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New solar indirect questions

komatik Member Posts: 2

I have a few somewhat related questions about a closed loop solar thermal system I intend to integrate into my heating system. The heated water is to be fed to an indirect heater for storage then into a tankless boiler, which is already in place.  It supplies DHW as well as heat for the radiant floor system through a Taco Xblock heat exchanger.  I plan on having three 4x10 flat plate collectors (Max 40,000 BTU/day on a clear day) on a ground mount tilted at 65 degrees.  I live in the Pacific Northwest north of Seattle. I suspect the three 4x10 panels will be overkill during the summer months but was intending to oversize the system so as to maximize any heat collected during the Oct-April heating season as well as make up for any heat loss due to the relatively long piping run from where the collector needs to be located.  Was thinking that one of the panels could be covered during the summer months to avoid over heating the system.  I plan on putiting in a finned radiator heat dump at the collector as a precaution for over heating anyway. Any thoughts?  I have seen drawings of the heat dumps placed on the return ("cool") side of the loop as well as on the supply ("hot") side.  Just wondering which is the best option.

Since there will be approximately 60' of underground piping from the array to the exterior of the house plus the run into the house, I was wondering how the line is to be drained when it comes time to replace the glycol.  I reckon it will have to be a compressed air purge?

Hot water storage - I am considering a Burnham Allaince AL119SL indirect heater.  Is this product a suitable indirect heater for such a system?  Is the 119 gallon tank overkill? Better off with the 70 gallon?  More storage better for my situation since any heat is also needed for heating season?

Thanks much for any info.





  • hot_rod
    hot_rod Member Posts: 20,826
    How much DHW

    do you generally use per day?

    I plugged in 60 gallons at 140F and came up with a solar fraction of 54% for Seattle, Boeing Field weather data. Nov- April, probably not much excess to contribute to a heating load with 120 square feet of collector.

    New solar controls do have over hast protection functions. Collector cooling allows the pump to run and over charge the tank if the collector 230F. Store cooling allows the pump to come on in the evening and cool the tank back down to setpoint or below.

    So for example a low DHW use day, the tank runs up to 160F or so, the pump comes back on after the sun is down and cools the tank. Since the collector is basically a heat exchanger heat energy can also be dissipated.

    It really depends on how much DHW your family uses. If you have family that uses 80 gallons or more per day, I doubt you will ever see the need to dump or enable over-heat protection.

    Over-heat features are handy for times when you may be away from home with little or any DHW loads.

    If you feel you need a dump, first consider an extra storage capacity. If a dump zone is the final answer use a 3 way zone valve at the solar pump station. It switches flow thru a fin tube or dump radiator.

    Some installers will trigger a heating zone as a dump load, a radiant garage slab or basement slab could provide enough dump for the small amount you may need to "shed".

    Is a drainback system an option? if the tank is below the level of the collectors a drainback could solve an over heat concerns.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • komatik
    komatik Member Posts: 2
    heat dumps

     Thanks for the prompt reply to some of the heat dump issues.  The numbers jibe with my evaluation.  We do not use more than 20-30 gpd of DHW as there are just two of us.  But the house is a 3 BR so I wanted to have it ready for more folks when we finally have to move.  Also during the June-Sept period I didn't want to worry about an overheating system if we were gone for extended spells, therefore the desire to put in a heat dump.  I can't put the panels on the roof so will have to put in a ground mount and I was planning on putting the finned heat dump behind the panels using a three way valve.  Somebody in one of the posts on this forum I think mentioned the Tempmatix valve and that seemed like a good way to go.



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