Active solar water heaters


In active solar water heaters, these types rely on electric pumps as well as controllers to circulate water using heat transfer fluids that go through the collectors. There are 2 types of active solar water heating systems on the market which are:



1. Direct-circulation systems which use pumps to circulate pressurized potable water directly through the collectors. These systems are perfect for places that do not experience winter or cold seasons for long periods and do not have hard or acidic water. If the systems use recirculation freeze protection, then they would not need approval by the Solar Rating & Certification Corporation (SRCC) because that requires electrical power for the protection to be effective.



2. The indirect-circulation systems pump up heat-transfer fluids through collectors. These systems have heat exchangers that transfer heat from the liquid to the potable water. There are two most common indirect systems which are:



a. Antifreeze- this type has a heat transfer fluid that is commonly a glycol-water based mixture with the glycol concentration depending on the expected minimum temperature. The glycol is usually food-grade propylene glycol because it is non-toxic and safe.





b. Drainback systems- this type uses pumps to circulate water through the collectors. The water in the collector loop flows into a reservoir tank when the pumps stop, thus making drainback systems a better choice especially in cold climates. These systems though need to be carefully installed in order to ensure that the piping always slopes downward to make sure that the water is completely drained out from the piping.



This can be difficult to achieve in some circumstances.





Passive solar water heaters



These systems work thanks to the power of gravity as it needs the water to naturally circulate as it is heated. Passive systems are generally more reliable and easier to maintain as they have no electrical components and possibly have a longer work life than active systems. The two most popular
1. Integral-collector storage systems- these systems usually have one or more storage tanks located in an insulated box with a glazed side facing the sun. These systems are ideal for locations that have little or no sunlight as well as good in places with significant daytime and evening hot-water needs; but they do not work well in areas with predominantly morning draws because they lose most of the collected energy by nightfall.



2. Thermosyphon systems- A more economical and reliable choice especially in new houses as they rely on natural convection of warm water that rises to the top and circulate through the collectors and to the tank which is located above the collector. As the water heats in the solar collector, it becomes lighter and rises naturally into the tank above. The cooler water meanwhile flows down the pipes to the bottom of the collector, enhancing the circulation. Most of these storage tanks for this kind of systems are often places in the house’s attic. Thermosyphon systems normally use glycol fluid in the collector loop making it ideal to be installed in freeze-prone climates if the piping in the unconditioned space is adequately protected.




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