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Water temperature and volme advice

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GeorgeAskew

Mechanical
May 6, 2008
5
Heres a bit of a different one chaps.
I am endeavoring to build a divers hotwater system. Supplying to 2, 4 or 6 divers. Seawater temp 14-17 degrees C. Depth 2-3 metres. Duration - up to several hours [Say 6]. Activity minimal. Wearing baggy suits tightened at ankles, wrists and neck with velcro. Head and feet insulated. Heat loss through conduction minimum /minute = 10% Max = 50%. Hose length max 15m - heat loss minimal say 3%. So how much water and at what temperature must the diver get it to be comfortable [say 28* C]?
Space for equipment is minimal as is electricity supply [If I install solar panels [max area available to support panels = 3x4m] but as sun can range from blazing to nil I see it as a bonus when there is sun.
I propose a combination of large size Propane gas water heaters as found in some bathrooms and electricity. Is there any difference which does primary and secondary heat. Just a wild guess I`d say the water needs to be heated to 30 *C - go into an insulated holding tank [What size?] then be pumped to the divers. [The inlet water will run thru about 30m of hose on the deck to be pre-warmed by the sun when its there. I feel the primary heat to the cold water should be gas and electric elements can keep the tank topped up.

I need the size of hose from tank to a manifold just above the surface [length 12m] with 6 take-offs [I`d guess it cant be more than 30mm OD. It can be rubber or galv iron or plastic [From manifold to diver - Probably 16mm ID Garden hose 4m long].
What size and type 220v pump?
How much electricity needs generating to drive pump and heat water?
How much Propane will be burnt?
How long will the gas heaters last with seawater in them or can one get non corrosive?
2nd part
Same senario. Air: Same kind of primary hose to a manifold and same length hoses to divers but smaller dia. How much air must each diver be supplied [minimum]with a free flow system or using 2nd stage scuba regulators?
Regulators usually work at 120 -200psi but a weakend spring and 40psi will be OK at this shallow depth.
The regulators should use less air but as bubbles may be a problem a free flow back to surface taking air from a T piece is ideal but will use more air.
What size compressor [CFM] storage tank unnecessary and what size 220v motor to drive it?
So there it is in a seashell - What are my power requirements etc
 
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Whoa! Slow down here a bit.

What the heck is this anyway. You are making a hot water system for a tank to hold up to 6 divers. Is the tank at the 2-3 m surface depths, or on the boat deck? 2, 4 or 6 hours makes a heck of a difference. Immersed in 25C water divers feel ice cold after 45 minutes! I think you need to ask the divers about what they think they need, then verify that with a medical diver's doctor.

Forget solar. First, its not reliable enough for this application and I don't think 12m2 will give you enough heat for a sustained flow for the supply times you need anyway. Assuming no wet or dry suits, temperature may need to be higher than 30C. Flowing water at anything less than body temperature itself can suck a lot of heat out of a human being. Then again, if their heads are not exposed to that water (they are wearing air filled diver's helmets?), it might be OK. I think divers doing no work will need about 100 cft/hr of air at around 40 psia (and that pressure is encountered at the 60 ft depth, not 2 to 3 meters), but as long as you're at it, verify that with the medical diving officer too. BTW diving regulators are balanced and feed air to the diver at the basically the same hydrostatic pressure of the water at whatever depth they happen to be at when they take a breath.

A further word. The detail design is up to you to do, not us. When you get to the point where you have a specific problem, or feel you need some specific advice, other than medical requirements for diving life support systems, feel free to come back and tell us about that.




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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)
 
Thank you for your thoughtful and helpful reply.
 
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