Heating power percentage and calling for heat
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@eezytiger, if you are able could you clarify a couple of things relating to your setup. If you only have 1 srt which is actually able to fire your boiler, then the maximum heat demand you could ask of the boiler via Tado would be 3 wavy lines from the aforementioned srt, is that correct? If all your other srts are independent and requesting heat at the same time as your controlling srt, will this be an additional demand on the boiler? ie are the demands of more than 1 srt cumulative with respect to the boiler regardless of whether or not a particular srt is able to actually tell the boiler to fire up? If that IS the case, then would Tado need to be set up in relay mode rather than digital ems mode for this to work effectively?
l currently am set up for ems digital control via an extension kit and my current understanding is that if all my srts are able to fire the boiler, obviously the boiler responds differently dependant on the number of srts demanding heat. Not sure how my boiler would react to only 1 srt instructing it to fire up, but perhaps another 6 independent srts looking for heat at the same time. Hope you’re following me here as I’m no expert!
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@Notascoobie I am using relay operation. I've tried eBus three times and ended up returning to relay each time within a few days. EBus did not work efficiently for me, with short cycling, but I may have misunderstood the reasons. I assumed the problem was related to flow temperature, but it may have been due to Tado's short boiler firing cycles, which I've had revised following contact with Tado Support. Relay is working well enough that I really don't care to rewire the boiler yet again. Flow temp is manually set to 50C and the boiler just touches that for a few minutes each day. I hardly need weather comp or load comp to reduce it further. Tado turns the boiler off before it gets there, most of the time.
As for the impact of my setup on boiler operation, other than opening and closing the independent valves as necessary, it appears to me that the boiler demands are made purely to satisfy the needs of the one SRT connected to the zone controller. Tado shows no interest in the fact that I might have eight thirsty radiators waiting in the wings. It heats the one radiator until its demands are satisfied, then shuts off. Other rads take whatever heat they can when it is available in the system. This will slow the rate of heating of the "ZC Radiator", so the boiler stays on longer as heat is shared with the extra rooms, but also my return temp is lower as there are more rads emitting heat.
How well this works depends very much on choosing the right room to be in charge of boiler switching, and in making well considered tweaks to the relative temperatures of all rooms. It is entirely possible that some rooms will end up a bit colder than set temp, but that's OK. The set temp for these rads is intended as an upper limit, not a mandatory target to be achieved.
If anything gets too far out of whack I might need to review my configuration, but it's working OK so far. Colder weather to come might need some changes, maybe not.
I hope that clears things up.
FWIW I'm still keeping consumption well below last year's equivalent monthly numbers, every single month so far, so I'm happy. :-)
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@GrayDav4276 Nothing that deserved the post being deleted, or so I thought, basically a break down of my findings of my test over the past few days. To but put it simply, I found little correlation between the tado˚ demand bars (the wavy lines) and boiler flow temps, at least when using "OpenTherm and modulation".
For example the demand line could be 1 and flow temp on boiler could be 26-32˚c, 2 and flow temp on boiler could be 30-48˚c, 3 and 42˚c-max flow, So just because you see 2 bars on tado info screen does not mean the demand on boiler is higher than it could be on 1 bar demand, or same between 3 and 2 bars.
I also found that if your are using "Digital Links" to control boiler the WTS needs time to adjust the AI to become stable, if you change ANYTHING in schedules (temps or times, etc).
I gone from this:
to this:
Using setback temps and adjusting my schedules, you can see Monday 28th is a colder day and still used less gas, but I have no way of know what boiler demand was apart from my GAS Meter readings.
And I concluded with it would be more beneficial to show the "Flow Temp" of boiler in graphs, and like to my request for that. see example for what i mean below.
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@eezytiger if you change from "Relay" to "Digital" I have found it takes at least 3-4 days for the WTS AI to become stable. After all the "tweaking" I have done lately with my setup, it has taken days for it to stabilise again. Might be worth another go, as you can see in my above post "modulation" really can save you money if done correctly. ATM my boiler is only reaching 30˚c when controlling setback temps, and last night it reached -1˚c and from 22:00 - 07:45 it only used 5.016KWh in gas to keep setback temp of 17.5˚c.
Here is the graph from my media room WTS, all my rooms have full boiler control with WTS's.
here is my worst room for controlling temps,
but even with demand for last night setback as it reached -1˚c, as I said above it only used 5KWh in gas, ATM with demand on 2 wavy lines boiler flow temps is 38˚c.
edit:
forgot to say, my return flow temps and pretty much the same as the flow temps, so boiler is mainly just running the pump, and on the odd occasion gas kicks in to raise the flow temp back to 38˚c as need.
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@andyblac Unfortunately, with 9 kW minimum output, it is impossible for my boiler to hold a low flow temp in the 30s. It will continue rising for as long as it is lit. This is especially so when the house is more or less up to temperature and the water in the system is already in the mid to high 20s, if not higher.
With eBus my boiler was repeatedly shutting down with, for example, Tado requesting 33C and the boiler rising to, say, 36C. I assumed the shutdown was due to the temperature overshoot, but it might have been due to the four minute minimum burn intervals set by Tado.
So there is nothing to be gained by wishing for lower flow temperatures with eBus when the boiler can't maintain them. It will only result in short cycling at worst or nothing useful at best. I need a boiler that can modulate down to around 2 W. So far this season even that would be excessive for continuous burn on all but two days.
This is exactly the problem with relatively old and oversized boilers.There is a Veissman that can drop as low as 2.5 W. WB can go as low as 3.2 W. But I'm not swapping a perfectly functional boiler that already delivers low bills until it NEEDS replacing. Then, maybe, it will be time for a heat pump.
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@eezytiger hmm, so your boiler can't just run in pump only mode?, my Baxi 836 does not seem to have a problem running at as low as 25˚c with no flame icon on boiler, it would come on for about 1-2 mins then just turn flame off and run pump only for 30 mins or so, or till target was reached.
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After finishing a burn the pump will continue running for five minutes to remove all residual heat from the heat exchanger. Then it will enter an anti-cycling mode for a time period depending on various factors, deliberately to stop wasteful short cycling.
It cannot drip feed heat on and off while continuously running the pump. So it is 9 kW or nothing. With the new ten minute minimum burn times from Tado it produces (OK, consumes) around 1.8 kWh with each burn, with longer burn times producing even more energy.
Typically, with maintenance heating of steady temps it might only deliver a single 10 minute burn every hour or even couple of hours.
Here's my gas consumption profile yesterday. There was a shower and some gas cooking to confuse things, but basically the boiler is off far more than it is on. You will see that almost every burn is just under 2 kWh. Then a large gap until the next burn.
Total kWh yesterday was 36, so an average of 1.5 kW required overall. 9 kW output from the boiler is 6X more than required. No choice but to cycle. I'd love a low output boiler, but I work with what I have.
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@eezytiger Thats interesting, so my boiler must be able to modulate the burner, I have been trying to find the minimum KW output for my boiler but I have been unable to find it. My boiler seems happy just to chug along at 25-40˚c all day with no issues. I see the pros and cons of low and slow vs short high bursts (like yours), mine will use more electricity for running pump for long periods, compared to yours, but I assume it is less stress on boiler ?
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@andyblac My boiler can modulate output. Full power is 24 kW for CH. After an easy start to the burn it would ramp up to 24 kW at the beginning of each cycle on default settings, increasing flow temp rapidly until it reached target. Then it would reduce output power as necessary, down to its minimum of 9 kW, until it could no longer stay below the flow target temp (+ c.2C overshoot), at which point it would shut off, pump overrun, anti-cycle.
It does not pulse the burner like yours.
I have range rated the boiler to the minimum 9 kW in the pursuit of low and slow operation as far as I am able. That's the only power output it can operate at, unless I change boiler settings. But I do not need more than 9 kW. 5 kW would keep the whole house sufficiently warm on the coldest winter day in the last five years. Maybe even less with improved insulation and knowledge since then.
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@eezytiger One of my rooms "Front Lounge Extension" has windows and patio doors on the 2 external walls (the last wall is dividing neighbours house and mine, I live in a semi), Even though the windows and patio doors are triple glazed it still looses heat, in dead of winter it can really struggle to reach and keep target temps. ATM I have my MAX Flow Temp set at 65˚c, atm it does not seem to be hitting it, I would really like to lower it to 50˚c, but I know that this room would really struggle to get up to target temps with that flow rate in the dead of winter ( -3˚c / -5˚c).
here is a pic of my graph from last year on a day with outside temps around 0˚c / 2˚c, as you can see the tado demand was at 3 bars for almost the whole day.
edit:
oh and my smart meter does not work in smart mode, I can't get fancy data like from gas meter like you do, I wish I could.
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@andyblac That overnight drop to 10C was tough to recover from. Keeping the heat on, with setback, might permit far less intensive heating and a lower flow temp.
My heaviest gas use in the past year was on 28th November last year, with 83 kWh consumed in 24 hours. But the heating was on 24x7, so the heating demand was spread fairly evenly. Here's my gas consumption back then, averaging less than 4 kWh per hour (2 kWh per half hour interval) overall.
Max outside temp was 4C
And the heaviest gas consumption day in November this year, the 21st, with 63 kWh consumed....
Max outside temp was 8C
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@eezytiger my heaviest gas usage from taking down meter readings was yesterday (as it reached -1˚c here), for that 24 hours i used 41 kWh consumed.. which I don't think is bad ?
Whats was your last for yesterday, and what temp did it get down too ?
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@eezytiger guess I'll see how it goes, next year i am looking at getting the whole outside of house externally insulated and rendered. A friend has had it done and he is still yet to turn on his heating. It is quite expensive to get done about £12-15K, but if it can do that kind of saving it will be well worth it for the long run, the way GAS Prices are going.
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My boiler is antique but it's fully modulating on hot water and CH. Lowest is 9kw. It just pops itself on bypass when it doesn't need the heat and starts heating again when it does again. Late 1970s house with later extension. Cavitiy wall and some of it might be insulated. 20c seems a natural temperature for this house.
Tado is still doing the massive morning hump then keeping a steady temperature. Temperature changes seem to make it odder. The room graphs look weird.
Lounge is independent so it's actually only heating when the Home has a grey bar. It's set to 22c with a 2C off set which keeps the room between 20-21C all day on an actual proper thermometer with just the small of amount of activity shown in the Home graph.
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I thought I would give the @eezytiger method a try but in ems control mode rather than relay control. Up until now the set back temp for my main living area has been 15c which I think has been giving the boiler a lot to do when the heating kicks in proper in the morning. Last night I increased the setback temp to 18c, and that was maintained really well overnight. Between midnight and 7am this morning my smart meter says I've used 14kwh of gas, so 2kw/hr. I'll see what the totals look like at the end of the day, but yesterday was about 68kwhrs for the 24 hrs period before adopting @eezytiger method.0
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A screen shot of the overnight temp in lounge area.0
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I have been researching quite about most of the day, and from what I understand (please tell me if I am wrong), But be careful when setting the MAX Flow temp when your using Tado with Digital Link (OpenTherm, EMS, Etc) as the adjusting the MF, WILL effect the Weather Compensation Curve.
as you can see below the Baxi Weather Compensation Kit says their kits should be used with a curve of 40 to 30, and that has a max flow 80˚c, setting the MF too low will result in the curve being way to low.
so @Jurian what Weather Compensation curve is Tado using ? can we have access to it?, this might be the reason some people are having issue with boilers not firing with low demand.
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I think you’re getting a bit mixed up here. That’s a curve for use when the boiler is using a weather compensation sensor. It doesn’t really apply to load compensation.0
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@johnnyp78 does "load compensation" not have the same type of curve ? that could be linked to Flow Temp
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No, load compensation varies by room so there won’t be a unified curve.0
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Well it seems Tado˚ system does have a heating curve linked to Max Flow, as i test i reset my max flow to 80˚c last night after I turned heating off. It used LESS gas than the night before, and was colder outside.
Max Flow 65˚c: gas used 00:00 to 10:00 21.231 KWh
Max Flow 80˚c: gas used 00:00 to 10:00 17.157 KWh (and it was colder outside over night)
I was up at 3am, and checked current boiler flow temp and it was at 32˚c
Can anyone explain this if there is no heat curve ?
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If you have Tado trvs in different rooms set to different target temperatures there will be no unified heat curve. If you have one Tado thermostat and nothing else then there will be a single heat curve. However it won’t operate like weather compensation, where you don’t set a target temperature but merely choose a curve for the system to operate on, with the idea being the heating is almost always on but providing heat at a slow and low temperature.0
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I have WTS in every room, yeah still testing but it all over the place, beginning to think there is no set curve, or the AI is just *naughtyword*, as in the morning (when was colder) used last gas, than this after noon when outside temp where higher but tado thought the demand should be higher, so used more gas.
Beginning the think i'm just chasing my tail on this. OpenTherm is Good and Bad at the same time.
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Can I ask what is your guys daily average gas usage in kWh ? mine is between 42 - 50 kWh.
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There is no set curve because you’re using load compensation, not weather compensation, so the system will be trying to heat to the target temperatures you’ve set, rather than adapting along a curve to weather conditions.0
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atm i have this schedule for the main Lounge:
00:00 to 07:45 17˚c
07:45 - 16:00 18.5˚c
16:00 - 21:30 20˚c
21:30 - 00:00 17˚c
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One thing though, I do wish the TRV Values would fully open regardless of heat demand. It does seem strange that they only open a little when 1 bar demand is requested.
I understand why it doing it, as in Europe they run a pressurised system, so the more they open the hotter the rads gets and can over shoot temp, but here in UK our combi boiler and rad don't work this way and restricting the rad valves is not a good idea, as most of us have balanced our radiators via the lock-shield valves and having a restriction on both ends is bad for heat output.
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