UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item Modeling of HVAC Configurations for De-Carbonization in a Mid-Size Hospital(2022) Grant, Zachary; Hwang, Yunho; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As the threat of climate change becomes more imminent, there has been increasing emphasis on technologies that reduce carbon emissions in the HVAC sector. The clear path forward given existing technologies is electrification since electricity production has future potential to become cleaner. In terms of building type, high ventilation requirements and near continuous occupancy make healthcare facilities some of the highest energy users. HVAC equipment runs all day and night in these facilities with little change. Conventional HVAC equipment such as a boiler is proven to consume more energy than heat pump systems. More specifically, the Variable Refrigerant Flow (VRF) heat pump and the Ground Source Heat Pump (GSHP) are areas of ongoing research. This analysis included creating whole-building energy models using EnergyPlus and OpenStudio to compare the energy consumption for these heat pump configurations and some cheaper electrification alternatives. The results suggested that the GSHP system possessed the greatest potential for energy savings and thus decarbonization given its higher efficiency during times of extreme ambient temperatures compared to other options.Item EXPERIMENTAL EVALUATION AND SIMULATION RESEARCH ON NOVEL VARIABLE REFRIGERANT FLOW SYSTEM(2017) Lin, Xiaojie; Radermacher, Reinhard; Srebric, Jelena; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Variable refrigerant flow (VRF) system is a popular building air conditioning system which could provide cooling or heating to individual rooms independently. The system is called “variable refrigerant flow” system due to its capability of regulating the refrigerant flow via the precise control of variable speed compressors and electronic expansion valves in each indoor unit. In this dissertation, an advanced VRF system which could provide space cooling, heating and water heating is experimentally evaluated in cooling and heating season for both heat recovery operation and water heating operation. The VRF system is simulated in EnergyPlus and validated with experimental data. Based on the deviation analysis and literature review, it is found that the existing VRF model could not fully reflect the operation characteristic of VRF systems, leading to a high uncertainty in cooling/heating energy and energy consumption. A new VRF model is thereafter proposed, validated in this research and resulted in a model uncertainty less than 5%. Based on the new model, the seasonal performance of an energy saving control strategy and the concept of chilled water storage are investigated. Meanwhile, to solve the mismatch between the building’s thermal load and cooling/heating capability of the VRF system, a new VRF system with phase change material (PCM) based thermal energy storage (TES) is proposed. The new VRF system utilizes single TES device to support both cooling and heating season operation. The performance of new VRF system with PCM based TES is investigated and compared to that of the baseline VRF system. It is found that the new VRF system with PCM based TES could achieve both energy efficiency and demand response goals in cooling and heating season. Based on the comparison, the effect of operation strategies and grid incentive program are discussed. Finally, the economic analysis of the new VRF system with PCM based TES based on annual performance is carried out.Item EXPERIMENTAL EVALUATION OF A MULTIFUNTIONAL VARIABLE REFRIGERANT FLOW SYSTEM IN AN EDUCATIONAL OFFICE BUILDING(2013) Kwon, Laeun; Hwang, Yunho; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The top three end uses - space heating, space cooling, and water heating - accounted for close to 41 percent of site energy consumption in U.S. building primary energy consumption. Therefore, energy efficient heating, ventilating and air-conditioning (HVAC) systems in buildings is essential for energy savings in the building sectors. A multifunctional variable refrigerant flow (MFVRF) system is finding its way into residential and commercial buildings since it can simultaneously provide space cooling, space heating and hot water. The MFVRF system was installed in an educational office building and fully instrumented to measure the performance of the system under a wide range of outdoor weather conditions. The effects of a part-load ratio (PLR) on the daily performance factor (DPF) and total energy consumption were experimentally investigated in the field performance tests. Although the higher PLR represents a more effective cooling and/or heating the system, the DPF is not always increased with PLR because the system is optimized at a certain range of PLR. Furthermore, the effects of the hot water demand and the heat recovery operation modes on the performance of the system were investigated in a field test for the heating and shoulder seasons. Integrating the water heating functions into the heat recovery type variable refrigerant flow (HR-VRF) system, not only supplies hot water year-round, it also improves the system performance. As the hot water demand for the MFVRF system increased, the PLR was improved, which resulted in an increase system heating performance. In the heat recovery operation mode, the heat absorbed from the indoor units operating in the cooling mode was transferred to other indoor units operating in the heating mode. The DPF was 2.14 and 3.54 when the ratio of daily total cooling energy to daily total heating energy was 13.0% and 28.4%, respectively, at the similar outdoor weather conditions. This enhancement was attributed to the waste heat recovered during the heat recovery operation mode and the decrease in pressure ratio, which is a result of the improvement of the compressor efficiency. Energy saving potential of the MFVRF system in a building with high internal heat gains, resulted in a high cooling load for the cooling season and a low heating load for the heating season, was verified through the field performance test. The performance of the MFVRF system for the heating and shoulder seasons was improved by transferring the recovered energy to the indoor space and supplying the hot water.