Just replaced an ancient 30KW Kingfisher II floor-standing lump with a
shiny new GlowWorm HXI 30KW condensor (credit due to IMM believe it or
not for http://www.uselessenergy.org.uk tip, saved £££s thanks).

The house is a large, Edwardian detached job with four big bedrooms.
Before replacing the boiler I did an approx size of all the rads and
came up with 27KW needed if you allow ~3.3KW for the HW cylinder, and
therefore went for a 30KW boiler. I also had the pump and S-Plan
control valves replaced as they were rather old, and took the
oppurtuinity to put the conservatory on a separate zone. The new pump
is an Alpha 15/60 (currently set to constant head setting as there is
a bypass).

The conservatory has two 3.3KW Double-panel convectors, and a 600W
single-panel convector. There is also 500W single-panel convector in
the bog adjacent to the conservatory, which will eventually be moved
back to the main rad zone (couldn't move it without ripping floor up
so it will have to wait a while).

One thing I've found is that it seems impossible to get a 20 degree C
drop across the conservatory rads when only that zone is calling for
heat. If you shut down the lockshields the boiler seems to get
insufficient flow, heats up really quickly in a couple of mins then
shuts down. Opening up the lockshields fully to increase flow seems to
suit the boiler more, and you do seem to get a bit more of a
temperature drop across the two big rads (approx 10 degrees). Closing
down the smaller rads doesn't really seem to acheive much as the flow
across the boiler drops and the temperature drop across the big rads
actually drops to virtually nothing, without actually increasing the
temp drop on the smaller rads.

One advantage of the low temp drop in this zone is the conservatory
heats up pretty quickly; I would guess the downside is less efficiency
in the boiler due to the high return temperature. Once the circuit has
heated up the boiler cuts out at about 70 degrees, drops to about 60
degrees then cuts in again for a couple of mins or so.

Can you confirm this behaviour is to be expected? Any
comments/observations?

TIA,

MH

One thing I've found is that it seems impossible to get a 20 degree C
drop across the conservatory rads when only that zone is calling for
heat.

Personally I wouldn't worry about it. Sounds like the pump is going too fast
when there is only conservatory load. TBH, this won't be a common case, as
the house zone will often be calling for heat too.

As you say, the radiators are well oversized and cause the conservatory to
heat up rapidly, so the slightly increased return temp will only apply for a
short period (10 minutes you suggest). Additional energy savings to be had
by reducing this the return temp for such a short period are very marginal.

Christian.

On 25 Nov 2004 08:28:52 -0800, (Mary Hinge)
wrote:

Just replaced an ancient 30KW Kingfisher II floor-standing lump with a
shiny new GlowWorm HXI 30KW condensor (credit due to IMM believe it or
not for http://www.uselessenergy.org.uk tip, saved £££s thanks).

Yes, it's a shame he spoils what good advice he has by the arrogant and
insulting nature of the majority of his posts. It means that any useful
advice he has can get lost in the welter of trivia.

The house is a large, Edwardian detached job with four big bedrooms.
Before replacing the boiler I did an approx size of all the rads and
came up with 27KW needed if you allow ~3.3KW for the HW cylinder, and
therefore went for a 30KW boiler. I also had the pump and S-Plan
control valves replaced as they were rather old, and took the
oppurtuinity to put the conservatory on a separate zone. The new pump
is an Alpha 15/60 (currently set to constant head setting as there is
a bypass).

I have not used that pump, but I'm sure Andy Hall will be able to advise
on its best settings.

The conservatory has two 3.3KW Double-panel convectors, and a 600W
single-panel convector. There is also 500W single-panel convector in
the bog adjacent to the conservatory, which will eventually be moved
back to the main rad zone (couldn't move it without ripping floor up
so it will have to wait a while).

One thing I've found is that it seems impossible to get a 20 degree C
drop across the conservatory rads when only that zone is calling for
heat. If you shut down the lockshields the boiler seems to get
insufficient flow, heats up really quickly in a couple of mins then
shuts down.

Well yes - shutting down LSVs does reduce the flow. 7.4kW is a
significant load and will need a decent flow rate to transfer that heat
from the boiler to the rads. You need to wait quite a long time after
throttling the LSV down to allow the rad too cool - are you waiting long
enough? Also if the rads are oversized you will want to throttle them
down to a *larger* temp drop than normal or the room will overheat.
Don't forget that a larger drop corresponds to *less* heat output
because the average surface temperature is reduced.

Opening up the lockshields fully to increase flow seems to
suit the boiler more, and you do seem to get a bit more of a
temperature drop across the two big rads (approx 10 degrees).

Confirms the above. With 10C or so across them they will be delivering
their full rated output.

Closing down the smaller rads doesn't really seem to acheive
much as the flow across the boiler drops

What do you mean by "the flow across the boiler drops"?

and the temperature drop across the big rads
actually drops to virtually nothing, without actually increasing the
temp drop on the smaller rads.

It sounds as though you initially had the small rads LSV wide open thus
bypassing the big rads. When you closed the small ones down, the big
ones were then able to get a decent flow. I think you need to re-read
the FAQ, as following it should sort all this out.

Do you ever want to run both zones together? If so you need to do the
balancing in that mode.

Please take special note of the Principle section of the Balancing FAQ,
especially 2nd paragraph, regarding not being able to get a specific
temperature drop across rads.

One advantage of the low temp drop in this zone is the conservatory
heats up pretty quickly; I would guess the downside is less efficiency
in the boiler due to the high return temperature. Once the circuit has
heated up the boiler cuts out at about 70 degrees, drops to about 60
degrees then cuts in again for a couple of mins or so.

It should not do that with a heat load of over 7kW. Lack of balance is a
likely cause. Also, adding extra rads may mean re-balancing the rest of
the house, depending on pipe layout. You should have one, and only one,
rad with its LSV wide open.

Can you confirm this behaviour is to be expected?

No.

Any comments/observations?

Read http://www.diyfaq.org.uk/plumbing/rad-balance.html and come back if
you have more questions.

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
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Phil Addison wrote in message . ..

Well yes - shutting down LSVs does reduce the flow. 7.4kW is a
significant load and will need a decent flow rate to transfer that heat
from the boiler to the rads. You need to wait quite a long time after
throttling the LSV down to allow the rad too cool - are you waiting long
enough? Also if the rads are oversized you will want to throttle them
down to a *larger* temp drop than normal or the room will overheat.
Don't forget that a larger drop corresponds to *less* heat output
because the average surface temperature is reduced.

Firstly I got my sums wrong, the two large rads are around 1.7 KW
each, so around 3.4KW *in total*. D'oh!

Yes I waited for the system to fully cool before attemping balancing.
Note that the conservatory is quite large, the heatloss program
suggests 4.8KW is required, currently we have around 4KW in total so
if anything slightly undersized. The room overheating is not possible
as the conservatory is a completely independent zone with it's own
thermostat.

What do you mean by "the flow across the boiler drops"?

I get the impression that not enough water seems to be going through
it so it cannot modulate down low enough (the manual states a minimum
flow of 1300 litres/hour).

Do you ever want to run both zones together? If so you need to do the
balancing in that mode.

In practice they don't seem to come on together very often. A lot of
the main house zone pipework is 1 inch with a lot of rads hanging off
of it, and doesn't seem to have much flow resistance so when both
zones are on it doesn't seem to affect the main house. The
conservatory zone is all in 15mm so has more flow resistance.

It should not do that with a heat load of over 7kW. Lack of balance is a
likely cause. Also, adding extra rads may mean re-balancing the rest of
the house, depending on pipe layout. You should have one, and only one,
rad with its LSV wide open.

As stated above I made an error in my original statement; the total
load is around 4.5KW

Thanks,

MH

On 26 Nov 2004 00:58:50 -0800, (Mary Hinge)
wrote:

A lot of
the main house zone pipework is 1 inch with a lot of rads hanging off
of it, and doesn't seem to have much flow resistance so when both
zones are on it doesn't seem to affect the main house. The
conservatory zone is all in 15mm so has more flow resistance.

Just a quick reply to this bit - I'll digest the rest of your post
later.

This 1 inch pipework sounds like a "single-pipe" system. This is an old
and discredited system for domestic properties and the balancing FAQ
process will not work with it. Is there a single 1" pipe passing under
each radiator, with both the flow and return of the rad connected to it?
Do you have calipers to check the diameter, because the old pipes were
1" *internal* diameter whereas modern ones are 22mm *outside* diameter?
I don't have the o/d of imperial pipes handy, but you could have 3/4"
i/d which has an o/d close to modern 22mm pipe.

If I am right about this, it could be that the pump is inadequate for
the new zone that you have, which presumably uses two separate 15mm flow
and return pipes. Can you see a make/model label on the pump?

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
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Phil Addison wrote in message . ..

This 1 inch pipework sounds like a "single-pipe" system. This is an old
and discredited system for domestic properties and the balancing FAQ
process will not work with it. Is there a single 1" pipe passing under
each radiator, with both the flow and return of the rad connected to it?
Do you have calipers to check the diameter, because the old pipes were
1" *internal* diameter whereas modern ones are 22mm *outside* diameter?
I don't have the o/d of imperial pipes handy, but you could have 3/4"
i/d which has an o/d close to modern 22mm pipe.

If I am right about this, it could be that the pump is inadequate for
the new zone that you have, which presumably uses two separate 15mm flow
and return pipes. Can you see a make/model label on the pump?

Definately not a single-pipe system. The 28mm feeds the main CH zone
(upstairs and downstairs rads) with separate flow and return, I
suspect it probably drops down to 22mm somewhere under the ground
floor after the 22mm flow and return for the upstairs rads splits off.

The pump is a brand new Grundfos Alpha 15-60 and yes as stated the
conservatory zone is all 15mm. You might need to re-read my original
post for more background.

Thanks,

MH

On 26 Nov 2004 10:56:33 -0800, (Mary Hinge)
wrote:

Phil Addison wrote in message . ..

This 1 inch pipework sounds like a "single-pipe" system. This is an old
and discredited system for domestic properties and the balancing FAQ
process will not work with it. Is there a single 1" pipe passing under
each radiator, with both the flow and return of the rad connected to it?
Do you have calipers to check the diameter, because the old pipes were
1" *internal* diameter whereas modern ones are 22mm *outside* diameter?
I don't have the o/d of imperial pipes handy, but you could have 3/4"
i/d which has an o/d close to modern 22mm pipe.

If I am right about this, it could be that the pump is inadequate for
the new zone that you have, which presumably uses two separate 15mm flow
and return pipes. Can you see a make/model label on the pump?

Definately not a single-pipe system. The 28mm feeds the main CH zone
(upstairs and downstairs rads) with separate flow and return, I
suspect it probably drops down to 22mm somewhere under the ground
floor after the 22mm flow and return for the upstairs rads splits off.

The pump is a brand new Grundfos Alpha 15-60 and yes as stated the
conservatory zone is all 15mm. You might need to re-read my original
post for more background.

Oops, yes forgot that - I remembered the Edwardian bit and mention of
some things being old. So basically, its back to what i said befo You
need to balance it properly before we can do anymore diagnoses. With the
info to date it appears to be an out of balance system, which is common
for a new installation - most plumbers just do not understand balancing
and either don't attempt it or don't achieve it.

You haven't yet said the make/model of the boiler, but assuming it is a
modulating one, at 30kW rating it may not modulate down to 3.4kW so you
may have to expect it to cycling on off to a degree.

Summarising the balance process, you put the pump on max, open all the
rad valves (LSVs, TRVs, or hand valves) and allow it to heat up.
Normally at least one rad will have a cooler return. Ignore those, and
go to the ones with very hot returns and start shutting down their LSVs.
That will send a greater flow to the cool ones which will show an
increased return temperature. Keep repeating this procedure until all
returns are very hot. Ideally use an IR thermometer to evaluate the
actual return temperature - it makes it easier. Don't try to get a
specific temperature drop, just get them all about the same.

If you can achieve that, then you can think about adjusting the pump.

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
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