Convective heat loss is calculated using the convection coefficient, surface area, and temperature difference. The convection coefficient accounts for geometry (shape factor), operating conditions (duty factor), temperature effects, and wind velocity.

\begin{equation}\label{eq:wall-qconv} Q_\text{conv} = h A \Delta T\end{equation}

Convection Coefficient

\begin{equation}\label{eq:wall-h} h = f_\text{shape} \cdot f_\text{duty} \cdot f_{\Delta T} \cdot f_{\bar{T}} \cdot f_\text{wind}\end{equation}

Factors

\begin{equation}\label{eq:wall-duty} f_\text{duty} = \left(\frac{1}{24}\right)^{0.2}\end{equation}

\begin{equation}\label{eq:wall-dTfactor} f_{\Delta T} = (\Delta T)^{0.266}\end{equation}

\begin{equation}\label{eq:wall-Tbarfactor} f_{\bar{T}} = \left(\frac{1}{\bar{T}}\right)^{0.181}\end{equation}

\begin{equation}\label{eq:wall-windfactor} f_\text{wind} = \sqrt{1 + 1.277 \cdot v_\text{wind}}\end{equation}

Temperature Definitions

\begin{equation}\label{eq:wall-dT} \Delta T = T_s - T_a\end{equation}

\begin{equation}\label{eq:wall-Tbar} \bar{T} = \frac{T_s + T_a}{2}\end{equation}

Symbols

\(Q_\text{conv}\)	Convective heat loss \([\unit{ \btu\per\hour}]\)
\(h\)	Convection coefficient \([\unit{ \btu\per\hour\foot\squared\degreeFahrenheit}]\)
\(A\)	Surface area \([\unit{ \foot\squared}]\)
\(\Delta T\)	Temperature difference between surface and ambient \([\unit{ \degreeFahrenheit}]\)
\(\bar{T}\)	Mean temperature \([\unit{ \degreeFahrenheit}]\)
\(f_\text{shape}\)	Shape factor \([\unit{ \unitless}]\)
\(f_\text{duty}\)	Duty factor \([\unit{ \unitless}]\)
\(f_{\Delta T}\)	Temperature difference factor \([\unit{ \unitless}]\)
\(f_{\bar{T}}\)	Mean temperature factor \([\unit{ \unitless}]\)
\(f_\text{wind}\)	Wind factor \([\unit{ \unitless}]\)
\(v_\text{wind}\)	Wind speed \([\unit{ \mile\per\hour}]\)
\(T_s\)	Surface temperature \([\unit{ \degreeFahrenheit}]\)
\(T_a\)	Ambient temperature \([\unit{ \degreeFahrenheit}]\)