Please I want to be a little Wiser what is the thermostat for?

[ericmark]

House from Wiser web site, bottom right room has a eTRV and a room thermostat, I just can't work out why with a hub and eTRV in every room one needs a thermostat? I thought idea is the eTRV tells hub if satisfied or not and the hub either tells the boiler to switch on and off or with opentherm how much heat is required.

So where does the room thermostat come into all of this? I have looked at Hive and Nest as well, and just can't see what they do other than act as a hub to read IFTTT commands from the eTRV. Although with opentherm it needs some computer to work out heat output levels, with the non opentherm boiler all it needs is a simple relay. If any eTRV has the target temperature above current temperature then run boiler, if all eTRV current temperatures are equal to or above target then switch boiler off.

What am I missing?

 

[DP]

Possibly bigger room so the sensor is in the middle of the room to control the evalve

 

[Dan Robinson]

Rads can be in boxes, behind furniture, in direct sunlight, next to patio doors.

When we're doing surveys for proper smart heating controls. Things like are all taken into account.

 

[ericmark]

Thank you, I think I get the idea, the thermostat does not connect to the boiler, but connects direct to the eTRV and just controls that valve. Plus of course telling the hub how much heat the valve is set to release. Is that how it works?

 

[Doggit]

The thermostat links to the boiler, and once the system has been balanced, it tells the boiler to switch off. The eTRVs allow you to control the individual temperatures in each room, so you could tell the bedrooms to be off during the day, and only swith on an hour before bedtime. And if you're not using a dowstairs room fr most of the day, you may set it 5C lower than the rooms either side of it, so they don't leak too much heat in to it.

Without the room stat, the boiler will keep running all the time, and only switch off when the water coming back to the boiler stops losing heat.

 

[Dan Robinson]

Without the room stat, the boiler will keep running all the time, and only switch off when the water coming back to the boiler stops losing heat.

Hhhmmm

 

[AGAS]

??????

 

[Doggit]

Okay Dan, I obviously didn't put that in the best manner, so I'll leave you to explain why there needs to be a room stat rather than just TRVs, or have I missed the concept of the eTRVs.

Hhhmmm covers a multitude of sins.

 

[ericmark]

This is what confuses me, I thought the eTRV's would report target and current and if target above current on any valve the boiler will run, and if target equals or is below current than boiler will switch off?

With my cheap system using Energenie eTRV's then there is no direct contact between the valve and boiler so it uses IFTTT to connect something like Nest which is set to follow the eTRV or some other trick is used to tell boiler when to run. So when the valve target moves from 16°C to 20°C it takes maybe 4 hours to hit new temperature, so in real terms the valve is set to go from 16°C to 24°C for 2 hours and then back down to 20°C or although the programmable thermostat in another room is set to go to 24°C at the same time as the eTRV steps up temperature it will not heat up in time and boiler will switch off before room has hit new heat. Putting it simple the anti hysteresis built into the eTRV is OTT so one has to cheat to allow valve to reach new temperature.

If the valve was directed connected to boiler it would not matter, even if it was a little slow heating room the boiler would still be running so room would continue to go up in temperature. The wall thermostat in my cheap and nasty system has to be in a room where the temperature does not vary over the day, in my case the hall, and I have a second thermostat in kitchen to give system morning boost as rooms using eTRV's change temperature. In the hall where wall thermostat is the TRV on radiator is cheapest of cheap as one needs a large operating range not an accurate temperature so as the hall warms up the TRV slows the heating rate but does not stop it to keep boiler running longer, in other words a right Heath Robinson set up because the eTRV's don't control boiler other than temperature of return water. MiHome is a cheap and nasty system and I may as well have installed Pegler Terrier i-temp i30 White Programmable Thermostatic Radiator Valve which does not have any hub and is completely stand alone, it would mean to alter room temperature I would not need to boot up a computer, they would actually as a result be better than the MiHome Energenie eTRV as easier to change temperature.

The MiHome Energenie eTRV is a cheap and nasty waste of money, as the hub does not connect to boiler. With the Drayton Wiser the wall plate is the same style as any standard programmer in other words unlike the MiHome Energenie it connects to the boiler.

Above is wiring for the Drayton Wiser hubs, the hub connects to old type boiler like mine the only way the thermostat can connect to boiler is wireless through hub, it does not seem to use opentherm it simply switches boiler off and on.

So I would expect the boiler is controlled primary by temperature of return water, as each TRV closes the by-pass valve starts to lift so non cooled water returns to boiler which in turn reduces flame height, once flame height reaches minimum then boiler starts to cycle, and once every valve is satisfied the hub turns off boiler. Where does the room thermostat fit in to that sequence of events?

 

[Hot&Cold]

ericmark,that diagram above is just an example of how components could be installed,there are lots of variations on how and which components can be installed.

Dont know where you found that diagram and in what context it represents but every new installation is tailor made to suit the individual property,retro fitting smart controls needs the existing system to be correctly installed,the end user has to understand there are limitations and a very smart installer.job done.

 

[Dan Robinson]

have I missed the concept of the eTRVs.

Yep, although, the OP is not making it easy to understand what he is actually talking about.

Not sure why he feels the need to cobble together half arsed mishmashes of multiple products.

Shoving different types of products under an imaginary banner of "etrv" doesn't help. The Peglar products don't provide an interlock. And neither do the Energenie things by the sounds of it.

 

[ericmark]

Sorry point of diagram was to show with the Wiser unlike the Energenie it does connect to boiler, since it is connected to boiler back to original question why a wall thermostat inside the house?

OK I can understand there are special cases, where the morning sun comes into a room through large bay windows for example you may wish some sensor to switch off the heating to that room to stop over heating, a thermostat positioned so morning sun will hit it. But that is a special and not some thing you would do with every house. Since Wiser is sold as a kit which always includes a hub and thermostat it does seem the thermostat is required, but what for?

 

[ericmark]

Yep, although, the OP is not making it easy to understand what he is actually talking about.

Not sure why he feels the need to cobble together half arsed mishmashes of multiple products.

Shoving different types of products under an imaginary banner of "etrv" doesn't help. The Peglar products don't provide an interlock. And neither do the Energenie things by the sounds of it.

You are correct, neither Peglar or Energenie connect to boiler, although latter can connect to Nest with follow commands. But Wiser and EvoHome both connect to boiler yet both seem also to have room thermostats although it does seem an option with EvoHome rather than a must. It may be the thermostat with Wiser is not really a standard thermostat but a HMI (Human machine interface) to allow you to set temperatures? If it is then it all makes sense, however it's called a thermostat and it just does not make sense to have a eTRV in every room and thermostat hence the question.

 

[Dan Robinson]

 

[SgtFoley]

Going back to the original question...
I was told that for TADO (a similar system with zoning capability) the eTRVs effectively speak to the boiler via the thermostat, so the thermostat is still needed even though you would think it is no longer necessary. Might be similar for Wiser...
Also, I suspect eTRVs were added to these 'systems' at a later stage of design, so bypassing the thermostat would have required extra work and reduced backward compatibility (you can currently use Wiser or Tado without eTRVs if you want).

I'm keen to know if ppl are using Wiser and how they find it...
Is there a risk of boiler firing on and off continuously with so many zones calling independently?