Several approaches are taken to control 

 cabin temperature: Hull insulation to retain 

 heat; electric heaters to produce heat; air 

 conditioners to remove heat; and circulation 

 of cabin air along the colder pressure hull to 

 cool it or across a block of ice to achieve the 

 same result. 



Insulating the hull is a practice in a few 

 vehicles and is adequate as long as sufficient 

 heat is being produced. Electric heaters are 

 effective if the power they require can be 

 spared. 



Air conditioning serves both a cooling and 

 humidity control function. Its use, however, 

 is governed by available electric power. On 

 JOHNSON SEA LINK the air conditioner's 

 motor and compressor are housed externally 

 in a pressure-resistant container and the 

 condensers consist of tubular frames behind 

 the acrylic sphere. Liquid freon enters the 

 sphere through a penetration with a ball 

 valve acting as a hullstop. Passing through 

 the evaporator the gasses pass out of the 

 sphere to the condenser via a return line 

 with a check valve hullstop. 



Because acrylic plastic has a low heat 

 transfer coefficient, the air inside traps solar 

 radiation and can produce extremely high 

 temperatures. Operators within NEMO expe- 

 rienced temperatures of 120 °F and 85 per- 

 cent relative humidity (13); consequently, a 

 system was designed for both NEMO and its 

 successor, MAKAKAI, to reduce such temper- 

 ature extremes and maintain a low relative 

 humidity as well. 



MAKAKAI's systems (14) consist of 25 

 pounds of ice stored in cannisters (under the 

 operators' seats) over which air is circulated 

 by fans. If the hull is covered until just prior 

 to the dive the cabin temperature can be 

 held at 82°F for 6 hours. The cooling system 

 also removes water vapor from the atmos- 

 phere by causing it to condense on the cool 

 ice containers. Various components of this 

 system are shown aboard NEMO in Figure 

 9.10. 



Humidity Control: 



The major sources of water vapor in a 

 submersible are the cabin air when the 

 hatch is closed and respiration and perspira- 

 tion of the occupants. Except for those vehi- 

 cles with air conditioning, the control or low- 



ering of humidity is accomplished by adding 

 a desiccant to the carbon dioxide scrubbing 

 compound, or by distributing small parcels of 

 desiccant throughout the vehicle. From all 

 available information, the only desiccant 

 used is silica gel, and its effectiveness can be 

 seen in Figure 9.9 which shows an immediate 

 decrease in relative humidity following de- 

 ployment of additional 5-pound, cloth-bound 

 packages. Many of the random fluctuations 

 in this figure correlate with temperature 

 variations. Other variations (decreases) may 

 be attributed to non-periodic but occasional 

 massaging and shaking of the packets. By 

 deployment of some 3,600 pounds of silica gel 

 throughout the 30-day mission the humidity 

 level was maintained at a comfortable level. 

 The effects of high humidity are more criti- 

 cal on equipment than on humans, especially 

 when the internal temperature drops to a 

 level where condensation occurs with subse- 

 quent drippage or collection of water on and 

 within electrical components. 



Atmospheric Monitoring Devices 



The one area where the submersible com- 

 munity does not lack off-the-shelf instrumen- 

 tation is in the means available to monitor 

 the cabin atmosphere. A wide variety of com- 

 pact, portable and inexpensive monitoring 

 devices is available from the mining and 

 aircraft industries, among others, which is 

 more than adequate for submersible opera- 

 tions. There is no doubt that improvements 

 can be made, but, for the present, progress in 

 deep submergence is not thwarted by lack of 

 atmospheric monitors. The variety of instru- 

 ments from which to choose is reflected on 

 the individual vehicles where few use the 

 same devices. Consequently, only one or two 

 instruments from each category are de- 

 scribed. 



Oxygen: 



Two factors need be known with regards to 

 oxygen: How much is in the flasks, and how 

 much is in the atmosphere? 



The simplest answer to the first question is 

 the pressure gage arrangement shown in 

 Figure 9.11. This system attaches directly to 

 the oxygen flasks and is manufactured by 

 National Cylinder Gas Corporation. The 

 main components are a gage to show pres- 



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