Notations and Units

 Symbol Quantity Unit $c_{\mathrm{m}}$ specific heat capacity of dry material $\mathrm{J} /(\mathrm{kg} \cdot \mathrm{K})$ $c_{\mathrm{w}}$ specific heat capacity of liquid water $\mathrm{J} /(\mathrm{kg} \cdot \mathrm{K})$ $D_{\mathrm{w}}$ moisture diffusivity $\mathrm{m}^{2} / \mathrm{s}$ $E_{\mathrm{sol}}$ total flux density of incident solar radiation $\mathrm{W} / \mathrm{m}^{2}$ $g$ density of moisture flow rate $\mathrm{kg} /\left(\mathrm{m}^{2} \cdot \mathrm{s}\right)$ $g_{\mathrm{p}}$ density of moisture flow rate of available water from precipitation $\mathrm{kg} /\left(\mathrm{m}^{2} \cdot \mathrm{s}\right)$ $g_{\mathrm{v}}$ density of water vapour flow rate $\mathrm{kg} /\left(\mathrm{m}^{2} \cdot \mathrm{s}\right)$ $g_{\mathrm{w}}$ density of liquid water flow rate $\mathrm{kg} /\left(\mathrm{m}^{2} \cdot \mathrm{s}\right)$ $g_{\mathrm{w}, \max }$ density of water flow rate which can be absorbed at the surface of a material $\mathrm {kg} /\left(\mathrm{m}^{2} \cdot \mathrm{s}\right)$ $h$ surface heat transfer coefficient $\mathrm{W} /\left(\mathrm{m}^{2} \cdot \mathrm{K}\right)$ $h_{\mathrm{c}}$ convective heat transfer coefficient $\mathrm{W} /\left(\mathrm{m}^{2} \cdot \mathrm{K}\right)$ $h_{\mathrm{e}}$ specific latent enthalpy of evaporation or condensation $\mathrm{J} / \mathrm{kg}$ $h_{\mathrm{r}}$ radiative heat transfer coefficient $\mathrm{W} /\left(\mathrm{m}^{2} \cdot \mathrm{K}\right)$ $K$ liquid conductivity $\mathrm{s} / \mathrm{m}$ $p_{\mathrm{a}}$ ambient atmospheric pressure $\mathrm{Pa}$ $p_{\text {suc }}$ suction pressure $\mathrm{Pa}$ $p_{\mathrm{v}}$ partial water vapour pressure $\mathrm{Pa}$ $p_{\mathrm{v}, \mathrm{a}}$ partial water vapour pressure in the air $\mathrm{Pa}$ $p_{\mathrm{v}, \mathrm{s}}$ partial water vapour pressure at a surface $\mathrm{Pa}$ $p_{\mathrm{v}, \mathrm{sat}}$ saturated water vapour pressure $\mathrm{Pa}$ $p_{\mathrm{w}}$ water pressure inside pores $\mathrm{Pa}$ $q$ density of heat flow rate $\mathrm{W} / \mathrm{m}^{2}$ $q_{\text {lat }}$ density of latent heat flow rate $\mathrm{W} / \mathrm{m}^{2}$ $q_{\text {sens }}$ density of sensible heat flow rate $\mathrm{W} / \mathrm{m}^{2}$ $R_{\mathrm{w}}$ liquid moisture flow resistance of interface $\mathrm{m} / \mathrm{s}$ $R_{\mathrm{H} 2 \mathrm{O}}$ gas constant of water vapour $\mathrm{J} /(\mathrm{kg} \cdot \mathrm{K})$ $s_{\mathrm{d}, \mathrm{s}}$ equivalent vapour diffusion thickness of a surface layer $\mathrm{m}$ $T$ thermodynamic temperature $\mathrm{K}$ $T_{\mathrm{a}}$ air temperature of the surrounding environment $\mathrm{K}$ $T_{\mathrm{eq}}$ equivalent temperature of the surrounding environment $\mathrm{K}$ $T_{\mathrm{r}}$ mean radiant temperature of the surrounding environment $\mathrm{K}$ $T_{\text {surf }}$ surface temperature $\mathrm{K}$ $t$ time $\mathrm{s}$ $v$ wind speed $\mathrm{m} / \mathrm{s}$ $w$ moisture content $\mathrm{kg} / \mathrm{m}^{3}$ $\alpha_{\mathrm{sol}}$ distance $\mathrm{m}$ $\delta_{0}$ solar absorptance $\mathrm{kg} /(\mathrm{m} \cdot \mathrm{s} \cdot \mathrm{Pa})$ $\delta_{\mathrm{p}}$ vapour permeability of still air $\mathrm{kg} /(\mathrm{m} \cdot \mathrm{s} \cdot \mathrm{Pa})$ $\varepsilon$ vapour permeability of material $-$ $\lambda$ longwave emissivity of the external surface $\mathrm{W} / \mathrm{m} \cdot \mathrm{K})$ $\varphi$ thermal conductivity $-$ $\mu$ relative humidity $\mathrm{kg} / \mathrm{m}^{3}$ $\rho_{\mathrm{a}}$ diffusion resistance factor $\mathrm{kg} / \mathrm{m}^{3}$ $\rho_{\mathrm{m}}$ density of air $\mathrm{kg} / \mathrm{m}^{3}$ $\sigma_{\mathrm{w}}$ density of solid matrix $\mathrm{density}$ of liquid water $\rho_{\mathrm{w}}$ density of liquid water $\mathrm{kg} / \mathrm{m}^{3}$ $\sigma_{\mathrm{s}}$ Stefan-Boltzmann constant $\mathrm{W} /\left(\mathrm{m}^{2} \cdot \mathrm{K}^{4}\right)$