Air Conditioning System

Gulfstream GVII

Eddie sez:

The G500 air conditioning system is fairly standard for a Gulfstream: it takes very hot air from the engines or APU and cools that with two air cycle machines to produce cold air. Two computers take crew and passenger inputs to blend the hot and the cold air to produce comfortable conditioned air.

For a quick refresher or a good intro, be sure to see Ivan Luciani's notes: G500 Air Conditioning System Notes.

There are also a few flash cards here: G500 Flashcards, G500 Air Conditioning System Audio Flash Cards, and Quizlet.

Everything here is from the references shown below, with a few comments in an alternate color.

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Photo: G500 Air conditioning flow, from Eddie's notes.
Click photo for a larger image

How it Works . . .

The Components in Greater Detail . . .

Limitations and Abnormal Procedures . . .

Last revision:

2020-09-04


How it Works . . .


The Big Idea

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Photo: GVII air conditioning system component layout, GVII SDM, §21-00-00, Figure 1
Click photo for a larger image

[System Description Manual, §21-00-00, ¶1]

    Hot air from the engine 4th and 8th stage compressors leaves the pre-cooler heat exchanges and enters the bleed air duct at 400°F normally, or 500°F when hotter air is needed by the Wing Anti-Ice crossover duct. See: GVII Pneumatic System.

  • Hot air from the APU or the engines is drawn from and delivered to the common (APU) or independent (engine) bleed air manifolds and subsequently delivered through two different offtakes for the left and right Pack Inlet Valves (PIV).
  • The Pack Inlet Valves simply open or shut the hot bleed air to the PACKs through cockpit overhead panel switches. See: Pneumatic Air Conditioning Kits (PACKs).

  • Each offtake through each PIV delivers air through two pack assemblies consisting of an Air Cycle Machine (ACM) which cools the hot air to a nominal sub-freezing temperature. The cool air from the pack assemblies is then introduced to separate offtakes of hot air. Mixing of the hot and cold air creates conditioned air. How much hot air is introduced to the cold air is regulated from the cockpit. As the air enters the cabin it is distributed to three zones: cockpit, forward cabin and aft cabin. Temperature in each of the three zones is independently controlled through OHPTS.
  • A hot air manifold splits the hot air from the bleed system into three zones. A cold air manifold splits the conditioned air from the PACKs into three zones. A trim air valve on each of the hot zones reduces the amount of hot air so as to temperature control the resulting air. See: Air Manifolds and Trim Air Valves.

Air Flow Distribution

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Photo: GVII air conditioning system distribution, PAS, p. 1-11
Click photo for a larger image

[System Description Manual, §21-00-00, ¶1]

  • The hot and cold air mixture is distributed through the forward and aft cabin zones through the cabin silencers to the foot level ducting and to the baggage compartment. It is also distributed through ductwork and a silencer to the cockpit. Additionally, air directly from the cold air manifold is distributed to both the cabin zones and the cockpit through the gaspers.
  • It is important to realize the air normally flows into the cabin from ducts along the floor siewalls and that this air will be at the duct temperature shown on the synoptics, say 70 degrees. If the ducts along the sidewalls are blocked by throw carpets, blankets, or luggage, you will have less airflow and less of this conditioned air. Air also enters through the gaspers overhead. This air has not been "trimmed" with hot air and if you want to get the cabin colder, faster, open the gaspers.

  • As conditioned air enters the cabin (floor level) it exits through the return air ducts (eye level). The left and right fan draw the air from the return air ducts to cool and ventilate the avionic components where the conditioned air eventually exits overboard through the thrust recovery outflow valve below the floor.

Air Conditioned Air Temperature Control

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Photo: GVII OHPTS ECS, PAS, p. 2-11
Click photo for a larger image

[System Description Manual, §21-00-00, ¶1]

  • The system controller for the air conditioning system is called the Air Conditioning Controller (ACC). There are two controllers for two independent systems. For temperature control, the left ACC controls the forward and aft zones while the right ACC controls the cockpit; however for airflow control, the right pack and its subcomponents communicate to the right ACC while the left pack and its subcomponents communicates to the left ACC.

The temperature control system provides a way to select, control, and display the temperatures in the forward and aft cabins, and flightdeck zones. The desired temperature for each zone is selected via dedicated zone’s temperature selectors on any of the three flightdeck overhead panel touchscreens. More about this: Normal Operations.

Two independent temperature control modes, automatic and manual are provided by the L and R Air Conditioning Controllers (ACC). The L ACC controls the forward and aft cabin zones while the R ACC controls the flightdeck zone. More about this: Air Conditioning Controllers.

Normal Operations

Automatic Operations

[PAS, p. 1-12]

  • Engine Starts

    • ECS packs are controlled by DCN. When Engine Start Button is pressed, the left pack switches off. (The right pack remains on.)
    • 10 seconds after the Starter Air Valve closes, the left pack switches on.

  • Main Entrance Door Operation

    • When the MED is closing, both packs automatically switch off.

    • Once the MED is closed, the left pack turns on. The right pack turns on 5 seconds later.

    • The MED opening does not affect pack positions.

Temperature Control

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Photo: Air conditioning system OHPTS ECS page, PAS, p. 1-13
Click photo for a larger image

[PAS, p. 1-13]

  • 3 temp zones: Cockpit, Forward Cabin, Aft Cabin

  • Each zone displays

    • Actual temp → White (ACC derives from zone temp sensors)

    • Desired temp → Blue. From the cockpit the auto mode has a range of 60 - 90°F. From the cabin, passengers can adjust +/- 6º on GCMS. The cabin adjusted temperature is seen on the → ECS / Press synoptic, the crew adjusted temperature is seen on the OHPTS ECS page.

    • Duct %

      • Auto mode → Duct Temp → White (desired duct temp not selectable)

      • Manual mode → Trim Air Valve % Open → Blue; desired duct temp not selectable; select percentage (0 -100%) of available hot air allowed into duct by that zone’s trim air valve. 0% correlates to 35°F duct air (no hot air), 100% correlates to approximately 230°F duct air.


The Components in Greater Detail . . .


Air Conditioning Controllers (ACCs)

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Photo: Air conditioning packs, PAS, p. 1-2
Click photo for a larger image

[System Description Manual, §21-00-00, ¶1]

  • Two air conditioning controllers are located in the baggage compartment forward bulkhead. Each ACC accommodates both automatic and manual modes of temperature control.
  • Each Air Conditioning Controller is a self-contained computer, identical to the Bleed Air Controllers.

  • The left air conditioning controller controls the temperature in the two cabin zones and the right one controls the cockpit zone. The air conditioning controllers receive crew input for desired temperature in each zone. They also receive actual temperature data from the zone and duct temperature sensors. They provide control of their associated trim air valve torque motors based on a selected and actual zone and duct temperature. Selected temperature range is from 60° - 90°F (15° - 32°C) in the AUTO mode of operation.
  • You will see three temperatures for each zone in the OHPTS: actual, desired, and duct. You set the "desired" and the system adjusts the "duct" to result in the "actual."

  • The air conditioning controller also limits supply duct temperature to 160°F (71°C) for the two cabin zones and 180°F (82°C) for the cockpit in the AUTO mode and transmits temperature data to the cockpit temperature indicator and EICAS.
  • The particular computer learns its role by the electrical connector which has an "identity pin."

  • The ACC is a common part number with the bleed air controller. The controllers have identical hardware and software. The controllers are configured as either a cockpit or cabin ACC or a left / right bleed air controller through external connector identity pin jumpering.

Air Manifolds and Trim Air Valves

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Photo: Hot and cold air manifolds and trim air valves, PAS, p. 1-5
Click photo for a larger image

[PAS, p. 1-5]

  • The cold air manifold is located with the hot air manifold under the baggage compartment floor. It receives cold air discharged from left and right PACKs and delivers a constant supply of 35°F air to three zone delivery ducts.
  • If the PACKs are operating normally, the cold air manifold always receives 35°F air. The gaspers should produce this minus any temperature losses along the way to each individual gasper.

  • The hot air manifold is also under the baggage floor, but it is above the cold air manifold. It receives precooler bleed air from the L and R BAS ducting which has bypassed the PACKs. The manifold divides this air into three zones.
  • This air will be no hotter than 400°F unless the wing anti-ice crossover duct is need to send wing anti-ice air from one side to the other, in which case it can be as hot at 500°F. In both cases, the temperature can at times be lower, depending on thrust setting.

  • Three trim air valves, one for each zone (cockpit, forward cabin, aft cabin), mix hot air into the cold air to produce the desired temperature requested by the temperature control panel.

Equipment Cooling Subsystem

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Photo: Equipment cooling subsystem, PAS, p. 1-6
Click photo for a larger image

[PAS, p. 1-6]

  • Cools portions of aircraft that build up heat from electronics including: Electronic Equipment Racks (LEER and REER), Power Distribution Boxes (PDBs), Display Units, and Transformer Rectifier Units (TRUs).

  • Utilizes conditioned cabin air supplied through floor ducting drawn forward through cabin overhead return ducting by the following cooling fans:

    • Personal Service Unit (PSU) Fan; located under floor in vestibule area, provides cooling for TRUs, connected to left overhead return ducting, normally operates on low speed, switches to high speed operation if Remote Data Concentrator 17 fails or smoke detected in baggage compartment.

    • LEER Fan; from left overhead return ducting, provides cooling for LEER.

    • REER Fan; from right overhead return ducting, provides cooling for REER.

  • Air then flows out of TROV.

  • LEER and REER cooling fans signaled by ACC to change speeds through a 35K relay switch. Fans are at high speed when at or below 35,000' and low speed when above, provided both ECS packs are operating.

  • There are two aft equipment fans behind the right forward baggage compartment wall, one for each baggage EER.

Ozone Filter

If, like me, you've wondered how that ozone filter works, you have probably looked in vain for an explanation. One of these days I'll do some proper research, but for now this is what I know. (If you have something more definitive, please send it along.

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Photo: Ozone filter from Eddie's G500 (right side shown)
Click photo for a larger image

  • The oxygen molecule (O2) is fairly stable. The ozone molecule (O3) is an oxygen molecule with an extra electron and is less stable.
  • Ozone naturally decays back to oxygen with time. It just happens.
  • Ozone decays at 390°C back to oxygen.
  • Light destroys ozone.
  • Various other chemical, such as chlorine, bromine, or some oxides of sulfur and turn ozone into oxygen. I've heard that our ozone filters are filled with platinum for this reason.

[System Description Manual, §21-00-00, ¶1.1.1.1.2] Two ozone converters are located downstream of the PIV, outboard and forward of each pack. It is a nonrepairable unit consisting of an Inco housing and inner monolithic matrix (honeycomb) coated with a proprietary precious metal formulation catalyst. Precooled bleed air flows through the ozone converter prior to entering the Environmental Control System (ECS) pack. Extreme caution should be observed when working anywhere around the housing. It is extremely hot when the ECS system is operating.

Pneumatic Air Conditioning Kits (Packs)

In one of my past airplanes, the Boeing 707, we were required to draw a schematic of a PACK from memory. The PACK in that airplane was so unreliable that having the knowledge helped with troubleshooting. Why don't we need to do that now? Well they are so reliable they are like magic: hot air goes in, cold air comes out. What is a "PACK" any way? It originally meant Pneumatic Air Conditioning Kit (PACK). The PACK from that Boeing 707 looks a lot like the PACK in the GVII, but the parts are made better, put together better, and there is an element of computer control to make sure everything behaves. Here is my latest drawing:

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Photo: Left PACK, Eddie's drawing
Click photo for a larger image

[PAS, p. 1-2]

  • Air Conditioning Packs are also referred to as Environmental Control System (ECS) Packs. The left and right packs are identical.

  • The packs are located in the tail compartment. They are pneumatically powered by high temperature, high pressure bleed air from the 4th or 8th stage air, downstream of the precoolers.

  • The packs produce air that is dry, cold (35°F), and conditioned. The air is warmed by mixing with hot air from Trim Air Valves (TAVs).

  • Single pack operation is allowed up to 48,000 feet.

You may be wondering how the PACK turns 400°F or hotter air into 35°F air with no freon other refrigerant. It is magic. The magic has a name: thermodynamics. In a nutshell, when you compress a gas or fluid, it gets hotter. When you expand a gas or fluid, it gets colder. You can click on the PACK diagram above for a larger, easier to read version and the follow along:

Primary Heat Exchanger

The PACK will operate with no electrical power, it just needs air which is allowed in with a Pack Inlet Valves (PIV). The air is sent through a Primary Heat Exchanger which is nothing more than a radiator cooled by air passing through it. The air comes from the ram air scoop just forward of the vertical fin and is exhausted underneath the tail on the left side. A fan inside the plenum near the exhaust encourages air flow over the heat exchanger when the aircraft is not moving. This cools the hot bleed air a little, but not a lot. It next goes to the air cycle machine.

Air Cycle Machine (ACM)

[System Description Manual, §21-00-00, ¶1.1.7]

  • The ACM is a three wheel (fan, compressor and turbine) assembly that is a subcomponent of the air conditioning pack. High pressure and high temperature bleed air enters the compressor inlet of the ACM where it is compressed by the compressor impeller.
  • The secondary heat exchanger is just like the first, but this time the input air is cooled quite a bit and the output air is therefore even cooler. This air snakes around a reheater and condenser into a turbine.

  • The reheater and condenser assembly is mounted on the forward end of the air conditioning pack assembly. This is a single pass, cross-flow assembly which is a double heat exchanger. Both sections are single pass, cross-flow plate and fin construction. There are primary flow duct connections and low limit valve sense ports, a turbine bypass valve inlet connector, the pack servo regulator tap off and a condenser leading edge anti-ice inlet port. This is a single welded, dual-flow heat exchanger assembly. Its purpose is to cool the air to condense moisture content for water extraction, then reheat the air prior to it entering the turbine.
  • The drawing can be confusing since the air from the secondary heat exchanger appears to go over the reheatear and condenser, in that order. But this air is actually used by double heat exhanger. The air itself is treated the second time around, first by the reheater.

  • The reheater adds heat to the turbine inlet to reduce the possibility of moisture droplets entering the turbine inlet and eroding the blades of the turbine. It also cools the secondary heat exchanger outlet air before it enters the condenser to improve condenser efficiency. The reheater outlet duct contains the port for the supply pressure connection to the servo pressure regulator
  • The condenser lowers the temperature of the air to improve the performance of the water extractor at removing moisture. It also helps raise the temperature of the turbine outlet air above freezing so less additional heat must be added to prevent ice from forming.
  • Allowing the air to expand in the turbine section does two things. First, it pushes the turbine blades which drives the compressor and the fan in the ram air duct. Second, a gas that is expanded cools.

  • The turbine also generates the shaft power which drives the compressor and fan impellers. A fan supplies ram air cooling airflow for the primary and secondary heat exchangers. The work extracted from the airstream in the turbine wheel is absorbed by operating a compressor rotor. The compressor is directly shafted to the turbine wheel but is located in a separate chamber on the upstream side of the unit. A large percentage of the work which is extracted by the turbine is used by the compressor. As the compressor compresses the upstream air, its pressure and temperature are increased. This air is then delivered through the secondary heat exchanger and next to the turbine. The turbine extracts the energy from the air and uses it to drive the compressor. This is called the bootstrap principle, which is actually a pressure recovery system used in modern air cycle systems. The ACM maximum operating speed is approximately 95,000 - 100,000 rpm.

Water Extraction

[System Description Manual, §21-00-00, ¶1.1.7.5.1]

  • The reheater and condenser assembly is mounted on the forward end of the air conditioning pack assembly. This is a single pass, cross-flow assembly which is a double heat exchanger. Both sections are single pass, cross-flow plate and fin construction. There are primary flow duct connections and low limit valve sense ports, a turbine bypass valve inlet connector, the pack servo regulator tap off and a condenser leading edge anti-ice inlet port. This is a single welded, dual-flow heat exchanger assembly. Its purpose is to cool the air to condense moisture content for water extraction, then reheat the air prior to it entering the turbine. See Figure 28. Reheater and Condenser.
  • The condenser lowers the temperature of the air to improve the performance of the water extractor at removing moisture. It also helps raise the temperature of the turbine outlet air above freezing so less additional heat must be added to prevent ice from forming. The reheater adds heat to the turbine inlet to reduce the possibility of moisture droplets entering the turbine inlet and eroding the blades of the turbine.
  • It also cools the secondary heat exchanger outlet air before it enters the condenser to improve condenser efficiency. The reheater outlet duct contains the port for the supply pressure connection to the servo pressure regulator.

Temperature Control

[System Description Manual, §21-00-00, ¶1.1.8]

  • The temperature control system provides a means to control the temperature of conditioned air delivered to the cockpit, forward cabin and aft cabin areas within the pressure vessel. Temperature for each of these zones is selected by each zones dedicated temperature selector located on the overhead switch panel.
  • The air cycle machine uses the various heat exchangers, compressors, and turbines to cool the air and a number of valves to ensure the air doesn't get cold enough to freeze whatever moisture remains in the air.

  • The low limit valve is a spring-loaded closed pneumatically operated modulating valve, mounted on the air cycle machine turbine outlet duct. Both a torque motor and a differential pressure servo control this valve. The valve has two modes of operation. It provides hot air to maintain a minimum of 35°F (1°C) pack outlet temperature through the torque motor. The valve also provides hot air to deice the condenser through the differential pressure servo.
  • Turbine Bypass Valve: These normally closed, pneumatically actuated, solenoid operated valves allow airflow around the turbine section of the ACM when the valve is open to increase airflow at altitudes above 35,000 feet.
  • The turbine inlet temperature control valve is mounted in-line between the reheater outlet and the turbine inlet. Its purpose is to direct flow from the reheater to the turbine and ensure that ice crystals do not enter the turbine. The valve is operated by a thermal sensing element, which is both sensor and actuator. It contains a wax eutectic that contracts when chilled. The valve opens when reheater outlet air temperature drops below 75°F (23°C). This allows hot air from the air cycle machine compressor outlet duct to enter as needed to restore the temperature level to a minimum of 75°F (23°C). Should this valve fail to control the minimum temperature it is detected by the turbine inlet temperature sensor and annunciated through the air conditioning controller.

Pack Inlet Valves (PIVs)

[System Description Manual, §21-00-00, ¶1.1.1.1.1]

  • The PIVs are located above and forward of each pack assembly in the tail compartment and are designed to regulate the flow of bleed air into the air conditioning system. It operates on a predefined open loop flow schedule based on a standard air pressure and air temperature and is controlled by the ACC.
  • The PIVs simply block or allow air from the bleed air system to enter the PACKs. They are spring loaded open — they need electrical power to close — so if you have bleed air on the airplane and no electricity, the PACKs will operate.

  • The pack inlet valve is a 2.5 inch diameter, spring-loaded open, variable schedule, venturi flow control and shut-off valve. The valve consists of a control pressure regulator, delta-P servo, relief valve, shut-off solenoid, torque motor and actuator assembly. A position indicator is located on the top of the valve housing to indicate valve position

Ram Air

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Photo: Ram air intake and plenum, PAS, p. 1-3
Click photo for a larger image

[PAS, pp. 1-3 to 1-4]

  • Ram Air is the outside air forced into Dorsal Fin Air Intake in flight and delivered via dual ducted Plenum to primary and Secondary Heat exchangers on L / R ECS Packs.

  • This ram air provides 1st and 2nd stage of bleed air cooling by packs. There is a view port on each Pack to inspect heat exchanger inlets. Air is exhausted overboard via ducting through side of aft fuselage.

  • The ram air duct allows ram air to bypass the left ECS pack to join the cold air manifold, through a ram air check valve. The check valve is located on the left pack just prior to the heat exchanger. It is closed during normal operations. When selected on via OHPTS → ECS page, it shuts off both packs, the TROV auto closes. The check valve opens only when RAM air pressure exceeds cabin pressure.

  • Ram air is used for over pressurization due to loss of system control, aircraft interior smoke removal, and ditching.

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Photo: Ram air switch, PAS, p. 1-9
Click photo for a larger image

[PAS, p. 1-9]

  • Uses: over pressurization due to loss of system control, smoke from gaspers and / or floor vents, ditching.

  • Selected Off → White guarded; Upstate, default at power up, allows normal operation of ECS Packs. One way RAM air check valve is closed when cabin pressure inside > outside ram air pressure.

  • Selected On → Amber guarded; Downstate, turns off both ECS packs (both ECS Pack Inlet Valves close), one way RAM air check valve opens when outside RAM air press > cabin pressure inside. The aircraft pressurization leak rate is approximately 1000' / minute at 25,000'. You can expedite this by selecting CABIN PRESSURE CONTROL → MANUAL and opening the outflow valve.

Synoptic

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Photo: Air conditioning system 2/3 synoptic, PAS, p. 1-17
Click photo for a larger image

[PAS, p. 1-17]

  • Temp color codes — Actual → White, Desired → Blue, Abnormal → Amber

  • Synoptic color codes — Normal → Green, Off → White, Abnormal → Amber

  • Aircraft zone temps

  • Zone duct temps

  • Left and Right Packs — Represented by pump impellers, pack outlet temp → 35°F target temp

  • Flow tubes depict flow of air — To Packs from Bleed Air system, from packs to zone ducts, from zone ducts to each aircraft zone

  • Info below ECS — Wing Anti-Ice, pneumatics, pressurization


Limitations and Abnormal Procedures


Limitations

[G500 AFM, §01-21-10]

  • Landing Field Elevation (LFE): Limited to less than 10,000 MSL with the CPCS in Semi Mode except during an emergency.

  • Maximum Cabin Differential Pressure (In Flight): 10.69 PSI

  • Maximum Cabin Differential Pressures (Taxi, Takeoff, Landing): 0.3 PSI

  • ECS Duct Temperature: Duct temperatures above 200°F (93°C) are prohibited during manual zone control.

  • ECS Pack Operation: During ground operations with SAT greater than 98°F (37°C), a minimum of one ECS pack must be operating with APU or Engines operating.

  • Single Pack Operation: Must comply with abnormal procedures for operating with a single pack failure, 03-01-10, Pack Failure - Single.
  • This limitation is found in Section 3:

    [03-01-10]] Maximum altitude for single pack operations is 48,000 feet.

From one of Eddie's readers:

We had to manually control the aft cabin temperature recently. Turns out the temp sensor behind the aft facing seat across from the divan became disconnected behind the side panel and gave an incorrect cold temp reading. The actual temp in back was in high 70’s, the temp sensor was saying 50f, and duct was 160f before selecting manual. Manual mode allows direct valve positions shown as a percentage for conditioned air rather than setting a temp in auto, pic attached. As soon as we selected manual we were able to get a comfortable temp in the back after a few adjustments. At our destination FAST techs found the issue and reconnected the temp sensor. We haven’t had any issues since.

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Photo: Aft cabin manual temperature control
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Photo: Aft cabin temperature sensor
Click photo for a larger image


See Also:

Gulfstream GVII-G500 Airplane Flight Manual, Issue 1, March 21, 2020

Gulfstream GVII-G500 Production Aircraft Systems, Revision 5, April 13, 2020

Gulfstream GVII-G500 System Description Manual, Revision 2, December 15/19