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Default CH balancing

Hi,

I printed out the page from the faq but I'm getting really fed-up with
trying to balance these radiators!

I bought an IR thermometer. I'm holding it close to the pipe to get a
narrow beam but even so, just a slight movement gives a temperature
drop of 10C. I put masking tape on the pipes. Is this causing some of
the problem? Should I be using insulating tape instead?

Should I start with the lockshields where they are and tweak or should
I start with them all open?

Do you make changes to several radiators at the end of each run or
just one radiator per run? Or do you tweak as you go along?

How long should I wait for things to stabilise before re-measuring?

Thanks.
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In an earlier contribution to this discussion,
Fred wrote:

Hi,

I printed out the page from the faq but I'm getting really fed-up with
trying to balance these radiators!

I bought an IR thermometer. I'm holding it close to the pipe to get a
narrow beam but even so, just a slight movement gives a temperature
drop of 10C. I put masking tape on the pipes. Is this causing some of
the problem? Should I be using insulating tape instead?

I use little squares of black tape on a flat surface of the radiators - just
inboard of the valve connections.

Should I start with the lockshields where they are and tweak or should
I start with them all open?

If the system has previously been balanced, and is in a *reasonable* state
of balance, start with them where they are. Otherwise start with them fully
open.

Do you make changes to several radiators at the end of each run or
just one radiator per run? Or do you tweak as you go along?

2 or 3 at the most. Turn down the ones with the smallest temperature
differential.

How long should I wait for things to stabilise before re-measuring?

Probably about 10 minutes - but you need to make sure that the system is
running the whole time - so turn any room stats up to max, and open some
windows if necessary.
--
Cheers,
Roger
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Default CH balancing

On Tue, 19 Feb 2008 16:39:22 -0000, "Roger Mills"
wrote:

I use little squares of black tape on a flat surface of the radiators - just
inboard of the valve connections.


Thanks. I'll give that a try.

If the system has previously been balanced, and is in a *reasonable* state
of balance, start with them where they are. Otherwise start with them fully
open.


I think the FAQ advises 1/4 turn adjustments. I thought that valves
like lock shields are non-linear. Does this mean that the first few
turns will make no difference and then near the end, the slightest
turn will make a difference? Should I use turns smaller than 1/4 to
fine tune?

I've got an assortment of radiators all with different lock shields so
each radiator requires a different spanner to adjust the lock shield!
(I can't use the cap off the other valve as these have been replaced
with TRVS).

Do you make changes to several radiators at the end of each run or
just one radiator per run? Or do you tweak as you go along?

2 or 3 at the most. Turn down the ones with the smallest temperature
differential.


I'm having most problems with the towel radiator in the bathroom. It's
scalding hot to touch but not showing much of a temperature drop.
Should the drop across a towel radiator be the same as the
"conventional" radiators?

How accurate should I be in matching temperature drops. Should I try
to get each rad. to have a drop of say 10C, or does it matter if one
has 8C, another 12C, another 9C, etc?

How long should I wait for things to stabilise before re-measuring?

Probably about 10 minutes - but you need to make sure that the system is
running the whole time - so turn any room stats up to max, and open some
windows if necessary.


Daft question: does the boiler need to be firing? Or as long as the
pump is circulating hot water is that enough?

Thanks again.
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Default CH balancing

In an earlier contribution to this discussion,
Fred wrote:


I think the FAQ advises 1/4 turn adjustments. I thought that valves
like lock shields are non-linear. Does this mean that the first few
turns will make no difference and then near the end, the slightest
turn will make a difference? Should I use turns smaller than 1/4 to
fine tune?

It's certainly non-linear, and most of the action occurs when it's getting
on for closed, so you can certainly turn it down quite a lot - maybe
half-way - to start with. The rest is really 'suck it and see'!


I'm having most problems with the towel radiator in the bathroom. It's
scalding hot to touch but not showing much of a temperature drop.
Should the drop across a towel radiator be the same as the
"conventional" radiators?

Towel radiators are a waste of time as space heaters anyway, but you'll get
a *bit* more out of one by running it at a higher average temperature - i.e.
with a smaller drop. But don't go below (say) 5 or 6 degrees, or you'll be
at risk of starving the other radiators.

How accurate should I be in matching temperature drops. Should I try
to get each rad. to have a drop of say 10C, or does it matter if one
has 8C, another 12C, another 9C, etc?

It's not an exact science - and you'll never get then all exactly equal.
Variations of a couple of degrees don't really matter. What you are trying
to avoid is having some with a 2 degree drop and others with 20 degrees or
more - which is probably what you'll have at the beginning.


Daft question: does the boiler need to be firing? Or as long as the
pump is circulating hot water is that enough?

Ideally the boiler *should* be firing but that is virtually impossible to
achieve. Unless the system is dissipating the full output of the boiler, it
will inevitably cut in and out on its own thermostat. But that at least
means that the water being circulated is at a more or less constant
temperature - within the hysteresis of the boiler's stat. Don't forget that
you're measuring the *difference* across each rad, so if the flow
temperature varies slightly, it's not a disaster. It *is*, of course, vital
to keep the pump running - by turning up the room stat and, if necessary,
opening a few windows to stop the house getting too hot - although that
shouldn't be necessary this time of year!
--
Cheers,
Roger
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Default CH balancing

The message
from Fred contains these words:

I'm having most problems with the towel radiator in the bathroom. It's
scalding hot to touch but not showing much of a temperature drop.
Should the drop across a towel radiator be the same as the
"conventional" radiators?


I have not had any direct experience of towel radiators but as towel
radiators typically have a much smaller surface area than even a small
conventional radiator it may be difficult to find a point between little
temperature drop and practically off.

How accurate should I be in matching temperature drops. Should I try
to get each rad. to have a drop of say 10C, or does it matter if one
has 8C, another 12C, another 9C, etc?


The object of the exercise is to get the specific heat output of each
radiator to match but I wouldn't have thought at a 10% variation (or
perhaps even more) in temperature drop would be a problem and I suspect
that getting any closer would probably be an illusion. The larger the
radiator the larger the flow through the radiator for the same
temperature drop which is why you may have trouble adjusting a dinky
towel rail.

How long should I wait for things to stabilise before re-measuring?

Probably about 10 minutes - but you need to make sure that the system is
running the whole time - so turn any room stats up to max, and open some
windows if necessary.


Daft question: does the boiler need to be firing? Or as long as the
pump is circulating hot water is that enough?


Hobsons choice (unless you have a sophisticated modulating boiler). If
the boiler is firing the circulating water is being heated and the flow
temperature continuously rising and if the pump is on over run the
circulating water is being cooled. I think what you must avoid is the
warm-up phase below normal operating temperatures, any period during
which the water isn't circulating and any period shortly thereafter. If
the pump is running and the flow temperature is high enough you will
then only have the problem of finding a period when the inlet and outlet
temperatures of a particular radiator aren't varying fast enough to
invalidate your results.

It may be that it doesn't matter that you are getting a higher (or
lower) than true temperature drop across a radiator provided you
consistently opt for the firing or the over run phase or it might be
better if you take measurements from both phases and average. If my
central heating system is any guide I think you may have some difficulty
in finding any period where both inlet and outlet temperatures of a
radiator are stable.

--
Roger Chapman


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Default CH balancing

On Wed, 20 Feb 2008 11:34:50 GMT, Roger
wrote:

If my
central heating system is any guide I think you may have some difficulty
in finding any period where both inlet and outlet temperatures of a
radiator are stable.


But the same would be true for most CH systems, so what do people do?
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Default CH balancing

On Feb 20, 8:31 pm, Fred wrote:
On Wed, 20 Feb 2008 11:34:50 GMT, Roger
wrote:

If my
central heating system is any guide I think you may have some difficulty
in finding any period where both inlet and outlet temperatures of a
radiator are stable.


But the same would be true for most CH systems, so what do people do?


I balance systems so each radiator feels equally hot. Since I'm doing
this for a living (i.e. people are paying me to do it) I don't have
time (i.e. I don't charge them) for spending ages getting everything
right by the book. If it feels right to me and to them and
everything's nice & warm & toasty everyone's happy.

As for 'by the book' there's a lot said about getting temperature
*drops* across rads the same. However a radiator's heat output is a
function of its mean temperature, and it is this which we want to
equalise. Since the flow resistances of the pipework feeding each rad
is probably different (and/or these flow resistances are not in
proportion to the rads' own flow resistances) then getting the
temperature drop across each rad the same should ensure that each rad
is operating at the same mean temperature. In other words balancing
temperature drops are a means to the end of equalising rads' mean
surface temperatures.

IMHO, E&OE, YMMV, TGIF etc...
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