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intigrating solar , hydronic floor , and on demand heater

ALH_4 Member Posts: 1,790
Use a dual coil 80gal DHW pre-heat tank for storage. Connect the heating system to the upper coil, solar to the lower coil.

Before making the investment, it is worth evaluating whether solar space heating is appropriate for your application. A couple showers, laundry, dishwasher, etc will easily cool off that 80gal tank each day. It is worth figuring how much the tank might contribute to heating before you make the investment in the dual coil tank and piping/controls to integrate it with the heating system. You will probably be able to maximize your bang for the buck with a simple DHW pre-heat tank, particularly with a 1 or 2 collector system. Domestic hot water is almost always the best first line of attack when it comes to utilizing solar energy.


  • Tom Noftle
    Tom Noftle Member Posts: 16

    can someone point me in the right direction on integrating solar collectors w/ an 80 gal storage tank, closed loop hydronic floor heat, an on demand water heater which also heats potable water.
  • Tom Noftle
    Tom Noftle Member Posts: 16
    solar heat

    I've got a single coil 80 gal. DHW pre-heat tank and three collectors. I want to use a flat plate exchanger and keep the on demand heater on the potable side. can I put the coil liquid from the DHW in the same loop as the hydronic floor tubing or is that too complicated or impractical?
  • hot_rod
    hot_rod Member Posts: 22,154
    80 gallons

    of solar storage will not go far in the winter towards your heating load. You could send the solar water to the instantanous for just DHW preheat. That way it is a year 'round supplier.

    Be sure the brand of instantanous can accept warm water feed. Some do some don't. I think several manufacturers now offer solar models to work with pre-heat.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Tom Noftle
    Tom Noftle Member Posts: 16

    mine will accept warm water feed up to 107 F. does the solar tank get hotter than that? what if it can?
  • scott markle_2
    scott markle_2 Member Posts: 611

    Your location, your structure,your water usage and your ideas about comfort determine the design.

    I don't think an instantaneous heater makes a great boiler although rinnai does approve of the commercial units being used in heating applications.

    Depending on your location it's unlikely that 3 flat plate collectors will be able to supply 100% of dhw for the coldest winter months.Flat plate collector efficiency is effected more by ambient temperature than evacuated tube collectors.

    Because of the inverse relationship between thermal demands and solar radiation (winter), Active solar heating has some definite limitations. Evacuated tube collectors are better suited to this by nature, Although Flat plate collectors actually exceed tube collector efficiency slightly when ambient temps are higher (summer).

    A good quality modern instantaneous water heater can modulate quite wildly and might work well as a boost for the solar pre-heat. I had an old aquastar that supposedly modulated-it was not great to shower with, very sensitive to flow rate changes difficult to get a nice steady temp. The new generation units have solved these problems.

    I can't see a great way to integrate all these components. One thing to consider, your collectors will be able to harness more energy if you tank temperatures are low. One problem with two coil tanks is that the fuel side(boiler) often has no information to base it's contribution on besides tank temp. By maintaining the tank at a relatively high temperature (fuel input) we limit the amount of solar we can collect.

    In my estimation a preheat tank is preferable. Because this tank is allowed to drop when solar resources are deficient. This cooler tank water can more effectively draw heat from a a not so hot collector.

    Ironically a system that supply's a lower percentage of total annual demand can harness more solar energy per square ft. of collector than one that supplies a high percentage.

    This is especially true for a systems that must shed excess heat at peek production times. which is any system (in a temperate climate) that attempts at anything near 100% solar DHW

    From an economic/ecological stand point a system that supplies 60% of dhw at a high collector efficiency may be superior to one that supplies 90% of dhw at a significantly lower btu/sq.ft ratio.

    The collector itself has a energy/ecology dept to pay off from it's manufacturing, it does this faster if it is operating at a high efficiency.

    Two systems each supplying 50% of annual dhw load would have a higher environmental benefit than one system suppling 100% of the same load. Same amount of energy- less collectors.
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