Evacuated Tube Solar Hot Water Collectors
Heating water for a home's use is quite often one of the home's largest sources of energy usage. Many people interested in green homes and reducing their home's environmental impacts are turning to our nearest star, the Sun, to generate some or all of their home's power.
Solar Hot Water
Most people have images of solar panels on the roof generating electricity when they think of residential solar power. But the sun's energy can be used for more than just electrical generation. More and more, environmentally-minded people are using solar energy to heat their home's water.
If you are interested in a green home, a solar hot water system can be a cost-effective way to incorporate solar power into its design. Most solar hot water systems are used in conjunction with a traditional electric or gas water heater for times when the sun's energy isn't quite enough to heat water for the whole family. After all, nobody really enjoys a cold shower, do they?
Evacuated Tube Solar Hot Water
The solar collector is the portion of a solar hot water system where the heat of the sun is used to collect the energy necessary to heat the water for home usage. For an in-depth explanation of how the whole process works, see our article on solar hot water heating.
One type of solar water collector is the evacuated tube system. Traditionally used in commercial applications, they are becoming more popular for residential usage due to their effectiveness and affordability.
How an evacuated tube solar hot water collector works is actually quite simple. As anyone who has used a glass jug to brew sun tea during a hot sunny summer day knows, glass is a great conductor of heat. Make that glass dark and things can get real hot, real quick.
That's the basic idea behind evacuated tube solar hot water collectors. They use the same principle of using the sun's heat to heat a liquid. An evacuated tube hot water collector is a series of glass tubes connected to a copper header tube. Each glass tube has two layers of glass separated by a vacuum (that's the evacuated portion) to lock in heat. Just like a thermos filled with hot coffee is cool to the touch on the outside, so is the evacuated glass tube. The inner glass tube is black to absorb the sun's heat. Inside the inner tube is a copper heat pipe filled with a non-toxic liquid, typically glycol.
The sun's heat turns the liquid glycol into a hot vapor, and it rises to the top of the heat pipe into a copper header connecting all of the tubes. This header is also filled with a glycol fluid, which gets heated by the hot vapor from each tube. This heated fluid then passes through a heat exchanger in the water storage tank, transferring the heat to the water. In the evacuated tube, cooled vapor liquefies and returns to the bottom of the heat pipe to repeat the process continually.
This describes a closed-loop, or indirect, solar hot water system. Only the non-freezing glycol fluid is ever passed through the collectors, making it ideal for climates with freezing temperatures. For areas where the temperature never gets below freezing, a direct system replaces the glycol liquid with water, which flows directly through the collectors to be heated.
Benefits of Evacuated Tube Solar Hot Water Collectors
Evacuated tube collectors are much more efficient than other flat-type solar water collectors. Here are some of evacuated tube solar collector's advantages:
- Being a thermos-like vacuum, very little heat is lost from the fluid inside the tubes, and the tubes remain cool to the touch.
- Evacuated tube solar collectors can produce heat much quicker and at higher temperatures than flat panel collectors.
- The round shape of the evacuated tube collector gives them maximum sun exposure at different angles throughout the day.
- Their superior heating capabilities make them a superior choice in cold, cloudy climates. Evacuated tube collectors will work even in overcast conditions and operate in temperatures as low as -40 degrees fahrenheit.
- Individual tubes can be replaced if they break down or their vacuum seal is broken.
- In general, an evacuated tube solar collector using 22 tubes will usually provide hot water for a family of four, at a cost of around $1000. This cost doesn't include the other components of the solar hot water system.
Evacuated Tube Solar Hot Water Collectors: Part of a Complete Water System
Evacuated Tube collectors are used as part of a complete solar hot water heating system, which also includes the storage tank, pumps, and heat exchangers. Most manufacturers offer complete systems that include all necessary components for simple purchasing and installation.
Solar hot water systems may qualify for state or federal energy tax credits.
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