Linked system with solar thermal design advice please

[gg123]

Hello, I'm just trying to design a system for a new house, doing refurb now so have a few weeks to finalise design, and am stuck in a few places. Wasn't sure which section to post in, hope this is OK.

Sketch of system as follows:



Some parts are a little unconventional but reasons are:

- Designed so that if lazy (or new owners in future don't like it) can use Combi including DHW as normal boiler (will have swap over valves in airing cupboard to use combi HW instead of cylinder).

- Will use eVolution 26 with SCWS as sealed system + in Smoke Control zone.

- Vented HW cylinder so it can be pumped for (high) power shower.

- Small buffer store to be used ad hoc for in the mornings to heat a couple of radiators for a short while without having to light WBS. Radiator TRVs will probably be LightwaveRF. Not a combined TS with DHW for previous point reason, plus don't want to accidentally use hot water with the heating.

Significant control features are:

- WBS pump P1 controlled by flue stat T2 only
- Radiators zone pump Z1P controlled by T1 stat only (at quite a low temp), no timer or room stats
- TRVs will be LightwaveRF (individually time programmable)
- Tune the combi's return stat so that when its timer/room stat calling for heat but WBS is burning and keeping up, it will just circulate without firing.

So the bits I'm struggling with are:

1) How would I "charge" the buffer store at night when I know there will be no time in the morning to light the fire? The only thoughts so far are to use a LightwaveRF relay in series with T3 to energise the pump ZP3. Or a switch in the airing cupboard!

2) Similarly, how would I use the heat in the morning. Again, lightwaveRF relay my only idea so far.

3) How would I go about sizing the buffer store? It would be needed for maybe 20 mins of heat to radiators in bathroom (heat leak) and kitchen (others to be shut in with the TRVs) - sizes unknown as yet, but any rough and ready calculators?

4) From what I understand, it is only possible to connect 2 heat sources to a Systemlink manifold - their documentation states that for a 3rd source, two would have to be linked together with a pump, but no more info than that. Any ideas on this, or an alternative way perhaps to piggy back the buffer store on the combi flow/returns?

5) Solar thermal heat dump for hot days - I'm planning to use the spare relay on Delatasol ES and stat T4 to circulate pump Z2P when getting too hot. Being a neutral point manifold I guess it will just circulate around the coil loop, but be enough to heat the whole manifold to reach T1 setpoint, which will energise Z1P and lose heat around the radiators. Does that sound like it will work?

6) The SystemLex instructions refers to using the spare relays to enable Hot Water Priority, but not much more. Anyone with experience of that?

7) I will be handling a lot of the plumbing, but will need someone with wet HETAS for WBS installation and appropriate qualifications for the key parts and signing off the rest of the install for building regs. Am in Nottinghamshire - any recommendations?

Hopefully that's vaguely clear, many thanks in advance for any advice.

[gg123]

May have a solution for No4....see updated diagram:
 


This would piggy back the small store on Combi flow / return: Normally closed zone valve ZV1 and normally open zone valve ZV2 would be energised (somehow) when deploying the small store. ZV1 microswitch would energise pump P2.

The Automatic Bypass Valve and circuit I guess would only be required if combi not fitted with one already (in case combi circulating same time as store being used). Not sure if the check valve would be required to stop flow across the ABV when store being used.

Think that should work/be legal.

[gg123]

On reflection, previous modification for the thermal store control looks awful...pump and 2 check valves should do it...I think?

[nominous]

re the buffer store.
If you're planning for it to be used in the morning, that's suggesting you're adding heat to it in the previous evening.

Given that you want to heat radiators with it, and you say for only 20 mins (which doesn't seem long for my SWMBO for a weekday in winter), what temp are you planning to heat it too the previous evening, and what temp do you expect it to be when needed the next morning?
Would a FPHE and a direct cylinder not offer some advantages over the coil, as you'd be then normalising the temperature of the cylinder contents and mixing the layers that would have formed where the coil is placed - I may well be talking out my ass at this point.


Why not have the heat leak on Z2 ?
Perhaps with another valve to block out the cylinder, if needed.
But is the valved needed as if it's cold enough that you want the heating on, chances are you'll be heating the DHW too (depending on qty of tubes).
And if it's on Z2, it's easier to heat dump to it.
Bathroom towel rad etc.


My system aint anywhere near that complex. But I'm working towards it.
Thanks for sharing

[gg123]

Thanks - yes the plan would be to heat it the previous evening (flick a switch somehow, stoke the fire and go to bed) - at a complete guess to 75 degrees C, maybe 65 in the morning depending on lagging.

20 mins was a guess too - perhaps it should be longer, but it would only be to take the chill off the kitchen and bathroom.

I'll look into the FPHE idea too...thanks for that.

Ref the heat leak on Z2, could you give me some more info?

Thanks again

[nominous]

Am thinking out loud...

If the heat leak is on Z2, then when you have too much heat from the solar, you can be dumping heat to it.
If the rest of the system needs to dump heat (which is going to be when the solar isn't performing well) you can dump that into Z2 solar tank anyway as well as your store.

If the solar store was already up to temp, then sending excess heat to it from the system boiler wont make it any hotter than the system boiler's temperature.
And it could be that say the system is 75C the solar tank is on a really good day sitting at 80C, you might even pull heat from it back into the rest of the system ! -(in theory)

So with the leak on Z2, it's capable of dumping both excess solar heat and the rest of the system heat, depending on conditions.
If you ever want to use that solar for other things, say a few months where there is enough solar gain to heat that tank up and the buffer store but you might want rads on for SWMBO, then maybe the leak rad needs a valve on it to control dumping to it, or dumping to the storage tank.


It may well make more sense on Z3 as it is now.
What I'd do is map out out what might be supplying heat and when and from where to figure out the best position for it.
The reason I figure moving to Z2 is that it would survive in a power cut to stop your system stagnating, but if it was on Z3 and pumped, then you'd need power to make it work for the solar dump.
Conversely, if you have your wood burner on, what to do in case of power cut there ? As the system you've drawn still seems to need pumps for supporting the wood burner, which I've read many thread on here frowning upon it and not being to regs.

[gg123]

Thanks, some things to think about there...

The stove is the Broseley Evo26 with Safety Cold Water System so in the event of a power cut it will activate the mains cold water quench coil when it hits 90, or if that fails the blow off valve outside when it boils and goes over 3 bar.