been studying a colleague's heatbank setup.

the heatbank has an adjustable thermostatic mixing valve on the boiler
return, that appears to mix water from an tapping near the base of the
heat bank with water from a tapping at the top of the heat
bank....presumably to control the temp of the boiler return to get the
boiler into condensing mode all the time.... but why is it needed? why
not just take the boiler return from the bottom tapping full stop?

also it has two electrically interlinked thermostats vertically spaced
but only by about 100mm (heatbank is abt 2000mm tall) both are set to
60 degC ?

Seems only way for heat to be called is by using the HW channel on the
programmer. CH side of programmer causes radiator circulation pump to
run but not call for heat (even when hbank temp down to 40deg C on
gauge)???

Anyone else have a heatbank and recognise any of this?
or has he got a lemon ?

jim

On Sun, 03 May 2009 07:29:48 -0700, jim wrote:

been studying a colleague's heatbank setup.

There are various widely different heatbanks around. What's your
colleague's make & model?

--
John Stumbles -- http://yaph.co.uk

Thesaurus: extinct reptile noted for its wide vocabulary.

jim coughed up some electrons that declared:

been studying a colleague's heatbank setup.

the heatbank has an adjustable thermostatic mixing valve on the boiler
return, that appears to mix water from an tapping near the base of the
heat bank with water from a tapping at the top of the heat
bank....presumably to control the temp of the boiler return to get the
boiler into condensing mode all the time.... but why is it needed? why
not just take the boiler return from the bottom tapping full stop?

also it has two electrically interlinked thermostats vertically spaced
but only by about 100mm (heatbank is abt 2000mm tall) both are set to
60 degC ?

Seems only way for heat to be called is by using the HW channel on the
programmer. CH side of programmer causes radiator circulation pump to
run but not call for heat (even when hbank temp down to 40deg C on
gauge)???

Anyone else have a heatbank and recognise any of this?
or has he got a lemon ?

jim

The idea is to promote rapid heating of the top of the store to the final
temperature.

I'm not using a mixer in that position - instead I'm using a 3 speed pump to
the boiler. I'm hoping to find a speed that allows the boiler to dump its
full output (24kW) into the slowest moving water, which effectively
achieves the same thing, though if successful, my approach ought to feed
cold water for as long as possible into the boiler return, promoting max
efficiency from a condensing boiler.

We'll see...

Cheers

Tim

"jim" wrote in message
...
been studying a colleague's heatbank setup.

the heatbank has an adjustable thermostatic mixing valve on the boiler
return, that appears to mix water from an tapping near the base of the
heat bank with water from a tapping at the top of the heat
bank....presumably to control the temp of the boiler return to get the
boiler into condensing mode all the time.... but why is it needed? why
not just take the boiler return from the bottom tapping full stop?


For rapid reheat.

also it has two electrically interlinked thermostats vertically spaced
but only by about 100mm (heatbank is abt 2000mm tall) both are set to
60 degC ?

60C? must have lower higher than upper. They are to prevent boiler
cycling. Have bottom at say 70 and top 55 to 60C.

Seems only way for heat to be called is by using the HW channel on the
programmer. CH side of programmer causes radiator circulation pump to
run but not call for heat (even when hbank temp down to 40deg C on
gauge)???

About right. The DHW keeps the cyl hot. The CH runs the CH rad pump. You
can have a pipe stat set to say 50C on the CH flow from the cyl to prevent
cool rads.

Anyone else have a heatbank and recognise any of this?
or has he got a lemon ?

No, far from it. Just set the stats properly. Tell him to put in the
correct amount of inhibitor. He could also have TRVs on all rads and Wilo
Smart pump on the rad circuit.

On 4 May, 01:04, "Doctor Drivel" wrote:
"jim" wrote in message

...

been studying a colleague's heatbank setup.

the heatbank has an adjustable thermostatic mixing valve on the boiler
return, that appears to mix water from an tapping near the base of the
heat bank with water from a tapping at the top of the heat
bank....presumably to control the temp of the boiler return to get the
boiler into condensing mode all the time.... but why is it needed? why
not just take the boiler return from the bottom tapping full stop?

For rapid reheat.

ah ok - what should he set the return temp at for optimum performance?

also it has two electrically interlinked thermostats vertically spaced
but only by about 100mm (heatbank is abt 2000mm tall) both are set to
60 degC ?

60C? must have lower higher than upper. They are to prevent boiler
cycling. Have bottom at say 70 and top 55 to 60C.

can you talk me through how that works please?

Seems only way for heat to be called is by using the HW channel on the
programmer. CH side of programmer causes radiator circulation pump to
run but not call for heat (even when hbank temp down to 40deg C on
gauge)???

About right. The DHW keeps the cyl hot. The CH runs the CH rad pump. You
can have a pipe stat set to say 50C on the CH flow from the cyl to prevent
cool rads.

do you mean a pipe stat could call the boiler (and boiler circ pump)
if the temp of flow to rads dropped below 50deg?

thanks
jim

jim coughed up some electrons that declared:

On 4 May, 01:04, "Doctor Drivel" wrote:

For rapid reheat.

ah ok - what should he set the return temp at for optimum performance?

Viesmann told me optimum return was 45C or less, with progressive loss of
efficiency for higher return temperatures.

also it has two electrically interlinked thermostats vertically spaced
but only by about 100mm (heatbank is abt 2000mm tall) both are set to
60 degC ?

60C? must have lower higher than upper. They are to prevent boiler
cycling. Have bottom at say 70 and top 55 to 60C.

can you talk me through how that works please?

Top stat gets cold, boiler fires. Relay interlock requires bottom stat to
get hot (a while after top stat has got hot again) before disengaging
boiler.

Seems only way for heat to be called is by using the HW channel on the
programmer. CH side of programmer causes radiator circulation pump to
run but not call for heat (even when hbank temp down to 40deg C on
gauge)???

About right. The DHW keeps the cyl hot. The CH runs the CH rad pump.
You can have a pipe stat set to say 50C on the CH flow from the cyl to
prevent cool rads.

do you mean a pipe stat could call the boiler (and boiler circ pump)
if the temp of flow to rads dropped below 50deg?

No, the rads and the reheat of the tank are in different control domains.

All the tank has to worry about is staying hot - to this effect it controls
the demand for heat to the boiler.

The rad control circuit only has to respect the timer(s) and room stat(s) -
this signal normally fires a boiler and optionally switches a control valve
to send hot water to the rads. With a heatbank, it merely controls the rad
pump, assuming that the tank always contains hot water. It indirectly fires
the boiler when needed by depleting the tank of heat.

If you have underfloor heating, duplicate the radiator control system and
pump, add a mixer for cooler water (40 ish flow rather than 60-75 ish).

Tap hot water is also independant, the pump being controled by a flow
switch.

This isn't to say that you can't have a smart controller that takes account
of outside temp, date, general rad demand, expected output from solar, time
of day and stuff and overrides all the systems to perhaps:

a) Limit the boiler input when strong solar input is expected later in the
morning (ie leave some cold water for the solar to heat)

b) Up the boiler input if it's a cold mouldy day and maybe a weekend when
higher demand from radiators is expected;

c) Goes into minimal frost prevention for 2 weeks when you're on holiday

and so on.


HTH

Tim

"jim" wrote in message
...
On 4 May, 01:04, "Doctor Drivel" wrote:
"jim" wrote in message

...

been studying a colleague's heatbank setup.

the heatbank has an adjustable thermostatic mixing valve on the boiler
return, that appears to mix water from an tapping near the base of the
heat bank with water from a tapping at the top of the heat
bank....presumably to control the temp of the boiler return to get the
boiler into condensing mode all the time.... but why is it needed? why
not just take the boiler return from the bottom tapping full stop?

For rapid reheat.

ah ok - what should he set the return temp at for optimum performance?

The blending valve is usually set at 54C. The idea is to give what the
boilers thermal temperature rise is. If it is 30C and store temp of 75C is
needed, the return temp should be set should be set at 45C. A little
testing of flow and return temps is needed. The boiler is set to max temp.

Having a large boiler, say 45-55kW, a blending valve is not needed in a
domestic store. It has enough temp rise to cope, and reheats ASAP, like el
Zippo. The store doesn't care what size the boiler is, and it will not
cycle. Some large boilers can be bought reasonably cheaply. or use two 24kW
boilers, both having their own flow and return connections to the store,
both controlled by the cyl stats.

also it has two electrically interlinked thermostats vertically spaced
but only by about 100mm (heatbank is abt 2000mm tall) both are set to
60 degC ?

60C? must have lower higher than upper. They are to prevent boiler
cycling. Have bottom at say 70 and top 55 to 60C.

can you talk me through how that works please?

Cold start:
store heats up top down to 75C.
75C hits the first stat down set to 60C - stat is ignored.
75C hit the bottom stata and boioper switched out.

Store cools bottom up:
bottom stat is ignored.
top stat gets below 60C and brings in boiler.

No boiler cycling as boiler heats in one long efficient burn.

Having both to 60C will still give a lag, well with 1C between. Work
through the operation.

Seems only way for heat to be called is by using the HW channel on the
programmer. CH side of programmer causes radiator circulation pump to
run but not call for heat (even when hbank temp down to 40deg C on
gauge)???

About right. The DHW keeps the cyl hot. The CH runs the CH rad pump.
You
can have a pipe stat set to say 50C on the CH flow from the cyl to
prevent
cool rads.

do you mean a pipe stat could call the boiler (and boiler circ pump)
if the temp of flow to rads dropped below 50deg?

The pipe stat holds off the CH pump pumping to the rads. Above 50C the pump
comnes in. Fitr pipe stat near the boioer sop herat floats out of cylinder
into pipe. A cylidner stat at the point of the rad flow tapping is better.

Most do not find the rad pump pump a problem. The boiler will come in and
re-heat ASAP.

On 4 May, 13:38, "Doctor Drivel" wrote:

also it has two electrically interlinked thermostats vertically spaced
but only by about 100mm (heatbank is abt 2000mm tall) both are set to
60 degC ?

60C? must have lower higher than upper. They are to prevent boiler
cycling. Have bottom at say 70 and top 55 to 60C.

can you talk me through how that works please?

Cold start:
store heats up top down to 75C.
75C hits the first stat down set to 60C - stat is ignored.
75C hit the bottom stata and boioper switched out.

Store cools bottom up:
bottom stat is ignored.
top stat gets below 60C and brings in boiler.

No boiler cycling as boiler heats in one long efficient burn.

Having both to 60C will still give a lag, well with 1C between. Work
through the operation.

interesting
- additionally there's a further "overheat" stat near the top of the
cylinder set at 85 degC - would it be actually possible to satisfy the
two stats (only 4" vertically" apart, half way up the cylinder)
without triggering the overheat stat and (as i understand it) dumping
the "excess" heat into the rad circuit?

if that happened the boiler would be firing most of the time (to try
to satisfy the two anti-cycling stats) and the heatbank would be
dumping heat into the rads (even if the CH programmer channel + room
stats were "off") to stop the overheat stat from being
triggered.....??

Seems only way for heat to be called is by using the HW channel on the
programmer. CH side of programmer causes radiator circulation pump to
run but not call for heat (even when hbank temp down to 40deg C on
gauge)???

About right. The DHW keeps the cyl hot. The CH runs the CH rad pump.
You
can have a pipe stat set to say 50C on the CH flow from the cyl to
prevent
cool rads.

do you mean a pipe stat could call the boiler (and boiler circ pump)
if the temp of flow to rads dropped below 50deg?

The pipe stat holds off the CH pump pumping to the rads. Above 50C the pump
comnes in. Fitr pipe stat near the boioer sop herat floats out of cylinder
into pipe. A cylidner stat at the point of the rad flow tapping is better.

Most do not find the rad pump pump a problem. The boiler will come in and
re-heat ASAP.

so presumably *only* the "HW" channel on the programmer plus the
thermostats, control when/if the boiler fires?
the heatbank thermostats *should* limit cycling of the boiler

so real question is - with the location, spacing and settings of the
two "anti-cycling" stats, can the heatbank work as it should and limit
boiler cycling without overheating and dumping heat to the rads??

any thoughts on how we could go about testing the theories please?

thanks
jim

"jim" wrote in message
...
On 4 May, 13:38, "Doctor Drivel" wrote:

also it has two electrically interlinked thermostats vertically
spaced
but only by about 100mm (heatbank is abt 2000mm tall) both are set
to
60 degC ?

60C? must have lower higher than upper. They are to prevent boiler
cycling. Have bottom at say 70 and top 55 to 60C.

can you talk me through how that works please?

Cold start:
store heats up top down to 75C.
75C hits the first stat down set to 60C - stat is ignored.
75C hit the bottom stata and boioper switched out.

Store cools bottom up:
bottom stat is ignored.
top stat gets below 60C and brings in boiler.

No boiler cycling as boiler heats in one long efficient burn.

Having both to 60C will still give a lag, well with 1C between. Work
through the operation.

interesting
- additionally there's a further "overheat" stat near the top of the
cylinder set at 85 degC - would it be actually possible to satisfy the
two stats (only 4" vertically" apart, half way up the cylinder)
without triggering the overheat stat and (as i understand it) dumping
the "excess" heat into the rad circuit?

The boiler can only give out 82C. The top stat is a high limit only.

if that happened the boiler would be firing most of the time (to try
to satisfy the two anti-cycling stats) and the heatbank would be
dumping heat into the rads (even if the CH programmer channel + room
stats were "off") to stop the overheat stat from being
triggered.....??

Not sure what you mean. The CH pump only comes on when the programmers say
it can..,.and if a room stat is fitted and says it can.

The DHW must be on to get hot water for CH.

The boiler is controlled only by the two anti-cycle stats. The boiler does
fire most of the time at all. The bonier is off most of the time. It heat
the cylinder and only comes in when the heat is exhausted to an useable
level and re-heats in one burn.

Seems only way for heat to be called is by using the HW channel on
the
programmer. CH side of programmer causes radiator circulation pump
to
run but not call for heat (even when hbank temp down to 40deg C on
gauge)???

About right. The DHW keeps the cyl hot. The CH runs the CH rad pump.
You
can have a pipe stat set to say 50C on the CH flow from the cyl to
prevent
cool rads.

do you mean a pipe stat could call the boiler (and boiler circ pump)
if the temp of flow to rads dropped below 50deg?

The pipe stat holds off the CH pump pumping to the rads. Above 50C the
pump
comnes in. Fitr pipe stat near the boioer sop herat floats out of
cylinder
into pipe. A cylidner stat at the point of the rad flow tapping is
better.

Most do not find the rad pump pump a problem. The boiler will come in and
re-heat ASAP.

so presumably *only* the "HW" channel on the programmer plus the
thermostats, control when/if the boiler fires?

the heatbank thermostats *should* limit cycling of the boiler

Yep. The stats prevent cycling. The prime purpose.

so real question is - with the location, spacing and settings of the
two "anti-cycling" stats, can the heatbank work as it should and limit
boiler cycling without overheating and dumping heat to the rads??

Yes. set to 70C at the bottom and 55C at the top and see what happens. In
summer you get away with 65C if using a plate heat exchanger.

any thoughts on how we could go about testing the theories please?

Just set as I say and see how it goes.

"jim" wrote in message
...
On 4 May, 01:04, "Doctor Drivel" wrote:
"jim" wrote in message

...

been studying a colleague's heatbank setup.

the heatbank has an adjustable thermostatic mixing valve on the boiler
return, that appears to mix water from an tapping near the base of the
heat bank with water from a tapping at the top of the heat
bank....presumably to control the temp of the boiler return to get the
boiler into condensing mode all the time.... but why is it needed? why
not just take the boiler return from the bottom tapping full stop?

For rapid reheat.

ah ok - what should he set the return temp at for optimum performance?

The blending valve is usually set at 54C. The idea is to give what the
boilers thermal temperature rise is. If it is 30C and store temp of 75C is
needed, the return temp should be set should be set at 45C. A little
testing of flow and return temps is needed. The boiler is set to max temp.

Having a large boiler, say 45-55kW, a blending valve is not needed in a
domestic store. It has enough temp rise to cope, and reheats ASAP, like el
Zippo. The store doesn't care what size the boiler is, and it will not
cycle. Some large boilers can be bought reasonably cheaply. or use two 24kW
boilers, both having their own flow and return connections to the store,
both controlled by the cyl stats.

also it has two electrically interlinked thermostats vertically spaced
but only by about 100mm (heatbank is abt 2000mm tall) both are set to
60 degC ?

60C? must have lower higher than upper. They are to prevent boiler
cycling. Have bottom at say 70 and top 55 to 60C.

can you talk me through how that works please?

Cold start:
store heats up top down to 75C.
75C hits the first stat down set to 60C - stat is ignored.
75C hit the bottom stata and boioper switched out.

Store cools bottom up:
bottom stat is ignored.
top stat gets below 60C and brings in boiler.

No boiler cycling as boiler heats in one long efficient burn.

Having both to 60C will still give a lag, well with 1C between. Work
through the operation.

Seems only way for heat to be called is by using the HW channel on the
programmer. CH side of programmer causes radiator circulation pump to
run but not call for heat (even when hbank temp down to 40deg C on
gauge)???

About right. The DHW keeps the cyl hot. The CH runs the CH rad pump.
You
can have a pipe stat set to say 50C on the CH flow from the cyl to
prevent
cool rads.

do you mean a pipe stat could call the boiler (and boiler circ pump)
if the temp of flow to rads dropped below 50deg?

The boiler heating the cylinder is independent of DHW or CH demand. The
pipe stat holds off the CH pump pumping to the rads. Above 50C the pump
comes in. Fit pipe stat near the boiler sop heat floats out of cylinder
into pipe. A cylinder stat at the point of the rad flow tapping is better.

Most do not find the rad pump pumping a problem. The boiler will come in and
re-heat ASAP.