System design

[ALEC1]

if you want to match "neatly" your system to the house (which you should!), then it is worth bearing in mind that modern boilers have a multitude of tweaks and levers. All these come free with the boiler. Why not use what comes with the boiler...

The advantage is that if you install to a manufacturers specification then you do get a system that works...it takes out the speculation and guess work...

 

[Norcon]

Solar - unvented - I read your post wrong :doh: - I agree with you, we are planning on the TS to be vented

In a thermal store the solar is usually connected to a solar coil. (integron)
The solar circuit will then be sealed.

If you are intending on connecting the solar panel direct to the store and the panel is at a higher elevation than the store, then every time the solar pump operates fresh water will be drawn into the system.
When the pump stops gravity will push the water back up the feed pipe and very likely out the overflow.

Correctly installed there is nothing unsafe with a sealed solar circuit connected to an unvented cylinder.
Just as there is nothing unsafe when a solid fuel system is correctly connected to a sealed system also.

 

[SimonH2]

As part of our house rebuild I have been working on our heating and hot water system design. I'm looking for any comments (constructive) that anybody might have so I can optimise and get a consensus point of view.

Consensus on here - not a chance !
Many will tell you that there's no way a thermal store can ever work - the implication being that they'll magically create half a ton of sludge. Tick, some of those have chirped up.
Others seem wedded to the idea of a single (specific) manufacturer and their controls. Tick.
Some seem wedded to unvented DHW cylinders. Tick.
The only POV not ticked is the one that says you're an idiot for considering stored heat and should fit a combi !

Your design looks OK to me, and is probably about what I'd design for the same set of inputs and outputs. I'd probably have less sealed systems, have the boiler connected direct for example.

What few here seem to want to accept is that you can use even low grade solar input with a thermal store - even if you only get the bottom of the store up to 20 or 30˚ then that will still put heat into the DHW and reduce the boiler load.

One of the issues I have not fully bottomed out is the location of the boiler tank stat(s) to maximise the solar input before the boiler kicks in.

You probably need more than one for best effect.

In winter you'll have little/no solar input and cold mains water - for that you'll want a stat fairly low down.
In summer, with plenty of solar input and warm mains, you can probably get by with only a fairly small upper section that's boiler heated.

Of course, that assumes a direct connect boiler and top-down reheat. With an indirect boiler coil then you are limited to the position of the coil - you cannot heat anything below the coil, and without some deft flow control you cannot avoid heating everything above the bottom of the coil. The manufacturer will have provided a tapping/pocket for the stat and you'll have to use that.
I suspect that (as with a normal OV DHW cylinder) you'll struggle to get the boiler condensing without restricting the circuit flow to get a decent delta-T across the coil.

Another random thought ... Are you having all UFH or will there be rads ? For rads, a modulating pump and fully TRV system works very well.