Browsing by Author "Moorlach, Mascha"

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    Open Access
    An analysis of annual environmental conditions and heat gains, and theoretical assessment of approaches to improve summer thermal comfort, of the Energy Research Centre at the University of Cape Town
    (2017) Cunliffe, Guy Edward; Hibberd, Andrew; Moorlach, Mascha
    The Energy Research Centre (ERC), a research centre located at the University of Cape Town (UCT), is considering retrofitting its offices with measures to improve its occupants' thermal comfort, particularly during Cape Town's summer months. While a simple solution would be to install an active cooling system, first consideration should be given to the deployment of preventative cooling measures and retrofits. By these means, the costs of an active cooling system would be reduced, as well as the building's relative increase in energy consumption and indirect greenhouse gas emissions. This dissertation examines internal thermal conditions of the ERC under current building conditions and predicts levels of thermal discomfort likely to be experienced by occupants, with emphasis on Cape Town's summer season. Heat gain components to the ERC are quantified, and a Base Case cooling scenario is determined; this characterises the peak cooling load and active annual cooling energy required to alleviate summer thermal discomfort, if no other interventions are implemented. Thereafter, the impacts of a selection of preventative cooling measures on the Base Case cooling scenario are assessed, and a theoretical payback period for each progressive measure is evaluated, relative to projected installation and operational costs of an active system designed to meet the Base Case. A model of the ERC offices is developed in DesignBuilder, which characterises thermal properties of the building envelope, thermal loads of lighting, electronic equipment and building occupants, and effects of prevailing weather patterns and solar radiation at the site of the building. Physical energy simulations of the model are run in EnergyPlus, which uses a series of algorithms based on the Heat Balance Method to quantify internal psychrometric conditions and heat gains in half-hourly iterations. An EnergyPlus Ideal Loads Air System component is input into the simulation to quantify the active cooling load required to maintain comfortable design conditions. The results indicate that 7 814.5 hours of thermal discomfort are experienced annually across the ERC (divided into eight thermal zones in the DesignBuilder model), with 37.6% of discomfort hours occurring between December and March, and 12.8% in February alone. Notably, a greater proportion of discomfort hours, 38.9%, were predicted for winter months (June through August). However winter thermal discomfort was not addressed in detail here, as the scope of the dissertation was limited to analysing ERC cooling only. Solar gains through external windows were found to be the largest single source of annual heat gain (20.65 MWhth), followed by heat gains due to lighting heat emissions (19.99 MWhth). Profiles during typical summer conditions showed significant heat gain also arises from conduction through the ceiling, due to existing but sporadic and thin layers of fibreglass ceiling insulation, with gaps that allow thermal bridging between the roof space and ERC thermal zones. The Base Case annual cooling requirements were determined to be 27.64 MWhth, while peak cooling load was found to be 66.87 kWth. Sensible cooling dominated total cooling loads in summer months. East and west facing thermal zones required the greatest cooling energy (normalised per floor area), having been shown to experience the greatest normalised solar and lighting heat gains. Inclusion of a 75 mm polyester fibre insulation layer above the ceiling boards would result in a 13.6% decrease in annual discomfort hours, relative to the current building condition, and reduced peak cooling load by 19% relative to the Base Case. Increasing thickness above 75 mm resulted in increased ceiling thermal resistance and further reduced annual discomfort hours. However, the marginal improvements in thermal comfort were found to decrease with increased insulation thickness. A 75 mm thickness of polyester fibre insulation was therefore selected as the first preventative measure to be considered for the ERC, and was included in all further assessment of additional preventative options. Lighting retrofits were also considered, by means of two progressive measures: Delamping – the removal of fluorescent luminaires from overly lit thermal zones – and Relamping – replacement of remaining fluorescents and light fixtures with more energy efficient technology (as well as the Delamping and Insulation measures). Delamping was found, from simulation analysis, to reduce lighting heat gains by 31%, relative to the Base Case and annual cooling requirements by 24%, with total projected costs after 10 years reduced by 15.6% relative to the Base Case. Relamping had a less pronounced impact on cooling requirements, but resulted in 15 % lower lighting energy use compared to Delamping only. The final measure considered was a Shading measure, whereby the replacement of the existing solar window film, currently fitted to each of the ERC's external windows, with internal adjustable shading. The Shading retrofit (in addition to all previous preventative measures) was found to cause a 35% reduction in annual cooling energy relative to the Base Case, as well as a 7% relative to the Relamping scenario. However, cost evaluation showed that costs of implementing the Shading retrofit significantly outweighed net incremental annual savings achieved under the measure, and was thus not recommended as a preventative option for the ERC. Alternative shading options, such as fixed external shading, may prove more cost effective in mitigating the ERC's solar heat gains, and should be considered in further research. From these results, it was concluded that a combination of insulation and lighting upgrades would provide the greatest benefit, in terms of thermal comfort, to the ERC, and would result in a more cost effective active cooling system, should one be proposed. The dissertation ended with recommendations for further work, including further analysis of ERC heating requirements in winter, and investigation into additional and alternative cooling methods, such as passive or solar cooling.
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    Draft policy framework for efficient water use in energy production.
    (Energy Research Centre, University of Cape Town., 2014) Madhlopa, Amos; Keen, Samantha; Sparks, Debbie; Moorlach, Mascha
    South Africa faces imperatives to secure a supply of clean water and to protect water resources, as well as to provide a secure supply of energy. Over and above the mandates of ensuring clean water provision and of improving the coverage and security of a reliable energy supply, the government faces challenges of reducing poverty and unemployment, and of ensuring sustainable development. In order to meet these challenges, the national government has developed a set of progressive policies. Harmonisation of these policies is itself a considerable challenge.
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    Impact of Thermally Activated Building Systems (TABS) in Office Buildings
    (2023) Kgaladi, Lebogang; Moorlach, Mascha
    Thermal comfort can be described as the degree to which a person is satisfied with their thermal environment (Yau & Chew, 2014). It is a person's perception of whether they feel warm or cool within their surroundings. The Danish professor, Povl Ole Fanger, developed the Predictive Mean Vote (PMV), a model consisting of physical and personal variables to quantify a person's thermal comfort within a building. The physical variables include air temperature, relative humidity, mean radiant temperature, and air velocity, and the personal variables include activity level and clothing insulation (Yau & Chew, 2014). People control the physical variables using systems that provide heating and cooling to an environment, the earliest of which were found in 9 000-year-old remains from Eastern Turkey (Ma, Wang, & Guo, 2015). The remains consisted of an intermediate space beneath the floor that would have been filled with cold water from Kantara Creek to cool the interior during warm seasons. Personal variables are controlled by changing the individual's activities and clothes. Today there are various space heating and cooling systems implemented in buildings. This research describes Thermally Activated Building Systems (TABS) and conventional Heating, Ventilation and Air-conditioning (HVAC) systems. Both systems consist of components such as the boiler, chiller and heat pump to condition the fluid used to deliver the heating and cooling. The systems differ and are classified by their heating and cooling transfer processes within the building's interior. HVAC systems use the air to transfer heat by convection, and TABS use the buildings' internal surfaces to transfer heat by radiation (Rhee, Olesen, & Kim, 2012). HVAC systems include Air Handling Units (AHUs) to deliver the conditioned air and provide dehumidification. In contrast, TABS consists of conditioned water pumped through pipes embedded within the building's floor, walls, and ceilings to transfer heat between internal wall surfaces. The combination of water and building material has a higher thermal capacity than air, making TABS more energy-efficient at transferring heat than HVAC systems. This research presents case studies to determine the magnitude by which TABS is more energy-efficient by analysing and comparing both systems' energy consumption as they deliver thermal comfort. The first case study consisted of an office building located in Cape Town, South Africa, with a TABS installation. The pipe layout in the building's floors was designed and optimised using LoopCAD for its construction between November 2018 and September 2020. The office building was modelled, and the heat load was simulated in EnergyPlus to determine the cooling needed to achieve thermal comfort. The cooling required was used as input into a modified TABS calculator, derived from the calculator given in ISO 11855, to predict the energy usage of the chiller. The electricity consumption determined by the TABS calculator was consistent with the actual chiller's electricity consumption. The mean difference between actual and calculated results is 2.054. It was determined that the TABS calculator results have an 80% confidence level to be within 1.17 of the actual chiller demand. A PMV calculator, rewritten from the calculator given in ISO 7730 and ASHRAE-55, was used to predict the thermal comfort of the occupants in the building. The calculator was tested, and its results were compared with the standard's. It was determined that the calculator's PMV and PPD results have an 80% confidence level to be within 0.015 and 0.5, respectively, of the ISO 7730 calculator's results. The calculator used the results from the TABS calculator to determine that the occupants were likely satisfied with their thermal environment. The second case study consisted of an office building similar to the first case study, located in Cape Town, South Africa, except with a conventional HVAC installation. Its HVAC system was optimised by installing Variable Speed Drives (VSDs) at the pumps and fans. A simplified building model was developed in SketchUp Pro and imported into EnergyPlus to model and simulate the HVAC system. As with the first case study, the chiller's energy consumption determined by the simulation was consistent with the actual chiller energy consumption. It was determined that EnergyPlus results have an 80% confidence level to be within 0.57 of the actual chiller demand. The simulation also determined that the occupants were likely satisfied with their thermal environment. The case studies showed that the TABS calculator and EnergyPlus could accurately simulate the energy usage of TABS and conventional HVAC systems. The buildings in which the systems were installed had different cooling loads, occupancy levels and thermal insulation making it challenging to compare the systems. Therefore, the systems were modelled and simulated in the same building to prove the research hypothesis. The third case study, involving a simple office building, was modelled in SketchUp Pro and imported into EnergyPlus. As with the first case study, the cooling load determined from EnergyPlus simulations were used as inputs into the TABS calculator to determine the energy consumption of the chiller. A Variable Air Volume (VAV) HVAC system was modelled on the building, and the chiller energy consumption was simulated. When comparing the sensible energy consumption of both systems, the simulations show that TABS consumes 41.62% of the HVAC chiller's energy to provide the same neutral thermal experience. TABS' reduced energy consumption presented an opportunity for a business case of installing the system into an Eskom building with an HVAC system that had reached its end of life. The installed HVAC system used in the business case consumed 8 056 961 kWh annually and, using Eskom's 2018/19 electricity tariff, cost R5 858 518 to operate. Using an annual tariff increase of 6% (the South African Reserve Bank's maximum CPI target) and Eskom's discount rate of 10.4%, the business case resulted in the following options: 1. Replace the HVAC system with an energy-efficient HVAC system would cost R20 360 000 to install, consume 4 212 129 kWh annually and cost R3 062 797 to operate in the initial year. Compared to the current HVAC installation, the proposed installation would have a simple payback period of seven years and a discounted payback of ten years. 2. Install a more expensive TABS installation at a proposed cost of R29 581 440. Although installing TABS costs more than an energy-efficient HVAC system, the TABS would consume less electricity and cost less to operate. The system was estimated to consume 2 384 908 kWh annually and cost R 1 734 156 to operate in the initial year. Similar to the HVAC option, the TABS installation would have a simple payback period of seven years and a discounted payback of ten years. At first glance, it seems that there is no business case to opt for the TABS instead of the HVAC installation. However, the average increase in the electricity tariff has been 12.17% annually for Eskom's 2019/20 and 2020/21 financial years. The average tariff increase gives the TABS installation a simple and discounted payback period of 7 and 12 years, while the replacement HVAC system has a simple payback period of 9 years and no discounted payback period. TABS also has the added advantages of a consistent temperature gradient and mitigating cold draughts resulting from excessive air movements (Rhee, Olesen, & Kim, 2012)
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    Renewable energy choices and water requirements in South Africa
    (University of Cape Town., 2013) Madhlopa, Amos; Keen, Samantha; Sparks, Debbie; Moorlach, Mascha; Dane, Anthony
    South Africa (SA) is an arid country, where water supply is often obtained from distant sources. There is also increasing pressure on the limited water resources due to economic and population growth, with a concomitant increase in the energy requirement for water production. This problem will be exacerbated by the onset of climate change. Recently, there have been concerns about negative impacts arising from the exploitation of energy resources. In particular, the burning of fossil fuels is significantly contributing to climate change through the emission of carbon dioxide (major greenhouse gas). In addition, fossil fuels are getting depleted, thereby decreasing energy security. Consequently, the international community has initiated various interventions, including the transformation of policy and regulatory instruments, to promote sustainable energy. In view of this, SA is making policy and regulatory shifts in line with the international developments. Renewable energy is being promoted as one way of achieving sustainable energy provision in the country. However, some issues require scrutiny in order to understand the water footprint of renewable energy production. Due to the large gap that exists between water supply and demand, trade-offs in water allocation amongst different users are critical. In this vein, the main objective of this study was to investigate renewable energy choices and water requirements in SA. Data was acquired through a combination of a desktop study and expert interviews. Water withdrawal and consumption levels at a given stage of energy production were investigated at international and national levels. Most of the data was collected from secondary sources (literature) and therefore the assessment boundaries are not fully comparable. Results show that there are limited data on all aspects of water usage in the production of energy, accounting in part for the significant variations in the values of water intensity reported in the global literature. It is vital to take into account all aspects of the energy life cycle to enable isolation of stages where substantial amounts of water are used. Conventional fuels (nuclear and fossil fuels) withdraw significant quantities of water over the life-cycle of energy production, especially for thermoelectric power plants operated with a wetcooling system. The quality of water is also adversely affected in some stages of energy production from these fuels. On the other hand, solar photovoltaic and wind energy exhibit the lowest demand for water, and could perhaps be considered the most viable renewable energy options in terms of water withdrawal and consumption.
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    The Measurement & Verification of Energy Conservation Measures at a Coal-fired Power Plant
    (2018) Larmour, Richard; Moorlach, Mascha; Bennett, Kevin; Hibberd, Andrew
    The aim of this dissertation was to use Measurement & Verification (M&V) to determine the improvements in net heat rate at a South African coal-fired power plant (CFPP) following an extensive refurbishment programme. The CFPP consisted of multiple subcritical pulverised fuel generating units and the refurbishment programme aimed to improve the overall net heat rate by 1%. The purpose of using M&V is isolate the performance changes attributable to specific energy conservation measures from those changes brought about by other factors, or that would have occurred anyway for other reasons. An extensive literature review was undertaken, firstly into M&V and secondly into CFPP design and performance. The conventionally accepted methods for determining plant performance are the ‘direct method’ in which a measurement boundary is drawn around the entire plant, and the ‘components method’ which evaluates the boiler, the turbine-condenser cycle and the auxiliary loads separately. Caution is drawn to the fact that plant performance may be expressed in many ways depending on how HR is defined and on which coal measurement base is used. The physical factors affecting plant performance were classified as either fixed or variable. Fixed factors included vintage and design, size, condition of the major components (boiler, turbine and condenser), cooling water system type and pollutant controls. Variable factors included ambient conditions, flexibility of operations (such as running at part-load and load cycling) and the characteristics of the coal used including heating value, total moisture, hydrogen, ash, volatile matter, sulphur, hardness & abrasiveness. It is clear from the literature that the language used to describe flexible operations is inadequate and poorly defined. Other factors that may affect the calculated heat rate of a plant include coal weighing, stockpile surveys, length of assessment periods, changes to static stockpiles, measurement boundary selection and other assumptions. The literature review was used as a basis to develop an M&V methodology for the specific CFPP involved in the case study. The energy conservation measures were described in detail as well as constraints regarding availability and resolution of plant data. Although all measurement boundary options were considered, the whole facility approach was chosen (Option C). This approach was mainly motivated by the lack of data available and a high potential for interactive effects. Another reason is the fact that assessments need to capture the overall performance which could include deterioration in one part of the plant and simultaneous upgrades in other parts. The primary data required to find heat rate is the electrical energy use (exported, imported and auxiliary), the mass of coal consumed and the coal higher heating value. The M&V methodology included the development of a baseline adjustment model to adjust for changes in plant load, coal moisture and coal ash content. Ideally the model should have included changes in ambient conditions (temperature and relative humidity) but this was not possible as no ambient data was available and the assessment was done retrospectively. The absence of ambient data was mitigated by stipulating that assessment periods need to consist of a minimum of twelve consecutive months to account for changes in performance due to seasonal effects. The methodology also included a Monte Carlo analysis to quantify the combined uncertainties associated with electrical energy use, coal energy use, coal heating value and the adjustment model itself. The methodology was used to assess the change in net heat rate of the plant used in the case study for two separate twelve month reporting periods. The calculated impacts of the energy conservation measures were not as favourable as originally anticipated. A brief analysis of the results is provided with a discussion of potential reasons for the underperformance. A whole facility approach does not allow the reasons for performance changes to be pinpointed. One possibility is simply that the energy conservation measures had not been implemented as originally planned. An important finding was that the performance changes could not be solely attributed to the exclusion of any independent variables from the baseline adjustment model (e.g. ambient conditions). A more general discussion of the merits, shortcomings and limitations of the methodology is provided as well as some comments on the general interpretation of results. The baseline adjustment model is only applicable to the plant in the case study and is only valid for small changes in the independent variables. When calculating part-load operation, special attention must be given to generating units that have been derated. The application of a single part-load adjustment model to a multi-unit plant is discussed and found to result in conservative reporting. Factors which contribute to uncertainty, but which are unknown include staithe coal level changes, unknown stockpile dynamics, uncalibrated instruments, unrecorded coal movements and inaccuracy of aerial stockpile surveys. The dissertation concludes that the original hypothesis is supported: that a credible M&V methodology may be developed and applied to determine the heat rate improvements resulting from the refurbishment programme at a coal-fired power plant. Recommendations include an upfront agreement on which measurement reporting bases to use (both for heat rate and for coal), selection of a whole facility measurement boundary, a minimum assessment period of twelve months, installation of at least one accurate instrument to measure actual coal consumption (as opposed to coal delivered to the plant and then moved within the plant), sampling of coal, determination of heating value and collection of accurate ambient condition data from the start of the baseline period. Further recommendations are made to reduce uncertainty, determine static factors and to better interpret reported impacts.
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    Water considerations in selecting energy technologies
    (Energy Research Centre, University of Cape Town., 2014) Madhlopa, Amos; Keen, Samantha; Sparks, Debbie; Moorlach, Mascha
    Water plays a vital role in the socio-economic development of any nation. It is exploited in different economic sectors, including the energy sector. Water and energy are inextricably related, and this relationship is usually referred to as the water-energy nexus. Water is used for energy production in the abstraction, growth and preparation of some fuels as well as in some power plants. It is also used in the raw materials for plant infrastructure, manufacturing of plant components, and the construction of power generating infrastructure. The volume of water used in the raw materials will vary widely, not only with the technology, but also the material type and plant design. Furthermore, these materials can be imported from any location and the associated water use is not limited to any water catchment, water management area or local authority.