Hot Tub drainback system

SystemSystem Posts: 2,511 admin
Hi,

I'm contemplating adding a solar assist to my wood-fired hot tub. I live in Central Colorado where it freezes almost every night for 5-6 months per year

I have several solar thermal panels. I was planning on using one of the 4*8 panels as the collector. I'm thinking that I can build a drainback system powered by something like a 20-30w pv panel and 12v pump. The lift from the outlet on the hot tub to the top of the thermal panel would be about 10-12 feet.

Do you think this would work? Does the pump have to be primed?
Thanks
Steve

Comments

  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Hot Tub drainback system

    Steve,

    I'm not real clear. Are you looking for PV to use on the pumps to circulate the water, or to heat the water?

    I also have a wood fired tub, (snorkel). My problem is that the water stratifies so it gets very hot on top, and cold on the bottom. My low tech solution is to use a paddle every now and then to keep it stirred. I have toyed with the idea of a small 12vdc pump, but since I stoke the fire every hour or two while it is heating, I just give it a stir. 15 years on and I just haven't done anything to make it "automatic"

    Icarus
  • System2System2 Posts: 6,290 admin
    Re: Hot Tub drainback system

    Hi Icarus,
    The PV is to power a pump to circulate the water through a solar thermal panel (liquid collector). The idea is to keep the water warm during the day so it doesn't take so long to heat up with the Chofu heater at night when the tub is in use. I have >300 days of sunshine here that is going to waste!
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Hot Tub drainback system

    Steve,

    Good thought.

    I would read through the post in the water pumping section of this forum.

    I have an idea that a pump in the 1 gpm rate range would be about right. Question the is, would you build it in with differential t-stats so that it only runs when you have a temp delta?

    A small Surflo pump will move ~ 3 gpm drawing about 4amps/12vdc. It will self prime to 9'. If it were me, I would install a small 12volt battery to start the cover the starting surge from the pump. Solar panel in the ~ 75 watt range would run a pump like that all day when the sun is out. If you wanted to only run the pump during prime heating hours, you could use a smaller panel, charge the battery before the collector heats up, use a bit of battery during the heat cycle, then add a bit more charge in the late day, keeping the battery 100% every day.

    Sounds like a simple idea. You could make a collector out of a simple roll of poly pipe laid out in a coil on the dark ground if you really wanted to make it simple. Think how hot a garden hose gets just sitting around!

    Keep us posted.

    Icarus

    PS The surflo's are listed on the Naws site
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Hot Tub drainback system

    Steve,

    One more thought,,, (Tried to do an edit, but it wouldn't let me!)

    You could use a simple 12 vdc bilge pump, Drop one end in the tub, the other to the coils back into the tub. "Rule" makes a pretty simple cheap ones, ~$25

    Icarus
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