Thermal Store Wiring / Heating control

[juleshartley]

Hi,
I'm trying to design the heating control for my thermal store but I'm struggling to find anything that will do what I need even though it should be quite simple.

The logic I'd like to apply is:
- If top cylinder temp is over 85 degrees then turn on heating (irrespective of room therm's, timers etc.). NB: This is not my only overheat protection. I'd have a seperate mechanical dump at 95 c.
- If cylinder top temp is >50c (to prioritise DHW) and if the room thermostat and timer say 'go' then turn on the heating.

Has anyone got any advice on what kit to perform this logic?

Thanks!
Jules

 

[Norcon]

What thermal store do you have and how many heat inputs?
And what is the hydraulic arrangement?

 

[DP]

- If top cylinder temp is over 85 degrees then turn on heating (irrespective of room therm's, timers etc.). NB: This is not my only overheat protection. I'd have a seperate mechanical dump at 95 c.
- If cylinder top temp is >50c (to prioritise DHW) and if the room thermostat and timer say 'go' then turn on the heating.

While logic might not be flawed, fail to see the need as cylinder controls the boiler. Cylinder reaches set temperature, boiler if switched off. Roomstat calls for heat, second pump heats the rads.

While what OP desires can be done easily, I see that as waste of energy and complicating what is a simple setup

 

[juleshartley]

Ah, ok, I may not have been clear enough here...

The reason that this is not a waste is that there is not a boiler in the system. The heat sources are 2 woodburning stoves and a solar array.

The 2 stoves are on thermosyphons with thermostatic flue controls, but obviously I want the thermal store to make use of any excess heat rather than letting it get up to 95c

 

[juleshartley]

Store is a 350l Gledhill Torrent RE with some additional stove tappings

 

[Onetap]

Has anyone got any advice on what kit to perform this logic?

Electro-mechanical (thermostats) or electronic (thermistors and controller) routes.

Two thermostats and a fairly simple wiring job. Thermostats should be immersion types with the bulb in the thermal store, if possible.

Thermistor temperature sensors (as seen doing most temperature monitoring and control in most cars and boilers made in the past 10 years) and a compatible programmed electronic controller. Not very esoteric for this, I think Eurotherm and others do controllers, just a temperature display and set the temperatures at which the relay outputs operate.

Neither will work if the power fails.

 

[juleshartley]

Does anyone know of a control pack that includes the room thermostat and 7-day timer but can also relay cylinder thermostats and apply defined logic to output?

 

[Norcon]

If you fit timers and room stats then you'll likely have the scenario where a circulator is being energised and pumping cold water around the system and no heat in the store unless other controls are fitted adding complication.

Ultimately how you load the solid fuel boilers is what will determine the heat output.
So a sensor fitted to the store at the CH flow level energising the circulator is all that is necessary.
So on reaching 70c, circulator on and dropping to 60c circulator off.

 

[juleshartley]

Thanks Norcon - that's actually a valid point thinking about it...

 

[juleshartley]

Although with the logic that I was hoping for the CH wouldn't pump if the store was below, say 60 degs...

 

[Norcon]

A Siemens RAK-TW.1000B-H which comes complete with the kit for three different mounting positions is one option.
http://tinyurl.com/5t5497e
Available from climate center and are not expensive.
A fixed differential of 6c but you can position it in such a way that the bottom of the store will be 60c or slightly lower when it stops the circulator.

Or a KP78 available from Danfoss which has an adjustable differential between 5 and 15c.
More difficult to source and more expensive but top quality.
Also consider using the heat dump facility on the solar controller.