Smart TRV

Belenus

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.

Our one year old Vaillant EcoFIT Pure 625 System Condensing Boiler shuts off the burner for a while if it detects short cycling.

Presumably most, if not all, modern boilers also have anti short cycling measures.

Albermarle

FreeBear said:

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.

Notwithstanding the above, if some radiators are turned off, then surely the other radiators will heat up to temperature quicker? So that would heat up the those rooms a bit quicker, although the difference might not be that great?

FreeBear

Albermarle said:

FreeBear said:

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.

Notwithstanding the above, if some radiators are turned off, then surely the other radiators will heat up to temperature quicker? So that would heat up the those rooms a bit quicker, although the difference might not be that great?

If heating the water from cold, there would be less circulating in the system with some of the radiators shut down. It would save a few minutes before the active radiators started to heat up. But unlikely to make much difference in real terms.

Crunching a few numbers. My CH holds ~50l of water and the boiler for this discussion, rate limited to 12kW. Time to heat that water from 16°C to 60°C is 12:47 mins (discounting heat loss via the radiators). remove 7l from the equation that one radiator contains cuts the heating time to 11 minutes exactly.

Based on data collected so far, it takes around 30 minutes to raise the temperature in the house by 1°C, so that 1:47 min saving is not really going to be noticeable. Would save approximately 1.7kWh of gas plus what ever energy was needed to keep the rest of the house warm.

ThisIsWeird

Quite a few different scenarios here!

If RavinfMad's rads aren't balanced correctly, then shutting off the sitting room one could well cause the others to heat up more quickly. Given that a sitting room rad is usually a biggie - the biggest in the house - then this should help as well.

It makes complete sense to be able to shut it off when the stove is on. You could even do this via Alexa or similar.

FreeBear

ThisIsWeird said:If RavinfMad's rads aren't balanced correctly, then shutting off the sitting room one could well cause the others to heat up more quickly.

Given that some advocate balancing radiators by feel, poor balance could indeed be a contributory factor.

See this recent thread -> https://forums.moneysavingexpert.com/discussion/6558035/front-room-radiator-never-gets-hot/p2

RavingMad

We replaced our boiler in Aug and the engineer went round making sure they were all heating as expected.  The lounge radiator was replaced too with a bigger one as it never warmed the room sufficiently.

It's a WB heat only boiler so no flow temps to tinker with. I did think today to crank the one dial on the boiler to max rather than 70/80% that it's on now. That'll heat up the water quicker albeit use more energy?

FreeBear

A WB boiler made this year can be set to run at a lower flow temperature and yet still run hot to heat the tank (called Priority Domestic Hot Water).

With the right thermostat, it should also be able to dial back on the flow temperature as the house gets up to temperature (sometimes called modulation).

If you can't do PDHW or modulation, you need to get the installer back and ask why he didn't fit the right controls - Had a boiler fitted last year that allows me to control DHW & flow temperatures independently. Doing so, gets efficiency up as high as 98%, so I get to save gas and money.

ThisIsWeird

RavingMad said:

We replaced our boiler in Aug and the engineer went round making sure they were all heating as expected.  The lounge radiator was replaced too with a bigger one as it never warmed the room sufficiently.

It's a WB heat only boiler so no flow temps to tinker with. I did think today to crank the one dial on the boiler to max rather than 70/80% that it's on now. That'll heat up the water quicker albeit use more energy?

You could. Or just - from cold - open every rad's TRV to max, turn on the boiler, and visit each room in turn, repeatedly, and note how quickly each rad gets to temp. A piece of paper with each rad listed - temps at 5 mins, 10 mins, 15, etc. 'Warm'...'getting hot'...'can keep hand on for 20 seconds', '5 seconds', etc.
Obviously a rough guide, but see if any are way out of sync.
On a well-balanced system, they should all heat up at roughly the same speed.

ThisIsWeird

On the Smart TRV issue, I don't know how far you've gone with your Hive - you'll have your App control, I'm sure, but also 'voice' via Alexa or similar? 
You should be able to do the same with whichever other Smart TRV make you go for, so they are controlled just as easily; "Alexa, sitting room radiator off!".
And Hive uses the pretty standard ZigBee Comms protocol, I understand, so whether that would help to amalgamate them, I don't know.
Is it a reason of cost that you are considering a different make? Keep an eye on eBay for Hive bargains - they do come up.
The ultimate home CH control would, I think, consist of a Smart TRV on every rad that's in regular use (occasional rooms can be done manually), and each one with its own schedule - no wasted heat coming out of any rad when not required. No central 'stat either. But, not really worth the initial outlay, unless you got it cheap!

RavingMad

Thanks Weird.  I have a couple of Alexa's gathering dust as I'm happy controlling everything via the phone.

Something came up on Amazon, might have been Tado, which got me thinking of doing this.  I have seen Hive sets on eBay that people want rid of for various reasons but as you said big outlay for control that's more than I need/want at the moment