Another quite AC question - Geothermal? (aquathermal)

[rgranger]

I didn't want to hijack the other thread on this topic. I'd like to explore the idea of building a passive geothermal AC system for a boat. (should it be called aqua-thermal?)

If you are unfamiliar with geothermal.. here is a link

Building a New Home? Consider Adding Passive Geothermal Energy in Your Construction Plans

Passive/low-temperature geothermal systems use pipes underground and pumps to transfer natural heat and cold from the Earth's crust.

www.21stcentech.com

and a schematic for a house.

My first draft idea would be to use something similar to a solar water heater used to heat a pool as a heat exchanger. This would have the advantage of beeing flexible and able to roll it up and stow it when not at anchor...

Toss it overboard with quick disconnects to a closed system in the cabin when at anchor.

Then inside the cabin have a second one of these...

... that you blow a fan through to cool the air. A low amp pump to move the fluid between the two completes the system. I guess the one that goes overboard should be white in color to help deflect the heat. All that is left is to design a way to collect the condensation on the inboard side (maybe doubles as a water maker).

I see this as a hybrid between true geothermal and a split system AC unit.

Okay all you engineers.... how do we make this work and not take up too much space and keep the ease of use (portable)... all at the same time.

 

[Don S/V ILLusion]

In theory it works but efficacy is a function of water temperature. Kind of a Macgyver method of doing it.

 

[JamesG161]

I was about to do a long thread on how Boat AC systems work.

Ok as an Engineer

The Fast Way =

_______
The Long Way...
Perform an Overall Energy Balance

Then refer back to the Fast Way.
Jim...

PS: Your reference article does not work either.
PSS: Engineers have tried Geo-Heat Pumps.

 

[DeniseO30]

Without getting into the engineering or building air conditioning or heat pump systems geothermal solar assist
& other ways of doing it if you manage to create such a system which is not convenient to use, and If the water is cold enough. you probably wouldn't need air conditioning anyway. where my boat is
right now the water is 80 plus degrees closer to 90, people in the tropics are sailing on even warmer water if you're on the North Atlantic there's a good chance you don't need air conditioning, what it all comes down to is reaching what is called a "dew point" that is the point of coldness where water starts to condense from the the air and to confuse everybody, there is no such thing as cold, cold, is the absence of heat,
And Marine air conditioners are water cooled they are very common even more common is very large buildings it doesn't matter what the water source is or where it comes long as it exchanges the Heat of compression or evaporation which are the heating and cooling modes of reverse cycle IE heat pump systems

 

[kloudie1]

There were some coolers like that on the market. A couple of years ago. They eliminated the heat exchanger in the water by just pumping the water from a ways down through an exchanger and air handler (fan unit) in the boat. I think that they worked where the cool deep water was below the dew point in the boat. Same reason a “swamp cooler “ doesn’t work on a boat (except in a few inland lakes) .. too much humidity in the air.

 

[DeniseO30]

There were some coolers like that on the market. A couple of years ago. They eliminated the heat exchanger in the water by just pumping the water from a ways down through an exchanger and air handler (fan unit) in the boat. I think that they worked where the cool deep water was below the dew point in the boat. Same reason a “swamp cooler “ doesn’t work on a boat (except in a few inland lakes) .. too much humidity in the air.

Swamp coolers are scaled down versions of what are called "water towers" they were very large galvanized steel usually with hundreds of cedar wooden slats with water pumping up over and cascading down across the wooden slats and a fan would blow thru air and the water they found the air was somewhat cooler even though it was Laden with humidity and the water temperature dropped about 10°, enough for water cool refrigeration or ac systems to operate.
Of course over the years these systems have been replaced with big plastic water coolers


swamp coolers are still popular in the desert Southwest where the humidity is low but the temperatures are high.

 

[Tedd]

Refrigeration isn't a specialty of mine but I'm doubtful about a truly passive system working very well. If you don't mind a little more complexity, though, a solar powered pump might be able to drive a conventional refrigeration system, perhaps using the water as a heat sink, that would cool the boat somewhat. It would be "passive" in the sense that you wouldn't be using the boat's batteries.

 

[JamesG161]

a solar powered pump

Now you are doing the Energy Balance.

Solar Power is a INPUT of energy.
Jim...

 

[DeniseO30]

It takes horsepower to compress and move saturated gases even moving warm and cold water takes requiers power against things called lift and head applied to pumps and in order to move the amount of cool water even if it weren't cold would take probably the same amount of horsepower as an air conditioning compressor if not more because, water has to move a lot faster to get the cooling effect

thing is this is all fun to talk about but if it were practical somebody would have done it by now

 

[rgranger]

Now you are doing the Energy Balance.

Solar Power is a INPUT of energy.
Jim...

... and quoting myself...

... that you blow a fan through to cool the air. A low amp pump to move the fluid between the two completes the system.

I know I started off with the idea of a passive system but I think you would have to move a lot of water around.

So what I'm hearing is that this would probably only work in a deep lake with very cold water down low... Like where I so most of my sailing (Smith Mountain Lake VA).

 

[Tedd]

So what I'm hearing is that this would probably only work in a deep lake with very cold water down low... Like where I so most of my sailing (Smith Mountain Lake VA).

Without doing any calculations, I'd say there's a chance this could work. You'd certainly get some cooling, but I'd have to run some numbers before I could make a guess how much.

• Solar panel
• Battery (probably) to buffer energy
• Electric water pump with, say, 20 feet of suction head or more (depends on the depth of the thermocline in your lakes)
• Heat exchanger (something cheap and off the shelf, hopefully)
• Fan
• Hose, fittings, etc.

Pump up cold water and run it through the heat exchanger while the fan blows hot cabin air over it, then dump the water back into the lake.

 

[Johnb]

• Electric water pump with, say, 20 feet of suction head or more (depends on the depth of the thermocline in your lakes) No it only has to "suck" from surface level to the pump.
• Heat exchanger (something cheap and off the shelf, hopefully). How about a re purposed automobile cooling radiator from a wrecking yard. Look for a vehicle that got rear ended!
• Fan While you are the wrecking yard?

My experience with Lakes Meade, Tahoe, Don Pedro, Windermere and many others is that the cold water is not very far down, sometimes as little as 3 feet, so maybe you are on to something.

 

[Hayden Watson]

... and quoting myself...



I know I started off with the idea of a passive system but I think you would have to move a lot of water around.

So what I'm hearing is that this would probably only work in a deep lake with very cold water down low... Like where I so most of my sailing (Smith Mountain Lake VA).

If you are in a cold freshwater lake you do not need an exchanger for what you are talking about. Drop a weighted pickup deep enough to get below the thermocline and pump it through a filter and a fan coil. How well it would work would depend on the water temperature.

 

[Crusty Ol Salt]

I was about to do a long thread on how Boat AC systems work.

Ok as an Engineer

The Fast Way =

_______
The Long Way...
Perform an Overall Energy Balance

Then refer back to the Fast Way.
Jim...

PS: Your reference article does not work either.
PSS: Engineers have tried Geo-Heat Pumps.

As a guy that has work in the HVAC industry for 40 years and spent the last 22 testing HVAC systems, I am going to put this as simply as I can.

The math does not work.

 

[sesmith]

The reason geo systems (ground source heat pumps) and air source heat pumps work is because they use a refrigerant circuit that moves the heat by taking advantage of the phase change properties of the refrigerant between liquid and gas phases. You can move a lot of heat this way and the math works. Without the refrigerant circuit the math doesn't work for what you're proposing. There are water sourced cold plate refrigerators for boats, though, so if you could build a huge system like that, you could be onto something (probably a very expensive experiment at best).

 

[Davidasailor26]

There are water sourced cold plate refrigerators for boats, though, so if you could build a huge system like that, you could be onto something (probably a very expensive experiment at best).

Existing marine AC units basically work this way - they pump the relatively cool seawater past the refrigerant to carry the heat away.