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dual purpose heat exchanger in solar storage tank

Royboy Member Posts: 221
wondering if I could get some feedback on this piping concept for a small solar combisystem. the intent is to be able to extract some space heating energy from the solar water heater (with slightly oversized array) for a low-temp heating load (radiant slab) without adding a lot of components/cost to the system.

idea is to use a drainback system with a solar heat exchange coil in or around the bottom of the solar tank. when solar heat is available in the bottom of the tank for floor, a zone valve would reroute the continually circulating floor loop through the solar heat exchanger. here's a diagram, which includes a few details not essential to the concept. diagram shows flow with solar system on and solar heat being moved to slab. when solar heat is not wanted by slab, zone valve would redirect floor flow so it doesn't engage with solar loop.

not sure what the flow through the heat exchanger would look like with both pumps running - could be going either way or stagnant depending upon pump flows, but at that point the collected solar energy just going straight to the floor seems OK.

various details to work out here, including control strategy, but thought I'd see what others think of the basic concept.

I suppose there's no reason you couldn't do this with a closed loop-pressurized glycol system for that matter.


  • Karl_Northwind
    Karl_Northwind Member Posts: 139
    that looks ok

    but I think you'd want to put a second 3 way valve in the solar hot line.  send it to the solar tank or to the floor.

    I'll have to post my sketch for something similar, but using an air coil.  I have to sketch it up on cad first.  may get it posted this PM.

  • Karl_Northwind
    Karl_Northwind Member Posts: 139
    recirculating SHW

    This system ought to let me deposit heat to the tank during the day, and allow me to use the same circ, run with a different control, to use some of that heat again after the sun goes down, to keep the house temp up a touch. 

    this is what is going to be installed in my current house before it goes on the market.

    it currently has the tankenstein in the utility room.  to be replaced with a HTP SSC119 SE.

    the ball valve will be opened in the summer, closed in the winter.  all fluid passes thru a air coil.
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Watch out for induced flow

    Make sure the 3 way valve prevents flow through the floor in the summer.  The solar pump will induce some flow in that loop if it's piped this way.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • hot_rod
    hot_rod Member Posts: 16,301
    you have a few flow path

    potentials with that piping, Not sure which loop will get how much flow when the 3 way toggles from position to position. Another zone valve could prevent that potential, but what is the end goal?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
This discussion has been closed.