Review of external convective heat transfer coefficient models in building energy simulation programs: Implementation and uncertainty

Abstract

Convective heat transfer coefficients for external building surfaces (h c,ext ) are essential in building energy simulation (BES) to calculate convective heat gains and losses from building facades and roofs to the environment. These coefficients are complex functions of, among other factors, building geometry, building surroundings, building facade roughness, local air flow patterns and temperature differences. Previous research on h c,ext has led to a number of empirical models, many of which are implemented in BES programs. This paper first provides an extensive overview of such models for h c,ext calculation implemented in BES programs together with the corresponding assumptions. Next, the factors taken into account by each model are listed, in order to clarify model capabilities and deficiencies. Finally, the uncertainty related to the use of these models is discussed by means of a case study, where the use of different models shows deviations up to ± 30% in the yearly cooling energy demand (in relation to the average result) and ± 14% in the hourly peak cooling energy demand of an isolated, well-insulated building, while deviations in yearly heating energy demand are around ± 6%. The paper concludes that each model has a specific range of application, which is identified in this review paper. It also concludes that there is considerable uncertainty in the prediction of h c,ext , which can be transferred to the BES results. This large uncertainty highlights the importance of using an appropriate convection model for simulations of a specific building, certainly for calculating cooling demands and related important performance indicators such as indoor temperatures, indoor relatively humidity, thermal comfort, etc.

CFD Analysis of Convective Heat Transfer Coefficient on External Surfaces of Buildings

“…In order to validate the CFD numerical model, a comparison with four models (Table 1), recommended in the paper [12], of convective heat transfer coefficient calculation, implemented in a BES program (ESP-r), has been performed. It is also considered a numerical correlation (Table 1) studied by Defraeye et al [21].…”

“…As reported in [12] there is considerable uncertainty in the prediction of convective heat transfer coefficient related to the use of convection models. The four models chosen for the comparison are based on full-scale experiments and they are developed by: Loveday and Taki [20], ASHRAE task group [26], MoWITT [27] and Liu and Harris [19].…”

“…In [2,[3][4][5][6][7][8][9][10][11][12][13][14][15][16] it is shown that the average CHTC on the windward façade is not very sensitive to wind direction so that a wind direction of 45° from the normal can represent a wide range of wind directions between 0° and 60°.…”

A review on experimental research using scale models for buildings: Application and methodologies

“…Convection heat transfer coefficients are based on experimental results [177]. These experimental results are obtained through Fig.…”

“…Convection heat transfer coefficients extracted from reduced-scale models and implemented in building energy simulations (BES) [177].…”