Adding monitoring to existing solar thermal system

[J.P.M.]

Heat exchanger loop
Delivery of preheated water to the water heater
Cold usage of the home

Whatever. All of the above? If were easy to clamp a sensor to a pipe for flow, and I know it's not, why not measure everything?

I've designed and owned several residential solar thermal systems since 1975 or so. For direct systems I've used 4 sensors: One each at the array's inlet and outlet, and one each at the storage inlet and outlet.
If 4 seems like overkill, then there's a lot more to solar thermal or system monitoring than you may know.

For indirect systems, I've placed 2 additional sensors at the HX collector side (hot) inlet and outlet. For either type system, a way to measure flowrates is needed. Can't be done without it.
Direct systems use one rotometer for the flow to/from storage. Indirect systems need two rotometers to measure flowrates in/out of each side of the HX, or just one if it's an in tank HX.

I've always found attaching temp. sensors to a line is a cakewalk. The trick is to know where to attach it, making good thermal contact between sensor and pipe (use thermal grease), and equally or maybe even more importantly, making sure the insulation around the sensor between sensor and the ambient environment is robust and substantial while still enabling sensor checking/servicing.

[brycenesbitt]

Are you talking about for the solar loop or for household water?

Heat exchanger loop
Delivery of preheated water to the water heater
Cold usage of the home

Whatever. All of the above? If were easy to clamp a sensor to a pipe for flow, and I know it's not, why not measure everything?

[Stringpark]

I'd love to be able to understand flow as well.
Anyone have a suggestion for a 3/4 copper flowmeter, easy to monitor and count electronically?

Are you talking about for the solar loop or for household water?

[brycenesbitt]

I'd love to be able to understand flow as well.
Anyone have a suggestion for a 3/4 copper flowmeter, easy to monitor and count electronically?

[Stringpark]

brycenesbitt thx again for the suggestion! I didn't think about measuring the voltage from the controller through the sensor, I just had resistance on the brain. Anyway, turns out measuring the voltage was a perfect job for a particle photon that I had laying around, as the voltages are less than 3.3v (usually never gets over 2v). For those that may read this in the future and are bad at math like me, I used a trendline in an excel scatter chart to get the formula for converting the analog values reported by the photon over to temperature values. In my case the linear trendline seemed to fit the datapoints reasonably well (obviously the sample points were recorded by manual observation).
Correlating Datasets.PNG
So now I'm sending the temperature values to home assistant over MQTT and charting in Grafana. It's working great!

The last thing to do is to try to figure out what the SOM 7 controller is doing to calculate kWh. The manual says that it incorporates the temperature readings from the supply and return lines along with the flow rate (and I know it also asks for the glycol mixture ratio as well) to come up with kWh. Just by comparing to a simple calculation based on the on the temperature rise of the water stored in the tank (while no one is using hot water), it seems that the calc rendered by the SOM 7 is reasonable, so I'd love to be able to reproduce it.

[Stringpark]

Awesome, I’ll give it a go! Thx!

[brycenesbitt]

Anybody know if you can share the same PT1000 sensors with two devices (like my existing SOM 7 controller and maybe an arduino or something)?

If you keep the leads reasonably short, you can. Those are just variable resistor sensors.
Thus, the voltage at the leads on the SOM 7 will have a relationship to the temperature, which can be looked up in a table.

A raspberry Pi with an analog sensor would be super easy to program for remote viewing of data and data logging

https://learn.adafruit.com/reading-a-analog-in-and-controlling-audio-volume-with-the-raspberry-pi

[Stringpark]

So the system I'm working on uses a Stiebel Eltron SOM 7 SI controller that unfortunately doesn't include the VBUS option. Even if it did, I think I'd still need another datalogger unit (that is crazy expensive) to be able to get data to the internet. So, I'm looking for advise on the best way to add remote monitoring. Anybody know if you can share the same PT1000 sensors with two devices (like my existing SOM 7 controller and maybe an arduino or something)?