A paper recently published (Energy and Buildings. Vol. 81, pages 337-362) reports the analysis of a room facing north in a fully monitored office building located in Madrid (Spain), carried out by CIEMAT. The starting point of this work is previous experience testing building components using test cells. Being conscious that the step forwards are not trivial, experiment set up intends to take advantage of similarities, and alternatives are proposed to take differences into account. The work reported in this paper is the first part of a bottom-up approach that is being applied for the analysis of a more remarkably complex system such as a room in occupancy conditions. Additionally, South European climate boundary conditions incorporate difficulties to data analysis, derived from experimental campaigns in the presence of high level of solar radiation and relatively low differences between indoor and outdoor air temperatures.
Data corresponding to a period of more than two years, recorded while the building was regularly used, have been employed. The availability of such a long data set gives strong support to validate results and to demonstrate the robustness of the applied methods and conclusions. A regression analysis method based on averages has been applied. Although the used equation is analogous to the steady state, dynamic features of the test have been considered. A dynamic energy balance equation is first stated. Then this equation is integrated for a time interval long enough to make the accumulation term much lower than the other terms. Finally averages are used to estimate integrals. The minimum integration period that allows this simplification has been identified, studying integration periods from 1 to 20 days.
The capability to extract some of the main thermal parameters for the considered room, from the available data set has been demonstrated. The main contributions to the energy balance in this room have been identified. It has been also studied the most efficient way to incorporate the most relevant effects regarding the analysis in the model. A spread in the Overall Heat Transmission Coefficient (UA) estimated under 10 %, was found for a 7-day integration period. This narrow interval allows to hand this parameter as intrinsic in practical applications.
The work reported in this paper is a very useful basis for future work that will apply differential dynamic approaches, which drastically reduce the required test period. The integrated approach reported in this paper gives very useful criteria to select and model the main contributions to the energy balance equation that will be used in upcoming works. Also, the obtained parameters provide a very useful support for validation in other analysis approaches.
Photo: (left) External view of office building prototype at CIEMAT in Madrid, Spain; (right) Internal view of office building prototype at CIEMAT in Madrid, Spain