SNMP capable system to monitor current of three cooling systems

I have three 40KW cooling systems and need to monitor their energy use.

Fortunately each one has a single 400v three phase supply feed so I would have thought that a single current clamp on each would suffice for the measurement side.

Preferably I would want the data to be recorded on our Zenoss system which will be able to produce the historical graphs that I am looking for, although any means of recording and presenting the data that will show energy used over the year that can be broken down into daily graphs would be OK.

I would also want to add inlet/outlet temperature and humidity later if possible.

Is the OpenEnergyMonitor suitable for this? does anyone already do anything similar? or any advice?

I appreciate your time reading this.



Robert Wall's picture

Re: SNMP capable system to monitor current of three cooling systems

Basically, yes, the eMon system should be capable of that. If you want to inject the data into your own system, you will need to know the format that it requires. Emoncms can accept integers in csv or JSON but you can generate and send any format that your Zenoss system requires. Zenoss is probably best simply because you know it and the rest of your data is there.

I agree a single current transformer should be adequate, you might or might not need the system voltage, depending on whether you know it already and whether you need to record power and well as current.

The emonTx has 3 (the emonTx shield 4) current and one voltage input,  and a One-wire temperature input that is designed for use with the DS18B20 but is known to work with the DHT22 with a minor resistor change. Unfortunately, the DHT22 is not addressable so only one can be used and cannot be mixed with the DS18B20's.  You can use one or more DHT22s each on a separate input, though that would need a custom hardware extension - either to the emonTx or a custom shield..

So it's possible that one emonTx  + one base (to interface to Ethernet) + a small piece of stripboard,  or an Arduino + emonTx shield + Ethernet shield + custom shield will suit your needs.


scoobie's picture

Re: SNMP capable system to monitor current of three cooling systems


Thanks for the reply :)

From what I have read so far, I had thought that I could achieve what I want with the following -

one off - Pi with image and RFM12Pi as base station

one off - emonTX with 3 current clamps (CT sensors?) , one of which would be connected to a single phase on each of the 3 three phase supplies feeding the AC units.

I understand that measuring only one of the 3 phase wires would not be as accurate as measuring all 3 (requiring 9 CT sensors in total) I believe the current should be almost identical in each leg so should be accurate enough.

However further reading has now got me somewhat confused as I see there are emonTX shield alternatives to the emonTX, plus the emon TX V2, then I have to choose 433 or 868 MHz.

This is worse than ordering my Pizza!

Can I have a recommendation for model and frequency for linking to a Pi in the UK to get me started.




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