The present invention is directed to further improvement in efficiency of aqua-ammonia absorption systems. The circulation rate of the weak absorption fluid through an aqua-ammonia absorption system is an important factor in proper operation. The weak solution from the bottom end of the generator, also referred to herein as"weak liquor", has the lowest concentration of ammonia in the absorption cycle, typically between about 2% and about 20% ammonia, depending on operating mode (heating or cooling), operating conditions, and system design parameters.

Excess ammonia in weak liquor decreases the amount of refrigerant generated for a given circulation of solution through the absorption cycle. Thus, the circulation rate must be increased to generate the required amount of refrigerant. Increased solution circulation rate increases the required heat input to the generator, and decreases system efficiency. This efficiency degradation is especially pronounced for GAX systems where circulation rate must be sufficiently high to absorb all refrigerant passing through the condenser and evaporator, but low enough for weak liquor to be adequately depleted in ammonia, which is necessary for the solution to absorb ammonia refrigerant. Moreover, in the case of strong-liquor GAX, ammonia depletion is important to allow the GAX section of the absorber to operate at temperatures sufficiently high for heat <BR> <BR> transfer to the strong liquor, i. e. , absorption fluid solution having relatively high ammonia concentration. Weak liquor with excessive ammonia concentration and low bubble-point temperature reduces the amount of heat that can be recovered in the GAX absorber, thereby reducing system efficiency. Active control of weak liquor flow is needed for optimizing efficiency of the system by maintaining ammonia concentration in the weak liquor within a desired range when temperature conditions change or in systems where firing rate is changeable. As used herein,

active weak liquor flow control is intended to mean control and adjustment of weak liquor flow in response to changes in the system or operating conditions in contrast to use only of a fixed restriction such as a fixed orifice or capillary tube. Such weak liquor flow control may also be used advantageously with systems having variable speed or multiple speed burners or firing rates. The terms"burner speed"and"firing rates"are used interchangeably herein.

Summary of the Invention As described herein, the flow of weak liquor from the bottom of the generator to the absorber is actively controlled using one or more valves, operated or adjusted in response to a condition or property of the weak liquor, for example, temperature, pressure, concentration and/or, in cooperation with operating conditions, temperatures and/or other sensible parameters.

In one embodiment, a valve and a temperature-sensing device in thermal contact with weak liquor are used to actively control the flow of weak liquor from the bottom of the generator to the absorber assembly. A preferred valve is capable of a continuous adjustment of the weak liquor flow in response to sensed temperature. In another embodiment, weak liquor flow is actively controlled in discrete steps rather than by continuous adjustment.

In another embodiment, weak liquor flow control is used in a system also using active control of refrigerant flow to the evaporator for controlling vapor superheat.

Brief Description of the Drawings Fig. 1 is a schematic illustration showing a generator assembly and a valve and temperature-sensing bulb for controlling the flow of weak liquor; Fig. 2 is a schematic illustration of an aqua-ammonia absorption cooling system incorporating the valve and temperature-sensing bulb shown in Fig. 1 for controlling weak liquor flow from the generator to the absorber; Fig. 3 is a schematic illustration of an aqua-ammonia cooling system showing the use of combined discrete weak liquor flow control and TXV control of refrigerant flow to the evaporator; and Figs. 4a-f schematically illustrate different types of valving and flow restrictions for two- speed discrete flow control, and an example of valving used for three-speed flow control.

Detailed Description of the Preferred Embodiments Weak liquor flow control as described herein may be used with any aqua-ammonia absorption cooling and/or heating system having an absorber assembly, a generator assembly and an absorption fluid loop for directing absorption fluid between said absorber and generator assemblies. Such systems include a condenser, an evaporator and a refrigerant loop including piping for directing refrigerant from the generator assembly to the condenser and from the condenser to the evaporator. The aqua-ammonia absorption apparatus may perform cooling and/or

heating functions. The apparatus include chillers, heat pumps, refrigeration equipment, heating- only appliances, and dual-temperature appliances. The latter are a special type of heat pump that is not reversed, and in which both heating and cooling are produced simultaneously for beneficial use.

Such apparatus includes conventional aqua-ammonia systems as well as high-efficiency GAX apparatus, disclosed in the aforesaid patents and applications In an embodiment illustrated in Fig. 1, a temperature controlled valve 60 is used for controlling the flow of weak liquor from the generator 11 to an absorber (not shown). The valve is controlled by a temperature-sensing bulb 62 charged with a composition that produces pressure responsive to the temperature sensed by the bulb. The temperature-sensing bulb is installed in thermal contact with the weak liquor in the generator or as it passes through piping or heat exchange coils of the generator. Changes in bulb pressure resulting from changes in the pressure of the bulb charge composition, are directed to a moveable member such as a diaphragm or bellows in the valve resulting in opening and closing the valve in response to the pressure changes, or pressure differential between surfaces of the diaphragm. In the apparatus shown in Fig. 1, valve 60 is positioned between pipes 45 and 47 which direct the weak liquor from the bottom of generator 11 to an absorber (not shown). The valve assembly includes a temperature-sensing bulb 62 in thermal contact with weak-liquor pickup tube 68. Valve 60 is opened and closed in response to the temperature sensed by the bulb 62 in pipe 68 which directs the weak liquor from the bottom of the generator to the GHX (generator heat exchange) coil 65 and pipe 45. Alternatively, the bulb may be placed in thermal contact with the bottom of the generator, either on the outside of the shell where it indirectly measures solution temperature at the bottom of the generator, or in direct thermal contact with solution inside the bottom of the generator. The temperature-sensing bulb may be installed at any desirable location, preferably where the ammonia-weak solution is at or near its bubble-point temperature.

The valve is diaphragm-controlled with one side of the diaphragm exposed to the temperature-sensing bulb pressure and the other side to generator pressure. The valve components shown include inlet port 71, outlet port 72, diaphragm 73, actuator rod 74, valve plug 75, valve chamber 76 and spring 77. The valve 60 is installed so that the inlet port 71 of the valve receives weak liquor from the generator via pipe 45 and communicates with the valve chamber 76 which is exposed to the diaphragm 73, and the outlet port 72 communicates with pipe 47 for directing the weak liquor to the absorber assembly. The valve outlet port 72 is opened and closed in response to the pressure differential between the generator pressure and the temperature-sensing bulb pressure.

The valve regulates weak solution flow rate so as to maintain concentration of ammonia in the weak solution within a desired range. The response of the valve depends on valve design parameters including diaphragm diameter, seat diameter, spring force, and bulb charge. Process

parameters such as high-side and low-side pressures, i. e. , pressures on the two sides of the valve plug, affect performance.

A water-ammonia bulb charge works well for weak liquor flow control, with the amount of ammonia in the bulb being slightly higher than the desired concentration of ammonia in the weak liquor. Useful ammonia concentrations are between about 1-20% and preferably between about 3% and about 10%. Relatively constant weak liquor concentration is achieved using relatively low spring forces, combined with lower ammonia concentrations in the bulb charge. Increased spring force and slightly higher ammonia fraction in the bulb charge changes the valve response toward increased weak liquor ammonia concentration at higher pressures. Increasing the amount of ammonia in the weak liquor at higher pressures is often more desirable than constant concentration, since it helps to limit generator temperature at high ambient temperatures.

Other bulb charge compositions may be substituted for the water/ammonia mixtures discussed above to obtain good performance characteristics. For example, ammoniated complex compounds may be used, such as disclosed in U. S. Patent No. 4,848, 994. A specific complex compound found to be useful is FeC12 2/6 (NH3). Hydrated BaC12 having a coordination step of 1- 2 mols of water, i. e., BaCl2'1/2 (H20), or hydrated zeolites or carbon may also be used as suitable bulb charge.

Weak liquor is shown routed through GHX coil 65 in the lower section of the generator whereby heat is transferred from the hot weak liquor to the generator. As shown, the weak liquor flow control valve 60 is installed downstream of the GHX coil which is advantageous since it allows for maximum heat transfer from the weak liquor to the generator prior to decreasing pressure of the weak solution, thus allowing maximum heat recovery from the solution before flashing or letdown to lower pressure. Also, locating the valve in the coolest part of the weak liquor stream permits the valve to be designed for lower maximum operating temperature.

Other types of valves may be substituted for the diaphragm-operated valve described above. Any valve that responds to weak liquor temperature and/or pressure so as to maintain constant or near constant weak liquor concentration may be used. Another alternative is to use a valve responding directly to weak liquor concentration or to some physical property or condition correlated to weak liquor concentration. The apparatus may include one or more sensing devices for sensing or monitoring a condition of the absorption fluid, e. g. weak liquor, with the sensing device operatively communicating with a valve to control the valve in response to a sensed condition. The sensing device may be directly connected to the valve or indirectly operatively connected to the valve via an intermediate component, such as a control device, e. g. controller or microprocessor. Electronic valves operated in response to weak liquor temperature, pressure and/or concentration may also be used. For example, such electronic valves may be continuously

variable valves, or open-closed valves operated in a pulsed fashion, with pulse-width modulation or similar control algorithm to control the amount of the time the valve is open. A pulse-width operation controlled valve may be responsive to generator temperature, pressure or other physical properties or conditions correlated to weak solution concentration, or could be set to provide two or more different flow rates in response to operating conditions of the absorption system.

In a conventional system without the present invention, weak solution passes from the generator to the absorber without active control via a fixed flow restriction. Fig. 2 schematically illustrates an aqua-ammonia generator absorber heat-exchange (GAX) chiller system with continuous control of weak liquor flow using a valve as shown in Fig. 1. As shown in Fig. 2, weak solution passes from generator assembly 11 to absorber assembly 10 via valve 60 which continuously modulates the flow rate of the weak solution for maintaining the ammonia concentration therein within a desired range. The major components of the chiller system include an absorber assembly 10 comprising an absorber 12 and an absorber heat exchange section 30 which includes an absorber heat exchanger 31, sometimes referred to as a solution cooled absorber (SCA), and a GAX heat exchanger 33. The generator assembly 11 shown includes a generator heat exchanger 15, a boiler 26 having a burner 19 for heating and vaporizing the solution, an adiabatic section 16, and a rectifier section 17 with reflux coil 13. The burner may be of a single, multiple or variable capacity type, and may include a combustion air pre-heater. A condenser 14 and an evaporator 20 are the other major components of the system. The chiller system may also include a subcooler 52 for precooling refrigerant from the condenser with cold gaseous refrigerant from the evaporator. The absorber and condenser heat exchangers may be air or liquid cooled, and the rectifier 17 may be cooled by solution or water. Such a GAX chiller is well-known in the art, for example, U. S. Patent Nos. 5,490, 393 and 5,367, 884, and in the aforesaid Modahl et al. publication.

During the operation of the illustrated GAX chiller apparatus, the relatively cool refrigerant-rich absorption fluid solution is pumped from the absorber via pipe 46 to heat exchange coil 13 within rectifier 17 after which it is directed via pipe 49 to the absorber heat exchanger 31 and GAX heat exchanger 33. In the embodiment shown, a flow splitter 32 splits the ammonia-rich absorption fluid (rich liquor) passing from absorber heat exchanger (SCA) 31, a first portion to the generator via pipe 48 and a second portion to GAX heat exchanger 33 and then to the generator via pipe 50. The refrigerant vapor from evaporator 20 is directed via pipe 44 to the absorber assembly 10. Weak absorption fluid or weak liquor is directed to the absorber assembly 10 from the generator via pipe 45, valve 60 and pipe 47. As the weak solution from the generator passes over the GAX heat exchanger 33 inside the absorber and over the absorber heat exchanger 31, it absorbs ammonia vapor. The advantages of a GAX system with flow split of a portion of the rich absorption fluid through the GAX heat exchanger are discussed in more detail in the aforesaid

references, particularly in the Modahl et al. publication and the'884 patent. However, within the broad class of GAX systems, the present invention is not to be limited by the method of recovering GAX heat, whether it is by strong liquor, weak liquor, or a secondary fluid. Further, of strong liquor GAX recovery systems, the present invention is not to be limited by location of the flow split of rich liquor into GAX and non-GAX streams. In the Fig. 3 embodiment, the rich liquor is split at flow splitter 32'whereby a portion of rich liquor is directed to the generator via pipe 48'before rich liquor enters the SCA and GAX heat exchangers, whereas in Fig. 2 rich liquor flow splitter 32 is located between the SCA and GAX heat exchangers. The present invention is not limited to a GAX system and may be used in a conventional absorber heat exchange system, although the more efficient GAX cycle is preferred. The Fig. 2 embodiment is especially well suited for operation with continuously variable speed burner control.

Fig. 3 schematically illustrates another embodiment of an aqua-ammonia chiller utilizing active weak liquor flow control. Active control is especially advantageous in a system having a variable speed or multiple speed burner. In the Fig. 3 embodiment, weak liquor flow may be changed in discrete steps and is especially well suited for operation with discrete burner speed control. Discrete control of weak liquor flow is especially advantageous in a system having a burner with 2 or more discrete speeds. Such apparatus is disclosed in U. S. Patent Application Serial No. 10/125,125, filed April 16,2002 (ROCKYR. 113A). In the embodiment illustrated in Fig. 3, the weak liquor flow from generator assembly 11 to absorber assembly 10 is directed along pipe 47 to splitter 51 to first and second piping 55 and 70, respectively. First piping 55 includes an actively controlled valve 56 and first restrictor 57. Second piping 70 includes a second restrictor 59. These two weak liquor flows provide high and low flow to accommodate weak solution concentrations within desired concentration ranges. For a high weak liquor flow, valve 56 is opened and weak liquor flowing from the generator to the absorber via pipe 47 splits at flow splitter 51, with a first portion passing through pipe 55, valve 56 and restriction 57, and a second portion passing through pipe 70 and restriction 59. In a low-flow mode, valve 56 is closed and all weak liquor flowing to the absorber passes through pipe 70 and restriction 59. Restrictions 57 and 59 may be any combination of orifices, capillary tubes, nozzles, or other fluid flow resistance elements known to those skilled in the art. Flow switching may be accomplished in response to changing operating conditions, such as ambient or load temperatures or weak solution concentrations, so as to maintain desired concentration range. Reduced weak liquor flow rates may also be used to enhance absorption system startup. Increased weak solution flow may be used to achieve short- term increases in cooling capacity. In the embodiment shown, a controller 58 operatively communicates with valve control device 87 which operates to open and close valve 56 for controlling the flow rate of weak liquor. The valve opening may be variably controlled or a valve

which is open or closed. The valve may be mechanical or electronic. The controller is operatively connected to temperature-sensing device 53 in thermal contact with the bottom of generator 11 and operates valve 56 in response to the temperature sensed by device 53. Temperature-sensing device 53 may be placed within the generator in direct thermal contact with the solution inside the bottom of the generator rather than on the outside shell. Alternatively, a device for measuring some other physical property or condition of the weak liquor, such as refrigerant concentration, or a condition related to the weak liquor condition, or for sensing a condition of the apparatus or system such as load related conditions, for example, supply and/or return water temperature, or burner speed, may be substituted for temperature-sensing device 53 or used in combination with temperature sensing.

Such detection, alone or combined with temperature sensing, is monitored by controller 58 for operating valve 56 to maintain desired concentration of ammonia in the weak liquor supplied to the absorber. The controller may also be thermostatically operated for controlling the valve opening whereby generator heating and weak liquor flow are changed in response to temperature conditions for which the heating and/or cooling system is used. By way of example, controller 58 may incorporate pulse-width modulation control algorithm software or firmware for controlling operation of valve 56 and cycling the valve to rapidly open and close, and the controller or microprocessor configured to operate using pulsed-width modulation in response to changes in temperature, pressure, concentrations, etc.

Electronic control of the weak solution flow and/or the burner firing rate may be based on sensing of the building load or one or more parameters representing the load. For example, chilled water supply or return air temperature is one measure of the relative capacities of the chiller versus the building load. The dropping of the temperature of the chilled water supply (or return) below a previously determined set point temperature is an indication that the chiller is operating at a greater capacity than is needed by the building load. In such a case, one or more of the weak solution control valve (s) would be closed or modulated more towards closing to reduce flow of weak solution, and, in conjunction, the burner would be modulated to reduce the firing rate. Conversely, if the chilled water supply (or return) temperature increases above a set point, one or more of the weak solution valve (s) would open or be modulated more towards opening to increase the flow of weak solution, and, in conjunction, the burner would be modulated to increase the firing rate.

Electronic control apparatus, such as a controller or microprocessor such as described above, operatively connected to one or more components which sense the building load and/or parameters such as described may be used.

There are numerous ways of accomplishing switching of weak solution flow rates using <BR> <BR> valving, i. e. , one or more valves, in combination with various fixed fluid flow resistance components. Figs. 4a-f are illustrative of examples of different types of valving and flow

restrictions which may be used. Fig. 4a illustrates the use of a valve that, when closed, still allows fluid flow, but with more flow resistance than when the valve is open. An example of such a valve is one in which a hole is drilled in the valve plug, whereby a small fluid flow passes through the small orifice drilled in the plug when the plug is seated, and when the plug is lifted from the valve seat, greater fluid flow passes through the larger restriction defined by the valve seat. Such a valve may be operated by a solenoid, or other type of control. Fig. 4b illustrates a similar drilled valve having a small and a large restriction when closed or opened, respectively, used in series with a restriction providing an additional flow resistance, which may be used either upstream or downstream of the valve. In Fig. 4c, a parallel resistance in a by-pass line is used in combination with a valve. The valve may be drilled as previously described, or it may be fully closed or opened.

Again, the fixed resistance used in the same line with the valve may be upstream or downstream from the valve. Such an embodiment with parallel restrictions is like that illustrated in Fig. 3.

Fig. 4d illustrates series of resistances with a single valve used to by-pass one resistance for high- flow. Again, the valve may be drilled for high and low flow, or have variable valve openings, either of which valves may be controlled. Fig. 4e shows parallel flow restrictions with a valve in series with each restriction. Such an embodiment may be preferred to the embodiment illustrated in Fig. 4c when it is desired to terminate weak solution flow completely, for example, for shutdown or other operational reasons. The above valve and restriction embodiments are useful for two weak liquor flow modes, high and low flow, and for two burner speed systems. Fig. 4f illustrates an example of valving and flow restrictions for a three-speed or three-step flow control. It will be understood that different combinations of valve and flow restrictions may be used, expandable to any desired number of weak liquor fluid flow controls. Any one or more of the valves may be operated for being fully opened or closed, such as a solenoid-operated valve, or may be controlled for variable opening.

In another embodiment shown in Fig. 3, a valve and temperature-sensing bulb are used for controlling refrigerant flow to the evaporator and controlling vapor superheat. A TXV 40 is positioned along pipe 42 for controlling the flow of refrigerant to evaporator 20. A temperature- sensing bulb 23 is positioned at or near the evaporator outlet on pipe 44, with a pressure conduit 25 communicating between the temperature-sensing bulb 23 and valve 40. A preferred valve used in the apparatus of the invention is a pulsed operation control valve disclosed in U. S. Patent No.

5,675, 982. The use and operation of the valve for controlling superheat in such an apparatus is described in more detail in copending application Serial No. 10/125,125, filed April 16,2002 (ROCKYR. 104A).

In the aqua-ammonia systems, the absorber 12 may be air cooled as illustrated in Fig. 2 or may be cooled by refrigerant such as described in U. S. Patent Re. 36,684. For such absorber

cooling, Fig. 3 illustrates a portion of a refrigerant loop comprising a heat exchanger coil 84 in which condensed refrigerant supplied from condenser 14 is at least partially vaporized for cooling the absorber. Where such an embodiment is used, the apparatus may include a reservoir (not shown) for the condensed refrigerant. The refrigerant loop includes piping 83 which communicates with piping 85 for directing the vaporized refrigerant from the absorber heat exchanger coil where it is combined with refrigerant vapor from the rectifier 17 to piping 41 to the condenser 14. In such an embodiment, by combining refrigerant vaporized in cooling the absorber with refrigerant vapor from the rectifier flowing to the condenser, all heat rejection is achieved at the condenser. The rectifier 17 also preferably includes a reflux coil 13 for cooling and rectifying the vapor by heating and/or vaporizing refrigerant in the reflux coil or cooling coil. Such a refrigerant loop is also preferably used with valving such as one or more valves and more preferably a four-way valve for reversing refrigerant flow as disclosed in Re. 36,684. Such a valve-controlled refrigerant loop selectively directs the refrigerant to and from the condenser and the evaporator, each of which may alternately function to evaporate or condense refrigerant in a heat pump-type system. The above- described weak-liquor flow control and the absorber cooling and system heat rejection may be used in a dual-temperature appliance incorporating the aforesaid components and having a refrigerant loop in which refrigerant flow is not reversed and the condenser and evaporator heat exchange functions are not reversed.