I appreciate you comments Prunus, but I think the HP, TRVs and a “Nest” is quite a simple control system. Agree, turn off the location sensor. 
But the TRVs are just set, for the given room. Set the flow in/out temp on the HP & weather compensation. And the Nest calls for heat as required thru the day/night to the set temperature. 
Surely this is simpler than loads of additional controls/systems added?

Hi Prunus,

Like you I am a firm believer in KISS (Keep It Simple Stupid for those not familiar with the term).

My present control system consists of a PID Controller with two inputs using PT100 Resistance Temperature Detectors (RTD's). One senses the air temperature within our home and the other detects the temperature of the radiator in my office. The controller is set up in a Master - Slave configuration.

The controller calculates the required temperature for the radiators to achieve the desired indoor temperature, when the radiator temperature falls below this value it starts the central heating pump and fires up the gas boiler. It normally takes approximately 4 minutes for the temperature of the radiators to be brought back up to the required temperature, at which point the pump stops and the gas boiler is switched off.

In colder weather the controller calculates a higher required radiator temperature, so the pump and boiler run for slightly longer, but because the radiators cool down quicker, the pump and boiler switch on and off more frequently.

I have consider adding an ambient air temperature sensor, to start to increase the calculated radiator temperature, when the outside air temperature starts to fall.

In my limited understanding of the internal controls and operation of ASHP's, it would appear that there are two distinct types. One type has a fixed speed compressor and therefore switches off when the gas has reached the required pressure and temperature, whilst the other type has a variable speed drive and therefore matches it output to the required loading.

As far as the method used to set the desired water flow temperature is concerned, I suspect this may differ from manufacturer to manufacturer.

I do believe that on some units it has to be changed manually on the controller, and also there may also be a weather compensation facility incorporated within the design. This may be an ambient air temperature sensor located within the ASHP.

I have an Air to Air ASHP, which I run when I am getting 'green' electricity from my solar panels, the desired temperature being set using the hand control, though it does also have an app for your smart phone.

Like you, I am surprised that ASHP's do not appear to automatically vary the required water flow temperature to match the heat load. It would make sense to run the ASHP at the lowest water flow temperature consistent with meeting the required heat demand.

I had a quick look at the Home Assistant that you mentioned, I may be wrong, but it seems to be more aligned to switching equipment on and off rather than carrying out control algorithms or changing timing etc.

As far as electricity tariffs are concerned, each day, the next day pricing for Octopus Agile is posted at approximately 4:30pm, which it should be possible to extract with appropriate software. Though I wonder if it is worth the effort.

Since the indoor temperature changes relatively slowly, I would think that feeding a measurement of the ambient air temperature into your control system would be adequate.

On my solar PV diverter there are two current transformers (CT's) which measure the amount of energy imported or exported and the amount diverted. If required, it should be possible to use a CT to measure the energy produce by a solar PV system.

I don't have batteries or an EV, but I do believe it should be possible to extract data, though I am not certain what you would wish to do with it.

The multi-million pound systems on which I have worked would only be connected to the internet if deemed absolutely necessary and then only through a very robust firewall, so I cannot really help with that requirement.

As JulianC has stated, 'is this level of complexity really necessary'

Hi all, we are currently awaiting the install of our Hybrid ASHP system, but as it stands just now, we did have a Nest installed to control the heating in the house and while it was certainly better than the standard thermostat type system, I always felt that we were still wasting a hell of a lot of energy heating areas of the house unnecessarily, so I recently ripped it out and installed a Drayton Wiser system. This basically replaces the 'heat hub' from the nest (or your standard boiler controller) and tells the boiler when to fire. That is then controlled by the wiser smart TRVs (and/or room thermostats). it has in effect allowed me to have zonal/individual radiator control and scheduling throughout the house which in reality is a single zone system. Each TRV is capable of 'calling for heat' from the boiler directly. Was very easy to setup and in comparison to other 'smart' TRV systems, relatively cheap (we were ~ £450 for replacing the heat hub controller, a room thermostat and 10 smart TRVs). Should also add that it is all also controllable via Google home (and Alexa I believe, but cannot vouch for the functionality there).

My biggest current concern is will the system play nice with the hybrid system (Vaillant Arotherm ASHP and Vaillant combi boiler) when installed (the installation company says it will, but the proof will be in the pudding I suppose! :))

Would love to know if you have any thoughts/comments (oh and if anyone want to buy a second hand Nest! 🙂 one careful previous owner!)

David

@dchilton, I haven’t used Drayton, but yes, the system should work with your hybrid setup. We have a bivalent (oil boiler and ASHP) and our heating controls, not dissimilar to yours, work very well, do I think you should be OK.

We’ve explained our heating controllers: