Central Heating Calculations

[cr0ft]

Help! I'm designing a central heating system (combi-boiler) and am happy with most of the calculations I need to do. I've worked out radiator sizes required and know I want a flow/return delta T of around 20 degrees giving me a rad/room delta T of around 40 degrees (I know this means oversizing rads by a factor but I want to do this right). I want to use a return temperature of 50 degrees and flow of 70. I can set the flow of 70 at the boiler obviously. How do I ensure that the return temperature is close to 50? Is there some equation I use to make sure this is the case?

I know I need to keep return under 55 or the boiler doesn't condense when powering the heating.

Thanks in advance for help!

 

[ecowarm]

You want sometime like this Testo 922 differential thermometer for fast temperature measurement and then ballance the system to give the return temp you want. (clip on flow and return on each rad and set return temp)

Eco