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  #1   Report Post  
Pandora
 
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Default Hot water cylinder

Does anybody know of a good quality hot water cylinder which has a facility
to replace the cylinder thermostat with a temperature sensor for better
control?

The hot water system will be unvented and I'll be using a condensing boiler.


  #2   Report Post  
IMM
 
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Default


"Pandora" wrote in message
...
Does anybody know of a good quality hot water cylinder which has a

facility
to replace the cylinder thermostat with a temperature sensor for better
control?

The hot water system will be unvented and I'll be using a condensing

boiler.

Use a quick recovery cylinder with a condensing boiler. Also use two
cylinder stats to prevent boiler cycling. One top one bottom. The stats
can be strap on. High accuracy stats are not required for a cylinder. Only
when the cylinder drops many degrees, differnce set by the two stats, will
the boiler kick in and re-heat with one long efficient burn.

Albion, Range do suitable cylidners. Travis Perkins do the Telford Typhoon
which is well priced.




  #3   Report Post  
Andy Hall
 
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On Wed, 3 Nov 2004 10:31:17 -0000, "Pandora"
wrote:

Does anybody know of a good quality hot water cylinder which has a facility
to replace the cylinder thermostat with a temperature sensor for better
control?

The hot water system will be unvented and I'll be using a condensing boiler.


If it's an unvented storage system you can't install it as a DIY job
in the UK. However, since your address suggests Belgium, maybe it
is allowed there.

To answer your question, though, there are electronic thermostats that
will fit a standard cylinder if you remove the insulation to give a
good contact. There is a separate sensor and controller.
A good example of that is the Danfoss Randall TP75 family (direct
wired and RF versions).

Alternatively there are boilers which will allow connection of a
bullet type temperature sensor (e.g. MAN Micromat).
For this type, the cylinder needs to have a pocket fitted by the
manufacturer. This is basically a closed tube into the cylinder and
the sensor is inserted into that, thus sensing the temperature in the
core of the cylinder rather than the surface of the copper.




--

..andy

To email, substitute .nospam with .gl
  #4   Report Post  
Dave Plowman (News)
 
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Default

In article ,
Pandora wrote:
Does anybody know of a good quality hot water cylinder which has a
facility to replace the cylinder thermostat with a temperature sensor
for better control?


Could I ask why you want better control than that provided by an ordinary
stat?

--
*The problem with the gene pool is that there is no lifeguard *

Dave Plowman London SW
To e-mail, change noise into sound.
  #5   Report Post  
John Aston
 
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Default


Dave Plowman (News) wrote in message
...
In article ,
Pandora wrote:
Does anybody know of a good quality hot water cylinder which has a
facility to replace the cylinder thermostat with a temperature sensor
for better control?


Could I ask why you want better control than that provided by an ordinary
stat?


As the hot water near its setpoint temperature, the boiler can slow the
primary heat rather than overshoot.




  #6   Report Post  
IMM
 
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Default


"Dave Plowman (News)" wrote in message
...
In article ,
Pandora wrote:
Does anybody know of a good quality hot water cylinder which has a
facility to replace the cylinder thermostat with a temperature sensor
for better control?


Could I ask why you want better control than that provided by an ordinary
stat?


See my post on this.


  #7   Report Post  
Dave Plowman (News)
 
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Default

In article ,
John Aston wrote:
Could I ask why you want better control than that provided by an
ordinary stat?


As the hot water near its setpoint temperature, the boiler can slow the
primary heat rather than overshoot.


So this wouldn't be a direct replacement for a cylinder stat? But
integrated into some form of microprocessor control?

--
*If you must choose between two evils, pick the one you've never tried before

Dave Plowman London SW
To e-mail, change noise into sound.
  #8   Report Post  
Pandora
 
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Dave Plowman (News) wrote in message
...

So this wouldn't be a direct replacement for a cylinder stat? But
integrated into some form of microprocessor control?


Yes, sorry if this was unclear. Some boilers have a facility to continuously
vary their output..


  #9   Report Post  
IMM
 
Posts: n/a
Default

"Pandora" wrote in message
...

Dave Plowman (News) wrote in message
...

So this wouldn't be a direct replacement for a cylinder stat? But
integrated into some form of microprocessor control?


Yes, sorry if this was unclear. Some boilers have a facility to

continuously
vary their output..


No need in cylinder re-heat with a quick recovery coil. You want the boiler
to dump all its heat ASAP into the cylinder and then shut off when up to
temperature.

Most modern boilers have some sort of burner modulation.



  #10   Report Post  
Christian McArdle
 
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Yes, sorry if this was unclear. Some boilers have a facility to
continuously
vary their output..


Indeed, but they don't really need a continuously variable input from the
hot water cylinder. The additional benefit of knowing this information to a
control system is marginal at best.

Due to stratification, the tank doesn't so much heat up uniformly, as divide
into a hot and a cold zone, the boundary between of which moves down as
heating progresses. A single thermometer will show a very rapid move from
cold to hot as this boundary passes its installed location. This is why it
is difficult to provide good hysterysis from a single cylinder thermostat.
You actually need to sense the temperature at different heights to get a
feel for the amount of hot water available, not know the temperature at one
height.

Room thermostats are a very different matter and much useful information
could be gleaned from an analogue output sensor.

Christian.





  #11   Report Post  
Andy Hall
 
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Default

On Wed, 3 Nov 2004 16:24:51 -0000, "Christian McArdle"
wrote:

Yes, sorry if this was unclear. Some boilers have a facility to

continuously
vary their output..


Indeed, but they don't really need a continuously variable input from the
hot water cylinder. The additional benefit of knowing this information to a
control system is marginal at best.


Actually there is some value.

In the past I've used bimetal type thermostats, more recently
thermostats with temperature sensor and electronic control and
currently an arrangement with temperature sensor inside the cylinder
in a pocket.

The bimetal type I found to have quite poor response and taking a
while before a rapid temperature drop is detected and hence firing up
the boiler. Moreover, the hysteresis was around +/- 5 degrees - 10 in
tota - for slow changes in temperature.. So, with a nominal set point
of 60 degrees, when a shower was started or the bath run, with
hysteresis plus poor response, the boiler wouldn't come on until the
cylinder surface temperature was at just over 50, then on the way up,
the boiler wouldn't go off until around 67 or 68 degrees. Accounting
for all of these things the response window is close to 20 degrees.

An electronic type(e.g. TP75) does rather better because although it
is a switch on/off type, the hysteresis was smaller (+/- 3 degrees,
IIRC) and the probe gives a faster and more accurate response as well.

In my current system, the sensor is wired directly back to the boiler
and the controller measures the temperature (and displays it).
The HW temperature is set to a nominal 60 degrees as before.
I've monitored the behaviour with a PC connected to the boiler and the
response is quite intelligent.

If the water temperature has been drifting slowly down through small
amounts being used, nothing happens until it drops below 55 degrees -
i.e. 5 degrees below set point. At that stage, a hot water cycle is
initiated with the boiler being wound up to full power. As the
temperature approaches the 60 degree set point, the burner and pump
are modulated down so that there is no overshoot of temperature. The
controller appears to learn the characteristics of the cylinder load
because the behaviour improves over a few cycles following a reset.

If I start a bath etc. and there is a more rapid drop in temperature,
then the HW cycle is started earlier - typically as the temperature is
falling through about 58.5 degrees.

The result is that even with some stratification, the water
temperature is maintained within a narrower temperature range than
with the simpler thermostat.


Due to stratification, the tank doesn't so much heat up uniformly, as divide
into a hot and a cold zone, the boundary between of which moves down as
heating progresses. A single thermometer will show a very rapid move from
cold to hot as this boundary passes its installed location. This is why it
is difficult to provide good hysterysis from a single cylinder thermostat.
You actually need to sense the temperature at different heights to get a
feel for the amount of hot water available, not know the temperature at one
height.


I've found the results to be remarkably consistent with the analogue
sensing by the boiler. It is monitoring temperature accurately as
well as rate of change so seems to do a good job of overall control


Room thermostats are a very different matter and much useful information
could be gleaned from an analogue output sensor.


Indeed. The room controller that I have does that and also allows
you to adjust the relative sensitivities of the terms for the indoor
loop and the weather compensation.



--

..andy

To email, substitute .nospam with .gl
  #12   Report Post  
Ed Sirett
 
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On Wed, 03 Nov 2004 18:32:03 +0000, Andy Hall wrote:

On Wed, 3 Nov 2004 16:24:51 -0000, "Christian McArdle"
wrote:

Yes, sorry if this was unclear. Some boilers have a facility to

continuously
vary their output..


Indeed, but they don't really need a continuously variable input from the
hot water cylinder. The additional benefit of knowing this information to a
control system is marginal at best.


Actually there is some value.

In the past I've used bimetal type thermostats, more recently
thermostats with temperature sensor and electronic control and
currently an arrangement with temperature sensor inside the cylinder
in a pocket.

The bimetal type I found to have quite poor response and taking a
while before a rapid temperature drop is detected and hence firing up
the boiler. Moreover, the hysteresis was around +/- 5 degrees - 10 in
tota - for slow changes in temperature.. So, with a nominal set point
of 60 degrees, when a shower was started or the bath run, with
hysteresis plus poor response, the boiler wouldn't come on until the
cylinder surface temperature was at just over 50, then on the way up,
the boiler wouldn't go off until around 67 or 68 degrees. Accounting
for all of these things the response window is close to 20 degrees.

An electronic type(e.g. TP75) does rather better because although it
is a switch on/off type, the hysteresis was smaller (+/- 3 degrees,
IIRC) and the probe gives a faster and more accurate response as well.

In my current system, the sensor is wired directly back to the boiler
and the controller measures the temperature (and displays it).
The HW temperature is set to a nominal 60 degrees as before.
I've monitored the behaviour with a PC connected to the boiler and the
response is quite intelligent.

If the water temperature has been drifting slowly down through small
amounts being used, nothing happens until it drops below 55 degrees -
i.e. 5 degrees below set point. At that stage, a hot water cycle is
initiated with the boiler being wound up to full power. As the
temperature approaches the 60 degree set point, the burner and pump
are modulated down so that there is no overshoot of temperature. The
controller appears to learn the characteristics of the cylinder load
because the behaviour improves over a few cycles following a reset.

If I start a bath etc. and there is a more rapid drop in temperature,
then the HW cycle is started earlier - typically as the temperature is
falling through about 58.5 degrees.

The result is that even with some stratification, the water
temperature is maintained within a narrower temperature range than
with the simpler thermostat.


Due to stratification, the tank doesn't so much heat up uniformly, as divide
into a hot and a cold zone, the boundary between of which moves down as
heating progresses. A single thermometer will show a very rapid move from
cold to hot as this boundary passes its installed location. This is why it
is difficult to provide good hysterysis from a single cylinder thermostat.
You actually need to sense the temperature at different heights to get a
feel for the amount of hot water available, not know the temperature at one
height.


I've found the results to be remarkably consistent with the analogue
sensing by the boiler. It is monitoring temperature accurately as
well as rate of change so seems to do a good job of overall control


I'm guessing but it looks like the boiler control system may well
implement a PID (or even just PD) type controller.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html


  #13   Report Post  
Ed Sirett
 
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Default

On Wed, 03 Nov 2004 10:42:10 +0000, IMM wrote:


"Pandora" wrote in message
...
Does anybody know of a good quality hot water cylinder which has a

facility
to replace the cylinder thermostat with a temperature sensor for better
control?

The hot water system will be unvented and I'll be using a condensing

boiler.

Use a quick recovery cylinder with a condensing boiler. Also use two
cylinder stats to prevent boiler cycling. One top one bottom. The stats
can be strap on. High accuracy stats are not required for a cylinder. Only
when the cylinder drops many degrees, differnce set by the two stats, will
the boiler kick in and re-heat with one long efficient burn.

Albion, Range do suitable cylidners. Travis Perkins do the Telford Typhoon
which is well priced.


Some of the control systems that are now being used in some boilers are a
significant (even you might say a quantum) leap ahead than simple on/offs.
Some of them are sophisticated enough to work out a good enough strategy
simply from the on/off signal and the return flow return temperatures.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html


  #14   Report Post  
IMM
 
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Default


"Ed Sirett" wrote in message
news
On Wed, 03 Nov 2004 10:42:10 +0000, IMM wrote:


"Pandora" wrote in message
...
Does anybody know of a good quality hot water cylinder which has a

facility
to replace the cylinder thermostat with a temperature sensor for better
control?

The hot water system will be unvented and I'll be using a condensing

boiler.

Use a quick recovery cylinder with a condensing boiler. Also use two
cylinder stats to prevent boiler cycling. One top one bottom. The

stats
can be strap on. High accuracy stats are not required for a cylinder.

Only
when the cylinder drops many degrees, differnce set by the two stats,

will
the boiler kick in and re-heat with one long efficient burn.

Albion, Range do suitable cylidners. Travis Perkins do the Telford

Typhoon
which is well priced.


Some of the control systems that are now being used in some boilers are a
significant (even you might say a quantum) leap ahead than simple on/offs.
Some of them are sophisticated enough to work out a good enough strategy
simply from the on/off signal and the return flow return temperatures.


They do and that is designed for the heating function. DHW usually throws
them, unless they know it is DHW by a signal from a stat.



  #15   Report Post  
Andy Hall
 
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Default

On Wed, 3 Nov 2004 20:56:25 -0000, "IMM" wrote:


"Ed Sirett" wrote in message
news
On Wed, 03 Nov 2004 10:42:10 +0000, IMM wrote:



Some of the control systems that are now being used in some boilers are a
significant (even you might say a quantum) leap ahead than simple on/offs.
Some of them are sophisticated enough to work out a good enough strategy
simply from the on/off signal and the return flow return temperatures.


They do and that is designed for the heating function. DHW usually throws
them, unless they know it is DHW by a signal from a stat.


Which is not that hard since something will be switching motorised
valve(s) anyway.

I have mine set up to work the opposite way around to conventional
Honeywell plans

The boiler is given outside temperature, cylinder temperature and room
controller data as inputs. There are a choice of functional
programs for different valve or external pump configurations using
three relay driven outputs.
I use one where the boiler has control of opening heating motorised
valve(s) or DHW valve as required - in effect an S plan configuration
but with the boiler acting as controller and no auxilliary contacts
used.

When a hot water cycle is needed as monitored by the cylinder sensor,
then CH valve is closed and HW opened together with full power.
On completion, the CH operation is recommenced by closing the HW valve
and reopening the CH.



--

..andy

To email, substitute .nospam with .gl


  #16   Report Post  
IMM
 
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Default


"Andy Hall" wrote in message
...
On Wed, 3 Nov 2004 20:56:25 -0000, "IMM" wrote:


"Ed Sirett" wrote in message
news
On Wed, 03 Nov 2004 10:42:10 +0000, IMM wrote:



Some of the control systems that are now being used in some boilers are

a
significant (even you might say a quantum) leap ahead than simple

on/offs.
Some of them are sophisticated enough to work out a good enough

strategy
simply from the on/off signal and the return flow return temperatures.


They do and that is designed for the heating function. DHW usually

throws
them, unless they know it is DHW by a signal from a stat.


Which is not that hard since something will be switching motorised
valve(s) anyway.

I have mine set up to work the opposite way around to conventional
Honeywell plans

The boiler is given outside temperature, cylinder temperature and room
controller data as inputs. There are a choice of functional
programs for different valve or external pump configurations using
three relay driven outputs.
I use one where the boiler has control of opening heating motorised
valve(s) or DHW valve as required - in effect an S plan configuration
but with the boiler acting as controller and no auxilliary contacts
used.

When a hot water cycle is needed as monitored by the cylinder sensor,
then CH valve is closed and HW opened together with full power.
On completion, the CH operation is recommenced by closing the HW valve
and reopening the CH.


You have a state of the art boiler, most cheaper versions: Ideal, Glow Worm
etc, do not have a simple function to bypass the modulating control system
and keep the burner full on. Or a function to tell the control system that
what it heating is not the heating circuit, so any self adaptive memory must
not be used. Ravenheat of all people, even have this.




  #17   Report Post  
Christian McArdle
 
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Default

The additional benefit of knowing this information to a
control system is marginal at best.

Actually there is some value.


Well, maybe some, but it isn't even slightly critical. A large amount of
hysterysis is actually desirable, so that the HWC can be heated in one
(relatively) long burn.

What your sensor isn't telling you is the relationship between the measured
temperature and the amount of energy stored. I strongly suspect that there
isn't a simple direct mapping between the two, as it depends on many
factors, such as the recent history of water takeoff and heating, leading to
different levels of stratification. A simple thermostat will turn the boiler
on when the stored energy is below a reasonable value, so it perfectly
adequete in terms of the function of the system. I doubt that an analogue
control system with a single analogue sensor could substantially increase
the seasonal efficiency of the system.

Have you done any calculations on your system to ascertain whether this is
true or false, though?

the boiler wouldn't come on until the cylinder surface temperature was
at just over 50, then on the way up, the boiler wouldn't go off until
around 67 or 68 degrees.


But that sounds quite good. It waits a minute or two for the bottom of the
cylinder to get properly cold before turning on and doesn't turn off until
the HWC is well and truely warm. It will only take maybe 10% of capacity for
the bottom to get cold enough to turn on the stat. Where this is useful is
overnight or other times without any hot water drawoff, as it allows the HWC
to cool down a bit, rather than trying to maintain a precise temperature,
which results in excessive burner firing and unnecessary primary circuit
losses.

Christian.


  #18   Report Post  
Andy Hall
 
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On Thu, 4 Nov 2004 10:04:16 -0000, "Christian McArdle"
wrote:

The additional benefit of knowing this information to a
control system is marginal at best.

Actually there is some value.


Well, maybe some, but it isn't even slightly critical. A large amount of
hysterysis is actually desirable, so that the HWC can be heated in one
(relatively) long burn.

What your sensor isn't telling you is the relationship between the measured
temperature and the amount of energy stored. I strongly suspect that there
isn't a simple direct mapping between the two, as it depends on many
factors, such as the recent history of water takeoff and heating, leading to
different levels of stratification.


Clearly it can't directly. Multiple sensors at different depths
would be needed to do that. However, it is certainly able to monitor
rate of use indirectly which was the main point.

A simple thermostat will turn the boiler
on when the stored energy is below a reasonable value, so it perfectly
adequete in terms of the function of the system. I doubt that an analogue
control system with a single analogue sensor could substantially increase
the seasonal efficiency of the system.


That would probably not be substantial. I felt that the behaviour
for heating the water was more interesting in the sense that the
temperature is maintained at a more constant level at the top of the
cylinder.


Have you done any calculations on your system to ascertain whether this is
true or false, though?


I do log the boiler behaviour, but have not run the sums.



the boiler wouldn't come on until the cylinder surface temperature was
at just over 50, then on the way up, the boiler wouldn't go off until
around 67 or 68 degrees.


But that sounds quite good. It waits a minute or two for the bottom of the
cylinder to get properly cold before turning on and doesn't turn off until
the HWC is well and truely warm. It will only take maybe 10% of capacity for
the bottom to get cold enough to turn on the stat. Where this is useful is
overnight or other times without any hot water drawoff, as it allows the HWC
to cool down a bit, rather than trying to maintain a precise temperature,
which results in excessive burner firing and unnecessary primary circuit
losses.



I found it to be poor on the old system because it was a long time
before the boiler would come on, by which time a lot of water had been
used. Then the temperature would overshoot by a long way and the
water too hot during later use.
Having more accurate control has helped that, and the issue of
reheating not happening during the night also taken care of because of
detection of rate of use,. I don't really care about primary circuit
losses because thay are into the house and I run the heating sith
setback anyway.






Christian.



--

..andy

To email, substitute .nospam with .gl
  #19   Report Post  
IMM
 
Posts: n/a
Default

"Andy Hall" wrote in message
...

I found it to be poor on the old system
because it was a long time
before the boiler would come on, by
which time a lot of water had been
used. Then the temperature would
overshoot by a long way and the
water too hot during later use.


The simplest method to re-heat a cylinder. Have two cylinder stats, top and
bottom of the cylinder either strap-on or immersed. Immersed is better, but
not that crucial. Have the bottom stat set to 60C for Legionella problems,
the top, about 1/4 of the way down and set to just below the desired DHW
temp you want. Have a DHW blending valve on hot draw-off pipe, which are to
become mandatory. Set this to your desired DHW temperature, say 50C. DHW
is then user adjustable.

When the cylinder is up to temp at 60C the bottom stat cut out the boiler.
When the temp get below say 48C, the top stat will bring the boiler in when
the temp is below say 47-48C. The boiler heats the cylinder with one long
burn and no inefficient boiler cycling.

If the cylinder is running out of hot water too quickly, then there are
three options:

1. Raise the bottom stat temperature to give more stored hot water, say up
to 65 to 70C. The DHW blending valve will ensure the draw-off temperature
is what the user wants.

2. Insert a flow switch into the pipework just before the high flow taps
(bath and shower), and install a third high limit cylinder stat, set to 80C.
The flow switch will bring in the boiler immediately heating the DHW
cylinder preventing the bottom of the cylinder being very cold with entering
cold water before the boiler cuts in.

3. Do both 1 and 3 above.

Doing the above effectively increases the size of your cylinder. Quite
simple and easy to do. Many people when installing full lengthy body jets
have a larger cylinder installed. This in many cases is unnecessary. The
above could be done and money saved in boiler efficiency.



  #20   Report Post  
Christian McArdle
 
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I found it to be poor on the old system because it was a long time
before the boiler would come on, by which time a lot of water had been
used. Then the temperature would overshoot by a long way and the
water too hot during later use.


Was your stat installed too high? My boiler cuts in about 20 seconds after
opening a tap. Besides it has enough capacity to fill two baths, so I'm not
worried about the boiler's additional 28kW cutting in. Also, I have a TMV on
the output, so the exact temperature of the store is irrelevent to me.
Temperature overshoot simply means greater energy storage, rather than a
trip to the burns department with the children.

Christian.




  #21   Report Post  
Andy Hall
 
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On Thu, 4 Nov 2004 11:32:40 -0000, "IMM" wrote:

"Andy Hall" wrote in message
.. .

I found it to be poor on the old system
because it was a long time
before the boiler would come on, by
which time a lot of water had been
used. Then the temperature would
overshoot by a long way and the
water too hot during later use.


The simplest method to re-heat a cylinder.


This isn't the simplest, and I am not sure that it has value in terms
of usability either.

Have two cylinder stats, top and
bottom of the cylinder either strap-on or immersed. Immersed is better, but
not that crucial. Have the bottom stat set to 60C for Legionella problems,
the top, about 1/4 of the way down and set to just below the desired DHW
temp you want. Have a DHW blending valve on hot draw-off pipe, which are to
become mandatory. Set this to your desired DHW temperature, say 50C. DHW
is then user adjustable.

When the cylinder is up to temp at 60C the bottom stat cut out the boiler.
When the temp get below say 48C, the top stat will bring the boiler in when
the temp is below say 47-48C. The boiler heats the cylinder with one long
burn and no inefficient boiler cycling.


This would need at least a latching relay arrangement to work.
The top stat, as I read the way you describe its use, would delay the
commencement of reheating until most of the contents had been used.
If you happen to be at the point when the cylinder is down to 25% of
capacity and then run a bath or shower, you are back into the same old
game of the water running out quickly and relying on the instantaneous
delivery rate of the boiler. Having the flow switch idea would
help the timing a bit at least but doesn't replace having a full
cylinder of water.

Boiler cycling would occur only if the heat production rate exceeds
the capacity of the cylinder to absorb it. That can be avoided if
the cylinder is a fast recovery type or if the boiler modulates down.



If the cylinder is running out of hot water too quickly, then there are
three options:

1. Raise the bottom stat temperature to give more stored hot water, say up
to 65 to 70C. The DHW blending valve will ensure the draw-off temperature
is what the user wants.


I think you mean water stored at a higher temperature at the top,
which when mixed gives more at the wanted temperature. Even this
is not going to compensate for letting the stored amount of heat fall
to 25% of the full capacity.



2. Insert a flow switch into the pipework just before the high flow taps
(bath and shower), and install a third high limit cylinder stat, set to 80C.
The flow switch will bring in the boiler immediately heating the DHW
cylinder preventing the bottom of the cylinder being very cold with entering
cold water before the boiler cuts in.


This could be worth doing to deal with the poor response of bimetal
thermostats.


3. Do both 1 and 3 above.







Doing the above effectively increases the size of your cylinder.


Actually it does the opposite as far as having the top thermostat
used. The flow detection is worth having and would "increase" the
effective capacity simply because heat is being added back earlier
than it would otherwise be.

Quite
simple and easy to do. Many people when installing full lengthy body jets
have a larger cylinder installed. This in many cases is unnecessary. The
above could be done and money saved in boiler efficiency.

The boiler efficiency argument here is marginal and is at the expense
of performance. You are sacrificing the stored capacity for a
presumed improvement in efficiency.

Whether there is an efficiency gain to be had really depends on the
type of boiler and cylinder.

If it's an older type cylinder, incapable of taking all the heat from
the boiler, then the cycling will happen anyway if the mismatch is
great even if the coil is effectively immersed in cold water because
the cylinder was allowed to drop to 25% of capacity.

If we assume that the cylinder is fast recovery, so will absorb all
the heat and therefore no cycling during recovery, then the question
becomes one of how long did the inefficient parts of the boiler cycle
vs. the efficient parts last as a proportion. The inefficient parts
relate mainly to energy used to heat up the heat exchanger before
useful heat is delivered to the load, .and at the end of running, heat
that is not usefully delivered to the load. If the heat
exchanger is not a high thermal inertia type such as cast iron, then
unless the recovery time is very small, the inefficient periods will
be a small proportion of the total.

With a condensing boiler, having a cooler load means that the run time
at lower temperatures is longer and hence the boiler is operating at a
more efficient point - however when it does run, it runs for longer.

I did some experiments on my system where the cylinder was recovered
totally from cold. I recorded the temperatures of flow and return
water and rate of rise of the cylinder temperature and also measured
the amount of gas used to do the reheat. The temperatures can all be
logged to a PC from the boiler. Modulation down of the output only
comes in the last 30 seconds or so of the run and is there to prevent
overshoot of temperature.

I then repeated the experiment in two different ways. The first was
to run off the same volume of hot water (basically a cylinder full)
continuously and letting the boiler do its thing of starting to
replenish when determined by the sensor.
The second was to run off small amounts of water more slowly so that
the boiler would come on as the cylinder temperature at the sensor had
reached 55 degrees. This is indicative of smaller use during the day.
I stopped running water as soon as the boiler came on and waited for
recovery. In total I drew the same amount of water in each of the
three cases.

In terms of total gas used for each, the amount was the same to within
about 2%. So in this context at least, I don't buy the long burn
argument as making a huge practical difference with recent equipment.







--

..andy

To email, substitute .nospam with .gl
  #22   Report Post  
Andy Hall
 
Posts: n/a
Default

On Thu, 4 Nov 2004 12:11:10 -0000, "Christian McArdle"
wrote:

I found it to be poor on the old system because it was a long time
before the boiler would come on, by which time a lot of water had been
used. Then the temperature would overshoot by a long way and the
water too hot during later use.


Was your stat installed too high? My boiler cuts in about 20 seconds after
opening a tap.


I don't think so. I experimented with it a quarter, third and half
way up. When lower, it came on sooner, but still not brilliant.
Using an electronic thermostat with sensor was rather better.


Besides it has enough capacity to fill two baths, so I'm not
worried about the boiler's additional 28kW cutting in.


I increased the cylinder size to a 200 litre one as well and had
double normal thickness of foam fitted. So there is pleny of
storage, which I prefer anyway.

Also, I have a TMV on
the output, so the exact temperature of the store is irrelevent to me.
Temperature overshoot simply means greater energy storage, rather than a
trip to the burns department with the children.


I suppose that with a heatbank, having additional temperature control
makes good sense anyway, since presumably if it's fully charged and
you open the tap to a trickle you would otherwise get very hot water.

A trip to the A&E at RBH is never a pleasurable experience at any time
:-)



Christian.



--

..andy

To email, substitute .nospam with .gl
  #23   Report Post  
Christian McArdle
 
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Default

The boiler efficiency argument here is marginal and is at the expense
of performance. You are sacrificing the stored capacity for a
presumed improvement in efficiency.


However, it could well produce good results, provided that the thermostats
are both near the bottom. It allows a much more precisely defined hysteresis
to be used. I'd probably use that at the 95% full (to turn the boiler off)
and 75% full (to turn the boiler off).

Should a flow switch kick option be required, this could be achieved without
a 3rd overheat thermostat, by kicking the latching relay into the on
position if the 75% full is happy with that. A further advantage of this
system over a separate overheat stat is that the boiler then fully recovers
the system when hot water has been used, meaning the tank is usually 95%
full. The only way for it to get less than that is through natural heat
loss. Simply blipping a tap on would ensure 95% capacity a few minutes
later.

As I have a heat bank, I already have a flow switch in circuit, so all I'd
need is a few relays and another thermostat to implement a full wide
hysteresis system.

I may even implement such a system, as I think I would gain much efficiency
using it. On my current system, the boiler is modulating down and keeping
the primary circuit running for very extended periods. Unfortunately, the
automatic bypass valve (which is on a long run of primary pipe that wouldn't
otherwise be used for DHW only) seems to be opening (despite the pump graph
and setting saying otherwise), wasting lots of energy, particularly as some
of the run is unlagged (buried in plaster).

Christian.



  #24   Report Post  
Christian McArdle
 
Posts: n/a
Default

A trip to the A&E at RBH is never a pleasurable experience at any time
:-)


Yes, I last went when my GLW decided to squirt half a bottle of superglue in
my eye from 2m away. She was quite a good shot and the nozzle does produce a
very tightly defined stream.

It has been completely rebuilt in the last few years, so isn't the shabby
shell it used to be.

Christian.


  #25   Report Post  
IMM
 
Posts: n/a
Default

"Andy Hall" wrote in message
...
On Thu, 4 Nov 2004 11:32:40 -0000, "IMM" wrote:

"Andy Hall" wrote in message
.. .

I found it to be poor on the old system
because it was a long time
before the boiler would come on, by
which time a lot of water had been
used. Then the temperature would
overshoot by a long way and the
water too hot during later use.


The simplest method to re-heat a cylinder.


This isn't the simplest,


It is.

and I am not sure that it has value in terms
of usability either.


You are not sure. I am sure. It has.

Have two cylinder stats, top and
bottom of the cylinder either strap-on or immersed. Immersed is better,

but
not that crucial. Have the bottom stat set to 60C for Legionella

problems,
the top, about 1/4 of the way down and set to just below the desired DHW
temp you want. Have a DHW blending valve on hot draw-off pipe, which are

to
become mandatory. Set this to your desired DHW temperature, say 50C.

DHW
is then user adjustable.

When the cylinder is up to temp at 60C the bottom stat cut out the

boiler.
When the temp get below say 48C, the top stat will bring the boiler in

when
the temp is below say 47-48C. The boiler heats the cylinder with one

long
burn and no inefficient boiler cycling.


This would need at least a latching relay arrangement to work.


yep.

The top stat, as I read the way you describe its use, would delay the
commencement of reheating until most of the contents had been used.
If you happen to be at the point when the cylinder is down to 25% of
capacity and then run a bath or shower, you are back into the same old
game of the water running out quickly and relying on the instantaneous
delivery rate of the boiler. Having the flow switch idea would
help the timing a bit at least but doesn't replace having a full
cylinder of water.


The stats can be set to give a half full cylinder if you like.

Boiler cycling would occur only if the heat production rate exceeds
the capacity of the cylinder to absorb it. That can be avoided if
the cylinder is a fast recovery type or if the boiler modulates down.


Fast recovery is highly desirable, modulation down? No.

If the cylinder is running out of hot water too quickly, then there are
three options:

1. Raise the bottom stat temperature to give more stored hot water, say

up
to 65 to 70C. The DHW blending valve will ensure the draw-off

temperature
is what the user wants.


I think you mean water stored at a
higher temperature at the top,
which when mixed gives more at
the wanted temperature.


No. water stored at a higher temp all through the cylinder.

Even this
is not going to compensate for letting the
stored amount of heat fall
to 25% of the full capacity.


Wrong.

2. Insert a flow switch into the pipework just before the high flow taps
(bath and shower), and install a third high limit cylinder stat, set to

80C.
The flow switch will bring in the boiler immediately heating the DHW
cylinder preventing the bottom of the cylinder being very cold with

entering
cold water before the boiler cuts in.


This could be worth doing to deal with the poor response of bimetal
thermostats.


3. Do both 1 and 3 above.


Doing the above effectively increases the size of your cylinder.


Actually it does the opposite


Wrong again.

Quite
simple and easy to do. Many people when installing full lengthy body

jets
have a larger cylinder installed. This in many cases is unnecessary. The
above could be done and money saved in boiler efficiency.

The boiler efficiency argument
here is marginal and is at the expense
of performance.


Wrong again.

You are sacrificing the stored capacity for a
presumed improvement in efficiency.

Whether there is an efficiency gain to be had really depends on the
type of boiler and cylinder.

If it's an older type cylinder, incapable of taking all the heat from
the boiler, then the cycling will happen anyway if the mismatch is
great even if the coil is effectively immersed in cold water because
the cylinder was allowed to drop to 25% of capacity.

If we assume that the cylinder is fast recovery, so will absorb all
the heat and therefore no cycling during recovery,


equals more efficient.

then the question
becomes one of how long did the inefficient parts of the boiler cycle
vs. the efficient parts last as a proportion. The inefficient parts
relate mainly to energy used to heat up the heat exchanger before
useful heat is delivered to the load, .and at the end of running, heat
that is not usefully delivered to the load. If the heat
exchanger is not a high thermal inertia type such as cast iron, then
unless the recovery time is very small, the inefficient periods will
be a small proportion of the total.

With a condensing boiler, having a cooler load means that the run time
at lower temperatures is longer and hence the boiler is operating at a
more efficient point - however when it does run, it runs for longer.

I did some experiments on my system where the cylinder was recovered
totally from cold. I recorded the temperatures of flow and return
water and rate of rise of the cylinder temperature and also measured
the amount of gas used to do the reheat. The temperatures can all be
logged to a PC from the boiler. Modulation down of the output only
comes in the last 30 seconds or so of the run and is there to prevent
overshoot of temperature.


When using a DHW blending valve overshoot doesn't matter.

I then repeated the experiment in two different ways. The first was
to run off the same volume of hot water (basically a cylinder full)
continuously and letting the boiler do its thing of starting to
replenish when determined by the sensor.
The second was to run off small amounts of water more slowly so that
the boiler would come on as the cylinder temperature at the sensor had
reached 55 degrees. This is indicative of smaller use during the day.
I stopped running water as soon as the boiler came on and waited for
recovery. In total I drew the same amount of water in each of the
three cases.

In terms of total gas used for each, the amount was the same to within
about 2%. So in this context at least, I don't buy the long burn
argument as making a huge practical difference with recent equipment.


As boiler cycles heat from the boioer is lost through the flue and primary
pipes when the boioer is in an off cycle period.





  #26   Report Post  
IMM
 
Posts: n/a
Default


"Andy Hall" wrote in message
...
On Thu, 4 Nov 2004 12:11:10 -0000, "Christian McArdle"
wrote:

I found it to be poor on the old system because it was a long time
before the boiler would come on, by which time a lot of water had been
used. Then the temperature would overshoot by a long way and the
water too hot during later use.


Was your stat installed too high? My boiler cuts in about 20 seconds

after
opening a tap.


I don't think so. I experimented with it a quarter, third and half
way up. When lower, it came on sooner, but still not brilliant.
Using an electronic thermostat with sensor was rather better.


Besides it has enough capacity to fill two baths, so I'm not
worried about the boiler's additional 28kW cutting in.


I increased the cylinder size to a 200 litre one as well and had
double normal thickness of foam fitted. So there is pleny of
storage, which I prefer anyway.


Over storage is a bad thing. No need for it when you have the boiler power
to have the least amount of storage you need.

Also, I have a TMV on
the output, so the exact temperature of the store is irrelevent to me.
Temperature overshoot simply means greater energy storage, rather than a
trip to the burns department with the children.


I suppose that with a heatbank, having additional temperature control
makes good sense anyway, since presumably if it's fully charged and
you open the tap to a trickle you would otherwise get very hot water.

A trip to the A&E at RBH is never a pleasurable experience at any time
:-)



Christian.



--

.andy

To email, substitute .nospam with .gl



  #27   Report Post  
Andy Hall
 
Posts: n/a
Default

On Thu, 4 Nov 2004 13:01:09 -0000, "IMM" wrote:

"Andy Hall" wrote in message
.. .
On Thu, 4 Nov 2004 11:32:40 -0000, "IMM" wrote:

"Andy Hall" wrote in message
.. .

I found it to be poor on the old system
because it was a long time
before the boiler would come on, by
which time a lot of water had been
used. Then the temperature would
overshoot by a long way and the
water too hot during later use.

The simplest method to re-heat a cylinder.


This isn't the simplest,


It is.


The simplest is to have one thermostat or sensor and done with it.

You've added an additional thermostat, a relay and a flow switch.



and I am not sure that it has value in terms
of usability either.


You are not sure. I am sure. It has.


So how does reducing the available volume of hot water in a storage
system improve usability?




The top stat, as I read the way you describe its use, would delay the
commencement of reheating until most of the contents had been used.
If you happen to be at the point when the cylinder is down to 25% of
capacity and then run a bath or shower, you are back into the same old
game of the water running out quickly and relying on the instantaneous
delivery rate of the boiler. Having the flow switch idea would
help the timing a bit at least but doesn't replace having a full
cylinder of water.


The stats can be set to give a half full cylinder if you like.


Or just have one at the bottom, maybe plus a flow switch and done with
it.


Boiler cycling would occur only if the heat production rate exceeds
the capacity of the cylinder to absorb it. That can be avoided if
the cylinder is a fast recovery type or if the boiler modulates down.


Fast recovery is highly desirable, modulation down? No.


This would only happen if the cylinder is incapable of absorbing all
the heat or as part of a control system to avoid overshoot.



If the cylinder is running out of hot water too quickly, then there are
three options:

1. Raise the bottom stat temperature to give more stored hot water, say

up
to 65 to 70C. The DHW blending valve will ensure the draw-off

temperature
is what the user wants.


I think you mean water stored at a
higher temperature at the top,
which when mixed gives more at
the wanted temperature.


No. water stored at a higher temp all through the cylinder.


Yes, but *much* higher at the top due to stratification.


Even this
is not going to compensate for letting the
stored amount of heat fall
to 25% of the full capacity.


Wrong.


Please explain how this scheme improves usability and makes more
stored water available.



2. Insert a flow switch into the pipework just before the high flow taps
(bath and shower), and install a third high limit cylinder stat, set to

80C.
The flow switch will bring in the boiler immediately heating the DHW
cylinder preventing the bottom of the cylinder being very cold with

entering
cold water before the boiler cuts in.


This could be worth doing to deal with the poor response of bimetal
thermostats.


3. Do both 1 and 3 above.


Doing the above effectively increases the size of your cylinder.


Actually it does the opposite


Wrong again.


Please explain how this scheme improves usability and makes more
stored water available.




Quite
simple and easy to do. Many people when installing full lengthy body

jets
have a larger cylinder installed. This in many cases is unnecessary. The
above could be done and money saved in boiler efficiency.

The boiler efficiency argument
here is marginal and is at the expense
of performance.


Wrong again.


I demonstrated, with figures how it makes little diference with recent
equipment. It might make more difference with older boilers.


You are sacrificing the stored capacity for a
presumed improvement in efficiency.

Whether there is an efficiency gain to be had really depends on the
type of boiler and cylinder.

If it's an older type cylinder, incapable of taking all the heat from
the boiler, then the cycling will happen anyway if the mismatch is
great even if the coil is effectively immersed in cold water because
the cylinder was allowed to drop to 25% of capacity.

If we assume that the cylinder is fast recovery, so will absorb all
the heat and therefore no cycling during recovery,


equals more efficient.


Obviously. The question is whether that is significant.



When using a DHW blending valve overshoot doesn't matter.


More complexity.


I then repeated the experiment in two different ways. The first was
to run off the same volume of hot water (basically a cylinder full)
continuously and letting the boiler do its thing of starting to
replenish when determined by the sensor.
The second was to run off small amounts of water more slowly so that
the boiler would come on as the cylinder temperature at the sensor had
reached 55 degrees. This is indicative of smaller use during the day.
I stopped running water as soon as the boiler came on and waited for
recovery. In total I drew the same amount of water in each of the
three cases.

In terms of total gas used for each, the amount was the same to within
about 2%. So in this context at least, I don't buy the long burn
argument as making a huge practical difference with recent equipment.


As boiler cycles heat from the boioer is lost through the flue and primary
pipes when the boioer is in an off cycle period.


If the boiler is of a fanned flue type, especially with small gauge
flue pipes, the flue loss is negligible. It might make more
difference with an old cast iron or natural air flow model.

Heat loss through primary pipes is in the building envelope so is
largely irrelevant.









--

..andy

To email, substitute .nospam with .gl
  #28   Report Post  
Andy Hall
 
Posts: n/a
Default

On Thu, 4 Nov 2004 13:04:24 -0000, "IMM" wrote:


"Andy Hall" wrote in message



I increased the cylinder size to a 200 litre one as well and had
double normal thickness of foam fitted. So there is pleny of
storage, which I prefer anyway.


Over storage is a bad thing. No need for it when you have the boiler power
to have the least amount of storage you need.


It makes very little difference as long as the cylinder is well
insulated.



--

..andy

To email, substitute .nospam with .gl
  #29   Report Post  
Christian McArdle
 
Posts: n/a
Default

Set the by-pass accordingly.

I think it might be knackered TBH. I've got it set around 0.8 bar or
somesuch, which shouldn't be achievable with an indirect coil right next to
the pump with no balancing valve.

I just don't have time to investigate.

Christian.


  #30   Report Post  
Christian McArdle
 
Posts: n/a
Default

This isn't the simplest,

It is.


Not it isn't "simplest" is a simple thermostat, not two and a latching
relay.

Actually, I've changed my mind. Simplest is no thermostat at all. Just
connected directly to an always on boiler.

Christian.




  #31   Report Post  
Christian McArdle
 
Posts: n/a
Default

If the store is full up to temp and you turn on the bath tap with the flow
switch activating the boiler, by kicking the latch will do nothing as the
bottom cyl stat will hold off the boiler.


Yes. But I can wait until the store gets below 95% before lighting the
boiler. The addition of boiler power before this is of marginal benefit,
given the additional complexity.

Christian.


  #32   Report Post  
Christian McArdle
 
Posts: n/a
Default

Heat loss through primary pipes is in the building envelope so is
largely irrelevant.


Except in summer, where it would be even worse with air con.

Christian.


  #33   Report Post  
IMM
 
Posts: n/a
Default


"Andy Hall" wrote in message
...

The simplest is to have one thermostat
or sensor and done with it.

You've added an additional thermostat,
a relay and a flow switch.


To improve efficiency, reduce boiler wear and in effect extend the cylinder
size, without installing a larger cylinder.

and I am not sure that it has value in terms
of usability either.


You are not sure. I am sure. It has.


So how does reducing the available
volume of hot water in a storage
system improve usability?


When you require that volume of hot water.

Or just have one at the bottom,
maybe plus a flow switch and done with
it.


That creates inefficient boiler cycling and excess wear on boiler controls.

Fast recovery is highly desirable, modulation down? No.


This would only happen if the cylinder
is incapable of absorbing all
the heat or as part of a control system
to avoid overshoot.


99% of boilers do not have sophisticated DHW controls.

Even this
is not going to compensate for letting the
stored amount of heat fall
to 25% of the full capacity.


Wrong.


Please explain how this scheme
improves usability


Usability? Stop making things up.

and makes more
stored water available.


Read again.

Doing the above effectively increases the size of your cylinder.

Actually it does the opposite


Wrong again.


Please explain how this scheme improves usability


Usability? Stop making things up.

and makes more
stored water available.


Read again.

Quite simple and easy to do.
Many people when installing full lengthy body
jets have a larger cylinder installed. This
in many cases is unnecessary. The
above could be done and money saved
in boiler efficiency.

The boiler efficiency argument
here is marginal and is at the expense
of performance.


Wrong again.


I demonstrated, with figures how
it makes little diference with recent
equipment. It might make more difference
with older boilers.


Figures from one sophisticated boiler which few people have heard of.

You are sacrificing the stored capacity for a
presumed improvement in efficiency.

Whether there is an efficiency gain to be had really depends on the
type of boiler and cylinder.

If it's an older type cylinder, incapable of taking all the heat from
the boiler, then the cycling will happen anyway if the mismatch is
great even if the coil is effectively immersed in cold water because
the cylinder was allowed to drop to 25% of capacity.

If we assume that the cylinder is fast recovery, so will absorb all
the heat and therefore no cycling during recovery,


equals more efficient.


Obviously. The question is whether that is significant.


yes.

When using a DHW blending valve overshoot doesn't matter.


More complexity.


They are to be mandatory soon, so get used to them. They are simple
mechanical devices.

As boiler cycles heat from the boiler is
lost through the flue and primary
pipes when the boioer is in an off cycle period.


If the boiler is of a fanned flue type,
especially with small gauge
flue pipes, the flue loss is negligible.


It is lost and adds up over the year, and over millions of houses too.

It might make more
difference with an old cast iron or
natural air flow model.

Heat loss through primary pipes is
in the building envelope so is
largely irrelevant.


In the summer it is not. There is also the wear of the boiler controls with
excessive unnecessary cycling.



  #34   Report Post  
IMM
 
Posts: n/a
Default


"Andy Hall" wrote in message
...
On Thu, 4 Nov 2004 13:04:24 -0000, "IMM" wrote:


"Andy Hall" wrote in message



I increased the cylinder size to a 200 litre one as well and had
double normal thickness of foam fitted. So there is pleny of
storage, which I prefer anyway.


Over storage is a bad thing. No need for it when you have the boiler

power
to have the least amount of storage you need.


It makes very little difference as long as the cylinder is well
insulated.


Extra cost and space taken up there ARE standing losses.


  #35   Report Post  
Andy Hall
 
Posts: n/a
Default

On Thu, 4 Nov 2004 14:07:26 -0000, "IMM" wrote:


"Andy Hall" wrote in message
.. .

The simplest is to have one thermostat
or sensor and done with it.

You've added an additional thermostat,
a relay and a flow switch.


To improve efficiency, reduce boiler wear and in effect extend the cylinder
size, without installing a larger cylinder.


Improvement in efficiency is going to be marginal at best unless it's
an old boiler.


and I am not sure that it has value in terms
of usability either.

You are not sure. I am sure. It has.


So how does reducing the available
volume of hot water in a storage
system improve usability?


When you require that volume of hot water.


So what happens when the cylinder contains 25% of nominal capacity as
hot water and you want a bath?

Answer. You use up the 25% very quickly indeed and then are down to
what the boiler can do on an instant delivery basis. In other words ,
a nonsense.


Or just have one at the bottom,
maybe plus a flow switch and done with
it.


That creates inefficient boiler cycling and excess wear on boiler controls.


Only on older boilers and inadequate cylinders.


Even this
is not going to compensate for letting the
stored amount of heat fall
to 25% of the full capacity.

Wrong.


Please explain how this scheme
improves usability


Usability? Stop making things up.


So explain how having only 25% of available hot water improves the
"size" of the cylinder and system usability.


again.

Quite simple and easy to do.
Many people when installing full lengthy body
jets have a larger cylinder installed. This
in many cases is unnecessary. The
above could be done and money saved
in boiler efficiency.

The boiler efficiency argument
here is marginal and is at the expense
of performance.

Wrong again.


I demonstrated, with figures how
it makes little diference with recent
equipment. It might make more difference
with older boilers.


Figures from one sophisticated boiler which few people have heard of.


I don't believe that in respect of an experiment like this that any
modern fan flued condensing boiler in the 90-91% SEDBUK category is
going to behave much differently. There would be more of a spread in
efficiency figures if so.




You are sacrificing the stored capacity for a
presumed improvement in efficiency.

Whether there is an efficiency gain to be had really depends on the
type of boiler and cylinder.

If it's an older type cylinder, incapable of taking all the heat from
the boiler, then the cycling will happen anyway if the mismatch is
great even if the coil is effectively immersed in cold water because
the cylinder was allowed to drop to 25% of capacity.

If we assume that the cylinder is fast recovery, so will absorb all
the heat and therefore no cycling during recovery,

equals more efficient.


Obviously. The question is whether that is significant.


yes.


As I said, this may be interesting for an old cast iron boiler, but
for a modern condensing one a 2% variation, which is largely
experimental tolerance anyway I suspect, is not important.




As boiler cycles heat from the boiler is
lost through the flue and primary
pipes when the boioer is in an off cycle period.


If the boiler is of a fanned flue type,
especially with small gauge
flue pipes, the flue loss is negligible.


It is lost and adds up over the year, and over millions of houses too.


and cows farting adds to greenhouse gases. Perhaps you should run
round and insert corks in their recta.



It might make more
difference with an old cast iron or
natural air flow model.

Heat loss through primary pipes is
in the building envelope so is
largely irrelevant.


In the summer it is not. There is also the wear of the boiler controls with
excessive unnecessary cycling.


Only if there is cycling.






--

..andy

To email, substitute .nospam with .gl


  #36   Report Post  
Andy Hall
 
Posts: n/a
Default

On Thu, 4 Nov 2004 14:08:18 -0000, "IMM" wrote:


"Andy Hall" wrote in message
.. .
On Thu, 4 Nov 2004 13:04:24 -0000, "IMM" wrote:


"Andy Hall" wrote in message



I increased the cylinder size to a 200 litre one as well and had
double normal thickness of foam fitted. So there is pleny of
storage, which I prefer anyway.

Over storage is a bad thing. No need for it when you have the boiler

power
to have the least amount of storage you need.


It makes very little difference as long as the cylinder is well
insulated.


Extra cost and space taken up there ARE standing losses.


The extra cost is negligible as is the space.

We had the discussion about standing losses several months ago, when I
demonstrated that these are insignificant as well if the cylinder is
well insulated.



--

..andy

To email, substitute .nospam with .gl
  #37   Report Post  
IMM
 
Posts: n/a
Default


"Andy Hall" wrote in message
...
On Thu, 4 Nov 2004 14:07:26 -0000, "IMM" wrote:


"Andy Hall" wrote in message
.. .

The simplest is to have one thermostat
or sensor and done with it.

You've added an additional thermostat,
a relay and a flow switch.


To improve efficiency, reduce boiler wear and in effect extend the

cylinder
size, without installing a larger cylinder.


Improvement in efficiency is going to
be marginal at best


Nonsense.

and I am not sure that it has value in terms
of usability either.

You are not sure. I am sure. It has.

So how does reducing the available
volume of hot water in a storage
system improve usability?


When you require that volume of hot water.


So what happens when the cylinder contains 25% of nominal capacity as
hot water and you want a bath?


You set it up so that it will always give a bath, and have a quick recovery
cylinder er and a powerful boiler taking all its heat.

snip drivel

Or just have one at the bottom,
maybe plus a flow switch and done with
it.


That creates inefficient boiler cycling and excess wear on boiler

controls.

Only on older boilers and inadequate cylinders.


Nonsense.

Even this
is not going to compensate for letting the
stored amount of heat fall
to 25% of the full capacity.

Wrong.

Please explain how this scheme
improves usability


Usability? Stop making things up.


So explain how having only 25%
of available hot water improves the
"size" of the cylinder and system usability.


You set it up to suit. Duh!

Quite simple and easy to do.
Many people when installing full lengthy body
jets have a larger cylinder installed. This
in many cases is unnecessary. The
above could be done and money saved
in boiler efficiency.

The boiler efficiency argument
here is marginal and is at the expense
of performance.

Wrong again.

I demonstrated, with figures how
it makes little diference with recent
equipment. It might make more difference
with older boilers.


Figures from one sophisticated boiler which few people have heard of.


I don't believe that in respect of
an experiment like this that any
modern fan flued condensing boiler
in the 90-91% SEDBUK category is
going to behave much differently.


I have just fitted a W-B Greenstar heating only boiler and it acts in no
such way.

There would be more of a spread in
efficiency figures if so.


You are sacrificing the stored capacity for a
presumed improvement in efficiency.

Whether there is an efficiency gain to be had really depends on the
type of boiler and cylinder.

If it's an older type cylinder, incapable of taking all the heat

from
the boiler, then the cycling will happen anyway if the mismatch is
great even if the coil is effectively immersed in cold water because
the cylinder was allowed to drop to 25% of capacity.

If we assume that the cylinder is fast recovery, so will absorb all
the heat and therefore no cycling during recovery,

equals more efficient.

Obviously. The question is whether that is significant.


yes.


As I said, this may be interesting for an old cast iron boiler, but
for a modern condensing one a 2% variation, which is largely
experimental tolerance anyway I suspect, is not important.


Total nonsense.

As boiler cycles heat from the boiler is
lost through the flue and primary
pipes when the boioer is in an off cycle period.

If the boiler is of a fanned flue type,
especially with small gauge
flue pipes, the flue loss is negligible.


It is lost and adds up over the year, and over millions of houses too.


snip drivel

It might make more
difference with an old cast iron or
natural air flow model.

Heat loss through primary pipes is
in the building envelope so is
largely irrelevant.


In the summer it is not. There is also the wear of the boiler controls

with
excessive unnecessary cycling.


Only if there is cycling.


There will be.

Now you know and your life is more complete.


  #38   Report Post  
IMM
 
Posts: n/a
Default


"Andy Hall" wrote in message
...
On Thu, 4 Nov 2004 14:08:18 -0000, "IMM" wrote:


"Andy Hall" wrote in message
.. .
On Thu, 4 Nov 2004 13:04:24 -0000, "IMM" wrote:


"Andy Hall" wrote in message


I increased the cylinder size to a 200 litre one as well and had
double normal thickness of foam fitted. So there is pleny of
storage, which I prefer anyway.

Over storage is a bad thing. No need for it when you have the boiler

power
to have the least amount of storage you need.

It makes very little difference as long as the cylinder is well
insulated.


Extra cost and space taken up there ARE standing losses.


The extra cost is negligible as is the space.

We had the discussion about standing losses several months ago, when I
demonstrated that these are insignificant as well if the cylinder is
well insulated.


You never.


  #39   Report Post  
IMM
 
Posts: n/a
Default


"Andy Hall" wrote in message
...

The simplest is to have one thermostat
or sensor and done with it.


snip much tripe by a man with an incomplete life

Look at the DPS web site, and two stats is a common option.



  #40   Report Post  
Christian McArdle
 
Posts: n/a
Default

or sensor and done with it.

Look at the DPS web site, and two stats is a common option.


He does not deny that it is sometimes done, merely that it is the simplest
option. The fact that it is an costed option, rather than standard would
indicate that it is not the simplest one.

Christian.


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