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.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    CHARACTERIZATION OF NON-DISPERSIVE INFRARED SENSORS FOR R-32 AND R-454B LEAKS
    (2022) Leahy, James Ryan O; Sunderland, Peter B; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Due to the increased concerns about climate change, multiple states including California havestarted to pass legislation that phases out high global warming potential (GWP) refrigerants in HVAC and refrigeration systems. The likely replacements are A2L refrigerant which have lower GWP and are mildly flammable. This will require area monitoring leak detection systems for all future applications of these refrigerants. These detection systems preferably need to operate continuously for up to 15 years. The UL 60335-2-40 (2019) standard defines the sensor response time which must alarm within 10 seconds of exposure to 100% of the refrigerant’s LFL. Development of sensors capable of meeting the UL 60335-2-40 standard has been slow with many different types of gas sensing technologies being used. One of these technologies that was identified as a potential candidate was non-dispersive infrared (NDIR). A sensor not yet available commercially was able to be obtained to test its response to A2L refrigerants R-32 and R-454B according to the UL 60335-2-40 standard. Three other competing sensing technologies were also obtained to compare the performance of other sensors about to hit the market. These sensors were characterized by their linearity to varying concentrations of A2L refrigerant, response time, and to contamination. All the tested sensors were able to meet the 10 second requirement for response time. However, all but the NDIR sensor experienced a change in output when exposed to a list of prescribed contaminants by the UL 60335-2-40 standard. After the contamination, the NDIR sensor showed no change in its output indicating it experienced no poisoning effect. The NDIR sensor was deemed to have the optimal performance out of the sensing technologies. Long term exposure, exposure to contaminants and refrigerant at the same time, and service lifetime are still concerns.
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    Dynamic Modeling of Vapor Compression Systems for Residential Heat Pump Applications with Alternative Low-GWP Refrigerants
    (2015) Bhanot, Viren; Hwang, Yunho; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    With the increased focus on reducing greenhouse gas emissions, low-GWP refrigerants, R32 and D2Y60, have been proposed as drop-in replacements for R410A in residential heat pumps. This thesis presents the development of a modeling framework in Simulink® for the dynamic simulations of such residential heat pumps. The framework is component-based, allowing arbitrary cycle configurations, and includes most of the relevant components. Finite-volume method has been applied to the heat exchanger. Compression and expansion processes are treated as quasi-steady state. The framework has been used to study the performance of the system using the baseline refrigerant and charge-optimized alternatives at ASHRAE test conditions, and the results have been compared against experimental data. Steady-state COP values fall within ±8% of experimental data. For the cyclic tests, the pressure and temperature behaviors compare well and accumulated capacity and power consumption errors are found to be within ±9%. Relative differences between the refrigerants are consistent between simulations and measurements. The framework shows potential for being used to simulate the operation of residential heat pumps under dynamic conditions.