Replacing oil boiler with condensing- return temps and buffer for ufh

[thompo5015]

Hello,

 

I currently have an old oil boiler running downstairs UFH + a towel rail and 4 rads.

I have a Condensing oil boiler to replace the old one, i have read some stuff about return temperatures having to be controlled by a mixing valve to ensure max efficiency and eliminate heat exchanger corrosion??, Is this necessary? I haven't found one in any of my friends or families houses and the literature for the boiler does not mention anything (Warmflow Kabinpak)

 

 

 

 

Looking at the installation above is a condensing boiler a simple replacement with no added mixers etc?

 

I have a spare twincoil 180l UVC and i have toyed with the idea of using it as a buffer for the UFH and also allow solar to help with heating vs DHW in winter but im unsure of the execution...

 

I can put a manual valve or (zone valve) on the solar to divert flow and make a box to switch the controller from 1 set of tank probes to the other.

Option to put a zone valve linked to the DHW demand to isolate the 2nd cylinder when DHW is needed to boost heatup.

Away from the solar would something as basic as this arrangement below give any savings? - I know a thermal store is the answer but budget doesn't go that far at the min and as i have most of this stuff, only cost will be a zone valve, expansion vessel and a bit of time.

Stats would be set to fire boiler when the top of cylinder falls below 40 and off when bottom hits 60 or boiler flow temp.

Any benefit heating the 2nd cylinder directly along with the UFH or having the UFH draw off via a coil? 

 

 

Thanks for any info.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited January 22, 2020 by thompo5015
too many pics

[A_L]

1 hour ago, thompo5015 said:

i have read some stuff about return temperatures having to be controlled by a mixing valve to ensure max efficiency and eliminate heat exchanger corrosion??,

 

I think your thinking about solid fuel stoves where this can be necessary. New condensing oil boilers will have corrosion resistant heat exchangers as condensation on them is obviously desirable. Heat output from a given amount of fuel rises as return temperatures fall.

 

from https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/648337/heating-controls-compensation-tpi-bre.pdf page 11

Edited January 22, 2020 by A_L
correct typing

[Temp]

5 hours ago, thompo5015 said:

i have read some stuff about return temperatures having to be controlled by a mixing valve to ensure max efficiency and eliminate heat exchanger corrosion??, Is this necessary?

 

I believe for our Grant the instructions say the return must be >40C and <55C at all times.

 

They recommended a mixer is used to ensure the return isn't too cold during startup as too cold apparently causes corrosion. On the other hand the boiler and load must be correctly sized or the return will be too hot preventing it operating in condensing mode or even cause short cycling.

 

That 15C window might be wider on boilers with Stainless Steel heat exchangers?

 

We struggled a bit to get it in the window. Had to fit smaller jets to reduce the power but the manual says that improves efficiency compared to standard jets. It started life as a 40kW feeding a 300L thermal store.

 

Edited January 22, 2020 by Temp

[dpmiller]

Our Turkington has a SS secondary HE and I don't believe there are any limits on the return temp.

[thompo5015]

Thanks, it seems the Warmflow boiler has a stainless condensing heat exchanger too so shouldnt need anything extra