Tee branch vs manifold vs hybrid or How loading units are confusing me...

[CymroSk]

On our (seemingly never-ending) extension/ remodel of our traditional farmhouse in Slovakia, we have learnt a lot since the initial restoration of the south half of the house in 2006/7.  First lot of workers seemed fine, but lots of niggles have presented themselves over the years.  This post is specifically about plumbing, so problems there include a fairly haphazard appreciation of maintaining acceptable pressure throughout the system, and mixing up the hot flow and the hot recirculating pipes such that the flow now goes to the furthest end of the system before returning and supplying the taps - resulting in stupidly long waiting times for hot water to arrive.

 

The new part of the system will attempt to learn from this, and I have been rather keen on the full house manifold idea ('house' meaning the half we're doing now - the first half will have to wait until we move out to the newer part).  However, on trying to identify what, where, how much, I started to look at the loading units.  Using the simplified method of BS EN 806-3 gives a branch type system with impressively large size piping, even though that method is supposed to limit over-sizing.  Some pipes have to be sized up because of their length.  I should say also that we are hamstrung in having to keep the existing location for the DHW supply, which is from an 800L heat store, heated in small part by a solar array (evac pipes) and more by the 9kW 3 phase immersion heater.  In a year or so we want to get an ASHP to supply that store.

 

To get to my question of the moment; if I use an old school tee off system (probably in Pex-a) I can get a workable system, but rather more elegantly done if taken to remote manifold for each supply area.  I can then drop down to much smaller pipe and even have serial supply resulting in absolutely no dead or little used legs at all.  This last point has some relevance, as we have a private borehole supply, with no chemical disinfection, so there is no low-level chlorine in standing water.  BUT the only way we could get hot water to the far reaches within a fortnight of turning the taps on is by having hot water recirculation, which can be done, but a) costs money and b) costs more money running it.

 

On browsing here over the last week or so, there is a definite pro- full house manifold camp, led it seems by 'Nick from Wales', who talks a lot of sense. but I can find no-one addressing the potential dead leg issue of long runs from a manifold.  If only one main manifold, many runs will be 10m+ and a few in excess of 18m (Kitchen and Ensuite).  At that distance, my understanding of the tables in EN 806 means that PEX pipe would need to be DN20.

 

Any comments?