pipe sizing help,zoned heating

[dancn]

Hi All,
I'm building my own house and I'm coming near the stage where I need to lay pipes for rads.
I'm not a plumber, so any tips welcome, I'd like to route the pipes myself as I know the house,
and there are a few tricky sections where I must be careful to maintain a steady fall to a drainpoint.
Here's a rough idea of my system plans,
I'm going with plastic pipe, 1/2" copper (irish) tee-d to rads.
3 zone sytem (maybe 4,see below),
DHW,
upstairs rads,
downstairs rads,
from a sealed system, hot press downstairs in utility room.
2 heating thermostats (up/downstairs), TRVs on nearly all rads.
Solid fuel boiler and large buffer tank in outhouse, ( a few metres underground piped from hotpress)
hot water from buffer tank as required to zones.
My query for now is downstairs loop:
I've did the calcs for space heating hope I've got them right, but my rads are coming in around 25KW downstairs only.
Physically this zone run is around 60metres long.
I'm thinking a 3/4" diameter pipe may be too small for this as one zone, I may have to split into 2 zones downstairs?.
Is there a way I can figure out the size of pipe required, do I need to factor in area rather than run length.
thanks for reading...

 

[justlead1]

Hi, I would not worry to much about falls to DOC's on 60 metre runs (You can always blow the water out if required) As for 3/4" on 60 m runs, 25kw to move and the add on for the use of elbows (DIY seem to use more than others) an increase in pipe size would be a wise move. Also take into account the expansion on long straight runs when concealed in floors etc. As the stress that can be achieved can lead to failure of fittings in the future.

 

[Gray0689]

As justlead says important to have expansion look on long runs
As for the 25kw for downstairs heating that's massive for a downstairs heating zone it must be a huge house?
Isit rads or underfloor?
What part of Ireland are you building in?

 

[doitmyself]

As you talk about a "hot press", I assume you are in Ireland.

25kW is a considerable amount of heat for just one floor.

As it is a new build, the house will have to meet current standards for insulation, glazing etc.

If you use the Boiler Size Calculator you will get a good estimate of the total heating requirement for your house.

 

[dancn]

thanks for input folks.
yeah it's a big house, building in donegal.
I'm going with rads due to quick response vs underfloor.
I may though put an underfloor loop in the main bathroom.
I will have another look at the layout and go up on pipe size or split into 2 downstairs zones.
I will be laying insulation on the sub floor, then pipes, then pouring finish floor screed.
On the expansion issue is it best to form lateral 'waves' in the pipe here and there to allow for movement.
If the pipes are lagged can they move a bit within the lagging.
I'm confident I can do these downstairs runs without joints other than the rad tee's.
upstairs a different matter as I'm routing pipes in a crawl space behind knee wall. the pipes can be clipped to studs and are not going to be burried, and I have to turn 90 degrees in places. Or I can clip the pipes to the floor of the crawl space allowing a wider sweep at turns.

 

[stevetheplumber]

Calculate the amount of expansion
of a 2.4 metre pipe installed at 20ºC
when running at 80ºC.
0.00013 x 2400 x 60 = 18.72mm
Where the pipe is totally restrained
in a concrete floor (e.g. as
underfloor heating), the stresses are
so low that they are absorbed by
the material.
reading this excert from he20 data sheets looks like you dont have to wory about expansion to much
clipped to the floor in your crawl space with wide sweepping bends looks good

 

[bob the plumber]

crikey dancn, your not a plumber and your going to try and take that on with a few tips here and there? If you can pull that lot off without good knowledge ill be very impressed, let us know how you get on

 

[justlead1]

Hi Steve. Have i lost the plot? The calculation is 2400 mm (8'-00") of pipe.? I may be reading is wrong?

 

[dancn]

around 1.3% for pex from 20 to 80degrees, does that sound right?
so for 2400mm length
3.12mm ?
when doing compresion joints, (rad tee) PTFE threads or boss white?