Canopy urban heat island and its association with climate conditions in Dubai, UAE

The impact that climate change and urbanization are having on the thermal-energy balance of the built environment is a major environmental concern today. Urban heat island (UHI) is another phenomenon that can raise the temperature in cities. This study aims to examine the UHI magnitude and its association with the main meteorological parameters (i.e., temperature, wind speed, and wind direction) in Dubai, United Arab Emirates. Five years of hourly weather data (2014–2018) obtained from weather stations located in an urban, suburban, and rural area, were post-processed by means of a clustering technique. Six clusters characterized by different ranges of wind directions were analyzed. The analysis reveals that UHI is affected by the synoptic weather conditions (i.e., sea breeze and hot air coming from the desert) and is larger at night. In the urban area, air temperature and night-time UHI intensity, averaged on the five year period, are 1.3 °C and 3.3 °C higher with respect to the rural area, respectively, and the UHI and air temperature are independent of each other only when the wind comes from the desert. A negative and inverse correlation was found between the UHI and wind speed for all the wind directions, except for the northern wind where no correlation was observed. In the suburban area, the UHI and both temperatures and wind speed ranged between the strong and a weak negative correlation considering all the wind directions, while a strong negative correlation was observed in the rural area. This paper concludes that UHI intensity is strongly associated with local climatic parameters and to the changes in wind direction

Thermal comfort standards in the Middle East: Current and future challenges

Cooling energy demand has increased three-fold in the Middle East (ME) over the last 30-years. This is driven by the need to maintain thermal comfort in an extremely hot climate, and supported by rising incomes, falling costs of air-conditioning and growth in the number of buildings. The definition of thermal comfort in these buildings is drawn from “international” standards, which, though empirically derived, have no basis data from this region. Hence, we ask, to what extent do indoor conditions in the ME fall within the standards recommended range of thermal comfort, and when they do, whether they are found to be comfortable by their occupants. We present the first large-scale study of thermal comfort in the ME, consisting of two approaches: (i) a meta-analysis of data from existing studies, (ii) independent field data covering four countries representing 27% of the region's population, 31 air-conditioned buildings of different types, including “green” buildings, and 1,101 subjects. The meta-analysis demonstrates that current thermal comfort standards fail to predict thermal sensation of 94% of occupants. Our own data show that, while indoor conditions are within standards-recommended ranges 58% of the time, only 40% of occupants find these conditions acceptable. We find evidence of overcooling in summers, with 39% occupants expressing cold discomfort. Computer models suggest that this is likely to have increased annual cooling energy demand between 13% and 20%, compared to non-overcooled conditions. These results suggest the necessity of localised thermal comfort standards that mitigate excess cooling energy demand, without compromising occupant thermal comfort.</p

Solar hydrogen system for cooking applications: Experimental and numerical study

This paper describes the development of a semi-empirical numerical model for a solar hydrogen system consisting of a proton exchange membrane electrolyser (PEM) powered by photovoltaic panels to produce hydrogen as fuel for cooking applications, focussing on Jamaica as a suitable case-study. The model was developed in TRNSYS and includes a novel numerical component based on FORTRAN to model the operation of the PEM electrolyser. The numerical component was developed based on operational data from a purpose constructed small-scale experimental rig. The numerical model was calibrated using data from the experimental rig powered by operational data from a photovoltaic panel system in the UK and predicted photovoltaic panel power data from Jamaica. For the test conditions, experiments indicated an electrolysis maximum efficiency of 63.6%. The calibrated model was used to develop a case study analysis for a small community in Jamaica with a daily cooking demand of 39.6kWh or 1.7kg of H2 gas. Simulations indicate that the H2 production plan is sufficient for the cooking needs of the case-study.This project is partly funded by ACP Caribbean & Pacific Research Programme for Sustainable Development of the European Union (EuropeAid/130381/D/ACT/ACP)

Experimental and computational study of a solar powered hydrogen production system for domestic cooking applications in developing economies

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.In many developing economies, a high percentage of domestic energy demand is for cooking based on fossil and biomass fuels. Their use has serious health consequences affecting almost 3 billion people. Cleaner cooking systems have been promoted in these countries such as solar cooking and smokeless stoves with varying degrees of success. In parallel, solar electrolytic hydrogen systems have been developed and increasingly used during the last 25 years for electricity, heat and automobile fueling applications. This study has developed and tested experimentally in the laboratory a solar hydrogen plant numerical model suitable for small communities, to generate and store cooking fuel. The numerical model was developed in TRNSYS and consists of PV panels supplying a PEM electrolyser of 63.6% measured stack efficiency and hydrogen storage in metal hydride cylinders for household distribution. The model includes novel components for the operation of the PEM electrolyser, its controls and the metal hydride storage, developed based on data of hydrogen generation, stack temperature and energy use from a purpose constructed small-scale experimental rig. The model was validated by a second set of experiments that confirmed the accurate prediction of hydrogen generation and storage rates under direct power supply from PV panels. Based on the validated model, large-scale case studies for communities of 20 houses were developed. The system was sized to generate enough hydrogen to provide for typical domestic cooking demand for three case-studies; Jamaica, Ghana and Indonesia. The daily cooking demands were calculated to be 2.5kWh/day for Ghana, 1.98kWh/day for Jamaica and 2kWh/day for Indonesia using data mining and a specific quantitative survey for Ghana. The suitability of weather data used in the model was evaluated through Finkelstein Schafer statistics based on composite and recent weather data and by comparing simulation results. A difference of 0.9% indicated that the composite data can be confidently used. Simulations results indicate that a direct connection system to the PV plant rather than using a battery is the optimal design option based on increased efficiency and associated costs. They also show that on average 10tonnes of CO2/year/household can be saved by replacing biomass fuel with hydrogen. The potential of total savings in the three case-study countries is shown in the form of novel solar hydrogen potential maps. The results of this study are a contribution towards better understanding the use of hydrogen systems and enhancing their role in renewable energy policy.ACP Caribbean & Pacific Research Programme for Sustainable Development of the European Union (EuropeAid/130381/D/ACT/ACP