On Fri, 12 Nov 2004 00:39:49 -0000, "IMM" wrote:


"John Aston" wrote in message
...

"Aidan" wrote in message
om...

It (primary/secondary pumping) is very rare on UK domestic
installations, mainly because of the costs.

Interestingly, having spoken to their technical departments, both Viessman
and MHS *require* the installation of low loss headers if any pumps are
installed in the heating system (other than the boiler's pump, of course)
running off their modulated boilers.

MHS supply a Strata 1 boiler. It is a re-badged version of the Eco Hometec
Micromat EC. The Eco Hometec literature shows a Y-plan zone valve
installation with a supplementary pump in the radiator circuit. The MHS
literature shows almost the same arrangement as an example of an incorrect
installation!

(For flow control, Viessman Vitodens can be connected to a sensor that
monitors the header temperature. The Strata 1 just monitors the
temperature
within the boiler.)

I think that I've got enough information to come up with a draft heating
system design. I'll probably post it on the web and invite comments. This
newsgroup has been an excellent source of help in that respect.

With condensing boilers headers reduce efficiency. With a condenser you
don't want very hot water feeding right back into the return. This raises
the return temp which reduces efficiency. You want the return temp as low as
possible. Best use a heat bank or thermal store, which is a great neutral
point, and have the boiler heat that directly. For most of the re-heat the
return temp will be low.

Not if you are using a condensing boiler with wide modulating range
such as the MAN Micromat or Viessmann.

Putting a heat bank in the middle will do one of two things.

a) If the heatbank is used for HW as well as CH, and there is a
thermostat arrangement on the heatbank, the effect will be to prevent
the boiler from operating at the lower end of its temperature range
and will cause it to cycle on and off.

The whole point of this type of boiler is to have high output for a
short period to heat the heatbank/cylinder quickly for DHW use, and to
drive the heating system directly to allow modulation down to low
output levels.

or

b) If the heatbank is used solely for CH and no thermostat, it will
effectively create an equilibrium situation with heat in and out and
no real advantage over a much smaller header.

It is far more efficient to run this type of boiler continuously at
lower output than in bursts of high output.



All headers are neutral points for circuiots to tee into. A heat bank gives
you that and a DHW store with instant high pressure DHW. You only need cheap
simple boilers with a heat bank, one of its selling points.

I'll try and come up with some alternative systems.

This could be entertaining.....



--

..andy

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