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Solar Thermal Water Heating Systems

Ever want to use the sun to heat your water? If you have, you’re not alone. Solar water heating got its start in 1767 when Horace-Benedict de Saussure discovered the greenhouse effect. He observed that it was always hotter when the sunlight passed through a glass-covered structure, such as a coach or building, than it was when it passed into an open area. He went on to prove this theory by creating a box that is very similar to today’s panels for a solar water heater.

While the De Saussure discovered the science behind today’s solar water heaters, it wasn’t until 1891 when Clarence Kemp became the first person to patent a solar system that solar water heating came to the masses. The first system was a simple system called the Climax that heated the water using an insulated box that contained metal cylinders covered with glass. This system was typically mounted on the roof. Kemp originally marketed his units to the east coast but by 1897 1/3 of the homes in Pasadena, California had solar water heaters.

The invention and use of solar water heaters continued to climb until the 1920’s when the discovery of natural gas began the gradual decline of solar water heaters. After World War Two the increased cost of materials and decrease electrical rates the use of solar water heaters was effectively killed. It wasn’t until the energy crisis of the 70’s that the use of solar water heaters began to rise but this was short lived as in the late 80’s we experienced a second drop off.

In the past few years we have experienced another rise in the use of the solar water systems. This is due to the increase in energy cost and individuals consciousness of their environment. As the interest in solar thermal systems increase the general public’s need for knowledge about the systems also needs to increase. For that reason we will review some of the different types of systems that are available today.

Solar systems can be classified by the combination of two classification groups:

1. Water heating: This classification focuses on two different ways of heating the water.

  • Direct: The water is directly heated by the sun
  • Indirect: A transfer fluid is heated by the sun and transfers the heat to the water. In this case the water is never directly heated by the sun but rather a transfer fluid.

2. Water Movement: This classification focuses on how the water or transfer fluid is moved in the system.

  • Active: The water or fluid is moved using pumps and electricity.
  • Passive: The water moves using the natural properties of water in which cold water falls pushing warm water up creating a current or flow.

By combining either of the classifications from group one with group two you can define every type of solar water heating system on the market. While these classifications can define all types of heaters there are some types that are more prominent than others.

Drain Back System (Active Indirect): This system is one of the most common because it has very good freeze and over heating protection. This unit uses water as the transfer fluid and will drain the water out of the solar panels when it is not heating. This way during times of freeze or inactive use the unit does not have water in the panels. These units do use more power than other units and they can be noisy due to the need for larger pumps.

Pressurized Glycol System (Active Indirect): This system uses propylene glycol as the transfer fluid. These units use the glycol as the freeze protection of the system. The pumps are smaller because the fluid is pressurized and because of this a PV panel can be used to run the system. The disadvantages to this system are primarily due to the use of glycol as the transfer fluid. There is a reduction in the efficiency of the fluid to transfer heat and maintenance can be required to ensure the fluid has not deteriorated.

Drain Down System (Active Direct): This system differs from the above systems in that it directly heats the water that is used. The system is not as complicated as other systems and the heating efficiency is good. The downfall of this system comes from the freeze protection. This system must be manually drained and refilled every time the temperature falls to a point in which the water could freeze. Also the water for the home must be good so that it doesn’t cause corrosion and mineral deposits in the system.

Direct Thermosyphon (Passive Direct): Passive systems are the simplest systems on the market. Passive systems can use a storage tank and panels or heat the water in the tank itself. A thermosyphon system uses panels and a tank. The panel is installed below the tank and uses the natural flow of water to move the hot water into the tank for storage. As the water cools off it falls to the panel to be heated again. Passive systems are simple and reliable but they can be unappealing to some individuals.

Each unit has its application based on the site and user preferences. Prior to purchasing a unit it is highly recommended that you consult with a knowledgeable installer and have you site assessed to determine which unit is best for you.

Reuse your spray foam cans.

Spray foam is a great addition to your tool box when sealing up your home. One of the largest problems is that you can’t keep it in your tool box after you have used it. This is because the tip is hard if not impossible to clean once it has been used once. With this little tip however you can return the can to your tool box after the first use. Keep some tubing in your box as it can be used as the tip to the can. The tube can be a recycled such as the outer liner to 2 wire electrical wire or it can be water line tube with the correct inside diameter to fit over the can tip.