Optimising my set up with Opentherm

macca4848

Hi,

It’s such a knowledgeable forum I’m hoping I can get some advice to make sure my setup is fully optimised.

My setup is as follows

- Veissmann Vitodens 111-W

- Tado Wireless Extender Connected to boiler by Opentherm

- Ground Floor - Room 1 has 2 x SRTs controlled by 1 Wireless Temp Sensor. Other rooms have no Tado controls as they are cast iron rads and me wife doesn’t want “some white plastic stuck on the end” 😀

- Middle Floor - Room 1 has an SRT and a WTS. Room 2 and 3 have an SRT controlled by the same WTS

- Top Floor - 2 rooms with and SRT in each controlled by same WTS. One rad and one towel rail with no Tado controls

- Max Flow Temp reduced from 80 to 65 as the rads without Tado were getting stupidly hot when demand was coming from one Tado.

Reducing the max flow temp has definitely made temperature more balanced around the house but I’m not 100% convinced everything is optimised because…

1) Middle room 1 with own SRT and WTS can be demanding temp - seen as 1 flame in room and in card and protect - boiler flow temp is at 65 as other rooms demanding heat. But there is no heat at all getting to the rad, unless I force the temp up to get 3 flames and I can hear the valve open. I’ve read this is a setting that the can be adjusted by Tado Tech support, so I have an open ticket with them.

2) My neighbour has the same boiler, is running an external temperature compensator and no internal thermostats and gets flow rates of 30 degrees and 8% modulation and wonders if my system has been set up correctly

I got to this set up as the top of the house is colder than the bottom and the kids are up there. It’s definitely improved the situation but any further tips much appreciated.

PS I’ve not balanced it yet, as read different schools of thought on here.

Thanks in advance.

Nic

DM932187

Start with balancing the system. Open up all the TRVs to max and put the heating on to a high enough temp that it won't switch off when you're working.

As you say, there are different schools of thought on balancing, but fundamentally, anyone who says it's unnecessary is wrong. If the system is not balanced, some rads will almost always fail to heat up as desired. For example, we have a large system and if the balance is out the last couple of radiators (in the kitchen diner) don't get enough heat when the (dumb) TRVs on the rest are open. Balance sorts out your flow (and return) across the system.

The correct different schools are on what you're aiming to achieve. Purist thinking is an 11-12C drop across the flow and return valve of each radiator (determined using temp sensors on each end). Then there's the 'everything should heat up at the same rate' school. Then the 'every rad should get to the same temperature' school. And finally, the more contemporary 'does each room reach the target temperature for that room' school.

Personally, I aim for a blend of schools 2-4 (favouring 4 - why overheat a space?) and largely ignore school 1. You can over-engineer this. Law of diminishing returns, etc.

I'd aim to replicate your neighbour's set up through balancing (recognising you have load compensation rather than weather compensation), then apply tado as the control layer over the top.

You may also find that you can reduce the max flow temperature somewhat and still reach comfortable temperatures. I have weather comp rather than load comp, but even in a large old house, almost never need to exceed 55C flow temperature. Boiler never comes out of condensing (even when it's heating water - it's a Viessmann too, so throttles DHW flow to maintain 55C return). The heating will be running for longer, but you'll gain on condensing efficiencies and probably comfort. You'll need to avoid deep setback temperatures though (2-3C max).

Hope that's helpful

macca4848

Thanks for that very helpful indeed!

And I think the other “issue” of the room SRTs not doing anything on anything less than 3 flames might have been user error.
I had a 2 flame room earlier and rad was warm not roasting, so I checked the 1 flame rad and it was tepid at the top and cold at the inlet where I previously checked (who knew that heat rises 🤦‍♂️)

johnnyp78

You’re not really comparing like with like. You’re using load compensation, where the rooms are heated according to temperatures you set, your neighbour is using weather compensation, which is adjusting the house temp according to the weather conditions.

Maybe your neighbour has different comfort requirements, insulation, drought proofing and so on.

For the room not getting heat you could try adjusting the lock shield on the rad, sounds like it could have been throttled back.

macca4848

Another Q…which I feel like I know the answer as I type this now.

Original use case for Tado was to make sure the kids rooms were warm. We like it a bit cooler so had our room temp a degree lower. However, our room is on the same floor as one of the kids and whilst our rads are off, the kids is still going and room not warming up…feels obvious because the rad in the kids room is trying to heat the whole floor and with a limit on the flow temp it’s going to struggle. So…should I really be setting all the WTSs to the same temp and time schedule to really work well.

Thanks

DM932187

You're right that micro-zoning can have that effect, but one degree is unlikely to cause an issue.

Sounds very much to me like the system isn't balanced, and the flow to the cool rad isn't sufficient. Good guide here: https://www.heatgeek.com/balancing-heating-systems-the-ultimate-guide/

You should be able to keep some zoning once the system is balanced, and achieve a differential across the bedrooms. We use dumb TRVs set around 21C on the ground, 18C on the first and 16C on the rarely used second. No probs keeping everywhere warm this way, but having tried going lower on the second, I can confirm that does cause the first to feel colder, as the heat is sucked out.

macca4848

Thanks for taking the time to respond. I’m going to be borrowing my neighbours temp gun to balance it next week and see

DM932187

Hey, no worries. Let us know how you get on.

macca4848

Ok, read the article (a couple of times in case I’m missing something), but need a bit of guidance if I may.

I’ve opened up all the lock valves, opened up all the dumb TRVs and opened up all the SRVs by setting room temp to 25 in Tado. Also set the max flow rate of boiler to 70

The article says to measure the DT/flow rate at the boiler to make sure the pump is flowing fast enough, but then goes on to say on most systems don’t need to do this as burner and pump are linked and regulated. Should I be doing this on my new Viessmann Vitodens 111-W and playing with engineer menu if not giving at DT of 20 and is it right to measure the DT when all valves are open?

Second question is that three rads on the 1st floor are slower to heat than others, even slower than the rads on the top floor which are furthest away from boiler - I think each floor has its own feed from the main flow pipe rather than all being in the same continuous loop if that makes sense.

So where to start balancing? Do I throttle back the hotter radiator on the 1st floor and see what happens or should I be doing all of the hotter ones by the same amount? Other articles on balancing talk about seeing which rads heat first from a cold start and repeating the process over to balance out…

Any thoughts appreciated

DM932187

You shouldn't need to worry about the DT and flow rate. I believe Viessmann boilers throttle the burners to aim to maintain the DT, and as your is a combi, the pump likewise.

If you're getting heat to all the rads with all the valves fully open, then your system is pretty well balanced already (you don't have any rads that don't heat at all), but you've mentioned some differences in heat times and some rads not getting hot enough.

Having all the rads fully open will also increase your return temp, as the water will get round faster than it needs to. You can address this with the temp sensors you mentioned, or less scientifically, simply close the lockshields by quarter turns to slow the flow. Do the faster heating rads by an extra turn or two than the slower heating. It'll take a bit of trial an error.

Once you've got things adequately balanced (bearing in mind the law of diminishing returns), if you're still having problems with some rads heating fast enough, it could be the behaviour of any smart TRVs. I don't use them myself, but I have seen quite a few complaints about tado's algorithm's attempting to 'modulate' them up/down and therefore not giving the satisfactorily speedy responses. Assuming, of course, the relevant rads are on STRVs.

One other thing I noticed. Does your Viessmann have advanced weather comp capability? (Mine only has basic as it's older). I know you're currently working with OT, but if you have the ability to move to advanced WC instead, particularly if you have parallel shifting, then you'll probably find that vastly superior to OT. That's not to say you aren't/won't be happy with the OT, of course. More excellent info on WC/LC on heatgeek.com

macca4848

Update…

After many (too many to count but more than 15) cold boiler starts and walking round the house checking the return pipe heat with a temp gun and noting down all the temps after 30 mins and making quarter turn adjustments. I decided not to let perfection be the enemy of the good and reverted to hand testing and larger turns.
I’ve now got my system “balanced” and rads are heating up broadly the same rate and no cold rooms round the house and I can hear the SRV making tiny adjustments through the day and night. Bliss.

Thanks for all the help, so far…

I’m wondering if there is a level 2 I have progressed to

I’m running at 19 degrees temp which surprisingly has been a nice level of heat and I have limited the boiler flow temp to 50 degrees using the Tado engineer app and the boiler modulates as low as 30%

There are times when I’ve needed to give a boost to the temp when guests have come round.

For further optimisation should I be dropping the flow rate further and seeing if I can maintain 19 degrees at a lower flow temp and ability to boost higher as needed. Or should I just leave it and boiler will do it from here.

Cheers

Unknown

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macca4848

Can you run weather compensation with Tado SRVs or is it either or?

johnnyp78

You can do, but it would be unnecessary. You can just use dumb trvs if you want some rooms slightly cooler with weather comp, the house should be maintained at a comfort temp.

macca4848

Thanks…guess who just gave away all the dumb TRVs I’d kept hold of for two years after installing Tado.
I’ll look in to selling them and going the WC and dumber TRV route.