BoatBanter.com - passive solar ventilation

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passive solar ventilation

Spent a day working on my boat at the dock her in NW Florida and
nearly died of heat stroke while being down in the cabin even with all
hatches and vents open. I dont have too many fans because I have no
connection for shore power. There was an obvious temp differential
'tween outside and inside that got me thinking.

So..... Make a long fabric tube, say 10" diameter and 15' long with
upper end held up with the jib halyard and lower end in the forward
hatch with edges around it sealed. Upper half of the tube is black
and lower half is white. Here is what happens:

With a temp differential (hot inside, cooler outsside), you get a
chimney effect with hot air rising out of the tube and pulling cooler
air in from other ports. I can imagine getting a susbtantial flow
this way.

With little or no temp differential, sun still heats the black upper
half and heats air inside causing it to rise causing air to be pulled
through the tube giving air flow in the cabin. Steps could be taken
to maximize solar heating of teh upper part of the air column such as
better conducting baffles, passive solar fabric panels connected to
the upper tube etc. I could even imagine a fabric reflector shining
light onto the upper tube to maximize the effect.

All of this works compared to not working in a house because the
volume of the boat is fairly small compared to the volume of a house.

Let's go further. Now that we can produce air flow, can we use such
to actually produce cooling? Evaporation of water can produce a huge
amount of cooling. Close all vents to the outside except for a 10" or
so port and fill it with wetted baffles. Baffles can be wetted by
osmosis from a reservoir. Evaporation will cool the air stream.
Unfortunately, this will increase the humidity in the boat and reduce
the air flow (conservation of energy).

Any thoughts?

passive solar ventilation

Your idea holds merit - just not to include more moisture, as another poster
has observed.

I used to go camping on an island off the coast of Portland (well,
technically, Small Point, near Bath), Maine, with very fancy outhouses.
They were called solar holers, and didn't smell.

The way that was achieved was by having a "chimney" facing south, clear top
(outside) and black face (inside), with the intake at the business end of
the large (men's and women's, set up like rest rooms) houses. Never a
smell.

They also heated the water for the shower houses in the same fashion but
with rooftop snakes (back and forth over the entirety of the south-facing
rooftop of black pipe on black backgrounds). Almost never ran out of hot
water, despite however many showered.

Since this was in Maine, and the camping season was Memorial Day through
Labor Day, there were *long* hours of sunshine fueling all this free energy
accumulation!

L8R

Skip, original left below for reference...

--
Morgan 461 #2
SV Flying Pig
http://tinyurl.com/384p2

"And then again, when you sit at the helm of your little ship on a
clear night, and gaze at the countless stars overhead, and realize
that you are quite alone on a great, wide sea, it is apt to occur to
you that in the general scheme of things you are merely an
insignificant speck on the surface of the ocean; and are not nearly
so important or as self-sufficient as you thought you were. Which is
an exceedingly wholesome thought, and one that may effect a
permanent change in your deportment that will be greatly appreciated
by your friends." - James S. Pitkin

"Parallax" wrote in message
om...
Spent a day working on my boat at the dock her in NW Florida and
nearly died of heat stroke while being down in the cabin even with all
hatches and vents open. I dont have too many fans because I have no
connection for shore power. There was an obvious temp differential
'tween outside and inside that got me thinking.

So..... Make a long fabric tube, say 10" diameter and 15' long with
upper end held up with the jib halyard and lower end in the forward
hatch with edges around it sealed. Upper half of the tube is black
and lower half is white. Here is what happens:

With a temp differential (hot inside, cooler outsside), you get a
chimney effect with hot air rising out of the tube and pulling cooler
air in from other ports. I can imagine getting a susbtantial flow
this way.

With little or no temp differential, sun still heats the black upper
half and heats air inside causing it to rise causing air to be pulled
through the tube giving air flow in the cabin. Steps could be taken
to maximize solar heating of teh upper part of the air column such as
better conducting baffles, passive solar fabric panels connected to
the upper tube etc. I could even imagine a fabric reflector shining
light onto the upper tube to maximize the effect.

All of this works compared to not working in a house because the
volume of the boat is fairly small compared to the volume of a house.

Let's go further. Now that we can produce air flow, can we use such
to actually produce cooling? Evaporation of water can produce a huge
amount of cooling. Close all vents to the outside except for a 10" or
so port and fill it with wetted baffles. Baffles can be wetted by
osmosis from a reservoir. Evaporation will cool the air stream.
Unfortunately, this will increase the humidity in the boat and reduce
the air flow (conservation of energy).

Any thoughts?

passive solar ventilation

Couple:
Why paint only the top half black? surely you'd want as much heat in there
as possible.

Most fabric doesn't conduct heat very well.

If you have an alloy mast you have a chimny already, thermal coefficient is
good (probably don't have to paint it), large surface area , height is also
a positive factor (velocity). Only mod's req'd are to connect the bottom to
the cabin airspace and the top to "outside" without letting rain in.

Could go further if you don't mind a little extra windage up the fit a
weathercocking venturi at the masthead, any lurking breeze will add to the
effect, although it's probably something you'd only consider if performance
at anchor is more of a concern than racing.....

Mark.

"Parallax" wrote in message
om...

So..... Make a long fabric tube, say 10" diameter and 15' long with
upper end held up with the jib halyard and lower end in the forward
hatch with edges around it sealed. Upper half of the tube is black
and lower half is white.

Any thoughts?

passive solar ventilation

"Mark W" wrote in message ...

Mark:

I actually thought about using the mast as the chimney except my boat
has a deck stepped mast so this would be difficult. It might work
well on those Freedom boats with large diameter masts.

Couple:
Why paint only the top half black? surely you'd want as much heat in there
as possible.

Most fabric doesn't conduct heat very well.

If you have an alloy mast you have a chimny already, thermal coefficient is
good (probably don't have to paint it), large surface area , height is also
a positive factor (velocity). Only mod's req'd are to connect the bottom to
the cabin airspace and the top to "outside" without letting rain in.

Could go further if you don't mind a little extra windage up the fit a
weathercocking venturi at the masthead, any lurking breeze will add to the
effect, although it's probably something you'd only consider if performance
at anchor is more of a concern than racing.....

Mark.

"Parallax" wrote in message
om...

So..... Make a long fabric tube, say 10" diameter and 15' long with
upper end held up with the jib halyard and lower end in the forward
hatch with edges around it sealed. Upper half of the tube is black
and lower half is white.

Any thoughts?

passive solar ventilation

So build a hollow tabernacle which projects back (or fwd) far enough to
allow a dorade type baffle and a vent down into the cabin. Keep the mast
heel support low enough (not too much less than cross section area of mast
(about 30mm for a 125mm dia. spar) and you probably don't even have to trim
the mast.

I'm trying to figure out how to do it for bilge ventilation on my keel
stepped schooner but with internal halliards I'd get way too much wet down
there. Also the main is in the engineroom which is supposed to be able to be
made airtight if combustion becomes "external".

Luck,
Mark.

PS: don't have much simpathy anyway, it's bloody freezing here at the moment
:o)

"Parallax" wrote in message
m...

Mark:

I actually thought about using the mast as the chimney except my boat
has a deck stepped mast so this would be difficult. It might work
well on those Freedom boats with large diameter masts.

passive solar ventilation

"Mark W" wrote in message ...
So build a hollow tabernacle which projects back (or fwd) far enough to
allow a dorade type baffle and a vent down into the cabin. Keep the mast
heel support low enough (not too much less than cross section area of mast
(about 30mm for a 125mm dia. spar) and you probably don't even have to trim
the mast.

I'm trying to figure out how to do it for bilge ventilation on my keel
stepped schooner but with internal halliards I'd get way too much wet down
there. Also the main is in the engineroom which is supposed to be able to be
made airtight if combustion becomes "external".

Luck,
Mark.

PS: don't have much simpathy anyway, it's bloody freezing here at the moment
:o)

Mark, being in NZ, even in summer, you are surrounded by a big heat
sink called the pacific Ocean. In summer, we have a huge heat source
called the Gulf of Mexico very close by. Last week, the water temp
was 91 F (about 32C) and the air temp was 38 C with not even a breath
of wind and 95% humidity.
"Parallax" wrote in message
m...

Mark:

I actually thought about using the mast as the chimney except my boat
has a deck stepped mast so this would be difficult. It might work
well on those Freedom boats with large diameter masts.

passive solar ventilation

Now you're just being mean.
Actually it's worse, normal weather comes from ESE but every couple of weeks
through winter we get a southerly direct from Antarctica. Still rather live
where it actually changes...

Mark.

"Parallax" wrote in message
om...

Mark, being in NZ, even in summer, you are surrounded by a big heat
sink called the pacific Ocean. In summer, we have a huge heat source
called the Gulf of Mexico very close by. Last week, the water temp
was 91 F (about 32C) and the air temp was 38 C with not even a breath
of wind and 95% humidity.

passive solar ventilation

"Mark W" wrote in message ...
Now you're just being mean.
Actually it's worse, normal weather comes from ESE but every couple of weeks
through winter we get a southerly direct from Antarctica. Still rather live
where it actually changes...

Mark.

"Parallax" wrote in message
om...

Mark, being in NZ, even in summer, you are surrounded by a big heat
sink called the pacific Ocean. In summer, we have a huge heat source
called the Gulf of Mexico very close by. Last week, the water temp
was 91 F (about 32C) and the air temp was 38 C with not even a breath
of wind and 95% humidity.

The heat just makes me cranky.