A smarter thermostat

[Jon Connell]

Does anyone have a recommendation of a thermostat that is capable of using cues like outside temperature and previous times taken to reach a target temperature to adjust "on" times?

Jon

[Dave Liquorice]

There are a few about keywords to feed google "weather compensation", "optimum start" (though that is a maker specific phrase). TBH I don't think the weather compensation is worth it for a domestic installation if you have "optimum start". If it's cold outside the house will cool more and the heating will start earlier anyway.

[Jon Connell]

We have an old property and the outside temperature has a big impact on how quickly the house heats up and given how much oil we already burn, I don't want to set the on time too defensively to compensate with very cold mornings.

[Martin Brown]

That is what the smart start does without having to actually measure the outside temperature directly. You set a temperature and a target time and it computes from the initial temperature and the maximum rate at which the thermostat temperature climbs how soon it needs to fire the boiler and pump to meet that constraint. Basically it calibrates itself to match the thermal inertia of the house.

You can set a certain number of time temperature values through the day.

Full external sensor weather compensation is probably overkill. YMMV

[Michael Chare]

I don't have it, neither do I miss it. I do have a programmable thermostat which keeps the C/H on a night, but at a lower temperature.

[John Rumm]

You need an "optimising" stat... (sometimes called "optimal start" or similar).

Most don't have a direct reading of outside temp, but they do learn the characteristics of the building and take into account the starting temperature. So if you say I want 21 degrees at 7am, it works out when the heating needs to go on to achieve that.

[John Rumm]

The main advantage is increased efficiency and comfort when its not so cold outside. By telling the boiler to run flow temperatures as low as possible, it promotes condensing efficiency and also reduces overshoot. A side benefit is the heating system is often "quieter" since its normally running cooler you don't get as much noise from pipe expansion and contraction.

[Jon Connell]

That sounds about right, thanks.

[harryagain]

The keywords are "optimum Start thermostat". EG

It is standard for large installations. Some are self learning.

[The Natural Philosopher]

it is worth it if you have UFH or a lot of thermal mass inside the house.

I don't have a predictive stat on the UFH, and I get about 1-1.5C overshoot and a 4 hour lag between the heating coming on, and the rooms being where they are supposed to be..

Probably ought to build my own out of a raspberry pi..:-)

[dennis]

The fairly common cm827 wireless stat has it but you have to enable it in the installer menu.

[dennis]

S/827/927/

[Bernard Peek]

We have just had a British Gas Hive thermostat fitted. It doesn't sense external temperatures but you can plot temperature versus time and see how long the house takes to respond. You can also control temperature remotely. It seems to work OK.

[Andy Burns]

I have had a non-wifi (PRT-HW now given to parents) and wifi (PRT-HW-TS-WIFI) version of the heatmiser programmable stats, they're not cheap but they do the job you're after, and timed hot water too.

As for outdoor temperature monitoring, if it's cold/windy outside it'll tend to get colder indoors overnight, so the optimum start will turn the heating on earlier (learns the rate of rise for your system) if it's not cold indoors, who cares what it's doing outdoors?

[Andy Burns]

Now with link!

[Jon Connell]

Optimum start is indeed what I need.

The "optimum off" comments in that doc don't make sense to me though: surely the whole point of the thermostat is to turn off the boiler/pump when the ambient temperature is at the programmed target.

[Andy Burns]

I haven't read the doc, but is it about turning off early to avoid overshoot?

Here's what my Heatmiser was doing last December BTW, solid blue line is the programmed temperature thoughout the day, it aims to keep room temperature, solid red line, above that at all times, dotted blue line with (P) symbol is optimum start period, with (H) and (M) symbols are manually temperature override and manual temperature hold, orange bands are boiler "on" periods, dotted grey line is outdoor temperature from nearest met office observing station.

[Jon Connell]

I says "turn off the heating early if the inside temperature will still be comfortable until people leave for the day ? optimum off."

Which a thermostat should do anyway.

Cute. My inner geek is always going to like data :-)

[John Rumm]

Optimum off will try to minimise the overshoot. So it observes how much the temperature rises after the heating has been switched off, and adjusts the time so that it peaks close to the set point rather than over it.

[Dave Liquorice]

Well not quite

Agreed, essentially useless but still fascinating. But I'm not impressed by that stat letting the temp waggle about by 1 C, I'd notice that, either the peaks would be feeling a bit warm or the troughs starting to be cool.

Our Danfoss TP7000-RF holds within a few 1/10ths of a C. Set point say 18.5, heating fires up when temp is 18.4 off at 18.5, overshoot to perhaps 18.6 or 7.