2 Responses to ““Do-It-Yourself” Solar Water Heating Systems?”


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  1. Craig Kemper

    This is our vacation home, retirement home in 10 years. Existing 220v
    electric heat in ceiling, built in the ’70’s, wood floor with crawl space.
    Main priorty is to install a flat plate collector drain back radiant heat
    system, DHW to tankless water heater if conditions exist. Have approx. 144
    sq. ft. of collector area on South side of home (receives 100% sun from
    9:30am to 2:30pm in January.)to supply crawl space tank. Can install more
    collectors on roof if required. Heating 1100 sq.ft.-3 zones-4 loops @ 120′
    per zone. I’m thinking I need 500 gal. storage tank, 3-1″x300′ pex coils
    for exchangers (one for each zone) and if possible a smaller diameter
    exchanger set inside the 1″ pex for DHW. Would like to run circulation
    pumps from PV collectors. Am I anywhere close?

    • Dr. Ben


      Let’s see, you have a 1100 ft2 house built in the ’70s,. At this point, there is no way to tell what your heating requirements are without doing a professional heating load analysis.

      So, the first thing I would recommend is to check the insulation in the attic and under the floor. You need to max that out first. Recommended R values vary by region, but R30 in the ceiling and R19 in the floor are a good start. Then add double pane windows. These improvements could cut your energy bill up to 50%.

      Now you add solar to that. The performance of the solar is intimately related to you location and available sunlight. That is, the weather conditions, both in terms of heating your home and available solar radiation.

      You have 144 ft2 of collectors. That is not a lot. I recommend increasing the number of collectors as much as you can afford. Put the PV money toward that and use regular AC pumps.

      A typical tank gallons would be 1.5 x (collector ft2). Round that up to the nearest tank size. You can go bigger, but there are diminishing returns on cost vs performance. The tanks needs to be out of the weather and insulated well.

      I never recommend using plastic for exchangers, or any part of a solar collector system. This is one place where you can destroy the durability and efficiency of your system very quickly.

      You will need some detailed system design, which I am not able to give in this type of situation. Let me just say this, you need a steel tank and copper exchangers.

      There are designs that have no exchanger between the tank and the collectors, i.e., a drain back system. There are also ways to use no exchanger between the tank and the space heating. This depends on vertical distance between tank and radiant floor loop and whether the pumps can purge air out of the loops. If you could get the tank on the same level as the floors (or slightly above), this would be a good option. No exchangers for collectors and space heating would be the highest efficiency and lowest cost, but you can see it is too complicated to cover in this note.

      Domestic hot water always requires an exchanger, though.

      Plastic piping will work OK for the radiant slab floors. Radiant slab design and installation requires detailed planning of the size of the pipe, the layout in each room, pumping horsepower, and controls.

      I hope this helps.


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