Hi Ian,
I'm going to to sound like I'm being very critical to start with, but I hope you'll see that it is intended constructively.
Firstly the hydraulic layout/design:
I'm assuming the manifolds are in parallel with each other and they return to the torrent. In terms of efficient running the thermal store coupled to the UFH and solar systems is a complete mismatch. the thermal store requires a temperature of 20 deg plus over the DHW demand temperature an so when charged will usually be set to 80deg (where it has proportionally higher enviromental losses than a DHW cylinder at 55-60deg) charging this store runs your boiler straight up and out of condensing mode 10-15% efficiency loss at a stroke!
The UFH is designed to use a low flow temperature on a basic sytem this is fixed somewhere around 50 deg (an actively mixed system will adjust somewhwere between 25 - 55 deg based on outside temp) so your system is taking water at (allowing for some store stratification) 70-75 deg from the store and feeding it to your heating at somewhere near double the required temperature! Your boiler will be most efficient producing a flow temperature at 40deg and below (which it has the controls to do) which it could then feed straight to the manifolds, instead you are wasting gas and experiencing extra pipe and store losses by jacking the temp up to store levels and then mixing it back down - rather like driving a car with accelerator hard down and controlling speed with the brakes!!
With regard to the solar system - once again, you are asking the panels to charge into a high temperature store, all heat sources will be more efficient the lower the flow temp, this is particularly true of solar and heat pumps and is basic physics and you are severely curtailing your solar yield.
You may be wondering why thermal stores where invented at all? They allow a traditional boiler to run flat out into the store (no cycling - turning on and off) the most efficient mode for a heat source. This was facilitated by using a small boiler, user demand would be satisfied from the store and then the boiler would catch up. I dont't know the size of your property but 28kW sounds more than double that necessary for a 250 litre store
Traditionally you would find stores in commercial environments where providing boilers suffucient to meet peak demand was economically unviable - small stores crept into the domestic market in order to provide mains pressure hot water prior to 'megaflo' type cylinders being allowed in this country. Stores do have the odd niche advantage but....
So having been so negative about your shiny new system what could you do?
1. Well the first thing I would do is disconnet your space heating from the store and couple it to the boiler via a low loss header along with the thermal store which would require a loading pump. Your boiler has twin stats (DHW and heating) assign them approriately. You should see an instant 20% saving in space heating gas consumption.
2. Fit your boiler with a VRC430 controller and a VR61 interface to pumps. 10-15% saving
3. Fit a motorised mixing valve to your heating supplies (dial open the wax valves on the manifolds), driven by the VR61 to realise the full flexibility of the system and smooth out overheating spikes caused by store charging.
4. Depending on size of house (zoning requirements) your desire for independant control and the nth degree of efficiency provide independant mixing valves to each manifold and use the Vailant 630/2 range of controllers instead of 430 and 61
5. Install a DHW preheat cylinder (feeding the store HE) driven by your panels and controlled by VR68 module that integrates seamlessly into the 430/61 bus and interface (630/2 also has solar controllers) or more sensibly swap the store for a pressurised solar cylinder
I suggest these options in cost benefit order.
Secondly with regards to controls:
The bricks are, as dicussed here before, ideal to implement simple on off controls to manifold acuators or zone valves, based on schedules, one wire temp sensors or external stats of choice via DI/AI. Valve outputs may obviously be conditional on any other brick inputs as well. This type of control would sit on top of and independant from the types I have discussed above. Use of a gateway would allow further complexity to the timing, conditional structure and remote accesability of the valve outputs.
This type of control may be redily integrated into or form the implementation of traditional 'Honeywell Sundial' type control systems which are simple cascade on/off controls (in this country) usually at mains voltage and load currents. These type of controls are however far from the state of the art and give away 20-40% of potential system efficiency.
Ian with regard to the solar controls - I am not familar with Resol, but a quick gander at the literature does not reveal the presence of any RS232 port let alone it being featured with a process interface!
They have a system called Vbus - a proprietry bus (probably very similar to everybody elses eg Vailant Ebus) system It probably uses voltage signalling in one direction and current loop in the other. Their datalogging could probably be configured to export some parameters to a PC and hence into a gateway but it would be messy. I didn't find any convertors on the site, as you seem to imply in th eother thread?
I'm not quite sure what you wish to control with respect to the solar - surely you wish it to charge at any oppotunity whilst allowing it to operate within its own safety limits? Solar systems can generate VERY high temperatures on clear sunny days and they are not to be messed with unless you are very sure of the implications.
As a final point for Andy and Co - there exists an open standard for heating controls, which has been bought into by a significant number of large players, the 'lite' version of which might be simply implemented from a webbrick - I can send you a copy of the standard if it might be of interest?
Regards
Simon