Balancing rads - increased cycling/failed starts after balancing

[-rick-]

33 minutes ago, marshian said:

If the CH light is not going out then it's not interveening

 

By the CH light do you mean the flame icon? I don't tend to look at the thermostat but rather the app, but it has a representation of the same.

 

It doesn't appear to be directly connected to the opentherm requests. I've seen plenty of times when the boiler is active (and cycling) when the flame icon is off. I initially thought it was a bug (and my boiler was ignoring opentherm requests) but after a decent amount of observation I think the flame icon represents not matching the setpoint. ie, in a traditional on/off system, when the thermostat calls for heat. But with Opentherm it's trying to modulate the flow to maintain the set point to a much more precise degree (within 0.1C) and as long as it considers itself as successfully regulating that then the flame is off.

 

The relay signal to the boiler has stayed on all day barring once around dinner time when cooking pushed the temp a fair bit above set point at which point the relay switched off.

 

What I think is happening in my case is that Wiser adjusts the setpoint it wants from the boiler constantly based on the heating demand % supplied by the thermostat. Wiser wants the boiler on all the time to maintain the set point. The boiler is willing to exceed the set point by a certain amount but if it goes over that then it shuts off. I think there's more to it than this but feels like the main issue.

 

33 minutes ago, marshian said:

My solution to the issue was to set the room stat or a smart TRV to a higher target temp that cannot be achieved - that way the Wiser Hub doesn't get to screw around making the boiler cycle or stopping it mid burn (which is what it did with my old boiler when I had it set up with a really long anticycle timer to give the rads chance to dump the heat)

 

I assume you mean since you moved to weather comp and not using opentherm at all. That's not really something I want to do (given the amount of disruption running the cable would involve) and I'm not sure weather compensation would help when the CH system can't dump out the heat from the boiler at minimum modulation.

Edited Monday at 23:31 by -rick-

[marshian]

1 minute ago, -rick- said:

By the CH light do you mean the flame icon? I don't tend to look at the thermostat but rather the app, but it has a representation of the same.

 

It doesn't appear to be directly connected to the opentherm requests. I've seen plenty of times when the boiler is active (and cycling) when the flame icon is off. I initially thought it was a bug (and my boiler was ignoring opentherm requests) but after a decent amount of observation I think the flame icon represents not matching the setpoint. ie, in a traditional on/off system, when the thermostat calls for heat. But with Opentherm it's trying to modulate the flow to maintain the set point to a much more precise degree (within 0.1C) and as long as it considers itself as successfully regulating that then the flame is off.

 

The relay signal to the boiler has stayed on all day barring once around dinner time when cooking pushed the temp a fair bit above set point at which point the relay switched off.

 

What I think is happening in my case is that Wiser adjusts the setpoint it wants from the boiler constantly based on the heating demand % supplied by the thermostat. Wiser wants the boiler on all the time to maintain the set point. The boiler is willing to exceed the set point by a certain amount but if it goes over that then it shuts off. I think there's more to it than this but feels like the main issue.

 

No I mean the CH light on the Hub - flame on the app is just saying room is not at target temp - flame out says at target temp

[marshian]

3 minutes ago, -rick- said:

Then not really using Opentherm at all and relying on TRVs/max flow temp to limit room temp?

 

Old boiler couldn't support Open Therm - so yes I was managing room temps via TRV's however I had one room that needed much longer than all the others to hit target temp - so when other rooms reach temp and the Wiser Hub stopped the boiler it buggered up any chance of getting the one room to actually reach the temp required

[-rick-]

1 minute ago, marshian said:

No I mean the CH light on the Hub - flame on the app is just saying room is not at target temp - flame out says at target temp

 

Yeh that's basically been on all day.

[marshian]

1 minute ago, -rick- said:

 

Yeh that's basically been on all day.

 

If it's on and not clicking off then the cycling is down to the boiler

[-rick-]

1 minute ago, marshian said:

If it's on and not clicking off then the cycling is down to the boiler

 

Somewhat, it's down the the interaction between the boiler and how it meets the opentherm setpoint (which is set by Wiser and changed constantly).

 

When Wisers 'Heating Demand' measure started oscillating so did the boiler. I changed the set point then to force a long continuous burn and after I dropped the set point again we are now back to no oscillation and less cycling. Now I imagine there could easily be a feedback loop where the boiler cutting out due to insufficient modulation for my CH system triggers the oscillation. My comment earlier was that wiser doesn't offer a way to rate limit or filter this setting which makes cycling more likely. Opentherm also offers a way of turning the flame on and off remotely without using the relay. I don't know if wiser is using that ability or not.

 

This is all somewhat off-topic for this thread though. I want to optimise what I have to the best extent possible physically, then explore wiser more. My plan is:

1. Complete tweaking balance, etc

2. See how wiser works if asked to just manage the temp in the warm part of the home. (it should be able to satisfy that with lower temps and the colder unregulated rooms will act as a bigger heatsink to prevent cycling).

3. See what difference these fan kits I've ordered make (GPT suggests they could double the heat output of the radiators at high flow temps but don't help that much at low flow temps).

4. By the time I've done this I will have had more time to think about radiators. Looks like I can replace the two vastly undersized ones for ones with 2.5x the output for about £150 if I don't mind sacrificing matching the existing. I can't justify the cost of matching existing but moving to the cheap ones might get payback (and if I keep the old ones I can always swap them back in if the new ones cause issues with buyers/valuation).

5. If I do upgrade radiators then I go through the above again

6. If still having problems talk to wiser

 

Good news so far is that if I've done my sums right my gas usage is only about 50% more than normal heating the whole place vs what I was doing before. Given the heating is on for >14 hours a day vs maybe 6 before this doesn't seem to bad (more than I'd like long term though). This means I'm not in a huge rush to finalise this process and can take the time to try things out

[MrPotts]

15 hours ago, -rick- said:

Since yesterday, I've opened up various valves, the two most distant radiators fully open, and opened the towel rails a bit.

 

The system manages very long burns if allowed a higher temperature and it's not close to set point, but as it gets close to set point it drops the temperature and cycles more. By staring at the Home Assistant graphs, I'm still seeing some very short cycles but a lot of them I can connect to Wiser demand changing mid flow (which seems like a bad design from them). BTW I do have it set up as Oil boiler, which should limit things to 3 cycles per hour, but obviously getting a lot more than that.

 

You are looking at the wrong sensor for for when Wiser requests the boiler to fire, you should be looking at “Wiser Heating” sensor.

Edited 18 hours ago by MrPotts

[-rick-]

3 hours ago, MrPotts said:

You are looking at the wrong sensor for for when Wiser requests the boiler to fire, you should be looking at “Wiser Heating” sensor.

 

I think I covered this already, that sensor (reported as 'Wiser Heating Channel 1' for me) is on all the time (except during a short window after the temp exceeded set point due to cooking). On the graph in the post out quoted that sensor is shown just above where I snipped the screenshot.

 

A few days ago I limited the boiler max temp to 50C and during that time it wasn't enough to heat the flat so the wiser heating demand was above steady state. In that condition, the boiler attempted to heat and cycled according to the limitations of my CH systems ability to transmit heat and the minimum modulation of the boiler. That cycling was very orderly with consistent on/off times and about 6.5 cycles per hour.

 

Since then, I've upped the boiler max temp which has allowed wiser to reach setpoint ang obtain tight control (varying the boiler setpoint via opentherm). However, this seems to have lead to a significant increase in cycling, especially very short ones as explained above.

 

Fundamentally, I think the cause is that my CH system is badly sized and can't handle steady temp running. But equally, Wiser could likely be designed to handle this sort of system more gracefully.

[marshian]

2 minutes ago, -rick- said:

Fundamentally, I think the cause is that my CH system is badly sized and can't handle steady temp running. But equally, Wiser could likely be designed to handle this sort of system more gracefully.

 

I'd have to agree with that - boiler total kW oversized with a relatively high lowest modulation and rads that need higher flow temps to meet the heating needs of the property with a very low delta between flow and return

 

https://www.heatgeek.com/do-we-really-need-dt20

 

I think you'd have a huge change in house/room comfort and system performance going to conventional T22 rads sized for a less than 50 deg flow temp

 

Is it a possibility to swap the rads you have around to increase the sizes in some rooms and reduce the expense of purchasing more rads for all rooms?

 

I'd be very concerned about a 50% increase in gas usage for moving from scheduled to 24/7 (ish) I reckon mine is a good deal less than 10% increase for a move from scheduled to 24/7 (and that's with a boiler that miss-behaves occasionally)

[-rick-]

4 minutes ago, marshian said:

I think you'd have a huge change in house/room comfort and system performance going to conventional T22 rads sized for a less than 50 deg flow temp

 

If I was happy running as things are now (with associated bills and short cycling) then I think the comfort issue is mostly addressed. Even with the issues Wiser maintains the temp to within 0.2C and heating the whole flat feels much more comfortable than leaving some rooms unregulated. With my previous setup, the room I spend my time was kept at a reasonable temp but the heatloss to the cold room next door, and through the screeded floor meant that there was quite a temp gradiant which is not particularly comfortable (cold feet). Floor ~19-20C, desk height 23C.

 

4 minutes ago, marshian said:

Is it a possibility to swap the rads you have around to increase the sizes in some rooms and reduce the expense of purchasing more rads for all rooms?

 

I could swap one 800x500 with one 800x600, without changing pipe positions. Doesn't seem worth it given I think the its the coldest room with the 800x500 rads (2) and I think it's heat loss is well over 2kw (vs current spec rads rated at 1100W total at dT-air 50).

 

My best bet, if I do anything, is replacing the two 800x500 in the cold room with 800x600 T22 or 800x700 T22. I don't think that gets me to true low temp heating but I think it might by the boiler enough room to run sensibly (thinking running 50% duty cycle, lowest modulation = 3kw output). Replacing the 1000x600 in the kitchen with a T22 might be needed too. But so far all the other rads seem to be maintaining temp in their areas while being barely on.

 

Having said that, given I'm selling as soon as I can, I can't justify the cost of matching existing and I'm really worried that replacing these rads with something obviously different (and cheaper) will raise issues when selling. I've already lost 6 figures off the value of this place due to cladding issues and people in the building are getting to the point of selling at firesale prices (not much more than they paid in 2006) because they can't get BTL mortgages and no-one wants to buy after 100+ viewings.

 

4 minutes ago, marshian said:

I'd be very concerned about a 50% increase in gas usage for moving from scheduled to 24/7 (ish) I reckon mine is a good deal less than 10% increase for a move from scheduled to 24/7 (and that's with a boiler that miss-behaves occasionally)

 

It's not quite the same. It's moving from running the heating an hour at a time when I'm cold in one room, and not worrying about the temp in the other rooms, to regulating the temp in all rooms. So the increase is more than just running longer, its also heating a much bigger area. Gas bill this month prior to this experimentation was ~£60 so not a huge amount compared to some.

[JohnMo]

19 minutes ago, -rick- said:

Fundamentally, I think the cause is that my CH system is badly sized and can't handle steady temp running. But equally, Wiser could likely be designed to handle this sort of system more gracefully

Not sure any, especially an externally controller, would be able do anything graceful, with a boiler and heating system mismatch.

 

18 hours ago, -rick- said:

3. See what difference these fan kits I've ordered make

They should effectively act, the same way as if you have increased, the radiator a size, they will force heat transfer.

 

18 hours ago, -rick- said:

gas usage is only about 50% more than normal heating

 

26 minutes ago, -rick- said:

cycling was very orderly with consistent on/off times and about 6.5 cycles per hour

Would imagine increased gas consumption and cycling are closely related.

 

15 minutes ago, marshian said:

I'd be very concerned about a 50% increase in gas usage for moving from scheduled to 24/7 (ish) I reckon mine is a good deal less than 10% increase for a move from scheduled to 24/7

Would agree

 

I wonder if you would actually use less gas consumption, by making the boiler run harder. So not opentherm, but run on/off thermostat at around 0.5 to 1.0 hysteresis.  Then fiddle with flow temp to get boiler to run the whole call for heat period. But don't run any large setbacks so effectively run 24/7. Then modify your system as needed to work well. Then bring OT back online.

 

Can you or have you range rated the boiler output down?

 

 

[-rick-]

1 minute ago, JohnMo said:

I wonder if you would actually use less gas consumption, by making the boiler run harder. So not opentherm, but run on/off thermostat at around 0.5 to 1.0 hysteresis.  Then fiddle with flow temp to get boiler to run the whole call for heat period. But don't run any large setbacks so effectively run 24/7. Then modify your system as needed to work well. Then bring OT back online.

 

I expect so and that is one of the things I will try. I've also thought about just using the wiser scheduler to increase decrease the set point by 0.5C very frequently to keep the wiser outside the oscillation area.

 

1 minute ago, JohnMo said:

Can you or have you range rated the boiler output down?

 

I don't believe thats possible. The boiler is pretty basic.

[MrPotts]

I think Opentherm can be very hit or miss due to the “standard” not being particularly standardised amongst boiler manufacturers. I would second @JohnMo suggestion and try running wiser in on/off mode, at the end of the day heating is about comfort not necessarily about running the latest flavour of heating control.

 

BTW I forgot when posting my comment that you were running OT, in that case I would expect Wiser to be constantly firing the boiler and the cycling periods to only be relevant to on/off mode.

[marshian]

49 minutes ago, -rick- said:

I could swap one 800x500 with one 800x600, without changing pipe positions. Doesn't seem worth it given I think the its the coldest room with the 800x500 rads (2) and I think it's heat loss is well over 2kw (vs current spec rads rated at 1100W total at dT-air 50).

 

My best bet, if I do anything, is replacing the two 800x500 in the cold room with 800x600 T22 or 800x700 T22. I don't think that gets me to true low temp heating but I think it might by the boiler enough room to run sensibly (thinking running 50% duty cycle, lowest modulation = 3kw output). Replacing the 1000x600 in the kitchen with a T22 might be needed too. But so far all the other rads seem to be maintaining temp in their areas while being barely on.

 

Ouch if your heat loss in a room is well over 2kW and you current spec rads are 1100w at DT50 the the rad spec was bloody terrible for a condensing boiler - looks like the builders choose fancy over functionality and cheaped out on the size to minimise costs

 

You'd need rads rated for 5500w in total at T50 to run them at around 50 deg flow temp

 

I'm not even sure you can get K33's in 600 width that will hit that output.

[-rick-]

1 hour ago, marshian said:

Ouch if your heat loss in a room is well over 2kW and you current spec rads are 1100w at DT50 the the rad spec was bloody terrible for a condensing boiler - looks like the builders choose fancy over functionality and cheaped out on the size to minimise costs

 

They have put bigger radiators in the kitchen area which also has high heat loss. I suspect it's more of a screw up than deliberate undersizing. When I bought there was a big delay because the plans on the lease didn't reflect reality so had to be amended. So I think the design of my flat was changed at a rather late stage and I'd guess heating not reviewed after.

 

1 hour ago, marshian said:

You'd need rads rated for 5500w in total at T50 to run them at around 50 deg flow temp

 

Yeh, I don't think I'm going to be making the changes necessary to run at low temp all the time. If I change the rads I'd be aiming for it to be enough for low temp heating a large chunk of the time but require high temps during the coldest.

 

1 hour ago, marshian said:

I'm not even sure you can get K33's in 600 width that will hit that output.

 

800 wide, 600 tall.

[marshian]

40 minutes ago, -rick- said:

800 wide, 600 tall.

 

Ahh my error

 

800 wide 600 tall K3 Steelrad is 1911 w at T50

 

T50 to T30 = 1911 x 0.515 = 948 w so even two of them won't crack 2 kW heat loss although you could run them a little warmer

 

800 wide by 700 tall K3 Steelrad is 2170 at T50 so 1117 w at T30

 

OT

 

My K33 1400 x 700 is rated at just over 4kW at T50 - it'll happily keep the room at 19 deg C running WC flow temps

 

I'm running it at DT11................... I need 660 w in that room

 

Add two squidgy people in the mix and the temp climbs to 20.5 (which is about the limit of my comfort and the bottom of Mrs Alien's accept zone)

[-rick-]

18 minutes ago, marshian said:

800 wide 600 tall K3 Steelrad is 1911 w at T50

 

T50 to T30 = 1911 x 0.515 = 948 w so even two of them won't crack 2 kW heat loss although you could run them a little warmer

 

800 wide by 700 tall K3 Steelrad is 2170 at T50 so 1117 w at T30

 

If I decided I wanted to target full low temp system (ie, support low temps year round) I expect I would look to install wider radiators rather than go to triples. Triples will eat into the room in a negative way, longer rads not so much. But would involve redoing the pipework around the rads (and breaking into the plasterboard to do it). Having said that at this stage I think it's very unlikely I'd go that route.

 

15 minutes ago, marshian said:

20.5 (which is about the limit of my comfort and the bottom of Mrs Alien's accept zone)

 

Sounds like a recipe for harmony!

[marshian]

34 minutes ago, -rick- said:

If I decided I wanted to target full low temp system (ie, support low temps year round) I expect I would look to install wider radiators rather than go to triples. Triples will eat into the room in a negative way, longer rads not so much. But would involve redoing the pipework around the rads (and breaking into the plasterboard to do it). Having said that at this stage I think it's very unlikely I'd go that route.

 

I do get that but if you are fitting longer rads you can always raise the rads slightly and run the pipes from the original exit along the back of the rad hidden from view 

 

Issue for me with the K33 was wall space was at a premium - french doors at one end - fireplace in the middle on one side furniture on the other side - leave one wall with a doorway to fit a rad that just meets the requirement... It's thickness wasn't a problem as nothing else is there.

[marshian]

39 minutes ago, -rick- said:

1 hour ago, marshian said:

20.5 (which is about the limit of my comfort and the bottom of Mrs Alien's accept zone)

 

Sounds like a recipe for harmony!

 

Oh it isn't