Theoretical analysis and experimental investigation of ejector heat pumps and its water heating applications

This dissertation presents both theoretical and experimental work on ejector heat pump (EHP) systems and its water heating applications. The main goal is to improve performance, identify environmentally friendly working fluids, and determine how EHP technology can be applied to residential and commercial heating systems. The work combines analytical modeling, refrigerant screening, ejector geometry studies, and full-scale lab testing to create a design and evaluation framework for different EHP setups. Three theoretical models are presented. (1) A steam-based gas-fired EHP model was developed utilizing isentropic flow relations and a constant-pressure mixing assumption to study the effects of high- and low-temperature evaporator (HTE and LTE) conditions and ejector back pressure on COP. (2) A thermodynamic screening model used to evaluate ultra-low GWP refrigerants, identifying R1233zd(E) and several others capable of meeting the condensing temperature required for domestic water heating. (3) A simplified version of the steam EHP model was then applied to these top-performing refrigerants, focusing on the ejector's geometry and mapped out how area ratio, PF and SF temperatures, and critical condensing temperature affect the entrainment ratio and heating COP. Four experimental systems were built and tested based on these models. The standalone steam EHP was used to study the effect of nozzle exit position, primary nozzle size, back pressure, and COP under subcritical operation. The standalone R1233zd(E) EHP reached higher condensing temperatures and was able to operate at critical conditions for longer, outperforming steam in sustained efficiency. Updating the theoretical model with real-fluid properties allowed it to match experimental results within 5 percent. A gas-fired EHP (GFEHP) prototype with a combustion-based HTE showed performance improvements over the standalone R1233zd(E) system, while also identifying key areas to improve, such as heat losses, PF flow stability, and SF throttling. Finally, a vapor-compression ejector heat pump (VCEHP) water heater using R134a provided a baseline for integrating ejectors into high-efficiency heat pump systems and showed where nozzle and ejector geometry changes could improve flow rates and evaporator performance. Overall, the results show that EHP systems, especially with R1233zd(E), has promising potential to meet water heating performance targets while reducing environmental impact. The models, tools, and experimental results from this work give a strong foundation for optimizing EHP performance and moving the technology toward real-world use in sustainable heating applications.