Adding a buffer tank for UFH with condensing oil bolier to save fuel??

[thompo5015]

Hello,

I currently have an ancient Grant 70/90 with reilio burner running sealed and feeding a 250l unvented cylinder with 30tube solar for DHW, 3 small rads upstairs, 1 towel rail and ground floor UFH (150mm centres and Gypsum screed, tile floors) split into 7 zones + rads& DHW, all hooked up through a Heatmiser UH1.

Heating a 90m sq bungalow with attic conversion, solid brick walls and no insulation in roof, (solid floor has 100mm PIR though) needless to say insulation would be best option to curb excessive oil use but as we could be doing with a new roof and render in the next few years, that = new warm roof, dormer extension and EWI but thats a few years off yet.

Winter sees us get through 500l of oil a month, Mrs will be at home with baby this year so id like to cut this (oil use! not the mrs and kids)...

I have been given a 2008 vintage Warmflow 70 condensing boiler with only 6 months use (boiler replaced, house sold to a family friend, he fitted gas when moving in and its sat until they have decided to move again)
Whilst it should be more efficient than my old boiler its still going to suffer from short cycling due to UFH only needing low temp and oil not modulating.

I have found a used 200l Twin coil cylinder for not a lot. Not sure if it was destined to be sealed or vented, haven't looked it over yet.

My thinking.... is to use this as a buffer tank, just not sure on how best to hook it up.

Current plan connect UFH with the 200l tank, heated from top down by the indirect coil to 40 -50deg to minimise standing losses, 2 stats to control boiler demand, Or is it best to heat to normal temp of boiler and let the UFH manifold mix it down?

Solar linked into 2nd buffer coil and swapped manually with a valve for summer/winter to help with space heating or DHW (could be automated to do either or both with right logic). It currently lifts the DHW to around 25-30ºC during winter sun so that isn't far off the UFH temp and should help.

Boiler remains sealed and supplies the DHW coil, buffer tank coil and rads/towel rail direct.

I see this as giving quick heat up for the rads/towel rail/DHW coil (direct and sealed to minimise corrosion in rads/boiler) and putting a larger load to help stop cycling when UFH is required, corrosion should be less of an issue with the UFH as the only metal component is the manifold and valves.
Heating the buffer top down should allow the UFH to draw warm water quicker than waiting for the full 200l to heat?

Would this work, if so how best to optimise for condensing operation?
Is it likely to save more than the £200 or so it could cost to implement (DIY, no changes to unvented cylinder required.)

Cheers for any advice.
 

[Nickfromwales]

I’d do away with the UVC and fit a TS with a solar coil. Your additional standing losses would negate the effort IMO. 

Would the buffer be situated where the waste heat from it would lend itself to space heating ?

[Declan52]

What is your floor covering on the attic conversion?? Would it be possible to lift the floor and put some Rockwool in between the truss. Would help with your heat loss. 

[thompo5015]

The buffer would be beside the UVC in the utility room, along with wash machine and tumble. Standing losses would contribute little to heating the rest of the place, we are only ever in there when we need to be and door closed when machines are going.

 

I had planned for a Thermal store at the outset and got talked out of it by 3 different plumbers when I was getting quotes as "gas was coming". Ended up getting a great deal on UVC and fitted DIY, with 1 of the above plumbers coming to check and sign it off.

Gas came about 6months ago, the main runs past my drive way but I cant get it because the nearest low pressure supply stopped 600m down the road where the housing developments end

 

Would need weigh up cost of TS and savings Vs cost of buffer. Agree TS would have been the way to go!

 

Floor upstairs is chip board or  16mm floor boards. Given that we hope to have a warm roof + EWI (tea cosy idea) id prefer not to insulate the attic from any escaping heat below as it will be useful at some stage lol.

 

Ill start a thread in the relevant section on insulating the roof, got a couple of ideas.

 

Thanks