Heating System Design

Hello to all

I am currently refurbishing and old victorian farm cottage and propose to install a new heating system as per the attached diagram. I would appreciate advice/opinion as to the validity and efficacy of the proposed design attached. To pre empt some likely questions regarding heat source and design choices:

1. We do not have the room for an indoor boiler
2. There is no mains gas
3. I've used LPG before and changed it to kerosene before it bankrupted me
4. The exterior has been restored sympathetically and there is no unobtrusive location for the boiler near to the house
5. I see at lot of "greener" alternatives through my work, eg GSHP/ASHP/biomass-I've no time for any of them as they're either too expensive, unreliable or both.......
6. We do not have chimneys for solid fuel any more which precludes woodburner/duel fuel arrangements unfortunately.....

Thanks in advance

Hi TheMoneypit

First off I just want to say you clearly already have a decent understanding of systems like this, so any advice from me or anyone else you should have no problem visualising.

Question 1. I assume you missed out the appropriate returns? A LLH is one way of achieving hydraulic separation but there are others as well. Are you sure the boiler pump isn't man enough to cope with system demand? If its not then yes a system like you mentioned is best as as you know multiple pumps will be needed and without either of them interrupting each other.
Sizing a LLH is quite complicated, although many manufacturers either do it for you or have units off the shelf to suit most applications.
There are other options as well. See attachment.
This is an NRG zone system. The image shows DHW and two radiator circuits, although UFH zone/zones can be added. Ive not seen one in the flesh but have read a lot of their literature and this is another option, the use of your VT valves i imagine could be incorporated but dont quote me on that.
Question 2. The size of the boiler primaries should be such to carry the KW output, umongst minimum flow rates. Quickly looking at my design guide 22mm outer diameter can carry 23KW at delta t 20°c with a target velocity of .9m/s. I would of thought upping that to 28mm will be sufficient.
Question 3. Installation of non return valves will stop any reverse circulation.

Whether you're using a LLH and distribution header or something like the NRG zone system, calculations must be made for the correct sizing piping etc.