CH Balancing - Thermometers
Andy Baskett
Following the excellent advice and various discussions here and in the
DIY FAQ I decided to attempt to balance my central heating ...
I bought two clamp/strap on dial thermometers from B&Q and began ...
by about the third radiator I could get no differential - the brass nut
on the back of the dial was moving and therefore making the readings
nonsense !! I tried to carry on, but by then the second one was moving
... ARGGHHH ...
can anyone perhaps suggest alternative thermometers and tell me where I
can buy them ... (I can't take the B &Q ones back as they're covered in
heatsink compound - as are the radiators much to the displeasure of my
better half !)
TIA,
--
Andy Baskett
(remove nospam from address to reply)
Matthew Marks
In article <353F08...@nospam.inri.co.uk>,
Andy Baskett <ABas...@inri.co.uk> writes:
>
> (I can't take the B &Q ones back as they're covered in
> heatsink compound
Oh yes you can - they are not fit for purpose. DIY sheds aren't too fussy
about taking stuff back anyway, in my experience - usually, the cost of what
you are taking back is less than the cost to them of arguing about it. It goes
some way to explaining their high prices in the first place.
--
Matthew @rd.bbc.co.uk My opinions, not Auntie's *RETURN ADDRESS SPAMPROOFED*
Phil Addison
That kind of mechanical thermometer is sluggish, insensitive, and hard to
thermally bond. I gave up on them entirely when balancing my system. Others
apparently have better luck. Anyway I popped across to Maplin's and bought
a digital multimeter that also has a thermocouple temperature sensor
reading to 1 deg C resolution and 1/2 deg accuracy, and to 1 deg F
resolution (which is near enough 1/2 deg C... but you know that). It
responds in a couple of seconds to temperature. You can get a second
thermocouple on 1 m of wire so you can tape 2 couples to the rad and just
swap the connections at the meter to read flow and return. Note I said tape
- the couples are so small that this gives just as good a result as using
thermal-grease. Mind you, the meter cost 50 quid (3 years ago) but I reckon
it's damn good value if you can make use of the electrical reading
capability too.
Balancing is a labourious process because it takes a long time after each
adjustment of each lock-shield valve for the radiator temperatures to
stabilise, and all the time the house is getting hotter and hotter. I think
this is the main reason that so few systems are commissioned properly.
I've dreamed of making a multi-thermocouple device attached to a computer
so you can instrument all the rads, then have the computer tell you which
LSVs to adjust and by how much. Dream on...
--
Phil | If possible please direct replies to the newsgroup.
| If my 'From' address is anti-spammed, correct it
| by joining this> phil@severn. to this> demon.co.uk
T1MDownie
In article <3549d3eb...@news.demon.co.uk>, ph...@severn.demon.co*uk (Phil
Addison) writes:
>>Following the excellent advice and various discussions here and in the
>>DIY FAQ I decided to attempt to balance my central heating ...
>>I bought two clamp/strap on dial thermometers from B&Q and began ...
>>by about the third radiator I could get no differential - the brass nut
>>on the back of the dial was moving and therefore making the readings
>>nonsense !! I tried to carry on, but by then the second one was moving
>>... ARGGHHH ...
>>[snip]
>
>Balancing is a labourious process because it takes a long time after each
>adjustment of each lock-shield valve for the radiator temperatures to
>stabilise, and all the time the house is getting hotter and hotter. I think
>this is the main reason that so few systems are commissioned properly.
>[snip]
Isn't it about time that the piece on balancing radiators in the FAQ came with
a health warning? I went down this road after reading the FAQ and wasted the
better part of a day trying to do the impossible. In the end I screwed down
the lockshield valves closest to the boiler by half a turn with a little extra
adjustment on one radiator that seemed to get much hotter that the others. I
really don't think I can do better that this and it would seem this is other
peoples' experience as well.
One of the biggest problems with the balancing scheme is that it assumes that
all your radiators are perfectly matched to the room in terms of heat output
and heat loss. How many houses (particularly older mucked arround ones) meet
this ideal? So to balance your radiators to achieve identical temperature
drops across the input and output is not really as useful as it ought (ideally)
to be. If, say a radiator is relatively oversized for a room (due perhaps to
the fitting of fitted carpets and double glazing), then one might well want to
reduce the flow through that radiator. If a radiator is a bit undersized one
might want to run it at a higher temperature.
All in all, it seems an awful lot of time an effort to achieve a rather
arbitrary temperature drop figure in systems that are designed around
estimations of heat loss. (In the same way that it's not really worth being
too nit picking with the delivery driver over the exact weight of the tonne of
top soil you've ordered to fill a hole that you've estimated the volume of).
I'm really not sure it's worth the bother.
Just my thoughts on the subject.
TD
Andy Baskett
T1MDownie wrote:
>
> In article <3549d3eb...@news.demon.co.uk>, ph...@severn.demon.co*uk (Phil
> Addison) writes:
<snip>
> Isn't it about time that the piece on balancing radiators in the FAQ came with
> a health warning?
I must admit I agree, having tried it (so far unsuccessfully). It is a
hell of a job ... It was about 50 degrees in the house by the time I was
half way around and I gave up.
I must say I would probably still have given it a go, but I wouldn't
have minded knowing just what a nightmare it would be.
--
Andy Baskett
Phil Addison
On 24 Apr 1998 08:37:17 GMT, in uk.d-i-y T1MDownie wrote:
>Isn't it about time that the piece on balancing radiators in the FAQ came with
>better part of a day trying to do the impossible. In the end I screwed down
>the lockshield valves closest to the boiler by half a turn with a little extra
>adjustment on one radiator that seemed to get much hotter that the others. I
>really don't think I can do better that this and it would seem this is other
>peoples' experience as well.
>One of the biggest problems with the balancing scheme is that it assumes that
>all your radiators are perfectly matched to the room in terms of heat output
>and heat loss. How many houses (particularly older mucked arround ones) meet
>this ideal? So to balance your radiators to achieve identical temperature
>drops across the input and output is not really as useful as it ought (ideally)
>to be. If, say a radiator is relatively oversized for a room (due perhaps to
>the fitting of fitted carpets and double glazing), then one might well want to
>reduce the flow through that radiator. If a radiator is a bit undersized one
>might want to run it at a higher temperature.
>
>All in all, it seems an awful lot of time an effort to achieve a rather
>arbitrary temperature drop figure in systems that are designed around
>estimations of heat loss. (In the same way that it's not really worth being
>too nit picking with the delivery driver over the exact weight of the tonne of
>top soil you've ordered to fill a hole that you've estimated the volume of).
>I'm really not sure it's worth the bother.
>
>Just my thoughts on the subject.
>
>TD
Good points. Perhaps we could solicit a few other folks experiences with a
view to expanding Rick Hughes balancing section of FAQ3. Rick's basic
principles are fine but, as you say, balancing is not the exact science
that might be implied. Several questions come to mind, answers to which
could be added to the FAQ (OK, I know some of them are already addressed in
it), e.g...
What symptoms indicate my system needs balancing?
What should I check before starting?
Why some systems can never achieve correct temperatures?
Where does this 11 degC drop come from. Is it vital to achieve it?
I've got these spring attached thermometers and I can't distinguish any
consistent differential across the rads - what am I doing wrong?
How can I test these thermometers?
Isn't there a better way to measure the temperature difference?
It says to run the system flat out, but I've been working on these 10 rads
for 3 hours and the place is like a sauna - help.
I've done the job, got 11 degC on every radiator, but the lounge is still
cold and the kids room too hot, what now?
The radiator that won't get hot is a big one but it's fed by a microbore
pipe - can this be the trouble?
I'm getting results with the radiator balancing but I can't make sense of
the tank bypass gate-valve. The DHW is controlled by a diverter/separate
zone valve/always on.
I've turned up the pump to maximum but the boiler still spends more time
off than on, and now I can hear the water roaring round the system?
I've turned up the pump to maximum and now I've got hot water overflowing
in my header tank.
I'm sure the installer used too narrow/too long a pipe run to the lounge
rad, but he says it's OK. How can I prove it to him?
I've worked out the output needed in this room, now how can I tell if the
rad in it is the right size?
I've worked out the output needed in this room, and the rad fitted is too
small/big. Can I just replace it?
I've worked out the rad sizes needed. Is there any advantage/problems in
fitting oversized ones to give a faster heat-up and some reserve against
extra cold weather?
Starting the questions is the easy bit, are they the right ones?
If answered these questions could turn into a Radiator and Pipe Sizing FAQ.
:-)
Matthew Marks
In article <3540B0...@nospam.inri.co.uk>,
Andy Baskett <ABas...@inri.co.uk> writes:
>
> I must admit I agree, having tried it (so far unsuccessfully). It is a
> hell of a job ... It was about 50 degrees in the house by the time I was
> half way around and I gave up.
> I must say I would probably still have given it a go, but I wouldn't
> have minded knowing just what a nightmare it would be.
Is Ruck Hughes listening?
Matthew Marks
In article <3545a61f...@news.demon.co.uk>,
ph...@severn.demon.co*uk (Phil Addison) writes:
...17 questions
eeeek! <runs away and hides>
Richard Gethin
In article <3545a61f...@news.demon.co.uk>, Phil Addison
<ph...@severn.demon.co*uk> writes
snipperama
> Several questions come to mind, answers to which
>could be added to the FAQ (OK, I know some of them are already addressed in
>it), e.g...
>
>What symptoms indicate my system needs balancing?
Normally only new systems or those that have neen altered (or the
builing they heat altered) or systems that have never been balanced need
it.
>What should I check before starting?
That the radiators are big enough for the job and that the boiler is big
enough to provide the heat required. Use Myson's heatloss manager or
Which? book of plumbing and central heating or the Ravensbourne guide to
central heating to calculate heat losses. Then use a Plumb Center
catalogue to confirm sizes. Set the boiler stat to maximum, most systems
are designed with a flow temp of 80 to 82 deg C. Set the pump to the
lowest speed, open all lockshield valves, set all roomstats to maximum
and ensure all trvs etc are fully open (sorry, most of this is in the
FAQ)
>
>Why some systems can never achieve correct temperatures?
Either the radiator is not big enough, the radiator is big enough but
not enough hot water is arriving at it.
> Where does this 11 degC drop come from. Is it vital to achieve it?
The figure of 11 deg C is a standard used in the design of rads and
systems. It sort of goes like:- with this radiator if the water enters
at 82, leaves at 71 then the heat output will be so many watts or BThU.
>I've got these spring attached thermometers and I can't distinguish any
>consistent differential across the rads - what am I doing wrong?
As someone else has said, they are sluggish and have poor thermal
contact with the pipe.
>How can I test these thermometers?
Don't bother..
>Isn't there a better way to measure the temperature difference?
Personally I tend to look more closely at the temp difference across the
boiler (this should be 11 deg as well) and not worry so much about the
individual rads. This is where you really need two thermometers set up
for the whole exercise. (I use cheapish digitals with the probes pushed
inbetween some clip on foam insulation and the pipe). With the system up
to temp (preferably cold day and all windows open) monitor the
difference between the flow and return temperatures while the boiler is
firing. If the temp rise across the boiler is a lot higher than 10 - 15
deg C then either the boiler gas rate is too high for the system or the
pump speed is too low for the size of system.
>It says to run the system flat out, but I've been working on these 10 rads
>for 3 hours and the place is like a sauna - help.
Cold day windows open
>
>I've done the job, got 11 degC on every radiator, but the lounge is still
>cold and the kids room too hot, what now?
I wouldn't worry about the temp drop across each rad, as someone has
said they won't be exactly matched to heat loss anyway. Start by taking
a general feel around the system. Feel for rads that don't get hot at
all, rads where the retun is much cooler than the flow and rads that are
scalding all over. Use some common sense to throttle some of the
hottest, smaller rads nearest to the boiler and have another feel
around. From this point start to measure the temperatures of the rooms
at the room centre to decide which rads to throttle more.
Don't worry about sorting it one afternoon. Live with it and make a
mental note of which rads could take more throttling and have a tweak.
The bigger cooler rads further from the boiler will start to warm up as
the others are throttled. If you get most rooms to the right temp but
the living room (big rad) is still cool (i.e. the rad is not hot all
over) then turn the pump up a notch. This assumes the rad in the living
room is big enough. You may have to throttle previously throttled rads a
bit more now.
>The radiator that won't get hot is a big one but it's fed by a microbore
>pipe - can this be the trouble?
If the system is a combination of smallbore and microbore then the
lockshield valves on the smallbore parts will have to be quite
considerably throttled to send the water along the microbore pipe. Does
it get hot at all? There may be an airlock. If there is, turn all the
other rads off and use the full force of the pump to shift it.
>
>I'm getting results with the radiator balancing but I can't make sense of
>the tank bypass gate-valve. The DHW is controlled by a diverter/separate
>zone valve/always on.
I'm not sure quite what you mean here. If there is a gate valve in the
heating coil circuit then it will need to be fairly throttled or the
coil acts as a short circuit. Having said that on my own system and
others I have put in there is no valve at all. This gives a rapid reheat
of the cylinder and once its stat is satisfied all the effort of boiler
and pump go to the heating. Oh drat I've just realised you were posing
hypothetical questions! Sorry everyone for wittering on.
>I've turned up the pump to maximum but the boiler still spends more time
>off than on, and now I can hear the water roaring round the system?
Perhaps a bypass wide open between the flow and return near the pump or
as previously, the cylider coil is acting like a short cicuit. Perhaps
the boiler is grossly oversized or gas/oil rate is set too high.
>I've turned up the pump to maximum and now I've got hot water overflowing
>in my header tank.
Bad system design, relocate pump or vent pipe. Possibly may be cured by
raising height of vent pipe loop over tank.
>I'm sure the installer used too narrow/too long a pipe run to the lounge
>rad, but he says it's OK. How can I prove it to him?
Figures in Ravensbourne Heating or Which? book.
>I've worked out the output needed in this room, now how can I tell if the
>rad in it is the right size?
Plumb Center Catalogue
>I've worked out the output needed in this room, and the rad fitted is too
>small/big. Can I just replace it?
Of course. If fitting a bigger rad will the boiler/pipework/pump be big
enough? If smaller perhaps the boiler rate will need to be reduced. The
balancing of the system could well need adjusting after fitting.
>I've worked out the rad sizes needed. Is there any advantage/problems in
>fitting oversized ones to give a faster heat-up and some reserve against
>extra cold weather?
Most systems are designed with an external temp of minus 1 to minus 3
deg C and with a 10% margin on radiator size. Which should be ample for
most locations. If the house is heated intermittently (holiday home,
village hall, church) then a larger margin shoud be used to give an
acceptable heat up period. In a properly designed system oversizing
things will lead to large variations in air temperature as things switch
on and off (overshoot after the stat turns off and overcooling as the
dinosaur system gets back up to temperature).
>
>Starting the questions is the easy bit, are they the right ones?
>If answered these questions could turn into a Radiator and Pipe Sizing FAQ.
>:-)
>
>--
>Phil | If possible please direct replies to the newsgroup.
> | If my 'From' address is anti-spammed, correct it
> | by joining this> phil@severn. to this> demon.co.uk
I know it sounds like I work for them but I do recommend the Which?
book.
--
Richard Gethin
Phil Addison
On Fri, 24 Apr 1998 20:56:59 +0100, in uk.d-i-y Richard Gethin replied:
>to article <3545a61f...@news.demon.co.uk>, Phil Addison
><ph...@severn.demon.co*uk> wrote
>
>> Several questions come to mind, answers to which
>>could be added to the FAQ (OK, I know some of them are already addressed in
>>it), e.g...
the answers now, but I think others could find the answers useful. They're
questions which cropped up before I had access to uk.d-i-y, so I had to
find the answers myself. Richard's kicked off the answers, so I'll add my
solutions/comments. I have a suspicion I may finish up putting this lot
into a piece for the FAQ, unless Rick Hughes is thinking of doing it. Rick,
are you there?
>>1) What symptoms indicate my system needs balancing?
>Normally only new systems or those that have neen altered (or the
>builing they heat altered) or systems that have never been balanced need
>it.
Agreed, but my scenario is that I buy a house (not a new one) and discover
the room temperatures are not satisfactory, and I have heard of the
balancing problem. Could it be that?
Answer) If one or more radiators won't get hot it could be the balancing.
Other possible problems need to be eliminated first - see below.
>>2) What should I check before starting?
>That the radiators are big enough for the job and that the boiler is big
>enough to provide the heat required. Use Myson's heatloss manager or
>Which? book of plumbing and central heating or the Ravensbourne guide to
>central heating to calculate heat losses. Then use a Plumb Center
>catalogue to confirm sizes. Set the boiler stat to maximum, most systems
>are designed with a flow temp of 80 to 82 deg C. Set the pump to the
>lowest speed, open all lockshield valves, set all roomstats to maximum
>and ensure all trvs etc are fully open (sorry, most of this is in the
>FAQ)
... and there is no air in the radiators.
>>3)Why some systems can never achieve correct temperatures?
(a) If some radiators are warm enough, others not:
>Either the radiator is not big enough,
If a radiator is not big enough it will still balance, but the room won't
get warm enough.
>or the radiator is big enough but not enough hot water is arriving at it.
... and this would be caused by either a blockage or incorrect design, i.e.
(i) too high a flow resistance (pressure drop) caused by too long a pipe
run or too small a bore for a long run, (ii) underpowered pump.
(b) If the whole house is generally too cool it may be due to inadequate
boiler capacity or insufficient or undersized radiators.
>>4) Where does this 11 degC drop come from. Is it vital to achieve it?
>The figure of 11 deg C is a standard used in the design of rads and
>systems. It sort of goes like:- with this radiator if the water enters
>at 82, leaves at 71 then the heat output will be so many watts or BThU.
The figure was originally 20 degrees Fahrenheit and metrication converted
this to 11 degrees Celsius. It is a historical standard measure. You don't
*have* to adhere to it but it is convenient to do so and it is harder to
get output data for other values.
The radiator produces it's rated heat output when it is at the rated
temperature (the average of flow and return temperatures) relative to the
room temperature. You can get more (or less) heat from it by altering this
average temperature. Some radiator data sheets give a graph showing this
effect, but it is roughly linear in the likely range. As the radiator gives
out it's heat, the water cools correspondingly, and 11 degrees C of cooling
corresponds to a water flow rate which carries exactly the rated heat.
You might expect that a bigger drop would therefore mean more heat output,
but that is not so. A bigger temperature drop occurs when the flow rate is
throttled back by the lock-shield (or manual) control valve. Less hot water
then flows in a given time so it cools more, resulting in a lower average
radiator temperature and hence less heat output. Put another way, the
radiator heat is replenished more slowly so it gets cooler. The extreme of
this situation is apparent when the flow connection is hot but the return
is cold.
>>5) I've got these spring attached thermometers and I can't distinguish any
>>consistent differential across the rads - what am I doing wrong?
>As someone else has said, they are sluggish and have poor thermal
>contact with the pipe.
They are a poor way to measure the temperature but if you cannot
afford/obtain a digital probe thermometer you can make the best of them as
follows:
Try to borrow lots of thermometers so you don't have to keep moving them
from rad to rad.
Test to see if they both/all read the same when cold, and by fitting them
to the same pipe, when hot. If not you will have to make corrections to
readings.
Make sure the curved contact plate matches the pipe diameter.
Clean the contact area of the pipe.
Fill the contact gaps with thermal grease.
Insulate the contact area from the surrounding air with foam sponge and
tape.
Record the initial valve positions so you can return to them if it all goes
wrong. Find out how many turns of the valve there are between fully open
and shut.
Be methodical in writing down the temperature at intervals until it
stabilises.
Adjust the valve in binary increments, i.e. Start with it fully open. Then
close it 1/2 way. Establish if you need to open/close it further. If so
move it by 1/2 the *remaining* amount. Repeat as necessary halving each
time. Allow to stabilise each time.
As said elsewhere, open the windows and try to do it on a cold day (or you
will get sweating hot).
>>6) How can I test these thermometers?
>Don't bother..
See 5 above.
>>7) Isn't there a better way to measure the temperature difference?
>Personally I tend to look more closely at the temp difference across the
>boiler (this should be 11 deg as well) and not worry so much about the
>individual rads. This is where you really need two thermometers set up
>for the whole exercise. (I use cheapish digitals with the probes pushed
>inbetween some clip on foam insulation and the pipe). With the system up
>to temp (preferably cold day and all windows open) monitor the
>difference between the flow and return temperatures while the boiler is
>firing. If the temp rise across the boiler is a lot higher than 10 - 15
>deg C then either the boiler gas rate is too high for the system or the
>pump speed is too low for the size of system.
The best way I know is to use a digital thermometer with a thermocouple
probe. This responds very rapidly (1-2 seconds) due to it's tiny mass and
requires no (or hardly any) thermal grease and can be insulated easily. I
just polish the pipe and tape it on with PVC tape. If you have two (or
more) probes they can be fixed in advance and you only then have to plug
each into the digital thermometer to take a reading. I got mine from Maplin
but unfortunately they no longer stock it. RS have a similar multimeter
with a plug-in type-K welded tip probe for about 30 quid, and extra probes
at 3 quid.
>>8) It says to run the system flat out, but I've been working on these 10 rads
>>for 3 hours and the place is like a sauna - help.
>Cold day windows open
Good thinking, batman. Comments from Andy Baskett <ABas...@inri.co.uk> and
t1md...@aol.com (T1MDownie) acknowledged too.
>>9) I've done the job, got 11 degC on every radiator, but the lounge is still
>>cold and the kids room too hot, what now?
>I wouldn't worry about the temp drop across each rad, as someone has
>said they won't be exactly matched to heat loss anyway. Start by taking
>a general feel around the system. Feel for rads that don't get hot at
>all, rads where the retun is much cooler than the flow and rads that are
>scalding all over. Use some common sense to throttle some of the
>hottest, smaller rads nearest to the boiler and have another feel
>around. From this point start to measure the temperatures of the rooms
>at the room centre to decide which rads to throttle more.
A separate digital room thermometer will be useful for this. Duh, what
about the wide open windows? Do this before it gets too hot I guess.
>Don't worry about sorting it one afternoon. Live with it and make a
>mental note of which rads could take more throttling and have a tweak.
>The bigger cooler rads further from the boiler will start to warm up as
>the others are throttled. If you get most rooms to the right temp but
>the living room (big rad) is still cool (i.e. the rad is not hot all
>over) then turn the pump up a notch. This assumes the rad in the living
>room is big enough. You may have to throttle previously throttled rads a
>bit more now.
Very good point, as someone else said, there is interaction but this should
be minimal if you work as per FAQ from the radiators on the highest
resistance circuit, the so-called "index-circuit" (what naff terminology),
to the least. Highest resistance equals longest/thinnest pipe run.
>>10) The radiator that won't get hot is a big one but it's fed by a microbore
>>pipe - can this be the trouble?
>If the system is a combination of smallbore and microbore then the
>lockshield valves on the smallbore parts will have to be quite
>considerably throttled to send the water along the microbore pipe. Does
>it get hot at all? There may be an airlock. If there is, turn all the
>other rads off and use the full force of the pump to shift it.
In my case the answer was a resounding "yes". The system was put into a new
house by an installer who apparently knew more about the effects of pipe
bore on cost than on flow resistance. The main lounge rad was a hefty 3KW
fed by 10mm microbore and it was 7m horizontal from the manifold. Despite
my calcs showing that 15mm was required, I only convinced then to change it
when I got them to turn up on a cold day and view the room thermometer
which was well below acceptable levels.
I think the way to answer this question is to include some pipe
bore/length/loading charts in the FAQ, along with an explanation of how to
work out total head requirements.
>>11) I'm getting results with the radiator balancing but I can't make sense of
>>the tank bypass gate-valve. The DHW is controlled by a diverter/separate
>>zone valve/always on.
>I'm not sure quite what you mean here. If there is a gate valve in the
>heating coil circuit then it will need to be fairly throttled or the
>coil acts as a short circuit. Having said that on my own system and
>others I have put in there is no valve at all. This gives a rapid reheat
>of the cylinder and once its stat is satisfied all the effort of boiler
>and pump go to the heating. Oh drat I've just realised you were posing
>hypothetical questions! Sorry everyone for wittering on.
Don't apologise - it's all very relevant.
I was trying to draw out the options and their pros/cons for heating the
domestic hot water. You've mentioned a good system, but there are others
which folk may encounter (and decide to modify to yours, perhaps).
>>12) I've turned up the pump to maximum but the boiler still spends more time
>>off than on, and now I can hear the water roaring round the system?
>Perhaps a bypass wide open between the flow and return near the pump or
>as previously, the cylider coil is acting like a short cicuit. Perhaps
>the boiler is grossly oversized or gas/oil rate is set too high.
Yes, all possible. My intention was to open up discussion about:
(a) The short-cycling problem, and
(b) The limitation on cranking up pump pressure in an existing system due
to the noise limit on water velocity.
>>13) I've turned up the pump to maximum and now I've got hot water overflowing
>>in my header tank.
>Bad system design, relocate pump or vent pipe. Possibly may be cured by
>raising height of vent pipe loop over tank.
Absolutely; and guess what? I had that on the same system mentioned in 10
above. Well, actually it was the other way round, those guys managed to
place the pump so that it raised the level in the header tank via the feed
pipe. Thus a dollop of DHW was raised into the tank every time the pump
switched on, and cooler water was drawn back when it went off. Result after
a day of that was that the header was full of steaming hot water. It
couldn't be corrected without major re-routing, so in the end I
did-it-meself by fitting a non-return valve in the feed pipe. It fixed it,
and I think (*hope*) it is safe 'cos we sold the house soon after.
>>14) I'm sure the installer used too narrow/too long a pipe run to the lounge
>>rad, but he says it's OK. How can I prove it to him?
>Figures in Ravensbourne Heating or Which? book.
Wish I'd have thought of that at the time. I naively thought they would
understand and accept hydraulic calcs. See 10 above.
>>15) I've worked out the output needed in this room, now how can I tell if the
>>rad in it is the right size?
>Plumb Center Catalogue
Agreed.
This doesn't quite match the question, but somewhere we should point out
that different makes of radiators come in different increments of physical
sizes, so if you have a confined space you need to check several makes to
find the best fit. Also some makers make wider / narrower / taller /
shorter radiators than others.
>>16) I've worked out the output needed in this room, and the rad fitted is too
>>small/big. Can I just replace it?
>Of course. If fitting a bigger rad will the boiler/pipework/pump be big
>enough? If smaller perhaps the boiler rate will need to be reduced. The
>balancing of the system could well need adjusting after fitting.
Agreed. So the guy needs to learn about c/h, or get a man in (Eeeek!
Mathew's copyright acknowledged).
>>17) I've worked out the rad sizes needed. Is there any advantage/problems in
>>fitting oversized ones to give a faster heat-up and some reserve against
>>extra cold weather?
>Most systems are designed with an external temp of minus 1 to minus 3
>deg C and with a 10% margin on radiator size. Which should be ample for
>most locations. If the house is heated intermittently (holiday home,
>village hall, church) then a larger margin shoud be used to give an
>acceptable heat up period. In a properly designed system oversizing
>things will lead to large variations in air temperature as things switch
>on and off (overshoot after the stat turns off and overcooling as the
>dinosaur system gets back up to temperature).
Good points. I hadn't thought of the air temp variation snag. That could
presumably be overcome with a good control system that reduced the flow
temperature, or by thermostatic valves on the radiators? My philosophy was
that as I was saving so much by d-i-ying it, I could spend more cash on
bigger radiators than a pro would put in, thus giving me a bigger margin
and faster warm up.
>>Starting the questions is the easy bit, are they the right ones?
I'm beginning to think that a better format would be a more general piece
about the workings and troubleshooting of central heating. Balancing would
form a chapter in that, and let's see... pipe sizing, control systems,
zoning... what else?
>>If answered these questions could turn into a Radiator and Pipe Sizing FAQ.
>>:-)
... if not the Central Heating FAQ. Eeeek, again!
>I know it sounds like I work for them but I do recommend the Which? book.
I've got their 1966 edition!
Alan Briggs
Richard Gethin wrote:
>
> >Isn't there a better way to measure the temperature difference?
Personally I tend to look more closely at the temp difference across
the
> boiler (this should be 11 deg as well) and not worry so much about the
> individual rads. This is where you really need two thermometers set up
> for the whole exercise. (I use cheapish digitals with the probes pushed
> inbetween some clip on foam insulation and the pipe).
I have this idea, based on school physics, that you should be able to
measure differential temperature with two thermocouples and a suitably
sensitive voltmeter. You would connect a wire of the same metal from
each thermocouple together and measure the voltage between the two other
wires. The voltage will then be proportional to the temperature
difference and you can look up the conversion factor. If you put one of
the thermocouple tips in a glass of water and measured the water
temperature with a mercury thermometer then you can calculate the
abolute temperature of the other tip.
This probably sounds more complicated than it would be in practice.
Thermocouples are quite cheap but digital thermometers are costly,
particularly if you only want to use them to balance the heating. The
innards of a digital thermometer must just contain a reference junction
(i.e. the second thermocouple) and a DVM calibrated to give a
temperature readout.
I have yet to try out this idea so useful comments would be appreciated
--
- Alan Briggs -
Rick Hughes
> unless Rick Hughes is thinking of doing it. Rick, are you there?
Well I am sort of here ... I am actually in Hong Kong looking out of the Hotel
window watching the Star Ferry chugging away across the bay to Kowloon.
Anyway, I have no plans to update the scribblings I did for the FAQ a few years
ago.
I would be happy to take a look at any proposed additions and pass comments but
there are nowadays more qualified people on the list than when I put the FAQ
together, who may be better placed to "comment" ..... but by all means send me
something to read if you want to.
I am shortly to install a complete new central heating system, this time no
radiators at all .. so no balancing problems for rads.
Rads are a means to an end but they are far from ideal, inefficient as most of
heat immediately rises to ceiling level, and limits where you can put furniture.
The system will be underfloor heating, pipes buried in screed on first floor,
and clipped to underside on first floor "deck" on the upstairs.
This will have heated towel rails in the bathrooms, and a pumped hot water loop
... no delay in waiting for water to run hot.
It is all fed from a thermal store so the hot water is at full mains pressure.
It will be fired by a condensing gas boiler .
When I have completed the job I will probably post comments on how it went.
Rick
--
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( @ @ )
---------oOOo-(_)-oOOo---------
Welcome from Wales All comments are my own and
Rick_...@newbridge.com not attributable to my Employer
-------------------------------
John Fessey
Rick Hughes <rhu...@newbridge.com> wrote in article
<354855AC...@newbridge.com>...
> > unless Rick Hughes is thinking of doing it. Rick, are you there?
>
> Well I am sort of here ...
[snip]
> I am shortly to install a complete new central heating system, this time
no
> radiators at all .. so no balancing problems for rads.
But you will have to balance the 'loops'. Try to make them all a similar
length.
JohnF
Phil Addison
On Thu, 30 Apr 1998 10:43:01 +0000, in uk.d-i-y Rick Hughes wrote:
> Well I am sort of here ... I am actually in Hong Kong looking out of the Hotel
>window watching the Star Ferry chugging away across the bay to Kowloon.
>Anyway, I have no plans to update the scribblings I did for the FAQ a few years
>ago.
>I am shortly to install a complete new central heating system, this time no
>radiators at all .. so no balancing problems for rads.
>Rads are a means to an end but they are far from ideal, inefficient as most of
>heat immediately rises to ceiling level, and limits where you can put furniture.
> The system will be underfloor heating, pipes buried in screed on first floor,
>and clipped to underside on first floor "deck" on the upstairs.
All fine advantages, but won't there be a few hours (at least) response
delay after you twiddle the thermostat? But with all the cash swilling
around out there I suppose they can just open the windows or turn on the
air-conditioning to cool it down. <g>
>
[snippy]
>When I have completed the job I will probably post comments on how it went.
Should be interesting.
Rick Hughes
Phil Addison wrote:
> All fine advantages, but won't there be a few hours (at least) response
> delay after you twiddle the thermostat?
I will not rise to the bitching. :-)
UFH has an inherent delay, that is why you do not use ordinary thermostats, instead
you use digital set back controllers.
i.e. use set the room temp for normal use, then set it back a few degrees for non
use / night time.
This keeps the house at a warm ambient temp, and the system only has to bring it up
a couple of degrees for use, as UFH is usually hand in hand with high insulation
standards this does not mean higher running costs, usually reduced costs due to
higher efficiency of the system overall.
Most systems are installed with the pipes in a 65mm screed, below which is 50mm of
insulation, this then heats up and you have a radiator the size of your ground floor
... Like a very big storage battery, evens out the heat and due to the comfortably
warm feet gives a very high comfort factor.
Unlike the electric systems of the 60s, where the high temp of the few wires which
was needed to overcome very poor insulation standards meant uncomfortably hot feet
and discoloured furniture ... and very expensive running costs.
Some people also use external stats with compensater programmers to predict when
heating will be needed, supposed to increase performance ... but I have no
experience of these systems ... always seemed very expensive and complicated when I
have looked at them.
Rick
> Phil | If possible please direct replies to the newsgroup.
> | If my 'From' address is anti-spammed, correct it
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Phil Addison
On Sat, 02 May 1998 20:12:09 +0000, in uk.d-i-y Rick Hughes wrote:
>Phil Addison wrote:
>> All fine advantages, but won't there be a few hours (at least) response
>> delay after you twiddle the thermostat?
For late comers UFH = Under Floor Heating...
>UFH has an inherent delay, that is why you do not use ordinary thermostats, instead
>you use digital set back controllers.
>i.e. use set the room temp for normal use, then set it back a few degrees for non
>use / night time.
>
>This keeps the house at a warm ambient temp, and the system only has to bring it up
>a couple of degrees for use, as UFH is usually hand in hand with high insulation
>standards this does not mean higher running costs, usually reduced costs due to
>higher efficiency of the system overall.
>
>Most systems are installed with the pipes in a 65mm screed, below which is 50mm of
>insulation, this then heats up and you have a radiator the size of your ground floor
>... Like a very big storage battery, evens out the heat and due to the comfortably
>warm feet gives a very high comfort factor.
> Unlike the electric systems of the 60s, where the high temp of the few wires which
>was needed to overcome very poor insulation standards meant uncomfortably hot feet
>and discoloured furniture ... and very expensive running costs.
>
>Some people also use external stats with compensater programmers to predict when
>heating will be needed, supposed to increase performance ... but I have no
>experience of these systems ... always seemed very expensive and complicated when I
>have looked at them.
I admit my comments were based on the old electric systems, and it sounds
as if the technology has improved somewhat, and I take your points about
uniform comfort temperature. I suppose if the building is insulated such
that it's response time to the external environment is at least as long as
the heating lag it would be OK, or if the external environment doesn't
change very rapidly. Is that the case in Singapore perhaps?
On the other hand the temperature you want in the house varies according to
what you are/have been doing. e.g. coming in from strenuous work you would
want to turn the temp down. Now if you could get hold of some low thermal
capacity screed with high conductance...
--
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