System balancing when TRV's are fitted

[donrkebab]

I have just replaced 8 rads and fitted TRV's. I balanced the system by just feeling the warmth at each rad and now they all heat up at the same rate.

Do I need to do anymore? do I need to check actual temp drops at each rad? It seems to me that TRV's will always affect the balancing due to them continually opening and closing, so an accurately balanced system is pointless.

Am I right or wrong?

 

[Agile]

You should balance with all the TRVs fully open.

Con boiler to 15 C diff temp and non-con boiler to 11 C.

You can guess the diff with hands if you don't have a contact digi thermometer.

Tony

 

[D_Hailsham]

It seems to me that TRV's will always affect the balancing due to them continually opening and closing, so an accurately balanced system is pointless.

Am I right or wrong?

TRVs are not like a switch, on or off. They are more like the volume control on your TV: if it's too loud you turn it down a bit and vice versa. But in the case of the TRV it's fully automatic, keeping the room temperature constant by adjusting the flow through the radiator. If the system is correctly balanced, a change in the flow through one rad will have little effect on the other rads.

According to Drayton

Failure to correctly balance a system can lead to complaints of inefficient operation and criticism of the operational abilities of thermostatic radiator valves, when in fact the valves are not the source of the problem. Common complaints raised by home owners include:

• Rooms are slow to reach temperature even though radiators are sized correctly
• Some rooms with correctly sized radiators never reach temperature during cold periods
• Room temperatures fluctuate particularly if the TRV is on a low setting

It must be remembered that no amount of commissioning and adjustment will compensate for a poorly designed or installed system. There is no substitute for good design.

 

[FiremanT]

TRVs are not like a switch, on or off. They are more like the volume control on your TV: if it's too loud you turn it down a bit and vice versa. But in the case of the TRV it's fully automatic,]

No they are not.

They turn the rad on or off, but should maintain the ROOM at a desired temperature.

 

[Madrab]

I have to agree somewhat with Fireman, when a TRV reaches the desired temperature that it has been set to, it turns the flow to the radiator off, when it cools below the setting it opens again to restore the flow.

http://www.radiatorcontrol.com/gas_filled_design_works.aspx

That being said I suppose they are variable depending on how far the spindle is pushed by thermostatic valve...hmmmm...scratch that, they would be graduated.

 

[Onetap]

No they are not.
They turn the rad on or off, but should maintain the ROOM at a desired temperature.

Oh, yes they are!

They're a modulating control device that can vary from 0 to 100% open. In either extreme they will be fully open or fully closed, but they usually modulate to regulate the flow to maintain the required temperature.

http://heating.danfoss.co.uk/xxNewsx/759716fc-82db-4be4-bc4a-0e18ab022edb.html

"The TRV’s control action is modulating, i.e. it makes appropriate slight adjustments to the valve spindle position to increase or reduce the volume of heated water passing through the individual radiators."

You can get thermostatic controls that go from fully open to fully closed in one movement (car thermostat valves, T&PRVs) but TRVs usually move gradually in response to temperature changes.

 

[Agile]

The ideal is that they will more proportionally to give the exact flow which will maintain the set room temp.

In practice that will not always occur when humans are there as well. Opening dfoors/windows etc.

They can often overshoot and turn on/off but that's not really relevant to the occupiers as its the final room temperature that is important.

Tony

 

[D_Hailsham]

TRVs are not like a switch, on or off. They are more like the volume control on your TV: if it's too loud you turn it down a bit and vice versa. But in the case of the TRV it's fully automatic,]

No they are not.

They turn the rad on or off, but should maintain the ROOM at a desired temperature.

I'm not going to repeat what others have said but a fuller explanation can be found in Balancing of Radiator Systems, particularly section 2.4.

 

[donrkebab]

Thanks Guys, I think I've got it now, Its like boiling a full kettle of water to make one cuppa as apposed to boiling a cupful. Both methods get you a cuppa but the former method is very inefficient and uneconomic.

I bought one of these http://www.ebay.co.uk/itm/270887344...X:IT&_trksid=p3984.m1439.l2649#ht_7016wt_1164 But I only paid £13.98!!, they must have made a mistake with the price.