20% of all electricity in the USA is used by air conditioning units. The power consumption of air conditioners renders them incompatible with all but the largest domestic renewable energy systems, and so people living off-grid typically have to do without. In this article we will look at how a very cheap and simple room cooler can be put together, powered by a 12 Volt battery or directly from a PV Solar Panel.
DIY Groundsource Heat Pump Cool Fan
Once you dig more than a few feet down, the temperature of the ground is pretty much constant throughout the year. This is the key to Geothermal (Groundsource) Heat Pumps – systems which keep buildings cool in the summer and warm in the winter with great efficiency. Using this fact it is possible to put together a simple room cooler using nothing more than thin plastic tubing, a small circulation pump, a fan, and a few fittings.
A coil of plastic tubing is buried 1+ metres below ground level where it will find consistent temperatures of around 11-12 degrees Celcius year-round. It is connected through a hole drilled in the wall (or through a window / ventilation brick) to the fan via a closed loop. The hose, or ideally copper tubing is wound around in a spiral at the back of the fan, so the air drawn into the fan is pre-cooled to well below the ambient summer air temperature.
The tubing can be attached to the grille of the fan very easily using cable ties.
Anti-freeze or heavily salted water is ideal to act as the coolant pumped around the system since it will not freeze when the system lies dormant in the winter. Since the air in the room is hotter than the air in the ground, the coolant takes heat from the air before it is blown out from the fan and then deposits it in the ground. This set up is a basic heat exchanger.
Any small circulation pump can be used to move the coolant around the system. 12V aquarium pumps can be perfect, as can the pumps typically used in solar water heating systems, and in ornamental garden water fountains. All of these pumps have very low power consumption, and can be powered with a 12V battery.
Super Cooling Homemade Air Conditioner
If more rapid cooling is required, and energy efficiency is not such an issue, then an alternative to using the ground as a source of cool is to use an insulated container filled with icy salt water. Using a copper coil in the icy water, a copper coil at the front AND rear of the fan, and flexible tubing to complete the loop (via the pump), a hot room can be cooled to a comfortable level in 10-20 minutes.
Below is a video of exactly such a system in action as well as a description of how it was made:
And here is a link to a detailed guide showing how such a low power high efficiency air conditioner can be constructed: Homemade AC from the Instructables website.
Related REUK Articles
Heating is as much if not more of an energy hog than cooling. Take a look at our article Make a Simple Solar Air Heater to find out how you can also greatly reduce your heating bills.