On Sun, 14 Dec 2003 00:47:43 +0000 (GMT), "Dave Liquorice"
wrote:

On Sat, 13 Dec 2003 20:23:32 +0000, Steven Briggs wrote:

I glad Andy's pointed out his interpretation of part L, as I did
think I was technically non-compliant having no room stat.

Andy's setup if *very* sophisticated and in the 30th centuary compared
to most heating systems in the UK. I don't doubt that with such a
level of monitoring and control very good effciencies can be achieved
but those levels do not exist on the vast majority of installed
systems.

Don't forget though that this part of the Building Regulations only
apply when a new boiler is fitted either into an existing property or
a new one.

My description of my own system was by way of illustration more than
anything else.

My conclusion from looking through the Approved Document and the Good
Practice Guide is that they are aimed at practitioners in the trade
who are still installing conventional simple boilers and simple room
stats because a) they understand them and b) they are cheap.

Therefore, given that that is the status quo, the point that struck me
was that the authors are suggesting the marriage of the two as good
practice because realistically that is what is often installed. They
even refer to this as a minimum set of controls. With a simple boiler
firing to full output or off and with simple bimetal thermostats,
short cycle firing as a result of TRVs being virtually closed down is
going to use some amount of energy which can easily be saved by
hooking up a simple room stat.

However, even with a relatively simple modern condensing boiler is
modulating to quite a low level and most that I have seen fire up at a
level according to the amount of heat demand as referenced by the
water temperatures. After all 3kW firing up for a minute once an
hour is actually less than the pump uses.



The test is can the boiler fire to keep itself and/or a small primary
loop warm/hot, if can then then, IMHO, it fails Part L1. There are
many ways, from a simple room stat or flow switch to systems like
Andy's, to achieve the desired result.

My point was really that it strikes me that the Approved Document and
Good Practice Guide make a point about the interlock thing because it
can be easily achieved with what is often still installed today not
that the authors are prescribing what *must* be done.

The legislation requires only that reasonable provision is made to
save energy.

Once modulating and condensing boilers become the norm as it is
suggested that will be the case within two years, the energy to be
saved by interlocking the controls with a room stat is likely to be a
lot less significant to the point where I suspect that using one will
not make a whole lot of difference.

I am assuming here that time controls will indeed remain as they are
which is to fully shut down the boiler and pump (notwithstanding
overrun) when the heating period has finished.

Remember that with burner modulation the heat output goes down to a
few kW to balance the heat loss so the residue of what we would be
talking about would be on days when for *part* of the heating period
boiler heat is required, but because of rising temperatures outside
not for all of it. The number of days a year when that scenario
happens in such a way that a very low burn rate of a few kW once or
twice an hour is too much is very small.
From an engineering standpoint at that stage it becomes very much a
corner case to worry about switching everything off.





..andy

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