• Energy Research

Cool roofs are a long-term alternative for the creation of a building’s thermal comfort as they can reduce the energy required for cooling demands and mitigate the urban heat island effect, thus benefitting both buildings and cities. Interest in cool roofing has recently escalated and numerous concepts, techniques, and experiences are represented in various studies conducted for hot climates; however, in reviewing the literature, it was found that most of this research is limited to the investigation of these benefits at either the building or city scale. Indeed, only six attempts were found that integrated both scales. To assist with design decisions, several studies have concluded there is an urgent need for a multi-level, interdisciplinary assessment framework, but as yet no such framework has been constructed. Following the literature review, in this study, a general framework is proposed which permits current modelling to progress beyond typical protocols, by including data linking a specific urban microclimate at the neighbourhood/city level with that of a building, thus connecting the microclimatic environment with objective assessment of energy efficiency. It is hoped that this framework will promote the development of exclusive cool roof applications for buildings and outdoor urban settings.

A hybrid ventilation system combining both natural and mechanical ventilation has proven very promising in moderating indoor climate, based on its ability to ensure indoor air quality with low energy consumption. The system maintains indoor thermal comfort conditions by switching to mechanical mode whenever natural ventilation is not possible. However, the application of such a system in severe arid climates is still very limited and challenging, and almost half the urban peak load for energy demand is used to supply cooling and air-conditioning in summer. This paper assessed the application of the hybrid ventilation mode for an educational building in a hot, arid climate, with the aim of reducing the building’s energy consumption without compromising the occupants’ thermal comfort. A dynamic simulation was conducted using Integrated Environmental Simulation in a Virtual Environment building energy software, and the outcomes were validated against actual consumption data over one year. The results were then evaluated for indoor thermal comfort and energy reduction and showed the potential of the hybrid system to provide energy savings of 23% across the year. Better energy performance was achieved during the cooler seasons (33.5%) compared to hot (17.1%). When photovoltaic systems were incorporated, by examining different inclination angles and locations for energy savings and carbon emissions (CO2) reductions, the outcomes proved that photovoltaic south and a 25° tilt angle recorded the maximum energy and minimum CO2 emissions annually. This integration of hybrid ventilation and photovoltaics reduced the building’s energy consumption from 106.1 MWh to 36.6 MWh, saving almost 85% in total annual energy and cut down the carbon emissions from 55,227 kgCO2 to 6390 kgCO2.

The relationship between outdoor microclimate and indoor building conditions requires the input of hourly weather data on the typical meteorological characteristics of the specific location. These data, known as typical meteorological year (TMY), are mainly deduced from the multi-year records of meteorological stations outside urban centres, preventing the actual complex interactions between solar radiation, wind speed, and high urban density. These factors create the urban heat island effect and higher ambient air temperatures, skewing the assumptions for energy demand in buildings. This paper presents a computational method for assessing the effect of the urban climate in the generation of typical weather data for dynamic energy calculations. As such, the paper discusses an evaluation method of pairing ENVI-met 4 microclimate and IES-VE building energy modelling software to produce a typical urban specific weather dataset (USWDs) that reflects the actual microclimatic conditions. The ENVI-met results for the outdoor microclimate conditions were employed to determine the thermal boundaries for the IES-VE, and then used to compute the building’s energy consumption. The energy modelling that employed the USWDs achieved better performance compared to the TMY, as the former had just a 6% variation from the actual electricity consumption of the building compared to 15% for the latter.

This study calls for the integration of context-based socio-cultural habits and learning from local practices in providing outdoor thermal comfort in conservation areas. These parameters have direct impacts on outdoor activities, especially in hot arid climates. The study took place in two nearby locations one renovated and all external shadings removed to provide visual vistas to monuments while on the same street, no more than 1500 m apart, local shading practices were left in places. Sun-exposed as opposed to shaded sites were compared for subjective thermal comfort and outdoor activity, via structured interviews, observations, and wide-ranging micrometeorological measurements. The aim was to investigate psychological factors, including overall thermal comfort and perception, in addition to environmental parameters, such as solar radiation intensity and thermal adaptation. The analysis illustrates the importance of shading as a dominant factor in achieving thermal comfort on the urban scale, with a neutral temperature in summer of 29.9 °C and 29.2 °C for shaded and sun-exposed locations, respectively. The results suggest people may be more willing to tolerate higher temperatures in shaded rather than sun-exposed locations. Moreover, cultural constraints and context-based behaviour proved to have some influences on people’s levels of adaptation and their thermal behaviour.

Hybrid ventilation systems, strategically integrating natural and mechanical ventilation, hold significant promise for reducing building cooling energy consumption, particularly in hot climates. This study investigates the effectiveness of such a system in a Dubai office building, aiming to minimize energy use and carbon emissions within a challenging, arid climate where cooling demands are substantial. The research employs a two-pronged methodology. First, a systematic review of 84 research articles published between 2010 and early 2024, encompassing simulations, experiments, and case studies, reveals a wide range of reported energy savings from hybrid ventilation, underscoring the need for standardized performance comparisons. Building upon this foundation, the second phase employs a detailed case study. Using EnergyPlus software, a dynamic energy model of a Dubai office building was created and validated against a year’s worth of actual energy consumption data. This validated model was then modified to simulate implementing a hybrid ventilation system, directly addressing the performance variations highlighted in the literature review. Results demonstrate that the hybrid system can achieve a 23% annual reduction in energy consumption compared to a conventional system, with savings more pronounced during cooler seasons (29%) than in hotter months (13%). Furthermore, the system yielded a 20% reduction in carbon emissions. This research provides compelling, context-specific evidence for the efficacy of hybrid ventilation in reducing building energy consumption and carbon footprint in hot, arid climates, contributing to more sustainable building design practices.

There is increasing need to apply building information modeling (BIM) to low energy buildings, this includes building energy modeling (BEM). If a building energy model can be flawlessly generated from a BIM model, the energy simulation process can be better integrated within the design, can be more competent, and timesaving. However, concerns about both the reliability and integrity of the data transfer process and the interoperability between the BIM and BEM prevent any implementation of BIM-based energy modeling on a large scale. This study addresses the accuracy and integrity of BIM-based energy modeling by investigating how well Autodesk's Revit (BIM), in conjunction with two of the most used energy modeling programs (BEM) known as DesignBuilder and Virtual Environment (IES-ve), were integrated in terms of interoperability, including location and weather files, geometry, construction and materials, thermal zones, occupancy operating schedules, and HVAC systems. All misrepresented data during the interoperability process were identified, followed by benchmarking between the BIM-based energy modeling simulation outcomes and the actual energy consumption of the case study, to assess the reliability of the process. The investigation has revealed a number of interoperability issues regarding the BIM data input and BEM data interpretation. Overall, BIM-based energy modeling proved to be a promising tool for sustainable and low energy building design, however, the BIM to BEM process is a non-standardized method of producing building energy models as it varies from one modeler to another, and the BIM to BEM process. All these might slow down any possible application for the process and might cause some uncertainties for the professionals in the field applying it.

In arid climates, a significant portion of the urban peak energy demand is dedicated to cooling and air-conditioning during the summer. The rapid urbanization rates in developing countries, particularly in the Gulf Cooperation Council (GCC), have intensified the pressure on energy resources to meet the indoor comfort needs of residents. As a result, there has been a substantial increase in energy demand, with a 2.3% rise recorded in 2018. Electricity consumption in residential buildings accounted for over 48.6% of the total electricity consumption. The choice of building fabrics used in a residential building can significantly impact the building’s passive performance and carbon footprint. This study aimed to enhance our understanding of how specific fabric details influence cooling energy usage in arid climates. To achieve this, a validation simulation model was initially created as a base case for a residential housing typology in Al Ain, UAE. This was followed by a parametric energy evaluation of various building envelope features. The evaluation was based on the reduction of yearly cooling load energy. The simulation results indicate that incorporating 50 mm of expanded polystyrene insulation into the outside walls significantly reduced energy consumption for cooling requirements in the arid UAE climate. Furthermore, no substantial difference was observed in the various roofing choices, including cool and green roofs, gravels, and sand roofs. Additionally, we concluded that the total solar energy transmittance (g-value) of windows played a more significant role than thermal transmittance (U-value) in reducing solar heat gain within the spaces. These findings should guide strategic decisions on building envelope upgrading for sustainable societies.