The direct system open-loop system, also known as the most simple system, solar water heaters on the market. It uses a flat plate solar collectors. The system is not efficient, because other people, but it is very reliable, because fewer components, longer life. The system is named for the open-loop, because the water is open, from our house to the system input and output streams.
The system is any suitable climatic conditions, the temperature of the water in the freezing process within the system, however, can freeze and damage the system components. The main reason is to expand its volume, the water into ice.
Water in the collector is a clear sky, you can freeze the surrounding air temperature reaches 40 degrees Fahrenheit, or 4-5 degrees Celsius. This condition is referred to as the night sky radiation. Application in cold climates, the best practice is to use only three seasons, two seasons, depending on your climate behavior. Stop using the system in the winter or the cold, all water is removed from the system.
Two changes in the open-loop system, or use a pump or without pump. Without a pump system, which is called a passive system, because it does not transport water inside the system components. It works completely by the heat pipe, or liquid convection heat transfer. Cold water naturally moving toward the hot water (or solar collector), in order to achieve a balance. This process is continuous as long as the warm water than cold water solar collector.
The open-loop and passive is a good choice, because you do not need to waste electricity pump. Ambient temperature, so you just need to be careful it does not reach 40 degrees Fahrenheit, or 4-5 degrees Celsius. However, a drawback of the passive system, the system is located in the tank top of the solar collector, installed outside the home. Heat loss may be greater than if it was installed in our home.