All Glass Heat Pipe Evacuated Tube Collectors

[Art VanDelay]

Does anyone have any first hand experience with these?

all glass heat pipe.jpg


Since there is no copper, these must be very low cost.

I would expect some thermal shock problems... but...

Usually they are inserted into an unpressurized storage tank.

[hamish]

hi art, I have two systems using the plain evacuated tubes. They are quite common here, and work really well.
The ev tubes are about 10 dollars each retail here and ev tubes with heat pipe complete 20 dollars. The low pressure systems work very well. On a normal summers day they start boiling in the afternoon, the tank being open ended with a vent pipe becomes a solar kettle. I fill the kettle from a tap in the kitchen with a direct line to the geyser. It supplies the scullery and laundry as well where the low pressure works ok. The low pressure geysers are cheap as well with a stainless steel cylinder. The complete kit 12 tubes 100L geyser and stand cost 450 dollars.

[Art VanDelay]

On a normal summers day they start boiling in the afternoon, the tank being open ended with a vent pipe becomes a solar kettle. I fill the kettle from a tap in the kitchen with a direct line to the geyser. It supplies the scullery and laundry as well where the low pressure works ok. The low pressure geysers are cheap as well with a stainless steel cylinder. The complete kit 12 tubes 100L geyser and stand cost 450 dollars.

Thanks for the input Hamish. Translation: Geyser=water heater Scullery=especially in a large old house, a room next to the kitchen where pans are washed and vegetables are prepared for cooking
I've found a 27 tube model for $799US: http://www.seabirdsolar.com/scripts/gravity_system.php

Do you know what the usual solution is for increasing the pressure for showers? In most of the US, a gravity fed shower just won't do.

[MikeSolar]

These systems are for warm climates and really should not be used if the winters get more than a couple deg below freezing. Cheap though.

[hamish]

Looks like a good unit, gravity fed plumbing systems can work very well in bathrooms with mixers if basic principles are followed. No restrictions on supply pipes and on the mixers and obviously decent diameter of pipe sizes, 1/2 inch or 3/4 inch. The shower rose must also not be restricting and bigger in size 4 or six inch in
diameter to give you the classic rain shower.The other issue will be the cold supply which must be fed from a supply tank located on or in the roof or a stand outside or a low pressure control valve on the cold line. The main problem that I have seen with gravity systems that is the cold being high pressure and the hot low which results in no mixing as the hot and cold pressures are not balanced. The big bonus with a gravity fed system is water saving no 4 bar pressure gushing out the tap just to wash your hands.
Another way with the gravity fed geyser is to install a booster pump on the hot line which switches on as you open the tap, a common solution here where most houses are geared up for a high pressure system.
The high pressure solar systems are pricy here and going this route works out at less than half the price plus a new stainless steel tank which wont burst on you.

[Art VanDelay]

Natural Convection Loops for Supply Pipe Freeze Protection

These systems are for warm climates and really should not be used if the winters get more than a couple deg below freezing. Cheap though.

The few grams of water in the heat pipe won't damage anything when it freezes.

Some researchers at NREL have devised a way to prevent freezing of the supply and return lines

http://www.nrel.gov/docs/fy06osti/39664.pdf

And oh yeah, the tank itself is too big to freeze.

Note: Lots of field testing of these theories would be required. The easy solution to the pressure problem is having a coil of copper inside the unpressurized tank to transfer heat to the pressurized hot water. Unfortunately, that adds a couple hundred dollars to the cost.

[MikeSolar]

The few grams of water in the heat pipe won't damage anything when it freezes.

Some researchers at NREL have devised a way to prevent freezing of the supply and return lines

http://www.nrel.gov/docs/fy06osti/39664.pdf

And oh yeah, the tank itself is too big to freeze.

Note: Lots of field testing of these theories would be required. The easy solution to the pressure problem is having a coil of copper inside the unpressurized tank to transfer heat to the pressurized hot water. Unfortunately, that adds a couple hundred dollars to the cost.

The Canadian govt (when we had one that cared about renewables, which currently we don't) had much stricter rebates for solar thermal than the US. For a while the rebates were tied to the production of heat rather than just being "on the list" as SRCC is. There is a standard that details solar insolation, water usage in a small, medium and large family, including certain amounts of water taken out at particular times of the day and the size of the "typical" DHW system. The standards are ISO so they are used by everyone, pretty much.

The upshot of this is that the testing showed that a typical 2 flat panel system such as Viessmann, Thermo-dynamics (solar boiler), Steibel eltron, and the ones we built, typically put out about 2200-2400 kwh of heat annually under the mid sized family conditions. This is a real world output too as we have been involved in the test program.

The output of the tank on the roof system was just 600kwh and, in our climate (all of southern Canada and northern US), you needed to use electric heat trace cables to keep the lines from freezing in the winter. This technology has been around for years.

Every technology has its place and if you go back to China where they originated, look at what parts of China they are used and the conditions they are in. When you can replace a tube there for $1, and have no electrical backup, as they often do, it is a reasonable technology. The same is true in Greece and Israel and the middle east where freezing is rare.

[Art VanDelay]

Net Collected Energy?

Mike,

That's good information. Were those numbers net of the energy used to prevent freezing and pumping? Please direct me to the test results if possible.

Of course, if the tank on roof costs 1/3 of the conventional system, it's still worth doing for 1/3 the benefit, and less moving parts. (Your original point is well-taken - that Chinese evac. tube systems may still be inherently less reliable than flat plate)

[MikeSolar]

Mike,

That's good information. Were those numbers net of the energy used to prevent freezing and pumping? Please direct me to the test results if possible.

Of course, if the tank on roof costs 1/3 of the conventional system, it's still worth doing for 1/3 the benefit, and less moving parts. (Your original point is well-taken - that Chinese evac. tube systems may still be inherently less reliable than flat plate)

Those outputs do not include the use of electric trace cables. The govt tested it as they would any other system, on an annual basis but decided to declare the system "3 season" due to the amount of electricity used to keep it from freezing in a normal winter. I will try to find the data for electrical consumption.

[Art VanDelay]

Globe Solar in Toronto

In the 80's, lots of us concluded that heat trace cable wasn't a reliable enough method to prevent pipe freezing.

Globe Solar apparently has put in hundreds of systems, and is still in business. I think that thermosiphoning would be quite a bit more reliable, easier, and cheaper.

http://www.globesolarenergy.com/php_file/product/ip195/system_integrated.php

[MikeSolar]

In the 80's, lots of us concluded that heat trace cable wasn't a reliable enough method to prevent pipe freezing.

Globe Solar apparently has put in hundreds of systems, and is still in business. I think that thermosiphoning would be quite a bit more reliable, easier, and cheaper.

http://www.globesolarenergy.com/php_...integrated.php

yes, I know the people at GlobeSolar and they, like most of us that are primarily in solar hot water, had a hard time after the rebates were taken away. Globe, though, was the company that was hit hardest because the govt, when the rebates were still on and when testing the different systems, declared that 600kwh was not enough annual production to get full rebates. The solar community here doesn't think much of the tank on the roof systems in our climate.

If they are still around it is because of tenacity or a change to PV installs, which most of us also do.