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Calculate size of low Loss Header

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sambotc said:
Me and Chris Watkins had a look at it last night briefly and actually couldn't quite work out the example above. If I get a chance I will try and get confirmation from the source.
Click to expand...

Your formula is slightly wrong
The first part is right which gives you your flow rate in 3m/s
If you use 0.5 as your velocity through the header you are sizing for the worst case
The next part should be diameter of header(mm) = (square root of ((flow rate in m3/s x 1.28)/design flow velocity through the header)) x 1000
= 55mm header
You should really always go to the next size up so 67mm copper (in reality 54mm would do as the specific capacity of the water was rounded up when working out the flow rate) or 2" steel as steel (size for size) has a greater volume than copper.

A quicker way to do it is 3 x diameter of the primaries. That may oversize it but it won't be wrong.
 
So thats tonights maths lesson courtesy of UKPF

So after all that does gary need a header???
 
Low loss headers are sized on the heat input(total boiler kw as more than one boiler could be fitted) the delta T of the boiler(s) (between 11c and 20c depending on design) and the velocity of the header (normally less than 0.5 metres per second). Once you know this you can size the header from the CIBSE pipework charts.
 
If you guys were stood in front of the boiler and knew what was being connected to the boiler from the system, all the different circuits and the boiler needed to be 50kW as a rule of thumb, what length and diameter LLH would you suggest this chap fits, you must have some idea and as Tamz says it would not hurt to be even a few diameter oversized, " would it", shall I have a stab, 100 mm dia MS 750 mm long, am I anywhere near, have to be welded up and would not look good in a kitchen, just a thought rule of thumb.
 
Nostrum said:
If got a spread sheet somewhere for sizing LLH's i'll see if I can dig it out. Never used it myself, but was given to me by a heating consultant who teaches on HETAS courses so must be reasonably accurate, i hope!
Click to expand...

happyflyer said:
If you guys were stood in front of the boiler and knew what was being connected to the boiler from the system, all the different circuits and the boiler needed to be 50kW as a rule of thumb, what length and diameter LLH would you suggest this chap fits, you must have some idea and as Tamz says it would not hurt to be even a few diameter oversized, " would it", shall I have a stab, 100 mm dia MS 750 mm long, am I anywhere near, have to be welded up and would not look good in a kitchen, just a thought rule of thumb.
Click to expand...
Perfect
 
happyflyer said:
I shall I have a stab, 100 mm dia MS 750 mm long, am I anywhere near, have to be welded up and would not look good in a kitchen, just a thought rule of thumb.
Click to expand...

50kw boiler, 1¼" primaries x 3 = 3¾" = 4" :smile:
Near enough :wink:
 
If you have the Domestic Heating Design Guide it is section 13.8 (well it is in my old one)
flow rate = H / (TD x SH) = kg/s where
H = heat output in watts (50kW = 50,000 watts)
TD = temperature difference between flow & return in deg C (either 11 old or 20 new systems/boilers)
SH = specific heat of water in J/kg (which is 4186)

So flow rate = 50000 / (20 x 4186) = 50000 / 83720 = 0.5972 kg/s round it up to 0.6 kg/s
Using Tables 13.1a & b look down the column's of figures until you see >0.6 above the 0.5 m/s Velocity line that works it way across the table/page, in this case it appears in the first column on table 13.1b which is 42mm pipe size but it is only just, it might be better to use the next size up i.e 54mm in which case the velocity would drop to around 0.3 m/s.
So rule of thumb boilers up to 50kW can be connected to a 54mm copper or larger L.L.Header if using a delta T of 20deg C.
The pipe work connections should be arranged so that all the flows are at one end & all the return are at the other with a reasonable section of clear pipe between (say 150mm or 5 x inlet pipe dia minimum)
The F&R to boiler/s (or any draw off circuit) could be sized in the same way as above but normal velocity for domestic systems is </=1.0 m/s. Or use the quick pipe sizer 13.2 (28mm can carry upto 40,000 to little & 35mm upto 62,000) so 35mm it is.
Better to arrange header so it is in the vertical (air & dirt separation) & make sure it has an AAV on top end & drain off on bottom.
Anyone got any thing to add (have I got it right ?)
 
Last edited:
chris watkins said:
If you have the Domestic Heating Design Guide it is section 13.8 (well it is in my old one)
flow rate = H / (TD x SH) = kg/s where
H = heat output in watts (50kW = 50,000 watts)
TD = temperature difference between flow & return in deg C (either 11 old or 20 new systems/boilers)
SH = specific heat of water in J/kg (which is 4186)

So flow rate = 50000 / (20 x 4186) = 50000 / 83720 = 0.5972 kg/s round it up to 0.6 kg/s
Using Tables 13.1a & b look down the column's of figures until you see >0.6 above the 0.5 m/s Velocity line that works it way across the table/page, in this case it appears in the first column on table 13.1b which is 42mm pipe size but it is only just, it might be better to use the next size up i.e 54mm in which case the velocity would drop to around 0.3 m/s.
So rule of thumb boilers up to 50kW can be connected to a 54mm copper L.L.header if using a delta T of 20deg C.
The pipe work connections should be arranged so that all the flows are at one end & all the return are at the other with a reasonable section of clear pipe between (say 150mm or 5 x inlet pipe dia minimum)
The F&R to boiler/s could be sized in the same way as about but normal velocity for domestic systems is <1.0 m/s or use the quick pipe sizer 13.2 (28mm can carry upto 40,000 to little & 35mm upto 62,000) so 35mm it is.
Better to arrange header so it is in the vertical (air & dirt separation) & make sure it has an AAV on top end & drain off on bottom.
Anyone got any thing to add (have I got it right ?)
Click to expand...



You tell us you're the instructor, sounded impressive
 
Looks good to me, Chris and seems to tally up with the sizing and rating of the LLH manufacturers. Easier to understand than the original calculation suggestion I posted back in 2012.

This is is at bit of a thread resurrection.
 
lvh.jpg
 
happyflyer said:
View attachment 17393
Click to expand...

Thats not really a header. Its more like a spirocross air and dirt seperator.
You can make your own up just the same.
Design it at around 2 litres/kw with a flow rate of 0.1m/s or less. That allows for the muck to settle and stratification to take place.
You can make a better one yourself anyway. Its easy if you know how.
 
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