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.

 

[king of pipes]

You have crept into commercial heating here you need a double regulating valve in the return to the boiler and flow monitoring stations, and the equipment to measure said flow and return pressures you will not achieve this with guess work I'm afraid . Do you have a low loss header fitted what boiler is it post a few pictures up bud ?? . Kop

 

[ShaunCorbs]

Don’t need a low loss header as you don’t require separation eg different flow rates as there all just rads

as for drv you can balance the system from the rad lockshield valves your looking for approximately 15dc delta you may only get 10dc delta depending on who originally sized the rads

 

[John.g]

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

If the deltaT is 6C with 65C flow and 20C room temp then it will be ~ 8C with 65C flow and 10C room temp but the rad output will be ~ 30% more at the same flow rate.

 

[SJB060685]

If the deltaT is 6C with 65C flow and 20C room temp then it will be ~ 8C with 65C flow and 10C room temp but the rad output will be ~ 30% more at the same flow rate.

Using the spreadsheet you supplied me I get 3% more? What have I done wrong?

 

[John.g]

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]

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.