Boiler modulation and balancing

[Johnytuono]

I was reading an article about balancing and it said to balance to get Delta 20 whilst the boiler is at full output or maybe it will only show Delta 20c at full output, otherwise, if it modulates down to the minimum (6.9kw from 28kw i.e. 4:1 in my case), then only that delta will be shown at the boiler flow/return i.e. 5 C difference, which is what I get btw no matter what I do (even when the rads are balanced to 12C).Nothing is short circuiting, even the towel rad is balanced and the internal ABV is not faulty (according to the engineer anyway). I have also read a few posts where people are only getting 5C at the boiler despite balancing. Am I interpreting this correctly?
I have a minimum boiler kw setting on my WB of 6.9 kw (which it is set to), why is there an option to increase the power then as surely the lower modulation the better?
My rads total about 9 kw

 

[ericmark]

I tried to use an aim at surface type of thermometer. It did not work, I have a differential thermometer, but I have lost the sensors, and with electronic TRV heads, I really don't need to measure, it shows target and current, and unless there is some other form of heating, current should never exceed target, so if it does, I just throttle back a little on the lock shield valve.

We balance radiators when using TRV heads for two reasons.
1) So with all radiators heating, each radiator gets its fair share.
2) So the radiator heats up slow enough for the TRV to react in time to stop any hysteresis.

In an office complex, every room needs to be up to temperature within an hour, however this is not the case in the home, so reasonable to have the boiler with a two zone home, only large enough to reheat one zone in the hour, which would mean radiators kW output needs to be around double the output of the boiler, or likely a mark/space ratio would be needed to reduce output enough, which would in turn result in a high hysteresis.

I look at my own home, only the living room needs to be heated to 22°C, other rooms can be cooler, and the living room has around 4 kW of radiators, and the boiler is 20 kW, so it turns off, for far too long, and I get an unacceptable hysteresis, so to allow for the hysteresis the room is set to a higher temperature than really required. The only way I could increase radiator size, with furniture in the room, would be fan assisted radiators, so I put up with undersized radiators.

 

[denso13]

I was reading an article about balancing and it said to balance to get Delta 20 whilst the boiler is at full output or maybe it will only show Delta 20c at full output, otherwise, if it modulates down to the minimum (6.9kw from 28kw i.e. 4:1 in my case), then only that delta will be shown at the boiler flow/return i.e. 5 C difference, which is what I get btw no matter what I do (even when the rads are balanced to 12C).Nothing is short circuiting, even the towel rad is balanced and the internal ABV is not faulty (according to the engineer anyway). I have also read a few posts where people are only getting 5C at the boiler despite balancing. Am I interpreting this correctly?
I have a minimum boiler kw setting on my WB of 6.9 kw (which it is set to), why is there an option to increase the power then as surely the lower modulation the better?
My rads total about 9 kw

Are all the radiators heating up or are you having issues?

 

[Johnytuono]

Are all the radiators heating up or are you having issues?

All heating up but at different times.i.e. the one next to the boiler then the water loops upstairs and then feeds the hallway and living room/lounge. I've shut the l/s about 1/4 (apart from one bedroom which I want heating up earlier) and they all now heat up more or less the same time. Deltas range from about 14C to 5C (the bedroom I mentioned earlier). The thing is the last 2 in the lounge (big Type 22's where the room stat is in one of the rooms ) have their l/s FULLY open yet the Delta is naturally about 14C. The boiler, after it has run at the flow temp for a while (currently trying 60C) eventually settles to 5C Delta on the return (it shows on the menu screen). So, no matter what I do, the Delta is very narrow, that's why I was wondering if (like I've read) the boiler modulating has decreased the Delta. It also means that even if I used a 75C flow for example and balanced to 20C to get a return of 55C, then the boiler would only show 5C (i.e a big 70C temperature on the return !!) . It seems that all I've actually achieved at balancing is to alter the heat up ordering and not saving on the condensing side. Pump has 3 speeds, it is on 3 because the last rads don't seem to get the full flow temp. Also, why would there be an option to change the minimum output as surely minimum kw, for modulation purposes, is better? I can see how it would be useful to minimise the MAXIMUM output (but mine hasn't got that option)
Sorry for the long post

 

[Johnytuono]

I tried to use an aim at surface type of thermometer. View attachment 403933 It did not work, I have a differential thermometer, but I have lost the sensors, and with electronic TRV heads, I really don't need to measure, View attachment 403934 it shows target and current, and unless there is some other form of heating, current should never exceed target, so if it does, I just throttle back a little on the lock shield valve.

We balance radiators when using TRV heads for two reasons.
1) So with all radiators heating, each radiator gets its fair share.
2) So the radiator heats up slow enough for the TRV to react in time to stop any hysteresis.

In an office complex, every room needs to be up to temperature within an hour, however this is not the case in the home, so reasonable to have the boiler with a two zone home, only large enough to reheat one zone in the hour, which would mean radiators kW output needs to be around double the output of the boiler, or likely a mark/space ratio would be needed to reduce output enough, which would in turn result in a high hysteresis.

I look at my own home, only the living room needs to be heated to 22°C, other rooms can be cooler, and the living room has around 4 kW of radiators, and the boiler is 20 kW, so it turns off, for far too long, and I get an unacceptable hysteresis, so to allow for the hysteresis the room is set to a higher temperature than really required. The only way I could increase radiator size, with furniture in the room, would be fan assisted radiators, so I put up with undersized radiators.

So, you're saying that you overheat the living room so that it then cools to whatever temp you find acceptable?

 

[denso13]

and they all now heat up more or less the same time.

That would do for me.

 

[Johnytuono]

That would do for me.

Yeah, maybe I'm looking into it too much. Does it sound 'right' though that I've deliberately left one bedroom more open than the final (end of line) rads in order for it to heat up first? As an aside, so, even if people balanced to a set Delta, it doesn't necessarily mean that the order of heating up is even?