Time-to-temp and True Radiant

[SolihullRog]

I've had my Nest for several years and it still disappoints.

I've asked for details of Time-to-temp and True Radiant, and recently found that they are completely different.

I started a thread, and, at last, someone got close to addressing my questions.

Unfortunately, they shut-down the thread before my next question.

Then came a common problem.  I tried to reply to the person who shut-down the thread.  My email bounced.  It appearrs that this is the only way to ask my next question.

So here goes.

Hello,

Thank you for your message.

Please see item 2 of DracosC's message above.

I interpret this as follows:

Say I want my house to be at 20 degrees Celsius at 8 a.m. every morning.

Overnight in January the ambient temperature would probably be 0 degrees, and might take 2 hours, say, to heat to 20.

Overnight in May the ambient temperature would probably be 16 degrees, and might take 15 mins, say, to heat to 20.

I understand that my only method to achieve 20 at 8 am. in January would be to set the Max Duration to 2 hours.

This would switch the system on at 6 am. in January. 

Is this correct? If so, and I didn't continually adjust it, I would be wasting a lot of money during May.

If not, it must be continually re-learning, in which case ...

Is this documented?

How often does it occur?

How can I confirm its conclusions?

I've read about True Radiant, but although it makes a fleeting mention of 'learning', I have found no reference to this information.

PS.  Use of examples is often a good way of explaining things to people.

[DragosC]

Hi there, @SolihullRog.

Thanks for reaching out. The Time-to-Temperature is not something you can influence or change. It's just an indicator that shows you how much time is needed in order to reach the desired/target temperature.

Also, the True Radiant feature just starts the heating before the scheduled time, and the Time-to-temperature just shows how much time will it take. 

[SolihullRog]

TEST

[SolihullRog]

I posted a question on this forum.

I received a reply, which didn't address my question.

Subsequently, I received an email from the forum, asking if my problem was solved.

I clicked "Reply" and replied.

My message bounced.

Is there a logical reason?

Roger Fitton

[CristianC]

Hey @SolihullRog,

Thanks for getting back to us. I'm here to answer any questions you have. Do you need more information about True Radiant? What do you mean by "bounced"? Did your question not post?
 

[SolihullRog]

When I say "bounced" I mean that my email is rejected with a message of Address Not Found.

It has just happened again.

I have continually asked questions about my Next thermostat, but I usually get links which point to web pages which don't answer my question.

Then I get a follow-up email asking if my problem was solved.

When I reply to that email, it is rejected as "Address Not Found".

[CristianC]

That looks like an automatic email from the community forum. You cannot reply to that email. You can post your questions here and I'll give my best to answer them. 

[SolihullRog]

Hi Cristian,

I think I've just caught on.

I receive an email from 'the Community' asking me if my question has been answered.  Normally, when I receive an email asking me a question, I click "reply" and give the person my answer.  It came by email, so I reply by email.

But this is the Nest Community, so I don't do what I do with everybody else.  Instead I go off somewhere else to give my answer.

I get it now.

So this thread was started on Tuesday.  It was a continuation of a saga.

That initial post, on this thread contains questions about my basic issue.

I would be most grateful if you read that post and helped me with the answers.

Several people have tried already, but they usually send me links to pages on the website.  None of these links has yet pointed me at something which addresses my questions.

Thanks in anticipation.

[AlexD]

Thank you for the information @SolihullRog. To iterate on all points. 

Yes, Time to temp and True radiant are different. True Radiant basically turns on the system quicker in the mornings especially so that you have the temperature you requested at a specific time. So if you want 20 at 08:00 with True Radiant it will start quicker so at about 08:00 you already have 20 instead of just starting to heat at 08:00 till 20 is reached. 

Time to temp is an indicator that comes up if you manually increase the temperature. So if you rotate the ring or increase it in the app, it will give you an estimate on how long it would take to reach the requested temperature. 

Now as to how it learns. It bases it off the requested temperature. After repeated heatings to a set temperature at a certain point of the day, and using other information such as outside temperature, it will turn off when the requested temperature is reached. It will monitor how fast the temperature is reached and after turning it off, how long the system will keep heating. As radiators will stay hot for some time even if the boiler is off. Using that it will estimate how early it has to start and how early it needs to stop to maintain a requested temperature. 

As seasons and temperatures change so will it as it notices it takes longer or shorter to reach a temperature and how long the location keeps the heat. 

[SolihullRog]

Hello Alex,

Thank you for that answer.  But I am still a little puzzled.

From your description, it sounds as though the Maximum Duration is only used once in its life - which is before the system's first use?

Thereafter, you say that " it will estimate how early it has to start".  This leads me to the following issues:

(a) It seems strange that it isn't mentioned on the website.

(b) It strikes me that, on its first usage, it could simply start, say, 1 hour before the required  temperature time, and then go by its calculations and recalculations, for ever more.

(c) You don't refer to my three questions at the end of the first post to this thread.

(d) Given the amount of output available from the system (ie none apart from simple histograms of when the system is active), it appears that users must expend a tremendous amount of effort to confirm how accurately it is consuming their gas and electricity.

[george_t]

Hi @SolihullRog,

Let's try to clear some aspects. Maximum Duration is the preheat time allowed for True Radiant to run and it can be changed for how early your system can start preheating at night, it's not something that it is used one time by the thermostat. Changing True Radiant's Max Duration setting will only affect preheating during the night (specifically after 8 PM), since it's designed to keep you from being woken up too early by a noisy system turning on.
Nest thermostat will only use True Radiant to turn on your system early when someone is home. If everyone's away and your thermostat is set to Eco Temperatures, it will wait until the first person comes home to start heating.

True Radiant automatically adjusts when the system turns on and off. No need to guess how early you need to turn on the heat to get the desired temperature when you want it.

As my colleague explained, the thermostat will learn your patterns and based on the outside conditions will be able to better manage your heating system to save energy and at the same time to have a comfortable temperature in your home.

[SolihullRog]

Hi George,
Thank you for your interest.
I realise that I may be wrong in Max Duration only being used once. But, yet again, I have failed to elicit a logical explanation of what it does.
Please consider the following situation.
1. I want my house to be at 23 degrees at 8 am.
2. I set the Maxmum Duration to 2 hours.
3. On day 1 at 6 am. the temperature is 20 degrees. From previous experience, the Nest decides to start at 7.45. At 8 am. the house is at 23.
4. On day 2 at 6 am. the temperature is minus 30 degrees. Using the Max Duration the Nest starts at 6 am. At 8 am. the house is at 10 degrees. NOT GOOD.
5. So I set the Maximum Duration to 10 hours.
6. On day 3 at 6 am. the temperature is 20 degrees. From previous experience, the Nest decides to start at 7.45 am. At 8 am. the house is at 23.
7. On day 4 at 6 am. the temperature is minus 30 degrees. From previous experience, the Nest decides to start at 2.00 am. At 8 am. the house is at 23. GOOD. This sounds like a good system.
But I have a question. On days 3 and 4 the Max Duration has been made redundant. Why don't I just set the Max Duration to 24 hours and I'll be happy? (Or why does the Max Duration exist at all?)
EITHER the Max Duration is not needed, OR there is something wrong with my understanding of the operation on days 2 and 4.
Could you please explain where I'm going wrong.
Roger

[DragosC]

Thanks for your answers, @SolihullRog. 

To answer your question, the reason might be that the coldest it is , the longer it would take the boiler itself to warm up the house, regardless of the Max Duration. This depends very much on the power of the boiler. It should be technically impossible in a scenario where you need to reach 23 from -30 in 2 hours of full blast heating. You can leave it set for 5 hours just in case, and the thermostat should learn that it doesn't always need 5 hours to heat up and it should start whenever it's reachable. The 5 hours are only the threshold. 
 

[SolihullRog]

As usual with Nest Community, this is not an answer to my question.

[DragosC]

We're sorry for the inconvenience, we've provided an official solution to the question. There's no other answer or explanation we can provide on this matter. 

[SolihullRog]

I am not surprised at your answer.  I don't believe that anybody in Nest understands what the Maximum Duration is.  I don't know what the exact, scientific possibilities are, but I provided  approximate, sample, temperatures and times as possible scenarios.  You seem unable to understand these simple concepts.  Your reply included the following:

"To answer your question, the reason might be that the coldest it is , the longer it would take the boiler itself to warm up the house, regardless of the Max Duration. This depends very much on the power of the boiler."

THE ABOVE IS SO OBVIOUS THAT IT DOESN'T NEED STATING.  IT IS NOT RELATED TO MY EXAMPLE.

You also state:

"It should be technically impossible in a scenario where you need to reach 23 from -30 in 2 hours of full blast heating. You can leave it set for 5 hours just in case, and the thermostat should learn that it doesn't always need 5 hours to heat up and it should start whenever it's reachable. The 5 hours are only the threshold. "

YOU OBVIOUSLY DON'T KNOW WHAT THE MAXIMUM DURATION IS.  IT ALSO APPEARS THAT NOBODY ELSE IN NEST KNOW WHAT THE MAXIMUM DURATION IS.

DOES ANY MANAGER OR ANY EMPLOYEE OF GOOGLE KNOW WHAT THE MAXIMUM DURATION IS, OR ARE YOU SELLING AN ILLEGALLY_ADVERTISED PRODUCT?

[DragosC]

Could you please ask again the question that needs to be answered straightforward? 

[DragosC]

Hi there. I'm just following up on our last message. Do you still need our help? Keep us posted. 
 

[SolihullRog]

Thank you for your interest.

After many attempts, I failed to elicit a reply from the community which answered my question.

I decided to approach Nest directly.  Again they have failed to answer my question.

I have concluded that nobody understands exactly how the system works and why there is a necessity for the 'Maximum Duration' option.

Nobody appears able to describe how I set the system once for its maximum efficiency for ever.  The system requires continual adjustment to avoid unnecessary heating costs, and the reason for the Maxum Duration, also to avoid unnecessary heating costs, is unknown.

I've given up.

[DragosC]

Please accept our sincere apologies regarding any inconvenience caused. We cannot provide works for all set up for the device to work perfectly as there are outside factors that are also affecting this. It can depend on the heating band of the radiators, it can depend on the cooling time of the boiler.

19:06

[SolihullRog]

Nest sell a product with a feature but, apparently, nobody in the world can describe how the feature works.

All devices, of every kind, require a specification of how they work.

Your references to 'outside factors', the 'heating band of the radiators', and 'the cooling time of the boilers' are all completely irrelevant, and are typical of the complete failure of the company to address something which should be a simple question with a simple answer.

It is a complete disgrace.

[CristianC]

Hey @SolihullRog. If I understand correctly, you're asking why the max duration is not higher to avoid a scenario in which the temperature is - 30 C so it reaches 23 C in time. This scenario won't ever happen. Your thermostat has safety temperatures in place which do not allow the temperature in your room to fall below 4.5 C. So the worst scenario would be when the thermostat needs to reach 23 C while your room is at 4.5 C. The thermostat learns and knows how much time your heating system needs to reach your desired temperature. It can start the heating 5 hours early so you're already comfortable by the time you scheduled the heating. 

Hope this helps. 
 

[SolihullRog]

I don't believe this.  That was an exaggerated example to demonstrate a point!

Yet again, I get an answer which doesn't address my basic point.

Your explanation doesn't even mention the Maximum Duration - which is the basis of my question...

It didn't help.

Nobody knows!!!

(And I've had two different descriptions of what happens when it CAN reach the temperature on time - Helper A "It starts at the Max Duration time and starts stops up until the 'target time'.  Helper B "It doesn't start at the Max Duration time - it waits until the latest time at which it can hit the target temperature"!!!)

Hopeless

[CristianC]

Hey @SolihullRog. Max duration is a setting that only applies at night time. To not wake you up in the middle of the night, you can limit the time of True Radiant. During the day, the thermostat ignores Max Duration and it will activate the heating using a different feature called time to temperature. Your thermostat knows how long it takes to heat your home ( time to temperature ) and it will turn on your heating accordingly. 

[AnaM]

Hey there,

Do you need any further assitance?

[CristianC]

Hello again. I haven't heard from you in a while so I'm going to lock this thread. Should anything come up, feel free to open a new one. Have a great day!

[SolihullRog]

By the way.  The question at the top of this thread is still awaiting an answer.

I have had the issue for years, and raise it occasionally.

Recently it has involved myself and helpers in about 20 messages over the past two weeks.

But I am still nowhere near an answer which I would expect almost every Nest employee to know.