Abstracts for the Special Issue of Building & Environment on the subject of Outdoor testing, Analysis and Modelling are now available. The papers included in this special issue focus on developments made in a series of research projects funded by the Commission of the European Community, all of which have included a significant element of outdoor testing of building components.
* Energy Systems Research Unit, University of Strathclyde, Glasgow
# Centre for Research on Indoor Climate & Health, Glasgow Caledonian University, Glasgow
In 1993 , a set of papers was presented on the theme of thermal experiments in outdoor test cells. In the intervening 19 years, there have been several advances in the test procedures, the analysis of the measured data to extract standard performance characteristics, and the link with modelling and simulation. The papers included in this special issue focus on developments made in a series of research projects funded by the Commission of the European Community, all of which have included a significant element of outdoor testing of building components.
The arguments for using outdoor test cells are still relevant. High quality laboratory facilities exist for testing components (e.g. hot-box facilities for measuring thermal transmittance, spectrophotometric testing for optical properties of glazings, solar simulators and climatic chambers for testing the output from photovoltaic modules) that are accurate and repeatable. However, they tend to be steady state tests and do not take into account the dynamically varying boundary conditions that the components are subjected to when used in the building envelope. The obvious solution is to test the components when mounted on a building in typical operational mode. However, in practice this has been shown to be highly complex – even in unoccupied buildings, it is difficult to measure all the required inputs (e.g. constructional details, air movement, heating and cooling system operation, and external climate) to the level required to get reliable estimates of component performance. Although some attempts have been made to measure in dedicated full-scale buildings (e.g. -), the results can still have significant uncertainties and/or the facilities are very expensive to construct and monitor.
Outdoor test cells, where there is a high degree of control of the indoor environment, well-specified constructions and high levels of instrumentation, can fill the gap between laboratory testing and full-scale building testing. Most of the papers in this special issue are concerned with such testing, where the objective is to extract component performance characteristics that give some confidence as to how those components perform in realistic climatic conditions.
The other main use of testing in outdoor test cells is the link with simulation modelling. The argument here is that dynamic simulation programs have improved in capability and validity and can therefore be used with some confidence in predicting energy and environmental performance of buildings. However, where a new component is under development, for example an advanced glazing, a hybrid photovoltaic module or shading component, then high quality datasets from outdoor experiments can be used to ensure that the simulation program is capable of modelling that component. If so, it is considered that the simulation program can then be used to model the component when integrated into a full-scale building.
The original test cells used in the EC PASSYS Project  were highly specified and instrumented. Improvements were made in later projects to improve measurement accuracy, by fitting the cells with either a so-called “pseudo-adiabatic shell” or internally mounted heat flux tiles . Also, there was a move away from the original idea of common test facilities to one of common quality procedures for testing which includes the calibration of the test cell infrastructure and the associated data analysis. These improvements are reflected in the papers in this special issue.
An introductory paper sets the scene with a review of the range of building components that have been tested through a series of brief case studies. This is followed by a paper outlining the overall methodology for testing. There are three papers on the analysis techniques, the first by Jimenez, Madsen and Andersen giving an overview of identification methods, followed by papers on two specific implementations. The papers by Baker, and Androutsopoulos et al, show, respectively, the level of consistency obtained in extracting performance characteristics on the same component at different test sites, and consistency between different analysts with the same data set. Three papers then describe detailed applications: to blind systems, hybrid photovoltaic modules and ventilated windows. Lastly, one paper describes the role of modelling and simulation in extrapolating to performance in full-scale buildings. Although there is only one paper dedicated to the role of simulation in connection with the outdoor test cells, simulation is an important part of the overall methodology and is included as a part of several of the other papers.
The argument has been advanced that simulation models can effectively replace the need for outdoor test cells . However, there are still significant differences in predictions between simulation programs on even simple buildings, as can be seen by looking at the results from a range of programs in an empirical validation experiment in IEA21  and in the inter-program comparison results now embedded in the ASHRAE 140 Standard . Therefore, it is believed that experiments still have a role to play in providing a comparison with model predictions as well as building component characterisation.
Reviewing the papers as a whole, it is clear that there have been improvements in the testing and analysis techniques. However, the current situation is far from perfect – there are still uncertainties in estimation of the parameters, great care has to be paid to testing and analysis procedures to achieve consistent results, and the tests still require several days to several weeks to perform and are therefore expensive. The papers should provide a good background for those embarking on the creation of new test facilities, indicating the considerable time and effort required to ensure that accurate test results are achieved.
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The following papers are included in the special issue published by Building and Environment.
Strachan P A and Vandaele L, Case studies of outdoor testing and analysis of building components
Baker P H and van Dijk H A L, PASLINK and dynamic outdoor testing of building components
Jiménez M J and Madsen H, Models for describing the thermal characteristics of building components
Jiménez M J, Madsen and Andersen K K, Identification of the main thermal characteristics of building components using MATLAB
Androutsopoulos A, Bloem J J, van Dijk H A L and Baker P H, Comparison of user performance when applying system identification for assessment of the energy performance of building components
Leal V and Maldonado E, The role of the PASLINK test cell in the modelling and integrated simulation of an innovative window.