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Old January 12th 19, 10:23 AM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 11/01/2019 21:30, John Rumm wrote:
I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs as
cool as it thinks it can get away with and still be able to reach the
target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the rate
of heat loss of the building).

Currently the external temp is 6.5 deg C, and the flow temp is running
at 54 deg. If it were to go well below 0, then it might push the flow
temp up into the 70s. When its milder it might run flow temps down in
the 40s.


Annoying Worcester do not have a simple weather comp option for theirs
(you have to have the fancy controller and that precludes using your own
heating controller, according to them).

I oversized my rads as much as possible and I have been able to run on
64/54 in deep winter and 55/45 in the less cold parts of the year.


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Old January 12th 19, 10:25 AM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 07:30, John Rumm wrote:
On 12/01/2019 00:55, RJH wrote:
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

snip

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs
as cool as it thinks it can get away with and still be able to reach
the target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the
rate of heat loss of the building).


I don't follow how that can work properly, as for most homes different
rooms will have a different 'curve'. Or does tweaking the TRV compensate?


It seems to work well enough in practice. Each room also has a TRV, and
I have the place split into two zones; upstairs and downstairs, so that
will account for some variation.

It needs a little bit of experimentation to set the profile the first
time - basically waiting for colder days and seeing if the system still
heats the place comfortably and quickly enough. If it doesn't, then you
just tweak it up to a steeper curve. It also helps if you have
appropriate rad sizes for the rooms, and the system is balanced.

The response curves look like:

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

IIRC the system defaults to the 1.2 line. If you live in a super
insulted place / particularly sheltered location then you would tweak
down. In my case (exposed location - solid wall construction), I needed
to go up. I found the 1.8 curve worked well.

The system is also smart enough to automatically shift the response
curve vertically based on the currently demanded internal target
temperature[1]:

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

So if you tweak the room temp up or down during the day (or have
different times programmed with different set point temps), then it can
vary the flow temperature to match the requirement.

[1] Note that all the system temperatures sensors (internal downstairs,
internal upstairs, DHW cylinder, and external) are digitized and
processed as actual temperatures, not just as on/off "call for heat"
style demands.


Thanks for that, interesting. And I hadn't realised such systems had a
collection of sensors.

OT but loosely relevant, I use my CH as 2 zones - upstairs and
downstairs. I'm really not going to replumb to add a properly zones
system, and I was wondering if it's possible to isolate the upstairs
zone with a three way motorised valve - simply cutting out the upstairs
'circuit'.

A single switch would be easier than faffing about with 4 TRVs each evening.

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Old January 12th 19, 10:32 AM posted to uk.d-i-y
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Default how hot do you run you CH boiler

on 12/01/2019, [email protected] supposed :
Where is the room stat?


My stat is in the hall and it is generally set to a lower temperature
than we desire in the living room next to it.


That is the big problem with TRVs, you have to have the system run whenever
any rad wants heat and its difficult to impossible with only one room stat.


Generally, if our hall is below temperature, other parts of the house
will be too. So in practise it works pretty well.


Its a pretty crap way of doing it really.


It is a compromise of cost versus ideal with considerable extra
complexity. Ideal is a zone per room, a temperature sensor per room and
the means to use the data/ decide which rooms should be what
temperature at what times of day, maybe to include occupation sensors.
The boiler coming on if any zone requires heat input.
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Old January 12th 19, 10:55 AM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 09:09, Harry Bloomfield wrote:
After serious thinking harry wrote :
TRVs don't work. They are more influenced by the nearby radiator
temperature than the room air temp.
You can get them with remote sensors. They work.


They work absolutely fine here, once the heating has been on for a while
and the system has settled down. I am able to log/graph room
temperatures and once temperature is achieved, I only see variations of
around 0.5C in the graphs. What TRV's or any type of stat cannot cope
with is the overshoot, when the heating is suddenly turned on, or the
stat suddenly turned up to a much higher setting.


That's not a stat problem that's too much heat capacity in the radiators.

The stat stops the flow but the stuff in the rad is too hot.

You need to have low water content rads.

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Old January 12th 19, 11:01 AM posted to uk.d-i-y
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On 11/01/2019 23:48, Harry Bloomfield wrote:


If anyone knows a workaround, to allow split boiler output temperatures
on this boiler - do let me know please.


IIRC one of the add on controllers allows for different temps when
running HW and heating but I don't recall which.


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Old January 12th 19, 11:33 AM posted to uk.d-i-y
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[email protected] explained :
That's not a stat problem that's too much heat capacity in the radiators.

The stat stops the flow but the stuff in the rad is too hot.

You need to have low water content rads.


I agree, it was originally installed when the place had a much higher
heat loss. Single glazed, no CWI, not much insulation in the roof and
quite air leaky. But its a cost v benefit v need. Only one rad has
needed to be changed and that swapped for one half the capacity, in the
hall. The original boiler was around 32Kw, the new one 18Kw. The guy I
got to install it, even suggested that was probably borderline too big,
but I specced it.

Too much capacity has the advantage that - Nudge the stat up a couple
of degrees and it hits the selected new temperature very quickly. Then
once up to temperature, it barely ticks over.
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Old January 12th 19, 11:39 AM posted to uk.d-i-y
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[email protected] brought next idea :
IIRC one of the add on controllers allows for different temps when running HW
and heating but I don't recall which.


It would have to be something which interacted directly with the boiler
and Vailant said there was nothing able to do that, when I spoke to
them. The boiler has the built in interfaces for the fancier control
systems, I understand, but little detail to be found about these extra
systems.
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Old January 12th 19, 11:59 AM posted to uk.d-i-y
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On 12/01/2019 10:03, wrote:
On 12/01/2019 06:56, John Rumm wrote:
On 11/01/2019 22:25,
wrote:
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:


I had a new Combi fitted today (in the to-be-moved-to house).


[snip]

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

I have weather compensation on mine, and so it chooses its own

[snip]

Currently the external temp is 6.5 deg C, and the flow temp is
running at 54 deg. If it were to go well below 0, then it might push
the flow temp up into the 70s. When its milder it might run flow
temps down in the 40s.


I thought the advice was to heat DHW to 60 degrees to avoid the risk
of legionella, and that's not going to happen if the boiler's running
at a lower temp.


Oddly enough when I typed the reply above, I originally included
discussion of DHW, however deleted it since I thought it was detail
not required to answer the OP.

Yup, the system runs higher flow temperatures for DHW reheat (or at
least the later stages of them). It will modulate the flow temp during
the process to achieve maximum condensation efficiency, while also
ensuring good heat transfer rates). The coil in the cylinder will
allow a recharge at a maximum rate of around 20 - 22kW - just a little
bit less than the maximum output of the boiler.


Does the boiler have an input to tell it that it's heating the DHW, or
is the flow temperature adjusted automagically based on flow and return
characteristics?


Yes ;-)

The boiler knows what it is heating - you get a Tap logo pop up on its
LCD rather than a radiator logo. The information is conveyed over its
eBus rather than with a discrete input.

Also like many boilers, it can adjust its power output based on a number
of criteria including flow and return temps etc.

I'm fairly certain that weather compensation isn't available for my W-B
Greenstar 32/50 boiler, according to the book the manual adjustment
range is 60-82C.


ISTR that when I was looking for system boiler's that could do split
temp, there were some options for some of the WB boilers.

(I also considered paring a combi with an unvented cylinder, so one
could have fast potable DHW to the kitchen which is on a long pipe run)


Its a S plan+ system, but never actually runs he rads and DHW at the
same time.

My system is S+, but with Honeywell Evohome controls. Each room is a
unique zone (2 zones in the bathrooms), with its own thermostat and time
schedule. There is no "house" stat; the rads and DHW all operate
independently of one another.

I have it set to heat to 60 degrees for six days a week, and then it
runs an anti legionella cycle one day a week, where it heats it to 70.

Raising the temp to 70C for one day per week, and keeping it at 50C
(say) at other times, seems like a damned good idea. I'll make the
changes next time I'm fiddling with the settings.

There is a TMV on the output of the cylinder to limit the maximum DHW
temperature delivered to the points of use.

I thought about a TMV when I planned the system but decided not to
bother - perhaps an error.


I was not that keen on the idea that some times it would otherwise
deliver 70 degree water to the taps.

Having a TMV on the cylinder output is a bit of a compromise, since it
means you don't have the benefit of running the very hot water through
all the pipe work like you would with multiple TMVs at every point of use.

In the end I went for a high flow TMV, and set it at max temperature
(about 55 IIRC). That allows for some heat loss in the pipes and still
delivers water hot enough you can mix in some cold at the point of use -
giving shower valves etc a bit more control.


--
Cheers,

John.

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Old January 12th 19, 12:03 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On Sat, 12 Jan 2019 07:35:10 +0000, John Rumm wrote:

manual - adjust the flow temperature yourself in response to
particularly cold days - probably works quite well for users who are
clued up enough to understand the requirement.


This is what I do. The boiler is in the downstairs loo at the back of the
house, and I see it frequently!

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Old January 12th 19, 01:08 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

In article ,
tim... wrote:
Anyhow, at my current house it is 55 and works perfectly well


You must have rather oversized rads?

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