How TRVs actually work?

[fixitflav]

You actually mean: "how do you divert the flowrate from some zones to others?"

Yes, isn't that the same thing?

Does throttling all rads (including the poorly behaving one) seem a good idea (balancing)?
No. Of course not.

Who said it does? You wouldn't throttle the poorly behaving rad.

Do you look to make all rads work equally bad?

No, you try to make them all work equally well

Does this approach work with modern CP/PP control pumps?

AFAIK modern pumps have a choice of fixed curves or PP (my Grundfos UPS2 does anyway). The approach works OK with one of the fixed curves, at lowest speed unless higher speed needed.

Does this approach work where other rads in the system need the fill flowrate?

That doesn't make much sense, but this approach gives each rad the flow it needs

Does this approach work where the average temp drop has been engineered to keep the boiler in cond mode?

Yes, set the boiler flow temperature as low as possible consistent with adequate heating, either using weather compensation or manually.
I suppose it's possible to throttle all the rads more, or use a common throttling valve, to reduce the flowrate and get lower return temperature so more condensing, but I doubt it would make a noticeable reduction in gas usage.

You get my points?

Do you get mine? How about answering the question - what is your approach?

 

[Johntheo5]

OK chaps, relax, At tremendous expense I went back through my spreadsheets where I keep everything including my last and latest will.

The EPH TRV Kvs is 1 m3/h @ 1bar. (see later)
I had also taken some readings from a outside tap that I can feed from the CWST at 5.5M, 0.55bar.

Index 1.0 flowrate 3.0LPM
Index 2.0 flowrate 3.8LPM
Index 2.5 flowrate 3.9LPM
Index 3.0 flowrate 3.9LPM
Index 4.0 flowrate 3.9LPM
Index 5.0 flowrate 3.9 LPM (full open)
So once index set to 2.5 or > then flowrate at its max.

My calcs give a Kvs of Sq.root (1.0/0.55)*3.9*60/1000, 0.3155m3/h @ 1bar, quite low vs the claimed 1.0 m3/h @ 1 bar, I can't say that the head stayed at 5.5M while testing but it would have had to fall to 0.55M if the Kvs is 1.0. I reckon the head was still 3.5 to 4M at those flows so the KVs seems more like 0.534.
I also, just now, did the same flow test with the companion L/S valve from that TRV and it flowed 3.6LPM @ "5.5M", very close to the TRVs flow rate?.

Based on the above, a 1.5kw rad with a dT of 15C requires a flowrate of 1.43LPM and the head loss through the TVR and through the L/S would be ~ 0.74M each, total of say 1.5M, how does that sound??.

 

[BlueLoo]

OK chaps, relax, At tremendous expense I went back through my spreadsheets where I keep everything including my last and latest will.

The EPH TRV Kvs is 1 m3/h @ 1bar. (see later)
I had also taken some readings from a outside tap that I can feed from the CWST at 5.5M, 0.55bar.

Index 1.0 flowrate 3.0LPM
Index 2.0 flowrate 3.8LPM
Index 2.5 flowrate 3.9LPM
Index 3.0 flowrate 3.9LPM
Index 4.0 flowrate 3.9LPM
Index 5.0 flowrate 3.9 LPM (full open)
So once index set to 2.5 or > then flowrate at its max.

My calcs give a Kvs of Sq.root (1.0/0.55)*3.9*60/1000, 0.3155m3/h @ 1bar, quite low vs the claimed 1.0 m3/h @ 1 bar, I can't say that the head stayed at 5.5M while testing but it would have had to fall to 0.55M if the Kvs is 1.0. I reckon the head was still 3.5 to 4M at those flows so the KVs seems more like 0.534.
I also, just now, did the same flow test with the companion L/S valve from that TRV and it flowed 3.6LPM @ "5.5M", very close to the TRVs flow rate?.

Based on the above, a 1.5kw rad with a dT of 15C requires a flowrate of 1.43LPM and the head loss through the TVR and through the L/S would be ~ 0.74M each, total of say 1.5M, how does that sound??.

View attachment 325891

Nice to see someone using the math.

 

[BlueLoo]

Yes, isn't that the same thing?

Who said it does? You wouldn't throttle the poorly behaving rad.

No, you try to make them all work equally well

AFAIK modern pumps have a choice of fixed curves or PP (my Grundfos UPS2 does anyway). The approach works OK with one of the fixed curves, at lowest speed unless higher speed needed.

That doesn't make much sense, but this approach gives each rad the flow it needs

Yes, set the boiler flow temperature as low as possible consistent with adequate heating, either using weather compensation or manually.
I suppose it's possible to throttle all the rads more, or use a common throttling valve, to reduce the flowrate and get lower return temperature so more condensing, but I doubt it would make a noticeable reduction in gas usage.

Do you get mine? How about answering the question - what is your approach?

Typo on the point in the middle. Should have read "full".

Aside from knackered, badly designed, old systems, i fail to understand, nor has anyone tried to prove, why, the rad(s) have to be throttled aka "balanced".

Your point about pump modes confirms mine. You have to match the pump to the system.

Trvs throw the whole "balancing" premise in the bin.

Once they begin to close, they reduce flowrate, increase temp drop and bugger up any calcs or assumptions one has made about heat loss/gain management.

It's best, to design your system for the extreme conditions and let the system sort the bit in the middle out itself.

A boiler that can cope with all rads at full blast, or only one rad.

Being cognisant that either extreme isn't ideal.

Perhaps look at a plot of reasonable and extreme conditions and then design for the mean whilst considering the limits.

This also means looking at the room heat losses and gains and the rad sizing and placement.

By varying pump and boiler settings you likely get a system much better tuned (all valves opened) rather than throttling the entire shebang and ignoring the inputs or outputs.

This is what annoys me the most about the balancing ******. It is a template application to a uninvestigated condition.

 

[berty3000]

We all seem to be dancing on the head of a pin here and and probably wont achieve consensus.

I'm not sure whether any of this is of value to the OP and whether it helps him with his original request of not @berty3000, apologies if your post has rambled and been stomped on somewhat

Nah it's all good mate, I've enjoyed reading it all and have learnt quite a bit through all the contributions. Sometimes a meandering discussion and differences of opinion can be useful

I've also been checking rads and the boiler (and my thermometers) every day, making observations and tweaks. It seems that this is necessary to get to know a system and the individual quirks of different zones. In one room I have the TRV set a bit higher because it shuts the radiator down too quickly - probably because that TRV is in a tighter spot near to a bed and wardrobe where the air around it heats up quickly. In another room, the radiator seems to run hot for some reason, so I've throttled that one down using the TRV.

I have the max output of the boiler now on 8.6KW with a low pump speed setting - works absolutely fine. And in this warmish winter weather have had the flow temperature set to 50C. Rads generally set to 3. All working fine I think. Only problem is that the room without a TRV, which has the central thermostat, is a cold room (massive old patio door) and takes time to heat up and that seems to keep the boiler running for long spells. It doesn't bother me in terms of comfort as I don't use that room much and the system is running quite cheaply - but I'm not sure if it is good for the boiler to not reach the temperature in that room for a couple of hours? It does seem to take breaks throughout the periods I have it running.

 

[denso13]

but I'm not sure if it is good for the boiler to not reach the temperature in that room for a couple of hours?

It's fine, the rooms with TRV's will turn off anyway, only heating the one with the room stat, until it is satisfied.

 

[Madrab]

Nah it's all good mate, I've enjoyed reading it all and have learnt quite a bit through all the contributions. Sometimes a meandering discussion and differences of opinion can be useful

As long as you are able to sort out the wheat from the chaff, then there's a whole load of really useful information.

Let me tell you though, there can certainly be a lot of chaff in this forum

 

[berty3000]

As long as you are able to sort out the wheat from the chaff, then there's a whole load of really useful information.

Let me tell you though, there can certainly be a lot of chaff in this forum

Haha!

Yes - what's funny about this particular topic is that there are such divergent opinions. You'd think there wouldn't be any mystery about the way heating systems work and yet I've even found some professional boiler fitters I've spoken to aren't even consistent, or don't seem to know as much as people on here. Or just don't know how to discuss it maybe. Probably theory versus practice going on as well, plus all the variables involved doesn't help. Anyway, I think I'm basically happy with how my system is working now, accepting some of the strange goings on with TRVs, and have resisted the urge to mess about with lockshields, which I don't think will achieve much in my case.

Thanks again, and to Denso for answering that other point. Plus everybody else who has posted

 

[Madrab]

Probably theory versus practice going on as well

Certainly a lot of that goes on.

If the years of doing this job have taught me anything, is there can be a huge difference between theory and practice. I have found that in many instances certain fixes shouldn't work but they do and vice versa. Guess that is down to, as you suggest, the huge number of possible variables that can be found from one situation to another (when really they should be the same) and from one piece of the same hardware to another. As you have found out, all TRV's, even the exact same ones don't or won't operate in the same way.

Took me a long time to understand now to set up some systems correctly, it really is a 'learned' operation and comes down to experience, as every one is slightly different. The other issue is that things can change over time so have to adapt. That being said, there's nothing quite as satisfying than looking after a system over the years, that you installed and it stays nice and stable with very little work required.

 

[Mister Banks]

When I had my gas boiler installed a few years ago I asked the heating engineers to check the radiator balancing, they said it was simple just adjust the lock shields on all the downstairs radiators to fully open and all the upstairs radiators open half a turn. They said the TRVs could all be set to 4 on a 1-6 scale. I now know those recommendations to not necessarily correct although all my rads heat up evenly as it happens, more by luck I think.

 

[D4dog]

Didnt realise this was so controversial. Balancing ensures efficiency and uniformity. Assume a 22mm supply and return, with rads coming off in 15mm, occasionally supporting up to 3 rads.

You have a varispeed pump. These are desinged to maintain a constant head as rads open and close.

You then have a massive double panel radiator which is closest to boiler. You cannot be bothered to balance it, becuase it is, of course, twaddle. So at the first supply/return point on the system, you get a hugely hot radiator with minimal temp loss on the return.

Water returning to boiler is therefore hot, so boiler either cycles, or adjusts its output.

Radiator farthest from the heat source therefore gets lukewarm water, and doesnt heat up properly. Repeat this over 10-15 rads and the system simply will not work..radiators of random temperatures.

So:

Balance closest radiator to heatsource with trv fully open. Adjust lockshield so temp drop about 11 or 12c. Lockshield will likely be only slightly open. Repeat process for other rads...the one farthest from the heat source will likely have its LS fully open.

So we balance so that flow and return temperatures are about the same on each rad...if a particular rad is either off or closes down becuase it has a trv of somekind, the system remains in a steady state...the variable pump will reduce the output head based on flow resistance.

So you can either do it right, or approximate ( futher from heat source, LS more open), or not bother.

Not bother = inefficient system that wont work properly.

Entirely your call.

 

[Johntheo5]

Correction here as I found my pressure gauge and also found a valve throttling the gravity supply which I opened for the test so these are the actual corrected flow tests.

The EPH TRV Kvs is 1 m3/h @ 1bar. (see later)

Index 2.0 flowrate 6.8LPM
Index 2.5 flowrate 7.1LPM
Index 3.0 flowrate 7.1LPM
Index 4.0 flowrate 7.1LPM
Index 5.0 flowrate 7.1 LPM (full open)
So once index set to 2.5 or > then flowrate at its max.
Companion L/S valve very similiar.
The dynamic head was 3.0M, 0.3bar.

My calcs give a Kvs of Sq.root (1.0/0.30)*7.1*60/1000, 0.78 m3/h @ 1bar, not far from the quoted 1.0 m3/h @ 1 bar,

Based on the above, a 1.5kw rad with a dT of 15C requires a flowrate of 1.43LPM and the head loss through the TVR and through the L/S would be ~ 0.12M each, total of say 0.24M.

 

[BlueLoo]

Didnt realise this was so controversial. Balancing ensures efficiency and uniformity. Assume a 22mm supply and return, with rads coming off in 15mm, occasionally supporting up to 3 rads.

You have a varispeed pump. These are desinged to maintain a constant head as rads open and close.

You then have a massive double panel radiator which is closest to boiler. You cannot be bothered to balance it, becuase it is, of course, twaddle. So at the first supply/return point on the system, you get a hugely hot radiator with minimal temp loss on the return.

Water returning to boiler is therefore hot, so boiler either cycles, or adjusts its output.

Radiator farthest from the heat source therefore gets lukewarm water, and doesnt heat up properly. Repeat this over 10-15 rads and the system simply will not work..radiators of random temperatures.

So:

Balance closest radiator to heatsource with trv fully open. Adjust lockshield so temp drop about 11 or 12c. Lockshield will likely be only slightly open. Repeat process for other rads...the one farthest from the heat source will likely have its LS fully open.

So we balance so that flow and return temperatures are about the same on each rad...if a particular rad is either off or closes down becuase it has a trv of somekind, the system remains in a steady state...the variable pump will reduce the output head based on flow resistance.

So you can either do it right, or approximate ( futher from heat source, LS more open), or not bother.

Not bother = inefficient system that wont work properly.

Entirely your call.

The amount of twaddle in this post demonstrates that the industry and its agents should do a bit more studying.

 

[fixitflav]

My calcs give a Kvs of Sq.root (1.0/0.30)*7.1*60/1000, 0.78 m3/h @ 1bar, not far from the quoted 1.0 m3/h @ 1 bar,

That confused me till I realised your sq root only applies to (1.0/0.3), not 7.1*60/1000. But shouldn't it be 7.2?
Presumably the 0.3 bar is the pressure drop across the TRV (not sure what you mean by dynamic head, that's usually V^2/(2*g))

the head loss through the TVR and through the L/S would be ~ 0.12M each, total of say 0.44M.

Not with you. If it's 1.2 each isn't that 2.4m? Earlier you said 3m = 0.3 bar across the TRV, unless I'm misunderstanding you test.
BTW, TVR is (or was) a sports car

 

[Johntheo5]

The amount of twaddle in this post demonstrates that the industry and its agents should do a bit more studying.

The Heat Geek knows best??.

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The Ultimate Guide to balancing heating systems. Balancing a heating system is simply making sure all the radiators or emitters heat up evenly.

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