On Thu, 21 Jul 2005 11:04:49 +0100, "Doctor Drivel"
wrote:
A store can be many things. You can combine the outout of boiler and the
thermal store, moreso a heat bank than store, to improve DHW performace
using a smaller storage vessel.
We've been around that one before. There is a short term effect with
this which is dependent on the storage volume, the boiler capacity and
the rate of use of heat. It does not improve performance in the
sense of flow rate, and if used to make a worthwhile reduction in
cylinder size, the stored energy may well run out reducing the
performance and water temperature substantially - in effect creating a
combi. Not a very interesting solution.
You can promote greater condensing
efficiency by lowering the store temperature and having alarger store, or a
store matched to suit, etc.
Condensing efficiency is improved by operating the boiler at a lower
temperature not by increasing the size of the store. The effect of
the latter is only to reduce cycling and is only important when, as is
required with a store, the boiler runs at high temperature. That
argument is more applicable to non-condensing boilers which are
designed to run at high temperatures.
You can't have it both ways
You can.
It's behind you.
If the condensing boiler drives
the radiators directly,
This produces boiler cyling,
once the boiler kW has bottomed out.
There are boilers around with 5kW minimum.
Very few, and they still cycle, and
still need zone vale and problems with
TRVs.
Rubbish. There are no problems with TRVs at this level.
You require by-passes and a control interlock, which can be a bit involved,
if you want TRVs on all rads.
The need for bypasses or not depends purely on the boiler and even if
an external one is required, it is trivial. Likewise, control
interlock in the form of a room thermostat is also trivial for those
of average intelligence or above.
Taking the rad circuits from the store you
can have TRVs on all rads, by only having a Grundfos Alpha on the circuit.
You can have two CH zones directly off the store both with just an Alpha
pump and TRVs on all rads.
This is pointless. A modulating condensing boiler can do this
directly. Several have pump speed control as well so that the boiler
burn rate, water flow rate and temperatures can all be optimised for
maximum condensing efficiency and lack of cycling. Adding a store in
the middle defeats that and is pointless for space heating
applications.
Not if the minimum modulation level is reasonably low at 5kW or so.
Very rare, and only v expensive boilers and they still cycle.
Your understanding of heat storage
and distribution is quite limited,
isn't it....
It is 110%. Just read and take note. You don't have to understand. Just
accept it.
Is that what the rep told you? He's a nice guy, isn't he? Don't
forget to up that order for the Yorkshire fittings that he needs this
month, will you....
If you drive radiators directly from a modulating boiler,
When having two zones and TRVs on all rads complexities arise. 3kW is the
least you will get from a boiler and those boilers are "very" expensive.
There are several that will modulate down to low levels and will drive
the radiators directly perfectly well. If your idea were so
beneficial, it would be common practice and boilers would be designed
to do it. As it is, they are optimised to heat cylinders (or stores)
quickly for hot water purposes and to drive radiators directly. That
is the main point of arranging for them to modulate. The vast
majority do modulate, and very few are around that have fixed output,
simply because a store is not the best way to implement a space
heating solution unless other energy sources are being added in.
Any switching of the boiler will be on
a very long interval, just as it is with
a store. However, since this
is occuring at a much lower power
level than happens when driving a
store, there is less energy waste at
the time the boiler fires up. It
will also be working directly in its
most efficient temperature range.
By inserting an outside weather compensator that dictates the temperature of
the stored CH water in the thermla store, a condensing boiler operates to
max efficiency. Simple to do.
If you do that and reduce the temperature in the store, it is no
longer optimal for heating the water. Considering that with a
modulating boiler, the temperatures can be run as low as 45/25 degrees
to the radiators, the store is going to be pretty useless for heating
the water.
Plumbers merchants seem to
be full of people behind the counter who
spout about this or that in an "authoritative"
way.
Most have never heard of a thermal store, never mind how you apply it.
Presumably they have in your branch now though?
--
..andy
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