Limited outdoor-temperature reset calculator

Linear outdoor reset is limited by the minimum water temperature needed for equipment or service.

Units

T_{\text{cmd}} = \max\left(T_{\text{min}},\ T_{\text{sc}} + \frac{\left(T_{o} - T_{\text{oc}}\right) \times \left(T_{\text{sw}} - T_{\text{sc}}\right)}{T_{\text{ow}} - T_{\text{oc}}}\right)

Calculator

Enter the values you know and leave one box empty. Calculate finds the empty one, the result or any input.

Given

T_{\text{cmd}} = \max\left(145,\ 185 + \frac{\left(42 - 15\right) \times \left(125 - 185\right)}{65 - 15}\right) = 152.6

Symbol	Meaning	Unit
$T_{\text{cmd}}$	requested supply temperature	°F
$T_{\text{min}}$	minimum permitted supply temperature	°F
$T_{o}$	outdoor temperature	°F
$T_{\text{oc}}$	cold outdoor anchor	°F
$T_{\text{sc}}$	supply temperature at cold anchor	°F
$T_{\text{ow}}$	warm outdoor anchor	°F
$T_{\text{sw}}$	supply temperature at warm anchor	°F

Symbol	Meaning	Unit
$T_{\text{cmd}}$	requested supply temperature	°C
$T_{\text{min}}$	minimum permitted supply temperature	°C
$T_{o}$	outdoor temperature	°C
$T_{\text{oc}}$	cold outdoor anchor	°C
$T_{\text{sc}}$	supply temperature at cold anchor	°C
$T_{\text{ow}}$	warm outdoor anchor	°C
$T_{\text{sw}}$	supply temperature at warm anchor	°C

Results are estimates for study and screening. Check the inputs, units and assumptions before you use them for design, billing or contract decisions.