Alternative to roof vent...

[TimC]

I want to eliminate the typical roof vent/fan unit for two reasons. Forgetting to close it prior to/during a rainstorm and another potential hole for leaks to develop at. On a sailboat I just sold I had a 12v computer case fan attached to a snap disc (thermostat, on @ 90 deg-off @80 deg) which was attached directly to a solar panel (35w) which will also charge my battery. The fans I bought are 120mm, 45cfm, 19 dB-A (quiet), 1.8w, .15a. I want to duct the fans (one on each side) out above the cabin cabinets into the galley cabinets and duct down to through the floor. To provide make-up air I will have to put in a duct or two on the front or side wall(s) so the fans are not just providing negative air pressure in the cabin.

Has anyone done anything like this? Do you see a problem with ducting through any of the cabinets, out the floor, or any other concerns? I know it will keep the camper cool (relatively) and dry as my sailboat cabin was about twice the cubic ft. Air under the trailer will likely be cooler than the air around window screens and door screens. It will probably be more humid, but, the shelter of the ducts through the floor will be a good trade off me thinks!

[daveesl77]

I have done exactly this. I have a set of forward cabinets/shelves. When I did my design I specifically put in room to allow for ducting. So, in the front curved section I built in 2 ducts, an exhaust and an intake. These both exit underneath the trailer behind the first crossmember. I haven't installed the deflector/adapter yet, but the exterior part I'm making out of aluminum sheet. Primary vent faces backward and pulls/exhausts air from under the trailer. However, with the ideas the folks here came up with on adapting a window airconditioner to a diy petcool unit, the aluminum boxes also will have two 4" hose adapters in them. One for AC return air, one for AC supply air. Picked up a used 5000 btu unit for $15 and will build the adapter box for the unit out of aluminum sheet. This lets me mount the AC off the unit or under it. Hoses duct into the ductwork. Ducts have 2 5" fans in each section, exhaust and supply. I've been testing as building and here in Florida it has been steady in the mid 90s for a month now. Without air running and only the fans, the interior of the camper is 8-15 cooler than the outside temp in the shade. I also have foam insulation in walls/floor/roof.

It does work and I'm glad I did it.

Here is what I wrote on the posted photo...

Got the base cabinet/shelving/ductwork done today. Still need to wrap the ends with 1/8 ply, finish the doors. On the top the duct on the left is return and the one on the right is supply. Both exit through the floor, behind a crossmember. Both will end up having 12v fans in them. On the bottom part I'm fabricating a dual purpose vent mount, so I can either use it as straight ventilation or as an AC adapter, each duct is 5" x 8" opening on the bottom and 6x12 at the top. There will be another shelf on the right side, just above the powerstrip. Once the covers are all in you won't see any ductwork, wires, etc.



dave

[TimC]

Dave,

If I lived in Florida, or visited for that matter, I too would seriously look into A/C. I am in N. Wisconsin, a literal stones throw from Michigan's UP and we had frost the last two nights. Warming up a little tonight with a predicted low of 45. So, A/C is not in my plan. We typically have nights below 70 all summer long. We only run home A/C about six or eight days a summer.

I am going to experiment with a solar powered bucket swamp cooler for the chance we head south knowing that when the humidity is up it will not work, but, I can survive a few nights of sweaping (sleeping/sweating). The bucket swamp cooler will use the same power source as the vents and the same fans just adding a small 12v fountain pump. Your design has given me a couple ideas. I wasn't going to install front cabinets. That may change with some duct incorporated in them.

[daveesl77]

You don't have to build large ducts like I did, I just had the room and needed to fill the curved void so it kind of killed two birds with one stone. Hose will work fine, kind of depends on the size fans you have. That said, a 4 sided, foam board duct will be more efficient than a ribbed hose, but a hose allows for easy bends.

Whether you use AC or not doesn't really matter. I live in Florida, so it is kind of required. A swamp cooler is useless in high humidity areas.

dave

[woodywrkng]

I use this setup in Wisconsin and Minnesota every year, and it's worked fine. I too didn't want to put a hole in my roof, so there are 4 fans on each side of the trailer, for 8 total. Two fans in parallel on each side exhaust the bedroom into a box (which normally covers all the fans) under the galley hatch, and two more in series (physically, not electrically) blow the air through the sidewall. The second photo shows the air intake vent low in the front, and the smaller exhaust vent high in the rear. The first photo only shows one fan per side on the sidewall. I later added a second fan, for a total of 4 on each side, back to back with the one shown. They're 120 mm, 12 volt computer fans and are very quiet. I have metal screen under the stainless grilles shown to keep the bugs out, furnace filter material as well on the intakes, and have never had a problem with water getting through the grilles. These types of fans use about .15 amps each, which in my case adds up to 1.2 amps total with all 8 running. A 20 watt solar panel would work well enough in full sun.

[TimC]

Woody... thanks for the photos. That gives me some ideas. I bought a 200mm that moves 130cfm and is very quiet. Anxious to see how I can adapt your design to fit mine.