Wired OpenHAB Type Central Heating Control with Rad Valves and Room Sensing.

[axt]

Hello,

During recent renovation works I have installed a single gang pattress box in most rooms near the light switches with provision for wiring cat5 / 8 Core Alarm cable back to the airing cupboard / boiler control area. I am also putting in provision for getting 4 core alarm cable to each radiator. The idea being to install 24v thermal actuator heads on each rad valve and for each room to have a temp sensor / controller of sorts which signals back to a main controller and probably an attached embedded PC. This would then run a per-room schedule with influence from outside temp, flow and return temps from boiler / aggregate temp demands, weather forecast and time etc. Ideally with a local web server / page overview that would then be accessable on PCs in the house.
Goals being to have no part of the system wireless and for any computer software on the embedded PC to be open source (e.g. OpenHAB).

My ponderance is if there is any COTS systems that would work for the room control panels or central controller?
Ideally something with a display of current and target temp with ability to request boost / temporary override. This should then pull the target temp from the central system.I will (eventually) cook something up as a longer term DIY project if it does not exist but most openHAB stuff seems to have been done by the software engineering fraternity so hardware wise seems to mainly be lots of IoT and bluetooth / wireless widgits or COTS devices. I like the idea of a dedicated wall plate for interfacing with the system, rather than battery wireless sensors.

At the very least as an early revision, a wall box could just be a temp sensor and a push button with some feedback LEDs for if the room is being heated / overridden etc (so entirely passive)...

Is there any prior work or projects that anyone knows of in this area?

 

[ericmark]

Many years ago my son wired his house with basic same idea, with a server in the loft, however the cost of wired TRV heads was so much more than wireless, it ended up using a wireless system.

I found a problem with bluetooth was the eQ-3 heads I used would only connect to one device, and even the wifi found only connect to phone or tablet, with the computer needed to run an emulator.

If you look at a circularisation plan, any device under the radiator should monitor return air temperature, so the standard position of a TRV head is not really too bad, but my heads show the target and an current temperature, but it needs me to manually use the info. At 4:46 am I started to open the Kasa program with the emulator on this PC, 4:51 am gave up and opened on phone instead, it gives a great history, yesterday shown, heating not on so just shows room temperature and if over or under setting, it shows settings but again to get that info to turn the master wall thermostat on/off there seems to be no way to interconnect, my silly Nest Gen 3 seems to not integrate with anything.

So to get the TRV and some sort of hub to talk to each other, I would need to install a different wall thermostat, this does seem ideal, however Wiser and many more now allow the same, however the critical unit is the TRV, this was claimed to work with Nest, it does not really work with Nest, and it has no manual controls, I am forced to set it on the PC or phone, simply no manual method to set, this one is blue tooth, but can be manually set. And when I got them just £15 each, the Wiser TRV is claimed to work out time taken to heat room, and you set time you warm room warm by, rather than when the heating comes on.

The Energenie one shown was rather poor because the anti hysteresis software was OTT, set it to 20ºC at 7 am and nearly 10 am before it had got the room to 20ºC so would set to 22ºC at 7 am and 20ºC at 8 am and room would be at 20ºC at 8 am. However this means that the geofencing was useless.

With a modulating gas boiler the TRV's did work well, once lock shield set, they would maintain the room within 0.5ºC of setting, however with the oil fired boiler, (on/off) it did not work so well, and the other consideration is recovery time, having a geofencing system which will detect you are 30 minutes from home, so will turn on the heating, so nearly at comfort temperature as you arrive home seems great, however Nest has no option to set distance, it will turn the heating off when you leave home, but the temperature is not turned up early enough to be warm on arrival home, so only option is simple time setting.

Even the last house, from Eco to Comfort temperature (17ºC - 20ºC) it took an hour, so unless you work more than an hour from home, geofencing has no hope of getting the house warm on time. Today I use timed stage heating, so wall thermostat turns on at same time kitchen TRV turns on, 10 minutes latter the dinning room TRV turns on, and another 10 minutes and the living room turns on, another 10 minutes and other rooms wanted, so radiators heat up in sequence and far faster for rooms being used first to heat up, but more than 10 minutes and the boiler has turned off due to returning water being too hot, all the fancy controls seem great, until you try to use them.

 

[axt]

Hello,

Many thanks for the very detailed reply, I did read it on my phone when you posted and thought that it deserves a more detailed reply when I was next at my PC and then things got the better of me!

I have had many people suggest that individual room monitoring of temperature is a little pointless, and indeed that constantly opening and shutting rad valves can create more issues with boiler cycling etc but I am not really seeing it as being for that purpose.
Most of the arguments against wired rad valves and room stats is purely based upon the issues of running the wires. I have already done that, so its not an issue. Saving dozens of batteries a year has to be a benefit, as well as mitigating yet another wireless network and hubs to struggle with.

The main benefit from my eye is that you can have staged heating, I.E. my fairly small boiler can heat the downstairs with priority first with more efficiency, and then the valves for upstairs can open a little later to warm the upstairs more when it is nearer bed time (and these rooms would normally be cooler anyway.
It also allows for easier adjustment of the priorities for a day by day basis / keeping one room cooler on a schedule etc.

My main ponderance at the moment is on any decent COTS wall stats that are Ethernet / twisted pair low voltage. Otherwise I will end up making something with a RTD sensor, indicators and a push button with a pair each, and doing something at the central point. A cheap / DIY PoE based room node with a simple temp display / target / actual temp and a boost button would be ideal...

 

[martygturner]

I would point out that heating a downstairs and then an upstairs will cause a lot of drafts unless your bedroom doors are shut and reasonably air tight, to stage heating you really need to asses the airflow within the space as a whole. basic thermodynamics - temperature will always seek to achieve equilibrium. Your little boiler may end up trying to heat the whole house from just the downstairs rads. Staged installations tend to have self closing doors and draught excluders fitted to all the doors internally.

Why not just split the heating circuit into two zones with a zone valve, that way the downstairs can have all the heating until it reaches temp. In your plan the heating upstairs will still be receiving hot water but to no effect.

 

[axt]

The draught issue is a good point, but hopefully the general layout and flexibility will allow this to be fine tuned out, and the essential zoning down to radiator level has to be better than just two zones from this aspect...?

If both rads at the end of a flow and return leg are shut ok their trv, then no heat will flow down that leg, so nothing wasted?

Cheers.

 

[martygturner]

If both rads at the end of a flow and return leg are shut ok their trv, then no heat will flow down that leg, so nothing wasted?

That depends on the type of heating lay out you have... and where is fed first...