It is that time of year...

I was a bit taken by surprise when someone recently suggested that
condensing boilers work best at 65 deg. C. My thought was that it does
not leave much room for DHW at 60deg. to avoid bacteria.

My flow and return piping is insulated so there should not be much loss
tank coil to boiler.

The other question I have related to weather compensation. My system
boiler has provision (not fitted) for this but no other arrangement for
reducing the set temperature when running the underfloor heating. The
manifolds have local thermal control valves but it seems daft running
the boiler at 65 when 55 would be ample.

Could I fit a suitable fixed resistor in place of the Weather
compensation detector (assumed to be a thermistor of some sort)?

This weekend is *move the by-pass valve* event!


--
Tim Lamb

Tim Lamb used his keyboard to write :

I was a bit taken by surprise when someone recently suggested that condensing
boilers work best at 65 deg. C. My thought was that it does not leave much
room for DHW at 60deg. to avoid bacteria.

Modern boiler have separate temperatures for CH to HW. 65C is the
maximum for efficient condensing, ideally it needs to be less than that
- I have mine set for Max 60C for CH, Max 80C for HW production.


My flow and return piping is insulated so there should not be much loss tank
coil to boiler.

OK


The other question I have related to weather compensation. My system boiler
has provision (not fitted) for this but no other arrangement for reducing the
set temperature when running the underfloor heating. The manifolds have local
thermal control valves but it seems daft running the boiler at 65 when 55
would be ample.

Weather compensation and a clever control system, means the boiler
output can go up to the maximum set, but it certainly does not have to
hit the max temperature. It would only heat the water to what ever
temperature it decides is necessary to achieve your desired
temperature.

My system throttles the boiler back, as it near the set temperature, it
predicts the input power needed, so it does not over shoot.

Could I fit a suitable fixed resistor in place of the Weather compensation
detector (assumed to be a thermistor of some sort)?

What would be the point of that? The boiler needs the outdoor ambient
temperature detector, to improve it output Kw setting, to better match
the houses heat loss.

On 03/11/2020 19:08:29, Harry Bloomfield wrote:
Tim Lamb used his keyboard to write :

I was a bit taken by surprise when someone recently suggested that
condensing boilers work best at 65 deg. C.* My thought was that it
does not leave much room for DHW at 60deg. to avoid bacteria.

Modern boiler have separate temperatures for CH to HW. 65C is the
maximum for efficient condensing, ideally it needs to be less than that
- I have mine set for Max 60C for CH, Max 80C for HW production.

I thought efficiency was determined by return temperature, and not flow
side temperature?

On 03/11/2020 18:32, Tim Lamb wrote:

It is that time of year...

I was a bit taken by surprise when someone recently suggested that
condensing boilers work best at 65 deg. C.

Its the return temperature that matters most, since that dictates how
much it can cool the flue gases. The more water you can condense from
the flue gas, the more latent heat you recovered. The ideal temp is
usually suggested to be around 54 since you get a step improvement about
that temperature. (it will still condense above that - just not as
effectively).

If you balance the system for a total drop of around 20 degrees, then
that allows a flow temp of ~75.

(old system designs were often balanced for a total drop of only ~11
degrees - partly to *prevent* condensation in the main HX which would
cause accelerated corrosion on systems not expecting to have water
sloshing about the outside of the HX)

My thought was that it does
not leave much room for DHW at 60deg. to avoid bacteria.

Another trick you can play on some systems is split temperature
operation, when it uses different flow temps for heating the CH and DHW.

My flow and return piping is insulated so there should not be much loss
tank coil to boiler.

Is it a fast recovery cylinder? And what heating "plan" are you using?

Old cylinders had relatively short coils, and could probably only shift
5kW at best. So they were well suited to Y plan where the system could
run both at once, to provide adequate load to avoid short cycling.

Modern setups with a fast recovery cylinder may be able to swallow the
full output of the boiler, and so are well suited to W, S, S+ plan
setups and can still keep the boiler condensing for most of the DHW
recovery.

The other question I have related to weather compensation. My system
boiler has provision (not fitted) for this but no other arrangement for
reducing the set temperature when running the underfloor heating. The
manifolds have local thermal control valves but it seems daft running
the boiler at 65 when 55 would be ample.

Having split temp operation then gives you freedom use weather
compensation safe in the knowledge that it can decide to run the primary
flow into the CH at 40 degrees if it likes but you can still get a
proper DHW reheat.

With weather comp the flow temperature is set in sympathy with the
outside temperature, and also possibly the delta between current inside
temp and the inside set point temp and taking into account the heat lost
characteristics of the house.

That will lead to long gentle burns at "just enough" heat input to keep
the place comfortable.

However you normally still want blending valves on the UFH, since you
can't assume that the primary flow temp will always be cool enough to
run that directly - it might just be -5 outside and the weather comp
decides its time to run the CH at 75.

Could I fit a suitable fixed resistor in place of the Weather
compensation detector (assumed to be a thermistor of some sort)?

Yup it would be a way of tricking it into changing flow temperature in
response to some control event.

(and yes they are usually NTC thermistors)

This weekend is *move the by-pass valve* event!

Well it passes for entertainment during lockdown I suppose :-)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In message , Harry Bloomfield
writes
Tim Lamb used his keyboard to write :

snip.

My system throttles the boiler back, as it near the set temperature, it
predicts the input power needed, so it does not over shoot.

Could I fit a suitable fixed resistor in place of the Weather
compensation detector (assumed to be a thermistor of some sort)?

What would be the point of that? The boiler needs the outdoor ambient
temperature detector, to improve it output Kw setting, to better match
the houses heat loss.

The Veissmann has no provision for two different settings other than
using the weather compensation. Elderly, retired couple with underfloor
heating, 24 hour occupation and heating kept on.

Heating water temperature is limited to 50 deg. Is there any point in
circulating water at 65 with the boiler spending a lot of time on the
lowest burn?

--
Tim Lamb

In message , John
Rumm writes
On 03/11/2020 18:32, Tim Lamb wrote:

It is that time of year...
I was a bit taken by surprise when someone recently suggested that
condensing boilers work best at 65 deg. C.

Its the return temperature that matters most, since that dictates how
much it can cool the flue gases. The more water you can condense from
the flue gas, the more latent heat you recovered. The ideal temp is
usually suggested to be around 54 since you get a step improvement
about that temperature. (it will still condense above that - just not
as effectively).

If you balance the system for a total drop of around 20 degrees, then
that allows a flow temp of ~75.

(old system designs were often balanced for a total drop of only ~11
degrees - partly to *prevent* condensation in the main HX which would
cause accelerated corrosion on systems not expecting to have water
sloshing about the outside of the HX)

My thought was that it does not leave much room for DHW at 60deg. to
avoid bacteria.

Another trick you can play on some systems is split temperature
operation, when it uses different flow temps for heating the CH and DHW.

My flow and return piping is insulated so there should not be much
loss tank coil to boiler.

Is it a fast recovery cylinder? And what heating "plan" are you using?

Old cylinders had relatively short coils, and could probably only shift
5kW at best. So they were well suited to Y plan where the system could
run both at once, to provide adequate load to avoid short cycling.

Modern setups with a fast recovery cylinder may be able to swallow the
full output of the boiler, and so are well suited to W, S, S+ plan
setups and can still keep the boiler condensing for most of the DHW
recovery.

The other question I have related to weather compensation. My system
boiler has provision (not fitted) for this but no other arrangement
for reducing the set temperature when running the underfloor heating.
The manifolds have local thermal control valves but it seems daft
running the boiler at 65 when 55 would be ample.

Having split temp operation then gives you freedom use weather
compensation safe in the knowledge that it can decide to run the
primary flow into the CH at 40 degrees if it likes but you can still
get a proper DHW reheat.

With weather comp the flow temperature is set in sympathy with the
outside temperature, and also possibly the delta between current inside
temp and the inside set point temp and taking into account the heat
lost characteristics of the house.

That will lead to long gentle burns at "just enough" heat input to keep
the place comfortable.

However you normally still want blending valves on the UFH, since you
can't assume that the primary flow temp will always be cool enough to
run that directly - it might just be -5 outside and the weather comp
decides its time to run the CH at 75.

Could I fit a suitable fixed resistor in place of the Weather
compensation detector (assumed to be a thermistor of some sort)?

Yup it would be a way of tricking it into changing flow temperature in
response to some control event.

(and yes they are usually NTC thermistors)

This weekend is *move the by-pass valve* event!

Well it passes for entertainment during lockdown I suppose :-)

Fast recovery cylinder and W plan. Caused some raised eyebrows with the
plumbers!

There are blending valves on each of the manifolds. 9 underfloor
circuits in total.

While typing this I checked the price of the sensor and decided to buy
one:-) £57.84 del! Seems a lot for a thermistor in a plastic box. Oh
well.





--
Tim Lamb

John Rumm wrote:
My thought was that it does
not leave much room for DHW at 60deg. to avoid bacteria.

Another trick you can play on some systems is split temperature
operation, when it uses different flow temps for heating the CH and DHW.

Heat pumps often have a flow temp much below 60C. The trick some of them
use is to run an immersion once a week to boost the tank up to 60C - that's
sufficient to kill the bacteria.

Since the heat pump tries to keep the (well insulated) tank about 40C
anyway, it's only the weekly 20C boost that you're paying electric heating
prices for.

Theo

On 03/11/2020 19:08, Harry Bloomfield wrote:
.... snipped

Modern boiler have separate temperatures for CH to HW.
.... snipped
Really? A combi may have this but are there any system boilers with it?
If so, how is it signalled?

On 03/11/2020 22:22, Theo wrote:
John Rumm wrote:
My thought was that it does
not leave much room for DHW at 60deg. to avoid bacteria.

Another trick you can play on some systems is split temperature
operation, when it uses different flow temps for heating the CH and DHW.

Heat pumps often have a flow temp much below 60C. The trick some of them
use is to run an immersion once a week to boost the tank up to 60C - that's
sufficient to kill the bacteria.

Since the heat pump tries to keep the (well insulated) tank about 40C
anyway, it's only the weekly 20C boost that you're paying electric heating
prices for.

My Vaillant has an anti legionella cycle that you can enable. That
allows it to heat to the normal DHW set temp (60 in my case) for six
days a week, and then have one day where it heats to 70.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm posted
On 03/11/2020 22:22, Theo wrote:
John Rumm wrote:
My thought was that it does
not leave much room for DHW at 60deg. to avoid bacteria.

Another trick you can play on some systems is split temperature
operation, when it uses different flow temps for heating the CH and DHW.
Heat pumps often have a flow temp much below 60C. The trick some of
them
use is to run an immersion once a week to boost the tank up to 60C - that's
sufficient to kill the bacteria.
Since the heat pump tries to keep the (well insulated) tank about
40C
anyway, it's only the weekly 20C boost that you're paying electric heating
prices for.

My Vaillant has an anti legionella cycle that you can enable. That
allows it to heat to the normal DHW set temp (60 in my case) for six
days a week, and then have one day where it heats to 70.


Good plan. Mine also has a silver crucifix attached to the HW tank, to
prevent it being occupied by vampires. So far it has worked very well.

--
Algernon

On Tuesday, 3 November 2020 18:32:31 UTC, Tim Lamb wrote:
It is that time of year...

I was a bit taken by surprise when someone recently suggested that
condensing boilers work best at 65 deg. C. My thought was that it does
not leave much room for DHW at 60deg. to avoid bacteria.

My flow and return piping is insulated so there should not be much loss
tank coil to boiler.

The other question I have related to weather compensation. My system
boiler has provision (not fitted) for this but no other arrangement for
reducing the set temperature when running the underfloor heating. The
manifolds have local thermal control valves but it seems daft running
the boiler at 65 when 55 would be ample.

Could I fit a suitable fixed resistor in place of the Weather
compensation detector (assumed to be a thermistor of some sort)?

This weekend is *move the by-pass valve* event!

The purpose of "weather compensation" is to anticipate increased heat load by means of an outside temperature sensor.

So if it get cold outside the heating is boosted before there is any fall in temperature indoors.

The amount of "boost" needed depends on the house construction/insulation.
May or may not be adjustable.

In message , writes
On 03/11/2020 19:08, Harry Bloomfield wrote:
... snipped
Modern boiler have separate temperatures for CH to HW.
... snipped
Really? A combi may have this but are there any system boilers with it?
If so, how is it signalled?

I was thinking of cheating by making use of the weather compensation:-)

--
Tim Lamb

In article , Algernon Goss-Custard
wrote:
John Rumm posted
On 03/11/2020 22:22, Theo wrote:
John Rumm wrote:
My thought was that it does not leave much room for DHW at 60deg. to
avoid bacteria.

Another trick you can play on some systems is split temperature
operation, when it uses different flow temps for heating the CH and
DHW.
Heat pumps often have a flow temp much below 60C. The trick some of
them use is to run an immersion once a week to boost the tank up to 60C
- that's sufficient to kill the bacteria. Since the heat pump tries to
keep the (well insulated) tank about 40C anyway, it's only the weekly
20C boost that you're paying electric heating prices for.

My Vaillant has an anti legionella cycle that you can enable. That
allows it to heat to the normal DHW set temp (60 in my case) for six
days a week, and then have one day where it heats to 70.


Good plan. Mine also has a silver crucifix attached to the HW tank, to
prevent it being occupied by vampires. So far it has worked very well.

However, I have had Legionella, but never seen a vampire

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

On 03/11/2020 23:24, wrote:
On 03/11/2020 19:08, Harry Bloomfield wrote:
.... snipped

Modern boiler have separate temperatures for CH to HW.
.... snipped

Really? A combi may have this but are there any system boilers with it?

Yup, all the Vaillant range, a number of the WB, and a number of others
(most likely anything that supports weather compensation).

If so, how is it signalled?

Via eBus typically[1]. The programmer will understand the difference
between DHW and CH, and allow them to be independently controlled and
programmed.


[1] some may support independent simple "call for heat" style stat inputs.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/11/2020 09:00, harry wrote:
On Tuesday, 3 November 2020 18:32:31 UTC, Tim Lamb wrote:
It is that time of year...

I was a bit taken by surprise when someone recently suggested that
condensing boilers work best at 65 deg. C. My thought was that it
does not leave much room for DHW at 60deg. to avoid bacteria.

My flow and return piping is insulated so there should not be much
loss tank coil to boiler.

The other question I have related to weather compensation. My
system boiler has provision (not fitted) for this but no other
arrangement for reducing the set temperature when running the
underfloor heating. The manifolds have local thermal control valves
but it seems daft running the boiler at 65 when 55 would be ample.

Could I fit a suitable fixed resistor in place of the Weather
compensation detector (assumed to be a thermistor of some sort)?

This weekend is *move the by-pass valve* event!

The purpose of "weather compensation" is to anticipate increased heat
load by means of an outside temperature sensor.

Yup, although most I have looked at are reactive rather than
anticipatory... not quite sure how you would do an optimising weather
compensator.

So if it get cold outside the heating is boosted before there is any
fall in temperature indoors.

The amount of "boost" needed depends on the house
construction/insulation. May or may not be adjustable.

On my system, its by choosing a response curve:

http://wiki.diyfaq.org.uk/index.php/...tingCurve1.png

I believe the Viseman system boilers also use a similar approach.

On the Vaillant setup it also factors in the set point internal temp
shifts the whole curve up to force higher flow temperatures if the
temperature is set higher :

http://wiki.diyfaq.org.uk/index.php/...tingCurve2.png

So in this case it actually works the way many people think a thermostat
does - turn it up higher and it *does* heat up quicker! :-)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/11/2020 09:59, John Rumm wrote:
On 03/11/2020 23:24, wrote:
On 03/11/2020 19:08, Harry Bloomfield wrote:
.... snipped

Modern boiler have separate temperatures for CH to HW.
.... snipped

Really? A combi may have this but are there any system boilers with it?

Yup, all the Vaillant range, a number of the WB, and a number of others
(most likely anything that supports weather compensation).

If so, how is it signalled?

Via eBus typically[1]. The programmer will understand the difference
between DHW and CH, and allow them to be independently controlled and
programmed.


[1] some may support independent simple "call for heat" style stat inputs.

Thanks for the education, I'm slightly wiser than I was. My WB boiler
(Worcester 32/50 Danesmoor) is only a couple of years old but is pretty
basic.

My weather compensated Viessmann system boiler - quite old now - seems
happy enough to heat the water above 60c at all times, but modulates down
when driving the heating to the most economical temperature once the house
is up to the set temperature.

I have heating to get the house to the right temperature as quickly as
possible, rather than to save money.

Would likely be different with underfloor heating left on 24/7.

--
*Change is inevitable, except from a vending machine.

Dave Plowman London SW
To e-mail, change noise into sound.

In message , "Dave Plowman (News)"
writes
My weather compensated Viessmann system boiler - quite old now - seems
happy enough to heat the water above 60c at all times, but modulates down
when driving the heating to the most economical temperature once the house
is up to the set temperature.

I'll fit the transducer and see how it goes.

I have heating to get the house to the right temperature as quickly as
possible, rather than to save money.

Would likely be different with underfloor heating left on 24/7.

Indeed. Ground floor rooms in the original part of the house (where
there is much less insulation) get most heating at the moment.
I have been meaning to ask if exterior: ground level to foundation,
insulation would pay back and, if so, what would be a suitable material.


--
Tim Lamb

On Tuesday, 3 November 2020 at 23:24:19 UTC, wrote:
On 03/11/2020 19:08, Harry Bloomfield wrote:
... snipped

Modern boiler have separate temperatures for CH to HW.
... snipped
Really? A combi may have this but are there any system boilers with it?
If so, how is it signalled?

Two different "call for heat" signals. One for CH, one for HW. My Viessmann has this, and it works very well with the W-plan I have.