help please new system

[emailuserq]

hi , i am in the middle of an extension for my house , 2 adults 2 children 4 bedrooms , 1 bath 2 showers , used to have a combi , but due to new rooms etc i am changing the heating system.

Plan is to install a thermal store -- with a coil for the new ufh , a solar coil for future expansion , and a heat exchanger for the DHW, i have room for the thermal store and a system boiler ,

For Hot water i will use incoming mains into the mains feed on the store , with a mixing valve giving me the DHW

for the underfloor heating i will connect the ufh flow and return to the ufh manifold

To use the system boiler to heat the radiator circuit as well as heating the water in the store i plan to use a three port motorised valve to switch the boiler to heating the radiator circuit when needed

i have attached a pic of my basic plan ... a couple of questions , with a open vented Thermal store and a system gas boiler i do not need any extra expansion vessels do i ?

Do i need an extra pump for the radiator circuit ? , what else should i add to the connections ? View media item 38139

 

[Youllneverguess]

You will need to use an OV boiler otherwise it will need to heat through an additional heat exchanger, or an unvented store.

Why not run the rads off the store as well and negate the need for control valves?

Do not use a three port valve. If you must - use a 2 port valve and preferably 28mm valve and pipe to reduce reheat times.

You could use a boilers internal pump, or place your own on the combined return form the rads and store.

 

[muggles]

System boilers tend to be pressurised unit rather than open vented, although there are exceptions, but generally you'd need a heat only boiler and separate pump & controls

 

[emailuserq]

From what i have read it is not a good idea to run the rads from the store ... as i will have 8 rads ( 1 in each bedroom(4) , 1 in each bathroom (2) and 2 downstairs ) , so do thermal stores ( vented ) allways have open vented boilers ?

 

[MeldrewsMate]

...so do thermal stores ( vented ) allways have open vented boilers ?

Most thermal stores are open vented, so have their own seperate feed and expansion tank. Most system boilers need a minimum system pressure to allow them to run, so the two may not be compatable.

Secondly, thermal stores tend to run at high temperatures (80 degC), so you may find your rads have a very high touch temperature because there is only one temperature setting knob on the boiler. (Again, some boilers have more than one). A solution may be to drive the rads via an underfloor type mixing arrangement, but the downside is another pump is required.

Perhaps the best solution would be to use the CH output from the thermal store to drive the rads directly, and the UFH from its mixing valve: keeping with a regular heat only boiler into the open vented system.

If you went for an unvented thermal store you could use the system boiler, but bear in mind the extra system volume of the store would mean that an extra expansion vessel would most probably be needed.

MM

 

[Youllneverguess]

My 350 litre thermal store is unvented - and has a huge floor standing expansion vessel sitting next to it (although will be moved into the loft soon.

The rads are fed from just over half way up the store. The system boiler that feeds it thinks it is heating a cylinder directly so runs at full steam until the boiler return temperature hits 61 degrees. With a flow temperature of around 82 that gives me nearly a text book condensing burn with the boiler in condensing mode 99/9% of the time.

Hot water flow rate of around 40 litres per minute is possible, but not sustainable really. Unless I move from a 24 kW boiler to a much larger unit.