Swamp Cooler, Hydroponic, Rooftop Greenhouse

This instructable will teach you how to turn your swamp cooler into a rooftop garden during the off season (winter)!

For those not in the know, a swamp cooler (also known as an evaporative cooler) is a popular way of cooling homes in hot, dry climates like Tucson, Arizona. It is a very simple machine, just a box with a fan in it and wet pads as walls. The fan pulls dry air through the wet pads, thus evaporating water, and pushes the now moist air into the home. The simple act of evaporation causes the pads to get very cool, and thus will cool the air as it flows past. The humidification of air is a side effect, but is usually welcomed when it is very dry outside. This is the same basic principle of how sweat works. However, swamp coolers can only drop the temperature of air by a limited amount, and will only work when it is dry, which is why you only see them in certain regions and even then, many people prefer AC units (or both). But enough about swamp coolers, lets turn ours into something else!

The thought process here is that a swamp cooler is not needed in cooler months, when a greenhouse would be useful, and it already has the resources needed. It is an enclosed space with water and electricity, and is usually located on the roof of a building where it will get a lot of sun. The orientation of the swamp cooler does matter. The side with the duct should face north, but may also work if it face east or west. If it faces south it will block to much sun to make this useful. The roof of a swamp cooler is solid, but with the low winter sun it wasn't much of a problem.

You will need:

• a swamp cooler
• some vinyl tubing to reroute the water from the spider to the plants
• a rack of some sort to hold the plant above the water basin. I used a large wire mesh and PVC pipe.
• wood, screws and clear plastic (I used shower curtains) to make the clear panels that will replace the pads on three sides of the cooler
• hydroponic supplies (net pots, substrate and nutrients)
• various hand tools (wrench and screwdriver to prepare the cooler, drill to build the panels)

• optional: lights, fan, heater, and if you want to get technical, a control system and a datalogger.

First, we need to take off all of the panels and then take out the junk that is inside the cooler. We will leave the pump, but the motor and squirl cage fan have to go. Just look around for all of the screws and remove them, then pull it all out. This is most likely a two person job, as the fan is awkward and heavy. After removal, I just left this stuff on the roof covered by a tarp for the remainder of the winter.

I replaced the three padded walls with double walled windows that I built out of wood and clear shower curtain liners. The frames were very simple, 4 peices of 2x4 cut to the dimentions of the swamp cooler wall and screwed together. I then used glue to adhere the shower curtains to both sides. I used a single sheet wrapped around the entire frame. Doing a double wall in this way provides better insulation and will help the greenhouse stay a bit warmer at night.

Mounting these doors is a bit more complicated. I just used screws that went through some holes that were already drilled into the swamp cooler. If your swamp doesnt have pre-existing holes, you may have to get creative here. I had two of the three sides on hinges do swing open like a door, but you really only need one. To hold them tightly just, i used a bungee cord that acted like a latch. I also applied a weather strip around the frame where it met the cooler to provie a better seal.

The next step is to build a frame that will hold the plant pots above the water basin. I used PVC piping to make a frame that spans the entire floor plan, about 6 inches high, and then laid a large-opening wire mesh over the top. This mesh provided the right size holed for the pots to sit in. There are many other ways this could be accomplished with different material, like a peice of plywood with cutouts or tightly strung bailing wire.

The swamp cooler uses a pump to push water up from the basin, through a "spider" distrubuter, and into the three pads. This actually makes for a nice hydroponic distribution network. Simply attach some vinyl tubing to the end of the spider legs and route the water to where each pot will go.

We took this project to another level by incorporating lights, a fan, a water heater and an arduino powered datalogger/control system. The lights would come on for a few hours after sundown to supplement the short days, and were just on a simple timer. The fan was there to circulate air, as plants growing without airflow are very stringy. The water heater was made from an old coffee maker heating element. When it got too cold, the system would pump water through the coffee machine heating element and back into the water basin to raise it a few degrees in the middle of the night, which would raise the internal air temperature a bit. The arduino measured and logged the humidity, the internal air temperature, the water temp and the outside air temp. I used the logged data to adjust the heater control algorithm to try to maintain an appropriate temperature throughout the night. Plants respond to temperature averages, so as long as they are warm during the day they are ok to be cold at night, but only to a point. The goal here was mostly just to keep them from freezing.

Plant your plants in the pots and place them in the greenhouse. The space is limited, so you should choose smaller plants to grow. Space them out as evenly as possible. Route the water lines to each of the plants. I used some soda cans with multiple holes to spread the water out more within each of the pots. Add the nutrients directly to the water basin to be circulated through the plant roots. When I remembered to, I would usually climb on the roof and leave the greenhouse open during the day so it could get fresh air and more airflow. This also helped reduce the humidity, which was a bit on the high side due to the large open water basin at the bottom of the chamber. Too much humidity allows mold to grow on the plants.

I found that the duct in the back of the cooler acted as a nice shelf for the controls and hydroponic supplies, and any other tools frequently needed. We put some extra plastic up over the opening with magnets to keep the humidity away from the controls.

My plants were happy! And our house stood out, having a garden glowing in our swamp cooler at night. And when all was said and done, the swamp cooler didnt suffer any negative side affects from this.

One improvement I wanted to make but didn't was to position a fan to pull warm air from the house, through the ducts, into the swamp cooler at night. This would have been a more effective way to heat the greenhouse and would reduce the humidity at night, which could get really high with the doors closed. I also would have used black tubing for the water routing step, or some other opaque color, because the clear tubing grew algae inside.

Happy making!