Smart TRV's - are they worth it to add to a tado smart thermostat and boiler control?

A bit off topic but yes I agree ​@Peter E . The trend towards larger cylinders and larger coils does mean that when the cylinder start to reheat heat is drawn from the top of the cylinder to heat the cooler bottom half.

In many ways the Mixergy cylinder tries to address this by using a coil near the top to heat the water and a small pump to effectively push the thermocline down the cylinder. Unfortunately this doesn’t work well with heat pumps as the return temperature is high (reducing heat pump efficiency).

My home-made cylinder thermostat measures the cylinder temperature at four points. When the heating flow temperature is above the temperature at the top of the coil it opens the cylinder valve allowing the cylinder to heat alongside the heating.

Still wondering about heat pump and EV. Maybe I should share my reasoning for not changing just yet?

Yes. We do have a bit of thread wander here and I'm guilty as charged. I'm wondering if we stop this here to retain the original purpose and head off with another thread with this because it is an illuminating subject but not here. What do you think ​@BeePee ? Shall we head for pastures new?

The query was querying whether there was any benefit in having smart TRV’s instead of standard TRV’s when they already have a smart room thermostat so there has indeed been quite a drift.

If any reader wants to know more about valve types there’s plenty of reading material as well as YouTube videos e.g.  here’s one from the Chartered institute of Building Service Engineers (CIBSE) about different types of valves https://youtu.be/-nUceSN8pXs?feature=shared

Here’s another on smart valves https://youtu.be/YgvKoG-7T30?feature=shared 

I personally have not readjusted any of my manual TRV’s in the last five years at least.  If your system is properly balanced then there’s no need to unless, as I said you can clearly isolate rooms / zones without there being any risk of cross movement of air / droughts.    I have a (non-smart) room stat / timer in the hall (the only room without a TRV) and occasionally change the desired temperature if we’re feeling slightly cold as we keep it quite low for economy reasons.   It has multiple timed periods during each day and I occasionally over-ride that by turning the desired temperature down if we go out.  Reheat time is minimal when we return as the heating is on most of the time.

Two points which I don't think I have made already.

If you make the system too complex to understand how to make it work effectively then you may end up with a worse performance than now. One of my rules is to Keep it Simple. Like ​@Paul4AA I rarely adjust my TRVs but when I do I have tape marking the place where they have to be reset to.

An increase in efficiency may not pay back the cost of Smart TRVs, however, increased comfort may be your aim so that wouldn't be an issue.

Peter

Back on topic…

BEAMA produced a paper estimating the energy savings associated with fitting TRVs. On average this seems to be about 18%.

On a financial basis:-

• Assume annual gas heating bill is around £1000.
• 10 rooms with heating therefore cost per room £100
• Savings per room (18%) around £18 per annum

So fitting a standard TRV (DIY job ~£15 per valve) is probably worth it.

Additional savings from fitting a smart TRV are probably around 10% to 20% on top of the 18%, so an additional saving of around £3 per room per annum. Worth the additional £30? Probably not. As a first fit? Maybe? 

Don’t forget these are battery powered so expect to replace the batteries annually.

And as others have said TRVs are not recommended for use with heat pumps.

I have used both standard TRV’s and smart TRV’s but now only use the standard variety. 
My experiment with smart TRV’s was due to an extension recently built but not in the ‘standard’ flow of the heating in the rest of the house, therefore I thought the smart variety would help to adjust the new location. 
My standard TRV’s are all set to fully open and the system properly balanced as I found that any TRV was at times in conflict with the other variables in the heating system, at times operating against each other. 
With modern systems, so many auto adjustments are made that if additional components try to adjust the flow, you can end up with a poor performance. 
So, in the end I’ve found a well balanced system together with minimal extraneous automations works best .. in other words as others have intimated “keep it simple”.

Thanks ​@BeePee that was a useful document to read. A couple of points. Whereas I'm confident in installing TRVs I don't know many people, apart from plumber friends, who are, so the cost of having them professionally fitted would have to be added on.

There was an also an interesting final paragraph:

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We therefore conclude that these results should be taken with a high level of confidence. The
installation of TRVs, accompanied by practical advice to householders on how to use them (the
provision of which is already a requirement for installers under the Building Regulations) should be expected to yield significant energy savings across the UK housing stock.

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The key part is … practical advice on how to use them … As I have said before if you inadvertently have the TRVs set lower than an active thermostat in that room then the boiler will be thrashing away trying to heat the room up without ever succeeding. Perhaps an advantage of Smart TRVs is that the system would never let that happen but are all Smart controllers capable of preventing that situation from happening.

Sometimes we end up buying systens that are sold to save energy but they are too complicated for people to understand so you end up with disappointing results.

Peter

I’ve occasionally considered changing my room thermostat programmer for a smart thermostat, but am not convinced they save what the manufacturers claim, are as reliable as a traditional controller, and I don’t want to be possibly tied into a system that may not always be supported.  However, one of my concerns relates to the poor ways that they’re described / sold. 
 

What I’d like to know regarding the Tado thermostat is how it knows what the outside temperature is because there’s no outside stat in the box and no mechanism for measuring it is described on their web site at all.

I’d similarly like to know how it knows that a window is open as again there’s no door / window contact to measure that.

Hi ​@Paul4AA 

I can only speak of the Tuya app that controls my heat pump but you can select a location for the outside temperature and get it that way. There is an indirect reference to it in this link for Tado.

https://community.tado.com/en-gb/discussion/15768/weather-adaptation

For an open window a local temperature sensor will note a sudden decrease in temperature.

https://support.tado.com/en/articles/3387308-how-does-open-window-detection-work

Peter

Thanks ​@Peter E  which suggests to me that they’re gaining an approximation of the outside temperature from an online published weather forecast rather than a true measurement.  Possibly better than nothing but it won’t be accurate.  It’s similar with the window detection where they’re guessing at a window, or I assume door being open by a more rapid change in temperature than normally experienced.

Such a shame that TADO don’t give this information on their web site including their FAQ’s.