Radiator mean temperature

[Johnytuono]

Hopefully someone can explain this.
Boiler flow is 60c, have balanced the rads to about 12c with a differential thermometer.
For some reason the flow pipes show 51c and the return 39c yet the rad. mean temperature is around 50/52c, why is this if the flow pipe is less than the mean temp.?
I have 10mm Microbore tails, the boiler does show water heated to 60c and the return is about 10c(ish less) but obviously this rises as the boiler modulates.
Anyone?

 

[Wayners]

Outer pipe temp is lower than core temperature I guess

 

[Johntheo5]

Hopefully someone can explain this.
Boiler flow is 60c, have balanced the rads to about 12c with a differential thermometer.
For some reason the flow pipes show 51c and the return 39c yet the rad. mean temperature is around 50/52c, why is this if the flow pipe is less than the mean temp.?
I have 10mm Microbore tails, the boiler does show water heated to 60c and the return is about 10c(ish less) but obviously this rises as the boiler modulates.
Anyone?

all (if) system boilers have a internal bypass, the displayed and actual boiler temperature will always be higher than the measured return temperature, I have seen numbers on here of the boiler return being up to 7C higher than the measured return due to the internal recirc. The boiler flow temperature and your measured temperature though should be quite close.

 

[ericmark]

You have done well, I tried and failed, by time I had done the last one of eight radiators, returning to first, it was no where near what I had set.

But does it really matter? I reverted to using the TRV report, if the current exceeds the target, then lock shield needs closing a tad. So with electronic TRV heads, may as well use the reported temperature to set lock shield valve.

 

[Johnytuono]

all (if) system boilers have a internal bypass, the displayed and actual boiler temperature will always be higher than the measured return temperature, I have seen numbers on here of the boiler return being up to 7C higher than the measured return due to the internal recirc. The boiler flow temperature and your measured temperature though should be quite close.

This is at the rad I'm measuring John
Boiler flow is set at 60c but the radiator flow pipe (even on the very first rad) is around 51c, surely it should be about 60c, otherwise, if my rads were specced at Delta 50c (75/65c) the boiler flow temp would have to be ridiculous at about 85c in order for the temps and delta at the rad.
I can't understand how my rad mean temp can be higher than the actual flow temp at the rad unless the Microbore pipe is somehow affecting it. I'm running pump speed 3 btw.

 

[Johnytuono]

You have done well, I tried and failed, by time I had done the last one of eight radiators, returning to first, it was no where near what I had set.

But does it really matter? I reverted to using the TRV report, if the current exceeds the target, then lock shield needs closing a tad. So with electronic TRV heads, may as well use the reported temperature to set lock shield valve.

yep, I'm wondering wether I might be best just making sure all rads (apart from one undersized one) have the same mean temperature of 52c (boiler flow 60c).
I've even tried all l/s fully open and control the heating just by the TRV's.
Balancing doesn't seem to give me any real savings, does my head in

 

[Johntheo5]

What make model age boiler have you got? Some of the more modern Vaillants can be run on return temperature control by controlling the circ pump speed.

 

[ericmark]

What I found the hard way, i.e. I got it wrong to start with, is a TRV takes time to open and close, so first thing in the morning, wall thermostat and programmer turned on boiler, and living room radiator got really hot, before the TRV had chance to close, then the sun came out, shining through bay windows, and combination of hot radiator and sun, resulted in measuring 32°C in the living room. After setting lock shield still living room with sun could hit 26°C when set to 22°C but it was a big improvement. Other rooms without bay windows also had a small problem, set to 22°C at 7 am, it was 11 am before it reached 22°C, so cheated, set to 24°C at 7 am then 22°C at 8 am, and it was at 22°C at 8 am.

But once set, the target never exceeded the current, and unlike shown the rooms were spot on, but the same method has not worked here, the thermometer on table says 20.1°C for same room, the wall thermostat (Wiser) shows 20.5°C and other TRV head 21.3°C so same room 18 to 21.3°C. Two radiators set at 90° to each other do not help getting a thermal flow, earlier today did the same readings and that was completely different, and hall showing 15°C (TRV) and 17°C wall thermostat (Nest Gen 3).

So not all homes work out the same, this house oil fired boiler not a modulating type, parents house gas boiler condensing and modulating, and in there house setting the lock shield to stop TRV over shooting worked A1, in this house it did not.

This is why this house has 10 electronic TRV heads, because they worked so well with late parents house, they have saved me money, as only rooms used are heated, but do not work as well with on/off boiler as they did with a modulating boiler.

 

[Johnytuono]

WB 30 si compact about 10 years old, don't think there is a stand alone outdoor weather sensor tat I can use with my Nest, I think I have to buy the Sense or Wave, I can't remember.
What I do know is that when the boiler modulates to minimum output (6.9kw) on pump speed 3 the delta goes to a steady state of around 5c no matter what my rads are balanced to.
I have about 9.2 kw of radiators (8), the pumps is a 15/60. If I set the pump speed to 2, I lose a couple of degrees on my index rad at the flow pipe and the boiler delta eventually steadies at about 7c after it modulates.
I have been trying to suss this out for about 3 years...unfortunately...

 

[Johnytuono]

What I found the hard way, i.e. I got it wrong to start with, is a TRV takes time to open and close, so first thing in the morning, wall thermostat and programmer turned on boiler, and living room radiator got really hot, before the TRV had chance to close, then the sun came out, shining through bay windows, and combination of hot radiator and sun, resulted in measuring 32°C in the living room. After setting lock shield still living room with sun could hit 26°C when set to 22°C but it was a big improvement. Other rooms without bay windows also had a small problem, set to 22°C at 7 am, it was 11 am before it reached 22°C, so cheated, set to 24°C at 7 am then 22°C at 8 am, and it was at 22°C at 8 am.

But once set, View attachment 426451 the target never exceeded the current, and unlike shown the rooms were spot on, but the same method has not worked here, the thermometer on table says 20.1°C for same room, the wall thermostat (Wiser) shows 20.5°C and other TRV head 21.3°C so same room 18 to 21.3°C. Two radiators set at 90° to each other do not help getting a thermal flow, earlier today did the same readings and that was completely different, and hall showing 15°C (TRV) and 17°C wall thermostat (Nest Gen 3).

So not all homes work out the same, this house oil fired boiler not a modulating type, parents house gas boiler condensing and modulating, and in there house setting the lock shield to stop TRV over shooting worked A1, in this house it did not.

This is why this house has 10 electronic TRV heads, because they worked so well with late parents house, they have saved me money, as only rooms used are heated, but do not work as well with on/off boiler as they did with a modulating boiler.

If I had an electronic TRV head on the rad in my bedroom would it switch the heating on though, say I wanted the room warm just before going to bed. What I have to do now is put the room stat up a couple of degrees from normal and set the whole system to come on for an hour (Nest doesn't do half hours and there's no boost option).

 

[endecotp]

the flow pipes show 51c and the return 39c yet the rad. mean temperature is around 50/52c

What exactly do you mean by, and how are you measuring, the "radiator mean temperature"?

 

[ericmark]

I have only just tried, yes your right, 1 hour min for heating, ½ hour for water.

I had a problem with Nest Gen 3, one it would not work with Energenie since Google took over, two when it did it worked the wrong way around, and three my hall cools too slowly and if I use a USB cradle it will not work with a power cut.

So I now have Drayton Wiser as well, both in parallel to each other, and the Drayton Wiser allows multi thermostats to connect to the same hub, does not matter if that thermostat is wall mounted or a TRV, did have a problem with TRV head out of range, so use a socket adaptor to relay the signal, but now if wife's bedroom is too cold, it will fire the boiler, and her room always cooler than mine, so a cheap eQ-3 TRV head works great in my bedroom, as her head has already fired the boiler.

There is a small problem, 7 radiators are on outside walls, too expensive to move them, so in general before heating has started to run, and so we have a thermal air circulation, the TRV is showing a lot colder than the room really is.

With a non linked, not really a problem, if set at 18ºC and the wall is at 16ºC it will not fire the boiler, so not running a boiler because of one cold wall, but if linked it will fire the boiler, the Wiser does allow use of a wall thermostat and TRV head in the same room, and the wall thermostat then controls the TRV head, but then looking at a lot more money to set it up.

With non linked heads to boiler, our Kasa head can still link to a wall sensor or thermostat, so again true room temperature not wall temperature, but not bothered doing that. I was going to use Kasa, (TP-Link same as Tapo) but found the thermostat to connect to boiler is only done in a hard wired version, the sensors are battery, but not the thermostat/hub. So went for Wiser, which does seem to work very well. Not tried Wiser geo-fencing, told it is IFTTT, so will only work with one phone, Nest Gen 3 geo-fencing is useless, I have tried that, turns off OK, but only turns on again when you are within ½ mile of the house.

For geo-fencing to work, it needs to reduce the setting by ½ºC every 10 miles away from home, so it has time to recover, maybe some do that, told Tado is good, but never confirmed if it does work that way?

That's how I ended up with useless Nest, son had it and said how good it was, and I just believed him without checking. I have meant to ask him if he needed to change it, has his Gen 2 no longer supported.

 

[Spherehopper]

You still need to adjust the lockshield even if you have a TRV to balance the system. It's still possible for a rad to be "greedy" as it presents less impedance to the flow of water and deprive others further downstream of any hot water if the TRV opens calling for heat and the rad is only dropping, say 2C and hogs all the hot water, sending most back to the boiler which then thinks the system is satisfied.

Balancing CH systems properly takes ages which is why most plumbers don't do it. I've recently balanced my 11 zone UFH/ASHP system and already notice the difference (5C drop on the manifolds).

 

[Johntheo5]

@Johnytuono why not try it based on the outside temperature model, open all the lockshield valves fully, they can then be throttled individually later, then just keep reducing the boiler target flowtemp which reduces mean rad temperature and obviously the return temperature necessary for effective condensing and increased boiler efficiency.

 

[danfre]

Condensing boiler's should have a differential of around 20 degrees for the boiler to be in optimum use. Flow and return on radiators