Can anyone remember the rule of thumb capacity of central heating pipes
(15mm,22mm and 28mm)? I'm intending 70 degree flows. Just need to work out
if I need 28mm to the up/down zone valves. I'm sure 22mm is fine after
these.

Christian.

"IMM" wrote in message
...

"Christian McArdle" wrote in message
. net...

Can anyone remember the rule of thumb
capacity of central heating pipes
(15mm,22mm and 28mm)? I'm intending
70 degree flows. Just need to work out
if I need 28mm to the up/down zone valves.
I'm sure 22mm is fine after these.

Christian,

At 11C temp diff between flow and return:

15mm: 6 kW
22mm: 13.4 kW
28mm: 22.5 kW

If you are installing a condensing boiler size the rads for 60C flow and
40C
return, which is standard in most of Scandinavia.

See:
http://tinyurl.com/k0rx
Pipe Sizing and Flow Rates

It can be calculated, with a flow rate of 1.5m/s as recommended in BS4449,
that a 15mm pipe is able to carry 4.25kw of sensible heat a 22mm 12kW and a
28mm 35kW.

Due to the higher flow and return temperature differentials in a system
designed for condensing boilers (approximately twice that of traditional
systems) an equivalent size pipe would carry the same amount of heat.

Therefore it can be calculated that a 15mm pipe is able to carry 9kw, a 22mm
pipe 24kW and 28mm pipe 70kW.

When designing an installation, with radiators sized for a flow temperature
of 70oC with a return differential of 20oC, you may permit the use of
smaller pipe diameters for the heating circuits.




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If you are installing a condensing boiler size the rads for 60C flow
and 40C return, which is standard in most of Scandinavia.

The rads are already in (but need TRVs and zoning). I calculate my total
requirement as 12kW, even after allowing 50% extra for extra rapid warm up.
Looks like 22mm is fine. I may get a loft conversion in the future, but the
boiler will actually be sited in the loft, so won't go through the run I'm
considering here.

Christian.

When designing an installation, with radiators sized for a flow temperature
of 70oC with a return differential of 20oC, you may permit the use of
smaller pipe diameters for the heating circuits.

In any case 22mm will be quite enough. There won't be any saving to had
downsizing to 15mm and I'm happy with 22mm rather than 28mm as it will fit a
pipe bender. I haven't calculated the radiator powers yet, so don't know if
70/50 will be doable in reality. They look to be on the small side to my
eye.

Christian.

On Thu, 14 Aug 2003 17:12:44 +0100, "Christian McArdle"
wrote:

When designing an installation, with radiators sized for a flow temperature
of 70oC with a return differential of 20oC, you may permit the use of
smaller pipe diameters for the heating circuits.

In any case 22mm will be quite enough. There won't be any saving to had
downsizing to 15mm and I'm happy with 22mm rather than 28mm as it will fit a
pipe bender. I haven't calculated the radiator powers yet, so don't know if
70/50 will be doable in reality. They look to be on the small side to my
eye.

Christian.


Christian

The one to watch out for is not to drop from 22mm to 15mm too early,
in the sense of having too many radiators (actually too much capacity)
on 15mm runs.

If you are going to derate for 70/50 operation vs. 82/70, in general
it means dividing the required power level for the room by 0.6 rather
than 0.89 for most radiators, and then referring to the main table in
the manufacturer's data sheet to choose the radiators.

I found that when I refurbished my system, in some cases the radiators
were way oversized anyway so nothing to do, in some cases I moved
radiators from one room to another and in some cases I fitted new
radiators. However, there was only one case where I had to use a
radiator that had a larger footprint of wall space (if you follow my
meaning). For the others, it was possible to use a double panel or a
finned radiator where a lesser one had previously been.




..andy

To email, substitute .nospam with .gl

On Thu, 14 Aug 2003 19:26:09 +0100, "IMM" wrote:



At a given flow rate and temperature drop perhaps you can explain how a
28mm
pipe can carry eight times the heat of a 15mm pipe with only 3.5 times the
internal area?

It was taken from the web site URL given.


It must be right then.....




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..andy

To email, substitute .nospam with .gl

On Thu, 14 Aug 2003 16:10:02 +0100, "Christian McArdle"
wrote:

Can anyone remember the rule of thumb capacity of central heating pipes
(15mm,22mm and 28mm)? I'm intending 70 degree flows. Just need to work out
if I need 28mm to the up/down zone valves. I'm sure 22mm is fine after
these.

Christian.



There is a technical note published by the Copper Development
Association which covers how to easily calculate the pipe sizing
requirements using a simple set of tables to allow for fittings, pipe
lengths etc.

http://www.cda.org.uk/megab2/build/Pub150%20UKCB.pdf

The example given covers the conventional 82/70 degree system. It's
easy enough to substitute in the required mass flow rates for 70/50
operation

..andy

To email, substitute .nospam with .gl

If installing a quick recovery cylinder install a priority system.

The controls will be S-plan, with (eventually) four zones. Upstairs,
downstairs, loft conversion and conservatory.

The cylinder being next to the boiler should result in it getting some
priority, but I'll probably leave it at that. With the cylinder on 24/7, the
increased recovery times when the heating is on shouldn't be too bad.

Christian.

"Christian McArdle" wrote in message
. net...
If installing a quick recovery cylinder install a priority system.

The controls will be S-plan, with (eventually) four zones. Upstairs,
downstairs, loft conversion and conservatory.

The cylinder being next to the boiler should result in it getting some
priority, but I'll probably leave it at that. With the cylinder on 24/7,
the
increased recovery times when the heating is on shouldn't be too bad.

Christian,

Are you installing a quick recovery cylinder? If so, no need to keep it on
24/7. One advantage is that they heat so quick you can have a cold
cylinder, think I want a bath, switch it on, and by the time you have
phaffed about preparing soap and getting undressed you have a bath full of
water ready. They are approx 15-40% cheaper to run than simple part L
cylinders. You can have a simple diverter valve and your zone valves on
the CH circuit.

It is a far better setup. BTW, the Drayton 2 port valves with an end switch,
on sale at B&Q for approx £32, can have the plug screwed out the bottom and
a BSP to copper compression fitting screwed in to make it a 3-port.




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With 24 kW available you would be foolish not to go to a quick recovery
cylinder.

I'm probably going for something like a DPS heatbank with pressurised
primary coil, provided I can persuade them to make a 150L or 180L version
with the double plate heat exchanger (they only list the 300L with this as
standard). I need the double heat exchanger as I think the projected 30lpm
to 42C of the single is too low. I need pressuried DHW and heating circuits,
as I will be converting the loft and putting in a shower room and radiators.
Whilst in general, I'd prefer an unvented cylinder, the location in the loft
with no obvious safe and visible location for the pressurised vent makes the
heat bank more sense, despite the fact that it will reduce the opportunities
for the boiler to condense.

If you are fitting just two-port valves, then it is a simple matter
(maybe using a relay) to convert the system to quick recovery
priority.

I'm more likely to wire it up conventionally and put in relays if I find a
problem in practice, which I don't anticipate.

Christian.

"Christian McArdle" wrote in message
. net...

With 24 kW available you would be foolish not to go to a quick recovery
cylinder.

I'm probably going for something like
a DPS heatbank with pressurised
primary coil, provided I can persuade
them to make a 150L or 180L version
with the double plate heat exchanger
(they only list the 300L with this as
standard). I need the double heat
exchanger as I think the projected 30lpm
to 42C of the single is too low.

Good move. They will probably fit a quick recovery coil anyhow as standard,
but check. But!! go for a single plate heat exchanger with a 150/180L. If
it does not cope then insert another plate heat exchanger in parallel
yourself. This is a great advantage. DPS use push-fit brass fittings.
This would only take about an hour to fit. Try uprating the coil of an
unvented cylinder as you go along. Heat banks have that great flexibility.

I need pressuried DHW and heating circuits,
as I will be converting the loft and putting
in a shower room and radiators.
Whilst in general, I'd prefer an unvented cylinder,

Heat banks are far better than unvented cylinders and you can DIY them.

the location in the loft
with no obvious safe and visible location
for the pressurised vent makes the
heat bank more sense, despite the fact that
it will reduce the opportunities
for the boiler to condense.

The difference between condensing while heating an unvented cylinder or heat
bank is minimal. In fact greater overall efficiencies will be had from the
heat banks as the primary blending valve will be set approx to 55C. You
also have the rapid heat up of the heat bank and within a few minutes from
cold you will have usable hot water. Another advantage is that you don't
have to reduce the mains pressure, so if you have 6.5 bar, as I do, then you
can have this at your taps.

If you are fitting just two-port valves,
then it is a simple matter
(maybe using a relay) to convert the
system to quick recovery priority.

I'm more likely to wire it up conventionally
and put in relays if I find a
problem in practice, which I don't anticipate.

famous last words.


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The difference between condensing while heating an unvented cylinder
or heat bank is minimal.

I've just had a thought (just rambling, not thought through). Would it be a
good idea for the cylinder primary coil return pipe to go through a plate
exhanger with the incoming mains cold? This would pre-heat the incoming
mains a little and reduce the primary return line temperature quite
considerably, giving good condensing and something for the boiler to "push"
against. I can see a problem that you might unnecessarily heat a short
section of DHW piping when the cylinder is recovering but no DHW flowing,
but this could be dealt with by insulating the section to reduce losses and
this 82C heated section would be sorted out by the thermostatic output
valve, before it hit the taps, probably.

Opinions?

Christian.