Generator-absorber-heat exchange heat transfer apparatus and method and use thereof in a heat pump

Numerous embodiments and related methods for generator-absorber heat exchange (GAX) are disclosed, particularly for absorption heat pump systems. Such embodiments and related methods use, as the heat transfer medium, the working fluid of the absorption system taken from the generator at a location where the working fluid has a rich liquor concentration.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to refrigeration and heat pump systems and 
more particularly to an absorption refrigeration cycle of the 
generator-absorber heat exchange ("GAX") type. The invention is especially 
adapted for use in a gas-fired, air-to-air, absorption heat pump. 
2. Description of Related Art 
Absorption refrigeration cycles were developed in the mid 1800's and were 
used primarily in refrigeration systems. Such cycles operated by using a 
refrigerant/absorbent mixture, the refrigerant vapor being absorbed in an 
absorber into a liquid absorbent, thus producing heat, followed by heating 
the refrigerant/absorbent mixture in a generator to drive off the 
refrigerant vapor. A condenser, which also produced heat, and an 
evaporator, which extracted heat, completed the cycle. The heat produced 
by absorption in the absorber was discarded, along with that from the 
condenser, to a coolant, generally cooling water. 
These early "single stage" absorption cycle systems were energy inefficient 
but were often preferred to compression systems, before the advent of 
electric motors, because the cost of heat energy to operate them was low 
and they required much less mechanical energy than compression systems. 
For most applications, the use of these single stage absorption systems 
declined with changes in the relative cost of gas and electric energy and 
improvements in electrically operated compression systems. However, even 
today, these relatively inefficient single stage systems are still in use 
in low pressure lithium bromide commercial air conditioning systems and in 
refrigeration systems for recreational vehicles and hotel rooms. 
In 1913, an improved absorption cycle was devised by Altenkirch. This cycle 
was made more efficient than the early single stage cycles by transferring 
a portion of the heat produced in the absorber to the 
refrigerant/absorbent fluid circulated to the generator, and transferring 
to the generator a portion of the heat in the absorbent flowing from the 
generator to the absorber. This transfer of heat reduced the heat input 
required to the generator to evaporate the refrigerant from the 
refrigerant/absorbent mixture. This system has been called the absorber 
heat exchange (AHE) system. 
The AHE cycle was used in the early 1960's to produce absorption systems 
that were efficient enough to be cost effective air conditioners at that 
time. The AHE cycle has been used in residential, air cooled air 
conditioners, starting in 1965. However, even in these AHE systems, a 
large portion of the heat generated by the absorption process in the 
absorber was lost. The AHE cycle was also used experimentally in 
air-to-air gas heat pumps, which were also advantageous in heating, but 
were never commercially produced. As energy costs have increased, the AHE 
air conditioners have lost much of their operating cost advantages and 
today, have only a limited market. 
Also in 1913, Altenkirch devised another absorption cycle that recovered 
more of the heat of absorption from the absorber. This cycle, which has 
come to be known as the generator-absorber heat exchange (GAX) cycle, 
utilized an additional heat exchange system, whereby high temperature heat 
produced by the absorption process in the absorber was transferred via a 
heat exchange fluid to the generator. This GAX cycle concept is capable of 
recovering an additional large amount of heat from the absorber and 
capable of utilizing higher generator temperatures than the AHE system and 
thus is capable of achieving much higher energy efficiencies. The heating 
efficiency of such GAX systems, relative to the particular fuel used, can 
be much higher than that of furnaces, boilers, etc. 
However, prior art GAX cycle systems suffered from the disadvantage that a 
separate heat transfer circuit using a separate heat transfer fluid was 
required. This heat transfer circuit had to be hermetic, required an 
expansion chamber, required a hermetic pump capable of variable flow, and 
required a system to control the amount of flow of the heat transfer fluid 
to match the GAX heat to be transferred in either the cooling or heating 
cycle at the particular outdoor temperature. Also, using a fluid in the 
heat transfer circuit different from the working fluid created the danger 
of cross-contamination between the heat transfer circuit and the absorber 
or generator. These prior art GAX systems typically used a heat transfer 
fluid that remained in the liquid phase and thus could only use the 
sensible heat of the heat transfer liquid. 
Electric heat pumps, which operate with a standard condenser-evaporator 
cycle, have heretofore been utilized for residential and small commercial 
heating and cooling applications. However, while electric heat pumps can 
effectively satisfy the heating and cooling requirements of residential 
and small commercial buildings in areas having relatively warm climates, 
such as the southern states of the United States, these electric heat 
pumps are not capable of providing, without auxiliary heating equipment, 
the necessary heating in climates where the temperatures drop below about 
30.degree. F. In addition, these electric heat pump systems typically use 
refrigerants that may be hydrochlorofluorocarbons (HCFC's) or 
chlorofluorocarbons (CFC's), which are environmentally hazardous. 
Thus, the need exists for a generator-absorber heat exchange apparatus and 
method suitable for use in a residential or small commercial heat pump 
that efficiently transfers a large portion of the heat produced by the 
absorption process in the absorber to the generator without the use of a 
costly, possibly failure prone, independent heat transfer circuit. 
The instant invention satisfies that need by providing a generator-absorber 
heat exchange apparatus and method that can use an environmentally safe 
fluid as both the working fluid and the heat exchange fluid, that 
efficiently recovers a large proportion of the heat generated by the 
absorption process in the absorber, that does not require an elaborate 
system of controls, that advantageously may use either or both the latent 
heat and the sensible heat of the working fluid to transfer heat from the 
absorber to the generator by operating between its vapor and liquid 
phases, and that, because of size, cost and efficiency, can be used to 
satisfy residential and commercial heating and cooling requirements over a 
wide range of climates, including sufficient heating at temperatures below 
0.degree. F. 
Additional features and advantages of the invention will be set forth in 
the drawings and written description which follow, and in part will be 
apparent from the drawings and written description or may be learned from 
the practice of the invention. The advantages of the invention will be 
realized and attained by the generator-absorber heat exchange apparatus, 
the heat pump incorporating the generator-absorber heat exchange apparatus 
and the method for transferring heat between an absorber and generator in 
a generator-absorber heat exchange apparatus, particularly pointed out in 
the drawings, written description and claims hereof. 
SUMMARY OF THE INVENTION 
To achieve these and other advantages, and in accordance with the purpose 
of the invention as embodied and broadly described herein, the present 
invention, in one aspect, provides a generator-absorber heat exchange 
apparatus that includes a generator and an absorber. The absorber has an 
interior pressure lower than the interior pressure of the generator and 
each has high and low temperature regions at opposite ends establishing 
respective temperature ranges. The temperature ranges of the generator and 
absorber define respective overlapping heat transfer regions. A fluid flow 
pathway is provided for circulating a liquor having rich, intermediate and 
weak concentrations of refrigerant to and through the high temperature, 
heat transfer and low temperature regions of the generator and the 
absorber. A heat exchange circuit is provided, which circuit receives a 
liquor from the generator at a location where the liquor has a rich liquor 
concentration. The heat exchange circuit also circulates the liquor 
between the heat transfer regions of the absorber and the generator to 
transfer heat from the absorber to the generator. 
In a preferred embodiment, the heat exchange circuit further comprises a 
heat exchange element disposed in the heat transfer region of the absorber 
and a conduit conducting the rich liquor from the generator through the 
heat exchange element and between heat transfer regions. 
In a further preferred embodiment, the heat exchange circuit comprises a 
heat exchange element disposed in the heat transfer region of each of the 
generator and absorber, and a conduit conducting the rich liquor from the 
generator serially to each heat exchange element sequentially between heat 
transfer regions. 
In accordance with another aspect of the invention, the heat exchange 
circuit preferably includes an input end in fluid communication with the 
generator at a location where the liquor has a rich liquor concentration. 
The heat exchange circuit may also include an output end for distributing 
the rich liquor circulated between heat transfer regions within the 
generator. The liquor circulated between heat transfer regions of the 
generator and absorber is preferably a two phase mixture of liquid and 
vapor in at least a portion of the heat exchange circuit. 
The present invention, in another aspect, comprises a generator-absorber 
heat exchange apparatus that includes a generator containing a liquor 
having a concentration gradient that is rich proximate an upper end, weak 
proximate a lower end and intermediate therebetween, and a temperature 
gradient extending from low proximate the upper end to high proximate the 
lower end with a heat transfer region therebetween. The generator-absorber 
heat exchange (GAX) apparatus in this aspect of the invention also 
includes an absorber having a pressure in its interior lower than the 
interior pressure of the generator and containing a liquor having a 
concentration gradient that is weak proximate an upper end, rich proximate 
a lower end and intermediate therebetween, and a temperature gradient 
extending from high proximate the upper end to low proximate the lower end 
with a heat transfer region therebetween. The GAX apparatus in this aspect 
also includes a rich liquor conduit having an inlet in fluid communication 
with the absorber proximate the lower end thereof and an outlet disposed 
in the generator proximate the upper end thereof distributing rich liquor 
from the lower end of the absorber for passage along the concentration and 
temperature gradients of the generator. A pump in fluid communication with 
the rich liquor conduit is also provided for moving fluid through the 
conduit between the absorber and the generator. A weak liquor conduit is 
provided having an inlet in fluid communication with the generator 
proximate the lower end thereof and an outlet disposed in the absorber 
proximate the upper end thereof distributing weak liquor from the lower 
end of the generator for passage along the concentration and temperature 
gradients of the generator. A heater is disposed to heat liquor in the 
generator proximate the lower end thereof. The GAX apparatus in this 
aspect of the invention also includes a heat exchange circuit comprising: 
a heat exchange element in the heat transfer region of the absorber, the 
heat transfer regions of the generator and absorber having overlapping 
temperatures; and 
a heat exchange conduit having an input end receiving liquor from the 
generator at a location where the liquor has a rich liquor concentration 
and conveying the liquor between the heat transfer regions of the absorber 
and the generator for heat transfer therebetween. The heat exchange 
conduit may also have an output end distributing the rich liquor in the 
generator. 
The present invention also provides, in another aspect, a heat pump 
comprising an indoor liquid to air heat exchanger, an outdoor liquid to 
air heat exchanger, the generator-absorber heat exchange apparatus and an 
antifreeze circuit. The antifreeze circuit in accordance with this aspect 
of the invention circulates antifreeze fluid between the indoor and 
outdoor heat exchangers and the generator-absorber heat exchange apparatus 
for selectively extracting heat from one of the heat exchangers and 
transferring heat to the other of the heat exchangers. 
In accordance with another aspect of the present invention, a method is 
provided for transferring heat between an absorber and a generator in a 
generator-absorber heat exchange apparatus. This heat transfer is 
accomplished by circulating a rich liquor between a heat transfer region 
of the absorber and a heat transfer region of the generator. As mentioned 
above, the heat transfer region of the generator and the heat transfer 
region of the absorber have temperature gradients including a common 
temperature range. 
In accordance with another aspect of the invention, a method is provided 
for transferring heat between a region of low temperature and a region of 
medium temperature using the generator-absorber heat exchange apparatus of 
the invention. This method comprises circulating an antifreeze fluid 
between an indoor heat exchanger and at least one of an absorber heat 
exchanger, a condenser heat exchanger and a generator heat exchanger, 
thereby transferring heat via the antifreeze fluid from the at least one 
absorber, condenser and generator heat exchanger to the indoor heat 
exchanger. The method also comprises circulating an antifreeze fluid 
between an outdoor heat exchanger and an evaporator heat exchanger, 
thereby transferring heat via the antifreeze fluid from the outdoor heat 
exchanger to the evaporator heat exchanger. 
In accordance with another aspect of the invention, a method is provided 
for transferring heat between a region of high temperature and a region of 
medium temperature using the generator-absorber heat exchange apparatus of 
the invention. This method comprises circulating an antifreeze fluid 
between an outdoor heat exchanger and at least one of an absorber heat 
exchanger, a condenser heat exchanger and a generator heat exchanger, 
thereby transferring heat via the antifreeze fluid from the at least one 
absorber, condenser and generator heat exchanger to the outdoor heat 
exchanger. The method also comprises circulating an antifreeze fluid 
between an indoor heat exchanger and an evaporator heat exchanger, thereby 
transferring heat via the antifreeze fluid from the indoor heat exchanger 
to the evaporator heat exchanger. 
Although the invention is illustrated as embodied in a gas-fired 
residential heat pump, the invention as broadly claimed is not so limited 
and its benefits and advantages apply equally to other heating and 
refrigeration processes. The above and other advantages and features of 
this invention will become apparent upon review of the following 
specification in conjunction with the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance with the invention, the term "weak liquor" as used herein 
refers to the liquor in the high temperature region of the generator or 
absorber, i.e., the bottom portion of the generator or the top portion of 
the absorber. The term "rich liquor" as used herein refers to the liquor 
in the low temperature region of the generator or absorber, i.e., the 
bottom portion of the absorber or the top portion of the generator. As 
used herein, the term "intermediate liquor" refers to a liquor that has a 
concentration of refrigerant that is less than the rich liquor 
concentration but greater than the weak liquor concentration. The various 
intermediate liquors are present in the absorber and/or the generator. The 
terms "weak," "intermediate" and "rich" refer to the relative 
concentration of the absorbed component(s), i.e., refrigerant, to the 
concentration of the absorbent component(s), i.e., water. Thus, a weak 
liquor liquid has less absorbed refrigerant, such as ammonia, and more 
absorbent, such as water, than an equal amount of a rich liquor liquid. 
As noted above, both the absorbed component(s) and the absorbent 
component(s) constituting the weak liquor, intermediate liquor and rich 
liquor may be in either a vapor or liquid state or a combination of the 
two. Also, the term "heat pump" as used herein is intended to include any 
apparatus that transforms heat between low, medium and high temperature 
states and is intended to include not only the commonly understood meaning 
of the term, but also as used herein is intended to include heat 
transformers as well as more traditional systems such as refrigeration, 
air conditioning, and related processes. 
In the known prior art system illustrated in FIG. 1, a generator-absorber 
heat exchange apparatus 10 operating on the generator-absorber heat 
exchange (GAX) cycle generally comprises a generator 12, an absorber 14, a 
condenser 16, an evaporator 18, a solution pump 38, and working fluid 
pathways for circulation of a refrigerant/absorbent liquor to and through 
generator 12 and absorber 14 and circulation of a refrigerant liquor 
through condenser 16 and evaporator 18. In particular, the 
refrigerant/absorbent liquor pathway includes a rich liquor pathway 21 
providing fluid communication of rich liquor 32 from a low temperature 
region C of absorber 14 to a low temperature region D of generator 12, and 
a weak liquor pathway 22 providing fluid communication of weak liquor 46 
from a high temperature region E of generator 12 to a high temperature 
region F of absorber 14. The refrigerant/absorbent liquor pathway is 
completed by passage of liquor from weak liquor pathway 22 through high 
temperature, intermediate temperature and low temperature regions F, G, C 
of absorber 14 and by passage of liquor from rich liquor pathway 21 
through low temperature, intermediate temperature and high temperature 
regions D, I, E of generator 12. The working fluid pathway is completed 
from generator 12 to condenser 16 through conduit 24, from condenser 16 to 
evaporator 18 through conduit 26, and from evaporator 18 to absorber 14 
through conduit 28. 
The terms "low temperature region," "intermediate temperature region" and 
"high temperature region" as used herein are meant to refer to relative 
temperatures. As depicted in FIG. 1, each region will be defined by a 
range of temperatures which in each particular component is relatively 
higher or lower than the other region. Thus, for example, high temperature 
region E of generator 12 might have a temperature of around 400.degree. F. 
and low temperature region D of generator 12 might have a temperature of 
around 200.degree. F. On the other hand, high temperature region F of 
absorber 14 might have a temperature of around 300.degree. F. and low 
temperature region C of absorber 14 might have a temperature of around 
100.degree. F. In each of generator 12 and absorber 14 there is an area of 
overlapping temperature termed herein the heat transfer region. This heat 
transfer region is depicted in FIG. 1 as the area between regions D and I 
of generator 12 and the area between regions G and F of absorber 14. 
An absorption generator for use with ammonia/water (or other fluid where 
the absorbent is volatile) is, in essence, a distillation column, which 
has a stripping section and a rectifying section. The stripping section is 
the lower, hotter section corresponding to the portion between regions D 
and E, while the rectifier section is the upper, cooler section 
corresponding to the portion above region D. The dividing point between 
the stripping and rectifying sections, region D, is the region of the 
generator that has a temperature corresponding to the boiling point of the 
rich liquor liquid at the generator pressure. As used herein, the term 
"generator" commonly refers to the stripping section, and the terms "high 
temperature region" and "low temperature region" when referring to the 
generator apply to regions E and D of the stripping section, respectively. 
As depicted in FIG. 1, the vertical temperature gradients of absorber 14 
and generator 12 are reversed, i.e., the highest temperature region E of 
generator 12 is at or near its lower, or bottom end, whereas the highest 
temperature region F of absorber 14 is at or near its upper end. Thus, the 
orientation of the respective heat transfer regions D-I and G-F is 
similarly opposite. The temperature range defining heat transfer regions 
D-I and G-F is within the temperature overlap between the temperature 
range of generator 12 and the temperature range of absorber 14, which may 
be within the range of, for example, about 200.degree. F. to about 
300.degree. F. (at the conditions used for rating heat pumps in the United 
States). 
The known apparatus depicted in FIG. 1 includes a heat transfer circuit 30 
disposed between heat transfer regions D-I and G-F of generator 12 and 
absorber 14, which is oriented so as to conduct fluid directly between 
areas of the heat transfer regions. 
During operation of the known system of FIG. 1, a low pressure refrigerant, 
consisting primarily of a refrigerant, such as ammonia, but possibly 
containing a small amount of absorbent, especially if the absorbent is 
volatile, as is water, exits evaporator 18 mostly as a vapor and passes 
through conduit 28 to absorber 14 at low temperature region C. This 
refrigerant vapor rising upward through absorber 14 is absorbed into a 
countercurrent flow of weak liquor, thus producing a rich liquor 32 that 
accumulates in the liquid state at low temperature region C of absorber 
14. This process takes place at a temperature above that of the 
surroundings, generating heat, some of which is transferred to air, water, 
antifreeze or other heat transfer fluid circulating during this process 
through heat exchanger 36 located in a heat exchange circuit 34. 
Rich liquor 32 is then transferred along rich liquor pathway 21 by a rich 
liquor pump 38 to region D of generator 12, where a higher pressure is 
maintained. A higher pressure is maintained in generator 12 than in 
absorber 14. For example, the pressure in generator 12 may commonly be 
around 240-400 psia and the pressure in absorber 14 may be around 15-80 
psia, depending on the operating temperature. In accordance with the 
absorber heat exchange (AHE) cycle principle, heat exchanger 40 in rich 
liquor pathway 21 is used to transfer absorber heat to rich liquor 32. In 
one alternative, rich liquor 32 is heated in heat exchanger 40 essentially 
to its boiling point at the pressure of generator 12 and provided as a 
heat input to region D of generator 12. Alternatively, as shown in FIG. 1, 
rich liquor 32 is heated in heat exchanger 40 to a temperature below its 
boiling point and thereafter is heated in heat exchanger 41 in the 
rectifier section above region D of generator 12. In either alternative, 
rich liquor 32 is distributed within generator 12 at region D. 
Heat source 42 and heat transfer fins 44 cooperate to heat rich liquor 32 
as it passes downward through generator 12, thereby driving off 
refrigerant vapor from rich liquor 32 to form weak liquor 46 at high 
temperature region E of generator 12. Vapor having a concentration of near 
100% refrigerant is expelled from generator 12 through refrigerant pathway 
24 to condenser 16 where it is condensed and fed via conduit 26 through 
restriction means 48 to a lower pressure in evaporator 18. Weak liquor 46 
in high temperature region E of generator 22 is returned through weak 
liquor pathway 22 through restriction means 23 to high temperature region 
F of absorber 14. The sensible heat of weak liquor 46 is provided as a 
heat input to generator 12 at heat exchanger 52. Heat may also be 
transferred in a heat exchanger (not shown) between rich liquor pathway 21 
and weak liquor pathway 22. 
In the known generator-absorber heat exchange system illustrated in FIG. 1, 
heat transfer is performed by a GAX heat transfer circuit 30, including, 
for example, a pair of heat exchange coils 50 and 53 and a pump 54 to 
circulate heat transfer fluid such as pressurized water. Since the 
vertical temperature gradients of absorber 14 and generator 12 are 
reversed, it is necessary to cross-connect the pathways between coils 50 
and 53, as illustrated in FIG. 1. 
The principle of the GAX cycle is illustrated in the 
pressure-temperature-composition diagram of FIG. 2 in which point D 
represents the dividing point between the stripping and rectifying 
sections of generator 12, point E represents the high temperature region 
of generator 12, point C represents the low temperature region of absorber 
14, point F represents the high temperature region of absorber 14, point I 
represents the region of generator 12 that is at a temperature lower than 
the temperature of point F in absorber 14 by an amount sufficient to 
provide the necessary temperature difference for heat transfer between 
those regions, and point G represents the region of absorber 14 that is at 
a temperature higher than the temperature of point D in generator 12 by an 
amount sufficient to provide the necessary temperature difference for heat 
transfer between those regions. These regions in FIG. 2 correspond to 
regions D, E, C, F, I and G, respectively, in FIG. 1. 
In FIG. 2, line D-I represents the heat transfer region of generator 12 and 
line G-F represents the heat transfer region of absorber 14. Points A and 
B represent the condenser 16 and evaporator 18, respectively. The line 
from C to D represents rich liquor pathway 21 and the line from E to F 
represents weak liquor pathway 22. The multiple arrows in FIG. 2 extending 
from the G-F line to the D-I line indicate heat transfer from the heat 
transfer region of absorber 14 to the heat transfer region of generator 
12. The single arrows extending from the line EF to the line IE and from 
the line CG to the line CD indicate heat transfer from heat exchanger 52 
to generator 12 and from absorber 14 to heat exchanger 40, respectively. 
The heat to be transferred from absorber 14 to generator 12 is available 
over a temperature range in absorber 14 and should be transferred to a 
temperature range in generator 12 that is cooler only by the temperature 
differential required to transfer the heat. To do this most efficiently, 
the heat from the hottest segment of heat transfer region F of absorber 14 
should be transferred to the hottest segment of heat transfer region I in 
generator 12, and similarly for each of the progressively cooler segments 
of heat transfer regions of absorber 14 and generator 12. This means that 
the heat transfer fluid temperature range must fit between the heat 
transfer region temperature ranges of generator 12 and absorber 14, and 
each of the segments. 
In accordance with the present invention, as embodied and broadly described 
herein, a heat exchange circuit is provided in a generator-absorber heat 
exchange apparatus that includes a generator and an absorber. The absorber 
has an interior pressure lower than the pressure of the generator interior 
and each of the generator and absorber has high and low temperature 
regions with vertically opposed temperature gradients and a heat transfer 
region. The temperature ranges defining the respective heat transfer 
regions overlap. The generator-absorber heat exchange apparatus includes a 
fluid flow pathway for circulation of a liquor having rich, intermediate 
and weak concentrations of refrigerant to and through the high 
temperature, heat transfer and low temperature regions of the generator 
and absorber. 
Like copending application Ser. No. 08/347,255, the present invention 
provides various embodiments and methods for performing GAX heat transfer 
in a generator-absorber heat exchange apparatus using the 
refrigerant/absorbent working fluid of the system. However, unlike the 
copending application, which uses the intermediate liquor as the heat 
transfer medium, the present application uses rich liquor as the heat 
transfer medium. As mentioned earlier, as used herein, the term "rich 
liquor" refers to a liquor in the low temperature regions of the generator 
and absorber, i.e., the bottom portion of the absorber and the top portion 
of the generator. 
The apparatus of the present invention includes a heat exchange circuit 
that receives a liquor from the generator at a location where the liquor 
has a rich liquor concentration and circulates the rich liquor between the 
heat transfer regions of the absorber and the generator to transfer heat 
from the absorber to the generator. The term "heat transfer region" as 
used herein is intended to include not only regions in the interior of the 
generator and absorber having overlapping temperatures, but also those 
regions adjacent to or in heat transfer contact with the interior of the 
generator and absorber having overlapping temperatures. The transfer 
should preferably be provided over the full overlap temperature range. 
In accordance with the invention, as embodied and broadly described herein, 
the heat exchange circuit comprises a heat exchange element disposed in 
the heat transfer region of the absorber and a conduit conducting the rich 
liquor from the fluid flow pathway through the heat exchange element and 
between heat transfer regions. The heat exchange circuit of the invention 
may also include a heat exchange element disposed in the heat transfer 
region of the generator with a conduit conducting the rich liquor from the 
fluid flow pathway serially to each heat exchange element sequentially 
between heat transfer regions. The term "heat exchange element" as used in 
accordance with the invention refers to any apparatus or device that is 
capable of providing for the exchange of heat between fluids, such as a 
heat exchange coil. 
In accordance with the invention, as embodied and broadly described herein, 
the motive force for circulating the liquor in the heat exchange circuit 
is preferably provided by a liquid head, but may also be provided in some 
instances by a pump. The heat exchange circuit also preferably includes an 
input end in fluid communication with the fluid flow pathway for 
withdrawing rich liquor from the generator and an output end for 
distributing the liquor within the generator. 
The present invention, as illustrated in FIGS. 3 and 4, includes an input 
end in fluid communication with the generator at a location where the 
liquor has a rich liquor concentration, thus using the rich liquor as the 
heat transfer medium. This input end may consist of any suitable device 
for accumulating a liquid. 
The present invention, as illustrated in FIGS. 3 and 4, also includes an 
output end for the heat exchange circuit to distribute the rich liquor 
circulated between heat transfer regions into the generator. This output 
end may be any device capable of distributing a liquid or a vapor/liquid 
mixture, such as a distributor in the case of a liquid, or a 
separator/distributor in the case of vapor/liquid mixtures. 
The present invention, as illustrated by FIGS. 3 and 4, uses a working 
fluid as the heat transfer medium that is preferably a two phase 
liquid/vapor mixture in at least a portion of the heat exchange circuit 
and thus takes advantage of the latent heat of the working fluid. 
One embodiment of the invention, shown in FIG. 3, uses a working fluid 
removed from generator 12 as the heat transfer fluid. This working fluid 
is a liquid/vapor two phase fluid in at least a portion of the heat 
exchange circuit, and thus exploits the latent heat of the working fluid. 
Referring specifically to FIG. 3, a generator-absorber heat exchange 
apparatus 300 is illustrated. In this embodiment, the heat exchange 
circuit comprises heat exchange coil 352 located in the heat transfer 
region of absorber 14. A heat exchange conduit 356 is provided which 
includes an input end disposed to withdraw rich liquor from a location at 
or above region D of generator 12 and an output end that can be, for 
example, a separator/distributor 360 preferably located proximate to 
region I of generator 12 for distributing the rich liquor. The input end 
in FIG. 3 is shown as liquid accumulator 362, and may be any means to 
collect rich liquor liquid in the interior of generator 12. Heat exchange 
conduit 356 conducts the rich liquor between heat transfer regions of 
generator 12 and absorber 14. 
In accordance with this embodiment of the invention, the motive force for 
circulating rich liquor between generator 12 and absorber 14 may be 
gravity, in the form of the liquid head from the rich liquor collected by 
liquid accumulator 362. The rich liquor is circulated through heat 
exchange conduit 356 to heat exchange coil 352 where at least a portion of 
the rich liquor is vaporized by the heat of absorber 14. The two phase 
mixture of rich liquor is then circulated via heat exchange conduit 356 to 
separator/distributor 360 in generator 12. Separator/distributor 360 
separates the two phase mixture and provides the liquid and vapor to 
generator 12, preferably at a location where the temperature and pressure 
in generator 12 is the same or similar to the temperature and pressure of 
rich liquor exiting separator/distributor 360. In this embodiment, 
separator/distributor 360 is preferably located proximate to region I of 
generator 12. 
As mentioned, the rich liquor in this embodiment is a two phase mixture of 
vapor and liquid in at least a portion of heat exchange conduit 356. The 
rate of flow of rich liquor through heat exchange conduit 356 is 
controlled by the amount of liquid collected in liquid accumulator 362, 
the difference in height between liquid accumulator 362 and 
separator/distributor 360, the pressure drop through heat exchange conduit 
356 and by the amount of vapor evaporated from the rich liquor liquid in 
heat exchange coil 352. The inlet section of heat exchange conduit 356 
between liquid accumulator 362 and the bottom of heat exchange coil 352 is 
filled with rich liquor liquid. The liquor in heat exchange coil 352 is 
partly liquid and partly vapor, having a density well below that of the 
liquid in the inlet section of heat exchange conduit 356, thus increasing 
the head between the liquid accumulator 362 and separator/distributor 360. 
The extent to which the inlet liquid is vaporized in heat exchange coil 
352 thus helps control the flow through heat exchange conduit 356. By 
properly adjusting the pressure drop in heat exchange conduit 356, the 
flow of rich liquor can be controlled by the amount of heat transfer in 
heat exchange coil 352. It is important that the rich liquor collected by 
liquid accumulator 362 be greater than the largest amount of rich liquor 
to be used for heat transfer. In other words, there should be a small 
overflow from liquid accumulator 362 to maintain an appropriate height 
between the liquid surface in liquid accumulator 362 and the outlet of 
separator/distributor 360. 
Another embodiment of the invention, shown in FIG. 4, uses working fluid 
removed from generator 12 as the heat transfer fluid. This fluid is also a 
liquid/vapor two phase mixture in at least a portion of the heat exchange 
circuit, and thus takes advantage of the latent heat of the working fluid. 
Referring specifically to FIG. 4, a generator-absorber heat exchange 
apparatus 400 is illustrated. In this embodiment, the heat exchange 
circuit comprises heat exchange coil 442 located in the heat transfer 
region of absorber 14 and heat exchange coil 444 located in the heat 
transfer region of generator 12. A heat exchange conduit 430 is provided 
which includes an input end disposed to withdraw rich liquor from 
generator 12 and an output end that is preferably a distributor 435 for 
distributing the rich liquor. The input end in FIG. 4 is shown as liquid 
accumulator 440, which is preferably located proximate to region D of 
generator 12, and may be any means to collect rich liquor liquid in the 
interior of generator 12. 
In accordance with this embodiment of the invention, the motive force for 
circulating rich liquor between generator 12 and absorber 14 may be the 
liquid head between liquid accumulator 440 and the inlet of heat exchange 
coil 442, as in the embodiment of FIG. 3. Alternatively, if necessary, the 
motive force may be provided by heat exchange circuit pump 445, shown in 
FIG. 4. The rich liquor is circulated through heat exchange conduit 430 to 
heat exchange coil 442 in the heat transfer region of absorber 14 where at 
least a portion of the rich liquor is vaporized by the heat of absorber 
14. The two phase mixture of rich liquor is then circulated via heat 
exchange conduit 430 to heat exchange coil 444 in the heat transfer region 
of generator 12 where it is cooled and the vapor is reabsorbed, giving up 
its heat to the interior of generator 12. The rich liquor exits heat 
exchange coil 444 at distributor 435. Distributor 435 is preferably 
located where the temperature and pressure in generator 12 is the same or 
similar to the temperature and pressure of rich liquor exiting distributor 
435. In this embodiment, distributor 435 is preferably located at the same 
level or just below accumulator 440 in generator 12. 
As mentioned, the rich liquor in this embodiment is a two phase mixture of 
vapor and liquid in at least a portion of heat exchange conduit 430. The 
amount of flow of rich liquor between heat exchange coils 442 and 444 may 
be the total flow of rich liquor collected or may be controlled as 
described earlier herein, or by heat exchange circuit pump 445, to 
optimize the amount of heat transferred from absorber 14 to generator 12. 
As in the embodiment of FIG. 3, the liquid accumulator and distributor can 
be combined into a single accumulator/distributor, thereby allowing easy 
control of GAX heat transfer by controlling the flow rate of rich liquor 
through the heat exchange circuit. 
In all of the embodiments of the invention described herein and variations 
thereof, it is preferable to orient the flow of heat transfer liquid, or 
liquid and vapor mixture, vertically upwards when passing such through a 
heat exchange coil in either the generator or absorber. This flow 
orientation generally best matches the temperature gradients in the 
absorber and generator and provides the best counterflow temperature 
differentials between the rising coil contents and falling liquids in the 
absorber or generator. 
In accordance with the embodiments of the GAX heat transfer apparatus 
described herein, the heat exchange coils can be located in the interior 
of the generator and absorber. Alternatively, in accordance with the 
invention, the heat exchange coils can be located at the exterior of the 
generator and absorber adjacent to and/or in heat transfer contact through 
metal walls with the region in which heat transfer is desired. The term 
"heat transfer region" as used herein is meant to include the interior of 
the generator or absorber, as well as regions outside the generator or 
absorber adjacent to and/or in heat transfer contact with the region in 
which heat transfer is desired. 
The various embodiments of the generator-absorber heat exchange apparatus 
of the invention can advantageously be used in a heat pump. Referring to 
FIG. 5, a heat pump 700 is provided which uses one of the 
generator-absorber heat exchange apparatuses of the invention. The heat 
pump 700 includes an outdoor heat exchange coil 752 and an indoor heat 
exchange coil 754. Indoor heat exchange coil 754 may optionally include an 
air transport apparatus 756, such as a fan or blower for supplying heated 
or cooled air into a building. Outdoor heat exchange coil 752 may also 
optionally include an air transport apparatus 757, such as a fan or 
blower. Outdoor and indoor heat exchange coils 752 and 754, and air 
transport apparatuses 756 and 757, can be any of the standard, known 
equipment used in heat pump or air conditioning systems. 
Heat pump 700 is comprised of two major sections, the generator-absorber 
heat exchange apparatus (absorption unit) and the antifreeze fluid system. 
The generator absorber heat exchange apparatus in accordance with the 
invention can be made up of the components discussed earlier herein, 
including an absorber 14, generator 12, condenser 16 and evaporator 18. 
The antifreeze fluid system is divided into a cold fluid circuit and a hot 
fluid circuit. The antifreeze fluids that can be used in accordance with 
the invention include those fluids known to be useful in transferring 
heat. A preferred antifreeze fluid is a water solution including an 
antifreeze liquid that is nontoxic and nonflammable, such as, for example, 
propylene glycol. 
Contrary to standard heat pump systems that reverse the refrigeration 
circuit to change from cooling to heating, heat pump 700 of the invention, 
rather than reversing the refrigeration circuit, uses a system flow 
control apparatus 758, which is preferably an eight-way valve, that is 
capable of reversing the antifreeze circuits. System flow control 
apparatus 758 makes it possible to direct the cold and the hot antifreeze 
fluids from the cold evaporator 18 or from the hot condenser 16, absorber 
14 and rectifier of generator 12 either to the outdoor heat exchange coil 
752 or to the indoor heat exchange coil 754. 
The cold antifreeze circuit comprises evaporator 18, which chills the 
antifreeze fluid via evaporator heat exchange coil 786, extracting from 
the antifreeze fluid the heat removed from the house or building in the 
summer or from the outdoor air in winter. 
The hot antifreeze circuit comprises absorber 14, condenser 16 and 
rectifier of generator 12, which raise the temperature of the extracted 
heat to well above 100.degree. F. The sum of the heat outputs of absorber 
14, condenser 16 and rectifier of generator 12 is equal to the sum of the 
two heat input quantities, one from the gas flame and the other being the 
low temperature heat input to evaporator 18. Absorber 14, rectifier of 
generator 12 and condenser 16 transfer the system output heat to the hot 
antifreeze fluid via absorber heat exchange coil 778, rectifier heat 
exchange coil 772 and condenser heat exchange coil 768. In the winter, the 
hot antifreeze fluid transfers much more heat to the house or building 
than that from the gas flame. In many areas, supplemental heat may not be 
required. 
In one specific embodiment of the heat pump of the invention, illustrated 
in FIG. 5, the hot antifreeze circuit includes a first conduit 762 which 
transports the antifreeze fluid from system flow control apparatus 758 to 
a first flow control device 764, which can be, for instance, a flow 
splitter. A fluid transport apparatus 760, such as a pump, is used to 
circulate the antifreeze fluid through the hot antifreeze circuit. Fluid 
transport apparatus 760 can be located anywhere in the hot antifreeze 
circuit, but is preferably located in first conduit 762. 
In accordance with this embodiment, a first portion of the antifreeze fluid 
from first conduit 762 is directed via first flow control device 764 to a 
second conduit 766, which transports the antifreeze fluid to condenser 
heat exchange coil 768. In condenser heat exchange coil 768, heat is 
transferred from condenser 16 to the antifreeze fluid. The antifreeze 
fluid is transported from condenser heat exchange coil 768 to rectifier 
heat exchange coil 772 via third conduit 770. In rectifier heat exchange 
coil 772, heat is transferred from generator 12 to the antifreeze fluid. 
The antifreeze fluid is transported from rectifier heat exchange coil 772 
back to system flow control apparatus 758 via fourth conduit 774. 
A second portion of the antifreeze fluid in this embodiment from first 
conduit 762 is directed via first flow control device 764 to a fifth 
conduit 776, which transports the antifreeze fluid to absorber heat 
exchange coil 778. In absorber heat exchange coil 778, heat is transferred 
from absorber 14 to the antifreeze fluid. The antifreeze fluid is 
transported from absorber heat exchange coil 778 via sixth conduit 780 
into fourth conduit 774 and back to system flow control apparatus 758. 
The particular flow arrangement for the hot antifreeze circuit illustrated 
by FIG. 5 is meant to be illustrative only and should not limit the 
invention. Other flow arrangements for the antifreeze fluid between 
absorber 14, condenser 16 and generator 12 are within the scope of the 
invention. For example, the flow of antifreeze fluid through absorber 14, 
condenser 16 and generator 12 may be in parallel, as shown, or in series. 
However, depending on the application, it may be preferred that the flow 
through condenser 16 and absorber 14 be in parallel, as shown in FIG. 5. 
The cold antifreeze circuit includes a first conduit 782 which circulates 
antifreeze fluid from system flow control apparatus 758 to evaporator heat 
exchange coil 786. In evaporator heat exchange coil 786, heat is 
transferred from the antifreeze fluid to evaporator 18. The antifreeze 
fluid is transported from evaporator heat exchange coil 786 back to system 
flow control apparatus 758 via second conduit 788. A fluid transport 
apparatus 784, such as a pump, is used to circulate the antifreeze fluid 
through the cold antifreeze circuit. Fluid transport apparatus 784 can be 
located anywhere in the cold antifreeze circuit, but is preferably located 
in first conduit 782. The particular flow arrangement for the cold 
antifreeze circuit illustrated by FIG. 5 is meant to be illustrative only 
and should not limit the scope of the invention. 
System flow control apparatus 758 directs the cold antifreeze to indoor 
heat exchange coil 754 in summer and to outdoor heat exchange coil 752 in 
winter, at the same time directing the hot antifreeze to outdoor heat 
exchange coil 752 in summer and to indoor heat exchange coil 754 in 
winter. This method of reversing the flows to meet the household or 
building needs for heating or cooling also can also be used during the 
winter to defrost outdoor heat exchange coil 752, when desired, by 
reversing the flow to direct hot antifreeze to outdoor heat exchange coil 
752. 
The choice of materials of construction for all the embodiments described 
herein and variations thereof depends upon the components of the working 
fluid, i.e., the refrigerant and absorbent, and the expected operating 
pressure and temperature ranges. For an ammonia and water absorption 
solution operating up to about 300.degree. F. (thus excluding the lower 
region of the generator) and pressures up to about 300 psia, mild steel is 
the preferred choice of material for all components contacting the 
solution. Aluminum, however, may be used for the evaporator and condenser, 
which come into contact with ammonia. The choice of materials of 
construction for other solutions should be known to those skilled in the 
art of absorption systems. 
While the various GAX heat transfer means described herein have been 
illustrated in a residential or light commercial heat pump, their benefits 
are not limited to such applications. The enhanced performance provided by 
the various GAX heat transfer schemes set forth herein may be applied to 
processes requiring medium temperature heating and cooling such as 
brewing, food processing, pasteurizing and paper making, to mention but a 
few examples. Furthermore, the principles of the invention are not limited 
to absorption heat pump cycles that efficiently convert heat from a 
combination of low and high temperature heat sources to heat at a medium 
temperature. The invention is equally applicable to heat transformers 
which convert heat from a medium-high temperature, such as hot waste water 
discharged from a processing plant, to produce a useful high temperature 
output plus a lower temperature output. 
It will be apparent to those skilled in the art that various modifications 
and variations can be made in the generator-absorber heat exchange 
apparatus, heat pump and method of transferring heat between the generator 
and absorber without departing from the spirit or scope of the invention. 
Thus, it is intended that the present invention cover the modifications 
and variations of this invention provided that they come within the scope 
of the appended claims and their equivalents.