Radiator exit valve setting - ASHP

[H F]

The exit valve on radiators can be opened and closed. Should this valve be fully opened or semi-closed to generate the most heat bearing in mind that we have an ASHP with a flow rate of 45C?

 

My reason for asking is we have two rads that are not consistent in heating rooms. One some days the rooms are great on others they are significantly cooler, which is odd because they all have smart TRVs and should be heating to the same temperature everyday at the same time. I was wondering if the exit valve had anything to do with this?

[ProDave]

The valve is there to balance the system. With all TRV's open you adjust these to get all radiators to heat up equally.  If one is open too much, particularly if close to the start of the circuit, it might hog all the water flow and others further away get little water.

 

It sounds like some of yours are out of balance.  The ones that are struggling need the valve opened more and probably some of the others that are working really well need their valves closed a little.

[H F]

Thank you. Will try and balance things.

 

This may seem an odd question, but to close valves it’ll be righty tighty, and to open them turn left. 

[ProDave]

Yes, Righty tighty, Lefty loosy, just like an old fashioned tap.

[H F]

Is it a fair assumption that rads nearer the pump will receive priority (more pressure) when open than rads much further away?

 

And what happens if I completely close an exit valve - will the rad heat up?

[Pete]

No

[PeterW]

Pressure is equal in the system throughout. Only thing that changes is the flow rate through the rad dependent on the gate valve setting. 

[H F]

12 hours ago, PeterW said:

Pressure is equal in the system throughout. Only thing that changes is the flow rate through the rad dependent on the gate valve setting. 

Thanks Peter. Does the flow rate affect the efficiency and temperature of the rads? Ie. Would a reduced flow rate make the rad warmer or colder?

[A_L]

2 hours ago, Home Farm said:

Does the flow rate affect the efficiency and temperature of the rads? Ie. Would a reduced flow rate make the rad warmer or colder?

 

If by 'efficiency' you mean heat output then for a given input temperature a higher flow rate will mean a higher exit temperature because of a lower residence time in the radiator and thus a greater output because the mean temperature of the radiator will be higher. The converse applies for lower flow rates.

[H F]

In essence, we're struggling with keeping some rads consistent - some nights they're great on others they're cooler than they should be. For this rads, should I "slow down" the exit (closing the exit valve) to keep the heat in longer or should all rads throughout the house just be fully open. This is doing my head in.

[dpmiller]

you don't "keep the heat in", it takes flow to make heat in the rad. You're looking for a temperature differential across the rad so it (say) flow is 55c, the return should stabilise at (say) 45c. Less flow= greater differential.

The pump can only flow a certain amount so if some rads have too much flow others will lose out- that is, have too much of a differential.

[H F]

Right, so I’ll maximize flow through all our rads... and see what transpires.