Understanding Solar Hot Water Systems - The Drain Back Design

There are many kinds of solar domestic hot water systems - pressurized closed loop, pressurized open loop, drain back, thermosyphon, and variations called direct and indirect, speaking about the location in the heat exchanger. There are variations one of the variations. The two dominant types today would be the pressurized glycol system and the drain back system.
One version with the drain back system has been doing continuous operation considering that the late '70s. It has these six fundamental characteristics:


It is scalable to your size from your smallest residential system on the largest commercial system.

It works in almost any climate and will not freeze or boil.

It is easily the most efficient for two reasons. It uses plain water, containing the best heat transfer characteristics, and yes it does not have a heat exchanger between the tank as well as the collectors. Typical heat exchangers are 50-60% efficient in transferring heat between one for reds as well as the other. With no exchanger relating to the tank and collectors, the drain back system transfers 100% from the collector heat on the tank.

It is the most durable. Glycols deteriorate with time producing acids that eat piping. Pressurized glycol systems have around 30% shorter equipment life than drain back systems.

With fewer parts, no exchanger, no chemicals degradation, drain back systems are as trouble-free as possible

Trouble-free could result in no regular maintenance, just an occasional check up.
So just how do drain back solar hot water systems operate? There are two temperature sensors that control a solar system. One will be the Hi-temp sensor about the outlet from the collectors. The other is the Lo-temp sensor for the coldest part of the tank.
In the morning in the event the solar collector temperature rises to about 18oF hotter than the tank temperature, the controller turns the collector pump ON. Water is pumped through the bottom with the tank (the coldest part) through the collectors, buying heat as it goes. The warmed water spills on the return line to the drain back tank. This process continues on provided that the collectors are near least 5oF hotter compared to tank, heating the tank continually. At the end with the day in the event the difference falls below 5oF, the controller turns the pump off and the river drains in the collectors back to the tank.
Whenever someone uses warm water in the house, cold water experiences a copper coil heat exchanger inside solar tank then into the regular water heater. The solar tank preheats the lake and also the regular water heater finishes raising it to the final temperature. The warmer the lake is on its way into the water heater, the less heat it has to add. It is important to note that potable water never mixes with the water within the solar domestic Sutherland Shire Hot water water tank.
Solar heats water for dishwashing, clothes washing, bathing, spa, hot tub, pool, etc., that's termed as domestic domestic hot water, or DHW for short. Properly designed solar trouble systems can supply 30-60% from the year round trouble needs of an family.