Hybrid Stove & Solar Proposal (Spain)

[cye]

See attached schematic designed by Wyn, seeking views from others.

Here's a description of the proposed system provided by Wyn:

This allows the heating system to scavenge excess heat via 2 heat exchangers:
A. solar circuit via motorised valve VM1 - triggered by sensor T2 reaching 70º
B. the stove circuit via motorised valves VM2a & VM2b, diverting flow from the tank coil, when sensor T3 reaches 60º
C. from the tank via a manual 2 way tap, effectively running the heating circuit via the stove coil in the tank. This is more a safety measure for while we are away...

I'm still working on how to control it, though I'm pretty sure I've missed a few points, ie when its shuts off!!
- Any thoughts re which controller? If I can get away with jerry rigging the 12V controller I mentioned before, fantastic, Do u think its feasable?
- Otherwise its plan B, a bespoke system using an arduino with motor sheild, again another learning curve, unless you know someone who might be able to help to short cut this too?

- I have yet to work on expansion vessels / tanks, fill points & shut off valves.
Am going to build a prototype rad next week, although I was advised that the steel heat exchanger for the rads would be no good due to its narrow bore & low heat output. I was advised to use either 6mm or 1/2 inch copper... we'll see, I think there is going to be a few prototypes...!


Trades & suppliers here [spain] are very "old school" & the concept generally is to oversize everything & my concept of scavenging heat (& components leaves me a little out on a limb...!) Nothing 12V either.. Nonetheless I'm going to give it my best shot.

***and here is some earlier background provided by Wyn:

I'm an architect & our house is in southern spain where I've seen the panel regularly get up to 180º.
Summer day temps soar to 40º and drop to 12 at night,in winter we can have 25-30º during the day (& plenty of hot water) although the nights can drop to -5º. It snows here. Our existing mains wilo 220V pump has finally given up, so I've decided to redesign the system to incorporate additional heat from out 12kw stove, and trying to dump the excess to a rad circuit, and the overheat to superheat the top of the house to get a really good temp differential & draw through the house. As the house has 600mm thick walls, 3 storeys and a void running through the centre, it gets very cold on the ground floor, so I'm hoping that this system may balance things out a bit. As we're away quite a bit, & as the mains surges & trips out all the time, we tend to arrive back to a cold house with a stopped pump & the solar circuit boiled dry, or burst connectors. This is why I'm switching to 12V, electricty prices are going up & up, & I'd rather disconnect the house while we are away, reasonable safe in the knowledge that the system looks after itself....

Photos of the build here:

plus.google.com/photos/117719780504268851425/albums/5470903606903778081?banner=pwa

Attachments:

[cye]

Wyn

[1] Haven't studied in detail yet, but the solar coil would seem to be the upper coil in the tank, whereas conventionally it is the lower coil, firstly so because the solar works more efficiently when heating cold water, and secondly so that the tank can store more solar energy.

Is there a reason for having the top coil the solar coil?

[2] Many of us run our hot water tanks at 80c rather than 60 or 65c. Stores more energy. It does mean you risk scalding but this can be addressed by the user of TMV (thermostatic mixer valve) at hot water outlets.

More later

Regards

Cye

[cye]

Wyn,

I still can't say I understand the background to the current design proposal, but I do note that the rad circuit seems to be entirely isolated from both the solar and the stove via two separate heat exchangers. I also note that Wyn is following best practice with his stove by using an ESBE or Laddomat thermostatic mixer to ensure very cold water is not circulated around the stove boiler. (When cold water is circulated around a stove boiler this reduces the burn temperature and therefore the burn efficiency of the stove.)


Thinking some more, probably not in a straight line, I have a few 'devil's advocate' type questions for Wyn, the answers to which may help us understand better his proposed design:

[1] Why is the top coil not connected to the stove circuit and the rads part of the stove circuit? This would be a fairly traditional arrangement with the solar coil below the solid fuel coil, and the solid fuel coil used to extract excess heat from the tank (heat store) when the heat dump trigger temperature is reached. Such a proposal would potentially remove the need for the 2 additional hat exchangers as the tank exchangers would be used instead. In such a system of course the stove also acts as a radiator but perhaps that could be useful too?

[2] I understood that the laddomat TMVs were set at 60-65c, so perhaps the 40c proposed for the TMV at the stove is set too low?

Rgds

Cye

[cye]

More info from Wyn on his proposal. See attached additional schematic and the following further thoughts from Wyn:

Cye,

A little more detail re how the 3 circuits might be installed.
solar, stove & heating.

the text on the left explains how each scenario might work along with the positions of the motorised valves
ie translating the schematic a bit closer to an actual installation.

- I reckon that we could do this either with motorised valves (shown as VM) controlled either:
A. manually
B. Via thermostats
C. via a controller

Or VM's could be replaced by thermostatic mixer valves - this might make it easier, ie getting rid of controllers etc.
- can you recommend any thermostatic 3 port valves, or
- do you know of any thermostats that could switch a 3 port motorised valve remotely?

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