Air conditioning system

An air cycle air conditioning system including an air-air heat exchanger defining a first air flow path for air to be cooled and a second air flow path for air to pass therethrough and absorb heat from the air to be cooled and apparatus for supplying air to the second air flow path at sub-atmospheric pressure.

FIELD OF THE INVENTION 
The present invention relates to air cycle air conditioning systems and 
methods generally. 
BACKGROUND OF THE INVENTION 
The use of air cycle air conditioning systems as opposed to vapor cycle 
systems has become increasingly attractive due to growing environmentalist 
concern about the depletion of the earth's ozone layer resulting, inter 
alia, from release of fluorocarbons, which are used in vapor cycle 
systems. 
One type of air cycle air conditioning system is described in U.S. Pat. No. 
4,015,438 and employs inlet air at substantially ambient pressure which is 
cooled in a heat exchanger and introduced into an enclosure for cooling. 
SUMMARY OF THE INVENTION 
The present invention seeks to provide an improved air cycle air 
conditioning system and method which is significantly more energy 
efficient than prior art systems and which therefore may be employed, 
inter alia, for aircraft applications. 
There is thus provided in accordance with a preferred embodiment of the 
present invention an air cycle air conditioning system including an 
air-air heat exchanger defining a first air flow path for air to be cooled 
and a second air flow path for air to pass therethrough and absorb heat 
from the air to be cooled and apparatus for supplying air to the second 
air flow path at sub-atmospheric pressure. 
Additionally in accordance with a preferred embodiment of the present 
invention there is provided an air cycle air conditioning system including 
precooler apparatus for cooling pressurized air, apparatus downstream of 
the precooler for reducing the pressure of the pressurized air, turbine 
apparatus receiving the pressurized air, for being driven thereby and 
providing expansion thereof, thus lowering the temperature thereof, an 
air-air heat exchanger defining a first air flow path for air to be cooled 
and a second air flow path for the air at sub-atmospheric pressure to pass 
therethrough and absorb heat from the air to be cooled and compressor 
apparatus, at least partially driven by the turbine apparatus, for drawing 
air at said sub-atmospheric pressure through the second flow path. 
Further in accordance with a preferred embodiment of the present invention 
there is provided an aircraft air cycle air conditioning system including 
apparatus for receiving bleed air at elevated pressure and temperature 
from an aircraft jet engine compressor, a turbine receiving the bleed air, 
an air-air heat exchanger defining a first air flow path for air to be 
cooled and a second air flow path for air to pass therethrough and absorb 
heat from the air to be cooled and apparatus for supplying air from the 
turbine to the second air flow path at sub-atmospheric pressure. 
Additionally in accordance with a preferred embodiment of the present 
invention there is provided an aircraft air cycle air conditioning system 
including apparatus for receiving bleed air at elevated pressure and 
temperature from an aircraft jet engine compressor, precooler apparatus 
for cooling the received pressurized air, turbine apparatus receiving the 
pressurized air for being driven thereby and providing expansion thereof, 
thus lowering the temperature thereof, an air-air heat exchanger lowering 
the temperature thereof, an air-air heat exchanger defining a first air 
flow path for air to be cooled and supplied to an aircraft cabin and a 
second air flow path for air from the turbine apparatus to pass 
therethrough at sub-atmospheric pressure and absorb heat from the air to 
be cooled, and compressor apparatus, at least partially driven by the 
turbine apparatus, for drawing air at sub-atmospheric pressure through the 
second flow path. 
In accordance with a preferred embodiment of the present invention, a 
portion of the pressurized air downstream of the precooler is supplied to 
the first air flow path to be cooled and supplied to an enclosure for 
cooling and pressurization of the enclosure. 
Additionally in accordance with a preferred embodiment of the present 
invention, the pressurized air is further cooled by an intercooler 
disposed intermediate the precooler and the first air flow path. 
According to one embodiment of the invention, the compressor is operative 
to exhaust air received from the second flow path to the ambient. 
According to another embodiment of the invention, the compressor is 
operative to direct air received from the second flow path back through 
the first flow path. Preferably, the air from the compressor first passes 
through an intercooler before entering the first flow path.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Reference is now made to FIG. 1, which illustrates an air cycle cooling 
system constructed and operative in accordance with a preferred embodiment 
of the present invention. The system will be described herein with 
particular reference to a cooling system for aircraft, it being understood 
that the invention is not necessarily limited to aircraft applications. 
As illustrated in FIG. 1, bleed air from the compressor of a jet engine, 
typically at a pressure of 25-30 psi or above and a temperature of between 
280-450 degrees Fahrenheit, is received by a precooler 10, which typically 
comprises an air-air heat exchanger which receives a flow of ambient air 
driven by a fan 11 for cooling of the pressurized air. 
The pressurized air passes from the precooler 10 to a pressure regulator 
12, which reduces the pressure thereof to a predetermined pressure, such 
as 26 psi. 
From pressure regulator 12 a first flow of pressurized air is supplied to a 
turbine 14, which may be similar to a turbine of a conventional 
turbocharger, such as a Garrett Model T04 or a Brown Boveri Model RR151. 
This flow of pressurized air drives the turbine, producing rotation of a 
turbine shaft 16 as well as expansion of the pressurized air. The 
following effects are produced: 
a. lowering of the temperature of the air supplied to turbine 14, i.e. 
typically from a turbine input temperature of 145.degree. F. to 38.degree. 
F.; 
b. lowering of the pressure of the air to sub-atmospheric pressure, 
typically from a turbine input pressure of 26 psi to an output pressure of 
6 psi. This sub-atmospheric pressure is provided by suction produced by a 
downstream compressor 18, as described hereinbelow; and 
c. condensation of part of the water vapor contained in the air supplied to 
the turbine. 
The air at sub-atmospheric pressure from the turbine 14 is supplied to an 
air-air heat exchanger 17 defining a first air flow path for air to be 
cooled and a second air flow path for air to pass therethrough and absorb 
heat from the air to be cooled. The air from the turbine passes through 
the second air flow path and is heated, thus evaporating any liquid water 
present therein or injected via a pipe 26. 
Air passing through the second air flow path is sucked from the heat 
exchanger 17 by the operation of compressor 18, which is driven by turbine 
14 and as needed, by an integral motor-generator 19, whose rotor is fixed 
to shaft 16 and whose stator 20 is arranged thereabout. In the embodiment 
of FIG. 1, the compressor 18 is operative to exhaust the air sucked from 
the second air flow path to the ambient at a predetermined pressure. 
In this embodiment of the invention, pressurization of the cabin at an 
elevated altitude is realized by employing pressurized air from pressure 
regulator 12 via a valve 13 supplied to an intercooler 22, which is 
preferably an air-air heat exchanger cooled by a flow of ambient air, 
driven by a fan 25. From intercooler 22, the air passes along the first 
flow path of heat exchanger 17 for cooling thereby and is supplied to an 
enclosure, such as an aircraft cabin. 
For operation on the ground, cabin pressurization is not required. In one 
mode of ground operation, ambient air is supplied by fan 23 via a 
normally-closed valve 24 to the first flow path of heat exchanger 17, 
without requiring the cooling capacity of the intercooler 22 or the 
operation of fan 25. In this mode of ground operation, valve 13 is closed 
and thus there is no pressurized air flow from pressure reducer 12 to the 
heat exchanger 17. 
In another mode of ground operation, the jet engine is shut down and thus 
no bleed air is available. In this case, a normally-closed air inlet valve 
27 is opened to permit ambient air to reach the turbine 14. The 
turbocompressor is driven by electric motor 19 such that compressor 18 
produces suction upstream of the turbine 14, thus drawing in ambient air 
via valve 27. In this mode of operation, cooling is produced using only an 
external source of electrical energy to power motor 19. 
It is a particular feature of the present invention that in view of the 
sub-atmospheric pressure prevailing in the cold side (second flow path) of 
the heat exchanger, large quantities of water, tapped from condensation of 
humidity in the first flow path and supplied via pipe 26, may be 
evaporated thereat, without saturating the air flow. In view of this high 
energy absorption capability, the overall cooling efficiency of the heat 
exchanger 17 is significantly enhanced, thus reducing the cold massflow 
requirement per unit of hot massflow. Accordingly, relatively less energy 
must be expended in operation of the compressor. 
It is also a particular feature of the present invention that the efficient 
use of pressurized air from the jet engines of an aircraft enables 
efficient and sufficient cooling of an aircraft cabin to be realized even 
when the aircraft engines are idling or turned off, as during ground time, 
thus obviating the need for costly auxiliary airborne or ground based 
air-conditioning systems. 
It is appreciated that when relatively high pressurization levels are 
provided to the air supplied to the turbine, as during aircraft flight, 
the motor-generator may actually produce electricity for other uses. 
Reference is now made to FIG. 2, which illustrates an alternative 
embodiment of the invention. For the sake of conciseness and clarity, only 
the differences between the two embodiments of FIGS. 1 and 2 will be 
described, the substantially identical features being indicated in both 
figures by identical reference numerals. 
In the embodiment of FIG. 2, no flow of pressurized air is provided from 
the pressure regulator 12 to the first flow path of the heat exchanger, 
nor is ambient air supplied thereto via either of normally closed valves 
24 and 27. Instead, the first flow path of the heat exchanger receives air 
only from the output of the compressor 18, and its pressure is calibrated 
to the required cabin pressure by a valve 29. Thus the bleed air flow is 
reduced to about 50% of the flow needed in embodiment of FIG. 1, thereby 
reducing significantly the energy loss from the main turbine. 
It will be appreciated by persons skilled in the art that the present 
invention is not limited by what has been particularly shown and described 
hereinabove. Rather the scope of the present invention is defined only by 
the claims which follow: