Low delta t

[Matt0029]

I have installed a system and am only getting a 6degree difference between the flow and return. I have knuckled the locksheilds down on the rads closest the boiler and also lowered the pump speed. To increase it all that can be done is to knuckle the locksheilds down further? Though this is just about stopping enough heat getting too the rads. Thanks.

 

[Scott_D]

What boiler
Can you range rate it?

 

[ShaunCorbs]

Sounds like the rooms are upto temperature?

 

[SJB060685]

Boiler not range rated.
Boiler output too high.
Valves with poor authority.
Pump too big.

Could be a couple of things

 

[Matt0029]

It can't be range rated no. But will modulate down to 12kw.

 

[Matt0029]

Sounds like the rooms are upto temperature?

Suggesting the delta t maybe higher when the rooms are still trying to get to temperature?

 

[Matt0029]

The pumps set to variable speed 2. I could try it on variable speed 1.

 

[ShaunCorbs]

Suggesting the delta t maybe higher when the rooms are still trying to get to temperature?

correct you will get a lower delta when the rooms are upto temperature

 

[Matt0029]

Have limited the flow to 65 degrees the flow was at this temperature when tested not sure if the rooms where up to temp. Is there anyway of telling what flow rate the pump is giving me in litres per minute?

 

[John.g]

Are you measuring this deltaT at the boiler? if so, maybe by pass open.
If your boiler is still running (and not cycling) at 12kw then the flowrate is 28.7 LPM (1.72M3/hr) @ deltaT of 6C which seems extremely high from a pump on reduced speed, I would think most systems would circulate at ~ 1 M3/hr (max) which gives a deltaT of 10.3C @ 12kw.
If the boiler is cycling then you can get a small deltaT but with a fairly low boiler flow temp of maybe 40/45C. resulting in a low rad/boiler output.

 

[John.g]

Have limited the flow to 65 degrees the flow was at this temperature when tested not sure if the rooms where up to temp. Is there anyway of telling what flow rate the pump is giving me in litres per minute?

What is the pump model and present setting?.

 

[Matt0029]

Grundfos ups2 25-80 is set on proportional pressure 2 at the momment

 

[Matt0029]

I am measuring delta t on the flow and return connections at the boiler. Is this not correct? There is no bypass near the boiler as no zone valves. There is a bypass near then end of the heating run.

 

[Matt0029]

The boiler isn't cycling no.

 

[Matt0029]

That's what is concerning me.