Help on Removing hot air from houseboat to enhance natural cool air flow with solar 12V fans

  • #1
Ideas on moving hot air from houseboat to enhance natural flow with additional solar 12v fans. 50 foot pontoon houseboat mobile home style cabin in desert southwest. Boat has windows but takes hours to cool down in evening when outside temp is cooler. working to isolate why cabin stores so much heat even with windows open and outside breeze and want to learn more on positive negative airflow, hot cold transfer. Working to not cut additional holes in roof if possible.

Ideas are:
  • Push air our with 12v fans place high on side walls.
  • Pull air in from under boat in shady dry area between pontoons.
  • add small 12v powered swam cooler
  • more venting
Any thoughts appreciated.
 

Answers and Replies

  • #2
berkeman
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Welcome to PhysicsForums. :smile:

What is the water temperature typically? What are the typical daytime/nighttime air temperatures? How much battery power do you typically have available, and do you recharge each day with solar panels?

EDIT/ADD -- Paging @anorlunda @sophiecentaur :smile:
 
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  • #3
Lnewqban
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Welcome, Specialblend21! :cool:

Shield from solar radiation and walls and roof insulation are your friends.
Even if you can effectively ventilate indoors, there is certain thermal inertia of all the furniture and walls and roof, which delay to cool off after the Sun is down, continuing radiating heat towards indoors air.
 
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  • #4
anorlunda
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When I lived on a sailboat, inside temperatures were moderate because
  1. Water temperature was much lower than outside air temperature.
  2. Much of the hull was below the water line.
I think @berkeman was trying to steer you in that direction also. The water might be your best source of cooling. What are the answers to @berkeman 's questions?

Are you able to measure the water temperature at different depths? It might be a lot cooler 10 m down.

I used solar powered ventilation fans on my boat. They had their own solar panel and charged a battery to keep them spinning at night. Their RPM was very low to keep power consumption low.
 
  • #5
Welcome to PhysicsForums. :smile:

What is the water temperature typically? What are the typical daytime/nighttime air temperatures? How much battery power do you typically have available, and do you recharge each day with solar panels?

EDIT/ADD -- Paging @anorlunda @sophiecentaur :smile:
Great questions, Daytime temps can be as high as 104 deg. F day and low of 80 deg. F at night on hot months. (averages pasted)
June
90
62
70
July
97
71
76
August
94
69
80
September
88
60
76

Presently using a small solar system of 2 12v batteries charged by 3 30w solar panels (basically to keep batteries charged and run water pump & lights. Working on design of full solar system for boat to run fans and 12 v refrigerator.

Working to not use gas installed powered generator and 120 v air conditioners that are noisy. goal is use the 12x low power draw fans that run on thermostats.

Having some fun learning more on air flow and much appreciate your feedback.
 
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  • #6
Welcome, Specialblend21! :cool:

Shield from solar radiation and walls and roof insulation are your friends.
Even if you can effectively ventilate indoors, there is certain thermal inertia of all the furniture and walls and roof, which delay to cool off after the Sun is down, continuing radiating heat towards indoors air.
Hi Lnewqban,
Great info, I agree on the thermal heat storage, I am working on venting for the cabinet areas ( bread gets hot in there) Boat has 2 doors, 3 full size windows, 1 roof vent and 7 small windows, thinking you are on the right track of thermal inertia delaying cooldown as boat cabin stays fairly cool until mid afternoon, the really heats up......
Thanks!
 
  • #7
When I lived on a sailboat, inside temperatures were moderate because
  1. Water temperature was much lower than outside air temperature.
  2. Much of the hull was below the water line.
I think @berkeman was trying to steer you in that direction also. The water might be your best source of cooling. What are the answers to @berkeman 's questions?

Are you able to measure the water temperature at different depths? It might be a lot cooler 10 m down.

I used solar powered ventilation fans on my boat. They had their own solar panel and charged a battery to keep them spinning at night. Their RPM was very low to keep power consumption low.
Hello Anorlunda,
Great responses on the forum Thanks! , this helps a lot to design a good system. I do have ability to pull cool water and will check when back at boat. Average temps are: Temp High - Temp Low - Surface water temp
June
90
62
70
July
97
71
76
August
94
69
80
September
88
60
76
 
  • #8
anorlunda
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If you could get colder water from down deep, hopefully 50F or 60F. Then the best way to cool your boat is to pump up that cold water into a lawn sprinkler on the roof. Allow the cool water to run down over the roof and the outside walls 24 hours per day.

I'm unsure how much pump power you need for that. But I would not be surprised if you need to upgrade your solar PV to 400 watts. Maybe 600 watts. And to have two 6V golf cart batteries, wired in series to make 12V to run the pump when the sun is down.
 
  • #9
DaveC426913
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Your boat might be a bit big for this but: I soak a large blanket and throw it over the cabin.
As the water evaporates it cools the hull.
 
  • #10
Lnewqban
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Hi Lnewqban,
Great info, I agree on the thermal heat storage, I am working on venting for the cabinet areas ( bread gets hot in there) Boat has 2 doors, 3 full size windows, 1 roof vent and 7 small windows, thinking you are on the right track of thermal inertia delaying cooldown as boat cabin stays fairly cool until mid afternoon, the really heats up......
Thanks!
I am trying to say that internal ventilation alone is not very effective about removing solar load that was absorbed by internal massive objects between 11:00 am and 2:00 pm, when the UV intensity reaches its peak.

You have the additional problem of Sun light reflected by the water and hitting the sides of the boat and penetrating through the open windows and doors, early in the mornings and late in the afternoon.

Reducing that penetration of the boat envelope by radiating energy is key in improving night conditions for indoors.
Covering as much area of the roof with solar panels (electric or hot water) as possible could create a powerful shield effect.

Simple shields for roof and windows (including vegetation if possible), and R-30 roof and wall insulation, and white paint could make a huge difference.

Please, see:
https://www.nrel.gov/docs/legosti/old/17142.pdf

https://www.cce.ufl.edu/projects/past-projects/green-building/799-2/

https://www.myfloridahomeenergy.com...-energy-basics/#sthash.0tzrsno2.6hIFnVSy.dpbs

Perhaps you could modify the orientation of the boat in such a way that the bigger windows and wall surfaces do not face South.
Awnings or extended roof over-hangs are very effective regarding reducing the amount of solar radiation reaching the interior of the house (radiation that will become accumulted energy that will bounce back to you at night).
 
  • #11
Tom.G
Science Advisor
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A few more ideas, just not as effective or elegant as the earlier responses.

If you can't, or don't want to, shade the windows, try applying some Solar Film to the windows. It's available in various densities at the larger (big box) hardware stores and is fairly easy to apply, by the 2nd or 3rd window.

To speed cooling, use some intake fans blowing on the furniture. The increased cool air speed helps the heat transfer. And that higher air speed also cools you more.

Cheers,
Tom
 
  • #12
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If you could get colder water from down deep, hopefully 50F or 60F. Then the best way to cool your boat is to pump up that cold water into a lawn sprinkler on the roof.
If that's not practical by some reasons (for example, the water available is not clean enough) then you still can make a simple AC based on that water with a car radiator, a pump and a fan.
 
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  • #13
anorlunda
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Perhaps you could modify the orientation of the boat in such a way that the bigger windows and wall surfaces do not face South.
Awnings or extended roof over-hangs are very effective regarding reducing the amount of solar radiation reaching the interior of the house (radiation that will become accumulted energy that will bounce back to you at night).
There may be obstacles on a boat that are different than a house.
  • The boat may be riding at anchor, which means that it rotates to face the wind (or current if any).
  • External awnings and thunderstorms don't mix well. High winds might blow the awning away, or threaten the security of the boat. External objects on a boat must be very securely fastened.
  • When the boat is under way, all those awnings must come down and be securely stowed.
The OP didn't tell us much about his houseboat, but the photo shows the kinds typical on Lake Powell.
1621165758207.png


Fishermen report that the thermocline in Lake Powell is at about 20 feet. Below the thermocline, you can find cooler water. The water is fairly clear. The next photo shows a striper at 25 feet.
1621166334585.png
 
  • #14
Astronuc
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Great questions, Daytime temps can be as high as 104 deg. F day and low of 80 deg. F at night on hot months. (averages pasted)
I used to do iron work on the Gulf Coast during the summer where daytime temperatures were 90 - 100°F, but the iron was about 30°F hotter. One would probably need some additional shade on the outside surfaces adjacent to the inside volume that is too warm.
 
  • #15
anorlunda
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The best way to arrange for more shade on a boat is to move the boat, not to hang out awnings.

1621338814534.png
 
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  • #16
rc1
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With some boats fitting solar powered electric motors with large solar roofs they might absorb a lot of ir energy. If these roofs can be thermally isolated it could be better.
 
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  • #17
rc1
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You can get thermal camera's that can tell you where the heat is coming from but they're a little pricey. Maybe someone provides a service but that's probably also pricey. You could use a non-contact thermometer, much cheaper, to map out the temperature distributions at different times and places during the day, and identify sources and sinks.
 
  • #18
DaveC426913
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You can get thermal camera's that can tell you where the heat is coming from...
I don't think there's much of a mystery about where the heat is coming from..


1621791976577.png


Not being facetious. It's direct heating of the hull and conduction of heat to the interior. (The only convective transfer of heat is helping to cool the interior.) Even if you were to find hot spots with a thermal camera, its not like you can just stuff them with insulation. The whole boat is being heated, like in an oven - there is nowhere for heat to go.
 
  • #19
DaveC426913
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Shield from solar radiation and walls and roof insulation are your friends.
Even if you can effectively ventilate indoors, there is certain thermal inertia of all the furniture and walls and roof, which delay to cool off after the Sun is down, continuing radiating heat towards indoors air.
This.
It is way more effective to prevent heating in the first place than to try to cool it later.
Anything you can do to keep it from getting hot in the first place will be paid back with interest.

Although how you do that effectively will be a challenge.

(Have you considered merely sidling up to an even bigger houseboat? I live in the coolest bungalow on my street, thanks to the three story apartment to my immediate south.)
 
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  • #20
rc1
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I don't think there's much of a mystery about where the heat is coming from..


View attachment 283419

Not being facetious. It's direct heating of the hull and conduction of heat to the interior. (The only convective transfer of heat is helping to cool the interior.) Even if you were to find hot spots with a thermal camera, its not like you can just stuff them with insulation. The whole boat is being heated, like in an oven - there is nowhere for heat to go.

The active vs passive heating/cooling argument- both are useful depending on the circumstances, often active techniques are more effective at the cost of some maintenance and complexity and money. Yes I agree that knowing where the heating is coming from may not help you fix it, it might be easier to buy a different boat. But it may help the OP's piece of mind at least knowing the cause. We don't know everything about the OP's circumstances- as others have said- the color of the hull, walls, roof could be a factor- houseboats are made from a range of materials I expect; from wood, to fibre-glass, to steel- thermally isolating these; if possible could affect inside temperatures; the fact that it's hot inside the cupboard is suspicious, the cupboard could be getting high solar radiation perhaps through a window. When dealing with heat I often find myself going back to- convection, conduction, radiation- the 'vacuum bottle' approach- which is what you appear to have done.

I've known some people to put mylar emergency blankets over the windows in the summer cost $5. Some buildings bolt steel standout grills over the windows or walls to reflect/ stop solar radiation- most boats are painted white to reflect the radiation.

I agree with you that the internal heat is probably being caused by radiant heat.

Anyway the OP is probably long gone at this point.
 
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  • #21
sophiecentaur
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I just joined the thread and we've all been there in one form or another. I totally agree that insulation is the best way to stop the heat getting in for a start. I notice, on PF that many in hot climates seem to concentrate their efforts on Air Con but neglect the advantages of passive methods that people in extreme cold climates always go for first.

I once had a camper van with a huge elevating roof and the large overhead space below the roof was full of fabric and mattresses. The insulation it provided was fantastic in the hot Sun in the south of France. No air con was needed in the day. Head room is often a problem in boats but a layer of a few cm of internal roof and side insulation would be cheap.

A shiny awning could be one approach but not a good aesthetic long term solution. Also, shiny or white uppers can soon get to look scruffy. Super Glass works very well in large window areas.

12V, directly solar driven would turn fans during the hot daytime and not touch your battery charge.

A tall (removable) vertical flu from ceiling level could increase the flow of hot air by natural convection. If there's any breeze then a cowl - style roof vent on top Steerable to point to leward can encourage air movement without letting rain in.
The best way to arrange for more shade on a boat is to move the boat, not to hang out awnings.
Problem is that moorings aren't always available with just the right orientation (tidal swinging moorings would be the worst but that's unlikely for a live aboard).

Good luck with this project, btw.
 
  • #22
anorlunda
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See #8 and #13.

In the USA West, most houseboats are under way or at anchor when occupied. Not at a dock or a mooring. You have many choices where to anchor. But 7 meters down is a sink of cool water.
 
  • #23
DaveC426913
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See #8 and #13.

In the USA West, most houseboats are ... at anchor when occupied. ... You have many choices where to anchor.
Good for getting cold water, but not good for shielding if you're swinging on a (single) anchor. (I suppose houseboat owner would prefer bow and stern anchoring though.)
 
  • #24
anorlunda
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Good for getting cold water, but not good for shielding if you're swinging on a (single) anchor. (I suppose houseboat owner would prefer bow and stern anchoring though.)
Look at that picture in #15. Doesn't matter much which direction you swing. But my main point was getting cold water to spray over the decks and the hull. It would be hard to do better than that for cooling. I don't think shade or sun would matter much if you spray the cold water.
 
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  • #25
DaveC426913
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Look at that picture in #15. Doesn't matter much which direction you swing.
I thought we had ruled that out as a serious option.

(Also, since that appears to be a flowing river, anchor swing be reduced to a few degrees of "hunting".)


It would be hard to do better than that for cooling. I don't think shade or sun would matter much if you spray the cold water.
I dunno about that. Cooling something that's constantly being heated may still not be as efficient as not letting it get heated in the first place. But YMMV.
 
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