More TRV questions

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Hi guys, first post.

I've read a couple of threads on here about TRV's but they were quite old so i wondered what peoples prefs were nowadays.

I'm after some decent chrome TRV's for a house renovation. They will be feeding Stelrad compact range of rads.

I've been looking at Danfoss RAS-D² Chrome TRV 8/10/15mm Angled & L/S but heard they may be a bit cheap feeling? and also the Drayton TRV4 Chrome TRV 15mm Angled.

However on the Drayton the below review has put me off somewhat.

"Valves bodies are blank off apart from a small hole. As both ends take the same body the flow rate is restricted so if the radiators in question are not given priority the flow is practically non existent. Drayton's previous TRV which I've had 12 for approx 15 years have a 15mm opening in the lockshield and the TRV valve itself had only the valve with no added restriction of a small 6 mm hole (approx) drilled in the body opening".

Any thoughts or recommendations?
 
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I dont see any problems with Drayton TRVs used with a condensing boiler.

You might consider who said that!

Anyone can post on a forum like this and many things you may read will be personal viewpoints from householders and not from professionals in the heating industry.

Tony Glazier
 
However on the Drayton the below review has put me off somewhat.

...

Any thoughts or recommendations?
Yes, Drayton know what they are doing! Provided the rads are correctly balanced the "small" hole is perfectly adequate for the required flow.

Not many people know that the TRV4 has built-in balancing. If you remove the head you will see the numbers 1 to 6 on the block plastic round the brass shaft. Using the special spanner(free from Drayton) the opening in the side of the valve cqn be set to give the correct flow through the valve. There is then no need to use the LS valve for balancing.

The valve comes with the setting on 6, maximum opening. Here is a picture with it set to 1 (minimum).

View media item 18380
Provided you do not exceed the recommended 200mb pressure drop across the valve, that tiny rectangular opening will give the correct flow rate for a 600W radiator with an 11C crop across the rad. If you have a 20C drop, it is correct for a 1kW rad.

As sold, setting 6, the TRV could handle a 3kW rad at 11C or a 6W rad at 20C.
 
Its usually better to reduce the flow on the LS valve as the distributed flow resistance results in quieter operation.

Tony
 
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D_Hailsham thanks thats very informative.

You'll have to excuse my lack of experience with this, but from what you say the Danfoss should be fine.

Just one question though do i HAVE to adjust this opening from 6 if my rads are not quite 3kw?

e.g so far i'm looking at one room with Heat loss of ~3200W that i'm going to have 2 rads in. (1 at each end of the room on external walls). Rads i'm thinking of are around 1814 - 1966W so i'm just wondering will the danfoss set on 6 be ok for this.

I'm not entirely sure what i need to do with the lockshieid, or what that actually is TBH.

Previous experience is without TRV's and what i call normal flow and return valves. Basically the same valve but with a knob you can turn on the flow and just a cap on the return.

Any advise appreciated. Cheers
 
Its usually better to reduce the flow on the LS valve as the distributed flow resistance results in quieter operation.
I can't see that it will make any difference. The flow through through a radiator, from the Tee connection in the main flow to the Tee connection in the main return, will be controlled by the smaller orifice, whichever end of the rad it is situated.

If you are talking about TRV noise, this is normally due to an excessive pressure differential across the valve, which is why they recommend a maximum differential of 200mb.
 
..and how do you find out if the radiator will meet this < 200mb across the valve? Does that mean milli bar btw?? Excuse my ignorance :)

I've currently looked at stelrad compat rads and i can't see what the degree drop over them is either. They meet various standards would the info be contained there?
 
from what you say the Danfoss should be fine.
Do you mean Drayton?

If Danfoss, they are just as good. It's the cheap £5 ones from the DIY sheds you want to avoid.

do i HAVE to adjust this opening from 6 if my rads are not quite 3kw?
Again, are you talking about Drayton? And are you talking about 6 on the TRV head? If so, this is the temperature control; you set it to provide whatever room temperature you want. 4 is about 20C and 6 is about 28C.

The balancing control built into the TRV4 is really intended for large installations - offices etc. where they system has been designed by qualified engineers who have calculated all the flows and pressure drops round the system.

Previous experience is without TRV's and what i call normal flow and return valves. Basically the same valve but with a knob you can turn on the flow and just a cap on the return.
The TRV replaces the valve with a knob; the valve with a cap is the lockshield valve. If you remove the cap you will see that it is exactly the same as the wheel valve, but without the wheel!

Adjusting this valve, with a pair of pliers, controls the maximum flow through the radiator. This does two things: ensures the earlier rads do not get more than their fair share of the flow, thus depriving rads at the end of the line of any heat; sets the output of the radiator.

(Radiator output is determined by the flow rate though it as well as the temperature of the water entering and leaving the rad. Manufacturers test their rads with an "in" temperature of 75C and an "out" temperature of 65C.)

The easiest way for you do balance the rads, which is another way of saying "adjust the flow", is by using the lockshield valve.

Read How to balance a CH system.
 
Thanks loads for that i'll have a read.

Yes i meant Drayton instead of Danfoss. I think i like the aesthetics of the Drayton more and am sure it was recommended in a thread somewhere.

I just wanted to make sure it was decent enough :)

My previous house i put all the pipe work in for a combi boiler (didn't connect the gas obviously) and so knew which rads were fed first and off the main send.

With this house i've not a clue as it had an olde water tank/ hot water tank with a ventilated rad system and its now got bolted onto the same system a Air to water heat system. Ive currently got the gas boiler turned off but it drives the pumps that the AWHP needs.
 
..and how do you find out if the radiator will meet this < 200mb across the valve? Does that mean milli bar btw??
Yes mb is millibar. The pressure drop is determined by the design of the system and the pump setting, the radiator does not really enter the equation as the drop across a typical rad is normally less than 1mb (0.1kPa).

There is a natural pressure drop across the rad due to the pressure loss round the main circuit due to friction, so this is effectively fixed at design stage.

I don't think you have to worry about the pressure drop - the majority of installers don't. You would soon realize something is wrong when you start hearing a TRV making a lot of "chattering" noise as it tries to open and close.
 

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