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Old January 12th 19, 02:00 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 13:46, Dave Plowman (News) wrote:
In article ,
tim... wrote:


"Dave Plowman (News)" wrote in message
...
In article ,
tim... wrote:
Anyhow, at my current house it is 55 and works perfectly well

You must have rather oversized rads?


Nope


they are tiny


The physical size depends on the demand in that area.

they are on all day


The house is well insulated



Why do you think that wouldn't work?


Anything can work. But there is an ideal figure for rad temp for best
efficiency.

Best efficiency as far as the radiator is concerned is as hot as
practical - the higher the deltaT between radiator and the room air then
the more it radiates.
If you have the heating on 24/7 then yes you can get away with low rad.
temperatures, but for fastest response where the heating is timed then
hotter is better.
If you have intelligent thermostats like Hive or Nest then they will
learn the thermal characteristics of the monitored room and minimise
temperature overshoot by shutting down the boiler before the set
temperature is reached.

  #52   Report Post  
Old January 12th 19, 02:01 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler



"Dave Plowman (News)" wrote in message
...
In article ,
tim... wrote:


"Dave Plowman (News)" wrote in message
...
In article ,
tim... wrote:
Anyhow, at my current house it is 55 and works perfectly well

You must have rather oversized rads?


Nope


they are tiny


The physical size depends on the demand in that area.

they are on all day


The house is well insulated



Why do you think that wouldn't work?


Anything can work. But there is an ideal figure for rad temp for best
efficiency.


I'm not seeking efficiency

I'm seeking all of the rooms at the same temp

tim



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Old January 12th 19, 02:02 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 09:28, Harry Bloomfield wrote:
John Rumm formulated the question :
IME many of the Vaillant boilers do support split temperature
operation, but it does depends on what controls you have them paired
with.

The 400 series Vaillant I did (probably previous model range, since
this was
= 12 years ago), actually had separate knobs on the front for CH and
DHW flow temperatures. Although that was retrofitted into system with
traditional controls that could not distinguish between the source of
the call for heat - hence the DHW control never came into play and it
ran like your system does.


The blurb on their web site:

https://www.vaillant.co.uk/for-insta...ler-26116.html


Seems to suggest its compatible with the VRC 700 weather compensating
controls, so that ought to allow split temperature as well.


I have studied it and not found any obvious way to split the
temperature. I even spoke to Vailant and they confirmed there was no way
it could be done.


I suspect they are talking nonsense or at crossed purposes. It may be
that it can't be done with the installation you have, however if you are
prepared to add controls then it looks straight forward.

If it (the compensator) is anything like mine (a VR470), then you can
set the temperature for two "uncontrolled"[1] zones, and DHW separately
in the programming. I also have a VR61 control module that lets you
integrate traditional 240V zone valves etc into the controls.

[1] They seem to call what most people would think of as a zone
controlled with valves and a thermostat, an "uncontrolled" zone. They
reserve the term controlled for ones with active blending valves for UFH
where the controls can directly set the UFH zone flow temperature
independently of the main boiler flow temp.

Yup, have a look at:

https://www.vaillant.co.uk/downloads...al-1000027.pdf

See the user manual section 5.2.1.2:

https://www.vaillant.co.uk/downloads...03-1000692.pdf

That definitely allows independent control of CH and DHW temperatures.

(the VR700 has way more toys that you will need - I just picked that one
because it was listed on the 400 series page. I expect the older VR470
would be fine as well)


--
Cheers,

John.

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  #54   Report Post  
Old January 12th 19, 02:16 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 11:39, Harry Bloomfield wrote:
[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.


One of the problems I found with the Vaillant documentation, was that
there is lots of low level detail stuff, but not so much "big picture"
stuff to tell you what components you need to achieve which jobs.
(perhaps that is what they train their registered installers with!)

In the end it was just a case of reading through all the detail stuff
until you can mentally put together what bits are going to do what you need.

But basically you need a weather compensator, and probably an interface
box to let it communicate with traditional valves etc.

In my case I went for a VR470 and a VR61 (there is also another aux mini
controller / stat to monitor the upstairs temp - but you can do without
that).

You use the VR470 as the interface to configure and control everything
else. It acts as the central point for the timer / stat / weather
compensator, and then a load of other facilities if you want them[1].
The interface box converts the demands of the controller delivered over
eBus, to relays etc that can switch 240V to move 2/3 port valves.


[1] From the handy "cylinder boost", and "holiday mode", to the more
esoteric UFH screed drying programs, DHW anti legionella cycle,
ctrolling aux pumps like secondary circulation pumps or solar collection
pumps etc.






--
Cheers,

John.

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Old January 12th 19, 02:40 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

John Rumm formulated on Saturday :
I suspect they are talking nonsense or at crossed purposes. It may be that it
can't be done with the installation you have, however if you are prepared to
add controls then it looks straight forward.


All I have at the moment, is a Danfoss (I think) time clock, which sets
when CH and HW are available. A three port valve. A wireless room stat
and a wired HW cylinder stat.

The original boiler had just a live (when called) neutral and earth. I
added an extra pair in from boiler back to pump, to enable to boiler to
decide when the pump needed to be run, when the new boiler was
installed.


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Old January 12th 19, 02:53 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 10:25, RJH wrote:

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'.


If the pipework is in the right place a two port valve will isolate the
upstairs.


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


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Old January 12th 19, 03:25 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler



"Andy Bennet" wrote in message
...
On 12/01/2019 13:46, Dave Plowman (News) wrote:
In article ,
tim... wrote:


"Dave Plowman (News)" wrote in message
...
In article ,
tim... wrote:
Anyhow, at my current house it is 55 and works perfectly well

You must have rather oversized rads?


Nope


they are tiny


The physical size depends on the demand in that area.

they are on all day


The house is well insulated



Why do you think that wouldn't work?


Anything can work. But there is an ideal figure for rad temp for best
efficiency.

Best efficiency


efficient in what way?

as far as the radiator is concerned is as hot as practical - the higher the
deltaT between radiator and the room air then the more it radiates.
If you have the heating on 24/7 then yes you can get away with low rad.


Which is what I do have

temperatures, but for fastest response where the heating is timed then
hotter is better.


I have no need for faster response. I want constant moderate temperature

tim



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Old January 12th 19, 03:48 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

In article ,
tim... wrote:
Anything can work. But there is an ideal figure for rad temp for best
efficiency.


I'm not seeking efficiency


I'm seeking all of the rooms at the same temp


I'm curious about that. You said with the boiler set to 74 degrees, the
rad were too hot to touch?
How can that be with the rooms at the correct temperture if they are OK at
55 degrees?

--
*Nostalgia isn't what is used to be.

Dave Plowman London SW
To e-mail, change noise into sound.
  #59   Report Post  
Old January 12th 19, 04:47 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 13:32, tim... wrote:


"John Rumm" wrote in message
o.uk...
On 12/01/2019 09:28, wrote:
On 12/01/2019 08:56, tim... wrote:


wrote in message
...
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.

Which I thought far too high, as

Indeed...

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile
will result from having the radiators at the lower temperate for
longer period than a higher temperature for a shorter period

It might be required in particularly cold weather, but most of the
time you will be able to use less.


I tried to explain this but was met with

"The recommended temperature is required for the condenser to
have any effect"

You will most heat recovered from the condenser when the return
temperature is below about 54 degrees (the dew point of the flue
gasses).

and the completely bogus "the temperature of the water in the
radiators is set by the TRVs not the boiler temp.* I couldn't
persuade the guy that he was taking bollox, he played the "I'm
the experience heating engineer card and I know better than you"
card. ****

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).

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.

the temp for the hot water and CH system are set independently in a
combi



I was replying to John (but had forgotten about combis)


The combi won't usually get it any hotter (since flow rate and
temperature are mutually exclusive), but the again there is no
significant store of water to act as a breeding ground either.


the linked to article said that the water in a shower head was sufficient


Not much way round that unless you like 70 degree showers ;-)


--
Cheers,

John.

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http://www.internode.co.uk |
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Old January 12th 19, 04:58 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 14:40, Harry Bloomfield wrote:
John Rumm formulated on Saturday :
I suspect they are talking nonsense or at crossed purposes. It may be
that it can't be done with the installation you have, however if you
are prepared to add controls then it looks straight forward.


All I have at the moment, is a Danfoss (I think) time clock, which sets
when CH and HW are available. A three port valve. A wireless room stat
and a wired HW cylinder stat.

The original boiler had just a live (when called) neutral and earth. I
added an extra pair in from boiler back to pump, to enable to boiler to
decide when the pump needed to be run, when the new boiler was installed.


So you would need a bit of rejigging to move to split temperature
operation. The VR weather comp replaces the timer and stat. You probably
want a pair of two port valves in place of the mid position valve -
although with a bit of thought you may be able to achieve the logic
required with what you have. Swap the cylinder stat for a NTC
thermistor, and add a suitable wiring centre. You would need an extra
cable from the cylinder to the boiler (that threw me, I was expecting
the cylinder NTC to connect to the wiring centre!), and to install an
external NTC somewhere.

Doable enough, but whether its worth the hassle at this stage only you
can decide. It might knock a few percent off the gas bill, and will make
the place a bit more comfortable year round.


--
Cheers,

John.

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


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