Overnight Cooling Without Shore Power

[rslifkin]

Originally Posted by Dockhead

But what is the water temp 10 meters down? Isn't it a lot cooler than on the surface?


A water to air heat exchanger using cold water from deep down could be really interesting, if there really is cold water there. They air condition data centers and office buildings in Finland using this principle.

That principle would certainly work in the heat of summer in the Great Lakes. Hot, sticky, and 85* F at night sometimes. Water temp can be as high as 75 - 80, but go down far enough and you'll find water that's under 60, which would do just fine for cooling the boat.

[wsmurdoch]

Originally Posted by Dockhead

A water to air heat exchanger using cold water from deep down could be really interesting, if there really is cold water there.

I built one several years ago. A weighted hose went down 50 ft to get the water. A small pump moved the water thru the system. An automobile heater core from a junk yard was the heat exchanger. A squirrel cage fan moved the air. The waste water went overboard. Since we were on a lake, the deeper water was much colder than both the surface water and the air, 30F or more. As a cooler it worked fine. The amount of water that condensed from the air on the heat exchanger was impressive. The fan speed had to be limited to keep from blowing a mist from the unit and the collected condensate had to be disposed of.

I'm not sure there would be cool enough water below the surface in the tropics.

After using it a few times and getting bragging rights, it went in the attic. We have a sun awning and a Hella fan.

[malbert73]

My feeling is that: if you’re too hot during day with too much sunshine and not enough breeze, even a high powered AC will work hard. So generator is all you can use.
The water cooled system above only works with cool water and in those areas (lakes, NEw England, eg) where the nighttime air temp cools significantly after sun goes down. So not needed as fans are enough

[Dockhead]

Originally Posted by malbert73

My feeling is that: if you’re too hot during day with too much sunshine and not enough breeze, even a high powered AC will work hard. So generator is all you can use.
The water cooled system above only works with cool water and in those areas (lakes, NEw England, eg) where the nighttime air temp cools significantly after sun goes down. So not needed as fans are enough

I suspect that this is a correct analysis.

[a64pilot]

Originally Posted by Dockhead

But what is the water temp 10 meters down? Isn't it a lot cooler than on the surface?


A water to air heat exchanger using cold water from deep down could be really interesting, if there really is cold water there. They air condition data centers and office buildings in Finland using this principle.

Ten meters down is about 6 meters below the bottom, Bahamas bank is very shallow, and due to water turbulence it’s the same temp.
To work you need to be in real deep water, and find the thermocline, and that doesn’t always exist, but in WWII subs would hunt for the thermocline as the difference in water temp would of course cause a difference in water density and reflect Sonar to some extent, so they could sometimes hide under it. The thermocline was I believe almost always very deep, below any possible water movement from the waves.

But in any place on Earth pretty much that there is deep water, there is pretty cold water. Diving Trimix I would often hit it off the coast of Fl. Get a coupe of hundred feet down and you get cold, pretty darn cold, pretty much need a dry suit cold. I forget the temp but think it was in the 60’s, where water near the surface was in the 80’s.

But cool water and even cool air from caves etc has been used for centuries to aircondition houses etc, one of the US Presidents tied his house into some kind of cave of something for the cool air.
This Sanitarium was kept at 70 f with cave air
https://www.atlasobscura.com/article...r-conditioning
Many ground source heat pumps use of course the heat of the earth to boost efficiency, but air to air heat exchangers have gotten so good by being huge, that they never really caught on.
In North Fl where I cave dove, the cave water was always 68F year round, you could use spring water to both heat your house in Winter and cool it in Summer

[flyingnut40]

Has ANYONE noticed that the OP has not commented since post #1?

[a64pilot]

Originally Posted by Dockhead

Your units are all confused here. Let me see if I can sort it out, because this is really the heart of the matter.


600 watts * 50% duty cycle = 300 watt hours per hour or 0.3kWh per hour. So for 8 hours that's 2.4kWh. That's 100AH at 24v o r 200AH at 12v.



My present battery bank (which will be changed this spring) contains about 200AH of usable power at 24v when fully charged. So your scenario would work on my boat today and would work even much better with lithium.



I think actually it could be better than that -- I think you run the AC full blast with the generator on for a couple of hours before going to bed, get everything cooled off well, then let it coast on batteries -- might be much better than 50% duty cycle with no solar gain and assuming you have decent insulation.



Of purely theoretical interest to me since I have never been below 40N in more than 10 years of cruising with this boat and presently at 55N, so I'm heating year round and no AC.


When I was cruising warmer places we did have AC but no generator. As others have commented, at most hot latititudes you can be more or less comfortable at anchor without AC, but AC was a godsend in marinas. Excluding the Sea of Cortez in summer I guess.

But you really haven’t accomplished much, except restricting your generator run time to the day, you still will have to have a generator to recharge the batteries, and that’s the flaw in the logic of running an airconditioner off of batteries, of course it can be done, it’s simply a matter of scaling, WWII 2,400 ton 300’ long submarines could run for up to 48 hours on lead acid batteries, but then of course they surfaced and ran up to 4 huge locomotive sized engines to recharge that huge battery bank.

So bottom line running air conditioning on a boat, at least an AC of a size that will actually cool a boat better than passive ventilation will require a generator to recharge those batteries.
It’s no different than electric propulsion, it too can easily be done, but it’s going to take a generator to recharge or shore power.

But you can save a shed load of money and propel that boat directly with a fossil fuel engine, same with air conditioning, the few times it’s actually really needed, just run the generator.

[Dockhead]

Originally Posted by a64pilot

But you really haven’t accomplished much, except restricting your generator run time to the day, you still will have to have a generator to recharge the batteries, and that’s the flaw in the logic of running an airconditioner off of batteries, of course it can be done, it’s simply a matter of scaling, WWII 2,400 ton 300’ long submarines could run for up to 48 hours on lead acid batteries, but then of course they surfaced and ran up to 4 huge locomotive sized engines to recharge that huge battery bank.

So bottom line running air conditioning on a boat, at least an AC of a size that will actually cool a boat better than passive ventilation will require a generator to recharge those batteries.
It’s no different than electric propulsion, it too can easily be done, but it’s going to take a generator to recharge or shore power.

But you can save a shed load of money and propel that boat directly with a fossil fuel engine, same with air conditioning, the few times it’s actually really needed, just run the generator.

No question you need a generator, or mammoth alternator, or mammoth solar installation, to do this. But I actually think that it would be worthwhile to have this capability, for a couple of different reasons: (a) who the hell wants to run a generator all night; and (b) it is grossly inefficient and also hazardous to the generator's health to run it all night at low load when the AC mostly cycled off. In fact, being run all night to run AC which is not cycling much because -- it's night -- is the classic cause of generator bore polishing.


So potentially great benefits from running AC off batteries at night. Obviously this works the batteries much harder than normal use so for best results, you would want lithium, unless it's only an occasional thing.

[a64pilot]

You know in all honestly I have never seen a generator with polished bores that was broken in, and I’ve been around a great many that were regularly run, but never put under a load, they would stack and slobber but none had glazed bores, and now that I think of it, it’s glazed bores we are speaking of, polished bores are a different thing.
The very few glazed bores I have seen were all on pretty new engines that were improperly broken in, run for extended times often a lower RPM and very little load, but once broken in glazing doesn’t seem to happen, it’s the low load that gets them, it keeps an engine from reaching operating temp.
I’ve seen quite a few polished bores, often aircraft. What happens is they sit for extended times, the bores form a light rust coating that is of course cleaned off at every run, eventually the cross hatching is worn off and you have a polished bore. It’s from wear of course, only way to polish a bore is to wear off the cross hatching, and that’s the difference between polished and glazed, glazed is the cross hatching is clogged up with a varnish like material.
But if the generator isn’t putting out much power most of the time, you don’t need AC, and a very easy thing to do if your concerned about it is to open a hatch for ventilation, that will cause the AC to run more often.

Just about every military generator in the US is run weekly and never put under a load, it was called “motor pool” day and anyone that was in the Army can attest to it, plus every Hospital etc has standby generators that are often run and never put under a load, and this goes on for years.
Plant I worked at we had a two stroke Detroit that had been there since the plant opened in 1965, it powered the fire sprinkler pump and was usually run every week and was done that way for, well since 1965, it never actually pumped water so it was never put under a load, but fire regulations or maybe it was Insurence required it to be regularly run.
Stupid loud thing as it had no muffler and of course a Detroit sounds like it’s going to blow up cause it’s a two stroke and has twice as many ignition events per revolution than a four stroke.

If you ran your generator all night not under load and are the least concerned about it, turn on the water heater in the morning that’s plenty of load unless you have a huge generator.

Just about every big yacht there is runs it’s generator 24/7, they never stop, often they have more than one as a backup cause they can’t do without a generator, the whole boat is AC powered and they only have enough batteries to start engines, and they don’t glaze

[Dockhead]

Originally Posted by a64pilot

You know in all honestly I have never seen a generator with polished bores that was broken in, and I’ve been around a great many that were regularly run, but never put under a load, they would stack and slobber but none had glazed bores, and now that I think of it, it’s glazed bores we are speaking of, polished bores are a different thing.
The very few glazed bores I have seen were all on pretty new engines that were improperly broken in, run for extended times often a lower RPM and very little load, but once broken in glazing doesn’t seem to happen, it’s the low load that gets them, it keeps an engine from reaching operating temp.
I’ve seen quite a few polished bores, often aircraft. What happens is they sit for extended times, the bores form a light rust coating that is of course cleaned off at every run, eventually the cross hatching is worn off and you have a polished bore. It’s from wear of course, only way to polish a bore is to wear off the cross hatching, and that’s the difference between polished and glazed, glazed is the cross hatching is clogged up with a varnish like material.
But if the generator isn’t putting out much power most of the time, you don’t need AC, and a very easy thing to do if your concerned about it is to open a hatch for ventilation, that will cause the AC to run more often.

Just about every military generator in the US is run weekly and never put under a load, it was called “motor pool” day and anyone that was in the Army can attest to it, plus every Hospital etc has standby generators that are often run and never put under a load, and this goes on for years.
Plant I worked at we had a two stroke Detroit that had been there since the plant opened in 1965, it powered the fire sprinkler pump and was usually run every week and was done that way for, well since 1965, it never actually pumped water so it was never put under a load, but fire regulations or maybe it was Insurence required it to be regularly run.
Stupid loud thing as it had no muffler and of course a Detroit sounds like it’s going to blow up cause it’s a two stroke and has twice as many ignition events per revolution than a four stroke.

If you ran your generator all night not under load and are the least concerned about it, turn on the water heater in the morning that’s plenty of load unless you have a huge generator.

Just about every big yacht there is runs it’s generator 24/7, they never stop, often they have more than one as a backup cause they can’t do without a generator, the whole boat is AC powered and they only have enough batteries to start engines, and they don’t glaze

You might be right -- all I know is what I've heard. I've heard enough concrete stories to believe it is a problem, and if you think about it -- running at 1500 or 1800 RPM without any load at all has got to be the case which will polish bores, if this ever happens at all.


What happens on superyachts is not really applicable because those always have some load on. Running a large number of different compressors will aslo spread out the off cycles. To run a generator all night on a small yacht with only one AC unit working has got to be asking for trouble -- it seems to me -- but I can't prove it.


But you don't need polished bores as a reason not to do this -- think about all the wasted fuel, and all the wasted generator hours, each one of which is burning up your TBO and time between maintenance. It just seems stupid to me even putting aside the the possible polished bores issue. If I were doing this I would sure think about using batteries for the quiet hours of the night. Lithium with its high efficiency and very large cycle life would really shine in this application.

[rslifkin]

To me, given enough battery capacity and lots of solar / wind gen capacity, it would make sense to fire up the generator in the evening, crank up the A/Cs to cool the boat down, let the water heater re-heat, etc. Then shut the generator down and only run A/C for the cabin you're sleeping in over night.

The biggest thing stopping me from doing something like this on my boat is that batteries are heavy. The 10k BTU A/C in my aft cabin uses a max of 770 watts on cool, so figure 850 for worst case including the pump. Assuming a 40% duty cycle at night we're looking at about 280 amp-hours out of my 12v house bank in 10 hours. Add some inverter losses and we'll call it 300 amp-hours.

My 400ah house bank is definitely not big enough to support that. I'd have to at least double it to be comfortable with that situation, ideally a bit more than double, which means a good bit more weight added to a planing hull (so more fuel burn and less speed when moving).

Ignoring the battery weight issue, I can fit at least 800 watts of solar pretty easily. If I can squeeze 900 watts in there, that's enough to replenish 350+ amp-hours in a day. So provided I also get some charging from a once or twice a day generator run for heating water and using the electric stove, then keeping up with that power draw is definitely possible. But it's certainly pushing the limits of what's practical.

[wingssail]

Originally Posted by rslifkin

To me, given enough battery capacity and lots of solar / wind gen capacity, it would make sense to fire up the generator in the evening, crank up the A/Cs to cool the boat down, let the water heater re-heat, etc. Then shut the generator down and only run A/C for the cabin you're sleeping in over night.

The biggest thing stopping me from doing something like this on my boat is that batteries are heavy. The 10k BTU A/C in my aft cabin uses a max of 770 watts on cool, so figure 850 for worst case including the pump. Assuming a 40% duty cycle at night we're looking at about 280 amp-hours out of my 12v house bank in 10 hours. Add some inverter losses and we'll call it 300 amp-hours.

My 400ah house bank is definitely not big enough to support that. I'd have to at least double it to be comfortable with that situation, ideally a bit more than double, which means a good bit more weight added to a planing hull (so more fuel burn and less speed when moving).

Ignoring the battery weight issue, I can fit at least 800 watts of solar pretty easily. If I can squeeze 900 watts in there, that's enough to replenish 350+ amp-hours in a day. So provided I also get some charging from a once or twice a day generator run for heating water and using the electric stove, then keeping up with that power draw is definitely possible. But it's certainly pushing the limits of what's practical.

I think you'd need Lithium because that's a lot of heavy cycling for Lead Acid.

For me it's a non-starter. I don't want the expense (AND WEIGHT) of a genset, plus the room it takes, and the maintenance. I don't want the expense and complexity of Lithium batteries. I don't need Air Cond very often, never at anchor.

So I keep my boat absolutely simple. No genset, I charge off of solar and main engine. A drop dead simple L.A. battery bank, and a window air con which I put in the companionway when we are at the dock and it's hot.

This works fine for us, we're cool enough (lots of fans) and the boat is simple and light and fast and maint issues are minimal.

[witzgall]

Chris from Balmar here. We just introduced our 96 series alternators. There are two units, 60a and 100a @48v. The RV industry has several examples using 48v systems to power AC in class B units. Consider a lithium bank that can accept that sort of current and an appropriate inverter, and you have the start of a workable system.

Chris

[Dockhead]

Originally Posted by witzgall

Chris from Balmar here. We just introduced our 96 series alternators. There are two units, 60a and 100a @48v. . . .

That sounds great, but either of those would greatly exceed the maximum permitted power take off from the front of my 100hp Yanmar. So I'm not quite sure how any of us would drive one of those.

[a64pilot]

It may seem to be picking but bore polishing is a mechanical process where the cross hatching is worn away.
This differs from glazing in that glazing is a layer of varnish like material is deposited on the bores clogging the cross hatching, bore glazing can often be recovered from with a good detergent additive and hard running, but polishing has to be honed or often overbored, which is of course pretty much an overhaul.

But what JClark does in his sailboat is extremely common for powerboaters, that is the generator is started before shorepower cord is disconnected and not shut down until the shorepower cord is plugged back in.
It how we ran our Sportfishermen, the fuel usage of a smallish generator compared to a couple of large turbocharged V8’s is insignificant. Most powerboats then and I assume still don’t have battery banks for a house bank, or if they do they are small banks.
A good generator can’t be heard over the AC fans in a boat either.

But it boils down to how often do you need AC at night? If it’s that hot at night, how about in the day when the sun’s up?