Cooling and using thermoclines - questions

[avb3]

Have any of you experienced thermoclines at anchorage? If so, at what levels of depth in tropical or sub-tropical climes? I have seen differences in as little as 15 feet below the surface.

What are the thoughts of utilizing this differentiation in temperature as a source of cooling the interior of the cabin?

It would appear to me that one could get a relatively inexpensive "air conditioning" system set up by using what nature provides.

Thoughts?

[Blue Stocking]

Very interesting idea.
Would need to make sure no boomers were hiding in it.

[Pete7]

After 25 years of diving across the world I am struggling to remember thermoclines in sea water. However, in lakes it was a different story with thermoclines that could be both seen and felt. I suspect the tides and currents mix the water together more readily than in a lake.

In freshwater light reflects off the layer like a mirrored surface and decending between the two layers results in a blurry layer of several inches were the two layers mix together. Temperature wise the difference was very noticeable in both a wetsuit or a drysuit.

Pete

[Jetexas]

So if you had weighted tubing that sunk at least 15' deep, came into the boat and through a copper coil, then back out of the boat, you could put a 12v fan behind the copper coil to transfer the chill from the water into the cabin.

Setting it up so that the water moved through some sort of self-sustaining siphon action would save you the battery drain of a 12v water pump, but you've got gravity working against you.

It's been done with a container full of ice water before: http://myspew.com/technology/homemad...der-25-dollars

[Blue Stocking]

Its not exactly thermocline, but many commercial HVAC systems pull cooler water from the ground for the air handlers.

Pete, on occasion the tidal flow from deep to the shallow bay off my dock give a temp change, I would estimate, of 5*F at about 10ft depth.

[sailorchic34]

Oh a lovely question. It would be possible, though you would need water temperature say at least 10-20 degrees different then the air temp in the cabin. You need a temperature difference in the coil/water flow /air flow design. Normally lets say 10 degrees differential nominal. You could use 5 degree delta but the flow rate then doubles. Do to a 20 degree delta and flow is 1/2 of 10 degrees.

So for example for a 1 ton (12000 btuh) cooling load you would need 2.4 GPM at 10 degree delta and 5 gpm at 5 degrees.

You would need a pump, as a siphion would not work, plus hot water rises, cold falls.. Though pump head would be low, just hose/ pipe friction loss and coil loss and vertical head loss from water level to highest point in the system.

The trick is you'll want the water temperature say oh 70-75 degrees to really get any real cooling out of it Circulating 85 deg water to cool a 95 degree cabin would mean you really will only get a 3-5 degree drop to maybe 92 degrees, but your moving a whole lot of water and air. and your still HOT. Well I would be anyway. The problem is the delta T "approach" temperature in the water and air streams. So its a little more complicated then just circulating water.

For building HVAC systems, we like to circulate 40-45 degree water in the chilled water system (depending on dry and wet bulb temps), Normally drops the 70-75 degree return air temp down to 50 ish supply air temp. The ground water and or lake water would be used on the condenser side of the chiller, where the heat from the building is rejected into. Also used on water source heat pumps, which the typical marine A/C really is after all. BTW, you can't add cold to something you can only take away heat, and no its not the same thing.

[Dennis.G]

Listen to Sailorchic, she's spot on

Best approach might be to use the cooler water from depth as water source to a water cooled condenser. This will increase its efficiency a great deal. The logistics of pumping the cooler water up from depth are more than most people would want to put up with however. Besides, those that are on a tight energy budget will just turn on a fan (or sweat).

[Bash]

Hmmm. Assuming that most of us prefer anchoring in depths of no more than five fathoms, a true thermocline in such a shallow, tropical benthic environment is going to be extremely rare.

You'll probably get more mileage out of cabin fans and/or a good chute scoop.

[avb3]

Originally Posted by sailorchic34

Oh a lovely question. It would be possible, though you would need water temperature say at least 10-20 degrees different then the air temp in the cabin. ...............

........... Also used on water source heat pumps, which the typical marine A/C really is after all. BTW, you can't add cold to something you can only take away heat, and no its not the same thing.

Originally Posted by Dennis.G

Listen to Sailorchic, she's spot on

Best approach might be to use the cooler water from depth as water source to a water cooled condenser. This will increase its efficiency a great deal. The logistics of pumping the cooler water up from depth are more than most people would want to put up with however. Besides, those that are on a tight energy budget will just turn on a fan (or sweat).

So, could it be more energy efficient to pump the cooler water to the water cooled condensor (using what? ammonia? R-12? or?) than using the normal A/C electrical compressor?

I know in theory it could work, the question is, how practical is it? Is it more energy efficient? What about capital costs, or is that a moot point?

[Dennis.G]

Originally Posted by avb3

So, could it be more energy efficient to pump the cooler water to the water cooled condensor (using what? ammonia? R-12? or?) than using the normal A/C electrical compressor?

I know in theory it could work, the question is, how practical is it? Is it more energy efficient? What about capital costs, or is that a moot point?

The bigger the temperature difference between the evaporator and condenser side of the refrigeration system, the more work the compressor has to do. So with lower the condenser temperarure, the more efficient the system runs.

In general an air cooled condenser will be cheaper capitol costs but higher operating costs that a water cooled condenser. The water cooled system has more expensive components, but runs at cooler condensing temperatures.

Getting cooler water from deep down, as opposed to a surface level, would increase efficency of a water cooled system even more (and should cover the slight increase in pumping energy). The issue is designing a simple and reliable system to get the water from deep down. I think that design wise not hard, but result would be a system that would take a fair amount of fussing about. Most people with air conditioners just want to hit a switch and feel cool air, without any hassle.

[sailorchic34]

Well the typical Marine AC is a water source heat pump. Up to a point using cooler water will improve the efficiency of the condenser and provide a bit more cooling. For the typical 134A compressor, the point is where the evap coil will ice over. So doable.. to a point. But as Bash indicated most anchorages are not deep enough to really make a difference.

Really the water cooled condenser on the marine AC works pretty good as designed, the saving using cooler water would not really justify the extra costs for a larger pump and the fussing around with a long hose. I see a hose stuck in a prop when it was not retrieved.

In the deep ocean it would work great with a 100 foot hose or so. well up to the point where the hose got stuck between a dive plane and submarine hull, that could get interesting... Lets put that down as a worst case scenario

For the big HVAC chillers the driving force is leaving water temp which needs to be above 35 degrees to keep from freezing a tube bundle (so not good) You can add antifreeze to the chilled water but thats only goes so far. (it reduces efficiency and raises the KW/ton costs...)

Thermoclines do work, used them in large thermo energy storage systems. Storing 2000-3000 ton/hours in an insulated million gallon tank. In the right location it works great. But even in larger projects the cost can only be justified when you have cooling loads 24/7- 365 days a year (think Vegas) or where manufacturing requires process loads (think biotech), etc. Did this with a big deep pond at a casino in reno once ages ago... Also use full using ground temp with water source heat pumps with a geo-loop in large residential homes. So it has its applications.

BTW a ton of cooling comes from back in the days where Ice was used to cool the first movie theaters. A ton being a ton (weight) of Ice, which gives you about 12000 btu's with fans blowing across the ice....

[avb3]

That's what I love about this forum..... ask a question, and at least one subject matter expert can answer it.

OK, so it is a great theoretical thought, but practical, not so much on sailboats.

Thank you so much for the feedback!

Damn, and here I thought I might have been on to something good