Solar Heat Collection Tubes and Wind

[grow]

I have an odd question for you all. Has anyone come across any evidence of solar heat collection tubes getting warm when they vibrate in high wind?

We have a solar water heating system on the roof with a pump and closed loop type system with a coil retro-fitted to our existing hot-water tank.

Here in Derry we had gale-force icy winds overnight. I got up this morning when it was still dark, expecting the controller for our solar panel to be showing an upper sensor temperature of around 0°C but it was reporting 24°C. I walk past the controller every morning. I tend to think of it as a way to check on the weather outside and this is the first time I have noticed an effect like this.

I'll be keeping an eye on the temperature each morning to see if it happens again.

Sometimes the controller gets confused by temperature anomalies and keeps the pump on when it shouldn't but I am sure that is not what happened in this case - I would have heard the pump.

So I am left wondering is there some odd effect where high winds across the tubes can somehow cause them to heat up?

Has anyone come across such a thing?

Thanks

George

[caveman]

George,
We are in the west and get very strong winds. I was worried about wind loading and noise so I kept an eye on these issues for the first winter. There were no problems. I have never noticed any increase in temperature in high winds and if I had I would have been puzzled also.
Does your controller have a frost protection setting and if so could wind chill have caused it to run the pump briefly? The level of insulation in those manifolds is so high that a dose of hot water pumped up there would stay hot for a very long time.
I am keen to hear what Cye has to say about this.

[grow]

Ok It happened again last night. So now I don't think it had anything to do with wind!

When I checked the temperatures this morning the roof sensor was again reporting a temperature close to that at the bottom of the tank. I think it was 21°C when the outside temperature was about 2°C.

So now I think it must be some sort of convection effect. But why would this start to become noticable now after three years of normal behaviour.

The puzzling thing is that now at 10:30pm - dark since 5:30pm - the roof sensor is reading 8°C while the bottom of the tank is 24°C. That is about normal.

The only thing that is different recently is that we have had the central heating on more and it heats the water right to the bottom of the tank. I am sure that I did not notice this last winter when we had the heating on.

[cye]

hi George,

if you have a non return valve, perhaps it has stuck in the open position, thereby allowing reverse thermosyphoning at night? Colin Lloyd had a NRV seize on him after <2 years, though in his case it was in the closed or near closed position.

if the NRV is failing to close fully, it is conceivable that a night-time reverse syphon effect could kick off when there is enough of a temperature gradient, either caused by a good warm tank, very rapidly cooled pipework in the loft, or a combination of both factors. hot water would then rise to the panel, with the colder water falling back towards the tank. once a syphon gets going it doesn't take much to keep it going.

if you don't have a NRV, or if you do but it is fine and is a low resistance type of NRV, a newly observed syphon effect could be caused by degraded insulation, i.e., solar loop pipe insulation and also possibly manifold insulation if water has managed to get into the manifold housing. the insulation in most manifolds will be rockwool which will act like a sponge given the opportunity, though some manifolds use expanded polyiso or polyurethane foam which can still hold a little water as 5% of the cells are open.

how to prove the theory? if you have a gate valve in your solar loop then close it off at night. otherwise perhaps fit a few thermometers at various points on the pipework and study the behaviour when the pump is not running?

if you have a NRV, perhaps tapping it with a spanner/ hammer may free it?


hope this helps

cye

[caveman]

I can add my name to the list. I had a solar rated auto air bleed valve fail on my system. It was less than 2 years old. I think the solar loop temps. are so high that some of the materials just can't take it for very long. I would take a look at that NRV and give it a wee tap with a hammer. Another thought, is that NRV a flap type valve rather than the spring loaded type? If so is the orientation ok?
rgds
c