Evaluation of a building envelope Heat Transfer Coefficient in use: Bayesian approach to improve the inclusion of solar gains

Abstract

Accurately measuring the actual building performance would be a significant step toward performance contracting. Methods under occupancy have operational advantages but come with additional constraints due to the variability of weather and occupancy conditions, which cannot be overlooked. Especially in recent, well-insulated buildings, since solar gains are a larger contribution to the global heat balance. This work aims to enhance the accuracy of the Heat Transfer Coefficient estimation in an occupied building by taking better account of solar gains in multilinear regression models. The approach adopted here considers solar gains from both the incident solar heat flux through glazing and from the opaque elements of a building by calculating an equivalent outdoor temperature. This model feeds a multilinear regression model whose parameters are estimated by Bayesian inference. Our model for estimating HTC is validated against a set of virtual data from a simulated detached house under different weather conditions.

KEYWORDS:

• Thermal performance
• building envelope
• HTC
• solar gains
• Bayesian inference

Disclosure statement

No potential conflict of interest was reported by the author(s).

Informed consent statement

Written informed consent for publication of their details was obtained from all the co-authors.

Data availability statement

The data that support the findings of this study are available from the corresponding author, upon reasonable request.

Nomenclature

$A_f$	=	Area of a wall (m²)
$I_{\mathrm{dif},\mathrm{hz}}$	=	Diffuse horizontal irradiance (W/m²)
$F_{\mathrm{dif},f}$	=	Diffuse solar flux (W/m²)
$I_{\mathrm{dir},\mathrm{hz}}$	=	Direct horizontal irradiance (W/m²)
$F_{\mathrm{dir},f}$	=	Direct solar flux (W/m²)
${\phi }_{\mathrm{elec}}$	=	Electrical appliances heat gains (W)
$T_{\mathrm{ex}{t}_{\mathrm{eq}}}$	=	Equivalent outdoor temperature (K)
$T_{f_{\mathrm{eq}}}$	=	Equivalent outdoor temperature of a wall (K)
$h_{\mathrm{ce}}$	=	External convective heat exchange coefficient (W/m².K)
${\alpha }_e$	=	External energy absorption coefficient of a wall
$h_{\mathrm{re}}$	=	External radiative heat exchange coefficient (W/m².K)
$\mathrm{HTC}$	=	Heat Transfer Coefficient (W/K)
${\phi }_{\mathrm{heating}}$	=	Heating power (W)
$F_f$	=	Incident solar flux on a wall (W/m²)
$T_i$	=	Indoor temperature (K)
${\phi }_{\mathrm{ventilation}}$	=	Mechanical ventilation gains and losses (W)
${\phi }_{\mathrm{occupants}}$	=	Occupants heat gains (W)
$T_e$	=	Outdoor temperature (K)
$\theta$	=	Ratio of typical average transmittance to that at normal incidence
${\theta }_f$	=	Ratio of typical average transmittance to that at normal incidence per facade
$F_{\mathrm{ref},f}$	=	Reflected solar flux (W/m²)
$Z_f$	=	Solar access factor
${\phi }_{\mathrm{solar}}$	=	Solar heat gains (W)
$A{z}_s$	=	Sun azimuth (rad)
$H_s$	=	Sun height (rad)
$U_f$	=	Thermal transmittance coefficient of a wall (W/m².K)
$A_{w,f}$	=	Total glazed area of a wall (m²)
$g_f$	=	Total solar energy transmittance factor of the glazing
$A{z}_f$	=	Wall azimuth (rad)
$\beta$	=	Wall tilt (rad)