"Andy Hall" wrote in message
...
On Sat, 4 Sep 2004 10:51:59 +0100, "IMM" wrote:

It is when appropriate weather compensating
control is used, to ensure the
heat bank, or lower section of heat bank, is
maintained at the variable
setpoint dictated by the compensator.

The heatbank will always introduce a
dampening factor into the control
loop.

Not so. It will prevent/reduce boioer cycling that is for certain.

The element that is intended to be
controlled is the room
temperature, not the water temperature
of the heatbank.

Your comprehension is poor. The boiler/heat bank maintain the lowers section
of the heat bank at the temperature that the rads require for optimum
performance. That is very simple.

The weather compensator, if integrated
with the boiler should move the
operating curve of the boiler up and down
to match the load.

This weather compensator is NOT integrated with a boiler. This you can't
understand.

If you switch to maintaining the temperature
of part of the heatbank to maintain a set point
according to the outside temperature, you
introduce a double control loop.

Nope.

In the piece between the heatbank
and the boiler, if you use the
typical separate box type of weather
compensator, you will have an
analogue sensor for outside

Yes.

and one for inside,

?? One to sense the temp of the heat bank

plus an input for a
switched room thermostat.

Uh! Switched? room temp trimming is analogue unless to have a cheapo.

The inside analogue sensor would
normally be used on the boiler return,

Or boiler flow, which most operate on. Used on the heat bank here.

but could be used on the return
from the radiators to the heatbank.

Could be on the cylinder not far from the boiler/rads returns pipes.

Neither is ideal because
connecting it to the radiator
return means that the controlled device
(boiler) has the damping effect of the
heatbank in between which will
adversely influence the control loop.
Having it on the boiler return
means that the temperature being monitored
relates to heat use by the
heatbank and not the room space.

It is clear you do not understand. The rad circuits are off the bottom of
the heat bank and have their own pump. Easy. The boilers flow and return
is off the heat bank, at the bottom of the heat bank. The compensator has
a probe on the bottom section of the heat bank producing a mass of water at
the temp the rads require. The lower temp at the bottom on part load will
ensure low temp return for high efficient condenser operation, with an
expensive complex boiler.

You have to know what you are controlling
before you apply control. You
don't.

It is very obvious what is being controlled.
One part is the room temperature.

The room temp influence only trims.

The other part is controlling
the boiler firing level
most efficiently to match the room
requirement.

No. Get the boiler to heat a mass of water all at one time, to what
temperature the room requires.

In the case of a
modulating, condensing boiler,

No need for a modulating condensing boiler./ Most do modulate, but heating
boilers modulate on flow setpoint temp. As the boiler will be on full, when
heating the mass of water for CH very rare will it modulate.

In a system where the only source of heat input is a gas condensing
boiler, there is no point in putting a heat bank in the middle because
it simply distorts the control algorithm, and offers no advantages.

You still don't understand.

it also screws up the primary purpose
of the heatbank, which is to
provide an energy store to deliver
large amounts of energy quickly to
a heat exchanger.

Primary?

And to prevent boiler cycling and giving on-demand mains pressure hot water.
Eliminating cold water storage tanks. With a heat bank the DHW and CH
circuits don't care about the boiler. The boiler can be controlled more
efficiently by having it heat one mass of water very quickly and in one long
efficient burn. Taken further it can heat two masses of water at different
temperatures. High for DHW and low for CH. Taken further again, the CH mass
of water can be at variable temperatures to what the outside weather
dictates. When called to heat the CH mass of water it does it in one long
burn no matter what temperature the CH water mass is.

A BEM5000 costs £188

A diverter valve costs £56

You forgot the extra pump to run the radiator circuit - £56 for a
Grundfos

All prices from Discounted Heating. Total cost is £311.

You can buy a Worcester Greenstar 28HE for £725 from them.

What 28kW condensing boiler you going to buy from Discounted Heating
for £410 that is any good?

But you save a wedge on a 1.5K load compensating boiler and musch simpler.

When combined with heat banks and heating a large mass of water matters
are
very different. This you can't understand. This is very sad.

Of course they are very different
and I understand the difference
perfectly.

Not so.

The results, if using a condensing boiler as the sole
source of energy, will be inferior, by definition, than the direct
connection of the boiler to the radiators as the manufacturers intend
and design.

You clearly do not understand. "by definition, than the direct connection of
the boiler to the radiators as the manufacturers intend and design.". I am
not on about one of theses type of boiler.

The value in a heatbank is in its
ability to store energy at high
temperature to run a plate heat
exchanger for the hot water.

It is?

It is also useful in the introduction of
heat from other sources such as
solar.

...and a condensing boiler.

It provides no value in a path between
a modulating condensing boiler
and radiators.

You clearly do not understand.

Even with all the extra controls that you describe,
the efficiency will be worsened.

You clearly do not understand.

To suggest that coupling a
switching controller with a simple
boiler is an improvement is
laughable.

You clearly do not understand.