Temperature blending in a tee

hot_rod

This formula determines the mix temperature of two flows into, or out of a tee.
It helps demonstrate how fixed flow adjustment comes into play for boiler return protection.

T mix= (T-hot x T flow) + (T-hot = T flow)
÷
F-hot + f-cool

Keeping in mind what goes into a tee must come out of a tee, flow wise.
These examples show a 12 gpm flow split evenly between two inlet flows.

If a boiler starts at an ambient 68F and return fluid is 68F, within minutes a properly sized boiler could add maybe 20∆ to the supply. So blending 88SWT with 68 return = 78°

If the boiler was up to temperature, say 160F, blending the return 68 = 114°

If the boiler could supply a constant 180F, and the load could increase to 88F, uoou mix would be 132°

When the return gets up to 160F, 180SWT the return to to the boiler is 170.F
So return is blending up, dropping boiler efficiency a bit compared to a 160F return, that you would see if the system was running a 20∆.