IF YOU JUST WANT TO BUILD YOURSELF A RELIABLE EFFECTIVE SWAMP-COOLER, SKIP THIS POST AND FOLLOW ONE OF FIGJAM'S DESIGNS.
It contains explanations of details you don't need to understand in order to build his designs.
Wendle wrote:I also found these: which I feel help to hold the cooling pad upright against the bucket and even out the airflow over the pad. The gap between the basket and the bucket is perfect to hold one layer of aspen pad against the bucket, which would probably be about the same as one blue pad, but since it kind of directs the air downward over the pad it is increasing the amount of dwell time on the pad and is probably the same effect as having the air go directly across two pads; the air is quite cold coming out.
Good thinking, but holding the pad against the bucket is not the way to go
As you've described, with the pad held against the bucket and the basket held against the pad:
- the pad intake area is reduced to the area of the holes,
- the pad exhaust area is reduced by the the basket grid (which appears to reduce it to half in the grid area, plus what you lose for any of the solid area),
- the airflow is not evened out as the air will take the path of least resistance, limiting travel sideways through the extra resistance of more filter media to get out through the grid's limited pad exit points,
- the reduced effective pad intake area causes increased air velocity through the filter media, which greatly increases resistance to airflow, lowering the volume of air flowing through the cooler,
- the higher air velocity reduces dwell time,
- when processing hot dry playa air, you may find that the above points combine to deplete water in that greatly reduced air path, creating dry spots that will pass hot dusty air,
- in addition to possible dry spots, the above adds up to a reduced volume of air processed for the size of the bucket cooler. Well below it's potential.
It is very similar to using such a bucket as a water reservoir for a tiny filter pad.
Others have gone this way before, only to discover that once on playa, it does not perform well as the limitations become evident with processing hot dry playa air.
Note that aspen pads swelling with water have caused some people complications with their designs. Including swelling and filling the air gap required to maximize the bucket-cooler's potential, as described below.
Note that things touching the filter pad (like your basket) provide an alternate path for water to take, instead of flowing through the filter media, so you're also limiting the water flowing through
the pad, thereby increasing the chance of getting dry spots and of limiting the evapoarative cooling. (Note that with the uni-cooler and box-cooler, where the vent-screens contact the pads, they direct any water that gets/goes on them back onto the pad.)
FIGJAM's design requires an air gap between the side of the bucket and the pad.
As the fan sucks air out of the center space of the bucket, the negative pressure created in that space will suck air out of the entire inner surface area of the pad that is above water. That in turn will suck air into the filter pad on it's other side, wherever it is above water. Due to the air gap between the bucket and the pad, this means it sucks air through the entire outside area of the pad that's above water. The air in the gap is replenished by sucking air in through the holes in the side of the bucket. (Due to the extra resistance for air flow between the bucket and the pad, there is some bias for flow through the pad closer to the hole, and there's more dust appears on the pad inline with the hole as the dust doesn't change direction as easily as the air spreading out into the air gap.) As the air flow has the largest possible surface area for entering and exiting the pad, it has the lowest possible air velocity, for the longest dwell time possible and the least resistance to air flow (greatest CFM possible), all contributing to ensure that this maximized air flow gets its maximum possible cooling. The bucket cooler uses a lot more of the pad than one would intuitively conclude based on the size and area of the holes.
(if you want to mentally reverse that, you'll see why these swamp-coolers work well when sucking air out of the bucket, but not as good when someone decides to reverse the flow and gets the fan to force air through in the other direction)