I want to use one emonTX (running the single phase sketch), four CT’s and an AC adapter to monitor:
• A THREE phase Air Source Heat Pump (ASHP) approx 7 kW
• A SINGLE phase Water Circulation pump approx 1.1 kW
By monitor I mean to record the real power consumed and at what time.
This data will then be compared with power exported during the day (house & outbuildings are connected to a 30 kWp solar PV array).
From an answer to an earlier forum question, I understand that if I change realPower to apparentPower in the sketch and correct the two non AC adapter phases (multiply by -0.5) then I’ll have an approx apparent power consumed by each phase.
Can I then apply assumed Power Factors to apparent power to get a reasonable estimate of the real power consumed?
The ASHP is a compressor and a large fan motor and the Water Circulation pump is an induction motor I assume.
www.engineeringtoolbox.com suggests that for near fully loaded induction motors the PF is 0.83 (up to 5HP) to 0.85 (5HP – 20HP). Compressors seem to be in the 0.9 to 0.95 PF range
Any comments?
I think you’ve misread or mis-understood something there.
When you test the three-phase sketch on a single phase with a resistive load, then the 2nd & 3rd phases show half the true real power. Think of the phasor diagram and the projected length of the current phasor in the direction of the voltage & 1st current.
No, if you change the sketch to send apparent power, then the numbers that emonLib produces are the full & correct value - the product of rms voltage and current.
But why not use the 3-phase sketch and let that calculate real power from the product of (assumed for phases 2 & 3) instantaneous voltage and current? Then you get the true power factor. You can “connect” the 4th c.t. to whichever phase you wish.
You’re obviously getting your PV generation / house usage data from elsewhere?
Thx for the quick response.
Yes I will be getting the PV generation/house usage from other emonTx’s.
In fact it was from our forum exchange 3 Phase Generation Question 25th Feb that I thought I learned how to use the SINGLE phase sketch to determine the generated apparent power (assumed close to real power at the generation point) for each phase.
(I want to use the SINGLE phase sketch at the generation point because it has facility to connect an optical LED sensor which will be attached to the smart GENERATION meter).
Re monitoring pool equipment - I now realise I wasn’t seeing the wood for the trees - best to use the THREEE phase sketch (optical LED sensor not applicable at this monitoring point).
I’ll now order my 3rd emonTx and 4 CT’s.
Thx again
You can easily add the optical input to the 3-phase sketch.
Isn’t it in it? Unless somebody’s fiddled with the version on GitHub since I last updated my copy, it is.
Yes - I’ve just checked - pulse counting was added in ver 0.11 of the 3 phase sketch on 13th Feb.
The version I’m currently testing pre-dates this.
A case of crossed wires now uncrossed.
Greatly simpifies things for my application - I’m a happy bunny
Thx