Heating power percentage and calling for heat
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@Hunter By "Demand" I mean an SRT that talks to the zone controller and will command/demand the boiler to fire. By "Request" I mean an independent SRT that would like some heat, but can't force the boiler to come on.
@andyblac I understand your point, but I think I'd got myself in knots trying to configure an appropriate setup. I think the simple solution is that valves are either open or closed. No middle ground. And a valve that demands heat simply must remain fully open. Otherwise the heat it's demanded is going to end up somewhere else, as likely as not the bypass. Ludicrous!
And regarding lockshield valves - I've picked up from the forums that this is a British thing and may not apply on the continent or in alternate heating scenarios (district heating?) so the SRT has to perform a dual function of gatekeeper and flow limiter. Brits don't need the SRT to limit or slow the flow, just turn it on or off.
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I can understand why modulating the valves is beneficial but taking hive as an example, they try to find the real valve cracked open point during a long drawn out calibration process which detects a temp effect in the system. Tado does not have this so, unless you get it adjusted they will guess for your valve characteristic and then fire the boiler until they are successful in getting heat…….not convinced wide open is the way to go either give. It’s just on off control or am I missing something. Perhaps some user adjustability is the way to go.
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For whatever reason independent seems to crank open the valves far more. Modulating is useful as in the colder weather I found the lounge would get too hot with a normal valve and was also a bit too cold on other days. Tado SRT that is set to independent seems to have smoothed it out more as it cranks it wide open when it's chilly and then will cut it off a bit sooner than an old fashioned valve when it's up to temperature.
My boiler still has a minimum run time of about 30 seconds. It is short but as heat geeks pointed out it does mean a slow gentle start in some ways rather than going to straight from stone cold to red hot. I may have changed my mind on that now.
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Yes, an on/off control, but with all the flexibility of scheduled temperature adjustments.
My point is that either a radiator wants heating or it doesn't. If it wants heat, and there's already a lockshield valve limiting flow, then why would you want Tado to further restrict the flow to the radiator and risk forcing the water back round the bypass, either heating the wrong room, if you have a bypass rad, or raising the return temp needlessly and reducing efficiency of condensing boilers?
Dump the heat through the radiator that wants it and then stop. Simples. 😃
But do not have a radiator requesting or demanding heat and leave the valve closed, which is exactly the risk with this trickle feed system of partial opening.
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@eezytiger correctly implemented the modulation would give better control without doubt but I take the point of currently a traditional thermostat will turn on the heating and manage the temp with minimal overshoot without modulation. I can’t help but think I am missing the bigger picture here re what Tado are trying to achieve with the overall relay logic, intermittent short burst operation, bearly giving time for boiler to spin up, cycling the boiler after 4 mins very 20mins with varying SRV opening some of which are not open. Alas the logic is does not seem to be explained. The only benefits I can currently see is that the boiler partially spins up giving lower flow temps and more condensing, also the residual heat is expended in the rad at each step giving finer control which may or may not be required. I am running hive upstairs and that is traditional long burn times, but the hive TRVS stink.
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I think Tado might be trying to compromise between all the different type of rad heating systems, by that i mean UK vs EU vs US, from what i have been learning they all act different. For example in the UK, we tend to have both TRV valves and lockshield valves, in Germany some have pressurised type system, once the TRV is open the water flow causes the boiler to start firing, and does not necessarily need a signal from the Thermostat to fire the boiler.
It sounds to me either tado˚ need better algorithm for selected boiler type in setup, or give US manual control how choose the TRV behaves.
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@eezytiger - how do you set up the SRTs to be independent but not call for heat and turn the boiler on? I can’t find this anywhere in the app, at the moment all of them will call for heat if they drop below the room temperature.
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@phil9971 Go into the settings for the ROOM and you can make the room independent or connect it to the zone controller.
If connected and it wants heat then the boiler will fire.
If independent it will not force the boiler to fire, but you can still have scheduled temperature changes for the room. It will have to wait until the boiler is fired up by another room in order to receive any heat.
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@eezytiger Thank you! Couldn't find that anywhere.
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Looks like I have reached the end of the road with support who struggled to grasp my issue fully. Basically my worst affected room which is less well insulated and has a radiator which is large and thus has thermal inertia takes a few cycles from cold to raise back to setpoint from 0.3 C delta from setpoint. I think the main factor here is my setpoint of low flow temp of 55. I can get the flow temp up via the system bypass quite quickly but can’t get sufficient in the rad even with support having opened to the max they can (note can’t be fully open must be wave 1 limit). I can live with that, I don’t fire against closed valves anymore just need a few cycles for large cold rads. I am assuming that running at 55C overall is more efficient than not cycling the boiler for an extra 2 x 4mins. May increase flow temp and observe if the extra requirement for Tado switch ones remain.
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@Hunter I've been having a productive email exchange with Tado support and have had my minimum burn duration increased to 10 minutes. Previously it was 4 minutes, with an actual burn duration of 3:40 as it takes the boiler 20 seconds for a self check from relay switch on before the burner ignites.
I have continued tweaking my system configuration, but I still have only one room/radiator connected to the zone controller, leaving all other rooms independent. Now the lounge is in charge, with a target of 20C during the day and 18C overnight. This is doing a decent job of getting heat just where it needs to go and keeping a low return temp at the boiler.
Boiler flow limit is set to 50C. There has been a small overrun to 52C max for the flow, but return temp has remained below 45C, which is perfectly satisfactory.
Today's flow temperature distribution from midnight to 15:00 is shown below. Vertical scale is minutes spent within each temperature range listed on the x axis.
All rooms are at or above set temp except the kitchen, for which the SRT is in the corner of two external walls and with an air vent in the wall above. The room itself is fine, even if the SRT suggests it's a bit cooler than desired.
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@eezytiger My final request to support that was not answered but I just repeated was can on relay you elongate this 4mins, if they can then that will probably also make great strides to increase my efficiency. I am in a position now that it’s just a few cycles when the system is cold and a small drop in setpoint is seen. I can live with it, but given I have flow at my valves if that 4mins can be extended that will help.
Did it lead to significant overshoot? I can also increase my flow temp which is currently 55 but don’t really want to. I wonder if the min burn duration is still adjustable with the external temp sensor setup.
my set up is a little different to yours. I had problem siting a thermostat as I have a sun prone, low insulated room and a well insulated room that also gets sun in the afternoon. The result is that one or the other siting would lead to under over temp. So I have zoned both with SRTs and temp sensors, works great, initially tried it with hive TRVS that never really worked as expected. So at this time the two rooms are working without placing in independent with just the few cycle issue for the cold room. I have a SRT in the study that I have decided to keep on independent as it was dropping in temp and calling on heat frequently despite the core room temp being stable. So all ok but am trying to optimize the boiler switch on, which is entirely Tado driven.
disappointing as support basically told me nothing else could be done, which obviously is not true, that said the grasp of the issue is sometimes difficult and I have through 3 people to get to my current contact….I will await Tados feedback.
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I am on relay switching.
I have tried eBus three times in the past 13 months, but I (may have) misinterpreted short firing durations as a problem with eBus operation. Basically, Tado was requesting a flow temperature of 32-33C, which the boiler was quickly reaching and exceeding with its minimum 9 kW output. The target temp was impossibly low for my boiler to maintain and at about 36C the boiler would shut off. I'm not sure if the shutdown was caused by the temp or maybe the four minute time interval, but it did not appear to work at all well.
A 33C flow temp is not even the stuff of heat pumps, never mind gas boilers. Maybe if my boiler could output 2-3W minimum it could trickle along for hours at a time in the depths of winter, but not at any time with 9 kW. Within the past couple of years my highest consumption in one day is 125 kWh. Averaged over 24 hours that's pretty much 5 kW continuous, so, even on the worst day ever, my boiler is almost twice as powerful as necessary on minimum output.
So, relay switching has repeatedly been more successful for me (my boiler). Maybe I should try one more time with my new 10 minute minimum burn time, but quite honestly there seems little point. I cannot see anything to be gained from eBus control when the boiler is too powerful. I'm already running it as efficiently as possible. I do not believe there are any more gains to be made - except by replacing the boiler with something with a much higher modulation ratio.
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@eezytiger not sure what boiler you have and if EBUS is different to OpenThem, I have my MAX FLOW set 65c, but it rarely uses it, only when it -2 or less outside, and then only till the room gets up to temp, then my boiler quite happily chugs along at at 26-35c with 1 bar all day, burner cuts in and out as needed to keep the flow temp, I have used 52m3 this month up to now (about 2.3-2.5 m3 units per day). I used to have my MFT at 55c, but found that the room took longer to reach temp, and for boiler to throttle back, so in my case it was worse having a lower MFT even though the boiler should be more efficient.
that what is usually sits at.
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@andyblac I have a Vaillant Ecotec 831 Plus combi, almost 12 years old. AFAIK eBus and Opentherm basically have the same functional goals, but simply with a different language, so not interchangeable, but both more sophisticated than on/off.
Max flow temp is not as relevant to combi boiler efficiency as return temp and the lower the return the higher the efficiency. Of course, keeping the flow temp low absolutely forces the return to be even lower, but you don't want to encourage short cycling by having the boiler shut off due to hitting the temp limit before its job is done. So it can be a balancing act.
But, you can help lower the return temp by having multiple radiators in operation at once and thus dissipating more of the heat at once. You can't lose 9 kW (my minimum boiler output) of heat from a single radiator that is only rated at 1 kW at Delta T 50, especially when your system is running at Delta T 30. That is why I have set my system up to have as many radiators as possible with open valves whenever the boiler fires. Then the heat actually has somewhere to go.
In my case, the reason to aim for a lower flow temp than average is because I want to determine whether my radiators will be able to handle a switch to a heat pump and 40-45C flow temps in the future.
Of course, this would all be so much easier without a grossly oversized boiler, but you play the hand you're dealt.
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@eezytiger can i ask what setback temps are you using ?
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@andyblac The whole house is at 18C between 22:00 and 07:00. At 07:00 the bathroom and downstairs is set to 20C.
One thing I have learned is that raising temps takes a LOT more juice than maintaining them and the cost in gas is almost as much to raise temps from "cold" as to keep the heating ticking over throughout the night. By keeping a steady temperature we have greater comfort and far less boiler stress, not that it's stressed as such, but it's a steady marathon cruise overnight instead of an all out sprint at 07:00. Plus, walls, floors, furnishings all remain warm. No cold spots, no drafts, no condensation etc..
Note that this is a recent tweak as I've been experimenting, but hopefully the best one yet. My gas consumption has plummeted in 2022 vs 2021, so I'm happy with the way things are going.
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@eezytiger thanks, that good to know, i'll have to have a play
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@eezytiger how do you measure the return flow temp?0
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@phil9971 I have thermometers with external thermocouples attached to flow and return pipes. The top pair log temps every minute 24x7 and I have a phone app that reads the logs over Bluetooth. The smaller pair do not log, but are much faster - practically instant - to respond.
I actually have several of the smaller thermometers and use them for radiator balancing.
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Wow, thanks for the info!1
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Above is a link to the small thermometers. There are many similar, and I've bought a few sets with different branding, but the same/similar appearance, but these were the most consistent in temperature displayed and are still going well a year after purchase.
I'm afraid the logging thermometers are no longer listed on Amazon and I can't actually find them at all.
This one below doesn't appear to log, but has smart home integration and can send alerts, so maybe could serve as an alarm for action if the return temp exceeds a set limit.
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Thanks for the info 👍🏻0
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@andyblac FWIW I recorded my gas consumption between midnight last night and 07:00 and, to maintain 18C for eight hours it took exactly 9 kWh. Outside temperature was fairly steady at 8C.
In the next hour, in order to raise a few rooms to 20C, it took a further (almost) 7 kWh.
So, of course it costs money to maintain the heating overnight, but if I'd turned the heating off there would be a shortfall to be made up from 07:00. Hard to say how much. Not fully 9 kWh, but probably not far off it.
The last time I compared two days running with heating off vs heating on I think it cost about an extra 3 kWh (10p on my tariff) to keep the heating on.
But low and slow means less hard work for the boiler, allowing lower flow temps and even lower return temps, improving boiler efficiency (for a combi). And it's just more comfortable.
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Has anyone suggested re-balancing the radiators so that the big one in the cold room always gets the heat way before the others do? You can balance systems so all radiators heat up at roughly the same rate but if you have a slow room then you want that getting heat first.
Also a negative offset would have it stay on for a bit longer and generally moan it's colder for longer so that also might help.
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@srichards Hi thanks for the suggestions, I have a micro bore system that is not so sensitive to balancing, the SRV will be providing masses of pressure drop so I don’t think that would have much effect and if it did I think the remainder of the network would have to be gagged in to make a significant difference.
Re the offset I think any offset I would apply the system would just control to that and any boiler Tado cycles would still happen. If I was concerned with being below setpoint whilst the Tado cycles I could put an offset in or increase the setpoint slightly but it’s only fraction of degrees.
I think the best bet is to increase the min burn time to allow more heat into the rads for any given low cycle and thus minimise the number of cycles. I could also increase flow temperature but at 4 mins even with a system bypass the flow temp can be limited to 50 C. I await Tados action.
this is all an optimization, I have good control but struggle to hear my boiler firing and nothing significant happening to target room temp. Of course in reality heat is being added but not always where you want it.
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@eezytiger Normally I have been using about 4 units (55.05 KWh) per day this past week.
I did a test yesterday with setback of 17˚c overnight, from night before last at 22:00 (when heating went to setback) to till 22:00 last night (24hours), have used 2.682 units (30.77 KWh), Thats quite a big saving, I assume it is because the boiler does not have to work as hard to reach target temp in the morning. ATM I change temps 3 times a day, 7:45 to 18˚c / 15:00 19˚c / 18:45 20˚c, as I thought it would be cheaper to raise temps slowly.
I am now in the process of doing a test with 2 temp changes, see if it make much of a difference.
small update:
it seems the AI in the WTS need time to adjust to the changes see the difference between yesterday and today graphs (mornings)
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it seems the WTS is starting to learn....
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seems tado did not like my post, and have deleted it ????
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