MikeSharp01

So a resistive heater, EG your immersion heater, puts 100% (well very nearly - some energy is always converted into a less useful form) of the electricity consumed into your water but you cannot go the other way? I suppose a question might be "Is that because the 2nd law says so or that we just don't have a technology that does it." after all the Kelvin-Plank statement mentions, IIRC, that any device operating a 'cycle' cannot achieve this perhaps leaving open an opportunity for a device not using a cycle to achieve this.

One thing I have noticed, although I guess I could have worked out it was there, is the amount of power the inverter (ours is hybrid so ready for a battery) draws. I have not done the long term math yet but if feels like about 5-7% so for example at 6kW of generation the Inverter is using around 350W. I am somewhat with @nod - the numbers on the battery just don't add up but if I take the 'save the planet' line I can square the circle so if there is any money left at the end of the build we will get a couple of batteries.

How do you keep the data loggers running - batteries?

Yes we exported 26kWh today, frustrating waiting for the export MPAN number to come through after we commissioned the PV 3 weeks ago, then we can get our 15p per kWh!

Get yourself a BMW era Mini Cooper S, like driving a roller skate - fast enough to be fun, especially in 'SPORT' mode, looks great when clean, mostly comfortable - give run flat tyres a miss, and mine has 200K miles now - still smiling.

So are there two branches off the MVHR and are there two heat batteries, the things the water flows through and the air passes over on on its way to the rooms - one on each branch? The counter flow heat exchanger deals with the heat recovery bit of the job. If there is only one branch / heat battery then the problem must be a flow rate / balancing issue because the difference cannot be explained any other way I can see and even then its a long shot so something odd at the very least.

Good to see progress, keep on keeping on.

No I agree, mine runs on a PI 5. Yes we are using a hive cloud mainly because I have access via work but I can encrypt anything I want. My goal in using the phone is to show people how simple it can be but it has all the down sides of every other system of systems on the planet. They do, but that doesn't stop them being complex in all other respects and most people don't know what those respects are.

Not 100% sure, because there might be much more complex things coming, but I think the average modern car is a phemominally complex system of systems and some people others may define as 'right plonkers' seem to manage them in getting from A-B mostly without incident. So it looks like you can make extremely sophisticated systems work for the general humanity you find about the place - perhaps this should be our aim.

What if the house is autonomous - IE runs itself? Then the human interface can be a normal on/off switch for the heating, MVHR, lighting etc. (naturally with a parallel app interface to allow on/off from anywhere on or off the planet.)

Provided your sensors are sending MQTT messages you don't need Node Red on a PC to subscribe. The little app I feature above just needs you to enter the broker details and build simple tile based dashboard on your phone each tile can subscribe to one or more topics. So my graph subscribes to 3 topics and stores 1000 readings.- All free and no PC needed..

Welcome to THE forum for people like us.

One might ask why does nothing ever get better for customers

Yes Gus, for me it is fun, and I use aspects of it in the part time day job. Here is my latest Gizmo - an RPi Pico with a DHT22 temperature and humidity sensor attached. I have several of these around the place. This one also gathers information from the local weather station (local Temperature), gets readings from the other units (House Temperature) and interrogates the PV inverter before sending a bunch of MQTT messages to my hive cloud based broker from which I subscribe using my phone to get a great little dashboard. The MQTT dashboard app is a very lovely piece of work. See below for details. I may write all his up at some point. I won't I've using them to control anything but just to gather data I can use to set up the controls when I finally choose a system - probably home assistant. App is:

No so easy with Arable crops though!