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Here is a short list of the things that I learned from my experiences with this project.
I also wrote a follow-up article for Home Power Magazine that covers the changes and improvements

  • Make sure you don't shade your solar panels (or the collectors, but they are more shade tolerant)

  • The ideal ratio is 1.5 to 2 square feet of collector surface per gallon of storage.  Performance will suffer if you are far from this ratio.

  • When using an Aquastar heater in a closed loop system, pay attention to the size of your circulation pumps - they need to provide enough flow to trigger the Aquastar to turn on.  Ideally the circulation pump should be on the feed side of the heater, but that is not always practical.

  • Install the circulation pumps in the return side of  the heating loop.  They will stay cooler and last longer. 

  • In retrospect I would have used a brazed flat plate type heat exchanger as they perform better and can be easier to plumb in as well.

  • Ground all your collector and PV frames.  I lost 2 El-Sid solar powered circulation pumps to a static discharge in the fall of 2003 (not an actual lightning strike).  The electronic driver circuits in the pumps fried.  I then grounded everything to the service entry ground rod with 10 gauge copper wire.

  • When re-pressurizing the inside closed loop(s), make sure that the water is not warm (over 70F).  When the water cools your loop temperature will drop and bring the system pressure down too.  Closed loops tend to require at least 30psi to work reliably in my experience.  Since my system is isolated from household water pressure (40psi) - I use a fill pump that can only achieve 16psi.  I then augment that pressure by pumping air into the  expansion tank with a bicycle pump to get 30psi.

  • An interesting note.  My first year I only had the radiant slab installed and the return temperature from the slab was about 70F.  This became the default temperature of the storage tank - without any solar contribution.  Then I added 2 10 foot baseboard radiators on the 2nd floor.  The return temperature from this loop is 110F which raises the default temperature of the storage tank.  This significantly increases the system efficiency on cloudy days since that heat is recovered and re-used.

  • Place automatic air vents at the highest points in each loop.  For the outside loop use a manual key vent - the automatic ones may not survive weather extremes.  Check the vents yearly for leaks and to release air.

  • Insulate your collector plumbing - especially if you have long exterior runs.  Use Rubitex black rubber boiler insulation on the collector loop.  Domestic foam pipe insulation will melt at collector temperatures!  Been there, done that!

  • Install lots of temperature gauges.  Before and after the collectors.  Before and after the storage tank. Before and after the floor loop(s).  This really helps to diagnose problems.

  • Install lots of unions in the plumbing so that you can readily unscrew them to remove plumbing sections for repair or upgrades.

  • Install lots of ball valves so you can close off sections of the system for maintenance.  This saves you from having to drain the whole system just to replace a faulty gauge or spigot seal.

  • Use a fiberglass mix in your radiant floor concrete if it will see heavy use, or if it will be less than 4" thick, this adds a lot of strength.

  • In snowy climates pay attention to solar panel and collector location so that you can clear snow off relatively easily.  In northern locations the bottom of the collectors should be at least 4 ft from the ground to allow for snow shedding.

  • Be sure to use the appropriate mixture of antifreeze in your collectors!  Use the worst recorded temperature for your area to determine the level of protection you will need.  Refer to the manufacturer's charts for the right mixture.

  • Be sure to size your expansion tank to the volume and heating capacity of your system.

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