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.

 

[SJB060685]

Which one is that SJB?, even my will is in a spreadsheet.
Using T50, 20kw rads as the base then using flow/return 65/59C & 20C roomtemp I get a output of 15.94kw ("42deg rad") at a flowrate of 38.08LPM.
At the same flowrate and 10C roomtemp I get flow/return 65/57.3C & output of 20.58kw ("51.1deg rad") a increase of 29%.

 

[SJB060685]

I've run the maths and see my error

 

[John.g]

No problem, its amazing really what effect the room temp has but I suppose they would never heat up otherwise.

 

[SJB060685]

Another thing is and I think its been mentioned above? is the old system my have been designed for a lower delta t for non condensing boilers. Increasing the size of radiators will help promote the displacement of heat and drop the return temperature. I haven't really read my commercial book but will take a look later.

 

[John.g]

Old rads were designed as "60deg" rads and something like a deltaT of 11C (20F), to get the rated output at 20C room temp requires flow/return temps of 85.5C/74.5C. and even the 50deg rad requires 77.5C/62.5C (15C deltaT) to get rated output and a impossible 90C/50C (deltaT 40C) to get rated output with a 50C return.