Setting thermostatic radiator valves

quartzz

Hello, so one of these things



or yes more precisely (counts) 5 of them

(the following information is a guess and may be wrong, if you're a heating engineer, please feel free to correct me)

In a nutshell, what is the best number setting? I was thinking that keeping the dial number as low as possible (3 1/2 or 4 practically) would be a good idea. but thinking about it, if the room temperature is taking longer to get to the "target" because less hot water is allowed to flow inside the radiator, that means the boiler heating element (and pump motor I assume?) has to be "on" for longer (using more elec and presumably more heating oil), heating it up? 

since the water inside the radiator pipes is a closed system (again please correct me if), is there any advantage to having the dial on less than 5?

FreeBear

quartzz said: In a nutshell, what is the best number setting? I was thinking that keeping the dial number as low as possible (3 1/2 or 4 practically) would be a good idea. but thinking about it, if the room temperature is taking longer to get to the "target" because less hot water is allowed to flow inside the radiator, that means the boiler heating element (and pump motor I assume?) has to be "on" for longer (using more elec and presumably more heating oil), heating it up?

Changing the setting on the TRV (or thermostat) will not make the room heat up any faster. You either need bigger radiators, or a higher flow temperature (the latter will kill boiler efficiency). The TRV will only shut the flow of water off once the room has reached a certain temperature.

quartzz

I guess the question is, if the TRV is set to a lower setting, will that mean the boiler uses less electricity for its heating element, less motor pump or less heating oil. if the boiler itself uses the same heating element electricity, same motor pump electricity, and same heating oil, regardless of whether the TRV is set to 3.5, 4, or 5 (because it's just less water being allowed to flow through the radiator) then I may as well set the TRV to 5

I'm also curious (read; need to ask questions) about the TRV. as far as I can tell, there's no "intelligent" switching or temperature monitoring in there, the TRV is just a pin that gets slowly closed when the TRV dial is changed from 5 down to 1?

Reed_Richards

quartzz said:

... is there any advantage to having the dial on less than 5?

Yes, the advantage is that you won't have to strip down to your underwear to keep yourself cool enough.  Turn down the dial and you can keep your clothes on.

daveyjp

Location of thermostat is more important.  If the TRV is fully open and the thermostat is in the same room once that room reaches temperature the boiler will turn off so settings on other rads is irrelevant.

Our thermostat is currently in the lounge and both rads are set to 5.  Other rads are only set to about 1.5 as no heating is required in to those rooms most of the day, but its enough to take the chill off in the morning when the lounge is also cold.

quartzz

thermostat is in the hallway (the rads are only in rooms, with none in the hallways). so (and I'm guessing here) is it more efficient in terms of boiler heating element/motor pump/heating oil, to have the "reference" temperature in occupied rooms as TRV on 5, and to lower the other TRV's to for example 3.5

this is rather than, the current tactic of having the TRV's in occupied rooms at 3.5 to 4. being that I have just realised, that if my "maximum" TRV is set to 4, that actually means I'm wasting some boiler efficiency because I'm not using "20%" (in inverted commas) of the boiler output?

FreeBear

quartzz said:

I guess the question is, if the TRV is set to a lower setting, will that mean the boiler uses less electricity for its heating element, less motor pump or less heating oil. if the boiler itself uses the same heating element electricity, same motor pump electricity, and same heating oil, regardless of whether the TRV is set to 3.5, 4, or 5 (because it's just less water being allowed to flow through the radiator) then I may as well set the TRV to 5

I'm also curious (read; need to ask questions) about the TRV. as far as I can tell, there's no "intelligent" switching or temperature monitoring in there, the TRV is just a pin that gets slowly closed when the TRV dial is changed from 5 down to 1?

Once the TRV activates and turns a radiator off, the boiler should reduce the amount of heat being generated (assuming you have a fairly modern one that can modulate). Energy consumption by the pump and attendant electronics will remain fairly constant.

Note - If you have an electric boiler, that is probably the most inefficient and expensive way of heating a home. Cheapskate landlords like them because it means they don't have to get an annual Gas Safe certificate, and don't care about running costs.

And you are correct about (most) TRVs being dumb. You can get "smart" TRVs that, in combination with a home automation system, can call for heat. But at £70-100 each, along with the cost of a smart hub, are just an expensive gimmick for most people.

The_Green_Hornet

This may (or may not) be of help.

What is a Thermostatic Radiator Valve? - British Gas

QrizB

quartzz said:

I'm also curious (read; need to ask questions) about the TRV. as far as I can tell, there's no "intelligent" switching or temperature monitoring in there, the TRV is just a pin that gets slowly closed when the TRV dial is changed from 5 down to 1?

No, that isn't how TRVs work.

The TRV head (usually the knob bit) has a mechanism inside it that expands/contracts with temperature. Below the set temperature, the mechanism will be "short" and won't press out far enough to close the valve. Once the room is up to temperature, the mechanism expands and is "long" enough to close the valve.

It's not quite this simple as the mechanism only operates slowly and so there's a bit of a delay, but that's the principle.

Lorian

They vary a bit but roughly
Set it to 0 radiator never comes on
Set it to 5 and radiator never turns off (like not having TRVs)
Set to 2.5 turns off roughly at 19c
Bit too chilly in the room use 3. Bit too warm use 2.
If Radiator in same room as a  main system thermostat has a TRV set that one to 5. Keeping the doors shut between rooms with different settings helps create zones 
Too low in a room (0) and you are more likely to get condensation/mold in that room.

Speed of heating up is more a function of flow restrictions set when the radiators are balanced using the lockshield valves (done with all TRVs set to 5) but not in isolation, as when TRVs start to close down on the set point the flow to other radiators will start to increase (if set point not met). The water temperature may reduce at this point due to the boiler modulating down.

Overall quite a complex system, and your goal is not just to heat the right rooms up the quickest and to the right temperatures you are also aiming to keep your return temperatures low enough to keep the boiler condensing for efficiency.

quartzz

some reading needed I think. the boiler is a warmflow KC90HEE - described by one plumber as "not the best" but that could be for any number of reasons (maybe he wanted to sell me a new one). there's some features it doesn't seem to have that I think would be useful - maybe that's why it's "not the best". I think it's a condensing combi. installed 2007

my kitchen TRV also seems to be stuck - I can lower it from 5 to 1, but when I turn the dial from 1 to 5, it doesn't release the pin outwards. any time I want to turn it up, I need to unscrew the base of the dial and get a pair of pliers to "up" the pin. not a huge pain, just slightly annoying.

"The TRV head (usually the knob bit) has a mechanism inside it that expands/contracts with temperature" - ah, so it's a sort of mechanical temperature sensor? (like a bi metallic strip or something?)

.....is there any disadvantage to having the "reference" temperature as the TRV on 5, rather than 4? so the TRV is on maximum, rather than "not using" the capacity between 4 and 5?