Heating System

This invention relates to heating of aircraft cabins. More specifically, this invention relates to the use of engine bleed or compressor air to accomplish the heating.

Various devices have been used in the past for heating the cabins of aircraft. Among the more effective of these devices is the combustion heater. However, combustion heaters consume fuel from the aircraft's main engine fuel system, and present problems such as greater weight and complexity, increased fire hazard, and carbon monoxide poisoning.

The advent of gas turbine power plants with attendant large quantities of hot pressurized air has reduced the need for combustion heaters. A portion of the hot pressurized air, commonly referred to as bleed air, is used for direct heating of the cabin air. Such systems include, for example, direct infusion of the bleed air into the cabin space. However, these prior art systems are limited by an insufficiency of bleed air during certain phases of engine operation, or engine power penalties associated with use of bleed air for non-engine purposes. This requires the use of supplemental cabin heating means, such as a combustion heater or the like.

The present invention contemplates the more efficient use of the available quantity of bleed air for heating the cabin space of an aircraft. The bleed air is used to heat cabin air in a heat exchanger, and then to operate a heating device for additional heating of the cabin air. This results in the cabin being maintained at a comfortably warm temperature during phases of engine operation wherein the quantity of hot bleed air from the engine is at a minimum.

The heating system of this invention utilizes hot compressed air bled from the compressor section of a turbine power plant of a vehicle. This air, known as bleed air, is used for heating air which is circulated to the vehicle passenger space.

The system includes a heat exchanger mounted along a cabin air circulation path. Hot bleed air is routed to this heat exchanger for first stage heating of the cabin air. The system further includes an air cycle machine having a turbine located downstream of the heat exchanger in the bleed air path. This turbine is rotatably driven by the bleed air to extract additional energy from the bleed air, and the turbine in turn drives a fan of the air cycle machine. The fan is located in the cabin air stream, and serves to move the cabin air through the heat exchanger, to add further heat energy to the cabin air for second stage heating thereof, and to recirculate the cabin air to the cabin space.

The accompanying FIGURE is a schematic diagram of the heating system of this invention.

The heating system of this invention is shown schematically in the accompanying drawing FIGURE. As shown, a source 10 of hot, high pressure air, such as the compressor of an aircraft turbine power plant, provides heated compressed air through suitable ducting means 12 to a pressure regulator and shut-off valve 14. The pressure regulator and shut-off valve 14 is modulated in a suitable manner to provide constant pressure bleed air into an inlet duct 18 coupled to a heat exchanger 22.

The bleed air passed through a first flow path in the heat exchanger 22, and therein transfers thermal energy to cabin or passenger space air circulating through a recirculation duct 21 and a second flow path in the heat exchanger 22. The bleed air thereafter passes through a turbine inlet duct 30 and a turbine inlet valve 32 to an air cycle machine, shown generally as 28. Within the air cycle machine 28, the bleed air rotatably drives a turbine 26 mounted on a shaft 29. The rotating turbine 26 extracts energy from the bleed air to rotatably drive a fan 42, after which the bleed air is exhausted to atmosphere via a discharge duct 36.

The fan 42 is positioned along the recirculation duct 21 to move the cabin air through the second flow path of the heat exchanger 22. More specifically, the fan 42 is, in the preferred embodiment, positioned along the recirculation duct 21 downstream of the heat exchanger 22 to draw the cabin air from the cabin space 38 of the vehicle through the recirculation duct 21 and the heat exchanger 22. This action of the fan 42 loads the turbine 26 to transfer energy extracted by the turbine from the bleed air stream to the cabin air stream. This energy transfer both heats the cabin air, and recirculates the cabin air to the cabin space 38 through a muffler 44 and a distribution duct 46.

A bypass duct 20 is connected between the heat exchanger inlet 18 and the air cycle machine turbine 26 to facilitate control of the heating system of this invention. A temperature control valve 24 is disposed along the bypass duct 20, and operates in conjunction with the turbine inlet valve 32 to control the degree of heating of the cabin air. As shown, a suitable mechanical linkage 54 or the like interconnects the valves 24 and 32 to operate the turbine inlet valve 32 generally inversely with respect to the temperature control valve 24.

In operation, in the event that maximum cabin heating is desired, the temperature control valve 24 is moved to a fully closed position, and the turbine inlet valve 32 is moved to a fully opened position. In this condition, the entire available quantity of bleed air flows through the heat exchanger 22 for maximum utilization of bleed air energy to heat the cabin air both in the heat exchanger 22 and by means of the air cycle machine 28. If a lesser amount of heating is desired, the temperature control valve 24 is modulated to a partially open position to allow some of the bleed air to pass through the bypass duct 20, thereby bypassing the heat exchanger 22 to flow directly to the air cycle machine turbine 26. This causes relatively less heat energy to be transferred to the cabin air. Further, if even less heating of the cabin air is desired, the temperature control valve 24 is moved to a fully open position, and the linkage 54 operates to move the turbine inlet valve 32 to a fully closed position. In this condition, bleed air does not pass through the heat exchanger 22, but instead is entirely cycled through the air cycle machine turbine 26 for maintaining full circulation and ventilation of the aircraft cabin space.

The temperature control valve 24 and the turbine inlet valve 32 may be operated by a conventional cabin temperature sensing system. As shown, this system comprises a thermostatic device 50 or the like located within the cabin space 38 for providing a signal on signal line 49 to control the set point of a sensor/controller unit 48 mounted along the recirculation duct 21 immediately upstream of the distribution duct 46. The sensor/controller unit 48 in turn provides a suitable control signal to the temperature control valve 24 via a signal line 25 to control the operation of the temperature control valve 24 and the turbine inlet valve 32, as described above.

The description of the preferred embodiment of the invention is not intended to limit the scope of the invention, but is intended to be exemplary of that which is specifically claimed as follows: