solar water
heating systems

All domestic waters contain dissolved solids. Hardness is the measure of concentrated dissolved solids in water.  When water becomes supersaturated with dissolved solids, precipitation may occur. Scaling is a particular type of precipitation where the precipitation occurs directly on a surface, such as on a heat tranfser surface or pipe wall.   Most scale from domestic waters are 90+% pure calcium carbonate (CaCO3).  

Scale buildup increases dramitically as the water temperature rises. Therefore water that is undersaturated at a low temperature may become supersaturated when heated to a higher temperature.  This is why, in areas with hard water, scaling tends to be worst in appliances that heat water, such as solar hot water systems, electric water heaters, coffee makers and other water heating appliances.

It is ironic that most of the states that have the best solar radiation also have the worst water scaling issues.  As you can see from the map at top the majority of the U.S. has hard water.  Scale or calcium deposits will over time accumulate within the heat exchanger of a solar water system and greatly hinder its performance.  According to the Army Corp of Engineers 30% or more of a heat exchanger’s efficiency can easily be lost with just a slither of scale buildup.

A quality solar drainback system controls high temperatures and contrary to traditional water heaters that flash heat the water our system will over the course of a day gradually heat the water.  The lower temperatures of “all day” solar heating of the water causes much, much less sediment and scale buildup than a traditional water heater’s high temperautre flash heating.