Danfoss RAS-C2 TRV's radiator value adjustment

[PJ-DIY]

The hallway is 'L' shaped, with two front doors, a PVCu outer door and a timber inner door. The inner door opens inward hinged to the right as you walk in, the door opens back to the radiator so draughts are kept to a minimum (thinking of the radiator TRV at this stage)

As you enter the hall and turn right 'L' shaped hall, the room stat is on the right hand wall, just after the bathroom door. This should protect the room stat from any draughts from the front doors when opened. But there is a towel rail radiator in the bathroom, (room stat outside the door to the left, towel rad in bathroom to the right) so I am aware of heat from this affecting and cutting off the room stat. The bathroom rad doesn't have a TRV value so is always on when the system is on, we tend to make sure the bathroom towel rad is always covered with towels to absorb the heat from this radiator.

So the room stat in the hall should not be affected by draughts from the front door, and should not be affected by the bathroom door which we keep closed most of the time. The hall radiator is on #1, the room stat in the hall 25 C, so at this time of year the heating shouldn't come on, as we have not yet had cold autumn weather heating is probably only likely to come on at night, and the temperature in the hall would never be high enough to trip the room stat off. Doors to all rooms are closed at night time which means each TRV should control heat to just the rooms they are controlling, if I am understanding correctly, if not please say.

Some radiators, one in particular, we have found come on (through the day) with TRV at #2 to #2.5 when the room temperature is 20 C or just above.

Thank you for your help.

 

[PJ-DIY]

Only real exception is the hallway when the front door is opened. In this case, if thermostat is located in the hall then cold draft causes thermostat to call for heat with the effect of overheating rest of the house.

I agree with everything else you wrote - saved me writing it! However you seem to have forgotten that TRVs are controlling the temperature in other rooms so they will not overheat when a cold draught switches the wall stat on.

Hi, from the point of view of 'over heating', I see this as a radiator coming on with a TRV at only #2 or #2.5 when the room temperature is just over 20 C which does in effect cause over heating by increasing the overall room temperature until the stat trips off again. As I see it, correctly me if wrong, with doors shut the TRV should surely only come on if the room temperature (around the position of the stat) is low enough to trigger the switch on.

By heating coming on when the temperature is greater than that set on the TRV it can only increase the room temperature further.

 

[Agile]

Try swapping that head with another and see what effect that has.

These are pretty good but not precision items.

Most TRV4 will give about 21 C at about 3 1/2 setting.

Tony

 

[D_Hailsham]

The hall radiator is on #1, the room stat in the hall 25 C, so at this time of year the heating shouldn't come on, as we have not yet had cold autumn weather heating is probably only likely to come on at night, and the temperature in the hall would never be high enough to trip the room stat off.

If the hall rad is on #1 it will turn the rad off when the room temperature is about 15C, so the hall temperature will never rise to the 25°C set on the room stat. The only control over the boiler is then the boiler's own internal stat - set to about 70°C. The boiler will therefore continue to run, even when all the rooms are up to temperature. This wastes gas.

Obviously, if the doors are closed the TRV in a room will control that room's temperature; but don't forget that there is always some heat leaking between rooms through the walls.

Some radiators, one in particular, we have found come on (through the day) with TRV at #2 to #2.5 when the room temperature is 20 C or just above.

How are you performing this test? Are you leaving the TRV set to, say, #2, overnight and then checking the temperature during the next day and finding it's 20C and the rad is still giving out heat? If so, the TRV head may be faulty. Try swapping it for another head.

 

[jedi]

Have you seem this video? There is a special tool! Maybe someone has set up the valve this way... I have the same valves..

 

[Steelmasons]

Good luck balancing a system "the Drayton way"..

Using a Jet temp gauge says it all really. , absolute garbage.

With numerous temp and pressure gauges installed in a plant room they all read different.

11c dT ?

 

[Agile]

I am so surprised that so many of these guides are still being produced quoting just an 11 C temp drop.

That's appropriate for a non condensing boiler.

But for a condensing boiler it should be 15-20 C.

Tony

 

[D_Hailsham]

Good luck balancing a system "the Drayton way"

Have you ever tried it?

I had a spare Drayton body lying around and was curious what effect their balancing system had, so I obtained a couple of the special keys from Drayton - for free. Setting 6 on the body (not the TRV head) is fully open and can be seen in this pic:



Note how small the opening is compared to the 15mm diameter that the pipe fits into.

Setting 6 would handle a rad up to a max of 3kW with an 11C drop and 6kW at 20C

As you turn the adjuster the opening is reduced. This is (I think) set to 3 (number 1 is even smaller):



This would be used for a rad up to a max of 1250W at 11C or 2500W at 20C

Setting #1 (not shown) covers rads up to a max of 570W at 11C and 1kW at 20C

These figure are based on the differential pressure across the valve not exceeding the recommended maximum of 0.2 bar. Using a more realistic figure of 0.05 bar the rad sizes for the different settings of the TRV4 balance adjuster would be (20C differential - half for a 10C diff):
1 - 500W
2 - 725W
3 - 1150W
4 - 1800W
5 - 2400W
6 - 2900W

 

[Steelmasons]

Noise issues.

 

[PJ-DIY]

How are you performing this test? Are you leaving the TRV set to, say, #2, overnight and then checking the temperature during the next day and finding it's 20C and the rad is still giving out heat? If so, the TRV head may be faulty. Try swapping it for another head.

No, we have put the heating on 24 hours, and when the radiator comes on looking at the thermostat on the cupboard in the same room, which is in a central position away from the radiator, direct sun light or direction line of convection of the heat from the radiator.

 

[PJ-DIY]

The hall radiator is on #1, the room stat in the hall 25 C, so at this time of year the heating shouldn't come on, as we have not yet had cold autumn weather heating is probably only likely to come on at night, and the temperature in the hall would never be high enough to trip the room stat off.

If the hall rad is on #1 it will turn the rad off when the room temperature is about 15C, so the hall temperature will never rise to the 25°C set on the room stat. The only control over the boiler is then the boiler's own internal stat - set to about 70°C. The boiler will therefore continue to run, even when all the rooms are up to temperature. This wastes gas.

Obviously, if the doors are closed the TRV in a room will control that room's temperature; but don't forget that there is always some heat leaking between rooms through the walls.

There are a couple of issues being discussed that I am trying to get my head round, one of obviously the radiator/temperature issue stated.

The other is the room stat and radiator TRV issue.

Taking the latter... if as you say the hall TRV is set at number 2, est 15 C, and the room stat set at 25 C I can see what you say that it will never reach the room stat temperature so will never switch off, hence the reason the bathroom towel rail rad is always hot.

But, if I lower the room stat to say 20 C, and raise the hall TRV, if the hall heats up to the room stat temperature it switches off the 'whole system'. So if heat loss in one room is greater than all other rooms that room will cool down faster and the system will not come on again until the hall is cool enough to trigger the room stat and for the system to fire up again.

Comments welcome please?

 

[D_Hailsham]

How are you performing this test? Are you leaving the TRV set to, say, #2, overnight and then checking the temperature during the next day and finding it's 20C and the rad is still giving out heat? If so, the TRV head may be faulty. Try swapping it for another head.

No, we have put the heating on 24 hours, and when the radiator comes on looking at the thermostat on the cupboard in the same room, which is in a central position away from the radiator, direct sun light or direction line of convection of the heat from the radiator.

Still unsure what you are doing. You talked earlier the rad coming on at #2 or #2½ and now say "when the rad comes on", but how do you know it comes on at that value? Are you treating the TRV like a tap and slowly turning the head up from the * mark until you can feel the rad getting warmer, or even turning down from 6 until the rad goes cold?

If so, that will tell you nothing as a TRV takes about 20 minutes to react to changes. In any case, a TRV is not a tap, it's a flow control device. When you set the TRV to a number (which represents a room temperature, but not a specific one) the mechanism adjust the flow through the rad to maintain that temperature. If the room is cold, the flow is maximum; as the room warms up the flow automatically reduces until, when the set temperature is reached the flow is just enough for the rad output to balance the heat lost from the room. If it gets too hot for some reason (TV turned on, room fills with people etc) the TRV may stop the flow altogether, so the rad cools down.

If I lower the room stat to say 20 C, and raise the hall TRV, if the hall heats up to the room stat temperature it switches off the 'whole system'. So if heat loss in one room is greater than all other rooms that room will cool down faster and the system will not come on again until the hall is cool enough to trigger the room stat and for the system to fire up again.

The heat loss from a room is determined by its dimensions and construction, and by its surroundings - adjacent rooms etc. Just because one room has a heat loss of 2kW and another 4kW does not mean that the temperature in the 4kW room will drop twice as fast as the 2kW room.

 

[PJ-DIY]

How are you performing this test? Are you leaving the TRV set to, say, #2, overnight and then checking the temperature during the next day and finding it's 20C and the rad is still giving out heat? If so, the TRV head may be faulty. Try swapping it for another head.


Still unsure what you are doing. You talked earlier the rad coming on at #2 or #2½ and now say "when the rad comes on", but how do you know it comes on at that value? Are you treating the TRV like a tap and slowly turning the head up from the * mark until you can feel the rad getting warmer, or even turning down from 6 until the rad goes cold?

If so, that will tell you nothing as a TRV takes about 20 minutes to react to changes. In any case, a TRV is not a tap, it's a flow control device. When you set the TRV to a number (which represents a room temperature, but not a specific one) the mechanism adjust the flow through the rad to maintain that temperature. If the room is cold, the flow is maximum; as the room warms up the flow automatically reduces until, when the set temperature is reached the flow is just enough for the rad output to balance the heat lost from the room. If it gets too hot for some reason (TV turned on, room fills with people etc) the TRV may stop the flow altogether, so the rad cools down.

If I lower the room stat to say 20 C, and raise the hall TRV, if the hall heats up to the room stat temperature it switches off the 'whole system'. So if heat loss in one room is greater than all other rooms that room will cool down faster and the system will not come on again until the hall is cool enough to trigger the room stat and for the system to fire up again.

The heat loss from a room is determined by its dimensions and construction, and by its surroundings - adjacent rooms etc. Just because one room has a heat loss of 2kW and another 4kW does not mean that the temperature in the 4kW room will drop twice as fast as the 2kW room.

I can see your frustration understanding and can see why you say those things but, No, I am not confirming the things as you suggest.

I feel frustrated also as it does not make sense to me either, allow me to confirm.

I had the heating on 24 hours when I quoted the items stated, I did so to be able to monitor through the day when the room temperature was far higher than the TRV value was set. Since then I changed the heating to come on at 7pm and go off at 7am. Doing so means I can see what happens after 12 hours with the system switched off.

I sat a couple of meters from the radiator last night, the room temperature on my digital temperature screen showed 22.3 C, the radiator was cold as one would expect having been off for 12 hours. I cannot say exactly to the minute, but within 5 minutes of the heating system coming on I felt heat convecting from the radiator, I felt the rad and it was definitely warming up??? (I had not touched anything)

When I have said in the past the heating came on at the radiator what I am confirming is, although the TRV is far lower than the room temperature the radiator is warming up!

The portable digital thermometer is one of three I have that also show the relative humidity, I have checked them all and only get 0.1 C difference between each so know they are not faulty.

I will wait for the radiator coming on tonight around 7pm, I will check the room temperature at that time, I think I will also place the digital thermometer near to the TRV valve, before the heating comes on to, to see what the temperature is near the valve.

 

[PJ-DIY]

I was told by a friend the valves were Drayton TRV 4's.

I have just been looking on the internet, they are not the valves I was told they were, the ones on my radiators going by the picture on Screwfix website are Danfoss RAS-C2 White Chrome TRV's

Sorry for getting this wrong, I put Drayton TRV 4's as that was what I was told they were by a friend whom I though would know.

 

[PJ-DIY]

I have sat here waiting for the timer to reach 7pm and the heating cycle to come on if the heating levels require it to do so.

5 minutes before it came on, whilst the radiator was still cold, I took temperature readings.

On the Welch dresser it was 24.3 C, placing the digital thermometer on top of the TRV it dropped to 22.1 C

The TRV valve is set to 2.5 at that level the heating should not come on.

7.05pm the radiator is warming up!

No other radiator in the bungalow with TRV valves have come on, only the bathroom towel rail rad which doesn't have a TRV fitted.

The TRV valve in this room must be faulty, would you agree?

One other comment, the same thing happened last night, but when we got up this morning 7.45 am (heating timer had been on 7pm to 7am) the room temperature was 19.3 C and the radiator was only moderately warm. It hadn't over heated?

It is 7.20pm now and the radiator is quite warm to touch.