Evacuated Tube Collecter doesn't Heat Up ??

[ballyboing]

Hi All. great forum. This might sound ridiculous but i've just got an evacuated tube solar collector and it's not heating up ??!! although i've a built a solar heater with a few radiators and glass frontage I'm fairly new to all this evacuated tube stuff so maybe there is something obvious i'm doing wrong? its been 25C here the last 2 days and the tubes are cool to the touch after all day in the sun. the out and in pipes are also not very warm.Due to not having constant electricity here I'm doing the set up by convection i.e. The Panel is on the ground with the Hot water cylinder above it. any ideas would be very appreciated. Thanks All

[cssolar]

Hi,

It seem strange your vacuum tube system is not working,

It is normal for the exterior of the tubes to be cold to touch as the vacuum is a great insulator, but the heat pipe or water in the tube should heat up well, as long as there is plenty of sunshine.

Is the unit a compact type ( tubes fitting directly into the tank as one unit ) ?

Tony cssolar Spain

[ballyboing]

Hi tony. thanks for the reply. its the non compact (?) type. i.e. pipes coming from the collector and rising to the cylinder. i did think the tubes should get hot but what you say about the vacum makes a lot of sense so i've had another feel of the pipes themselves and they're just warm to touch.

[cssolar]

Hi Ballyboing,

Do the tubes have water in them or are they dry heat pipe type.?

did you make your own manifold?

Regards Tony

[ballyboing]

hi. they are the dry type i.e. they are glass tubes with metal down the middle that when it heats up they then warm an element that contains water across the top of the collector which then feeds the coil in the cylinder. is the manifold the bit across the top?- if so it was all part of the same collector and not made by me.cheers

[Art VanDelay]

Check the brand name

hi. they are the dry type i.e. they are glass tubes with metal down the middle that when it heats up they then warm an element that contains water across the top of the collector which then feeds the coil in the cylinder. is the manifold the bit across the top?- if so it was all part of the same collector and not made by me.cheers

Older Apricus collectors have a very high rate of heat pipe failure.

All the heat pipes should be well-seated into the manifold at the top. Thermal grease is usually used on the condensing bulb where it seats into the manifold. Most heat pipes won't work if they are laying down close to flat, or if they are tilted up to a vertical position. 85 degrees is considered the maximum tilt angle.

[russ]

Most heat pipes won't work if they are laying down close to flat, or if they are tilted up to a vertical position. 85 degrees is considered the maximum tilt angle.

The object being that they fluid/vapor inside the tube has to vaporize in the lower section and condense in the section in the header at the top. The reflux action is what makes a heat pipe work.

[LucMan]

The headers on most evacuated tube arrays are not conducive to convection or thermosyphon, you may not have any circulation from the header to the tank.
How hot are the inlet and out let connections on the manifold?

[cssolar]

Hi,

I think you may need a circulation pump, the units I have are direct plug type units and and the water circulates from tube to tank easily,

because your collector and tank are seperate the water may to be forced around.

Regards Tony

[Art VanDelay]

Most of these manifolds work well by Convection

We call it a thermosyphon. The manifold should be tilted slightly, with the cold inlet on the low side. The hot outlet should feed the top of the tank.

In this video, there is about 10 feet total of 3/4" piping in the collector loop.

The 50 gallon tank will boil in three days with no load.

The collector flowrate is about 1/4-1/2 gallon per minute when the sun is shining.

If your tank is completely above the collector, that's even better.

http://www.youtube.com/watch?v=Q5rKLsJl3cY

[ballyboing]

hi there and thanks for all the replys. sorry i didn't get around to looking at the thread earlier but i've been away for a few months now-gotta chase that work!
Art Van- thats 2 really good bits of information. your set up is very similar to mine-except my tank is also outside and my panel is lying at about 35degrees-maybe a bit too flat? when i get back i'm looking forward to changing the angle and hoping that works.

[MikeSolar]

We call it a thermosyphon. The manifold should be tilted slightly, with the cold inlet on the low side. The hot outlet should feed the top of the tank.

In this video, there is about 10 feet total of 3/4" piping in the collector loop.

The 50 gallon tank will boil in three days with no load.

The collector flowrate is about 1/4-1/2 gallon per minute when the sun is shining.

If your tank is completely above the collector, that's even better.

http://www.youtube.com/watch?v=Q5rKLsJl3cY

Ohhh man, un-insulated tubing going through a brick wall, PEX won't last, insulation may melt, it needs to be closed cell. The piping should be copper or stainless. Pressure relief will work for some unknown number of cycles before it starts to drip. They are not made for repeated use but as last ditch effort to keep a tank from going BOOM. he needs, at least, a domestic expansion tank.

[Art VanDelay]

Yep

Ohhh man, un-insulated tubing going through a brick wall, PEX won't last, insulation may melt, it needs to be closed cell. The piping should be copper or stainless. Pressure relief will work for some unknown number of cycles before it starts to drip. They are not made for repeated use but as last ditch effort to keep a tank from going BOOM. he needs, at least, a domestic expansion tank.

Mike,

You're right on all counts. PEX shouldn't be used in any closed collector loop. Hi temp/press. rubber or silicone or teflon hose would be freeze tolerant and stagnation tolerant.

This was a demostration system for proof of concept. A "split direct thermosyphon system for cold climates". The main concept I was testing was reverse thermosiphoning for freeze protection. With a short collector loop using 3/4" tubing or hose, it won't freeze down to -15F in Denver. And it doesn't lose more than 15% of it's daily collection to self freeze protect in the dead of winter.

[ballyboing]

Sounds about right, its very rare we have freezing temp in Ireland too. Do you think that increasing the angle will help in my situation?

[inetdog]

Sounds about right, its very rare we have freezing temp in Ireland too. Do you think that increasing the angle will help in my situation?

If the manifold itself is not getting hot, then changing the panel angle or the manifold angle is not going to to help. ]

Possibly the tubes are all bad or are not attached properly to the manifold. If you can borrow an infrared non-contact thermometer you can check the top and bottom temperatures of the inner collector tube. The temps should be high and almost identical between top and bottom?

If the inner tube is hot at the top and the manifold it not, then the thermal connection between the tubes and the manifold is bad.