Hi All - Doc here (aka Chuck).
I'm the one that worked up that swamp cooler that Whaleboy's been talking about. Thanks Whaleboy for picking up my reply slack while I've been busy in the default world.
Whaleboy pretty much nailed it with his awesome drawing. I uploaded some pics of the design that show most of the steps here: https://plus.google.com/photos/10275104 ... 4763177169
(I'm currently uploading these pics on a slow connection so they may not all be there if you check this right as this is posted.)
The part numbers for the wicking filter and the air filter are as posted by Whaleboy. The wicking filter works great, it absorbs water from the pool at the bottom of the bin and will go from dry to saturated in about 5 minutes. It'll stay totally saturated as the water evaporates. You must filter the incoming air or the filter will become very dirty and the deposits will impede water absorption. During the week on playa, you will notice mineral deposits forming on the filter due to the minerals in the water (and I suspect from minerals in the playa dust that make it past the air filter). The deposits will result in crusty areas that are not saturated but it's not significant during the time period of the burn. They can be removed with a vinegar solution which will dissolve the minerals but I only tested that once and didn't find the need to do it again. If you want to reuse the filters from year to year, you might want to do this.
As you can see from the photos, the wicking filter is simply placed almost vertical in the bin, leaning slightly against the wire that is used to hold it upright. The size of the filter is selected to fit the bin rather well. The top of the filter gets squeezed a little by the lid to the bin and you should check on it now and then to make sure that it hasn't shifted which could allow air around the filter.
I selected the fan based on design compromises between power use, noise and airflow. I don't have the fan model with me but I believe that at the high-end, I used a fan with a huge Cubic Foot per Minute (CFM) that drew .6 amps for my first build but we used a lower flow that only drew around .3-.4 amps for most of our swamp coolers. The more flow, the more better if you have the juice to supply it. Just about any normal sized 12 volt DC computer fan will work. Ones with an adjustable air flow knob are a plus but I believe I just maxed mine out the whole time. You'll see that in the pictures, I screwed the fan on but on playa, for most of our coolers, we simply hot-glued it in place and might have added some duct tape. You must hot glue it well and quickly because of the slipperyness of the bin.
The air filter is selected to fit the bin. We made an inverted v shape by folding it and then duct taped it to the bin lid and cut triangles of plastic for the ends. The bins are kinda slippery and the duct tape didn't adhere very well. That aspect of the design was the weakest link. It was selected for low cost and simplicity but I suspect there are better ways to do it. Make sure it is sealed well to prevent the playa dust. Playa dust is a killer of wicking filters and the reason that people dis this method for the playa. Many have failed because of the failure to add an air filter to the design. The air filters that I selected are a reasonable compromise between low air-flow restriction, fine particle filtration capability and cost. Conventional felted (blue) AC filters will not provide adequate dust filtration.
The bin is a Rubbermaid Roughneck 14 gallon bin. This size is optimal and the bin is high quality and rugged. The filters fit nicely to this size and it holds an adequate supply of water.
On playa, the swamp cooler performed well in the extreme low humidity. I've recorded a 35-40 degree temperature drop. It does humidify the environment inside the tent which isn't ideal but it is very comfortable. For this to work well, you must input the hot, dry air from outside your tent into the cooler. Then port the cool, wet air that leaves the cooler inside the tent. If you put the cooler inside the tent, (thus recycling the air) you'll be comfortable at first and then gradually get warmer and wetter. I've recorded a consumption of approximately 1/2 gallon/hour of water with this design. I would say that it is adequate to cool a large sized tent that is not in the sun. If your tent is in the sun, you will probably need the air flow to be pointed directly at your body to stay cool but even then you will probably not sleep past 9.
Future design tweaks that could be investigated:
- better connection of air filter.
- porting the air flow directly under a very light, thin parachute material sleeping blanket that is weighted at the edges so that it inflates and only cools the burners underneath. This may allow use in a sunny tent.
- I'm currently exploring "indirect evaporative cooling" which would use a heat exchanger to separate the wet air and transfer the cold to a dry stream to keep the tent cool and dry which would be extremely comfortable.
Those tweaks are only for nerdiness though as the thing works pretty well as it is.
I think that covers it - happy to answer questions.