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

[dsiomtw]

So we recently added solar to help heat our pool. On windy days I notice that the solar heating turns off and on quite a bit, and the pool doesn't get as warm as it should.

I know the solar will only run if the temperature up on the roof is at least 10 degrees warmer than the pool, so I assume there's a temp sensor up on the roof somewhere and the wind is causing it to read cooler than it is, thus shutting off the solar.

Seems like this would be a common issue that the installers would do something about. I am thinking of giving them a call, but I was wondering if there might be an easy fix. I was thinking along the lines of a clear plastic cup secured over the temperature sensor or something similar. It seems like that would block the wind and still allow accurate temp readings ...

 

[Richard320]

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

Sounds like it's worth a try!

I'd cut a hole in the top, so heat doesn't get trapped and throw it off the other way, but still blocks the breeze.

 

[Pool Clown]

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

Liquid Tide comes with a little clear plastic cup used to measure the soap. It works good but i have to replace it about once a summer as the sun breaks down the plastic.

 

[dsiomtw]

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??

 

[JohnT]

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

I think your sensor is working like it's supposed to. Pool solar has problems working in wind because the wind removes the heat from the panels. They just don't work on windy days.

The normal way to install the roof sensor is to mount it on a small section of panel so if that little panel section isn't warm, the panels probably aren't warm. Leave it alone. The sensor isn't really there to measure the temperature, but to determine how much heat energy is available in the panels.

 

[Dr_Obbins]

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

Leaving a temp sensor out in the open affects the readings in many ways. If the sun is shining on it, you will get a higher reading. The wind may cool it down to a more accurate reading. Here is a thread showing how us weather geeks protect out temp sensors. http://www.weather-watch.com/smf/index.php?topic=23736.0 It might be a little much for your application, but you get the idea.

 

[Soupy]

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

I would think that enough wind would turn the solar panel into a giant radiator that would cool the pool, rather than heat it. Probably depends on the air temp, water temp, sun, and wind.

 

[mas985]

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

I would think that enough wind would turn the solar panel into a giant radiator that would cool the pool, rather than heat it. Probably depends on the air temp, water temp, sun, and wind.

+1

If the wind is pulling heat away from the sensor, then it will probably pull heat away from the panels as well. During one of these windy days when the controller shuts off the solar, manually turn on the panels and measure the exit water temperature and see if you are getting any heat gain.

 

[dsiomtw]

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

Thanks for all the replies. Today was only mildly windy and the solar turned off and on at least 15 times in an 8 hour period. Just doesn't seem right. If nothing else I assume this is murder on my pumps, valves, etc. and will drastically reduce their lifespan...

 

[JohnT]

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

Leaving a temp sensor out in the open affects the readings in many ways. If the sun is shining on it, you will get a higher reading. The wind may cool it down to a more accurate reading. Here is a thread showing how us weather geeks protect out temp sensors. http://www.weather-watch.com/smf/index.php?topic=23736.0 It might be a little much for your application, but you get the idea.

Protecting a temperature sensor from those effects is one thing, but the sensor on a solar system is measuring available heat, not air temperature. Available heat is determined by measuring the temperature of a piece of material that is exposed to the cooling effect of the wind and heating effect of the sun. Available heat is affected by clouds and wind, which don't affect temperature as directly as they do the available heat.

 

[yeggim]

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

Can you adjust that 10 degree setting? Seems like a 4 degree setting would be more efficient. If the ambient air temp is higher than the water temp it doesn't matter how hard the wind is blowing. There will always be a net heat gain from the panels in that situation; even at night. If that 10 degree setting is not adjustable, I'd run the panels in manual as long as the air temp was higher than the water temp.

The beauty of an automated system comes into play early in the morning/season and later in the day/season. The air and water temp are usually close to each other (early season) or the water temp is higher than the ambient air (late season) temp. It allows you to scavenge those BTU's from sunlight without losing anything when it's too early or late in the day or gets cloudy and the solar radiation is not enough for a heat gain. I'm no expert but I'd want to extract every free BTU available no matter how small.

 

[JohnT]

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

Can you adjust that 10 degree setting? Seems like a 4 degree setting would be more efficient. If the ambient air temp is higher than the water temp it doesn't matter how hard the wind is blowing. There will always be a net heat gain from the panels in that situation; even at night. If that 10 degree setting is not adjustable, I'd run the panels in manual as long as the air temp was higher than the water temp.

The beauty of an automated system comes into play early in the morning/season and later in the day/season. The air and water temp are usually close to each other (early season) or the water temp is higher than the ambient air (late season) temp. It allows you to scavenge those BTU's from sunlight without losing anything when it's too early or late in the day or gets cloudy and the solar radiation is not enough for a heat gain. I'm no expert but I'd want to extract every free BTU available no matter how small.

At night, you have radiation losing heat even when the air is warmer. Unless the panels are in direct or nearly direct sunlight, the potential heat gain is far less than the energy expended by the pump to get it.

 

[dsiomtw]

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

I'm in So Cal so the temp of the air is pretty much always less than the pool. What I need to be concerned with is available heat, as JohnT points out. I don't understand the physics of it all, but I would assume there is "available heat" on a hot sunny So Cal day, even when the wind blows a little. Even when it's only 75 degrees out the sun is hot as heck. With the way my system is setup though it doesn't seem to agree. Any meaningful amount of wind shuts down the solar. Fortunately it's rarely windy.

 

[JohnT]

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

I'm in So Cal so the temp of the air is pretty much always less than the pool. What I need to be concerned with is available heat, as JohnT points out. I don't understand the physics of it all, but I would assume there is "available heat" on a hot sunny So Cal day, even when the wind blows a little. Even when it's only 75 degrees out the sun is hot as heck. With the way my system is setup though it doesn't seem to agree. Any meaningful amount of wind shuts down the solar. Fortunately it's rarely windy.

It may be that the trip points on your controller are set too tight. If it didn't turn on as soon as it it did, it might not do so much on and off cycling.

 

[yeggim]

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

Can you adjust that 10 degree setting? Seems like a 4 degree setting would be more efficient. If the ambient air temp is higher than the water temp it doesn't matter how hard the wind is blowing. There will always be a net heat gain from the panels in that situation; even at night. If that 10 degree setting is not adjustable, I'd run the panels in manual as long as the air temp was higher than the water temp.

The beauty of an automated system comes into play early in the morning/season and later in the day/season. The air and water temp are usually close to each other (early season) or the water temp is higher than the ambient air (late season) temp. It allows you to scavenge those BTU's from sunlight without losing anything when it's too early or late in the day or gets cloudy and the solar radiation is not enough for a heat gain. I'm no expert but I'd want to extract every free BTU available no matter how small.

At night, you have radiation losing heat even when the air is warmer. Unless the panels are in direct or nearly direct sunlight, the potential heat gain is far less than the energy expended by the pump to get it.

Economics aside, if the air temp is higher than the water temp any heat loss is lost from the panel to water. As the water and air temp get close to each other the heat transfer will of course be minimal but the second law will always be that the cooler object becomes hotter and the hotter object becomes cooler. I wasn't advocating running at night. Right now my water temp is 76 and the air temp is 82. It's overcast and 4 hours 20 minutes past solar noon. Since I have to run my filter anyway I have it running through my solar panels. I have a single speed pump so it's a no-brainer for me. I figure no matter how small the gain, it's like BTUs in the bank due to the heat sink properties of a pool.

I see that the OP has weighed in and his air temps are usually lower then the pool temp. Still, on a sunny day in the mid 70's there should be some heat gain during solar prime time and the solar should be on the whole time till it hits his desired temps.

 

[yeggim]

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

I'm in So Cal so the temp of the air is pretty much always less than the pool. What I need to be concerned with is available heat, as JohnT points out. I don't understand the physics of it all, but I would assume there is "available heat" on a hot sunny So Cal day, even when the wind blows a little. Even when it's only 75 degrees out the sun is hot as heck. With the way my system is setup though it doesn't seem to agree. Any meaningful amount of wind shuts down the solar. Fortunately it's rarely windy.

I think it's not so much the wind as that 10 degree differential setting. The reason I think a 4 degree setting is better is because most consumer grade sensors are usually plus or minus 2 degrees. So if your water sensor is reading two degrees cooler than actual and your solar sensor 2 degrees warmer than actual, it would be a wash when your water temp set point is close to the panel temp.

What model is your controller? The more I think about, unless your water temp is 85 degrees or higher I can't imagine your solar cycling that much in full California sun even with that 10 degree on setting. Are you sure of your settings? What exactly can you configure on your setup? What's your water temp now?

 

[dsiomtw]

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

The installers said it's a 10 degree differential. I didn't ask at the time but we have some fancy new controller so I'm positive it's adjustable - I'm just not too familiar with this stuff yet.

And yeah - the water is really warm. With the system we have the water can hit 90 when it's only 75 out. The sun is really strong here and our panels are in a good spot. I've been experimenting with different temps ... the kids like it really warm so right now the pool is set at 88. I figure why not - that's what we got the thing for. This way it starts out warmer in the morning and gets up to a good temp quicker the next day, etc.

Reducing the temp differential seems like it would help, but these guys have been installing solar systems for 35 years so I figure they know what they're doing. I'm waiting for a call back to see what they say.

I have a feeling they will say a 4 degree differential is too little. That will cause the pumps to run full speed when very little heat is available i.e. a waste of energy. I'm just guessing that's what they'll say.

Remember we're not just measuring air temp here. The reading up on the roof can be 100-120 when it's only 75 degrees out. A 4 degree differential would cause the system to run almost nonstop I imagine.

 

[bobby1017]

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

My temp sensor is affixed right to the roof surface with a gob of roofing "tar", no wind can blow around it. My solar panels turn on when the roof temp is 6 deg warmer than the pool water and will shutoff when the surface is 3 deg warmer than the water. From what I've seen they turn on and off once a day. We've had full sun after the fog burns off, it's never got cool enough for them to turn off untill the sun is off the panels.

 

[dsiomtw]

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

bobby1017 - not sure what you're saying about how your sensor is mounted but I'm real curious. If it's just stuck to the roof with some tar, what do you mean by "no wind can blow around it" ? What is keeping wind from blowing across it? Are you saying the entire thing is covered in tar??

 

[yeggim]

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

Here's an excerpt from a manual for a Goldline controller.

In the “AUTO” position, the GL-235 will heat the pool or spa (rotate valve to solar loop) when
the collector (solar) sensor temperature is higher than the pool/spa sensor temperature by 4ºF or
more AND the pool/spa temperature is less than the high limit setting. The GL-235 will stop heating
(return valve to pool loop) when the two sensor temperatures get to within 1.5ºF OR the pool/spa
sensor is above the high limit setting.