The summers in Germany are getting warmer every year. So, my father and I built a low power air conditioner for his summer house. The AC consists of a heat exchanger, a pump, and a water reservoir outside. The heat exchanger is made out of a car radiator and multiple CPU fans (Fig. 1a/b). The insulated water tank is located outside of the summer house and contains about 400 liters of cold water. During the day, the cold water is circulated through the heat exchanger cooling down the air inside the summer house. In the evening, the warmed up water is then used to water the plants. This dual use of the water correlates quite nicely. If the day was hot, the plants need more water and more of the water in the water tank has to be replaced by cold water. If the day was mild, less water is used. The power consumption of the whole setup is quite low. The fans require about 10 Watts of power, while the pump is rated at about 30 Watts.
More recently, I built a compact version for my apartment’s bathtub (fig. 2). Since my apartment is reasonably small I can use simple fans to distribute the cool air to the other rooms.
