There are a few essential components to any solar hot water system. First, a system for absorbing and heating the hot water, and then a system for storing it. Everything else basically varies, and generally exists to allow one of these two components to be installed or to operate correctly.
There are many schools of thought around the best, most efficient, most economical, most durable and highest quality solar thermal collectors. We have a few collector manufacturers whom we typically deal with, but would generally recommend not getting too focused on the outputs of collectors alone. Some collectors are cheaper, some are more expensive, but at the end of the day the cost of a system and the cost payback are far more dependent on external influences than the cost of collectors and output alone. For example, flow rates will impact the size and cost of piping as well as pumps. Smaller collectors will require less structure. Evacuated tube collectors will create less wind loads on the building, but may require adding and managing a heat dump for days when there's no hot water use.
Flate Plate Collectors:
Flat plate collectors look very similar to skylights, and involve the construction of an aluminum or steel framed “hot box” which contains a large absorber plate with thin copper piping fused to it's surface and covered with a distinctive coating to maximize solar gain. The unit is then encased with a glazed cover which allows solar energy to pass through, heat the absorber surface while trapping this heat for immediate exchange to fluid passing through the copper piping.
These collectors are a work-horse of the American & European solar industries. They are usually a more expensive option to pool heaters, but a low cost option for domestic hot water heating, with very reasonable paybacks.
Evacuated Tube Collectors:
These space age looking solar collectors are a series of glass tubes (usually about 8 foot in length each), which are connected to a manifold or header system. Inside the glass tubes are a copper 'heat pipe' with a solar absorber of some form or another. The absorber is connected directly to the tube, or formed into the inside face of the glass tube. The absorber is then heated by the sun and transfers heat to the copper pipe.
The copper pipe inside the tube basically contains a fluid with a low boiling point. When heated by the sun, it quickly turns to a gas and rises up the inside of the mini-copper pipe to a bulb at the top of the pipe. Typically this bulb sticks out of the glass tube and reaches very high temperatures. The bulb is usually made to plug right into a manifold that allows glycol or water to extract the heat from the bulbs via fluid circulation. When heat is extracted, the gas cools and drops to the bottom of the heat pipe to be heated again.
The balance of solar system includes a number of important components which include pump stations, heat exchangers, tanks and controllers.
In both commercial and residential applications, we find it important the include the use of a solar pump station provided as a package by the manufacturer. This approach increases warranty protection, optimizes system performance, and saves a ton of labor and materials. These pump stations typically include pre-engineered pumps, heat exchangers, pressure relief/safety valves and controllers in some instances.
There are primarily two types of storage tanks available for use with solar hot water systems. The first is a pressurized style tank, similar to that of a residential hot water tank (the tank is closed, and is at water pressure). These tanks tend to be most efficient and easiest to engineer around, however once larger commercial systems are being considered (over 10 collectors), the cost of pressurized storage can in some cases be cost prohibitive.
Any storage tank or combination of storage tanks larger than 119 gallons in size, requires an ASME rated vessel, which is very expensive for larger storage vessels. For this reason, many larger solar hot water systems make use of atmospheric storage tanks. These tanks can be as large as 10,000gallons or more, and are essentially maintained at room pressure (open to room pressure). An additional heat exchanger separates the water inside the atmospheric tank, and exchanges it's heat to incoming cold water lines.
We maintain a policy of having 24 hr monitoring and energy metering on all system installations. We use multiple solutions to achieve this. Feel free to contact us to learn more.
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