drainback set up

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ws9876
ws9876 Solar Expert Posts: 440 ✭✭✭
For a SHW you have a tank or coils in a tank, a pump, some valves and the collector.
If you want to do drainback, do you have to have another smaller tank to catch the glycol
or can you just fill the system to the point where fluid leaves the building ....and skip the second tank..??

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,502 admin
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    Re: drainback set up

    Here are some links to various solar thermal projects:

    Solar Shed and other Solar Thermal Links

    If you have grid power and no natural gas, the hybrid (heat pump based) hot water tanks can give solar a run for its money:
    I have been an advocate of solar thermal for almost a decade, but I'm rethinking this with the new generation of heat-pump based ( energy star ) hot water systems.

    With COP's of about 3-4 and one third the cost of typical solar thermal systems this would seem to be the best choice for total cost of ownership. I also like the fact they will cool the surrounding area for free great for cooling the garage in the summer!

    Solar thermal is far from maintenance free and its a major hassle to run the plumbing for roof mount collectors and worry about roof penetrations and leaks. The heat pump HW tanks is literally a simple swap with a standard domestic electric HW tank.

    http://www.geappliances.com/heat-pump-hot-water-heater/

    http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12840

    At a minimum, its nice to have a new choice in saving energy!

    Regarding your question--If it is a closed loop system with Glycol--Does your area get so cold that you still need drain back even with anti-freeze?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ws9876
    ws9876 Solar Expert Posts: 440 ✭✭✭
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    Re: drainback set up

    i wan to do a drainbk with solar dc pump. quits at dusk. thats why I asked...might use distilled water for shfluid...
    just realized that all the collector volume needs extra room to store... i must be a genius
  • LucMan
    LucMan Solar Expert Posts: 223 ✭✭✭
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    Re: drainback set up
    ws9876 wrote: »
    i wan to do a drainbk with solar dc pump. quits at dusk. thats why I asked...might use distilled water for shfluid...
    just realized that all the collector volume needs extra room to store... i must be a genius

    Drain back systems need a larger capacity pump to circulate water to the panels. I don't think that you will be able to find a cost effective PV powered pump that can handle the job. The pump must be able to over come the initial head of the system until a syphon is established. Some use 2 pumps in series , after 5=10 minutes the second pump is turned off after syphon is established

    A smaller tank is used as a drain back tank for the water usually a 10 gallon, depends on the number of panels and piping.
    Glycol is not required as the system turns off when there is any danger of freezing allowing the system to drain down.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: drainback set up

    I'm not clear why a drain back system needs glycol. A simple flat plate collector drain back system is pretty easy to do. Depending on how cold and for how long it stays cold, many hot water controllers offer an "anti-freeze" option that circulates water through the collector as needed to prevent freezing. I have used the Azel controller before and it works quite well on a flat plat system down to ~ 10F.


    Tony
  • ws9876
    ws9876 Solar Expert Posts: 440 ✭✭✭
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    Re: drainback set up

    we have 10 below F routinely .. wont a 100 watt panel run a DC circulator..??? doesnt Taco make one..??
  • Earthandsol
    Earthandsol Registered Users Posts: 12
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    Re: drainback set up

    Taco does not make a DC circulator that I am aware of- though they do have a new variable speed series of AC pumps with a built-in differential controller for drainback Solar Hot water systems :
    http://www.taco-hvac.com/en/products/Variable%20Speed%20Solar%20Control%20%2200%22%20Circulator/products.html?current_category=371
    they also make a pump for hydronic heating applications which has almost the same part name and does have a differential controller but is not for solar applications
    the solar Taco pump is great -I have used a few and no problems-
    as far as DC lift pumps - a very low head ( 6-9')Drainback application can be served by either a March Dc pump or a Laing D-5 Strong pump- I really like the Laing pumps and have had great results in small hydronic- radiant heat app's but as the main lift pump for the collector loop in a Drainback system I would have to call them somewhat experimental - I have had one is service for 18 mo's( no problems ) but am having issues with one- now two in my own Drainback system
    Chris
  • System2
    System2 Posts: 6,290 admin
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    Re: drainback set up
    icarus wrote: »
    I'm not clear why a drain back system needs glycol. A simple flat plate collector drain back system is pretty easy to do. Depending on how cold and for how long it stays cold, many hot water controllers offer an "anti-freeze" option that circulates water through the collector as needed to prevent freezing. I have used the Azel controller before and it works quite well on a flat plat system down to ~ 10F.


    Tony

    Tony,

    I agree. If a drainback system is properly installed, and working correctly, it's automatically freeze protected because the fluid is draining back to the tank when the collector temp. goes below the temp. of the tank. These guys at http://simpledrainback.com/ make a drainback system that uses plain old tap water as the solar fluid in a closed loop system. No messy glycol to worry about or pay for

    Cheers

    Sean
  • wdegrace
    wdegrace Registered Users Posts: 8
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    Re: drainback set up

    Why try to reinvent the wheel? No, drainbacks do not require glycol....when the outside temp drops below the storage tank temp the pump shuts off. When the pump shuts off...there is no water in the panels thus no freezing to worry about. One thing to consider about utilizing a DC powered pump is that over time the solar cell will lose power to aging, soiling, high temperatures etc. this may affect the flow rate/head of the pump which would ultimately equal poor system performance.

    At any rate - whatever you do make sure you install an atmospheric tank for the drainback tank or some way of relieving pressure.