Wind is affecting temp sensor for solar heating. What to do?

[bobby1017]

Re: Wind is affecting temp sensor for solar heating. What to

bobby1017 - Are you saying the entire thing is covered in tar??

Almost, there is a 2" dia "gob" of roofing tar on the roof with the sensor "squished" into it, the bottom side is completely imbedded, the topside is exposed to the air. Wind can blow over it but most is protected by the tar.

 

[mas985]

Re: Wind is affecting temp sensor for solar heating. What to

I wouldn't think the tar would have much of an affect at all since it has fairly good thermal conductivity. If it gets hot or cold, that is transfered directly to the sensor.

However, having thermal contact with the roof is like being connected to a huge heat sink. It would tend to average out temperature swings and it would not react as quickly to changes in temperature and incident sun energy. That can be a good thing or a bad thing depending on what you are after. It might delay the solar panels turning on in the morning but it also might extend the time in the evening. It might also leave the panels on when the clouds move over or when the wind picks up. This could be beneficial or maybe not depending on the conditions.

Most solar installations that I have seen, tie wrap the sensor mount to the return pipe but the sensor probe itself is not in direct contact with anything. If you rotate the sensor so it is on the side of the pipe, it tends to sheild the sensor some from wind but not so much that it would leave the panels on when it gets too cool.

 

[bobby1017]

Re: Wind is affecting temp sensor for solar heating. What to

Just a question, if the roof temp was 110 deg but there was a 30 mph wind and a 60 deg air temp, isnt the temp of the roof all that really matters?
I'm no expert but it seems to work good this way, and as mas985 said, tends to average the temp.

 

[mas985]

Re: Wind is affecting temp sensor for solar heating. What to

Just a question, if the roof temp was 110 deg but there was a 30 mph wind and a 60 deg air temp, isnt the temp of the roof all that really matters?

Not entirely. You have to look at the total heat transfer. There is conductive heat from the roof to the panels, there is heat gain from the sun to the panels but there is also heat loss from the panels. It doesn't always net out positive. But I would question if the roof could maintain 110 degrees in 30 MPH 60 degree wind even in the sun.

But one other thing to consider is if the roof is giving off that much heat, it would also heat up the sensor even by radiation. So if there is net heat gain, the sensor should detect that and turn on the solar. If there is net heat loss, then it will not turn on the solar. It should reflect the local conditions of the panels fairly closely. The sensor need only be placed in proximity to the panels and should reflect close to the same net heat transfer as the panels.

 

[bobby1017]

Re: Wind is affecting temp sensor for solar heating. What to

Just a question, if the roof temp was 110 deg but there was a 30 mph wind and a 60 deg air temp, isnt the temp of the roof all that really matters?

But I would question if the roof could maintain 110 degrees in 30 MPH 60 degree wind even in the sun.

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Yea, I was just making something up to try to understand better, thanks.

 

[Pool Clown]

Re: Wind is affecting temp sensor for solar heating. What to

Thanks for the replies. Pool Clown - do you poke any holes in the cup or just use it as is??

Just use it as is. keep the bottom open, so air can circulate thru it.

 

[rcy]

Re: Wind is affecting temp sensor for solar heating. What to

I don't know much about these systems either, except to say that mine works really well. The installer had 30 years in the solar industry at the time of the install, and has recently installed the largest system in Canada, consisting of 90 4x12 panels. I do know, mine is set to come on with a 3 degree differential.