Search

A considerable amount of energy is used in the building sector for air conditioning purposes. Additionally, the building sector contributes to the urban heat island (UHI) phenomenon which causes temperature rise in urban areas. Cool roof is an emerging passive cooling technology that can contribute to reduce the cooling energy use in buildings and to mitigate the UHI effects in the urban area. Cool roofs and reflective coatings, despite of being effective in terms of reducing the cooling thermal loads in buildings and decrease the UHI, can suffer from extreme thermal stress which negatively influences their lifespan and performance. Thermal energy storage (TES) is a promising technology which can be applied together with cool roof technology to decrease the extreme thermal stress due to solar radiation as well as providing thermal inertia to the building. In this study, simulation-based optimization will be used to optimize the PCM melting temperature when integrated into a polyurethane-based cool roof membrane to reduce the thermal stress of the cool roof and also to improve the annual energy performance of the building. The optimization results showed that the application of PCM and cool roof technologies together can reduce the severe thermal stress of the cool roof membrane when the optimization objective is the annual thermal stress of the cool roof. On the other hand, when PCM melting temperature is optimized to reduce the annual energy needs, higher annual energy savings could be achieved with acceptable reductions in the cool roof membrane thermal stress. [ABSTRACT FROM AUTHOR]

Buildings contribute to climate change by consuming a considerable amount of energy to provide thermal comfort for occupants. Cooling energy demands are expected to increase substantially in the world. On this basis, technologies and techniques providing high energy efficiency in buildings such as passive cooling are highly appreciated. Passive cooling by means of phase change materials (PCM) offers high potential to decrease the cooling energy demand and to improve the indoor comfort condition. However, in order to be appropriately characterized and implemented into the building envelope, the PCM use should be numerically analyzed. Whole-building energy simulation tools can enhance the capability of the engineers and designers to analyze the thermal behavior of PCM-enhanced buildings. In this paper, an extensive review has been made, with regard to whole-building energy simulation for passive cooling, addressing the possibilities of applying different PCM-enhanced components into the building envelope and also the feasibility of PCM passive cooling system under different climate conditions. The application of PCM has not always been as energy beneficial as expected, and actually its effectiveness is highly dependent on the climatic condition, on the PCM melting temperature and on the occupants behavior. Therefore, energy simulation of passive PCM systems is found to be a single-objective or multi-objective optimization problem which requires appropriate mathematical models for energy and comfort assessment which should be further investigated. Moreover, further research is required to analyze the influence of natural night ventilation on the cooling performance of PCM. [ABSTRACT FROM AUTHOR]

Cool roofs have been widely proved to represent an effective strategy for building thermal-energy performance improvement during the cooling season. However, their effectiveness along the whole year can be affected by building features and other boundary conditions. The present work aims at assessing the energy performance of high solar reflectance roof solutions in different climate zones, when implemented in a variety of building typologies. Therefore, an optimization study was carried out to select the optimum roof solar reflectance able to minimize building annual HVAC energy consumption. In this work, Italian climate zones were considered as case study conditions. The analysis was performed through dynamic simulation of validated standard ASHRAE building reference models. Moreover, the role of (i) type of HVAC system operating, (ii) presence and intensity of internal gains, and (iii) roof thermal insulation level was evaluated on the resulting optimum roof reflectance capability. Results show that the optimum roof solar reflectance varies under different climate conditions, mainly depending on heating or cooling dominated conditions. However, all further analyzed boundary conditions, i.e. building typology, HVAC system, internal gains, and roof insulation level, affect building energy performance and, therefore, the optimum roof reflectance identification. In the hottest climate, the optimum roof solar reflectance resulted to be consistently equal to the maximum considered, i.e. 0.8, also with varying the other parameters. Moreover, the annual HVAC energy need is more sensitive to roof reflectance in the apartment building, showing 17% of energy savings with standard model characteristics. On the other hand, in heating dominated climates, the optimum roof solar reflectance is more variable, ranging over all the considered values, because it is affected by the additional boundary conditions. On the contrary, the variability of HVAC need due to roof solar reflectance variation is generally lower. [ABSTRACT FROM AUTHOR]

Relocatable, transportable or off-site constructed lightweight buildings typically undergo sharp indoor temperature fluctuations in the heating and cooling seasons due to the lack of sufficient thermal mass in their envelopes, resulting in high energy consumption to provide the zone with comfort temperature. The application of phase change materials has been suggested as a promising solution to control the indoor thermal condition in buildings. This work is an attempt to support the application of PCM technology in lightweight relocatable buildings as a passive alternative to save energy under different weather conditions. The numerical results highlighted the potential of using PCM-enhanced gypsum boards in lightweight buildings to increase the energy performance during both heating and cooling seasons in arid and warm temperate main climate areas. [ABSTRACT FROM AUTHOR]

In buildings, HVAC systems consume a high amount of energy to provide thermal comfort for occupants. A methodology is presented in this paper to control thermostat operation of the buildings considering the effects of indoor and outdoor boundary conditions and phase change material (PCM) characteristics. EnergyPlus v8.1 building energy simulation software was used to analyze the energy performance of the PCM incorporated building models and to implement Fanger model to control HVAC thermostat operation according to BS EN 15251:2007 thermal comfort categories. Three types of building HVAC schedule, PCM with different melting points and layer thicknesses were studied for Madrid climate zone. Moreover, the impact of occupants clothing on the energy consumption was investigated. Furthermore, payback analysis was conducted to find out the economic benefits of PCM integration into the building envelopes. Application of PCM improved the cooling and heating energy performances except for the office model in winter (heating period). Additionally, higher energy savings and lower payback periods were observed when PCM with higher melting point was applied to the buildings. Eventually, energy savings in PCM incorporated models were found to improve further when occupants changed their clothing behavior in winter. [ABSTRACT FROM AUTHOR]

• PCM passive system was coupled with natural ventilation. • PCM melting temperature was optimized in different climate zones. • Airflow rates were numerically calculated based on the wind and buoyancy effects. • Two control strategies were implemented to maximize the utilization of ventilation. In recent years, the building sector has been responsible for continuous increase in energy consumption in the world. Space heating and cooling accounts for 34% of this energy consumption in buildings. In this context, using thermal energy storage (TES) can reduce energy consumption for space air conditioning. The use of phase change materials (PCM) as latent heat thermal energy storage (LHTES) system in the building envelope has been of great interest for passive cooling applications due to the high energy storage capacity of this technology. However, in order to utilize the full potential of a PCM, it needs to be fully charged at each cycle. Ventilation during the night is an effective method which can be used in PCM-enhanced office buildings with the aim of charging the PCM every required cycle. In the present study, PCM melting temperature of office building in various climate conditions was optimized using a simulation-based optimization and coupled with free cooling operation. Ventilation control strategies were used to improve the cooling energy performance of the PCM enhanced building integrated into envelopes. It was found that charging PCM with night ventilation, especially when using some specific control strategies of natural ventilation operated by external windows opening results in considerable cooling energy savings. The study was conducted for 15 different cities around the world. It was found that, in hot arid conditions, PCM passive cooling system was ineffective. Although, the energy savings were improved by coupling PCM and natural ventilation in these climate conditions. But the benefits were more or less similar to using natural ventilation only. On the other hand, in temperate condition, the effectiveness of PCM was increased from 3.32% to 25.62% by coupling a PCM passive system with night ventilation. It was further improved to 40% when using PCM with temperature-controlled ventilation. Moreover, it can be said that smart control of ventilation can lead to considerable energy savings. [ABSTRACT FROM AUTHOR]

Cool roof effectiveness in improving building thermal-energy performance is affected by different variables. In particular, roof insulation level and climate conditions are key parameters influencing cool roofs benefits and whole building energy performance. This work aims at assessing the role of cool roof in the optimum roof configuration, i.e., combination of solar reflectance capability and thermal insulation level, in terms of building energy performance in different climate conditions worldwide. To this aim, coupled dynamic thermal-energy simulation and optimization analysis is carried out. In detail, multi-dimensional optimization of combined building roof thermal insulation and solar reflectance is developed to minimize building annual energy consumption for heating–cooling. Results highlight how a high reflectance roof minimizes annual energy need for a small standard office building in the majority of considered climates. Moreover, building energy performance is more sensitive to roof solar reflectance than thermal insulation level, except for the coldest conditions. Therefore, for the selected building, the optimum roof typology presents high solar reflectance capability (0.8) and no/low insulation level (0.00–0.03 m), except for extremely hot or cold climate zones. Accordingly, this research shows how the classic approach of super-insulated buildings should be reframed for the office case toward truly environmentally friendly buildings. [ABSTRACT FROM AUTHOR]