Climate Friendly Room Cooling

The world is getting warmer and warmer, and people need to cool down. I have already described a long-term solution to global warming – namely, returning carbon to the soil – in a project on Terra Preta.

Today, as a quick fix for the heat, we are building an air-conditioning system: environmentally friendly, solar-powered, with no refrigerant gases, no condensation, cheap and quiet.

The idea behind the device is not new, but the design and installation are. We use a solar panel, Peltier elements and a fan. The peltier elements have one disadvantage: heat and cold are very close together. It is difficult to separate the two and utilise them accordingly.

There are two operating modes:

1. Generating cool air inside the room and dissipating the heat outside.
2. Generating cool air outside and bringing it into the room.

I have decided to go for the second option. I do not want to generate any more heat in a warm room. Nor do I cool warm outside air and feed it inside (which is inefficient); instead, I use indoor air, which is cooled in the cooling chamber. This prevents positive or negative pressure from building up in the room. One hose carries room air to the cooling unit, while a second one returns the cooled air. As the unit is located outside, this also reduces noise levels.

1. Solar panel 30 W (or please more)
2. buck converter
3. 2x peltier element
4. 2x aluminum heat sink (from old computer)
5. thermal paste
6. cooling fan (from old computer)
7. ventilation hose

As the Peltier elements and the fan each run on 12 volts, the solar panel needs to provide as much power as possible. For this project, I’m using a 30-watt panel, measuring 30 x 60 cm – not too big, so that it fits in front of the window to provide shade. Of course, a more powerful panel would be better

My panel outputs an unregulated 24 volts, so I’ve fitted a buck converter in the circuit. This control system, along with the cables, will later be tucked away in a small compartment beneath the cooling element.

After the buck converter, all three devices (2x Peltier units and 1x fan) are connected in parallel. Optionally, an on/off switch can be fitted between the load and the converter.

(Of course, a network power supply could also be used instead of the panel. That would certainly increase the system’s power output. But then it would no longer be environmentally friendly!)

The peltier elements consume the most energy. Physically speaking, cooling cannot be generated, but heat can be extracted and removed. Heat is generated on one side of the plates (up to 70 degrees), while the other side becomes cold. Both sides require cooling elements to remove and distribute the heat and cold.

We allow the cold air to remain in the (wooden) cooling cell, where it is carried into the room by the fan’s airflow. We transfer the heat to the outside without using a fan.

To ensure effective heat transfer between the peltier modules and the cooling elements, the use of thermal paste is recommended.

The cooling fins and peltier modules are pressed together using wires.

To ensure the best possible connection to the cooling unit, I’ve designed two adaptors using 3D printing.

They are screwed onto the fan and glued to the cooling unit.

The system is optimised for a top-hung window of the type commonly found in Germany. With just a few minor adjustments, it can also be adapted for other types of window.

First, I cut a board to size so that it fits into the upper window slot. Two cut-outs (approx. 5 x 10 cm) are for the air hoses. The solar panel is attached to the board using two or more brackets. It also acts as a sunshade for the window and the air conditioning unit itself. At the bottom of the panel, we fit a support to ensure that the board and the entire system are securely anchored and cannot fall off.

Our cooling unit is also fitted to the board and beneath the panel, as close as possible to the openings to keep the hoses short.

With tilt-and-turn windows in Germany, we also have triangular openings on the sides. We need to seal these to prevent warm air from entering the room. This can be done using plywood or thin plastic.

Now our cooling system is ready: quiet, cheap and, above all, environmentally friendly!

Have a great summer!