| dc.description.abstract | Net zero energy buildings have captured the attention of many researchers and governments due to high energy consumption by traditional buildings. The design stage of a net zero energy house is the most crucial and cost effective step to focus on. The orientation of the building, proper insulation, high-efficiency windows, natural ventilation and other techniques are used to curb down heat transfer from and to the building. These robust energy measures combined with using highly efficient domestic appliances, lighting fixtures, seasonal air-conditioning equipment with high coefficient of performance (COP) and thermal heating techniques reduce energy to the level where the remaining electricity required to power the building can be produced by renewable energy systems.
This PhD research aims at designing and assessing the performance of net zero energy house (NZEH). Three novel multigeneration energy systems are developed, where renewable energies will be the prime sources to supply electricity, fresh and hot water, seasonal heating and cooling.
In order to achieve NZEH, the study starts by choosing the right orientation of the house, selecting the building materials and fixtures that would save on energy, and then optimizing the thicknesses of the acoustical and thermal insulation materials used and followed by heat load calculations. After which, the total connected electrical load to the house is determined and the power system is optimized and selected. Moreover, thermodynamic modeling for all systems components is developed and design parameters are varied to note their effect on efficiencies. Exergoeconomic and exergoenvironmental analyses are performed to determine exergy destructions and greenhouse gas emission costs. In addition, design variables are optimized to maximize renewable energy use while reducing exergy destruction and minimizing total system cost and greenhouse gas emissions.
The ultimate goal of this study is to produce sustainable energy options for residential buildings with low noise pollution and very low level of greenhouse gases emissions. In this regard, three new systems are considered.
System I is composed of a photovoltaic (PV) system, wind turbine, diesel generator, battery bank and an electrical control system that supply power to the house, while solar panels power absorption and liquid desiccant systems which provide air-conditioning and fresh water. Hot water is produced by solar heat, photovoltaic thermal system (PV/T) and from a ground thermal storage, where hot water from solar panels passes through during the long summer months, raising the earth temperature, which is used in winter to heat the cold water circulated through. The optimization results show that system I with a net present cost (NPC) of US $56,558.00 in 2013 currency, and levelized cost of energy $0.127/kWh satisfies the connected load requirements. A power system optimization yields a 0.998 renewable energy penetration factor and 73 kg/yr of CO2 emissions. While exergoeconomic analysis gives a total system cost of $107,000.00 and exergy analysis gives overall system exergy efficiency of 41 % and 26 % at 8.00 am and 2.00 pm respectively.
System II consists of organic Rankine cycle system (ORC) with a battery array to supply electricity to the house, while solar panels power a liquid desiccant system and absorption chiller system that provide the house with air-conditioning and fresh water. Hot water is produced by solar heat. The optimized power system with a NPC of $52,505.00 and LCE of $0.118/kWh, renewable energy fraction of 1.00 and zero kg/yr CO2 emissions provides for the house.
The overall system exergetic efficiency varies between 44.76 %, 23.57 % and 36.22 % at 8.00 am, 2.00pm and 5.00 pm, due to solar energy changes, while the overall system efficiency varies between 60 %, 36.62 % and 53.95 % at 8.00 am, 2.00 pm and 5.00 pm. While exergoeconomic analysis gives a total system cost of $117,700.00 compared to $128,500.00 after running the multiobjective optimization.
System III consists of hydro turbine system, PV and battery systems with electrical control mechanism that supplies power to the house. A ground source heat pump integrated with a heat exchanger provides seasonal air-conditioning and part of the hot water. A heat transformer powered by solar energy combined to a distillation system provides the house with fresh and hot water. Hot water from the separation unit of the
distillation system heats earth soil in a ground thermal storage where cold water will be heated in the winter.
The power scheme is optimized to the total NPC $40,420.00 and LCE 0.091$/kWh with 1.00 renewable energy fraction and zero kg/yr CO2 emission. The overall system exergetic efficiency varies from 50%, 37% and 51% at 8:00 am, 2:00 pm and 5:00 pm respectively, while the overall system cost is $68,192.25 compared to $74,384.00 after running the multiobjective optimization. | en |
