Refrigeration and Air Conditioning
It may surprise you to discover that a fridge or freezer uses more electricity than many other appliances. That's not because it takes a lot of power, but because your fridge is switched on all day, every day. That means that a small difference in the amount of power a fridge consumes makes a big difference to your daily energy usage. If you can, try to do without a fridge at all; it will save you a lot on your solar power system.
Types of fridges
There are two basic types of refrigerators. These are absorption and compression. How do you choose which type to use?
How do you choose which type to use?
Firstly think about the smallest fridge you can get away with and secondly think about how you are going to power it. If you have a caravan then you probably have an absorption fridge which runs on gas. It's best to keep it this way; don't be tempted to use it on 12 Volts except when traveling because they use loads of power in this mode. Absorption fridges are best suited to use with gas or kerosene.
If it has to run on electricity, use a compressor fridge because they're much more efficient. Normal mains fridges are compressor fridges but for solar applications you're probably better off with a low voltage model. If you're on the mains then just choose the most efficient model possible.
A number of 12 Volt cool boxes are available. These are neither compressor nor absorption fridges but operate on a principle known as the peltier effect. They consume quite a lot of power but are useful for occasional use or use in a vehicle. If that's what you need then they're now available from camping shops.
Solar Air conditioning
Should buildings be cooled with the help of solar energy, then water-assisted air conditioning systems or ventilation systems can be powered with heat that is made available by solar collectors. No long-term intermediate storage is necessary in months of high solar energy gain in southern lands. The sun can, at least seasonally at our latitudes, provide a substantial part of the energy needed for air conditioning. Combination water-assisted systems and ventilation systems are also possibilities.
How does Solar Air conditioning Work?
The basic principle behind (solar-) thermal driven cooling is the thermo-chemical process of sorption: a liquid or gaseous substance is either attached to a solid, porous material (adsorption) or is taken in by a liquid or solid material (absorption).
The sorbent (i.e. silica gel, a substance with a large inner surface area) is provided with heat (i.e. from a solar heater) and is dehumidified. After this "drying", or adsorption, the process can be repeated in the opposite direction. When providing water vapor or steam, it is stored in the porous storage medium (adsorption) and simultaneously heat is released.
Processes are differentiated between closed refrigerant circulation systems (for producing cold water) and open systems according to the way in which the process is carried out: that is, whether or not the refrigerant comes into contact with the atmosphere. The latter is used for dehumidification and evaporative cooling. Both processes can further be classified according to either liquid or solid sorbents. In addition to the available refrigerating capacity, the relationship between drive heat and realized cold energy (coefficient of performance; COP) is also an essential performance figure of such systems.