Smart TRV

RavingMad

We have Hive heating and it does the job. Thinking of sticking a smart TRV in the living room so that I can choose to heat it in the morning if it's cold but not heat in the evening when I use the log stove (but still heating the rest of the house, especially upstairs)

Do I need to stick with Hive or will any brand do the job? I'm fine with having to use a separate app to control it

Thanks 

Mark_d

Any brand would do as they can operate independently from the boiler thermostat. My smart thermostat is Nest but I have Kasa TRVs.  Yes it means a separate app but I certainly don't have an issue with that.

ThisIsWeird

The only issue with using a different make, tho' I doubt it'll be one for you, is that the Hive TRV can be set to operate in two different ways; one is to just 'passively' come on and off to the temp you require or program, and the rad will then heat up if the CH is already running, and the other way is that the TRV will also tell the CH to come on with it.
But, it sounds like a good idea, and saves the manual hassle!
Where is the Hive itself located? I'm sure you realise that if it's in the log-fired sitting room, this will affect the rest of the house. 

RavingMad

The TRV can tell the CH to come on? How does that work out of interest?

In my mind, by not having the living room rad come on, the other rads upstairs get to temp quicker?  Generally if the lounge gets too warm, I'll open the door to let some heat out so not overly bothered if the lounge rad is on.

So it's not a cost cutting exercise but rather an efficiency thing if that makes sense?

The Hive is upstairs in the daughter's room as that gets no solar gain during the day and she complains if she's cold lol

tacpot12

Most Smart TRVs communicate with the central thermostat to tell it that there is a demand for heat in the room. (The TRV is acting as a remote thermostat in this case). The central thermostat causes the boiler to fire. 

In theory, a network of Smart TRVs (or remote Thermostats) can each tell the central themostat how much difference these is between the temperature in the room and their set point so that the central thermostat can use OpenTherm to tell the boiler how much heat to produce - small heat demands from all rooms would cause the boiler to fire on its lowest setting, high het demands from all rooms would cause it to fire on its highest setting (even if the temperature outside was relatively mild), and a mix of demands would produce some intermediate level of firning. I've no idea if Hive is this sophisticated or not. 

ic

Your existing TRV will turn off the living room radiator when the room is up to heat - which I imagine is pretty quick after you light the log fire.  So I'm not sure what you're gaining by getting a smart TRV.

Tado, Hive, Drayton Wiser, Bosch EasyControl are all examples of smart thermostats that also can be extended with Smart TRVs - allowing individual rooms to be zoned and given their own schedule.  Any room with a smart TRV can demand heat from the boiler.

FreeBear

RavingMad said:

The TRV can tell the CH to come on? How does that work out of interest?

In my mind, by not having the living room rad come on, the other rads upstairs get to temp quicker?  Generally if the lounge gets too warm, I'll open the door to let some heat out so not overly bothered if the lounge rad is on.

With a smart TRV integrated in to a heating control system (or home automation), it is acting as a thermostat and can call for heat when the temperature drops. When heat is not needed, it shuts off the radiator and allows smart TRVs in other rooms to call for heat. Only when all are up to temperature does the boiler switch off or the TRV/boiler is overridden by a timer. And if the lounge is getting too hot with the existing radiator, just turn the TRV down a notch or two.

A radiator will only dissipate a set amount of heat, so shutting one down in (for example) the lounge won't make the bedroom heat up any faster. To do that, you need a bigger bedroom radiator.

Instead, what will happen, is the load on the boiler will reduce, and if it can modulate, the amount of heat produced will drop (burning less gas in the process). However, there is a minimum amount of heat the boiler can produce, and once below this, the boiler starts to short cycle which is bad for efficiency and long term reliability - Market leading boilers such as the WB Greenstar 8000 and Viessmann 050 can go down to ~3.2kW, budget end boilers, typically 6-7kW.

If you have a conventional TRV, it will shut the radiator down as the room temperature rises. Light the wood burner to heat the room, and the TRV will respond, shutting the radiator off - It doesn't care where the heat is coming from. Smart TRVs only really make sense if you are integrating them in to a whole house automation system and want fine grained zoning & temperatures on a room by room basis.

RavingMad

So I've wrongly thought that not having the lounge radiator on would mean hot water wouldn't travel through it and thus heat up other rooms quicker. Haven't really thought that the boiler would modulate down, saving gas (not the purpose of this exercise)

Even though I've got it set on 3 in the lounge, it stills gets warm when the room is toasty already, probably because it's behind a settee 

rob7475

I don't think smart TRV's are needed in most scenarios. A standard TRV will do the job just fine. If your log burner heats the room, a standard TRV will switch off the flow to the radiator as the room will be up the temperature set on the TRV.

I doubt any savings made will recoup the initial cost of a smart TRV and ongoing battery replacement etc.

Investing in a smart thermostat that has good weather compensation and ideally geofencing features is the best way to make decent savings. You also need to make sure that the thermostat can communicate properly with your boiler to fully utilise any modulating features your boiler has.

ThisIsWeird

RavingMad said:

The TRV can tell the CH to come on? How does that work out of interest?
In my mind, by not having the living room rad come on, the other rads upstairs get to temp quicker?  Generally if the lounge gets too warm, I'll open the door to let some heat out so not overly bothered if the lounge rad is on.
So it's not a cost cutting exercise but rather an efficiency thing if that makes sense?
The Hive is upstairs in the daughter's room as that gets no solar gain during the day and she complains if she's cold lol

It's a setting in the App. The Smart TRV communicates with the same receiver as the actual Hive, so can turn the receiver on and off if you want.

The Smart TRV appears on the App just like another zone - I have two zones, for example (main house, and extension), and one bedroom TRV on the 'main house' zone. 

Each has a programmed schedule and all the overrides you want. Each can also tell the boiler to come on as they work via the same receiver. So, there's a setting for the TRV in the App where you can ask it to control the boiler independently, or to just open/close according to temp, and it'll only work if the boiler is already on.

I have mine set to only open and close at the set times, because if it were to also turn the boiler on, all the other rads on that 'main house' zone would also heat up, which I don't want! Instead, I have it set for my bedroom TRV to open and close when I ask, but it will only heat the rad if the 'main house' heating is already on.

If you had a full Smart-TRV setup - one on each rad - then you'd have ultimate control over your house's heating. And each TRV would be set to also turn on the boiler as required - only the 'demanding' TRVs would receive heat.

I just didn't want that bedroom TRV to be turning the rest of the 'main' house on when it wasn't needed.

If you go for a different make of Smart TRV, I assuming it won't be connected to your existing Hive boiler circuit, so won't have any control over the boiler? Ie, it'll 'only' turn that TRV on and off, which is absolutely fine in your situation.

You also have your main Hive 'stat in a bedroom - unusual, but also pretty good, as that will be a steady temp, and not affected by your stove.

FreeBear

RavingMad said:

So I've wrongly thought that not having the lounge radiator on would mean hot water wouldn't travel through it and thus heat up other rooms quicker. Haven't really thought that the boiler would modulate down, saving gas (not the purpose of this exercise)

Even though I've got it set on 3 in the lounge, it stills gets warm when the room is toasty already, probably because it's behind a settee 

To get a room to heat up faster, you either need a bigger radiator, or crank the flow temperature up (bad for efficiency). Heat output is a function of temperature differential of room & water and radiator surface area. Basic thermodynamics (I didn't pay much attention to it at school either).

If the lounge is getting too hot at 3, turn the TRV down to 2.5 or even 2 - It doesn't have to be set at whole numbers, and you can tune it to suit your needs by going between the dots.