Newbie questions - how's this system?

Hi all,

I'm new, I'm thinking about building myself a system for home, in New Zealand. I pay for power at the current national floating rate, unlike most people in NZ who pay a fixed rate, so I'd like to track and analyse consumption. I'd like to track when and where power is used, correlated with temperature. Ideally I want to measure the temperature in a few locations around my average sized residential property, including my greenhouse. I have a couple of questions and I want to check my understanding is correct.

I have an EDMI Mk7C digital meter, with a flashing LED to show power consumption. My main energy users are electric hot water and two heat pumps - reverse cycle air conditioners is another name for them. Ideally I'd like to track power usage for the main energy consumers, but if I can't it's not so bad because I can generally guess what's using power based on time of day. I happen to have a spare Raspberry Pi v1 model B lying around.

Proposed system (total £230 / NZ$520 shipped according to the online store, no VAT)

1. EmonBase. I understand this is a wireless receiver, getting data from the various transmitters. It uploads data to the web, powered by USB. £36 if I use my existing R.Pi.

2. EmonTx v3. This would sit in my meter box with a pulse counter, counting power usage, with 3xAA batteries. £65. This is the most expensive part of the system.

3. EmonTH #1. This would go in my greenhouse, battery powered, with an external sensor so I could have internal and external temperature readings. £34

4. EmonTH #2 and #3. This would go inside my house, one in each section of the house £25 each.



1. How far will the EmonTX transmit? I have a greenhouse out back, behind a shed made of bricks. Right now the US$100 Ambient Weather WS-10 system, that reaches the house, just, I had to use a piece of wire as an external antenna.

2. If I have an EmonTX can I potentially put a sensor on lines to my hot water and two heat pumps to estimate energy use? Given I really don't want to mess with the meter board this is potentially a job for an electrician to do. I understand they don't electrically connect, the sensors sit around the wire.

3. If I decide just to measure overall power consumption with a pulse counter do I need the EmonTX v3, or is there a cheaper option? Can I get the pulse sensor and connect it to a R.Pi with a Wifi adapter?

4. How difficult is it to get all this working together, talking to the online system? Is it easy enough to view it on PC and Android? I'm an engineer and I can mess with things if required, but I don't really want to.

5. Any way to get the price down a bit? My wife might not want me to spend this much when I already have something that does part of the job.

Thanks for any thoughts or advice :)

goodfidelity's picture

Re: Newbie questions - how's this system?

Hi Timnz!


I am also interested in tracking the energyconsumption regarding to the temperature.


There is a really good graph for this called the E/T diagram, energy vs. temperature.

You can read about it here:

However i dont know how to set it up in the moncms.

The neat thinking about this diagram is that after logging for one year you will know how much energy should be used at at certain outdoor average temperature.

So if you make changes to the heating/cooling system or the isolation or windows you can immediately se if there is an improvement from previous measured results for the exact same average outdoor temperature.

And also this diagram is really good for setting up alarms. If energy consumption is "off" the chart with some % you can trigger alarms or something like this. That way you can have alarms for energy usage that will alert you if doors or windows are open and you have a heat leakage or similar. 

The same way you will be alerted if you have equipment running that should not be running.

What do yout think about a diagram like that?


ET diagram


Best regards


timnz's picture

Re: Newbie questions - how's this system?

Thanks goodfidelity, that's interesting. I have to work out first if I've picked the right set of components and whether I'll go ahead with the full system or any system at all. Hopefully someone comes along who can help with the questions I asked :)

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