This is my plan. I would appreciate any feedback from anyone who has experience using heated water for thermal mass or has experience with solar hot water systems...or anyone that just has an opinion.
I am building a solar powered hot water system for use as thermal mass storage for night time heating in cold weather. My plan is to circulate water from the solar collector through 4 – 55 gallon steel drums, gradually increasing the water temperature throughout the day so it can be released back into the greenhouse during the night.
I am building the solar collector using ½" OD x .062 Wall Black LLDPE Tubing and 9 - 4" x 48" Solar Hot Water Heater Absorber Fins with 5/8" channel. The collector will measure 12' long x 1' high with a collection area of 12 square feet using 36 linear feet of tubing. The collector will be housed in an insulated box with the interior painted flat black and it will have a plexiglass cover. This collector will be situated inside my greenhouse approximately 7 feet off the ground and mounted in a horizontal position. The total run in tubing will be approximately 56 linear feet when I take into account the collector, up feed to collector, down feed to drums and piping between drums.
I plan to place the solar panel outside the greenhouse and the pump inside. I am doing the whole project this way to protect the system from freezing on cold winter nights, figuring the 210 gallons of thermal mass and an electric backup heater will keep the pump and tubing from freezing. I know I could use a closed glycol system and heat exchanger, thus allowing me to place the collector and pump outside, but I think this system will work.