TRV and lockshield valves

[volks]

With TRV valves that control the water flow to match the temperature, should the lockshield valve on the other end be fully open or cracked based on the radiators distance from the boiler?

Usually you balance the trv to match a manual valve on the inlet but with the trv it doesn't need doing. So should the lockshield just remain fully open to let the water out or what?

 

[denso13]

So should the lockshield just remain fully open to let the water out or what?

It is adjusted to balance the system and allow the correct temp drop across the radiator, However, if you are happy with the system and it is working ok then no real need to worry about how they are set.

 

[volks]

It is adjusted to balance the system and allow the correct temp drop across the radiator, However, if you are happy with the system and it is working ok then no real need to worry about how they are set.

Thanks for the reply! I had been misinformed they should only need adjustment if the valves weren't TRV. Good to know they'll need balancing regardless

 

[Mister Banks]

Balancing of radiators with TRV's seems to be a contentious subject. Some say balancing is required whilst others will say its a waste of time due to the TRV messing up the balancing owing to its operation.

 

[ericmark]

I can only talk about my own experience at my mothers old house. I was using electronic heads which reported current and target temperatures to the PC. I realised the temperatures were over shooting, set to 20ºC I was seeing the room heat to 22ºC, I realised what was happening was the radiator would get stinking hot, and so was still heating the room even when the TRV had closed, when the TRV's exercise at 12 midday every Saturday it takes around 3.5 minutes to do whole cycle, and it takes time for heat to reach the TRV to start with.

So the report makes it easy, if any radiator in winter has the current above target I closed the lock shield a little, after some time I had got it so every room except for living room was spot on, living room was a problem as it had bay windows, so morning sun could cause the room temperature to raise above setting even when central heating not running, nothing I could really do about that, except did not adjust on sunny days.

The thing I noted after it was adjusted is the boiler would modulate better, (Worcester Bosch rather old) and the radiators were not longer stinking hot, but just warm enough to maintain the room temperature. And there seemed very little hysteresis in the room temperatures.

I had observed another problem with my sons house, he had not set any TRV's, and the house heated up a room at a time, so easiest room for water to flow to heated first, once house was warm it worked A1, but let the house cool down, then try to reheat, it would take an age, reason was simple, if hot water returns to boiler the boiler modulates, so he had a 28 kW boiler but it was only running at around 6 kW as the returning hot water was turning down the boiler.

So looking at those two homes with modulating boilers the lock shield setting was important. However in this house the oil fired boiler does not modulate, it can only cycle on/off, and trying the same method as used with mothers house did not seem to work very well, also this house is micro bore piping, with this house having the lock shield valves not wide open, but not throttled back like other two homes seems to work better.

I now have 9 electronic TRV heads, non connected to the wall thermostat, unfortunately Nest Gen 3 does not support that, so only radiator where the lock shield valve setting seems important is the hall, if hall heats up too fast it turns off boiler prematurely. But other than hall it does not seem to matter how the lock shields are set.

So from these three homes, I would say with modulating boilers the lock shield valve setting is very important, but not so important if the boiler does not modulate, my oil boiler only monitors output water temperature, it does not monitor the return water temperature.

 

[desktop987456]

I can only talk about my own experience at my mothers old house. I was using electronic heads which reported current and target temperatures to the PC. I realised

Not trying to hijack OPs post but I had a same question as a newbie: my non condensing boiler fires when the return temperature setting gets to a preset temperature (that I can set), would throttling back LSV's matters to a non condensing boiler? (I have no TRVs on my rads)

 

[ericmark]

With a non modulating boiler normally it is only the output temperature that is monitored, if all the lock shield valves are wide open, it does not really matter as long as all radiators get hot. But with a modulating boiler the reason to modulate is so the return water is cool enough so water will condense out of flue gases releasing the latent heat, so return temperature is very important.

So with a non modulating boiler there is no need for TRV's if you can share the output between the rooms using the lock shield valves, in fact my old house the water flow through the fan assisted radiator was uncontrolled, and the fan turned on when room needed heating, and off when warm enough, and water circulated much faster than required, but it did not matter as long as the output temperature was below the setting the boiler ran.

With a modulating condensing boiler the lock shield valve, TRV, and by-pass valve are an integral part of the system, all radiators need to have a TRV so that the by-pass placed very close to the boiler will open once all rooms are satisfied and turn down the boiler (modulate it) and then cause the boiler to cycle. Most boilers has anti-cycle software, in a simple form this simply changes the off time.

So if the boiler starts and the hot water returns within a set time, (i.e. the by-pass has opened) then the boiler shuts down and increases the off time, if however it takes over the set time it decreases the off time. So the boiler has longer and longer off times if the return water is quickly returned hot.

This however can be upset if there is flow through the whole system, so old Myson fan assisted radiators or towel rails or a radiator in the room with thermostat on the wall with no TRV will defeat the anti-cycle software, it is possible some manufacturers use a more complex system to get around this problem, but I don't know how each manufacturer programs their PIC (programmable integrated circuit) I have had this problem with PLC's (Programmable logic controllers) where some one has used some clever method to remove a problem, one which comes to mind was if a sensor showed 0°C it shut down the machine as clearly the sensor was faulty, as the factory would never be that cold, but there was nothing in the instructions to say it would do that, I had to read the program to find out.

Remember I am talking as an electrical engineer not a heating and ventilation engineer, maybe they are told by the manufacturers what is programmed into the boiler?

If central heating works we pay it no attention, it is only when it is not working, that we look at why, so if a boiler cycles on a regular basis we don't flag this up as a fault, no one looks at the fuel consumption and says there must be something wrong here, it's using too much fuel, if it works, then we sit back satisfied.

So if the wall thermostat is controlling the home temperature instead of the TRV's we don't realise that the boiler is not gaining the latent heat, the heating engineer may look at the flue and say that moisture should not be coming out of the flue it should be going down a drain, but as the user we have no idea if the flue is right or wrong, and that includes me.

What I can't understand is why we have wall thermostats with systems using linked TRV's, they seem to be pointless. To my simple mind if the current temperature is below target temperature on any TRV the boiler should run. Otherwise the boiler should stop. So we need a hub to collect information from each TRV, but I see no place for the wall thermostat.

However if the TRV is not linked, one thing it can't do, is once the boiler has turned off, tell the boiler it is needed again, as once it has turned off, the water stops flowing. So if the TRV is set to 20°C and the room hits 21°C clearly the boiler is not required, so if there is a wall thermostat set just 1°C higher than the TRV, as warm weather arrives it will switch off.

However this may work with a fan assisted radiators where the air is circulated around the room, but in most rooms if you place thermometers around the rooms you will see readings which are widely different, at the moment to right of my PC at TRV height it says 16.6°C but at head height while sitting the thermometer says 19.7°C less than 3 foot apart.

So we place the wall thermostat at 1600 mm high and the TRV at 300 mm high, so they will never match while the heating is required. I can look at my hall TRV which says 18°C and my wall thermostat which says 17°C which to be frank is unusual to see them so close when outside it says 4.4°C normally there is around 4°C difference between them, I will guess when I walk down stairs I will find kitchen door open which has cooled the wall thermostat.

So in this house the wall thermostat is more like a timer, it slowly through the day increases temperature set by 0.5°C so boiler will run at regular intervals, as the TRV can't set room temperature if boiler is not running.

I have said before near enough engineering, every house is different, sun through windows, cooling winds, doors left open or closed, fan sucking air out of bathrooms and kitchens, and air up disused chimneys, heat from the flat below or alongside, there is no magic formula, there is a reason the heating engineer is called an engineer, he needs a lot of training to over level 3 i.e. degree standard to be able to walk into a house and work out what is required, I did not cover that with my degree, I touched on it when training for heat treatment and stress relief, but I was working at 600°C not 20°C.

You can't expect a plumber to work out how central heating needs setting up, he may be able to seal a flat roof, although today not using lead which is what a Plumber by definition is trained to work in, but he may have an idea like anyone else how central heating works, but that is not what he has trained to do. He has trained to do what 100 years ago would have been done using lead. He may use modern materials instead of lead, but he is not an engineer.

 

[desktop987456]

Thanks for the detailed reply. I have a fan assisted coil unit, I have observed when it is running my boiler's burner stay lit a lot longer resulting in a lot of gas consumption which I am desperately trying to conserve these days! Any pointers why is that?

 

[volks]

With TRV valves that control the water flow to match the temperature, should the lockshield valve on the other end be fully open or cracked based on the radiators distance from the boiler?

Usually you balance the trv to match a manual valve on the inlet but with the trv it doesn't need doing. So should the lockshield just remain fully open to let the water out or what?

Hey all!

So I gave this a go today. Most my radiators show a drop of about 6 degrees between flow in and flow out.

This is with the lock shield fully open. If I close it, the temperature of the rad drops but the drop between in and out is still around 6 degrees difference.

Feels like there isn't a lot I can do to resolve this, but I guess as my drop is consistently around 6 degrees on most radiators it's fairly balanced, just not at the magic number of 12 degrees as people recommend.

 

[Johntheo5]

Its quite difficult IMO to balance rads using LSVs as the difference between 1/8 and 1/4 of a turn open can be huge in the rad dT. You can get TRVs with a inbuilt index that will allegedly give very fine control of the max flow/dT.
Even mechanical TRVs give in my own experience very good control down to about 50% of a rads rated output as the return temperature will then be down to almost room temperature, they will then shut off until the room temperature falls before they commence reopening and don't give quite the same control but still not bad. If you reduce the boiler temp down to say 50C then they will still be in full control down to 30% of the rated rad output.
I have 10 TRVd rads, all unbalanced and all work quite well.

 

[desktop987456]

Hey all!

So I gave this a go today. Most my radiators show a drop of about 6 degrees between flow in and flow out.

Thanks. Yours must be a condensing boiler? Have you checked your gas consumption while you adjust LSVs? Does it go down with restricted flow? Just curious and want to know.

 

[volks]

Thanks. Yours must be a condensing boiler? Have you checked your gas consumption while you adjust LSVs? Does it go down with restricted flow? Just curious and want to know.

It is a condensing boiler. Not checked gas consumption not really been bothered by that, just wanted to get the most heat out I could without turning up the boiler temp.

 

[Johntheo5]

It is a condensing boiler. Not checked gas consumption not really been bothered by that, just wanted to get the most heat out I could without turning up the boiler temp.

 

[Johntheo5]

It is a condensing boiler. Not checked gas consumption not really been bothered by that, just wanted to get the most heat out I could without turning up the boiler temp.

You will get ~ the following outputs/temperatures assuming you had a 100% rated rad (50deg rad)
So assuming flow/return/(dT) of 75/65/(10)C to give 100% output with a room temp of 20C.....

63.8C/56.2C/7.6C gives 75% output
51.9C/46.9C/5.0C gives 50% output
38.5C/36.0C/2.5C gives 25% output

The above assumes that the flowrate remains the same at ~ 1.43LPM/kw

 

[desktop987456]

You will get ~ the following outputs/temperatures assuming you had a 100% rated rad (50deg rad)
So assuming flow/return/(dT) of 75/65/(10)C to give 100% output with a room temp of 20C.....

63.8C/56.2C/7.6C gives 75% output
51.9C/46.9C/5.0C gives 50% output
38.5C/36.0C/2.5C gives 25% output

The above assumes that the flowrate remains the same at ~ 1.43LPM/kw

Interesting, I have a question on flow rate calculation, how much water a radiator 600x1200mm can hold. It surely depends if you have choked back the LSVs? Correct?