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This paper presents new correlations to calculate natural convection heat transfer coefficients (CHTC) in enclosures for building performance simulation. Current work related to the development of correlations is not oriented to building enclosures, and the influence of high numbers of Rayleigh (Ra) and aspect ratio on the CHTC has not been studied in detail. In this work, two new correlations have been developed for a vertical wall, one in laminar regime (Ra < 10 7) and another one in turbulent regime (10 7 < Ra < 10 11). Moreover, two new correlations have been developed for floor and ceiling, one in laminar regime (Ra < 10 6) and another one in turbulent regime (Ra > 10 6). All correlations have been developed as function of the aspect ratio (H/L) and Ra numbers calculated from the enclosure average air temperature and wall surface temperature. By contrast, in previous works the Ra numbers have been calculated from the temperature difference of opposite walls. Computer Fluid Dynamics (CFD) simulations for different aspect ratios (H/L = 0.5-1-2) and Ra numbers (10 3-10 11) have been carried out in order to obtain these correlations. The SIMPLE algorithm has been used for the solution of the Navier-Stokes equations and the realizable turbulence k-ε model with an enhanced wall-function treatment has been used. The correlations developed follow the expected trend for the low number of Ra in comparison with the expressions developed by other authors. For a high number of Ra, our correlations improve the previous correlations, because it is a function of the aspect ratio of the enclosure and the average air temperature of the enclosure. This approach is simple to implement in the construction of thermal simulation programs with low computational cost.

In most countries, energy efficiency at the residential level has been largely delegated to the dynamics of realestate markets after setting a minimum level. This regulatory definition is in certain cases supplemented by energy performance certificates, such as in the case of the European Union. This approach is based on the understanding that avoided energy-consumption costs positively affect the willingness to pay for them, thus leading to higher prices capable of offsetting production costs and thereby encouraging developers. The case of the private housing market in Santiago de Chile was selected as a reference for a developing country in which energy performance certificates, although they exist as an instrument, are not required to be applied in property transactions. However, unlike most of the research performed in developed countries, it is difficult to analyse price formation using methods based on observed preferences in areas in which there are few energy-certified buildings. Using the technique of contingent valuation, such as the method based on stated preferences, enables one to overcome this difficulty. This article investigates willingness to pay for improvements in the energy efficiency of buyers for new homes based on a representative investment/operation cost analysis. This approach has been addressed to open the debate on the convenience of modify the national construction code and rethink the energy certification scheme as well as an exploratory study to undercover further research lines to support the aforementioned debate. The results suggests that there is a number of potential home buyers ready to pay for energy efficiency when they are informed on the cost savings associated to structural modifications and the cost of providing such improvements and such willingness to pay is not monolithic across the respondents, but seems to be influenced by the education level plausibly associated to the purchase power.