TECHNICAL FEATURE FIGURE 4 Conditions in the cabin and envelope with a partial flow blocker. Temperature (R) if not redirected. Similarly, an airplane operated in humid climates on short routes with open-air passenger loading will condense water as the structure cycles from cold in flight to warm on the ground. To try to prevent this, water-absorbent felt was placed in areas where the structure passing through the insulation was exposed beyond the insulation, and layers of plastic were placed on various surfaces to redirect the water flow to areas that would not drip into the cabin. The insulation blankets overlay each other much like roofing shingles, so that the water flows downward on overlapping layers. The blankets are fiberglass, so they are placed in waterproof bags to allow water to flow over them. The water then flows around the cabin through the walls to underfloor drain holes on the belly of the airplane. Of course, this doesn't prevent the buildup of water over time if the airplane is operated in cold ground level climates. Note: These measures do not affect envelope ELA or change the amount of cold fuselage condensation. Other Types of Insulation. Some have proposed foamin insulation within the walls in a way that's similar to building use. But airplanes require periodic inspection of the structure for corrosion. They also require access to ducting and wiring that pass through the walls. The airframe flexes with static weight load on the ground and aerodynamic load in flight, which affects the adhesion of the foam, including mechanical degradation if 36 ASHRAE JOURNAL ashrae.org M AY 2020 2.16E+00 2.08E+00 2.00E+00 1.93E+00 1.85E+00 1.77E+00 1.69E+00 1.61E+00 1.54E+00 1.46E+00 1.38E+00 1.30E+00 1.22E+00 1.14E+00 1.07E+00 9.87E-01 9.09E-01 8.31E-01 7.52E-01 6.74E-01 5.18E-01 4.39E-01 3.61E-01 2.83E-01 2.05E-01 1.26E-01 4.81E-02 -3.01E-02 -1.08E-01 -1.87E-01 Stringers Envelope Cabin Partial Flow Blocker FIGURE 5 Stack pressure driven flows including the flow of dehumidified cabin air and open crown insulation associated with the CCDS and the downward airflow in the insulation. Dimension Lines (Inches) Wet Air No Liner Dry Air Air Travels Down Envelope Driven By Stack Pressure R1=120 R2=116 Air Enters Air Reenters Crown Through Cabin Through Gaps in Ceiling 95 Nozzles 77 68 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 Inches Flow Around the Blocker Static Pressure (Pa) 5.39E+02 5.35E+02 5.32E+02 5.28E+02 5.25E+02 5.21E+02 5.17E+02 5.14E+02 5.10E+02 5.07E+02 5.03E+02 5.00E+02 4.96E+02 4.93E+02 4.89E+02 4.85E+02 4.82E+02 4.78E+02 4.75E+02 4.71E+02 4.68E+02 4.64E+02 4.60E+02 4.57E+02 4.53E+02 4.50E+02 4.46E+02 4.43E+02 4.39E+02 4.36E+02 4.32E+02 135 Velocity Vectors (ft/s) 3.91E+00 3.78E+00 3.64E+00 3.51E+00 3.37E+00 3.24E+00 3.10E+00 2.97E+00 2.83E+00 2.70E+00 2.56E+00 2.43E+00 2.29E+00 2.16E+00 2.02E+00 1.89E+00 1.75E+00 1.62E+00 1.48E+00 1.35E+00 1.21E+00 1.08E+00 9.44E-01 8.09E-01 6.74E-01 5.39E-01 4.04E-01 2.70E-01 1.35E-01 0.00E+00 No Liner Outflow Valve 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 Inches rigid. Fiberglass blankets are used because of the above and because they have the advantage of lower weight for the same heat loss and acoustic properties and low flammability. Crown Cavity Dehumidifier Systems (CCDS). Crown cavity dehumidifier systems (CCDS) are added to reduce condensation in the crown of the aircraft. Since this involves leaving the insulation open to the airflow, thehttps://www.ashrae.org/