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Heat Dump ?

MJS
MJS Member Posts: 18
I have a job that will have 180 vacuum tubes tied into two 120 gallon dual coil tanks. An existing 120 gallon single coil tank will be at the end of the line and will be heated by a boiler when needed. This is a vacation home with four baths which should use more than the solar can put out when the owners are visiting. My problem is when they are not home for weeks at a time. They want to use the solar to do something usefull, not just dump it. No pool or hot tub, just radiant heat and snowmelt. The snowmelt will be a good dump for the summer months. I'm trying to keep this as simple as possible. Anyone have experience with a system like this? Thanks.

Comments

  • hot_rod
    hot_rod Member Posts: 15,003
    yes

    it's called a drainback system :)



    It sounds like you might end up spending more energy dollars to dump un-useable energy, then they actually harvest and consume, if the home is not occupied much.



    Crunch some number with RET screen or one of the solar design programs using actual occupied days of DHW used.



    Or solar powered AC units.



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • MJS
    MJS Member Posts: 18
    Options?

    Thanks Hot Rod. Drainback is not an option because of location. The builder and owner both think after the tanks are satisfied it shouldn't be a problem to have the solar heat some of the house or melt a little snow. Easier said than done as I'm finding out.   
  • hot_rod
    hot_rod Member Posts: 15,003
    edited September 2010
    sounds like a lot of collector

    check the manufacturers or SRCC data to see what sort of output you can expect from that size array. Then figure out where it will go all summer because it may cover the DHW load in just a few hours, IF they use some DHW. If not it may run to dump all day long on the days when the home is empty.



    Here is a dump radiator that was installed on a large commercial system I visited. The cost of running the pump and two large fans bites into that "free energy" figure.



    Also a dump formula that may help you, thanks to Siggy and Appropriate Designs



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • MJS
    MJS Member Posts: 18
    A lighter shade of green

    I will push for a smaller array. I've come to the conclusion that the mechanical room is too small and the system gets too complicated to try and move solar heat around the house if and when its needed. I do it at my own home, but that's different. Thanks HR for your thoughtful responses. 
  • kcopp
    kcopp Member Posts: 3,814
    ask a dumb Quest....

    why wont drainback work? What is special about your project that it can't work?
  • MJS
    MJS Member Posts: 18
    Structural issues...

    you would have to go up to make it back down. A trap in the line.
  • Karl_Northwind
    Karl_Northwind Member Posts: 139
    location?

    you didn't mention where the system is located, and what sort of heating load is present.

    if  a drainback isn't possible, and the customer wants to do a large system, you could  use the system to dump heat into the snowmelt loops (assuming they're big enough), but  that will use power.



      if you want a dedicated dump that will not use much more power than the original system, use a diverting zone valve on the supply to the panels that diverts solar fluid to a set of fin tube elements.  based on advice from older installers, I've used 1 foot of E-75 (3/4") element per 4 square feet of net apature of collector and had an unloaded temperature of 160 on the hot side, a 5 degree drop thru the 200 feet of piping to the house and whatnot, and then 15 degree drop thru the fin tube element.



    I've also just pumped the supply to the collectors to a caleffi high flow TMV, which diverts anything over 150F to a dump loop designed similarly.  works great with no additional power usage.  just use a valve with a high CV and you'll be fine.
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Steamback

    See the Steamback Design thread to understand how you can reject the heat before it is collected.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Vacation Homes

    Putting solar on a rarely used vacation home is a bad use of resources,  and no one has yet been successful with seasonal thermal storage.



    Grid-tied PV IS good at seasonal storage, however, and would therefore be a much better investment.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
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