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passive solar ventilation
Dan Best wrote:
Swamp coolers work well in a low humidity environment and while very energy efficient when compared to "heat pump" refridgeration, consume a fair amount of fresh water. I've never heard of one that used salt water. Upon thinking about it, corrosion might become an issue, but as long as you let most of the water drain off so the water never gets too briney, it seems like it should work. Hank wrote: Do a search for "swamp cooler" - they're the evap coolers used in AZ, NZ etc before we all got rich and burn up electricity. They might work well in the Sea of Cortez in MX because of the very low humidity - but I wouldn't want a boat in FL to be any wetter inside than it normally is. Buy a solar panel and a fan. On 6 Jul 2004 08:44:14 -0700, (Parallax) wrote: 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? Plumb an old car heater radiator or alternating direction layered plastic signboard material, to circulate sea water and air through it, using a small pump of some sort, or locate the radiator underwater and plumb the airlines to it. (air is easier to move, especially with a convective chimney) route your ventilation air through the radiator. The air should be cooled somewhat and it should lose a lot of water if it is really humid. That water would be fresh, and possibly useable r. Mixing the cooled air with outside air should give you a net reduction in temperature and humidity. Every little bit helps when it's desperate hot and muggy. Deeper water is cooler than surface water. Perhaps a few feet of plastic 3" pipe could push an air box down to deeper, cooler water? Two such pipes could conduct air through the radiator. You might even construct a device to be left behind, sitting like a deadhead at a mooring with flex hoses to attach your boat when moored? A bilge pump of sorts would be necessary to keep the radiator from filling up with distilled water. Perhaps a soda straw extended to the bottom of the air box would keep you hydrated as you work? Evaporative coolers clog with salt if the water used is not fresh. Possible alternative forms of evaporator use a fabric only damp with water laid against the side of the air handler box. The cloth is removed, rinsed, and re-wet, possibly on a conveyor system. Large amounts of water defeat the evaporative cooling process by cooling the water on the evaporator with only a very little cooling of the air traveling through it. The plastic signboard material available is like a flat layer of square soda straws, is polyester or polyethylene, and is used as a heat exchanger in home heat exchanger ventilators because it conducts heat very well. I got a bunch of castoff campaign posters after the last election, for experimentation. With November approaching, you may get a windfall of signs to pick for cheap, the day after the election. You might ask permission to assist cleaning up signs after the big day. They likely won't mind if a few go missing after action. The nicest signs are on this material, and tell a tale of who has the most money to blow on advertising. Layered in alternate directions, it makes an excellent heat exchanger for air, and should handle low pressure water OK. 5200 sticks to it quite well, especially under a little compression in final assembly from clamps, etc. Plastic sewer pipe could be used for air box ends, etc. Heck, painted aluminum and flipped up out of the water, it might make a cool radar reflector if you take it with you sailing. Flexible air lines might enable towing a flat air cooler through the water. With your smokestack ventilator providing air evacuation from the cabin, you will need to ensure the cabin is almost airtight to ensure control over air inflow. A stork nesting at the top could asphyxiate occupants. Other air routing arrangements seem possible. Submerged heat exchangers would need some regular cleaning, so you would want to be able to disassemble or otherwise access the layered signboards, fortunately, you only need to scrape the flat outside surfaces, and sea growth shouldn't stick to it real well. Instead of alternating direction, perhaps simple spacers between the air carrying layers would enable easy cleaning without total disassembly. An appropriately sized scraper might make rodding out the water spaces a snap. The heat exchanger material might be cheap enough to enable simple swaps of the fouled elements. It should work with minimum external energy input. Let us know how you make out. If you get rich off of this, you owe me a fair royalty. Good luck! Terry K |
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