Hi Klas,

It sounds like a well engineered system. Anytime one can use a new design themselves over an extended period of time the bugs get ironed out. If I had your type of system I would be interested but mine is natural gas forced air. Even if you don't get any bites it would be fun to see what you have built.

John

Here is my Pi mounted on the wall. Not very elegant. It has monitor, mouse and keyboard connected but should not need to. 4 GPIO pins in use. 3 for switching 3 radiators. 1 for reading temperature sensors. Temperature sensors are Dallas DS18B20 connected in parallel I use 3. Internet via WiFi. My little strip-board has one LED per radiator and Wago connectors to the world. The rightmost cable down is a 12V feed for the one radiator where I still use a 12V relay. The leftmost down cable is just stealing 12V for a completely unrelated circuit. So the middle cable is the connection to the flat. Ground, Sensors, Radiator1,2 and 3. (+12V feed that will eventually go)

My major head ache has always been the physical operation of the radiators. My first solution was hacking into the radiators adding a 12V relay as in the next picture.

This is still in use but I hope to be able to retire it soon. All radiators are set to full blast and I achieve  the amount of heating I need by on-time. Off time is always 7:00 UTC since that is when night time tariff ends.

In a newer switch design I use a triac. Circuit straight out if the datasheet for MOC3043. Triac is BTA16.

I had this circuit running successfully for a good two years on my bedroom radiator where it is just sitting on the floor. (No risk of any kids being in my bedroom between 0 and 7 UTC.)

A recent attempt to package this into a standard electric box was less successful.

After only two hours of operation the plastic box starts to cave in. The Triac generates 10W of heat according to the data sheet.

Need bigger metal box.

But my latest design is the same circuit driving a 240V relay. Can use a lesser triac. Found relay Finder 40.61. Remains to be built.

As for software I have written an Android app that can show the current sensor readings and show the heating plans.

Also you can see the weather for the next 24h.

Everything is recorded in a MySQL database on the Pi. If you choose to add monitor and keyboard to the Pi, you can run my monitoring software on it

or you can run it elsewhere where python is installed.

Why not use a solid state relay in the radiator ?

From UK sources:

Rapid Electronics 60-1598, about £10,

Kudom KSIM380D25-L Panel Mount SSR 4-32VDC 48-440VAC 25A Load - LED Zero Cross

cheapest similar part from Farnell is about £20.

If you are feeling bold try a Chinese one:

https://www.aliexpress.com/item/NEW-single-phase-ssr-solid-state-relay-SSR-25DA-25A/32354498764.html?spm=2114.search0104…

about £2.00 each including free postage to UK

On Aliexpress you'll also find similar parts with heat sinks.

I have use one or two of them, can't remember now which one, and they were OK. I would test the insulation carefully before using one in my house.

MK

Thank you Michael. I looked into solid state relays a long time ago and I think I discarded the idea due to price.

I will order one and try it out. Control voltage: it say 5-24V in the table and 3-32V on the items. Is it going to work with 3.3V from the raspberry?

It also looks like it is going to be hot. A problem I had with my Triac design. It will be some time before I can let you know the outcome.

Cheers

klas

Thank you Michael. I looked into solid state relays a long time ago and I think I discarded the idea due to price.

I will order one and try it out. Control voltage: it say 5-24V in the table and 3-32V on the items. Is it going to work with 3.3V from the raspberry?

It also looks like it is going to be hot. A problem I had with my Triac design. It will be some time before I can let you know the outcome.

Cheers

klas

Kias,

I have used something like this for mains switching from the RPi. I fed it a separate 5V supply (not though the PI, but the same power supply as the pi) and it worked fine. The 10A switching load should be fine up to 2KW radiators (technically 2.3, but I wouldn't push it). The opto isolation is a nice safety feature too.

For the mounting box, I would suggest a galvanised 3"X3" adaptable box, and try and arrange it so the triac can dissipate heat through the side of the box (a bit of Thermal grease would be good). Just remember to earth the box (safety first!)!

Nice system though. I don't like storage heaters, but needs must, and forecast integration is a great way to assist with it!

Good luck!

Thank you David for your suggestions.

Your 5V relays are essentially the same solution as my first solution - with a 12V relay and a transistor switch.
I still use one of those circuits. Supplying the necessary voltage for the relay is a pain though.

My latest design is the triac circuit driving a 240V relay instead of the radiator.

I expect to build this within the next month or so.

I had success using a

Solid State Relay SSR-50DA 3-32VDC 50A/250V Output 24-380VAC

for less than $7 canadian. I switched on a 120VAC car block heater when temperatures dropped below minus 15 celsius using the SSR connected to a Raspberry PiB.

Sean