Air conditioner for an automobile

An air conditioner for an automobile includes two pairs of hydrogen storage cells. Each cell includes a hydride-forming material, which absorbs hydrogen while generating heat, and releases hydrogen while absorbing heat. One pair of cells operates as an air conditioner, absorbing heat from the interior of the automobile and discharging heat to the outside. The other pair of cells is regenerated by supplying heat from the engine exhaust to one of the cells, while allowing heat generated at the other cell of the pair to be discharged to the outside. A system of valves is arranged such that one cell pair is always functioning as an air conditioner while the other cell pair is being regenerated.

BACKGROUND OF THE INVENTION 
This invention relates to a heat pump for cooling an automobile. The heat 
pump is driven by waste heat from the engine. The present invention 
eliminates the need for a compressor. In conventional air conditioners, a 
compressor consumes a significant part of the engine horsepower. The 
present invention also eliminates the need for chlorofluorocarbons, which 
destroy ozone in the upper atmosphere. 
A typical heat load for an automobile air conditioner is 12,000 BTU per 
hour. It takes about 18,000 BTU per hour to drive the heat pump of the 
present invention. A typical engine produces about 11 pounds of exhaust 
gas at 500.degree. C. per horsepower-hour. Thus, if the engine is 
operating at 20 horsepower, and the gas is cooled by 200.degree. C., the 
amount of heat produced by the engine, per hour, is 
EQU (20 hp)(11 lb/hp/hr)(200.degree. C.)(0.45 Btu/lb/.degree.C.), 
where 0.45 Btu/lb/.degree.C. is the specific heat of air. The above 
expression equals 19,800 Btu per hour, which is sufficient to drive the 
heat pump. 
An essential component of the heat pump of the present invention is the 
hydrogen storage cell described in U.S. Pat. No. 4,599,867. The cell 
comprises a nest of metal fins that are traversed by tubes that carry a 
heat transfer fluid. The fins are coated with a metal hydride or with a 
metal capable of forming a hydride. Also essential to this heat pump is 
U.S. Pat. No. 4,799,360, entitled "Method of Binding a Metal Hydride to a 
Surface". The disclosures of the above-cited patents are incorporated by 
reference herein. 
SUMMARY OF THE INVENTION 
In the preferred embodiment, the present invention includes two pairs of 
hydrogen storage cells. All of the cells are substantially identical, and 
can be constructed according to the teachings of the above-cited patents. 
The cells are connected, in a manner to be described, with first, second, 
and third heat exchangers. The first heat exchanger continuously absorbs 
heat from the interior of the automobile. The second heat exchanger 
continuously rejects heat to the ambient air outside of the automobile. 
The third heat exchanger continuously absorbs heat generated by the 
engine. A heat transfer fluid circulates between the cells and the heat 
exchangers. There is also a hydrogen conduit connecting the two cells of 
each pair. 
The invention also includes an arrangement of valves for routing the flow 
of heat transfer fluid between the heat exchangers and the hydrogen 
storage cells. The connections are made as follows: 
______________________________________ 
During any During the next 
interval of time 
interval of time 
______________________________________ 
First exchanger: 
First cell of the 
First cell of 
first pair the second pair 
Second exchanger: 
Second cell of the 
Second cell of the 
first pair, and 
second pair, and 
first cell of the 
first cell of the 
second pair first pair 
Third exchanger: 
Second cell of the 
Second cell of the 
second pair first pair. 
______________________________________ 
The operation of the apparatus is summarized as follows. The first 
exchanger absorbs heat from the interior of the automobile, and this heat 
is conveyed to the first cell of the first pair of cells. When the cell 
absorbs heat, it releases hydrogen, and this hydrogen is conveyed to the 
second cell of the first pair of cells. The hydrogen is absorbed by this 
second cell, which generates heat, and this heat is discharged to the 
outside by the second heat exchanger. 
While the first cell pair is operating as an air conditioner, the second 
cell pair is being regenerated. Heat from the engine exhaust is absorbed 
by the third heat exchanger, which conveys this heat to the second cell of 
the second pair of cells. This second cell releases hydrogen which is 
conveyed to the first cell of the second pair of cells. The latter cell 
absorbs the hydrogen, releasing heat, and this heat is discharged to the 
outside by the second heat exchanger. 
Periodically, the valves are switched to their second position. In the 
second position, the second cell pair is connected to do the air 
conditioning and the first cell pair is regenerated, in the same manner as 
described above. Then, after a predetermined interval, the valves are 
switched again to their first position. Because the valves are 
continuously switched back and forth, at predetermined intervals, the air 
conditioner can operate without interruption. 
It is therefore an object of the invention to provide an air conditioner 
for an automobile, in which the air conditioner uses the principle of 
hydriding and dehydriding to pump the heat. 
It is another object to provide an air conditioner for an automobile that 
is driven by waste heat in the exhaust gas. 
It is another object to provide an air conditioner for an automobile, 
wherein the air conditioner includes two pairs of hydrogen storage cells, 
and wherein one cell of each pair is always being regenerated, so that the 
air conditioner can operate substantially without interruption. 
It is another object to provide a heat pump that can be driven by waste 
heat from any source.

DETAILED DESCRIPTION OF THE INVENTION 
When a metal absorbs hydrogen to form a hydride, heat is evolved. 
Conversely, when the hydride evolves its hydrogen, heat is absorbed. A 
metal hydride heat pump requires two hydrides. If the hydrides are at the 
same temperature, one of the hydrides must exert a higher pressure of 
hydrogen than the other hydride. Conversely, for a hydride at a given 
temperature, there exists another temperature, different from the first, 
such that another hydride operating at this second temperature will exert 
the same pressure as the first. Thus, the high-pressure hydride can evolve 
hydrogen at a low temperature, and absorb heat, while the evolved hydrogen 
is being absorbed by the low-pressure hydride at some higher temperature, 
where the heat is being rejected. In the present case, the lower 
temperature is somewhat below that inside the automobile, and the higher 
temperature is somewhat above that of the air outside the automobile. 
A pair of hydrogen storage cells therefore can function as an air 
conditioner, as follows. One of the cells absorbs heat from the interior 
of the automobile, thereby giving off hydrogen. The evolved hydrogen is 
absorbed by the other cell, thereby causing that cell to release heat. If 
the heat given off by the second cell is discharged to the outside, there 
is a net transfer of heat from the interior to the exterior of the 
automobile. 
In the arrangement described above, the hydrogen must periodically be 
evolved from the second hydride and reabsorbed into the first hydride. 
This process is called regeneration. Regeneration must be driven by heat 
available at a temperature above that of the ambient air. In the present 
invention, the engine exhaust is the source of this high temperature heat. 
To accomplish regeneration, the second hydride is heated, indirectly, by 
the engine exhaust, and the first hydride is cooled, indirectly, by the 
ambient air. 
To provide continuous cooling, it is necessary to have first and second 
pairs of hydrogen storage cells. One pair performs the cooling while the 
other pair is being regenerated. At all times, heat is being absorbed 
continuously from the air inside the automobile, continuously rejected to 
the outside air, and continuously absorbed from the exhaust. The heat 
transfer is accomplished most efficiently by providing first, second, and 
third heat exchangers, one for each heat transfer task. Each exchanger 
operates at a constant temperature, so that it does not impose a parasitic 
cooling load when the hydrogen storage cells alternate between cooling and 
regeneration. It is only necessary to reroute the flow when the cells 
switch from cooling to regenerating. 
FIG. 1 shows the essential components of the invention in schematic form. 
There are four hydrogen storage cells, identified by reference numerals 
10, 11, 12, and 13. Cells 10 and 11 form the first pair of cells, and 
cells 12 and 13 form the second pair. Cells 10 and 11 are connected by a 
hydrogen conduit, represented symbolically by dotted line 60. Cells 12 and 
13 are similarly connected by a hydrogen conduit represented by dotted 
line 61. The construction of all of the hydrogen storage cells can be as 
described in U.S. Pat. No. 4,599,867. 
Cells 10 and 12 are designated as the first cells of their respective 
pairs; cells 11 and 13 are the second cells of their pairs. In the 
figures, the pairs are identified by numbers (e.g. "Pair 1") and the cells 
within a pair are identified by letters (e.g. "Cell A"). 
There are three heat exchangers 20, 21, and 22. Exchanger 20 absorbs heat 
from the air inside the automobile. Exchanger 21 rejects heat to the 
outside air. Exchanger 22 absorbs heat from the engine exhaust. These 
exchangers can be of the type resembling automobile radiators, i.e. a nest 
of fins traversed by heat transfer tubes, but are not limited to a 
particular structure. 
There are five valves, 30, 31, 32, 33, and 34, for routing the flow of the 
heat transfer fluid. FIG. 1 shows these valves in a first of two 
positions. There are also four check valves 35, 36, 37, and 38, which 
permit the fluid to flow in only one direction. There are three pumps 40, 
41, and 42 for circulating the heat transfer fluid. 
At the interval of time captured in FIG. 1, the cells and exchangers are 
connected as follows: 
Cell 10 with exchanger 20 
Cell 11 with exchanger 21 
Cell 12 with exchanger 21 
Cell 13 with exchanger 22 
During this time interval, heat from the interior of the automobile is 
absorbed by exchanger 20, and transferred to cell 10. Cell 10 absorbs this 
heat and gives off hydrogen. The hydrogen is conveyed to cell 11, the 
second cell of the pair. Cell 11 absorbs the hydrogen while releasing 
heat, and this heat is conveyed to exchanger 21, which transfers the heat 
to the outside. Thus, cells 10 and 11, the first cell pair, function as an 
air conditioner. 
At the same time, cells 12 and 13, the second cell pair, are being 
regenerated. Heat from the engine exhaust is absorbed by exchanger 22 and 
transferred to cell 13, the second cell of the second pair of cells. When 
heat is applied to cell 13, the cell gives off hydrogen, which is conveyed 
to cell 12, the first cell of the pair. Cell 12 absorbs the hydrogen, and 
gives off heat, and this heat is conveyed to exchanger 21, which transfers 
the heat to the outside. 
During the next interval of time, the cells and exchangers are connected in 
this way: 
Cell 10 with exchanger 21 
Cell 11 with exchanger 22 
Cell 12 with exchanger 20 
Cell 13 with exchanger 21 
This arrangement is shown in FIG. 2. In FIG. 2, the reference numerals are 
unchanged, as the components are the same. The only difference is in the 
position of the three-way valves. 
In the valve position shown in FIG. 2, heat from the automobile interior is 
absorbed by exchanger 20 and conveyed to cell 12. This heat is absorbed by 
cell 12, which generates hydrogen. The hydrogen is conveyed to cell 13, 
which absorbs the hydrogen, and gives off heat. This heat is discharged to 
the outside, through exchanger 21. 
At the same time, as shown in FIG. 2, heat from the automobile exhaust is 
absorbed by exchanger 22, and conveyed to cell 11. This heat is absorbed 
by cell 11, which gives off hydrogen, and the hydrogen is carried to cell 
10. Cell 10 absorbs the hydrogen, and gives off heat which is discharged 
to the outside through exchanger 21. 
Thus, in FIG. 2, cells 12 and 13 comprise the pair which is doing the 
cooling, and cells 10 and 11 comprise the pair which is being regenerated. 
The valves are periodically switched from the position shown in FIG. 1 to 
the position shown in FIG. 2, and back. Thus, at all times, there is one 
pair of cells doing the air conditioning and the other pair of cells being 
regenerated. 
The same heat transfer fluid circulates through all of the cells and 
exchangers in FIGS. 1 and 2. Advantageously, this is the same glycol-water 
mixture that is used for engine coolant. In one embodiment, hot coolant 
from the engine could be used to drive the heat pump. 
It would be possible to reconstruct FIGS. 1 and 2 so that each of the four 
cells has its own heat exchanger. The exchangers connected to cells 10 and 
12 would alternate between being contacted with cool air inside the 
automobile and warm air outside the automobile. Cooling the mass of the 
exchanger imposes a parasitic load on the heat pump. The exchangers 
connected to cells 11 and 13 would alternate between outside air and 
exhaust gas. 
There are several reasons to prefer the arrangement of FIG. 1: 
1. There are three exchangers instead of four: 
2. The parasitic load for cooling two exchangers is eliminated; 
3. Only one exchanger must withstand hot, corrosive exhaust gas; 
4. Each exchanger can be optimally sized to do just one task; and 
5. Valves for routing heat transfer liquid are smaller and cheaper than 
valves for routing gases. 
The five two-position three-way valves in FIG. 1 are the minimum number of 
valves needed to prevent the mixing of liquids circulating at different 
temperatures. Consider the circuit of cell 10, exchanger 20, and pump 40, 
in FIG. 1. All of the liquid emerging from cell 10 must return to the 
circuit via line 50. There is only a small amount of inout surge through 
line 51, because the lines are completely filled with liquid, and because 
there is no return path for the liquid. The same applies to the circuit of 
cell 13, exchanger 22, and pump 41. And, no liquid can escape from the 
circuit that comprises cells 11 and 12 in parallel, pump 42, and exchanger 
21. It is important to prevent warmer liquid from mixing with the cold 
liquid that is circulating through cell 10, because this would create 
parasitic heat load. Check valves 35, 36, 37, and 38 are needed to prevent 
this mixing. 
In the position represented by FIG. 2, fluid flows in line 51, but does not 
flow from cells 11 and 12 towards pump 42, because there is again no 
return path for the fluid. 
Note that each of the heat exchangers 20, 21, and 22 is operating at a 
constant temperature, and does its heat transfer task continuously. If the 
heat exchangers were not at constant temperatures, one would need to 
expend energy to change the temperatures of the ex-hangers, and to do so 
would be wasteful. 
This heat pump is not limited to cooling automobiles. Trucks, ships, and 
army tanks also need cooling. Some commercial buildings have waste heat 
that could drive a heat pump. 
Although the invention has been described with respect to the particular 
embodiment shown, it is understood that other variations are possible. The 
invention is not limited by the types of valves or by the specific 
construction of the hydrogen storage cells. As stated above, other circuit 
topologies could be used. These and other modifications should be deemed 
within the spirit and scope of the following claims.