Browsing by Subject "energy use"

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    Numerical analysis of the thermal performance of vapour compression heat pump heat exchanger using Python and computational fluids dynamics (CFD)
    (2024) Sehobai, Sehobai Elliot; Bello-Ochende, Tunde
    Numerical analysis on fin and tube heat exchangers contributes towards the implementation of energy-efficient technologies in the industrial and building sectors. Fin and tube heat exchangers are found in various mechanical applications including heating, ventilation, and air conditioning (HVAC) and refrigeration systems, the oil and gas extraction industry, power plants and many more. Due to the rapid depletion of energy resources worldwide, there is a need to reduce energy consumption, especially for systems that use electricity such as heat pump systems. This led to several studies on the heat exchangers used in heat pumps including analyses of the heat exchanger geometry and working fluid impacts on the thermal performance. This study describes numerical analyses on the fin and tube heat exchanger model developed in Python, using nonuniform airflow velocities calculated in Ansys Fluent. The geometrical parameters of the modelled heat exchanger are based on the literature values. The heat transfer rates, pressure losses, vapour quality and all refrigerant properties are calculated by discretizing each tube on each tube circuit and tube row into several increments and incorporating nonuniform airflow in three dimensional. The model is validated using experimental data which shows that the maximum variation between the model and experimental results is less than 10.0%. The velocity contours from the Ansys Fluent heat exchanger model suggest that airflow varies significantly in three dimensional. The results from the modelled heat exchanger in Python show that the nonuniformity of airflow consequently affects the refrigerant pressure losses, heat transfer and vapour quality in the refrigerant tubes. Thus, assuming uniform airflow over the heat exchanger results in underestimating the actual refrigerant pressure losses, heat transfer and vapour quality in the upper refrigerant tube circuits (those located closer to the top of the heat exchanger) while overestimating these parameters on lower tube circuits (those located towards the bottom, farther from the fan location). This leads to a maximum variation exceeding 10.0%. Moreover, the coefficient of performance (COP) was also calculated from the heap pump model developed in Python. These model results suggest that generally, assuming uniform airflow on the heat exchanger underpredicts the heat pump COP by a maximum variation of 11,07% for all four operating conditions of the heat pump discussed in this study. These results highlight the importance of performing analysis in three-dimensional space, considering non uniform airflow.
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    Open Access
    Policies and scenarios for Cape Town's energy future: options for sustainable city energy development
    (University of Cape Town, 2006) Winkler, H; Borchers, M; Hughes, A; Visagie, E; Heinrich, G
    This study examines a set of energy policy interventions, which can make a major contribution to sustainable development for the City of Cape Town – economically, environmentally and socially. Major energy savings can be made from modal shifts in the transport sector, and with efficient lighting. The savings make a contribution to economic development, by freeing up resources. The savings from energy efficiency also have important social benefits in energy savings, reducing energy bills for poor households. From an environmental point of view, implementing the city’s renewable energy target will have significant costs, but these can be partly off-set by selling carbon credits through the Clean Development Mechanism, and will result in indirect health benefits. Targeted interventions can reduce local air pollution, and help Cape Town become a leader in addressing greenhouse gas emissions. Apart from examining the social, economic and environmental dimensions of each policy, this paper compares policies to one another. Of particular interest for sustainable energy development are those policies which are viable in terms of costs, social benefits and the environment. Compact Fluorescent Lamps (CFLs) in residential, commercial and government sectors and heating ventilation and air conditioning (HVAC) in commerce and government sectors stand out as policies that have benefits from every angle. The paper builds on previous work done on the ‘state of energy’ for Cape Town and develops a tool that can paint a picture of what might happen to energy in the future. Using the Long-Range Energy Alternatives Planning (LEAP) modelling tool, a set of energy policies have been simulated.
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    Open Access