Portable Evaporative Room Cooler

Beat the heat with this awesome DIY mini portable evaporative room cooler!

At the very first sight, this thing looks like a little model of traditional Indian swamp coolers which are/used to be very common in most of the households. Of course these have been replaced by air conditioners in the recent years. However, this idea continues to be one of the most creative.

The principle behind the working is as simple as, 'evaporation causes cooling'. When air passes through a damp pad usually made of 'Khus', it results in a cooling effect. The pads are mounted on a steel/iron box and are exposed. A pump is added to wet these pads and an exhaust is used to suck air through these pads and then blow the cooled air.

"Khus is a native Indian grass which has traditionally been used as a coolant in Indian households. Largely used as evaporative mats and screens, the dry air cools as it passes through layers of wet khus. Cultivated in Madhya Pradesh and Rajasthan, the grass is transported largely across North India during summers. With the air conditioners contributing incessantly to the pollution, one might want to give the traditional khus mats a relook." (source: Link)

(image source: Link)

Now coming to the point, I decided to build a smaller/portable/battery operated version of the same after I saw some vanaspati (ghee) metal containers being thrown away, which could actually be brought to some great use. Not that I would use this thing daily, but this can be helpful for rural areas and hostels/dorms where air conditioners aren't allowed.

The biggest advantage if such coolers is that they do not cause any kind of pollution and this one being operated using a 12V battery, does not consume much power.

However, this cooler would not work in humid/damp conditions because in such cases, air already holds a lot of moisture due to which rate of evaporation is low hence low cooling.

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Though this one still was an interesting and enjoyable build. I hope you like it as well.

The basic parts used here include a 12V motor with blades, a 12V water pump and a PWM powered by LM555 IC circuit to control the speed of the motor. Power supply can either be a 12V battery or an adapter.

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Here's a complete video tutorial of the project:

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Step 1: Parts and Tools

The following parts and tools are required to make this project:

Parts:

• A steel/iron box/enclosure with lid (32.5 cm height, 22 cm length and width)
• Wire mesh (140 cm x 70 cm)
• Dried/dehydrated grass used in evaporative mats (known as 'Khus' in India, see picture above)
• 12V DC motor
• A blade for the motor
• 12V Water pump (I used the submersible one) (there are hundreds of tutorials to make one yourself)
• Rubber tubing
• 25mm diameter PVC pipe
• White M-seal/epoxy compund
• 2.5" x 2.5" plastic box with lid
• Red oxide primer (Anti-rust paint)
• Red and White enamel paints
• Turpentine oil
• Brushes
• Wire

Electronics:

• 1x LM555 IC
• 1x 8 pin IC socket
• 1x 100K ohm potentiometer
• 1x Knob for the potentiometer
• 1x IRF Z44N MOSFET
• 2x On/Off switches
• 2x Red LEDs
• 2x 1K ohm resistors
• 1x 10K ohm resistor
• 2x 0.1uf capacitor
• 1x 0.01uf capacitor
• 2x IN4007 diodes
• 1x Screw terminal
• Perforated board

Tools:

• Multi purpose rotatory tool
• Attachments for drilling/cutting/sanding
• Soldering iron w/ wire
• Hot glue gun
• Super glue
• Wire cutter/stripper
• Pliers
• Scissors
• Sand paper

Total cost of the parts: $10.14 approx. (650 INR)

Step 2: Mark and Cut

Start by marking the enclosure on left, right and back walls, squares of 17x17 cm each such that there is some space for storing water in the lower part of the box.

Mark a circle in the front wall which should be a little bigger than the motor blade you are using.

Use a rotatory tool with the cutter wheel attachment to cut the marked portions. Since it's metal, use proper glasses and gloves for safety.

Use fiberglass wheels instead of resin ones, because they may break easily. You may need to replace them because they will wear away.

Step 3: Sand the Edges and Clean

The edges may be sharp and can hurt you. So, clean them up using sand paper.

At last, carefully wash the enclosure with water and detergent and wipe it immediately so it doesn't form rust. Keep it out in the sun for some time.

Step 4: Apply Red Oxide Primer (Anti-Rust Paint)

We are dealing with evaporative coolers so the box will always be full of moisture. Hence, it can easily form rust which will corrode the metal. This isn't needed if the box is made of aluminium or any other material that doesn't rust.

The primer is initially very thick, so take some in a bowl and add a little amount of turpentine oil. Mix it properly and apply it on the box (both inside and outside) using a brush. Let the first layer dry for at least 10-12 hours. Minimum 2 layers are needed so repeat the process until it looks perfect.

Step 5: Paint the Inner Walls White

After the primer has dried completely, use white enamel paint and a brush to paint the inner walls. You can try any other color as well.

Again it would take at least 2 coats to get a good finish. Use turpentine oil to make the paint thinner. There should be a gap of 12 hours between two coats.

Step 6: Paint the Outer Walls Red

Choice of color is yours.

Use paper tape to make sure the paint does't drip over the white color. Carefully paint the outer walls 2-3 times for a good finish. Let it dry in the sun for a day, with the lid open.

Step 7: Make the Pads

To make the evaporative pads, first cut a piece of wire mesh measuring 40x20 cm using pliers/scissors.

Fold in half along the 40cm length. Now add sufficient amount of dried grass such that it covers the entire portion.

Using pliers, tie the wires together from all the sides to seal it such that the grass doesn't come out.

Repeat the process and make 3 similar pads.

(Refer the above images in order)

Step 8: Place the Pads

Drill 4 holes near each corner of square pieces you had cut from the left, right and back walls. Rotatory tool may not be powerful enough to make sure not to break the drill bit.

Use a hammer and screwdriver to make the task easier.

Now take some insulated metal wire and cut 12 pieces measuring 4 cm each.

Bring one part of the wire through the corner of the evaporative pad and pass it through the drilled hole from inside the box. Now twist both the free ends of the wire such that the pad is tied to the metal box.

Repeat this process for all the four corners of all the 3 pads. In the end, they should be fixed completely to the enclosure and should not move. Add some hot glue to the wires make it sturdy.

(Refer the above images in order)

Step 9: Solder the PWM Circuit and Connect the Switches

PWM (Pulse Width Modulation) circuit is added here to control the speed of the fan, which is an awesome feature but still not mandatory to add.

For this I chose the most commonly used 555 circuit. 555 generates high and low pulses at a very fast rate. The time interval between these pulses can be adjusted with the help of a potentiometer. More time means less speed. The output of this IC is fed to a MOSFET which acts as a switching device (used because 555 can't generate enough output current to drive a motor).

Have a careful look at the circuit and solder everything according to it on a piece of perforated board. I added a screw terminal to connect the power supply wires later. Use an IC socket rather then directly soldering the chip to prevent it from burning.

After you are done with the circuit, solder the potentiometer and the switches (one each for fan and pump). All the wires are soldered to the main circuit board.

I took a 2.5"x2.5" square wooden piece to act as a lid to the plastic box where the circuitry and switches will be placed. So I drilled respective holes for the potentiometer and switches and fixed them later with hot glue.

(Refer the above images in order)

(For a clearer schematic, download the pdf attachment below)

Step 10: Attach the Motor to the Box

First solder two wires to the motor terminals such that when connected in the correct polarity, it turns clockwise. Secure the connections with some hot glue

Now since the motor has to be at a height, I used PVC pipe to keep it in place. Wood cannot be used here because the lower part will be dipped in water.

Cut a piece of pipe with height enough for the motor blade to be exposed from the circular cut made in the box. The lower part of the pipe has to be flat.

Sand and make a U-shape grove on the upper part so that the motor fits in easily. Use plenty of hot glue to fix it in place keeping in mind that the connection has to be strong because the motor vibrates while rotating.

For the lower part, I used hot glue along with epoxy compound to attach the pipe to the base. The bond should be water proof and very strong.

Step 11: Add Some LEDs (Optional)

(330 ohm resistor is shown in the picture above which was later changed to 1K ohm)

I wanted to add a power indicator LED in the circuit box. The enclosure was painted red so I decided to add two red LEDs within the enclosure itself.

They are wired as such that when the motor is on, these LEDs turn on thus producing a glowing effect inside and acting as power indicators at the same time.

First you need to diffuse the LEDs so the light spreads out uniformly rather than getting concentrated on a small area.

Next, connect a 1K ohm resistor in series to the +ve terminal to both the LEDs. Connect both the LEDs in parallel and then extend the two wires so that it reaches the main circuit.

Hot glue both of them to the roof of the box (the lid) at a distance, facing downwards.

Step 12: Seal the Pump Motor

The pump I bought had to be submersed for it to push water. The motor present inside could short circuit and easily malfunction if submersed directly.

Hence I used lots of white M-seal/epoxy compound to seal the motor and make the pump water proof.

First of all solder wires to the respective terminals, with the correct polarity. Add plenty of hot glue at the joints.

Seal the motor and any other exposed part completely with the compound. Power the motor at specific time intervals so that the shaft doesn't get jammed.

Let it dry until it becomes hard. Check and power the pump again.

Step 13: Add Water Dripping Pipes

After water is pushed up from the pump below, to make it fall on the pads there are small holes made in the tubing which is spread just above the pads.

Take proper measurements with the rubber tubing and make 1-2mm holes at small intervals such that each pad should have 6 holes.

Seal the end of the tube with glue.

Hot glue the tubing as shown in pictures, just above the evaporating pads with the holes facing downwards. Water should drip from them and fall straight on the pads.

At last, take another tube and connect it to the water outlet of pump.

Now join both the tubings with a small piece cut from a drinking straw.

Step 14: Finish

So we are at the last stage now. Start by drilling two holes on the box lid for the wires to pass through.

Hot glue the plastic box at the top of the lid. Now solder and connect the fan, pump and LEDs to the main circuit. (schematic is given in Step 9)

Connect wires to screw terminals which will be used for powering the project.

Add some hot glue to any remaining loose connections and close the box with wooden lid.

Finally add a knob to the potentiometer.

Use a 12V battery or adapter to power it.

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And that's it! You're done with this awesome project. Enjoy the cool air..

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Thanks for reading! :)