Heat pump

Heat pump apparatus employing a continuous loop passageway containing a plurality of freely-movable, unrestrained bodies. The bodies are accelerated around the passageway in one direction by adiabatic expansion of a fluid between the bodies in an expander region of the passageway. The expanded, cooler fluid is discharged from the passageway via one or more vent-intake ports in the passageway beyond the expander region. Warmer fluid enters the passageway via said ports and is compressed between the propelled bodies in a compression region of the passageway, thereby raising its temperature from a first temperature (e.g., the temperature of the outdoor atmosphere or an industrial waste heat stream) to a second temperature higher than the first. The compressed, warmer fluid is thereafter passed through a heat exchanger to extract heat. In passing through the compression region the bodies are decelerated and they then pass through a thruster region of the passageway wherein a force is applied to the bodies to counterbalance the external forces acting against the bodies as they move around the loop passageway. From the thruster region the bodies pass to the expander region to repeat the cycle. From the heat exchanger the fluid, typically together with additional compressed fluid from an external source, is introduced into the expander region to again accelerate the bodies.

BACKGROUND OF THE INVENTION 
As is known, the usual heat pump used to heat buildings, for example, 
includes an electrically-driven compressor, a throttling valve, an 
evaporator located in the ambient atmosphere outside the building, and a 
condenser within the building which discharges heat as a refrigerant is 
condensed. Such systems are relatively complicated, have low coefficients 
of performance based upon actual thermal conversion and, of course, 
require a liquid refrigerant which tends to be expensive and may have 
toxic properties. Furthermore, the energy input into the system is usually 
electrical and, hence, does not utilize the heat rejected in the 
electrical energy production. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a heat pump is provided which can 
be used with a heat source (such as natural gas, oil or coal), or a 
motor-driven compressor and which can operate on simple fluids such as air 
in contrast to the more expensive and toxic refrigerants used in 
conventional prior art heat pumps. At the same time, the heat pump of the 
invention is of relatively simple construction and has a high coefficient 
of performance. 
The invention is based on certain of the principles set forth in Fawcett et 
al U.S. Pat. No. 3,859,789 directed to a unidirectional energy converter 
wherein bodies movable around a continuous loop passageway are utilized to 
convert one form of energy to another form of energy. In contrast to the 
apparatus shown in U.S. Pat. No. 3,859,789, however, the purpose of the 
present invention is to increase the heat content, and therefore, the 
temperature, of a fluid such as air at one location and decrease it at 
another. That is, the apparatus is used to move or "pump" heat from a 
reservoir at a colder temperature (for example, the outdoor air or a waste 
heat stream) to a reservoir at a warmer temperature (for example, the 
indoor air or a process heat stream). When used for cooling purposes, the 
reservoirs are simply reversed with the heat pump taking heat from the 
cooler indoors and exhausting it to the warmer outdoors as in a 
conventional air-conditioning system. 
Specifically, in accordance with the invention, there is provided a 
continuous loop passageway containing a plurality of freely-movable, 
unrestrained bodies. A source of compressible fluid (e.g., air or a 
liquefiable vapor such as Freon, etc.) under pressure is provided for 
generating a force to accelerate successive ones of the bodies in one 
direction around the passageway. Energy transfer takes place in which 
process adiabatic expansion of the fluid is used to impart kinetic energy 
to the bodies. In a region in the passageway beyond the region in which 
fluid expansion takes place (i.e., the expander region), ports are 
provided to permit the exhaust of the very cool working fluid and entrance 
of a warmer charge of fluid such as outdoor air. In a closed system (e.g., 
Freon, etc. fluid), these ports are simply connected to an in-line heat 
exchanger. Following these ports is a compression region in the passageway 
wherein the fluid is compressed between successive ones of the propelled 
bodies. In this region, energy transfer takes place in which process the 
kinetic energy of the bodies is used to adiabatically compress the fluid. 
The compressed fluid is removed from the passageway and passed through an 
optional, but preferred, check valve and then through heat exchanger means 
connected to the passageway at the end of the compression region for 
extracting heat from the fluid thus compressed. An optional, but 
preferred, latch extends into the passageway at the end of the compression 
region to prevent backward motion of the bodies. The cooled compression 
fluid is reintroduced into the passageway together with an additional 
charge of compressed fluid from the external compressor to repeat the 
cycle.

With reference now to the drawings, and particularly to FIG. 1, the 
apparatus shown includes a closed-loop passageway 10 defined by a housing 
having walls which are preferably smooth and formed from metal. Disposed 
within the passageway 10 is a plurality of pistons 12, shown in the 
embodiment of FIG. 1 as solid spheroids. The tolerances or clearances 
between the surfaces of the spheroids and the inside walls of the 
passageway 10 are such as to permit the spheroids to move freely along the 
passageway 10. However, fluid flow past the spheroids within the 
passageway is substantially prevented. In the embodiment shown in FIG. 1, 
for example, the loop passageway 10 has a circular cross section, but with 
other shaped bodies, other cross sections may be utilized including 
elliptical or polygonal cross sections. In some cases, it is advantageous 
to weld two spheroids together as shown in FIG. 2. The body 12A, 
comprising two spheroids welded at 13, now has two circumferential lines 
of contact 15 and 17 with the inside walls of the passageway 10. This 
arrangement does not impede the movement of the body, but increases the 
sealing effect between the body and the interior wall. At the same time, 
it decreases the chances of having the spheroids pit the interior wall 
surface of the passageway in those embodiments of the invention where a 
sharp bend occurs in the passageway and, further, reduces clearance 
problems due to deformations of the spheroids from impacts. 
As shown in FIG. 1, the continuous loop passageway 10 is divided into 
sections. In an expander section, compressed air from a suitable 
compressor, not shown, enters the passageway 10 through conduit 14. This 
causes successive ones of the bodies 12 to be propelled around the 
passageway 10 in a counterclockwise direction as viewed in FIG. 1. That 
is, the compressed air from conduit 14 along with compressed air from heat 
exchanger 22, as described below, enters the passageway 10 and expands 
adiabatically imparting kinetic energy in the form of increased forward 
velocity to each body 12 while the gas between successive ones of the 
bodies is reduced in temperature. As the bodies pass port 16 connected to 
the passageway 10, the cooler air which has been adiabatically expanded 
exits to the atmosphere and air from the ambient atmosphere enters the 
passageway through port 18 and is thereafter compressed in a compression 
region of the passageway. If a liquefiable vapor, rather than air, is 
used, or if for any other reason it is desired to maintain a closed 
system, the ports may be arranged and connected to conventional heat 
exchanger means (not shown) in any known manner. In a typical embodiment 
of the invention, a plurality of ports 16 and 18 is provided. The kinetic 
energy of the moving bodies is used to compress the gas entering at port 
18, and the compressed gas exits from the passageway 10 through conduit 20 
connected to one side of a heat exchanger 22 via check valve 23. In the 
compression process, the temperature of the air is, of course, increased 
as well as its heat content. Part of the heat is extracted by means of the 
heat exchanger 22. The gas which passes through the heat exchanger 22 is 
then combined in conduit 14 with the compressed air from an external 
source (not shown) to propel the bodies 12 in the expander section. 
Another optional, but preferred, feature of the invention comprises latch 
means 21 located at or near the end of the compression region and adapted 
to prevent backward motion of the bodies in this region after their 
kinetic energy has been reduced. Any conventional latch means may be used, 
such as, for example, a spring-powered, beveled latch 21 (spring not 
shown) operating in a manner similar to an ordinary door latch. That is, 
the latch projects slightly into the passageway 10 and is beveled in the 
direction of approach of the bodies so that as each body comes into 
contact with the latch in a counterclockwise direction it will depress the 
latch allowing it to pass, but the latch will not depress to allow the 
bodies to retreat in a clockwise direction. 
One possible thermodynamic cycle used in the heat pump of the invention is 
shown in FIG. 3 and is similar to a Brayton cycle. Between successive ones 
of the bodies there is what can be termed a unit cell. Gas enters the 
expander section from conduit 14. The unit cell between successive bodies 
in the expander section then seals off the inlet conduit 14 and 
adiabatically expands between points 2 and 1 in FIG. 3 to a pressure 
P.sub.1 and volume V.sub.1 at temperature T.sub.1. For simplicity, it will 
be assumed that the pressure P.sub.1 is atmospheric pressure. The velocity 
of the lead body 12 is now v.sub.1, its maximum value. 
The residual gas, whose temperature has been reduced to T.sub.1 in the 
adiabatic expansion, is then purged through port 16 and ambient air at a 
higher temperature enters through port 18 and occupies the unit volume 
between successive spheroids. Thus, heat is absorbed in this process from 
the cold reservoir (e.g., outdoor air). The actual volume between the 
spheroids remains essentially constant during this operation, but the 
specific volume increases to V.sub.4 between points 1 and 4 in FIG. 3. In 
other words, less mass of gas enters the loop through port 18 in each unit 
cell than was exhausted from the unit cells via port 16. This difference 
in mass is made up by the additional air which enters the system from the 
external compressor via conduit 14. 
The fresh charge of gas is then compressed adiabatically between points 4 
and 3 in FIG. 3 to volume V.sub.3 at temperature T.sub.3 and pressure 
P.sub.2. The pressurized heated gas is then exhausted from the compressor 
section via conduit 20 through check valve 23, and heat is extracted 
through the heat exchanger 22. The unit cell collapses and the cycle is 
then repeated, the total work being represented by the area within the 
lines between points 1, 2, 3 and 4 in FIG. 3. 
The air-conditioning (i.e., cooling) mode of operation of the heat pump is 
shown in FIG. 4. The system is essentially the same as that of FIG. 1 and, 
accordingly, elements in FIG. 4 which correspond to those of FIG. 1 are 
identified by like reference numerals. In this case, port 16 corresponds 
to the cool air duct of an air-conditioning system; whereas port 18 
corresponds to the warm return. As an optional feature, heat exchanger 
means 17 may be connected to ports 16 and 18, necessitating a slight 
rearrangement of these ports as shown. The heat exchanger 22, in an 
air-conditioning system, will be located external to the building which is 
being cooled and would correspond to a conventional condensing coil in a 
refrigeration system. The same basic thermodynamic cycle shown in FIG. 3 
is employed; however cycles other than the Brayton refrigeration cycle are 
also possible. 
In the air-conditioning mode between points 2 and 1 in FIG. 3, the expander 
region takes air from the outdoor heat exchanger 22 and adiabatically 
expands it to a temperature lower than the indoor temperature. The cooler 
air is exhausted into the indoors through exit port 16; or it can be 
passed through an indoor heat exchanger. Between points 1 and 4 of FIG. 3, 
the unit cell picks up a charge of warmer indoor air (Q.sub.1). Between 
points 4 and 3, this warmer air is adiabatically compressed to a higher 
pressure and temperature; and between points 2 and 3, the heat is 
exhausted to the outdoors at constant pressure via the heat exchanger 22 
(Q.sub.A). The net work to drive the cycle is provided by make-up air from 
an air compressor, not shown, passing into the expander section through 
conduit 14. The difference between the cooling and heating modes is, of 
course, that in the heating mode, heat is taken from outdoors and pumped 
indoors; whereas in the cooling mode, heat is taken from the indoors and 
pumped outdoors. 
In FIG. 5, an embodiment of the invention is shown wherein unidirectional 
energy converters are employed both as the heat pump and as the air 
compressor designed to supply compressed air to the heat pump. In FIG. 5, 
the air compressor loop is indicated generally by the reference numeral 24 
and the heat pump loop by the numeral 26. Each of the loop subsystems 24 
and 26 incorporates two unidirectional energy converters in series. 
The air compressor loop 24 operates as follows. One portion of atmospheric 
air (m.sub.1 +m.sub.2) enters the lower leg 26 of the loop at 28 via 
conduit 50 and then is compressed as the pistons or bodies 30 move 
upwardly in the leg 26. Part of the compressed gas exiting from the top of 
the leg 26, m.sub.1, passes through a heat exchanger 32 where heat is 
added from an external heat source Q.sub.1. This source may, for example, 
comprise burning natural gas or any other suitable source of heat. The 
heated, compressed gas is used in an upper leg 34 to propel the bodies 30 
to the left by adiabatic expansion. After it has been adiabatically 
expanded, and reduced in temperaure, in leg 34, the gas, m.sub.1, exits at 
36; while a new charge of atmospheric air (m.sub.1 +m.sub.2) enters at 38 
where it is compressed by the propelled bodies 30 and exits at 40. Part of 
the compressed gas, m.sub.1, is passed through a heat exchanger 42 where 
heat is added, as described above, the resulting compressed and heated gas 
being reintroduced into the lower leg 26 at 44 where it adiabatically 
expands to propel the bodies 30 to the right. After it has been 
adiabatically expanded, and reduced in temperature, in leg 26, the gas, 
m.sub.1, exits at 37. The two portions (2m.sub.1), comprising the 
adiabatically expanded gas, are then combined in conduit 52, with 
additional atmospheric air, 2(m.sub.3 -m.sub.1), being added in conduit 55 
to yield a quantity of gas of 2m.sub.3. One-half of this quantity, or 
m.sub.3, then enters the input 56 and the remaining half, m.sub.3, enters 
input 58, the respective inputs of the two compressor sections of the heat 
pump loop 26. 
It will be noted that the two individual portions m.sub.2 of the compressed 
and heated gas which exit from the air compressor loop 24 are passed 
through conduits 60 and 62, respectively, to the heat exchangers 48 and 
46, respectively, in the heat pump loop 26. In the heat pump loop these 
two portions of gas m.sub.2 are individually combined with the two 
respective compressed gas portions m.sub.3 exiting from the two respective 
compressor sections at 66 and 64. The heat exchangers 46 and 48 can be of 
the finned-tube type through which air is blown by means of a fan to heat 
the air within a building to a temperature much higher than the 
atmospheric air initially entering the system, the heat emanating from the 
heat exchangers being indicated by the arrows Q'.sub.1 in FIG. 5. The 
portion (m.sub.2 +m.sub.3) passing through the heat exchanger 46 is again 
introduced into the loop 26 at 68 to propel the bodies 30 by adiabatic 
expansion; and that portion (m.sub.2 +m.sub.3) passing through heat 
exchanger 48 is fed back into the loop at 70 to adiabatically expand and 
propel the bodies forwardly in the lower leg of the loop 26. The two 
portions of adiabatically expanded gas, 2(m.sub.2 +m.sub.3), of reduced 
temperature are then exhausted through conduit 72 to the atmosphere; or 
can be passed through an additional heat exchanger located within a 
building when the system is used as an air-conditioning system. In the 
latter case, the heat exchangers 46 and 48 will, of course, be located 
outside the building. 
As the fluid is compressed by the freely-movable bodies in the compressor 
sections, most of the kinetic energy of each body is transferred to 
increase the enthalpy of the gas and to remove the gas from the compressor 
section under increased pressure. Similarly, as the fluid in the expander 
sections of the loop is adiabatically expanded between successive bodies 
in the expander sections, the enthalpy of gas is decreased and energy is 
transferred to increase the kinetic energy of the bodies. The energy 
transferred in the various processes around the loop, of course, must be 
conserved so that at any time the total energy of a particular loop system 
is constant and the energy input and output is equal in steady-state 
operation. 
The thermodynamics of the expander and compressor sections of the heat pump 
of the present invention can be analyzed from ideal considerations as 
undergoing isentropic processes. However, in actual operation, because of 
internal losses to the working fluid, the processes are not precisely 
isentropic. The processes take place, very nearly, as adiabatic processes, 
i.e., with no external heat losses, particularly when adequate and and 
properly arranged insulation is attached to the outer walls of the 
passageway forming the expander and compressor sections. Thus, while 
isentropic operation might be assumed for the purpose of analysis, 
nevertheless the actual operating processes of the heat pump are better 
described as adiabatic. 
In a similar fashion, the total external forces acting on the 
freely-movable bodies as they move around the loop must integrate to zero 
over time period for a particular body to completely transit the loop 
system under steady-state operation. This is simply in accordance with 
Newton's second law of motion. Since the movable bodies will encounter 
friction forces opposing the direction of motion around the loop, these 
friction forces must be counterbalanced by some external force acting in 
the direction of motion. If the loop passageway around which the bodies 
travel is in a vertical, or near vertical, plane, such as shown, for 
example, in the embodiment of FIGS. 1 and 5, the force of gravity can be 
used to provide at least part of the thrust to counterbalance the friction 
forces. If the loop passagway must be in a horizontal plane, alternative 
external thruster forces may be applied to the bodies to counterbalance 
the frictional forces. For example, mechanically-powered devices such as 
cams, sprocket wheels, or worm gears, or a linear magnetic motor may be 
used. 
The number of bodies used in the heat pump of this invention, the length of 
the various regions (i.e., expander and compressor) of the closed 
passageway and the total length of the closed-loop passageways are 
constants for a particular heat pump design. This means that the control 
system of the compressor and heat pump loops must regulate the operating 
parameters to maintain approximately constant distribution of pistons 
around the loop for all operating levels. 
As will be appreciated, the invention has great flexibility in design and 
performance in that it can be constructed in a continuum of sizes for 
heating or cooling capability. Furthermore, it can be constructed as a 
multipleunit system in which various of the units can be turned ON or OFF 
as the load requires. This also aids reliability since if one of the units 
should fail, the system is still operable. 
The system employs conduits, pistons or movable bodies, simple check 
valves, latches, and heat exchangers which should contribute greatly to 
reliability and economy for home heating and cooling systems presently 
utilized in natural gas or oil heating. 
It is also possible to use the invention in an arrangement in which the 
external compressor is replaced by a "pressurizer" which is an in-line 
component of the heat pump loop system between the compressor and expander 
regions. In this mode of operation, the apparatus would be designed to 
take in the same mass flow rate of gas as it exhaust in the vent-intake 
region, but consequently would compress to a lower pressure than required 
at the expander inlet. The role of the pressurizer, then, is to pressure 
the gas sufficiently to make up this difference using any known method for 
pressurizing. The energy input to the pressurizer is the energy source for 
running the heat pump, as will be understood. 
In a typical installation, the overall length of the heat pump loop shown 
in FIG. 5, for example, will be about thirty-four times the diameter of 
the bodies 30; while the overall length of the air compressor loop will be 
about twenty-seven times the diameter of the bodies 30. 
In FIG. 6, a further embodiment of the invention is shown wherein 
serially-arranged unidirectional energy converters form a compound heat 
engine and heat pump. The heat engine uses a high pressure stage to 
convert heat energy into net mechanical energy which is then converted in 
a low pressure stage of the heat pump to heat energy. More specifically, 
the unidirectional energy converter according to the embodiment shown in 
FIG. 6 is comprised of two heat engines and two heat pumps operating in 
parallel. A "racetrack" shaped tubular passageway extends within a 
vertical plane to form a continuous loop passageway 80 containing a 
plurality of pistons 81. The pistons 81 may be spheroids or other desired 
configuration but preferably the pistons take the form as shown in FIG. 7, 
of hollowed members having a cylindrical configuration with sperical end 
surfaces. The leading end surface 82, in regard to the direction of travel 
by a piston, is convex; whereas the trailing end 83 of the piston is 
concave. Piston rings 84 are located in recesses formed within the outer 
cylindrical surface of the piston adjacent the convex cylindrical end 82 
and the concave cylindrical end 83. The hollow design of the pistons 
provides the necessary design mass and permits greater flexibility to the 
selection of material for the construction of the pistons independent of 
the mass required for design operation. The pistons rings, which are 
lightly loaded, reduce losses to a minimum due to leakage of the fluid 
medium around the pistons. Also, the use of rings places less stringent 
manufacturing tolerances for the production of the pistons. The pistons 
freely move within the passageway 80 and operate under light loads, 
particularly as compared to the loads imposed on the pistons of an 
internal combustion engine. The maximum velocity of the pistons 81 is 
typically the same as the velocity of pistons in an internal combustion 
engine. A thin film of oil such as, for example, SAE 20 or molybdenum 
disulfide dry powder may be used, if desired, for lubrication between the 
pistons and the raceway since the fluid temperature does not exceed 
1500.degree. F. and usually does not exceed 1200.degree. F. 
As is shown in FIG. 6, the continuous loop passageway 80 is divided into 
regions. In an expander region, hot compressed air enters the passageway 
80 through an entry port coupled to a conduit 85 whereby each piston is 
accelerated, in succession, upwardly through the lower right quadrant of 
the passageway. When a second piston passes the entry port for conduit 85, 
a portion of the hot air is closed off from the source, thus forming a 
unit cell of hot compressed air. The hot compressed air in the unit cell 
is expanded adiabatically until the leading piston passes a point in the 
passageway containing an entry port coupled with conduit line 86. As the 
leading piston passes this entry port, more compressed air at a lower 
entry temperature and pressure is fed into the unit cell between the 
piston from conduit line 86. The combined compressed air of the unit cell 
is further expanded adiabatically until the leading piston passes an exit 
port communicating with an exhaust manifold 87 in a vent region. The 
region of the raceway between the entrance port for conduit 85 and the 
exit port for the exhaust manifold 87 forms an expander region of the 
passageway wherein energy of the hot compressed air from conduits 85 and 
86 is converted to kinetic energy of the pistons. The exhaust manifold 
coextends with the vent region wherein cold air is purged from each unit 
cell between the pistons in the passageway and replaced by fresh air fed 
through an entry port by a manifold 88 from the outside. The manifolds 87 
and 88 in the vent section terminate at the beginning portion of a 
compression region where the fresh air in the unit cell between pistons is 
compressed abiabatically by the kinetic energy of the pistons. 
The compression region has two stages in series. The largest portion and 
first of the compression stages extends to a discharge port for a conduit 
89. The largest portion of the air that is compressed between the pistons 
is passed from the unit cell through conduit 89 into heat exchanger 90 
where the compressed air is cooled by heat exchange with room air. From 
the heat exchanger, the cooled compressed air is reintroduced by conduit 
89 into the passageway through a port in the second expander region where 
the air is further cooled adiabatically in a unit cell and exhausted to 
the atmosphere below atmospheric temperature. 
Returning, now, to the compressor region, the second stage thereof utilizes 
the remaining kinetic energy of the pistons to further compress a small 
quantity of air remaining in the unit cell. The second stage of the 
compressor region terminates at a port for a conduit 91 to deliver the 
compressed air from the second stage into a combustion chamber 92 where 
the compressed air is heated and then fed by conduit 91 to reenter the 
passageway through a port at the entrance of the second expander region. 
Unit cells of air are formed between the pistons after the pistons are 
passed through a thruster section wherein their direction of travel is 
altered, and thereafter the pistons pass downwardly along the passageway. 
The downward path of travel by the pistons is accompanied by the formation 
of unit cells therebetween while the pistons pass along a second expander 
region, second vent region and second compression region that are 
essentially duplicates as far as function is concerned to the 
corresponding regions already described above. The unit cells formed 
between the pistons during their downward travel along the passageway are 
supplied with heated compressed air from conduit 91 and supplied with 
further quantities of compressed air from conduit 89. As the leading 
piston of a unit cell passes from the expander section and enters the vent 
section, the hot compressed air is expanded adiabatically whereupon the 
heat energy of the air is converted to kinetic energy of the pistons. The 
lower, successively-arranged vent region includes a manifold 93 wherein 
cold air is purged from the unit cell between pistons while the space 
between the pistons is replenished with fresh air from outside. 
As shown in FIG. 6, for convenience, manifolds 87 and 93 communicate with a 
common duct to exhaust the cold air to the atmosphere. The temperature of 
the exhaust cold air is below atmospheric temperature. Below the vent 
region formed by manifold 93 is the second compression region consisting 
of two stages, the first of which terminates at an exit port for conduit 
86 coupled to a heat exchanger 94 to exchange heat with room air. The 
second stage of the compression region extends between the exit port for 
conduit 86 and an exit port for conduit 85. The remaining kinetic energy 
of the pistons is utilized to further compress a small quantity of air 
remaining in the unit cell. The remaining air in the unit cell is fed by 
conduit 85 to a combustion chamber 95. Combustion chamber 95 functions in 
the same manner as combustion chamber 92 by reheating the heated 
compressed air for delivery by conduit 85 into the lower portion of the 
expander region to form a unit cell between pistons for their upward 
travel along passageway 80. Thus, in this manner the cycle is repeated 
with the pistons traveling upwardly against the force of gravity along the 
vent and compressor regions at one side of the vertically-arranged 
passageway. A parallelly-arranged heat engine and heat pump is formed by 
the expander, vent and compressor regions at the opposite vertical side of 
the passageway where the piston travels downwardly under the force of 
gravity. Thruster regions which take the form of U-shaped passageway 
sections feed the pistons at the discharge side of the compression regions 
through the use of sprocket wheels or the like into the entry side of the 
expander regions. The thruster regions function to provide a net external 
force to the pistons in their direction of motion around the passageway to 
equalize the forces due to friction which act to oppose the piston motion. 
It is now apparent that the unidirectional energy conversion loop described 
above is a compound heat engine and heat pump, thermodynamically a double 
Brayton cycle. The high-pressure states, i.e., the expander regions, 
convert heat energy into a net mechanical energy that drives the reverse 
Brayton cycle of a low-pressure stage, i.e., the compressor regions, as a 
heat pump. The compound heat engine and heat pump of this embodiment 
offers a system wherein the working fluid conveniently takes the form of 
air throughout the system, thus providing ecomomy, simplicity and 
environmental cleanliness. The straight vertical portions of the 
passageway conduct the pistons while traveling at their highest velocity, 
thus minimizing the forces and frictional losses that would otherwise 
adversely affect travel of the pistons. The porting of air or other fluid 
medium used in the system is performed preferably by the pistons, thus 
reducing the number and complexity of in-line valves for the conduit. 
The thruster regions in the schematic illustration include means for 
conducting the piston about the U-shaped configuration of the passageway 
at the ends of the vertical portions thereof. While the U-shaped 
configuration to the passageway can be readily designed to utilize gravity 
to guide the pistons about their reverse direction of travel, it is 
nevertheless preferred to provide means such as a sprocket wheel, a linear 
electromagnetic drive or a linear latch system to insure movement of the 
pistons throughout the thruster regions. In FIG. 6, a sprocket wheel 96 is 
shown at both thruster regions to conduct the pistons therealong. Each 
thruster wheel is coupled by a drive shaft to a pulley 97. The pulleys are 
interconnected by a timing belt 98. One of the pulleys 97 includes a 
second pulley section 99 coupled by a belt to a pulley on the output shaft 
of a suitable motor 100. This form of drive system provides 
synchronization between both sprocket wheels 96. The motor 100 is 
preferably a constant speed motor which may be coupled, as an alternative 
to a belt drive system, by a drive shaft through bevel gears on arbors for 
the sprocket wheel. 
The heat exchangers 90 and 94 are typically counter-flow air-to-air 
exchangers. Heat exchangers of the state-of-the-art construction are 
capable of accommodating at the high temperature side at maximum 
temperatures of several hundred degrees Fahrenheit. The combustion 
chambers 92 and 95 may typically take the form of a chamber for the direct 
combustion of compressed natural gas with the working compressed air or, 
alternatively, a conventional gas-fired furnace may be utilized. Other 
conventional external heat sources may also be employed. However, when a 
direct combustion chamber is utilized, the heat of combustion is 
completely utilized by the heat pump and gases will be exhausted at 
subatmospheric temperatures. While, as described hereinbefore, the pistons 
form necessary valving at ports for the conduits, it may nevertheless be 
desirable to incorporate check valves at compressor outlets to minimize a 
backflow of air in part of the cycle. High frequency of response and low 
pressure drop characteristics are important criteria for selecting such 
check valves. Reed valves are suitable to form such check valves. 
A back latch mechanism for the pistons may be conveniently used for 
start-up and shutdown operations of the heat engine and heat pump. At 
shutdown, it is necessary that the pistons come to rest and remain at 
predetermined positions so that they will be in the proper position for 
smooth start-up. This can be achieved by magnetically-operated latches 
which are actuated at shutdown and retract at start-up. Moreover, at 
start-up, an air compressor or accumulator may be utilized for the 
start-up operation. 
A vertically-arranged loop passageway 80 has been shown in FIG. 6 and 
described above solely for convenience of description. Other variations in 
the arrangement of the passageway, including horizontal arrangement, are 
possible. 
Although the invention has been shown in connection with certain specific 
embodiments, it will be readily apparent to those skilled in the art that 
various changes in form and arrangement of parts may be made to suit 
requirements without departing from the spirit and scope of the invention.