa).
The ozone depletion potential (ODP) and global warming potential (GWP) of various refrigerants is a key issue of concern. R245fa may be used as a low ODP working fluid in a Rankine power cycle. However, R245fa has a substantial GWP of around 990 in comparison to carbon dioxide. Additionally, R245fa is non-flammable. Thus, the possibility exists for using R245fa as a refrigerant, but it has a boiling point of around 15° C., which is generally considered to be too high for most air conditioning applications, where the typical evaporation temperature is desired to be around 10° C.
R152a, or HFC 152a, has the advantage of having zero ODP and a GWP of 140. However, HFC 152a is a flammable gas. A container of pure HFC 152a can easily be ignited and the product of ignition is the hazardous material hydrogen fluoride, which is harmful to humans and is also corrosive. Pure R152a has low toxicity and its OSHA limit of exposure is equal to other non-toxic Freon gases; i.e., approximately 1000 ppm. However, in a mixture ratio of approximately 5% to 25% of R152a with approximately 95% to 75% R245fa, with the most preferable ratio being approximately 10% R152a and 90% R245fa, the mixture of R152a and R245fa produces an optimal refrigerant mixture. The mixture is essentially non-flammable, i.e., far less flammable than R152a on its own, and the mixture has a substantially lower boiling point than R245fa on its own. In the ratio described above, the mixture has a boiling point of approximately 2° to 4° C. Additionally, the vapor pressure of the mixture is slightly above atmospheric pressure, over the “glide” range, of approximately 30 to approximately 10° C. Moreover, both R152a and R245fa are absorbed efficiently by the Genosorb® 1843.
The GWP of the mixture is substantially lower than the GWP of pure R245fa and when used in conjunction with Genosorb® 1843, the resulting system pressure is slightly below atmospheric pressure during times when the system is not in operation. Thus, the loss of the mixture is essentially zero during the time of non-operation, which represents the vast majority of hours over the life of a typical air conditioning system.
The vapor pressure of the refrigerant mixture is higher than the vapor pressure of pure R245fa, thereby increasing the mechanical output power of the expander device 80 of system 10. This results in a lower cost of generated electrical power by generator 90 and thus a more economical system.
The proportions of the refrigerant mixture can be optimized for particular locations. For example, in cold climates, the ratio of R152a may be increased to approximately 13% to 20%. In warm climates, the optimal mixture will have a lower concentration of R152a, typically from approximately 3% to 9%. It should be apparent that such “tuning” of the refrigerant would be impossible in systems utilizing only a single pure material, such as R245fa or R152a alone.
Another advantage of using the refrigerant mixture is that the toxicity thereof is lower than the toxicity of pure R245fa. The mixture is further particularly advantageous for systems where a vapor ejector is used as the device for converting the expansion energy. This is because the average molecular weight of the hot vapor is nearly equal to the molecular weight of pure R245fa, while the average molecular weight of the “pumped gas” can be arranged to be closer to the molecular weight of R152a. A prudently selected absorption material, such as Genosorb® 1843, will have a higher affinity for R245fa than for R152a, and as a result, the working mixture in the lower pressure environment of the evaporator will have a higher concentration of R152a than of R245fa. The molecular weight of R152a is only 33, while the molecular weight of R245fa is 134, and the large difference in molecular weight results in highly efficient pumping of R152a refrigerant by the motive gas consisting primarily of R245fa.
Additionally, the change in entropy of the mixture as a function of pressure change is such that entropy decreases as pressure decreases. This means that the mixture is “dry” as it expands in either the scroll expander or a vapor jet pump.
As a further advantage, the mixture of R245fa, R152a, and Genosorb® 1843 is completely compatible with all materials of construction of the system 10. Therefore, the system can be entirely hermetically sealed. The specific characteristics of a polyglycol dibutyl ether such as Genosorb®1843 and those of the refrigerants include very low electrical conductivity, and no tendency to attack materials such as wires, insulation, bearings, etc.
In one embodiment, chlorotetrafluoroethane (HCFC 124) is used as the refrigerant. Though HCF 245fa may be utilized, as described above, in combination with Genosorb® 1843, HFC 245fa has a poor attraction to the Genosorb® 1843 molecule. Neither the HFC 152a nor the HFC 245fa have chlorine molecules in their molecular make-up.
Chloride-containing refrigerant molecules result in far greater attraction between a refrigerant and other molecules because the hydrogen bond is stronger. Thus, HFC 124a will provide a stronger attraction, and thus better refrigerant qualities in the mixture, with Genosorb® 1843. Additionally, compounds such as phosphites and zinc compounds may be utilized as additives in order to reduce interaction between the refrigerant and absorption compounds.
With regard to the brine solution, the brine solution may be a salt dissolved in water. The salt may be lithium chloride, lithium bromide, magnesium chloride, calcium chloride, or glycol.
In the certain embodiments utilizing HFC-245fa as a refrigerant and NMP as an absorption material, lower temperatures may be produced than are produced by the alternate compositions described above. The HFC-245fa/NMP working pair further has desirable properties such as low ozone depletion potential, high thermal conductivity, stability, virtually zero loss of refrigerant during shut-down mode and low production costs.
VI. Single-Effect Absorption Cycle
The mixture is passed through heat exchanger 240 into boiler 250. Once in the boiler 250, the refrigerant described above in Section V, is driven off from the absorption fluid. The concentration of the refrigerant is reduced from approximately 40% refrigerant to approximately 12.5% refrigerant. This process requires considerably higher temperature than the temperature required for boiling pure fluid, because the refrigerant concentration is only present in a relatively small fraction (one part in 1.5, at the start, and about one part in 9 at the end of the process).
As an approximation, the “activity” of the refrigerant is about 1.0. To produce an absolute pressure of 4 atmospheres with a concentration of 40%, the refrigerant must be heated to a temperature where the pure material is (1/0.4)×4 atm=10 atm. These conditions occur at a temperature of approximately 75° C. The refrigerant at this temperature begins to give off refrigerant vapor at 4 atmospheres of pressure. At the end of the boiling process, the effective temperature must be such that the effective pure refrigerant has a vapor pressure of (1/0.125)×4 atm=32 atm. This occurs when the pure refrigerant temperature is approximately 135° C.
As shown in
Upon exiting the boiler, the refrigerant vapor is superheated to approximately 80° C. Superheated vapor exits the boiler and enters the condenser device 260, which is similar in construction to the liquid-vapor converter 130 of the embodiment of
Once in the liquid-vapor converter or condenser 260, the vapor is condensed and heat is given up to the environment by air flowing through the condenser 260. Exiting the condenser, the liquid refrigerant mix expands adiabatically and at constant enthalpy in expansion valve 280.
The vapor mixture is now at a state between liquid and vapor. The “quality” of this mixture is estimated to be approximately 80% liquid and 20% vapor at a temperature of approximately 2° C. and at a pressure of 1 atmosphere. The cool mixture evaporates completely with an evaporator 290, which is similar to the second liquid-vapor converter 150 of the embodiment shown in
The refrigerant reaches a total vapor state after its temperature is increased from approximately 2° C. to approximately 10° C. This expansion process absorbs heat, thus creating a cooling effect for air passing through the evaporator 290. The vapor mixture at this point is at approximately 1 atmosphere of pressure and approximately 10° C., and has a “quality” of 100%.
The vapor is then directed back into the absorption tank 220, where it mixes with the NMP, which is also at a pressure of approximately 1 atmosphere, and at near room temperature.
The NMP, at this point, has been depleted to approximately 10% refrigerant by the boiling process. The NMP then absorbs the refrigerant, releasing heat. The final concentration of the refrigerant in the NMP material is approximately 40%. The mixture of refrigerant and NMP is then pressurized by the pump 230 from approximately 1 atmosphere to about 4 atmospheres, and the process is repeated.
VII. Shaft-Coupled Mechanical Compressor System
In the embodiment shown in
In a cooling mode, a mixture of refrigerant and absorbant, as described above with regard to
In the embodiment of
Gaseous refrigerant exiting scroll expander 370 is directed, through first selector valve 390 into condenser 410. As in the embodiment shown in
Liquid refrigerant exiting the condenser 410 enters an expansion valve 440, where the liquid refrigerant is depressurized from approximately 4 atmospheres to approximately 1 atmosphere. The liquid refrigerant evaporates within evaporator 430, producing gaseous or vaporized refrigerant.
The vaporized refrigerant then passes through the second selector valve 400 to be input back into the absorbant tank 320, where it is mixed with the absorbant to form the mixture of refrigerant and absorbant.
Following the process of this embodiment, mechanical power is produced, representing approximately 10% of the input heat energy. A typical mechanical compressor using a scroll-type design operates with a mechanical coefficient of performance (COP) of approximately 4 to 6. Thus, in considering the effective refrigeration output vs. heat input, the mechanical “Rankine” cycle portion operates with an effective COP of approximately 0.5.
In addition to the cooling effect produced by the mechanical compressor, cooling is produced in the absorption section. As shown in
VIII. Alternative Construction Materials
As previously stated, the implementation of various components through lower-cost materials is among the many beneficial features the present invention. For example, the utilization of NMP as an absorbant in combination with a refrigerant containing HFC-245fa allows boiler fluid operating pressures below 100 psi. At such moderate pressures, certain components in the boiler fluid circuit, such as the heat exchanger, may be constructed from a lighter material, such as aluminum. It should be apparent to the skilled artisan that significant savings in construction costs may be secured by the use of alternative materials such as aluminum.
In certain embodiments of the present invention, the components constructed from lower-cost materials may be treated on the surface thereof to further protect the component from corrosion by exposure to the absorbant/refrigerant mixture. For example, where aluminum is used, the surface of components may be treated by processes that include one or more of the steps of: etching, passivation and sealing. Such processes are well-known and an exemplary treatment of aluminum is provided in U.S. Pat. No. 6,579,472, issued to Chung, et al.
In certain embodiments, aluminum components, such as heat exchangers and boiler fluid tubing, are etched by an etchant, such as phosphoric acid. The etchant is rinsed off and the components are subjected to passivation. The surface of the components are passivated by a chromic acid based conversion coating such as Alodine® 1200, (Alodine is a registered trademark of the American Chemical Paint Company). Alternatively, the component may be treated by a non-chromic conversion coating, such as Alodine® 5200. The aluminum components may be passivated, also, by nitric acid, fluorine gas or other chemicals known in the art that are compatible for use with the absorbant/refrigerant mixture.
Once the surface conversion treatment has been completed, the surface of the components may be sealed using, for example: a silane surface treatment, such as Z-6040 manufactured by Dow Corning®, a sol-gel, such as that disclosed in the above-referenced U.S. patent issued to Chung, et al., or a paint, such as a silicon based paint.
It should be noted that it is not required that all components of the inventive system be surface treated in the same way, i.e., components having different surface characteristics may be incorporated in any given system. This allows flexibility for particular field installations. Furthermore, it should be noted that the list of exemplary surface treatments provided above is not exhaustive. Other treatments are, and will be available that are compatible with a particular absorbent/refrigerant mixture of the present invention.
Although this invention has been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the spirit or scope of the invention. For example, functionally equivalent elements may be substituted for those specifically shown and described, proportional quantities of the elements shown and described may be varied, and in the method steps described, particular steps may be reversed or interposed, all without departing from the spirit or scope of the invention as defined in the appended claims.
This patent application is a Continuation-in-part Application of application Ser. No. 10/910,294, filed on 4 Aug. 2004, currently pending, which is based on Provisional Applications Ser. No. 60/543,929, filed on 13 Feb. 2004; Ser. No. 60/571,938, filed 18 May 2004; Ser. No. 60/562,546, filed 16 Apr. 2004; Ser. No. 60/523,679 filed 21 Nov. 2003; and Ser. No. 60/513,999 filed on 27 Oct. 2003.
| Number | Date | Country | |
|---|---|---|---|
| 60543929 | Feb 2004 | US | |
| 60571938 | May 2004 | US | |
| 60562546 | Apr 2004 | US | |
| 60523679 | Nov 2003 | US | |
| 60513999 | Oct 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10910294 | Aug 2004 | US |
| Child | 11120946 | May 2005 | US |
