Efficient way to run boiler?
VAG_dude
Our house has a total 16kw - 17kw of radiators, the boiler is capable
of supplying 28kw. On the boilers diagnostic menu you can adjust the
maximum kw from 12kw right to 28kw, it came factory set at 28kw but I
thought we could use a little less gas by running in exactly at 17kw
which is the maximum ever required, however this what I have observed:
When on 28kw the boiler fires at 12kw for a minute, ramps right up to
28kw and quickly achieves the flow temperature of 70ºc, it then
modulates down slowly and happily maintains 70ºc until the thermostat
stops calling for heat. The house warms up pretty quickly.
When on 17kw, again the boiler starts on 12kw, ramps up to 17kw and
takes a fair bit longer to get to 70ºc, once at 70ºc it will modulate
down and maintain 70ºc as it does when on 28kw. The house takes a bit
longer to get warm but still reaches the set temperature in a
satisfactory amount of time, just not quite as rapidly as before.
So the question is what is the better way to run the boiler, will it
save gas running on 28kw as the boiler modulates down quicker? I have
heard it's best to run at 17kw as it stops putting unnecessary strain
on the main heat exchanger, how true is this?
The boiler is a Vaillant Ecotec plus 937 (37kw Dhw, 12kw-28kw Ch)
Thanks.
The Natural Philosopher
really knows the answer to, except it almost certainly won't be simple.
Its definitely one that I would want to strap a standard boiler to a
calorimeter or whatever, and run a months worth of tests on.
Similar questions include
- how much extra fuel does a power station have to burn when its output
is being ramped up and down to cope with windpower fluctuations (answer
seems to be between, 0.5 and 1.1 of the windpower generated, thus
rendering windmills fucking useless)
- what is the best speed for maximum mpg to drive a car at? (answer
totally car and engine dependent in the fine limits. Certainly in top
gear, but beyond that somewhere between 30mph and 70mph seems to cover
all tested cases, which is again not helpful).
- how long is a piece of string (never long enough or you wouldnt be
asking).
harry
You want to run it at as low a setting as possible. (That's why it's
got lower settings in the first place)
It will use less fuel because it will go on and off less frequently.
Every time it shuts down, it blows cold air trough the boiler and also
before it starts. This represents a heat loss. (It does this to clear
combustion gases and as a safety precaution in case a gas valve has
leaked).
Your boiler is oversized and will always be less efficient than it
might be. When set at the top of it's range it should be right for
Winter. The lower range is for the "shoulder periods" ie Spring
Autumn. Because it's oversize it will be cycling on off on off far
too frequently. That is the idea of being able to vary the output, to
match climate, not to allow for the incompetence of whoever has sized
it.
This is a common problem with dozy heating engineers that don't know
how to correctly size a boiler The "cover my arse" syndrome.
BTW, ignore the old fart above, I believe he has dementia:-)
PeterC
Similar here, but my boiler is 20kW CH for about 11kW rads. (need the boiler
for DHW). The boiler can be reduced to 50% but even that is too much at
times.
Trouble is, I run the main rooms at 18C and the bedrooms, on TRVs, at 14C,
so over half the system is shutting off most of the time.
Currently trying 60% at 70C output to see what happens.
It's difficult to get meaningful figures under real-world conditions as
there are so many variables, so I go for an acceptable warm-up time and
minimal short-cycling.
--
Peter.
The gods will stay away
whilst religions hold sway
ransley
Longer cycles are easier on controls, less cycles means longer life
and less cycles give longer run times at full efficiency. It takes
maybe 5 minutes to get to full efficiency, but I am just guessing.
Less cycles you will have fewer cool down periods where the
electronocs and pump are running. Longer cycles give more even
heating. The only thing I wonder is Is 70c past the boilers peak
efficiency temp, is that a factory set temp or is for example 65c or
less the boilers peak efficency rating. You need to know at what temp
the boiler starts to loose efficiency and not run above that temp if
possible except on the coldest days. For a boiler to be sized right it
should need to run most of the time on the coldest days, since it isnt
cold out yet maybe you are sized right. I would find out from the
manufacturer the temp at which it looses efficency it should be online
or in their literature you recieved, and set boiler temp at that
level, if it heats ok at less overall output then try it, overall
output is not water temp.
newshound
>
> The boiler is a Vaillant Ecotec plus 937 (37kw Dhw, 12kw-28kw Ch)
>
> Thanks.
Are you happy with it otherwise? Although I had almost decided never to buy
another combi, the characteristics of this one might well suit my (larger
than normal) house. I do like the look of the very comprehensive
diagnostics.
VAG_dude
Indeed I am, this boiler was installed almost 2 years back and it
hasn't missed a beat, it was ideal for our needs as we had no space
for an unvented cylinder. DHW is excellent, the boiler runs quietly
and it's a very solid and well built piece of kit. We have 2 heating
zones in our house so at the time we couldn't use Vaillant controls, I
would have preferred the Vaillant controls because if you set them to
2 point analogue operation they automatically adjust the boiler flow
temperature according to what the room temperature is. At the time
Vaillant controls weren't suitable for 2 zone systems unless you had
the VR61 mixer module which was only available in Germany, it is now
available here.
newshound
"VAG_dude" <dawoo...@gmail.com> wrote in message
news:f9dfb77e-4819-4e6c...@x42g2000yqx.googlegroups.com...
That's useful to know as I have two zones as well
VAG_dude
All quite interesting :)
VAG_dude
Hmm the manual states that it is not necessary to range rate the
boiler as it is a modulating appliance however you can range it if
need be, there has to be a reason for the setting!
> It will use less fuel because it will go on and off less frequently.
> Every time it shuts down, it blows cold air trough the boiler and also
> before it starts. This represents a heat loss. (It does this to clear
> combustion gases and as a safety precaution in case a gas valve has
> leaked).
How will it go on and off less frequently? It doesn't cycle on any kw
rating unless the Honeywell CM927 tell it to; which it does as it
approaches the set temperature.
>
> Your boiler is oversized and will always be less efficient than it
> might be. When set at the top of it's range it should be right for
> Winter. The lower range is for the "shoulder periods" ie Spring
> Autumn. Because it's oversize it will be cycling on off on off far
> too frequently. That is the idea of being able to vary the output, to
> match climate, not to allow for the incompetence of whoever has sized
> it.
> This is a common problem with dozy heating engineers that don't know
> how to correctly size a boiler The "cover my arse" syndrome.
As it is a combi boiler it is sized on DHW demand. However the
installer did not size radiators or pipes correctly but then that's a
different issue.
VAG_dude
> "VAG_dude" <dawoods...@gmail.com> wrote in message
Glad I could help, out of interest do you have space for a cylinder?
Rick Hughes
"harry" <harol...@aol.com> wrote in message news:7937bfad-ca81-4d61-a7b8-
>You want to run it at as low a setting as possible. (That's why it's
>got lower settings in the first place)
>It will use less fuel because it will go on and off less frequently.
What logic are you using here ? why would it go on and off more on high
output setting ..... either setting would see it come on when there is a
heat demand, and off when there isn't ....
On a high output setting it would serve demand quicker but would not result
in any fewer 'on/off' cycles.
Dave Liquorice
>> You want to run it at as low a setting as possible. (That's why
it's
>> got lower settings in the first place) It will use less fuel
because it
>> will go on and off less frequently.
>
> What logic are you using here ?
"harry" logic. Our most recent poster of ill informed, badly thought
out comments.
As to the OP, the house will need x amount of energy to keep it at
the required temperature. All that energy comes from the boiler, that
appears to keep itself operating in it's most effcient condensing
mode by keeping the flow at 70C and modulating the burner back as the
return temp increases.
All that limiting the maximum power the boiler can use will do is
slow down how fast the house heats up, as the OP says. If the rads
can't dump the heat into the house fast enough the return temp goes
up and the boiler simply modulates down.
--
Cheers
Dave.
harry
wrote:
The higher the output setting, the quicker it reaches it's set point,
so reducing the overall cycle time. This means there are more cycles
per any given time. Every time a cycle runs, energy is lost. The
ideal would be that it never quite reached set point, ie ran
continuously. There would be no cold air purges and hence no energy
loss through purges.
I e the boiler output should be set close to or slightly less than the
maximum heating requirements for the the likely weather.
If the boiler is oversized, this may not be possible all the time or
even any time. This has always been true even before modulating
boilers existed.
So, from cold the boiler should modulate to full output. Ideally when
the set temperature is approached, it should modulate back an then run
continuously at a lower setting, maintaining the called for
temperature.
The higher the turndown ratio, the more likely it is that it can do
this.
In practice turndown ratios are not able to exceed four or five.
This is the benifit of modulating boilers over on/off boilers in the
past.
The boiler output in practical terms needs fiddling with so that it
goes off a little as possible. Ideally as weather warms up, the
output should be reduced.
With industrial sized boilers this function can be done automatically
with outside heat sensors. It's not usually considered economical to
provide domestic sized boilers with such more advanced control gear.
Ronald Raygun
> On Sun, 5 Sep 2010 16:12:11 +0100, Rick Hughes wrote:
>>>
>>> You want to run it at as low a setting as possible. (That's why
>>> it's got lower settings in the first place) It will use less fuel
>>> because it will go on and off less frequently.
>>
>> What logic are you using here ?
>
> "harry" logic. Our most recent poster of ill informed, badly thought
> out comments.
>
> As to the OP, the house will need x amount of energy to keep it at
> the required temperature.
Correction: The house will need x amount of energy *per unit of time*.
In other words it will need on average a certain amount of *power*.
It is obvious that the boiler will cycle on/off more often on a high
power setting than on low. To see why, read on.
Ignore any ability of the boiler to "modulate back", this does not
affect the principle of the cycling frequency changing with the maximum
power setting, though it will affect the size of the difference. So
suppose the boiler is either off, or delivers 14kW or 28kW. Suppose the
house needs on average 7kW (168kWh/d) to keep warm.
Therefore at 14kW the boiler will be on for half the time (12h/d),
and at 28kW it will be on for a quarter of the time (6h/d).
The house is losing power to the environment at (on average) a constant
7kW, and is taking in energy from the boiler at either 14 or 28kW, so
the house's net power inflow at any moment is either +7kW (boiler on low,
i.e. 14kW-7kW) or +21kW (with boiler on high, i.e. 28kW-7kW) or -7kW
(boiler off, i.e. 0kW-7kW).
The house temperature ramps up and down between the thermostat's switching
limits. It does so at a rate more or less proportional to the net power
inflow. Suppose it takes on average 15 mins for the house temperature to
ramp down from the time the boiler switches off until it switches on again.
Then on low setting it will also take 15 mins for the temperature to ramp
up, while on high setting it will only take 5 mins. Thus on low, each cycle
last 30 mins (15 on 15 off), while on high it lasts only 20 mins (5 on 15
off).
Therefore on high setting there will be three cycles per hour while on low
there will only be two.
Note that this does not affect efficiency directly, since the boiler, if on
low, is still on for 12h per day (actually 15 mins per half hour), and if
on high is on for 6h per day (actually 5 mins in each 20). In both cases
the boiler is consuming an average 7kW (168kWh per day).
The efficiency could be affected, though, if there is a fixed overhead
penalty per cycle in which some energy is lost from the boiler directly
to the environment without benefiting the house, or from delays in the
sensors allowing the temperature to overshoot more on high than on low.
cynic
Are you or swmbo happy for the house "to take a bit longer to get
warm"?
You have an automatic system with the capability of warming your house
quickly then reducing its ouput to match the maintaining temperature
requirement. For the sake of curiosity you could bugger about with it
but whats the point of potentially upsetting a working system?
IF IT AINT BROKE DON'T TRY TO FIX IT
The Natural Philosopher
The details are
1/. The variations in boiler efficiency with output level
2/. The heat loss from the house when warming up. Is a short warm up
period actually losing less heat on average?
3/. The actual fuel used to start the boiler and get it up to temp.
When you are chasing optimal settings, you cant ignore any off these,.
None are instantly obvious.
Which is why I refuse to get drawn into this, beyond pointing out its a
total can of worms.
Mark
If the house heats up more quickly with the boiler set at 29kw vs 17kw
then you must have more than 17kw of radiators.
>The boiler is a Vaillant Ecotec plus 937 (37kw Dhw, 12kw-28kw Ch)
>
>Thanks.
--
(\__/) M.
(='.'=) Due to the amount of spam posted via googlegroups and
(")_(") their inaction to the problem. I am blocking some articles
posted from there. If you wish your postings to be seen by
everyone you will need use a different method of posting.
dennis@home
"The Natural Philosopher" <t...@invalid.invalid> wrote in message
news:i62ioi$nct$1...@news.albasani.net...
> The details are
>
> 1/. The variations in boiler efficiency with output level
True and boiler dependent.
> 2/. The heat loss from the house when warming up. Is a short warm up
> period actually losing less heat on average?
No.
Draw a graph, the house loses less heat when its cool, if its cool for
longer it will lose less heat.
A quick warm up means it has a higher average temp and will lose more heat.
Of course the devil is in the detail and if the house isn't in use during
the warm up period the heat is wasted.
> 3/. The actual fuel used to start the boiler and get it up to temp.
Assuming the water is at a lower temp it is probably more efficient than
when the water is up to temp.
Its not obvious how to design a boiler heat exchanger that works less well
when its cold than it does when its hot.
>
> When you are chasing optimal settings, you cant ignore any off these,.
> None are instantly obvious.
To whom?
fred
<76c63bc1-9e4a-4513...@m1g2000yqo.googlegroups.com>,
VAG_dude <dawoo...@gmail.com> writes
>
>How will it go on and off less frequently? It doesn't cycle on any kw
>rating unless the Honeywell CM927 tell it to; which it does as it
>approaches the set temperature.
>
lowest level that can just maintain the temperature in the property but
you then need to tweak the mod level to match the weather or it wont
reach temperature during a cold snap. I favour this because it means
that the rads stay at a low but consistent temp which in my view gives a
greater comfort level.
Good luck finding controls that will support this kind of operation
though, Honeywell controls are fixed in proportional mode meaning that
they force you to cycle the boiler multiple times per hour (6 on default
setting) which they claim gives better temperature accuracy but IMV
results in excessive component stressing[2] and inefficiency. There is a
quality electronic stat on the market that has selectable proportional
control so you can disable it if you think you know better but I can't
remember which one it is, poss Danfoss.
The choice, as they say, is yours.
[1] Traffic light racing analogies do apply.
[2] Add up the cycles per hour, mult by the hours on per day then factor
that into the spec'd cycle life of zone valves and boiler ignition
circuits and you'll find that the life is shorter than you think. 3
years I think in my case when calculated.
--
fred
FIVE TV's superbright logo - not the DOG's, it's bollocks
harry
I see you can't get your head round the difference between a boiler
with a fixed output and a modulating boiler.
If it were an ideal modulating boiler it would start up, run up to
temperature and then run continuously, modulating it's output to meet
demand.
It's not technically possible to make such a boiler as the turndown
ratio would need to be infinity. Ie it would need to be capable of
running all the way from maximum output to zero.
So we have to accept less than perfection. At some point it will turn
off. Which is the whole problem. But some degree of modulation is
better than none.
I think you'd better google "modulate" and "turndown ratio" as you
don't seem to understand either.
VAG_dude
> In article
> <76c63bc1-9e4a-4513-9a58-32fa9d98b...@m1g2000yqo.googlegroups.com>,
> VAG_dude <dawoods...@gmail.com> writes
>
> >How will it go on and off less frequently? It doesn't cycle on any kw
> >rating unless the Honeywell CM927 tell it to; which it does as it
> >approaches the set temperature.
>
> My own pref is for a long slow burn[1], ie boiler mod'd down to the
> lowest level that can just maintain the temperature in the property but
> you then need to tweak the mod level to match the weather or it wont
> reach temperature during a cold snap. I favour this because it means
> that the rads stay at a low but consistent temp which in my view gives a
> greater comfort level.
Makes sense.
>
> Good luck finding controls that will support this kind of operation
> though, Honeywell controls are fixed in proportional mode meaning that
> they force you to cycle the boiler multiple times per hour (6 on default
> setting) which they claim gives better temperature accuracy but IMV
> results in excessive component stressing[2] and inefficiency
I agree with you on this one, the boiler seems to be constantly on and
off and on again etc etc And once the house has reached the
temperature the boiler cools down a bit but before you know it the
thermostat is calling for heat again to keep the temperature steady
and the boiler starts all over again on full tilt and usually does not
even get a chance to modulate down as the thermostat has stopped
calling for heat.
. There is a
> quality electronic stat on the market that has selectable proportional
> control so you can disable it if you think you know better but I can't
> remember which one it is, poss Danfoss.
Interesting,
>
> The choice, as they say, is yours.
>
> [1] Traffic light racing analogies do apply.
>
> [2] Add up the cycles per hour, mult by the hours on per day then factor
> that into the spec'd cycle life of zone valves and boiler ignition
> circuits and you'll find that the life is shorter than you think. 3
> years I think in my case when calculated.
What boiler do you have? We have Honeywell 2-port valves and a
Vaillant boiler.
harry
>
> - Show quoted text -
Any boiler is at maximum efficiency at it's lowest output.
As to heat loss, when the house is cold heat loss is zero. When it's
at desired temperature, heat loss in any given depends on the outside
temperature and wind. What goes on between these points depends on
the thermal inertia of the house. But can be calculated and is for
large buildingd where it's of signiifcance.
The fuel used is niether here nor there for heat loss calculations.
harry
>
> - Show quoted text -
There is no such thing as any "Kw of radiators" The energy they emit
depends on many factors. You haven't read my previous posts or you
wouldn't make such stupid statements.
Doctor Drivel
> Any boiler is at maximum efficiency at
> it's lowest output.
You need to look into boilers a lot more.
Doctor Drivel
Hi there,
Our house has a total 16kw - 17kw of radiators, the boiler is capable
of supplying 28kw. On the boilers diagnostic menu you can adjust the
maximum kw from 12kw right to 28kw, it came factory set at 28kw but I
thought we could use a little less gas by running in exactly at 17kw
which is the maximum ever required, however this what I have observed:
When on 28kw the boiler fires at 12kw for a minute, ramps right up to
28kw and quickly achieves the flow temperature of 70şc, it then
modulates down slowly and happily maintains 70şc until the thermostat
stops calling for heat. The house warms up pretty quickly.
When on 17kw, again the boiler starts on 12kw, ramps up to 17kw and
takes a fair bit longer to get to 70şc, once at 70şc it will modulate
down and maintain 70şc as it does when on 28kw. The house takes a bit
longer to get warm but still reaches the set temperature in a
satisfactory amount of time, just not quite as rapidly as before.
So the question is what is the better way to run the boiler, will it
save gas running on 28kw as the boiler modulates down quicker? I have
heard it's best to run at 17kw as it stops putting unnecessary strain
on the main heat exchanger, how true is this?
The boiler is a Vaillant Ecotec plus 937 (37kw Dhw, 12kw-28kw Ch)
____________
Leave the boiler on maximum as it gets hotter quicker. This means you can
reduce the warm up times.
The boiler modulates from 12kW to 28kW. Inefficiencies start when the
demand is below 12kW and cycling starts. Lowering to 17kW achieves nothing
as the controls modulate from 12KW to 28kW and all between.
The only way you can save is lower the flow temperature, then the return
temp reduces promoting condensing efficiencies.
I would consider fitting an outside weather compensator to this model. It
can have one.
The Natural Philosopher
>
> The fuel used is niether here nor there for heat loss calculations.
Classic!
A sentence for the archives of sheer fuckwittedness.
And you cant spell neither, either.
fred
<53427007-285d-469a...@b34g2000yqm.googlegroups.com>,
VAG_dude <dawoo...@gmail.com> writes
>Vaillant boiler.
>
running off a clunky & crappy Towerstat wired electronic stat and
despite it not switching as accurately as I would like, the boiler had
karma and pottered away on its low (actually mid) setting, often for
hours with the stat just cutting out every now and again to stop the
rooms going over temp. In winter I would turn the mod control up and
ease it off in warmer times.
It now has a Honeywell CM907 (the wired version of yours I think) and
now it is forced to cycle 3 times per hour (reduced from default) so the
boiler thrashes for a few mins to get to temp and switches off again
almost before it gets a chance to mod down. There are lots of features I
like on the Honeywell but it's not controlling the system how I would
like it. Also, I have a multi zone setup that I'd like to fully
configure but it is impossible to sync the wired Honeywell electronic
stats in any meaningful way which is the ideal way to do it.
dennis@home
"VAG_dude" <dawoo...@gmail.com> wrote in message
news:53427007-285d-469a...@b34g2000yqm.googlegroups.com...
> I agree with you on this one, the boiler seems to be constantly on and
> off and on again etc etc And once the house has reached the
> temperature the boiler cools down a bit but before you know it the
> thermostat is calling for heat again to keep the temperature steady
> and the boiler starts all over again on full tilt and usually does not
> even get a chance to modulate down as the thermostat has stopped
> calling for heat.
Not all boilers are efficient when modulating, the efficiency may well be
different at different modulation points.
You need a graph of efficiency vs. modulation before you can decide whats
best.
My boiler doesn't modulate at all but runs at the maximum efficiency on and
off.
The supposed inefficiency of boiler cycling doesn't apply to a boiler that
is designed to be cycled.
What is pretty certain is that you want the water temp as low as possible
for a condensing boiler even though it means having radiators twice as big.
VAG_dude
> In article
> VAG_dude <dawoods...@gmail.com> writes
Seems that you have the same issue as me, I don't particularly like
the proportional control on the Honeywell CM927/CM907.
dennis@home
"The Natural Philosopher" <t...@invalid.invalid> wrote in message
news:i635gf$jgo$1...@news.albasani.net...
TNP can't read either, for heat loss the fuel *doesn't* matter.
For cost calculation it does matter.
newshound
"VAG_dude" <dawoo...@gmail.com> wrote in message
news:9fa7e9a3-bd6f-4384...@j18g2000yqd.googlegroups.com...
I currently have a direct vented electric cylinder for a shower. I could, as
phase 2, replace it with with an unvented one. My original plan was to go
for a "system" (non-combi) boiler with a small high output cylinder next to
the boiler, as I have limited space there. But I'm definitely coming round
to the idea of a 937 instead. My other thought is whether I could run an
extra circuit off the 937 to an external plate heat exchanger, and use that
to heat the current vented direct cylinder (with an extra pump on the
secondary side). Again, that could be a "Phase 2" job.
Doctor Drivel
"The Natural Philosopher" <t...@invalid.invalid> wrote in message
> VAG_dude wrote:
>> Hi there,
>>
>> Our house has a total 16kw - 17kw of radiators, the boiler is capable
>> of supplying 28kw. On the boilers diagnostic menu you can adjust the
>> maximum kw from 12kw right to 28kw, it came factory set at 28kw but I
>> thought we could use a little less gas by running in exactly at 17kw
>> which is the maximum ever required, however this what I have observed:
>>
>> When on 28kw the boiler fires at 12kw for a minute, ramps right up to
>> modulates down slowly and happily maintains 70ºc until the thermostat
>> stops calling for heat. The house warms up pretty quickly.
>>
>> When on 17kw, again the boiler starts on 12kw, ramps up to 17kw and
>> down and maintain 70ºc as it does when on 28kw. The house takes a bit
>> longer to get warm but still reaches the set temperature in a
>> satisfactory amount of time, just not quite as rapidly as before.
>>
>> So the question is what is the better way to run the boiler, will it
>> save gas running on 28kw as the boiler modulates down quicker? I have
>> heard it's best to run at 17kw as it stops putting unnecessary strain
>> on the main heat exchanger, how true is this?
>>
>>
>> Thanks.
> I suspect this is one of those stunningly awkward questions that no one
> really knows the answer to, except it almost certainly won't be simple.
It will not be simple to someone like you.
Doctor Drivel
"newshound" <news...@fairadsl.co.uk> wrote in message
news:8ehfj...@mid.individual.net...
>
>
>>
>> The boiler is a Vaillant Ecotec plus 937 (37kw Dhw, 12kw-28kw Ch)
>>
>> Thanks.
>
> buy another combi, the characteristics of this one might well suit my
> (larger than normal) house. I do like the look of the very comprehensive
> diagnostics.
Look at the ATAG 51kW. This is far better.
Doctor Drivel
Hmm the manual states that it is not necessary to range rate the
boiler as it is a modulating appliance however you can range it if
need be, there has to be a reason for the setting!
___________
It can supply the copper coil heat exchanger to a forced air system, where
you will need a constant temp and range rating to near as you can get.
Doctor Drivel
"Dave Liquorice" <allsortsn...@howhill.com> wrote in message
news:nyyfbegfubjuvyypb...@srv1.howhill.co.uk...
> As to the OP, the house will need x amount of energy to keep it at
> the required temperature. All that energy comes from the boiler, that
> appears to keep itself operating in it's most effcient condensing
> mode by keeping the flow at 70C and modulating the burner back as the
> return temp increases.
Not so. This boiler is maintaining a flow temp and modulates to suit. This
is not efficiency mode. To maximise condensing efficiency it is best for the
contol system to lower the flow temp by comparing the difference to the flow
and return temps, and have to keep the return temp as low as possible.
fred
<b5246250-9eff-4fe5...@g17g2000yqe.googlegroups.com>,
VAG_dude <dawoo...@gmail.com> writes
>
>Seems that you have the same issue as me, I don't particularly like
>the proportional control on the Honeywell CM927/CM907.
>
the Danfoss TP7000 range, avail as wired or wireless. I don't think
they're as featuresome, pretty or as easy to use as the Honeywell but if
it's pissing you off that much then it might be worth the 100quid it'll
cost you to switch (for the RF version).
These guys have them at a good price and it's where I got my Honeywell
from, they seem good to deal with:
http://www.buyaparcel.com/pageview.php?page=show_product&ecommerce_stockcode=087N741800
Doctor Drivel
"fred" <n...@for.mail> wrote in message news:LGzCdgAq2OhMFwie@y.z...
> In article
> <76c63bc1-9e4a-4513...@m1g2000yqo.googlegroups.com>,
> VAG_dude <dawoo...@gmail.com> writes
>>
>>How will it go on and off less frequently? It doesn't cycle on any kw
>>rating unless the Honeywell CM927 tell it to; which it does as it
>>approaches the set temperature.
>>
> My own pref is for a long slow burn[1], ie boiler mod'd down to the lowest
> level that can just maintain the temperature in the property but you then
> need to tweak the mod level to match the weather or it wont reach
> temperature during a cold snap. I favour this because it means that the
> rads stay at a low but consistent temp which in my view gives a greater
> comfort level.
>
> Good luck finding controls that will support this kind of operation
Valliant supply a weather compensator. Once demand is below 12kW it will
cycle, as it can't go down low, but in a controlled manner, not hunting.
Some boilers can modulate down to 3kW.
VAG_dude
> In article
> VAG_dude <dawoods...@gmail.com> writes
>
> >Seems that you have the same issue as me, I don't particularly like
> >the proportional control on the Honeywell CM927/CM907.
>
> Just checked and the one that lets you choose propo or normal on/off is
> the Danfoss TP7000 range, avail as wired or wireless. I don't think
> they're as featuresome, pretty or as easy to use as the Honeywell but if
> it's pissing you off that much then it might be worth the 100quid it'll
> cost you to switch (for the RF version).
>
> These guys have them at a good price and it's where I got my Honeywell
>
> --
> fred
> FIVE TV's superbright logo - not the DOG's, it's bollocks
Cheers, think I'll try limiting the Honeywell to 3 cycles per hour and
see how I get on.
harry
>
> - Show quoted text -
Chuck the whole lot out and get an instantaneous electric shower.
You're losing money due to the unneccesary heat loss from the cylinder.
The Natural Philosopher
>
> Chuck the whole lot out and get an instantaneous electric shower.
> You're losing money due to the unneccesary heat loss from the cylinder.
As opposed to the losses in the power station, transmission lines and of
course, your bank account.
Dire to the fact that electricity is twice the price of oil or gas. For
the above reasons.
newshound
"The Natural Philosopher" <t...@invalid.invalid> wrote in message
news:i65tu0$lkc$1...@news.albasani.net...
You have to do the whole sum.
An instantaneous electric would need a very long run of 6 mm^2 and still not
give me the flow I get now. The heat loss from a modern cylinder isn't too
bad. I originally had the shower plumbed direct from the combi, but it took
an age for hot water to come through, and even with a thermostatic mixer the
shower temperature varied too much with other water demands. (I didn't
design or fit that system). What I may do when I get a better boiler is put
in an external plate heat exchanger with a pumped secondary to heat this
shower cylinder. It doesn't make sense to throw away a whole pile of kit
which works.
harry
> "The Natural Philosopher" <t...@invalid.invalid> wrote in messagenews:i65tu0$lkc$1...@news.albasani.net...
I think your "external heat exchanger" ???will cost a lot more than a
bit of wire.
As for "pile of kit that works", think more about chucking good money
after bad. The cost of energy is going to increase massivley in the
near future. Someone's going to have to pay for all these windmills
but it needn't be you.
The Natural Philosopher
OTOH if someone sees sense and builds nuclear power stations, then
electricity will be the cheapest form around.
harry
>
> - Show quoted text -
We were promised in the 60's it would be free from nuclear power. We
haven't yet seen the full cost of expended fuel disposal.
The Natural Philosopher
That's because no one has decided what that actually means.
If its fully expended of course, its not radioactive.
Still even at the worst possible (political) case its still only about
4p per unit electricity from nukes. A lot depends on interest rates of
course.
roughly comparable with oil, and gas right now.
Ad they are set to rise..
Andy Champ
>
> We were promised in the 60's it would be free from nuclear power. We
> haven't yet seen the full cost of expended fuel disposal.
You mean, like global warming? Acid rain?
Or isn't that the fuel you were thinking of?
Andy
Mark
<t...@invalid.invalid> wrote:
Because they can't?
>If its fully expended of course, its not radioactive.
AFAIK most fuel is still radioactive, even when not longer useful.
Most of the waste is low grade but there is still some with long half
lifes. Also remember that most fuels are highly toxic in their own
right.
>Still even at the worst possible (political) case its still only about
>4p per unit electricity from nukes. A lot depends on interest rates of
>course.
>
>roughly comparable with oil, and gas right now.
But we can't take this on faith. Until the sums are done, including
/all/ the factors, then I am remaining skeptical that one fuel is
"better" than another. To me it's desirable to use a good diversity
of fuels so that we are not totally reliant on one.
>Ad they are set to rise..
True.
harry
> "VAG_dude" <dawoods...@gmail.com> wrote in message
Your last remark is true. The rest is rubbish.
dennis@home
"harry" <harol...@aol.com> wrote in message
news:89bdf668-4d1f-4926...@y3g2000vbm.googlegroups.com...
The rest is true even if you don't like it.
Doctor Drivel
"harry" <harol...@aol.com> wrote in message
news:89bdf668-4d1f-4926...@y3g2000vbm.googlegroups.com...
>> "VAG_dude" <dawoods...@gmail.com> wrote in message
>>
>> news:53427007-285d-469a...@b34g2000yqm.googlegroups.com...
>>
>> > I agree with you on this one, the boiler seems to be constantly on and
>> > off and on again etc etc And once the house has reached the
>> > temperature the boiler cools down a bit but before you know it the
>> > thermostat is calling for heat again to keep the temperature steady
>> > and the boiler starts all over again on full tilt and usually does not
>> > even get a chance to modulate down as the thermostat has stopped
>> > calling for heat.
>>
>> Not all boilers are efficient when modulating,
>> the efficiency may well be different at different
>> modulation points.
They are efficient but the efficiency may vary at differnt modulation
rates - half true.
>> You need a graph of efficiency vs. modulation
>> before you can decide whats best.
To do what? The boiler decide on what rate to modulate. Only if the boiler
is range rated can it be set once finding the most efficient level.
>> The supposed inefficiency of boiler cycling
>> doesn't apply to a boiler that
>> is designed to be cycled.
None are designed to be cycled. They should be engineered into a system the
eliminates or vastly reduces cycling. Using a thermal store/heat bank with
correct blending controls on the boiler return with "eliminate" cycling.
I used a regular boiler with the return temp, using a blending valve, set to
just above dew-point, so the boiler never condenses. The efficiency was
better than a condensing boiler on the heat bank without a blending valve.
>> What is pretty certain is that you want the water temp as low as possible
>> for a condensing boiler even though it means having radiators twice as
>> big.
>
> Your last remark is true. The rest is rubbish.
Only half was true. Modern condensing boilers with load sensing controls
will reduce the return temperature to the building/room load. A properly
designed "system" is on part load for 90% plus of running time as the rads
are designed to run at -3C outside and most of the time it is above -3C. In
short, most of the time the rads are oversized. Insulation and incidental
heat gain in the house will impact again.
Doctor Drivel
"dennis@home" <den...@killspam.kicks-ass.net> wrote in message
news:i6a856$6io$1...@news.datemas.de...
>> Your last remark is true. The rest is rubbish.
>
> The rest is true even if you don't like it.
Very little of it was true. Sad but true.
dennis@home
"Doctor Drivel" <kill...@invalid.invalid> wrote in message
news:i6a9sr$irr$1...@news.eternal-september.org...
>
> "harry" <harol...@aol.com> wrote in message
> news:89bdf668-4d1f-4926...@y3g2000vbm.googlegroups.com...
>> On 6 Sep, 20:47, "dennis@home" <den...@killspam.kicks-ass.net> wrote:
>>> "VAG_dude" <dawoods...@gmail.com> wrote in message
>>>
>>> news:53427007-285d-469a...@b34g2000yqm.googlegroups.com...
>>>
>>> > I agree with you on this one, the boiler seems to be constantly on and
>>> > off and on again etc etc And once the house has reached the
>>> > temperature the boiler cools down a bit but before you know it the
>>> > thermostat is calling for heat again to keep the temperature steady
>>> > and the boiler starts all over again on full tilt and usually does not
>>> > even get a chance to modulate down as the thermostat has stopped
>>> > calling for heat.
>>>
>>> Not all boilers are efficient when modulating,
>>> the efficiency may well be different at different
>>> modulation points.
>
> They are efficient but the efficiency may vary at differnt modulation
> rates - half true.
Correct, what you have just said is half true.
In this context efficient tends to mean maximum efficiency and as you say
they are not as efficient at different modulation points which is what I
said.
>
>>> You need a graph of efficiency vs. modulation
>>> before you can decide whats best.
>
> To do what? The boiler decide on what rate to modulate. Only if the
> boiler is range rated can it be set once finding the most efficient level.
To decide if it is more efficient to let the boiler modulate.
>
>>> The supposed inefficiency of boiler cycling
>>> doesn't apply to a boiler that
>>> is designed to be cycled.
>
> None are designed to be cycled. They should be engineered into a system
> the eliminates or vastly reduces cycling. Using a thermal store/heat bank
> with correct blending controls on the boiler return with "eliminate"
> cycling.
Untrue, many boilers don't lose heat to the outside when the gas valve is
off (they don't all blow the hot air out of the flu you know) and if its
lost to the water it ends up in the heating system where it can be used to
heat. The only time it isn't true is when the system no longer calls for
heat and that is the same for any system.
>
> I used a regular boiler with the return temp, using a blending valve, set
> to just above dew-point, so the boiler never condenses. The efficiency was
> better than a condensing boiler on the heat bank without a blending valve.
That depends on what temperature you are heating the store to.
If its above ~70C the condensing boiler will stop condensing and then it may
be less efficient than a normal boiler.
Doctor Drivel
>
>
> "Doctor Drivel" <kill...@invalid.invalid> wrote in message
> news:i6a9sr$irr$1...@news.eternal-september.org...
>>
>> "harry" <harol...@aol.com> wrote in message
>> news:89bdf668-4d1f-4926...@y3g2000vbm.googlegroups.com...
>>> On 6 Sep, 20:47, "dennis@home" <den...@killspam.kicks-ass.net> wrote:
>>>> "VAG_dude" <dawoods...@gmail.com> wrote in message
>>>>
>>>> news:53427007-285d-469a...@b34g2000yqm.googlegroups.com...
>>>>
>>>> > I agree with you on this one, the boiler seems to be constantly on
>>>> > and
>>>> > off and on again etc etc And once the house has reached the
>>>> > temperature the boiler cools down a bit but before you know it the
>>>> > thermostat is calling for heat again to keep the temperature steady
>>>> > and the boiler starts all over again on full tilt and usually does
>>>> > not
>>>> > even get a chance to modulate down as the thermostat has stopped
>>>> > calling for heat.
>>>>
>>>> Not all boilers are efficient when modulating,
>>>> the efficiency may well be different at different
>>>> modulation points.
>>
>> They are efficient but the efficiency may vary at differnt modulation
>> rates - half true.
>
> Correct, what you have just said is half true.
You wrote, "Not all boilers are efficient when modulating", which was not
true.
>>>> You need a graph of efficiency vs. modulation
>>>> before you can decide whats best.
>>
>> To do what? The boiler decide on what rate to modulate. Only if the
>> boiler is range rated can it be set once finding the most efficient
>> level.
>
> To decide if it is more efficient to let the boiler modulate.
That was inane babble.
>>>> The supposed inefficiency of boiler cycling
>>>> doesn't apply to a boiler that
>>>> is designed to be cycled.
>>
>> None are designed to be cycled. They should be engineered into a system
>> the eliminates or vastly reduces cycling. Using a thermal store/heat
>> bank with correct blending controls on the boiler return with "eliminate"
>> cycling.
>
> Untrue, many boilers
<snip inane babble>
>> I used a regular boiler with the return temp, using a blending valve, set
>> to just above dew-point, so the boiler never condenses. The efficiency
>> was better than a condensing boiler on the heat bank without a blending
>> valve.
>
> That depends on what temperature you are heating the store to.
> If its above ~70C the condensing boiler will stop condensing and then it
> may be less efficient than a normal boiler.
Total bollocks. Even if a thermal store is set to 80C setpoint it condenses
80% of reheat time.
Doctor Drivel
"The Natural Philosopher" <t...@invalid.invalid> wrote in message
> OTOH if someone sees sense and builds nuclear power stations, then
> electricity will be the cheapest form around.
This man is a nut.