thermal store/rayburn what else do i need?

[igotalake]

sorry for resurrecting but now i do want to redesign the viessmann system a little bit. i haven't got round to implementing the heat store plan yet but i am going to move my dhw tank in preparation and rather than double up the heavy pipework installation from the boiler to the new tank position i would like to utilise the existing radiator pipework with a motorised valve to allow heating of the dhw tank. my question is how do i connect a motorised vlave to the vissmann control?
anyone have any ideas?

 

[Norcon]

The boiler here is a Vitola 100 oil boiler afaik.

Four pipe system off the boiler. Your diagram doesn't show it but I assume another pump is fitted on the cylinder circuit.
And you want the CH pump to provide flow to the cylinder.

Change it over too S plan.
Just connect the dhw feed to the motorized valve instead of the pump and the end switches will energise the CH pump.
And blank the two old f&r's off. And then extend the cylinder sensor to the new location.
Simples.

The controller might need protected from a backfeed so relays might be needed.
This is kintergarden stuff.

 

[SimonH2]

If you choose a suitable thermal store then you can arrange for Adolf to keep just the upper section above a minimum to provide hot water and heating, and then the Rayburn will heat the rest.
I'd think that the required store size for this to work would be not larger, probably smaller, than the combined size of store and unvented cylinder in your design.

If I were designing a system then I'd go further, and have more than one stat on the store. One to set minimum temperature for the hot water supply, and a second to set minimum temperature for the CH drawoff which would normally be lower down the store. Whenever the Rayburn is providing enough heat to satisfy demand, then the stats will keep Adolf turned off altogether.
If you don't have the Rayburn lit, then Adolf will get called upon only to keep the upper part of the store hot - and still leave (say) half of it "cool" and ready to take heat from the Rayburn.
If you fit a modulating pump to the CH circuit, then you'll also find you get a nice quiet system - without the need for "always on" rads or bypasses to keep the boiler happy.

Don't forget that the design of the DHW heating coil is such that it can take heat even from the cooler lower part of the store - as long as the incoming mains is cooler than the bottom of the store then this will happen. So the DHW coil will (in the absence of warmer return from from the CH) get the bottom of the store down close to the mains supply temperature.

All assuming that you design the system to allow the stratification to be maintained.

 

[igotalake]

thanks for the good ideas simonh2. i am dealing with a previously installed situation and trying to re-use whatever bits i can sensibly use to achieve my desired result and that puts constraints on my designs. basically i don't want to spend thousands on a system that will take forever to pay for itself so i have been planning this for ages and the plans keep changing.
norcon, i know i am clueless and i forget that sometimes but i thought that the viessmann control may have a simple terminal connection that would achieve what i want to do with the motorised valve whilst allowing the controller to know what is going on. i've never known a boiler with such controls as this one and just hoped it would have a direct connection for this one outlet system. if i was to use the dhw pump voltage to energise the motorised valve and the CH pump, would there be a problem when the controller has the voltage acrross it's CH pump terminals when it believes the CH pump is off? or is this where the relays are required? that sounds too complicated.

 

[Norcon]

if i was to use the dhw pump voltage to energise the motorised valve and the CH pump, would there be a problem when the controller has the voltage acrross it's CH pump terminals when it believes the CH pump is off? or is this where the relays are required? that sounds too complicated.

The relay is a simple device.
All panel builders use them to protect expensive controllers.

So a wrong connection on site by a spark only blows up a cheap relay costing a few quid and not an expensive controller costing thousands.

 

[igotalake]

ok, so there would be a normally closed contact that normally allows the controller output to supply the CH pump through it.
the dhw pump output from the controller then comes alive and energises the relay which physically disconnects the controller from the CH pump. the motorised valve operates at this time as well and the contacts on it subsequently supplying the CH pump from the dhw pump voltage. i think i get it.

next point is that the CH pipes coming into the house are 34mm immediately dropping to 32mm. there are 12 rads almost all being cast iron. i haven't found a motorised valve that is bigger than 28mm or 1" and i think that is fine for the water cylinder but would it be a waste to throttle the CH at all when someone has gone to the trouble and expense to use 32mm as the main pipework. (in fact the immediate pipwork off the boiler for CH is about 2" dropping to 34mm somewhere in the boxng accross the patio and then 32 as it enters the house).

 

[Norcon]

The easiest with the relay is connect the ch output to the coil. Then N/O to the mv. End switches for the pump.
End switches on the hw valve act as the other relay.

28mm zv shoud be fine. Check its pressure drop on MI's specs sheet.
Danfoss HPV28 shoe type has 0.05 bar p/d for 40kw. So is well within their specified maximum of 0.7 bar.
22mm should be fine for the dhw.

 

[igotalake]

thanks for your advice, i am now watching a couple of 28mm 3 port valves on ebay.