# Vacume tube water heater system?



## Dutch 106 (Feb 12, 2008)

Hi Guys I have no doubt that there is on the net somewhere a how to on using a vacuum tube array to preheat hot water. I'm using an electric water just the now it came with the house and works well just the now, my intention is when it goes to replace it with a tank less ng system I'd like in the mean time to build a preheat system using a 10- 20 tube vacuum tube system to preheat using a home made heat exchanger in a blue plastic barrel (55-60 gal) A low watt pump and a solar panel to power the pump thru the day if there not enough light there will be no solar heat so no need.
Dutch


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## Darren (May 10, 2002)

I know someone with a vacuum setup or at least it was. The problem is maintaining the vacuum. Without a vacuum, it's a waste of money.


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## Dutch 106 (Feb 12, 2008)

The vacuum I'm talking about is the glass tube with a copper tube running thru. I would think the vacuum is a constant till someone hits it with a baseball?


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## Darren (May 10, 2002)

They purchased a system. I have no idea how the vacuum was lost. When I looked at the system on the roof, I didn't see any damage. The system is useless now.


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## JeepHammer (May 12, 2015)

I have radiant floor heat, so evacuated tube panels make sense for me since I can circulate from tubes directly to the floor.
Since I have a super insulated house, and the tubes will regularly produce 120*F. liquid,
Sometimes up to 160*F., we have to run the boiler very little, which saves a ton on propane.

I use a closed loop, anti-freeze mix (non-oxygenated) and a couple of valves to switch from floor heat to heat exchanger, pre-heating incoming water to the boiler/water heater.
Closed loop allows for continous, year round use,

While open loop can NOT be allowed to freeze, and needs to use oxygenated rated plumbing.
This is simply heating the incoming water before it hits the water heater,
Or when an open tank type heat exchanger is used.

Open tank heat exchangers allow air spaces, and that oxygenates the circulation liquid.

Anyway, they make free heat once installed, I wish I had a third panel or two for the shop!

There are two basic types, a metal tube that is bonded into a glass tube,
And a glass liquid tube bonded into the vacuum tube.
I have the glass/glass tube type, and 5 or 6 years down the road, no issues, and they were used when I got them.
Glass bonds to glass really well...

Metal bonds to glass less well, but they are cheaper to make and I've heard about failures,
But I've not owned them and I've seen them, but not seen failures.

I can't recommend mine enough! 
Especially since they only cost me about $120 in gas to go get them!

Don't forget to insulate your line sets!
You can loose a TON of heat without insulation on the lines!


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## Darren (May 10, 2002)

That's a good point about metal vs. glass. IIRC, the setup I saw used copper and glass. Glass to glass makes more sense.


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## Darren (May 10, 2002)

An open loop that allows intake of oxygen requires treatment to control water chemistry to prevent corrosion in the heater/boiler.


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## JeepHammer (May 12, 2015)

I mention open and closed loop,
Oxygenated vs. Non-Oxygenated because the two require different tubing/piping.

The OP mentioned a plastic barrel for a heat exchanger.
Heavily insulated, I guess that would work,
But depending on design, you could wind up with a mixed system that would require two different types of pipe/tubing.

I've tried it three ways,
Circulating anti-freeze through the panels (via pump),
That anti-freeze dumped into an open tank with incoming water in coils in the tank,
And the anti-freeze sucks out of the open tank, pumped back to the panels.

This is an open system, oxygenated, the panels need to be plumbed with oxygenated lines.
And yes, you have to keep up on the antifreeze mix since it evaporates...

-----

The second way I tried was coils, closed loop, in the tank,
A heat transfer liquid (Anti-Freeze) in the tank,
And coils of incoming water in the same tank.

The water/antifreeze mix in the tank needs to be watched because it will stagnate.
Closed loops on both sides, the liquid in the tank never moves.

------

The third way was with a proper heat exchanger tank,
The panels circulated anti-freeze through coils in a SEALED tank,
The incoming water fills the SEALED tank, just like a regular water heater.

The third heat exchanger tank is by far the most efficient.

------

Now, in my case,
I circulate the panel heated anti-freeze mix through the floor directly.
The panel heated mix drops (exchanges) its heat DIRECTLY to the concrete floor,
Heat rises, concrete modulates the heat through thermal mass,
And in the spring/fall I use virtually no propane to heat the house.

When the boiler kicks on, solenoid valves transfer panel antifreeze through a heat exchanger, which feeds/pre-heats the antifreeze feeding boiler/floor.

The reason for heat exchanger is so at night, when cold, the panels don't COOL the boiler/floor loop.
Its a little complicated to set up, but once done, it saves a tremendous amount of propane!

The same arrangement can easily be converted to pre-heat incoming water for the hot water heater, Especally if you use the professional heat exchanger tank and tankless water heater... BIG energy savings there!


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## JeepHammer (May 12, 2015)

On a side note,
I tried soldering two coils of metal tubing together to make a 'Tankless' heat exchanger...
I don't recommend it...
If they made 'D' shaped tubing where you would increase surface/heat transfer area, maybe practical...

A HUGE pain in the butt, and the results were mixed at best.


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## Dutch 106 (Feb 12, 2008)

Hey,
My intention was that the heating loop is 50/50 antifreeze with its own little burp tank at the top of the loop. and with a solar panel powering the pump, it would only work when the sun was well up. And yea its obvious that you would need good insulation on the heat exchanger. I was thinking of a box made out of expanded polly and the open space filled with loose fiberglass, one problem I had heard of was excess heat in the high summer? one of the reasons I wanted to go to a large heat exchange tank.
Dutch


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## JeepHammer (May 12, 2015)

Ok, what you described was a closed loop to the panels.
Non-oxygenated line sets, circulation pump, pressure tank, panels.

About the same thing I did...

Insulated line sets help get the anti-freeze to/from the panels with minimum losses.
Most people argue insulating the panel feed line, but the warmer the antifreeze is when it reaches the panel, the warmer it will be when it exits since the flow rate (pump volume) doesn't change.

The coil in your heat exchanger tank will make a big difference,
I use 'Plastic' line sets to/from, 
But I use metal in the heat exchanger, aluminum in particular.
Aluminum sheds heat really quickly in the exchanger, and its fairly cheap.

Now, your anti-freeze will need to protect aluminum if you do this or the aluminum will rot through pretty quickly! Ask me how I know that...
Most anti-freeze has aluminum protectors added, but they wear out every 3 years, so it needs to be changed or more aluminum protection added.

I didn't know this recently, but a foil lined insulation facing the heat source will increase effifiency. I always thought that foil only worked with infra-red heat sources,
I was mistaken.
I don't know what the efficiency increase is, but all the professional heat exchanger tanks all use foil.

Once the heat is produced in the panels and transfered to the heat exchanger/tank,
Are you going to use a transfer medium (water?),
Or circulate the incoming water directly around the heated coils?

Direct transfer takes a food grade pressure tank with the coils installed...
A pain in the butt to build yourself!

A transfer medium tank doesn't have to be pressurized.
Coils from the panel, coils from the water line, surrounded by transfer medium in an open tank.

Frankly, while a little less efficient, its safer since an antifreeze leak can't directly contaminate your drinking water.
For a guy building his own system with common components, this should take a load off your mind!
Nothing like having that safety buffer between the line sets!

When I did an open tank, which I still use as a humidifier,
It started life as a liquid tank,
4'x4'x4' plastic in a metal cage, you see them for cheap everywhere for sale.
They have a drain valve in the bottom... Real handy.

I built a wooden box with about 10" of space around, under and over the tank,
Laid in insulation, set the tank on the insulation, then insulated the sides up to about 10" over the top of the tank,
Then built an insulated lid, since you have to cut a hole in the top of the tank to get line sets in.

If your lid gets warm on the OUTSIDE, then you don't have enough insulation.
By using a combination of hard foam board, and expanding foam to fill cracks, you can get a really good thermal seal,
And by making your lid a 'Press Fit' to seal things up, you will keep that heat where it does you some good...

I did mine with simple carpentry & plumbing, there were probably better ways...
I'm no carpenter or master plumber, but it made a big difference anyway!


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## Dutch 106 (Feb 12, 2008)

Hey,
Thanks that does answer some questions and you make several good points no I don't want to drink antifreeze, dangerous ---- stuff!
Ever tried the low wattage pump and solar panel gag?
Dutch


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## JeepHammer (May 12, 2015)

I've tried a lot of crazy things...

Home made solar themal panel,
Small, cheap solar panel,
Cordless drill hooked to the solar panel to turn a pump.

That's how we partally heated the greenhouse for the first two years.
Sun comes up, warms the water, comes up and starts the drill turning.
Warm water dumped into, and drawn from a large tank in the greenhouse,
Large tank = thermal mass.
Water tank warms up, sheds heat all night...

Water tank is also handy in a green house, racks/tables on top of it for plants,
And a ready source of water when tending plants.
Good way to keep fertilized water recycling, so you don't lose the fertilizer.

Sun goes down, pump stops, warm wasn't lost outside the greenhouse.

I went through several drills, but at $5 from yard sales, who cares...
The little cheap plastic circulation pumps lasted longer in the fertilizer than the more expensive metal pumps did...
That was a fluke, proof of concept was a cheap plastic pump,
When I got to building a better system, I upgraded to a real pump/motor, and kept having to rebuild the pump instead of replace the drill motor...

Finally went to a fertilizer yard sprayer motor/pump,
They come DC since you pull them with a tractor/mower,
The pumps are plastic so the fertilizer doesn't eat them in a month, and the rebuild kits are $12...
$12 a season is pretty cheap, beats the $550 for a stainless steel fertilizer rated pump that still has to be rebuilt every year.

No comparison between my home made solar thermal panel and the evacuated tube panels.
If I could get a 20 degree temp difference, I was doing good.
The tube panels will regularly throw an 80 degree difference, sometimes 100 degrees.


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