"Andy Hall" aka Matt wrote in message
...
On Tue, 23 May 2006 13:23:47 +0100, Doctor Drivel wrote
(in article ews.net):


"Andy Hall" akak Matt wrote in message
...
On Tue, 23 May 2006 00:27:58 +0100, Doctor Drivel wrote
(in article ews.net):


"Andy Hall" aka Matt wrote in message
...
On Mon, 22 May 2006 13:50:31 +0100, Doctor Drivel wrote
(in article
ews.net):

Buy a Danfoss BEM 5000, that will do
they job for you. I saw one on ebay
that went for £22 brand new plus £5 postage.
£200 worth of compensator for
buttons. Most don't understand them and
can't see what they can get from
them, thinking a modulating boiler is the answer.
Modulating on a setpoint boiler temp is not
the same as load compensation.

This type of thing is a very poor option
in comparison with a proper weather
compensation on the boiler controller
whereby it knows what the temperature
is.

Matt, it knows what the temperature is as it senses the return
temperature
of the heating.

In the context of this I am obviously referring to the outside
temperature
and not the boiler return temperature.



It might be worth £22, but certainly not £200.

Matt, you must have brain damage.

I thought that that was more in your area of life.

Ever thought about why it was only
being sold for £22? Doesn't work well for
example? Can't sell them?

Hot?

That could be another reason, although I can't see Arthur Daley finding a
ready market.



Control of the boiler is on/off which is
the weak part of the whole thing.
While it is able to take outside temperature
into account and be reasonable
if one already has a simple switched boiler,
it has to resort to timed
anticycle to prevent reduction in efficiency
as a result of on/off firing.

The boiler will still modulate. If the flow and return temperature
close
up
the burner modulates.

It will do to an extent, but this can be based only on water
temperatures
on
the boiler because that is the only sensing of temperature available to
it.

Other than that, all that it is getting is an on off signal. This
will
mean that on each operating cycle it will begin by running hotter than
needed
and will then modulate down.

If the boiler controller has outside and room temperature information by
direct measurement, then it only ever needs to cycle off when the room
temperature exceeds the set point. Other than that, it can run
continuously at (if need be) very low output.

As the compensator knows roughly what the return temp
should be in relation to the outside temp and the return temp is stable
anyhow, cycling will be minimal. The boiler has anticycle control too.

This can never be as good as a single controller having all of the
sensing
inputs giving measured values as opposed to on/off control and doing
complete
analogue control of burner and pump as well.

Viessmann do it this way as well.

http://www.viessmann.co.uk/articles/...-explained.php

No one has said the on-off is superior at all. But a very near thing can
be
obtained much.much cheaper

Without going into the exact detail, it is not possible to say whether it
is
near or not.




The better option is undoubtedly an
integrated weather compensator coupled
with room temperature sensing and boiler
and pump output control.

But these cost a hell of a lot, and having one with DHW priority too
(running up the boioer temp to max) is not that common.

The question was about a specific make and model, and that one does have
this
capability.

There are others such as the Viessmann with the same functionality.

The best for Robin is a "direct" DPS CX heat bank that integrates the DHW
and CH. The CH water section can be controlled by a Danfoss weather
compensator. Store the CH water at the right temp rather than store the
water hot and drop the temperature. Then the BEM 5000 controls the
boiler
directly on CH. This "eliminates" boiler cycling as the mass of water
stored
acts as an anti-cyle buffer. It also ensures maximum efficiency of
condesning boiler operation. A simple cheap Glow Worm HXi condensing
boiler
can be used. A direct probe sensor for the BEM 500 may have to be bought
as
an extra to sense the store CH water. Worth for the gains it gives.

This is waffle

You clearly do not understand.

The CH circuit is taken off the store and using a Grunfoss Alpha pump and
TRVs on all rads no problem at all. That is what I would do. It gives a
superior solution all around and more cost effective in installation.

I am sure that Robin can make his own decisions on what he would like to
do
without it being organised for him

It's best a professional organises him rather than an amateur.