How TRVs actually work?

[JohnD]

@berty3000

Do your own research before deciding to ignore blueloo's ill-informed advice.

 

[BlueLoo]

@berty3000

Do your own research before deciding to ignore blueloo's ill-informed advice.

Exactly, do your own research.

Before following anyone's bad habits and practices

 

[D4dog]

In a mixed source heating system TRVs are useful for reducing the use of the radiators where you have eg a wood burner. In theory (but rarely in practice), if the radiators are balanced AND CORRECTLY SIZED FOR EACH ROOM, then the TRV should not really be needed...all the rads will have the same temp differential, and the boiler will turn off once central stat is happy that house is warm. TRV are best cosidered as a secondary control function where you want cooler rooms eg bedrooms) than the central part of the house, or in any room with additional heating.

Use the LS to properly balance the rad (11 or 12c), and set your central stat to the required temp. Use TRVs to vary that temperature downwards.

I have solid fuel boiler, heatstore, backup oil boiler 2 log burners and split zone heating. The TRVs sre effective and shutting down already warm rooms, and the two central stats (one for each zone) ensure house stays at required temp. Oil boiler is rarely if ever used!

That said, havent tried the trvs with remote stas...in theory they will work more accurately, but still a blunt tool.

 

[Johntheo5]

Some, like Evohome simply use the (old) TRV body as a spring loaded valve but thats where the similarity to TRVs stops, the Evohome head monitors the room temperature and also incorporates a (battery powered) motorized geared actuator that controls the valve opening from a controller that gets a signal from every head every 4 minutes (I think) and then signals the motorized valve to move to its required position.

 

[BlueLoo]

In a mixed source heating system TRVs are useful for reducing the use of the radiators where you have eg a wood burner. In theory (but rarely in practice), if the radiators are balanced AND CORRECTLY SIZED FOR EACH ROOM, then the TRV should not really be needed...all the rads will have the same temp differential, and the boiler will turn off once central stat is happy that house is warm. TRV are best cosidered as a secondary control function where you want cooler rooms eg bedrooms) than the central part of the house, or in any room with additional heating.

Use the LS to properly balance the rad (11 or 12c), and set your central stat to the required temp. Use TRVs to vary that temperature downwards.

I have solid fuel boiler, heatstore, backup oil boiler 2 log burners and split zone heating. The TRVs sre effective and shutting down already warm rooms, and the two central stats (one for each zone) ensure house stays at required temp. Oil boiler is rarely if ever used!

That said, havent tried the trvs with remote stas...in theory they will work more accurately, but still a blunt tool.

A great example of the absolute twaddle repeated about radiator "Balancing".

You've quoted stuff there without a dogs clue as to what or why.

 

[opps]

Low temps are unhealthy to. No one should have to endure 15c indoor temps, IMO 18-20c should be the aim for most people.

I haven't read the whole of this post...

I am not sure that I agree that 15c is necessarily bad. 18-20c might simply be considered more "comfortable" by some people.

According to the Curious Cases of Rutherford and Fry, women tend to feel colder than men at lower temperatures.

I am currently working on scaffolding. I can confirm that being cold seems to force my body to expend more energy to stay warm. Day one of the job- it was minus 2 when I left (I only did a short day). I was wearing two cotton t-shirts, a cardigan and two coats. The next day it was about 5 degrees, I took off one of my coats.

In my, limited, experience, most people would rather sleep at 15c than 20c.

I am not dismissing what you say, but... as someone that occasionally finds themselves working out doors over winter, your body can adjust, and adding layers makes a massive difference. Granted, someone sitting in a house on the sofa, they may find 18-20c more comfortable.

 

[Mister Banks]

I haven't read the whole of this post...

I am not sure that I agree that 15c is necessarily bad. 18-20c might simply be considered more "comfortable" by some people.

According to the Curious Cases of Rutherford and Fry, women tend to feel colder than men at lower temperatures.

I am currently working on scaffolding. I can confirm that being cold seems to force my body to expend more energy to stay warm. Day one of the job- it was minus 2 when I left (I only did a short day). I was wearing two cotton t-shirts, a cardigan and two coats. The next day it was about 5 degrees, I took off one of my coats.

In my, limited, experience, most people would rather sleep at 15c than 20c.

I am not dismissing what you say, but... as someone that occasionally finds themselves working out doors over winter, your body can adjust, and adding layers makes a massive difference. Granted, someone sitting in a house on the sofa, they may find 18-20c more comfortable.

You're right that being physically active results in our bodies being able to tolerate lower temperatures and feel comfortable but when at home sitting watching TV, reading a book or doing other less active tasks I think, IMO, that 15c is pretty low.

 

[JohnD]

...women tend to feel colder than men at lower temperatures....

Shock news to any married man.

 

[Johntheo5]

No. If you do that the room with TRV might get too warm before the timer or central thermostat stops the boiler, wasting gas. If it's left at the setting you want the room won't heat any more slowly, as the TRV is wide open until temperature is reached.

EPH are of the same view "By turning to a higher figure setting will not heat the room any faster" I have used their TRVs for years but afraid I can't agree with this, I came across a test I did a few years ago using a new TRV and using a digital thermometer and a vernier calipers to measure the valve opening.
With head removed the maximum (stroke) opening of the valve was 3.48mm, with the head attached and set to index 2.5 and left in a room at 14.9C for over a hour the valve opening was 1.42mm, when placed in a room at 20.9C it fully closed after ~ 18 minutes. I find that a setting of 2.5 on these TRVs gives me a very consistent 20.2C/20.5C.
The room would/will definitely heat up faster if the head was fully rotated to allow a opening of 3.48mm but simply cannot heat it up in the same time with a opening of 1.42mm, it will also start throttling down as the air temperature starts rising, but these certainly arn't on/off controllers.

 

[Madrab]

A great example of the absolute twaddle repeated about radiator "Balancing"

Have seen this comment a few times and have to disagree, it seems to be your opinion that balancing is somehow not relative in modern systems, I'm afraid to say that you couldn't be more wrong. Balancing is a key processes that's used when setting up a central heating system to minimising warm up times and thereby helping to maximise efficiency.

Try telling some of my clients with larger properties whose radiators just wouldn't heat up properly or evenly, without their system being balanced. Balancing is not just about temp drops across the radiators.

 

[BlueLoo]

Have seen this comment a few times and have to disagree, it seems to be your opinion that balancing is somehow not relative in modern systems, I'm afraid to say that you couldn't be more wrong. Balancing is a key processes that's used when setting up a central heating system to minimising warm up times and thereby helping to maximise efficiency.

Try telling some of my clients with larger properties whose radiators just wouldn't heat up properly or evenly, without their system being balanced. Balancing is not just about temp drops across the radiators.

What is it you think is being balanced?

 

[Madrab]

What is it you think is being balanced?

I don't 'think' that anything is being balanced.

By controlling the flow to each radiator to ensure that the heat from the boiler reaches each of them at roughly the same time and at the same rate, that then ensures that all the radiators will heat up evenly and consistently and therefore heat the space up evenly and consistently. To me if that is achieved and the radiators receive their heat at the same time and at the same rate, evenly and consistently then that is one component of the system being 'balanced'.

Could you use other words to indicate that - equilibrium, stable, equalised - yes but balanced is just as indicative.

 

[Johntheo5]

I've seen it suggested that the rads should be balanced with the TRVs (if installed) fully open, I would suggest that the rads are balanced (re the L/S valves) with a cold/cool system and with the TRVs set to their normal index, even in their cool condition the TRVs will cause a restriction in the flow rate, (see post #54 in "How TRvs actually work") where I found that the TRV (EPH, new) was only open 1.42mm at a index setting of 2.5 (21C/22C I find with these TRVs), the full stroke opening is 3.48mm with the head removed or fully opened.

 

[Madrab]

with a cold/cool system and with the TRVs set to their normal index

That would seem to make perfect sense, especially if all TRV's when sitting 'fully open' do exert some force on the pin and close the valve to some degree, not sure they all do though? I haven't definitively tested that fact but when fitting some TRV there is a feel that the pin isn't being depressed by very much. I suppose it's gaining an understanding as to just how much that actually effects the flow through the valve. i.e. how closed does a valve need to be before it starts to affect the flow.
I guess where I'm coming from with that is that there can be huge difference in flow into a rad by the turning of a lockshield (compression type valve) by even a 1/6th of a turn and that's only after opening the valve half a turn in some cases. I guess it would need to be understood how much of an opening of the valve (increase in flow) that 1/6th of a turn creates, surely can't be that much, rather than a straight up and down movement created by the TRV head. That is then coupled with how sensitive a (Wax/liquid) TRV head is and how much it opens a valve when operating.

 

[BlueLoo]

I don't 'think' that anything is being balanced.

By controlling the flow to each radiator to ensure that the heat from the boiler reaches each of them at roughly the same time and at the same rate, that then ensures that all the radiators will heat up evenly and consistently and therefore heat the space up evenly and consistently. To me if that is achieved and the radiators receive their heat at the same time and at the same rate, evenly and consistently then that is one component of the system being 'balanced'.

Could you use other words to indicate that - equilibrium, stable, equalised - yes but balanced is just as indicative.

Great answer.

But,

"Balancing" as you've put it does NOT ensure the space is heater up evenly (With-respect-to other-spaces).

Quite the opposite.

This is why i have such a problem with the whole thing. It does nothing to consider the causes, only looks to provide a blanket solution to an unknown symptom.

It's utterly un-engineering.

When these issues are brought up (in fact, balancing is insisted upon regardless), nobody asks what the system actually is. Nobody asks about conditions. Nobody asks about heat loads etc.

You've dynamic control valves (Trvs), dynamic circulation (pumps) dynamic heat outputs (modulation) dynamic sensors (open therm, weather sensors) etc etc.

You can't apply a global static solution to dynamically localised components.

"I've a rad that is slow"
The solution isn't to kill all the other rads. The solution is to speed the slow one up.

I've written about this.