"Andy Hall" wrote in message
...
On Sat, 4 Sep 2004 21:53:07 +0100, "IMM" wrote:

It does if it is going to be involved
in an efficient control system
where the heat output to the radiators
and the heating space are
measured

They are measured by the weather
compensator, with any room temp influence
to drop the slope if need be.

It should be the other way round of course.

failed again.

We are not trying to
control the weather here, but the
temperature in the house.

You don't say.....

The outside temperature is monitored
to provide a correction to the slope.

failed again. I'm fed up marking you as it's always a poor score. The
outside weather gives the slope and the internal temp sensor (if one fitted.
Many internal temp sensors can be fitted and the temps averaged on large
buildings) raise or lowers it to suit.

For you:

1. With heat bank and a weather compensator, a mass of water is heated at
the bottom of a heat bank to the temperature what the building requires (the
rads). The temp can be anything from 25C to 80C depending on the outside
conditions. The temp of the lower mass of water is dictated by the weather
compensator, which is near enough the correct temperature that the rads will
require.

2. A load compensating modulating boiler generally goes down to about
5-7kW, any lower than that it cycles on-off. Some super expensive boilers
go down to 3kW. As most of the time buildings are up to temp (part load on
the heating system) this will be significant cycling in most modulating
boilers. These boilers tend to be complex and expensive and have more
expensive parts and servicing to go wrong on them.

- With a heat bank the rad circuit(s) can draw-off only 1 kW of heat from
the heat bank and no cycling from the boiler. Only when the whole mass of
water cools does the boiler come in and re-heat the mass of water in one
long efficient no boiler cycling burn.

- The temp of the mass of water is not totally fixed as the temp will drop
slightly as the mass of water is cooling. This is insignificant and TRVs
trim off local temps. Weather compensating slopes are never fully accurate
and may out by +-5%. The slope is a best fit at the best of times. An
internal temp sensor (if one fitted), raise or lowers the slope it to suit.
Many internal temp sensors can be fitted and the temps averaged on large
buildings for greater accuracy..

- A simpler, and cheaper, condensing boiler can be used, similar to any
regular heating boiler, that can have the optimum flow through the boiler
at all times for greater efficiency and boiler longevity.

- A variable speed Alpha pump can be used on the rad circuits reducing noise
electricity consumption.

- If having a heat bank for DHW, then increasing the size to provide:
* a cheaper, simpler and more reliable boiler,
* a neutral point for all circuits,
* weather compensation
* elimination of boiler cycling when on part load, which gives far greater
boiler longevity on all components.
* oversized rads to cope with a condensing boiler giving lower return
temperatures.
* Variable speed pumps(s) on rad circuits.
* instant heat available first things in the mornings. Rads are fully
heated with afew minutes.

Now understand this if you can. It is not difficult. If there are parts
you are confused about, just accept it as right.