Wireless communication from multiple temperature sensors - Interested?

[Julian Jameson]

I recently built a low voltage circuit that enables Bluetooth transmission of data from five wired temperature sensors. This sensors can be installed into your solar heater(s) and the device transmits all the temperature data via Bluetooth (sending human-friendly data every second).

My questions are: Would you be interested in such a product? And if so, what sort of features would you expect?

With this device, you can log all data by connecting a Bluetooth enabled laptop, PC or Mac.

We also have an Android app available for download, where you can see the temperatures in real-time.

Here's the board, enclosure and sensors (in it's current state):

IMG_20140907_201714 small.jpg

Power connector is USB.
Two of the sensors are connected by 9' wire lengths.
Another two sensors are connected by 4' wire lengths.
The fifth sensor is mounted on the circuit board and monitors the ambient temperature.

[J.P.M.]

I recently built a low voltage circuit that enables Bluetooth transmission of data from five wired temperature sensors. This sensors can be installed into your solar heater(s) and the device transmits all the temperature data via Bluetooth (sending human-friendly data every second).

My questions are: Would you be interested in such a product? And if so, what sort of features would you expect?

With this device, you can log all data by connecting a Bluetooth enabled laptop, PC or Mac.

We also have an Android app available for download, where you can see the temperatures in real-time.

Here's the board, enclosure and sensors (in it's current state):

[ATTACH=CONFIG]4795[/ATTACH]

Power connector is USB.
Two of the sensors are connected by 9' wire lengths.
Another two sensors are connected by 4' wire lengths.
The fifth sensor is mounted on the circuit board and monitors the ambient temperature.

FWIW, I currently measure 16 panel temps from under the array in 3 to 5 places each with an infrared thermometer at the min. solar incidence angle every 10 days, PITA, but I don't think there's a big market for that sort of thing just now unless the # of solar whackos increases.

Best feature : FREE. If so, holler back.
Besides, sounds like you're trolling for business.

[Julian Jameson]

Not trolling for business (at least, not yet!). This is more about a solar air heating enthusiast designing a product for similar people, based on mutual design requirements.

The device is really intended to monitor inlet, outlet, room temperature and ambient temperature values. However, the sensors could be placed wherever you want inside solar collectors. Also, multiple units can be connected concurrently to the Android app, so monitoring five, ten, fifteen or twenty+ sensors in real-time is possible (as well as logging and graphing that data).

BTW, I'm intrigued about the infrared thermometer measurements you're recording. Are you measuring through IR invisible surfaces or measuring the surface temperatures of the array casings? I have quite a bit of experience with thermography and understand that with all glazing types, any IR measurements will be surface temperature + any IR reflected onto that surface from the camera side. With regard to any casing that is not IR invisible (e.g. extremely thin plastics), the reading will likely be the surface temperature, possible skewed be reflexivity of that surface.

FWIW, I currently measure 16 panel temps from under the array in 3 to 5 places each with an infrared thermometer at the min. solar incidence angle every 10 days, PITA, but I don't think there's a big market for that sort of thing just now unless the # of solar whackos increases.

Best feature : FREE. If so, holler back.
Besides, sounds like you're trolling for business.

[SunEagle]

Not trolling for business (at least, not yet!). This is more about a solar air heating enthusiast designing a product for similar people, based on mutual design requirements.

The device is really intended to monitor inlet, outlet, room temperature and ambient temperature values. However, the sensors could be placed wherever you want inside solar collectors. Also, multiple units can be connected concurrently to the Android app, so monitoring five, ten, fifteen or twenty+ sensors in real-time is possible (as well as logging and graphing that data).

BTW, I'm intrigued about the infrared thermometer measurements you're recording. Are you measuring through IR invisible surfaces or measuring the surface temperatures of the array casings? I have quite a bit of experience with thermography and understand that with all glazing types, any IR measurements will be surface temperature + any IR reflected onto that surface from the camera side. With regard to any casing that is not IR invisible (e.g. extremely thin plastics), the reading will likely be the surface temperature, possible skewed be reflexivity of that surface.

Your explanation on using IR cameras is correct. If you point it at an object with a low emissivity or high reflectivity (like metal) you are getting a false reading. Better to have a target like electricians tape or cable insulation which have emissivity above 0.95.

I had a Level One classification in Thermography a while back but let it lapse. An IR camera is a very good tool to identify issues before they become breakdowns.

[SunEagle]

FWIW, I currently measure 16 panel temps from under the array in 3 to 5 places each with an infrared thermometer at the min. solar incidence angle every 10 days, PITA, but I don't think there's a big market for that sort of thing just now unless the # of solar whackos increases.

Best feature : FREE. If so, holler back.
Besides, sounds like you're trolling for business.

You take those temp readings every 10 days. Yeah I would call that a PITA.

Having a fixed temperature measuring device that sends real time data remotely to a computer would be a nice tool for many industries. Although something like that for the Solar PV industry would probably not be high on demand.

[russ]

I recently built a low voltage circuit that enables Bluetooth transmission of data from five wired temperature sensors. This sensors can be installed into your solar heater(s) and the device transmits all the temperature data via Bluetooth (sending human-friendly data every second).

My questions are: Would you be interested in such a product? And if so, what sort of features would you expect?

With this device, you can log all data by connecting a Bluetooth enabled laptop, PC or Mac.

We also have an Android app available for download, where you can see the temperatures in real-time.

Here's the board, enclosure and sensors (in it's current state):

[ATTACH=CONFIG]4795[/ATTACH]

Power connector is USB.
Two of the sensors are connected by 9' wire lengths.
Another two sensors are connected by 4' wire lengths.
The fifth sensor is mounted on the circuit board and monitors the ambient temperature.

Look at www.rfxcom.com they and others market this stuff now.

[Julian Jameson]

Thanks Russ.

Interesting technology but at first glance, appears quite expensive!

Look at www.rfxcom.com they and others market this stuff now.

[J.P.M.]

You take those temp readings every 10 days. Yeah I would call that a PITA.

Having a fixed temperature measuring device that sends real time data remotely to a computer would be a nice tool for many industries. Although something like that for the Solar PV industry would probably not be high on demand.

A labor of love. Takes about 8 min./ series. Start 12 min. before min. incidence angle, read/record monitor data, start 2d round of readings 4 min. later and finish 8 min. after that. Hopefully, temps. are symmetric around min. incid.. angle time. All needed for ongoing est. of panel fouling as f(time) - every 10 days til it rains and probably thereafter. Lots of interesting stuff along the way. So far ave. measured temps seem to agree +/- 2 F. or so with an algor. I conjured up. ( FWIW, depending on wind vector panel temps. about 44-48 F. higher than roof amb. which runs about 5-10F or so above ground level amb. Also, working on est. for wind heat trans. coeff.

[inetdog]

It sounds like someone should give you a research grant.

[SunEagle]

A labor of love. Takes about 8 min./ series. Start 12 min. before min. incidence angle, read/record monitor data, start 2d round of readings 4 min. later and finish 8 min. after that. Hopefully, temps. are symmetric around min. incid.. angle time. All needed for ongoing est. of panel fouling as f(time) - every 10 days til it rains and probably thereafter. Lots of interesting stuff along the way. So far ave. measured temps seem to agree +/- 2 F. or so with an algor. I conjured up. ( FWIW, depending on wind vector panel temps. about 44-48 F. higher than roof amb. which runs about 5-10F or so above ground level amb. Also, working on est. for wind heat trans. coeff.

I'm impressed. I wouldn't have thought the panels would be that much hotter than the roof but I guess since they get the sunlight and the roof is in the shade it would be at a lower temp.

[Mike90250]

re the Bluetooth radio, is this the short range (10ft) or the longer range (40ft) ? Have you looked into zigbee radio (but that does not work with 90% cell phones?

[SunEagle]

re the Bluetooth radio, is this the short range (10ft) or the longer range (40ft) ? Have you looked into zigbee radio (but that does not work with 90% cell phones?

Even if it is the short range Bluetooth you can use a booster to get the data to your wireless router. Once it is on the web then you just need the app to access it.

Getting live temperature readings is useful data for different applications but how the "sensor" (thermocouple, RTD, etc.) is collecting the data is real important to the material it is attached to.

A surface temperature measuring device has a number of efficiency issues due to compatibility of the sensor material and what it is attached to.

An IR camera (not one of those little gun type that you just point and get a temperature reading) is a much better way of collecting real accurate temperature data as long as you have set up the camera for the correct material emissivity, the target is larger than the sensing "cone" area and it has a good "focus" of the target.

While IR cameras were very expensive 5 to 10 years ago ($5k to $35k) they have now come way down in price to to below $1000 for a basic model. There are even miniature IR cameras used in the RC model industry that provide very good pictures even at night.

[J.P.M.]

I'm impressed. I wouldn't have thought the panels would be that much hotter than the roof but I guess since they get the sunlight and the roof is in the shade it would be at a lower temp.

It's not an exact science - or much science at all really. Being retired with more time than money and more money than brains affords me the opp. to buy things I've done without for 30 or so yrs. like a dedicated weather station and pyranometer 4 ft. from the array and some other stuff and fart around to my heart's content.

The temp. readings get confirmed, if it can be called that, by doing an energy/heat bal. on the array. The eff. rad. sky temp. come from several empirical correlations from solar and meteorological journals and other open lit. stuff as well as some other methods I worked out. The view factors for solar reflectance and IR to/from the surroundings come from radiation heat transfer. The roof temps. under the array and the exposed roof are also measured w/the IR thermometer which is adjustable for surface emissivity (I'm a bit dubious about that accuracy, but so far the numbers seem to make some sense). The biggest unknown is the convection heat transfer and particularly the effects of the wind vector and its variability. So far, that seems to agree pretty well with a fairly large body of published stuff of varying applicability and accuracy on that sub aspect of convective heat transfer. Anyone who's done a lit. search probably knows what I'm talking about.

The 44 - 48F. above roof amb. for the array temp. I mentioned is about as high as it gets under "full" sun with low wind velocity, but under those conditions it's not that uncommon. It's a ballpark # for a sunny day.

I'd like to get a piece of the Sunpower glazing by itself and see if I can figure out if their magic anti reflectance coating affects glass emissivity in the IR region. So far my guess is that it does not, or at least not to the degree that my meager attempts can detect.

The array has about 10+" of clearance under it allowing me to get under it in a snug but still safe (?) way for measurements. FWIW, the array top (sky facing) temps. are usually a couple of deg. F cooler than underneath the array under full sun. I would have thought different. It may have something to do with better convection/rad. heat transfer on top. Another blast of the obvious: the array temp. variation follows the wind direction with array temps. being lower upwind and increasing by about 2F. to about 6F. downwind along the way, depending on wind vector and variability. That seems to correlate quite well with the 10 min. ave. wind direction as recorded by the weather station - a Davis Inst. Pro 2 Plus.

[SunEagle]

It's not an exact science - or much science at all really. Being retired with more time than money and more money than brains affords me the opp. to buy things I've done without for 30 or so yrs. like a dedicated weather station and pyranometer 4 ft. from the array and some other stuff and fart around to my heart's content.

The temp. readings get confirmed, if it can be called that, by doing an energy/heat bal. on the array. The eff. rad. sky temp. come from several empirical correlations from solar and meteorological journals and other open lit. stuff as well as some other methods I worked out. The view factors for solar reflectance and IR to/from the surroundings come from radiation heat transfer. The roof temps. under the array and the exposed roof are also measured w/the IR thermometer which is adjustable for surface emissivity (I'm a bit dubious about that accuracy, but so far the numbers seem to make some sense). The biggest unknown is the convection heat transfer and particularly the effects of the wind vector and its variability. So far, that seems to agree pretty well with a fairly large body of published stuff of varying applicability and accuracy on that sub aspect of convective heat transfer. Anyone who's done a lit. search probably knows what I'm talking about.

The 44 - 48F. above roof amb. for the array temp. I mentioned is about as high as it gets under "full" sun with low wind velocity, but under those conditions it's not that uncommon. It's a ballpark # for a sunny day.

I'd like to get a piece of the Sunpower glazing by itself and see if I can figure out if their magic anti reflectance coating affects glass emissivity in the IR region. So far my guess is that it does not, or at least not to the degree that my meager attempts can detect.

The array has about 10+" of clearance under it allowing me to get under it in a snug but still safe (?) way for measurements. FWIW, the array top (sky facing) temps. are usually a couple of deg. F cooler than underneath the array under full sun. I would have thought different. It may have something to do with better convection/rad. heat transfer on top. Another blast of the obvious: the array temp. variation follows the wind direction with array temps. being lower upwind and increasing by about 2F. to about 6F. downwind along the way, depending on wind vector and variability. That seems to correlate quite well with the 10 min. ave. wind direction as recorded by the weather station - a Davis Inst. Pro 2 Plus.

Yep. Wind velocity and air moisture content can both affect material temperatures and IR readings. You just have to be aware of the environment to understand how it affects your temperature data.

As for a 10" crawlspace under the panels as being "safe".. that is where I would be looking for a more permanent temperature measuring device. But if you got the time then go for it. Just be safe doing it.

[J.P.M.]

It sounds like someone should give you a research grant.

No thanks. Been there, done that in a prior iteration of life. I work alone and do what I want - not what someone else thinks I ought to be doing.

Besides, paraphrasing a famous scientist, it takes time if I'm going to find out not only what nature is telling me, but more importantly what nature is whispering. People holding purse strings are not known for having a lot of patience for such pastimes. Screwum.

For me, the race is over, the rats lost. I now get to bloviate, pretty much with impunity in places like this forum, and regale a few folks with salient wit/wisdom/mental spoor.