Thursday, May 30, 2013

Solar Hot Water Heaters

     The first time I heard the phrase 'Solar Hot Water Heater', my mom and grandmother were reminiscing about when they first came to live in St. Petersburg.  They had been packed up by My grandfather and moved south without a say so.  Men made decisions, then.  Women followed.  The thinking was they would move in with an elderly Uncle and wait him out until the reading of the will.  Apparently, the grandfather I met twice in my life, was a bit of a mercenary and the uncle knew it.  He was left nothing.  BUT, the hot water heater was a bit of fascinating technology the uncle had in his home.
     Mother remembered the almost unlimited amount of hot water, something she didn't remember enjoying in Pennsylvania.  Gram remembered it was just a huge copper tank positioned on top of the house with copper pipes that went through the roof and into the house. This tank was found in a UK gas appliance catalog and is used to recover steam in a closed heating system or to hold any other overflow.  I suppose you could find one  a similar US appliance website.

      When mom couldn't recall the tank, Gram told her it was not a big round 50+ gallon barrel, it was a tank that measured just about 12" deep and almost four' by six' across it's face.  You hardly noticed it against the green shingles of the roof as it weathered to a verde gris color.  She thought it was just some bit of salvage he rescued from the early days of the railroads in Florida but, she wasn't sure.  What she did know for sure was the water was very warm and never very hot.  It was perfect for bathing but needed heat to make coffee, even her favorite instant, and to rinse the dishes, but with a supply of very warm water, it took less time to come to a boil for any reason.  

     We have probably all seen a solar shower from the camp store.  It is just a bag that absorbs sun rays to warm the water in the bag.  It really helps to heat the water in one of those camp showers if you squeeze the bag a couple times throughout the day to stir the water so it is all an even temperature.  

      A tank that both gathers the heat, stores the water and delivers the water through gravity is probably the most Passive Solar water heating system.  However, a Passive system just means basically, there is no circulating pump for the water.
     Any tank that holds water in close proximity to a heat source is a 'system'.      I go to a powwow with the family that is held in a huge hay field after the hay is cut.  The promoters provide a solar shower for the campers.  It is just two large copper tanks (drum shaped 100 gallon tanks).  The tanks were perched on top of what used to be an old horse shed.  A garden hose is connected to the spigot.  It fills one tank that is connected to another with a copper pipe.  When tank one is full, it over flows into the other tank.  When the two tanks are full, they turn off the hose, there is NO high end plumbing fill valves or cut off float valves used here!  

    The tanks are exposed to the sun, the wooden shed frame is roofed with tin.  The pipes that deliver the hot water to the shower are copper and are attached to the under side of the roof.  The cold water is delivered through a system of garden hoses and zip ties!  It is crazy!  There are two shower heads that allow the water to overlap as it rains down on you.  You adjust the cold and hot, then get in and good luck!  The best time to shower is mid afternoon, the water is boiling by then and the tourists have had their cool morning showers!
Illustration of a passive, batch solar water heater. Cold water enters a pipe and can either enter a solar storage/backup water heater tank or the batch collector, depending on which bypass valve is opened. If the valve to the batch collector is open, a vertical pipe (which also has a spigot drain valve for cold climates) carries the water up into the batch collector. The batch collector is a large box holding a tank and covered with a glaze that faces the sun. Water is heated in this tank, and another pipe takes the heated water from the batch collector into the solar storage/backup water heater, where it is then carried to the house.

Illustration of an active, closed loop solar water heater. A large, flat panel called a flat plate collector is connected to a tank called a solar storage/backup water heater by two pipes. One of these pipes is runs through a cylindrical pump into the bottom of the tank, where it becomes a coil called a double-wall heat exchanger. This coil runs up through the tank and out again to the flat plate collector. Antifreeze fluid runs only through this collector loop. Two pipes run out the top of the water heater tank; one is a cold water supply into the tank, and the other sends hot water to the house.
     Today, we use solar panels or reflective panels with pipes of fluid that is heated to circulate through the tank that holds the water.  The Active system includes the use of pumps to to keep the fluid circulating from the heat source to the water holding system and back to the heating panel.  
This coil of hot fluid replaces the gas heated or electric coil that heats your water now.  

I have included two graphics here from  Just to show the next steps in a simplified form.  

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