Built Environment

Green roofs have been proposed for energy saving purposes in many countries with different climatic conditions. However, their cooling and heating potential strongly depends on the climate and building characteristics. In particular, the increase of the thermal capacity of green roofs compared to traditional roofs, if not controlled with insulation, may lead to higher cooling and heating loads. This paper discusses the energy saving potential of green roofs adopting a variable insulation strategy. A system consisting of a plenum located between a green roof and the room underneath and a sensor-operated fan that couples (or decouples) the green roof mass with the indoor environment was developed. The fan is activated and stopped using temperature based rules; the plenum is ventilated only when the fan works, creating a variable insulation system. Four cells with an insulated traditional roof, a non-insulated green roof, an insulated green roof, and a green roof with the variable insulation system have been tested in a hot and dry climate with mild winters over several years. This paper compares and discusses different plenum control algorithms. Results are particularly promising because the variable insulating system proved to adjust the thermal capacity of the roof effectively. In summer, the non-insulated green roof and the green roof with variable insulation system achieved the lowest indoor temperature; in winter, the insulated traditional roof and the variable insulation green roof system achieved the highest indoor temperatures. Measurements are hence compared with simulations. Finally, the energy saving potential of the new green roof system is evaluated.

The paper highlights how the knowledge of users is complex and still defective in the area of European affordable housing. Although demand is far more changeable than supply, more market research has been carried out on existing housing stock than on behavioral/cultural models. Furthermore, there is a lack of design research capable of generating innovative design inputs.
The significance of this article lies in proposing a systematization of the detection of user requirements. In the field of affordable housing, there is still a widespread traditional top-down approach which assigns designers with an external intuitive analysis of user requirements. This paper suggests that the European local systems should equip themselves firstly with housing market research concentrated on behavioral/cultural models and secondly with design research conducted by research-oriented professionals.
The paper focuses on some research methods which could be used by design researchers during their inquiry into user requirements. The results of such research would be the starting points for individual design practices which would be based upon solider and more detailed research foundations.

Present methods to estimate U-values from in-situ measurements require long time series data to reduce thermal mass effects. Surveys are restricted to the winter season, when the temperature gradient is large and the influence of solar radiation is negligible. A new analysis method using a lumped thermal mass and Bayesian statistics is presented. It needs less data, which could potentially be collected during summer. The new technique was used to analyse 15 weeks of data recorded on a north-west-facing wall from August to November 2013. Results show the importance of solar radiation on the time taken for the analysis to converge and its effects on the U-value estimation.