Complicated System Design - Help!

Hi All,
Delighted to have stumbled across the OEM project, just exactly what I was looking for. I hope in time I can contribute. We run a small lighting company and have various things like a 3D printer farm, laser cutting, SMT assembly etc.

Here’s the background…For the last 5 years I’ve been stubbornly building our dream house by ourselves. Some images are attached. Now almost complete I’m turning my attention to the monitoring side of things. I’ve done a lot of reading, and think I’m now ready to ask some noob questions. Apologies for the length of this post!

For the sake of context here’s some info on the house:

  • Mains supply is three phase with conventional (new) meter located outside the house in a metal feeder pillar.
  • House wired on a three phase board, a feed from this runs a 15kva UPS, and the UPS output powers a second three phase board which runs all the critical stuff (lighting, fridges, network, CCTV etc).
  • A separate plant room houses a hybrid heating system comprising an oil boiler, and NIBE 12kw GSHP. All the heating circuits are metered and run from separate circuits. The heat pump also has a Kampstrup meter fitted already.
  • Heat loads are various underfloor circuits, radiators, DHW coil, swimming pool water-to-air heater, and pool heat exchanger.
  • Currently we have 5.5kw of PV on a (3.6kw limited) inverter one one phase, mounted in the plant room. The end goal later this year is another two of these systems mounted on the garage, on the other two phases.

The overall concept is that we will be producing a lot of surplus solar, where possible we will run the heat pump, and use oil only for periods when 12kw of heat isn’t enough. I would like to divert excess PV into the DHW initially, then further excess can be dumped into the pool via a cheap in-line electric pool heater.

In terms of design I need to monitor the three phase input/meter in the feeder pillar. I therefore reckon I need the following:

EmonTX at meter position
*3x CT’s *
*1x AC 9v power supply/sensing *
1x Optical Pulse Counter
1x encapsulated temp sensor (for external temp - why not!)
Three Phase Firmware

I’m not a massive fan of RF where a wired connection is possible. I’m also not convinced this would like reliably back to the plant room. There’s a metal enclosure and a LOT of masonry in the way, distance about 30m. I’m therefore thinking to use a wired connection to the EmonPI GPIO?

Back in the plant room I’m thinking to mount the following:

EmonPI at sub-board
1x CT for solar PV inverter 1
1x CT for heat pump
1x 5v DC supply (no AC sensing as already done at meter position)

And later this year in the garage:

EmonTX at sub-board
1x CT for solar PV inverter 2
1x CT for solar PV inverter 3

Hopefully the above makes sense, now for my questions:

  1. When I add my second EmonTX how should I connect this? Can I add a second wired EmonTX to the GPIO on the Pi? Or should I be trying to make the second one work on the RF as its a bit closer?

  2. I would like to add two channels of diversion. Firstly a 3kw immersion heater in the DHW tank, and secondly an in-line electric pool heater. Both are in the plant room. I’ve read about the Mk2 and PLL Diverter. Could I ask what the latest approach is, and how I could handle two channels of diversion?

  3. Again in terms of diversion can the system handle three phases of solar input when calculating diversion? Or should I be looking towards trying to consider diversion as separate systems? For example does the solar on phase 1 divert to the DHW heater on phase 1?

  4. To what extent could I consider using OEM for my heating controls? It would seem a sensible approach since it knows a lot more about the system than anything else in the house. Good approach?

Many thanks in advance for your input,

Welcome, Duncan, to the OEM forum.

You were not wrong when you wrote “Complicated System Design”!

The first thing to point out is the OEM system is essentially a monitoring system, not a control system. However, it integrates well with control systems, but there are others here far more knowledgeable than I in that area who will be able to help with that aspect.

But I can address some of the other points.

The meter position.
Why do you want the optical pulse counter for the meter? It’s most unlikely to read exported energy, or if it does, it can’t tell the difference between import and export. If you only want it as a cross-check on imported energy, then fair enough.
You do need a socket to power the emonTx there. Most people don’t have one.
The alternative is to move the monitoring position to inside the house on the incomers of the distribution board.

The RPi has only one serial port, and in the emonPi that’s used for the radio, so your options would seem to be: Serial from the emonTx to a serial-USB adapter at the emonPi end, or a serial to Ethernet at the emonTx end.

Plant Room emonPi.
You will only read apparent power using a guessed value for voltage if you don’t have the a.c. adapter. You can correct the guess in the processing using the emonTx’s voltage, but you’ll still not get real power.

Q1. If you don’t fancy using the radio for the garage, then the options are as wrote above. Wired Ethernet would give you by far the most flexibility in the future (will your inverters talk Ethernet?)

Q3. I would handle diversion as a separate sub-system. Both Robin’s and MartinR’s are designed as self-contained systems, though they can report values by radio (by design, probably with minor changes by serial too).

Q2. Talk to Robin. He offers a 3-phase unit as a kit (prevented by EU regulations from selling a completed unit) and I know he offers sketches for single-phase multiple loads.
I did make (but never installed) a single phase, 3-load diverter based on Robin’s early sketches.

Normally, that will be the case, Whether you want to do it differently will depend on how your meter reacts. If it emulates exactly a 3-phase Ferraris meter movement, then it will register the nett energy across all three phases, so you could divert to a load on a different phase. If your meter sees your installation as three single phases, then you may well get charged the full rate for import on one phase but paid a much lower amount for exporting most or all of it on a different phase.
Reading: Learn | OpenEnergyMonitor and the linked PDF
There isn’t a body of experience yet to know how ‘smart’ meters react to diversion.

Q4. There are others who can better answer this.

Hi Robert,
Many thanks for your welcome, and such a wealth of input. Much appreciated. In response:

I’ve got some other options for control. But I’d value input from others on how they would approach it.

I’m thinking of the optical since the meter position is a PITA to get to, so just for cross check.

That’s not a problem thankfully.

I’d love to do this. Unfortunately the main board in the meter position feeds things like the plant room/garage on separate cables. So its my only option to measure everything the meter sees.

Thanks for the info. I’ve got Ethernet everywhere in the house so that wouldn’t a problem. I’m assuming I could run both on ethernet-serial converters? Is there a particular one you recommend?

Good point. For all the cost I’ll add an AC for the emonPi.

I don’t think so, they are older ABB PVI 3.6, I’ll have a scan over the manual. I think they are just serial communication, and I’m not sure what info you can pull from them.

Thanks. I’ll look into that.

I think I’m good on that subject. Its a new meter (Elster 1100) that has a single kwh reading which I believe is a nett value. I’ve noticed that I can export solar on one phase and draw on other phase without it counting up. The red LED in the picture is static when I’m nett exporting.

Sorry, I don’t have any experience of those. And a quick search here doesn’t show a recommendation either.

Ultra clean installation. VERY nice!

Thanks! That’s part of the LED system, all centrally wired with a ton of sensors.

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No problem. I’ll hunt around and ask a couple of contacts of mine.

If you have smart meters installed consider monitoring those from the energy supplier side instead of on premises. The energy supplier may have an API that you can communicate with over the internet.

Octopus energy is one such supplier.

This way you don’t need to install anything near the meters. Down side is likely to be the reading granularity, probably 30mins.

Thanks Stuart, been talking to a number of suppliers including octopus. I’d love to be on their ‘agile’ tariff. But at the moment nobody will commit to a 3 phase smart meter around here. Hopefully in time that will resolve itself.