ABSORPTION COOLING SYSTEM

The absorption cooling system is capable of continuous operation both day and night while using only solar power for its basic operation. The system is an absorption type system using phase changes of aqua-ammonia and a storage system for storing chilled refrigerant for operations when solar power is not available. When solar power is available during the day, the system operates according to the principles of absorption cooling systems, and also stores a reserve of chilled refrigerant in the storage unit. The stored refrigerant then continues the absorption process during the night when solar energy is not available, thereby providing uninterrupted cooling during the day, and also at night when solar energy is not available.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The absorption cooling system100as illustrated inFIG. 1provides for continuous cooling of an enclosed space or area while minimizing energy consumption. The system100utilizes aqua-ammonia (ammonium hydroxide) as the refrigerant fluid. The system changes the ammonia:water ratio and the ratio of the liquid and gaseous phases of the fluid to produce the cooling process. The cooling system100comprises five basic components: a generator unit200(FIG. 2), a condenser unit300(FIG. 3), an evaporator unit400(FIG. 4), an absorption unit500(FIG. 5), and a storage tank system600(FIG. 6). The interconnecting pipe network700for the above components is illustrated inFIG. 7.

The description of the various components and their operation will begin with the generator unit200ofFIG. 2. The generator unit200acts as a heat exchanger to produce or generate concentrated ammonia vapor, i.e., containing little water therewith. The resulting strong ammonia vapor passes through other components of the system (as described further below) to produce the resulting cooling effect. The generator unit200includes a case202that is substantially closed (except for inlet and outlet passages). The case202has a lower portion204, an upper portion206, a first side208, and a second side210opposite the first side. The front panel of the generator unit200is removed inFIG. 2to better illustrate the interior components, but the generator unit200in theFIG. 1drawing of the entire absorption cooling system100is shown with the front panel in place.

The lower portion204of the generator200contains a first plurality of heat exchange tubes212therein. The tubes212are arranged in a sinusoidal array, generally as shown inFIG. 2. The tubes212do not contain any of the aqua-ammonia refrigerant fluid, but instead connect to a solar collector214(FIG. 1) via an inlet line or pipe216from the collector214to the generator unit200, and a return line218from the generator200to the solar collector214. The working fluid in this subsystem may be water or other economical fluid capable of producing heat transfer. The fluid is heated in the solar collector214and rises therein due to thermosiphon effect, and then flows through the inlet line216to the top of the heat exchange tubes212. The fluid gradually cools as it releases its heat to the aqua-ammonia within the case202of the generator unit200. The fluid settles to the lower portion of the heat exchange tubes212, and then flows back to the lower portion of the solar collector214via the return line218.

The temperature differential between the solar collector fluid and the aqua-ammonia solution at the upper or inlet portion and the lower or outlet portion of the heat exchange tubes212results in greater heating of the aqua-ammonia liquid around the upper portion of the heat exchanger212. This greater heating drives off more ammonia vapor from the liquid refrigerant near the upper portion of the heat exchanger tubes212. The relatively lower temperature differential in the lower portion of the tubes212does not generate as much heat, so comparatively less ammonia vapor is driven off from the aqua-ammonia liquid in the lowermost portion of the case202. As the strong aqua-ammonia solution moves from the upper portion to the lower portion of the heat exchanger tubes212while continuously driving off ammonia vapors, this results in a relatively weak aqua-ammonia solution near the lowermost portion of the case202.

Nevertheless, circulation within the generator200around the heat exchanger tubes212results in the aqua-ammonia liquid in the lowermost portion of the generator containing a larger fraction of water. This liquid is circulated through a second plurality of heat exchange tubes220in the upper portion206of the generator200, due to the pump708of the plumbing system700, shown inFIG. 7of the drawings. The aqua-ammonia liquid is drawn from the bottom of the generator case202through a series of return tubes222athrough222e. These tubes222athrough222eare configured to draw the aqua-ammonia liquid more or less evenly from the bottom of the generator unit200. In order to do so, the tubes222athrough222eare of different lengths to extend to various points across the bottom of the generator case202. Accordingly, the various tubes222athrough222eare of correspondingly different diameters. The longest tube222ahas the largest diameter, to reduce internal resistance in accordance with its greater length. The next longest tube222bhas the next largest diameter, and the lengths and corresponding diameters decrease down to the shortest and smallest diameter return tube222e. In this manner, the flow of aqua-ammonia liquid from the various areas at the bottom of the case202remains reasonably constant between the two sides208and210of the case202.

The return tubes222athrough222eare connected to a header224formed along the second side210of the case202. The aqua-ammonia liquid flows from the tubes222athrough222einto the lower end of the header224, and rises in the header224as the liquid is drawn into the second plurality of heat exchanger tubes220due to the pump708(FIG. 7). The heat exchanger tubes220connect to the header224just below a baffle226that prevents the liquid from rising further in the header224. The heated aqua-ammonia liquid inside the heat exchanger tubes220rejects heat to the relatively strong aqua-ammonia solution for heat recovery process within the system. After heat recovery, the aqua-ammonia liquid then exits the upper ends of the second plurality of heat exchanger tubes220and passes from the generator unit200via an exit manifold and pipe or tube228.

Due to the heat generated within the generator200, nearly all of the aqua-ammonia vapors generated in the lower portion204move to the upper portion206of the generator200. Additional strong or concentrated ammonia liquid is pumped into the generator unit200through an inlet pipe230. This additional liquid results from mixing concentrated ammonia liquid supplied from the tank system600ofFIG. 6(discussed in detail further below) and the one supplied from the absorption unit500ofFIG. 5(discussed in detail further below). The mixing takes place at a tee located next to the valve704just before the pump708inFIG. 7(discussed in detail further below). The inlet pipe230has a closed lower end that is welded to a perforated distributor tray232within the upper portion206of the case202. However, two inlet holes or passages234are provided in the lower end of the inlet pipe230, one of which is shown in the perspective view ofFIG. 2. This subsystem permits an approximately uniform distribution of additional strong aqua-ammonia liquid into the upper portion of the generator200. The upper portion206of the generator unit200between the second plurality of heat exchanger tubes220and the distributor tray232comprises a vapor chamber, which contains a combination rectifier and dephlegmator packing236in the form of a stainless steel mesh, steel wool, or net material. This material236may also surround the heat exchanger tubes220and allows the free passage of ammonia liquid and vapor therethrough, while providing additional heat transfer. Also, as the interior of the generator200is pressurized due to the pumping of the ammonia liquid into the inlet pipe or line230, a plurality of panel connector plates238are provided to connect the two flat panels to one another for structural integrity of the unit. These plates238also act as baffles to produce greater turbulence and mixing in the flow of fluid therearound. The heated and concentrated ammonia vapor leaves the generator unit200by one or more (preferably two) vapor outlets240aand240bextending from the upper portion206of the case202.

The two vapor outlets240a,240bpass the concentrated ammonia vapor to a condenser unit300.FIG. 3provides a side elevation view in section through one side or portion of the unit300. The condenser unit300comprises a liquid tank302having a lower portion304and an upper portion306. The upper portion comprises three vertical elements defining first and second air channels308aand308b(shown inFIG. 1) therethrough. Two of the air channels308aand308bare identical to one another, and each has an open inlet end310and an opposite open outlet end312, and a condenser fan314installed at the outlet end.

The lower portion304of the liquid ammonia tank302includes a plurality of vapor-liquid heat exchanger tubes316therein, which are disposed in a sinusoidal array, much like the first and second heat exchanger tubes212and220of the generator unit200. These tubes316are connected to the evaporator400. This portion of the operation is explained further below. A baffle318is placed immediately above the heat exchanger tubes316. A plurality of vapor condenser tubes320is disposed across each of the air channels. These condenser tubes320are shown in end view in the cross section elevation ofFIG. 3. The ends of the condenser tubes320open into the walls of the upper portions306of the liquid tank302. The internal volume of the tank302thus communicates with the internal volumes of the condenser tubes320.

The condenser unit300receives the rich, heated ammonia vapor from the generator200through the vapor outlets240aand240bthat extend from the upper portion of the generator200to the central upper tank portion306, as shown inFIG. 1. These vapor outlets240aand240balso comprise the vapor inlet tubes for the condenser unit300. The rich, heated ammonia vapor flows from the central upper tank portion306across to the other upper tank portions via the condenser tubes320that extend across the air channels308aand308bbetween the upper tank portions. The air fans314draw cooling air through the channels and around the condenser tubes320, cooling and condensing the rich ammonia vapor within the tubes320. The liquefied vapor drains from the tubes320to collect in the lower portion304of the liquid tank302.

The cooled, concentrated liquid ammonia flows from the lower tank304of the condenser unit300through an outlet tube322containing a throttling valve or expansion valve (not shown). The outlet tube322also comprises the inlet tube to the evaporator unit400, shown inFIG. 4. The evaporator unit400comprises a closed tank402(except for the inlets and outlets) having a fluid ammonia inlet404, to which the condenser outlet tube322is connected. The drop in pressure of the incoming highly concentrated ammonia across the throttling valve results in an extremely cold ammonia vapor-liquid mixture flowing into the evaporator unit400.

A plurality of coolant tubes406is disposed within the evaporator tank402, preferably in a sinusoidal array, as shown inFIG. 4. The tubes406enter the tank402at the coolant tube inlets408, and depart the tank at the coolant tube outlets410. The coolant tubes contain a brine solution or other fluid having a freezing point well below that of pure water in order to remain in a liquid state throughout the process. The brine or other solution within the tubes406is isolated from the ammonia fluid within the remainder of the tank402, so that the two fluids remain separate from one another. The brine solution releases heat to vaporize the chilled ammonia liquid that flows into the tank402at its fluid ammonia inlet404. The resulting chilled brine solution is used to cool or refrigerate the desired structure (e.g., a home or office, refrigeration system, etc.).

Under some operating conditions, the ammonia entering the evaporator unit400may comprise a certain fraction that remains in a vapor state. The evaporator tank402also serves as a separator for the segregation of the liquid phase from the vapor phase. As the cooling effect is produced from the vaporizing of chilled liquid ammonia, it is preferable that the tubes406only come into contact with the liquid phase. Eventually, the liquid ammonia may fill the evaporator tank400, in which case proper segregation of the liquid and vapor phases may not occur. This can greatly reduce the cooling effect to the coolant tubes406. Accordingly, a flotation control valve is provided at the ammonia fluid inlet404. The valve comprises a float412that rides between two guides or supports414. If too much liquid ammonia enters the tank402, the float412will rise to cover the inlet404until sufficient ammonia escapes the tank402through the ammonia fluid outlet416. Thus, precooled ammonia flows from the liquid tank302of the condenser unit300to the evaporator unit400via the exit tube or line322(FIG. 3). The chilled ammonia vapor then returns to the condenser unit300(FIG. 3) to flow through the vapor-liquid heat exchanger tubes316disposed in the lower tank304of the condenser300, entering the tubes316at the inlet324and exiting the tubes316and condenser300at the outlet326.

An absorption unit500is illustrated in partial section inFIG. 5of the drawings. The absorption unit500is another heat exchanger. The heated aqua-ammonia solution rejects heat to the ambient air. The absorption unit500comprises a closed case502(except for the inlets and outlet) having a first end504, an opposite second end506, and a plurality of airflow tubes508extending through the case from the first end504through the second end506. The open ends of the tubes508pass through the first and second ends504and506of the case502, allowing air to flow through the case502from one end to the other. The tubes508are supported by a plurality of alternating, generally semicircular baffles510disposed within the case502. Air is drawn through the airflow tubes508by a fan512installed at the second end506of the case502.

During daytime operations, i.e., when solar heating is available from the solar collector214, the absorption unit500accepts a weak liquid aqua-ammonia solution from the exit manifold and pipe228of the generator unit200, through a valve and plumbing network described further below, into a first (fluid) inlet514. However, at night when no solar heating is available, the absorption unit500receives weak liquid aqua-ammonia solution from the storage tank system600(shown inFIG. 6, and discussed further below). In order to complete, the absorption process throughout the day and night, a second (vapor) inlet516receives the heated ammonia vapor after it passes through the vapor-liquid heat exchanger tubes316of the condenser unit300. In either case, as the absorption process is an endothermic process, heat is rejected from the absorption unit500through the airflow tubes508due to the operation of the fan512. The only reason that two inlets514and516are needed for the absorption unit500is due to the different sources of the ammonia vapor and weak liquid aqua-ammonia solution entering the absorption unit500, depending upon day or night operation of the system. The absorption of ammonia vapor by relatively weak liquid solutions results in an increase of strength, i.e., a higher ammonia fraction, in those solutions.

The storage tank system600for storing various concentrations of aqua-ammonia solution is shown inFIG. 6. The storage tank system600actually comprises two concentric tanks, having a first or outer storage tank602and a second or inner storage tank604disposed within the outer tank602. The two tanks602and604are sealed to one another at their bottom ends, but the inner tank604has an open upper end606just below the closed top608of the outer tank602. The upper end606of the inner tank604and the top608of the outer tank602define a gap610therebetween for the flow of aqua-ammonia vapor between the two tanks. The different diameters of the two tanks602and604define an annular ammonia storage volume612therebetween. The inner tank604defines an inner storage volume614. The annular storage volume612stores a strong ammonia solution that is used during daytime operation, while the inner volume614provides a weaker, i.e., more dilute, ammonia solution for night operation. The two tanks602and604are nominally only half-filled in volume, as the strong ammonia solution that is depleted from the annular storage volume612during daytime operation is returned to the inner tank604during this operation. Conversely, the weaker ammonia solution that is removed from the inner tank604during night operation is returned as a stronger solution to the annular volume612.

Each of the tanks602and604has its own dedicated inlet and outlet. During daytime operation the strong aqua-ammonia solution is drawn from the outer tank outlet616. The aqua-ammonia from this source ultimately is delivered to the upper inlet230of the generator unit200. Weaker aqua-ammonia solution is returned from the exit manifold and pipe228of the generator unit200, back to the second or inner tank inlet618. At night the flow to and from the tanks602and604is reversed, so that relatively weak aqua-ammonia solution is drawn from the second or inner tank outlet620and delivered to the first (fluid) inlet514of the absorption unit500. Relatively strong aqua-ammonia solution is returned from the outlet or return line518of the absorption unit500, and back to the return inlet622of the first or outer tank602.

FIG. 7provides a perspective view of the pipe or plumbing system700of the absorption cooling system100. InFIG. 7, the inlet and outlet ends of the various pipes are designated by the same reference numerals as used to designate those inlets and outlets of the various components ofFIGS. 1 through 6, discussed further above. Much of the flow of the ammonia fluid, in both its liquid and vapor states and in its varying concentrations, is reversed, depending upon the operation of the solar collector214(FIG. 1) during daylight operation or at night when energy from the solar collector is not available.

Daylight operation utilizes the solar collector214to heat a working fluid. The heat energy is transferred to the ammonia fluid in the generator200, as noted further above. A relatively strong ammonia solution is supplied to the generator200from both the first or outer tank outlet616and the outlet518of the absorption unit500. The first tank outlet is connected to a first delivery pipe702(mostly concealed by other pipes, only its leftmost portion being visible inFIG. 7). The first delivery pipe702extends to a valve704at a tee. Additional strong ammonia solution flows from the outlet518of the absorption unit500through a second delivery pipe706. The combined flow of strong ammonia solution from the first delivery pipe702from the first or outer tank602and the second delivery pipe706from the absorption unit500passes through the valve704at the tee, and is then drawn through a first pump708and a third delivery pipe710to the inlet230at the top of the generator unit200. Relatively weak ammonia solution is returned from the exit manifold and outlet pipe228of the generator unit200, and passes through a throttling or expansion valve712and is split into two parts. One part passes to a first return pipe714, back to the inlet618for the second or inner tank604, while the second part passes on through valve724to the inlet516of the absorption unit500(FIG. 5).

The flow is considerably different for night operation, when the solar collector214is ineffective. At night, the relatively weak ammonia solution is drawn from the second or inner tank outlet620by a second pump716, and passes through a fourth delivery pipe718and valve720. Upon leaving the second pump716, the ammonia solution passes through another valve722and a tee, and on through yet another valve724to the inlet516of the absorption unit500(FIG. 5). Return flow back to the first or outer tank602is from the outlet518of the absorption unit500and through the second delivery pipe706, where the aqua ammonia solution is routed to the second return line726by a closed valve728between the first pump708and the tee joining lines706and726.

The above-described absorption cooling system100requires relatively little energy for its operation, in comparison to systems using large compressors to produce high working pressures in portions of the system. Although the first pump708used for daytime operation does operate to increase the working pressure of the fluid passing therethrough, the pressures produced and the corresponding power required are relatively low. Accordingly, the power required for daytime operation of the first pump708, the fans314of the condenser unit300, and the fan512of the absorption unit500may be provided by a plurality of solar panels730, as shown inFIG. 1of the drawings. Surplus electrical energy may be stored in a conventional electrical storage battery system732(FIG. 1) to power the second pump716and the fans314and512as required for night operation. In the event that battery power is insufficient, the relatively small amount of additional electrical power required to operate the system may be provided by a small electrical generator or the conventional electrical grid. In any event, the absorption cooling system100is an economical system for providing cooling or refrigeration to virtually any area or structure requiring such cooling.