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Thermosiphon

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Member Posts: 2,239
Anyone have a formula to calculate flow rates and pipe sizing for gravity flow/thermosiphon?

I have been enlisted to help a local Amish man put together an electrictricity free solar system.

• Member Posts: 23,302
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Oh brother, @Harvey Ramer -- you do come up with some winners. I don't have a handy dandy formula; I suppose there may be one. But. Your driving force will be the difference in density between the heated water and the cooler returning water, so if you know the water temperatures, you can figure the pressure difference -- with a little gymnastics on the calculator -- and from that figure the pipe size you need for a given flow.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 2,239
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Here's the thing though, Jamie. Outside influence aside, the temperature difference depends on the flow rate and the flow rate is determined by the temp difference.

I was hoping for a formula that would solve the problem rather than trial and error till I find the balance between temp and flow.
• Member Posts: 3,296
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Hi, The old books have the formula you're looking for. I'm not at my books now, but when I can will see if I can find the info. I built a gravity driven radiant system in my house and remember that getting the math to design it was a challenge. I think I found the info from a book written in the 1890s.

Yours, Larry
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That would be a big help Larry! I'll stay tuned.
• Member Posts: 23,302
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Simultaneous equations, Harvey -- but if Larry can dig it out, that'll do it!
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 7,376
edited June 2018
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Unless you or he are gonna attempt to build the panels with over-sized piping, the 1/2" tubing in manufactured panels will probably be too restrictive for Gravity flow.

I've always been amused by the lengths that our Amish friends will go to to get the benefits that electricity would provide without using it. Please don't tell them that God made our bodies to operate on electrical impulses.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 2,239
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Haha, true story. I have to say though, there ordinance of abstaining from electricity has made them a resourceful bunch.

In my immediate area, there are quite a few that like to push the bar, if you will. I have seen 500' of 12-2 romex direct buried and run into a house to power a washing machine and a circulator pump. Both were well hidden in a secret room. The circulator pump was for the radiant heating powered by the outdoor wood stove.

The electric was hijacked off of a chicken barn, which was being leased, therefore, was permitted to have electricity. The house however, was not. In this wild-man's eyes though, though miniscual amount of electricity they used for the house, also made the sin insignificant. The 500' of buried romex didn't bother him. Electricity is like magic after all. Wire is wire. Why pay more when you can pay less?

Just 20 miles away, on the other side of the mountain they are a completely different bunch. They will compete to be the plainest and likely wouldn't even need a set of ordinances. This group won't even use cordless tools. Everything is air powered. Everyone, including adults, will go barefoot during the summer so they can get a few more years out of their shoes. They have never been accused of frivilous spending.

Back to the solar.
This setup will have evacuated tubes. The tops of the tubes, heating part, insert into a horizontal tank of water. This whole unit sits outside. My job is to figure out how to set it up to get the most from it. Obstacles include, lack of electricity, freezing, and overheating.
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If the panels are at the highest point in the system, how will gravity work?
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 2,239
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I still have to do a site visit to determine the exact layout of everything.
If the solar collectors are higher than the water system, I could use something like a Turbomax at a higher point in the house. Pipe the incoming water up to it and then back down. Incoming water is pressurized with an air pump.
• Member Posts: 22,144
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The height difference also drives thermosiphoning. Usually the tank is above the collectors, and the piping needs to be sloped upward. The earliest versions solar thermo-siphon date back to 1909.

Evac tube typically are not ideal for drainback or gravity flow, depending on which type you have, flow thru or heat pipe style? Both have fairly restrictive water ways.

If they are heat pipe style, just build some dry wells to stick the vac tube condenser bulb right into the tank, that is how the roof top tank/ collector systems are built, very common in China. Called batch style solar heaters.

Here is my solar tea cup, powered by a single Oventrop aka Seico heat pipe style collector, into a dry copper well.

Need more data after a site visit.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 609
edited June 2018
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This is likely cheating. But what if you power a small ECM pump from a small solar panel. It's electricity, but not grid powered.
Engineer 775 on you tube has some videos where he pumps wells this way into reservoirs. using Grundfos pumps. Apparently they can accept a wide range of DC power direct from the solar panel in addition to AC.

• Member Posts: 3,541
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> @Harvey Ramer said:
> Haha, true story. I have to say though, there ordinance of abstaining from electricity has made them a resourceful bunch.
>
> In my immediate area, there are quite a few that like to push the bar, if you will. I have seen 500' of 12-2 romex direct buried and run into a house to power a washing machine and a circulator pump. Both were well hidden in a secret room. The circulator pump was for the radiant heating powered by the outdoor wood stove.
>
> The electric was hijacked off of a chicken barn, which was being leased, therefore, was permitted to have electricity. The house however, was not. In this wild-man's eyes though, though miniscual amount of electricity they used for the house, also made the sin insignificant. The 500' of buried romex didn't bother him. Electricity is like magic after all. Wire is wire. Why pay more when you can pay less?
>
> Just 20 miles away, on the other side of the mountain they are a completely different bunch. They will compete to be the plainest and likely wouldn't even need a set of ordinances. This group won't even use cordless tools. Everything is air powered. Everyone, including adults, will go barefoot during the summer so they can get a few more years out of their shoes. They have never been accused of frivilous spending.
>
> Back to the solar.
> This setup will have evacuated tubes. The tops of the tubes, heating part, insert into a horizontal tank of water. This whole unit sits outside. My job is to figure out how to set it up to get the most from it. Obstacles include, lack of electricity, freezing, and overheating.

Those are some obstacles!!
• Member Posts: 6,506
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I respect the fact that they want to stick to the 'old ways', but you have to admit there is some hypocrisy there.
I've spent some time up in Amish country. They will hide the fact that they are using these modern technologies. I've been in Amish homes with in ground pools w/pool heaters, seen telephones, and 65k Suburban trucks on the property (the 'kids' use that stuff).
And they seem to think that using air tools, run by a compressor that uses kerosene, is ok.
I've also seen when weather creates a harvest crises and they'll lose crops, bringing in the power equipment.
They'll also take a car battery, and inverter, and hook it up to a credit card machine to process payments at their store.
It's just hilarious to me that they will use all this modern technology to take advantage of solar, but then won't let you hook up a pump because it uses 'modern' electricity.
Why not get a solar panel and a bunch of batteries to power a dc pump?
steve
• Member Posts: 60
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That was my thought too, a circ powered from a panel.
• Member Posts: 3,296
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Hi Harvey, Here are some images from an old book. There is a lot more than just a formula, but hopefully it helps. The dead men were smart!

Yours, Larry

• Member Posts: 2,239
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Thanks Larry! That looks like a good sunday read.
• Member Posts: 1,907
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I'm interested to hear how this turns out. We've got a whole lot of Amish in the area here, and a lot of them do "cheat". There is a community nearby that builds beautiful electric fireplaces; I cannot help but laugh every time I think about it. Technically they only build the woodwork around it and place the electric insert inside, but it's still pretty humorous. Last winter I installed an outdoor wood boiler for another community, serving 4 homes and a sawmill building, each with their own hydro-air system. All pumps and blowers powered by a central 12KW diesel generator, which apparently was okay. One of the stranger ones I've been a part of
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(the 'kids' use that stuff).

Amish are Anabaptists, which as I understand it, the kids aren't yet members of the church; they don't get baptized and join up until they reach adulthood; therefore they are allowed to use the modern stuff.

Some of them do ride in cars, if non-Amish drive them. The ones around Lancaster also use electric lights on their buggies, powered by an axle-driven alternator... and I was at a motel in Ronks one Sunday evening last summer, studying Talmud on the porch, and in the distance I hear a really loud car radio approaching. No cars anywhere in the neighborhood, though, and I eventually realized it was coming from the horse-and-buggy that just passed.

I also remember being passed on the road by a couple of young men on a pedal-less bicycle. They operated it by pushing at the ground with their feet, Flintstone style, and they got some pretty impressive speed out of it.