measurements

M. J. Jimenez; B. Porcar; M. R. Heras

Department of Renewable Energies, "Bioclimatic Architecture Research Programme”, CIEMAT, Madrid, E-28040, Spain; Tel:+34 91 3466305,fax: +34 91 3466037, e-mail:

miose. iimenez@psa. es

Introduction

The use of passive design strategies to benefit from the solar energy in order to reduce heating and cooling loads in buildings but maintaining indoors comfort is a very important concern regarding environmental aspects.

The application of these design strategies requires an accurate knowledge on the parameters that characterise the thermal behaviour of each building component used, such as the heat transmission coefficient, U, and the total solar energy transmittance, g, values and time constants. These parameters are required to apply the mandatory national standards and regulations that impose the minimum requirements regarding energy consumption in buildings (eg. The Spanish NBE-CT- 79). The availability of these parameters for each component included in the building envelop is also important because they are required as input for most of the simulation programs which estimate heating and cooling loads and evaluate the thermal behaviour of buildings that include these components in its envelop.

In both cases, the accuracy in the final results depends on the accuracy on the estimation of the parameters of each individual component. It is possible to estimate these parameters, according to national standards, from tabulated values of the integrating parts of the component, but in this case their accuracy depends on the degree of knowledge of the composition of the enclosure. Outdoors testing (Vandaele, 1994) and in-situ measurements (ISO 9869:1994) are very useful and reliable alternative to provide more accurate estimations of these parameters.

This paper presents the experimental determination of the U value of each wall of a quite simple mono-zone building, located at the Plataforma Solar de Almerfa (Tabernas, Almerfa, Spain), by in-situ measurements and dynamical analysis. These values have been compared with those obtained from tabulated values according to national standards. Comparisons have been considered in order to obtain information on the predictable degree of agreement between both approaches.

The studied building is considered especially suitable for analysis as far as its simplicity and the high degree of knowledge about its construction and components allow undertaking relatively good estimations from tabulated values according to national standards in comparison to the usual quality of these calculations from tabulated values. Its performance is also interesting because it includes some passive strategies to reduce heating and cooling loads and to improve thermal comfort.