Good control of your solar water heating circulating pump with appropriate set points can make a big difference in the efficiency of the solar water heater.  On my system I set the turn ON point for the pump when the temperature of the collector rises 6 degrees C above the temperature in the bottom of the solar storage tank.  I then set the turn OFF point at 2 degrees C above the storage tank.  This allows the collector to get a little ahead of the storage tank temperature so that the pump does not turn on … cool the collector and then turn off, only to turn back on as soon as the collector again rises above the storage tank set point.  The controller manufacturer suggests that the turn ON set point be at 12 degrees C and the OFF set point at 8 degrees C.  I set mine a little closer because my collector does not see the sun until around 9:15 A.M. this time of year.  By that time the sun has a lot of power so the collector can usually keep ahead of the storage tank temperature and not turn ON and OFF too many times.  In the evening the sun goes behind the trees around 4:30 P.M. and the collector has a lot of stored heat so the pump can run quite awhile after the sun goes down.  By the time the temperature differential gets down to 2 degrees C, there is not much heat left in the collector so there is not much turning ON and OFF in the evening.  The consideration of course is to get as much heat as you can from the collector, but not run the 100 Watt pump for a degree or two of temperature.  Anyone needing a top notch Solar Controller can buy one of ours at nuSun, inc.  We have two types in stock, but I only have one listed on the nuSun site at the moment.

This entry was posted on Wednesday, May 20th, 2009 at 3:52 pm and is filed under Solar Water Heaters. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.