The system is MTHW. On the generation side of the header, there is 6
boilers and associated pumps. On the distribution side there are a
number of pumps and exchangers to provide space heating for buildings
and hot water for absorption chilling. I take on board what you are
saying but as there are pumps I don't think it is for natural
convection. We are looking at physical sizes of 1.5m diameter and 7m
high.
My initial thoughts were that it was some sort of thermal buffer with
a thermal gradient up its length. Smoothing out any steps when
tunring boilers on and off.
- In PipingDesign@yahoogroups.com, "Steve McKenzie" <Mechproj@x>
wrote:
> Hi Mike
> I assume you have either LTHW or MTHW boilers feeding some
radiators or fin
> coil units. With this type of boiler, best performance is normally
achieved
> by maintaining a fairly constant flow rate through the boilers and
varying
> the firing rate according to the boiler discharge temperature,
modified by
> boiler differential temperature. The heating distribution mains is
normally
> variable volume with constant differential pressure across the
distribution
> circuits. This means that the distribution mains flow rate varies
with the
> heat demand, but a constant flow rate through the boiler is
required.
> There are normally two approaches to this. The first is to use an
injection
> system.
> This has two duty pumps; one to circulate through the boiler at a
fairly
> constant rate, and a second to circulate through the (secondary)
> distribution system. Heated boiler water is bled off the primary
circuit
> into the secondary via a control valve. The valve is controlled by
the
> secondary circuit flow temperature. This is the only way to go when
> distribution circuit pressure loss is high (long pipe runs).
> The second is to use the primary boiler circuit and pump with an
orifice
> plate or control valve to generate a pressure difference for the
> distribution mains and circuits. Good for short runs and low
pressure drops.
> As hot water rises, a bit more head is available by buoyancy but
the effect
> is normally not much.This is probably the intent of your low loss
header -
> very little if you are using pumps.
> If you have a natural convection system you will have no pumps,
very large
> pipes, temperature control will be difficult and you will
definitely need
> the low loss header.
> Natural convection can be and is engineered (e.g. nuke subs to
eliminate
> pump noise) but it seldom has a place nowadays in general
engineering single
> phase distribution services.
> A couple of diagrams sure would help.
>
> Cheers
>
> Steve Mckenzie
>
>
> -----Original Message-----
> From: mikekdixon [mailto:mikekdixon@y...]
> Sent: Wednesday, March 26, 2003 10:45 PM
> To: <a href="/group/PipingDesign/post?postID=Rq3aBhn3By53n7mIm-EfDzEhSQeUkNsPamlBmFHgIg2QgHFZvRvRltZepMHMtiqjHPfpUhUs979-W0adUqaS1tsO">PipingDesign@yahoogroups.com</a>
> Subject: [PipingDesign] Low Loss Vertical Mixing Header
>
>
> I have received a P&ID from one of our clients for a hot water
> production and distribution system and there is an item called
a 'Low
> Loss Vertical Mixing Header' on it. It has hot water going in and
> coming off at the top and the cold water returns coming in and going
> back to the boilers at the bottom. I think it is intended to be
some
> sort of thermal buffer. Is there any experience of these or
> explanations behind them?
>
>
>
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Received on Wed Mar 26 09:14:00 2003