A hybrid cooling, heating and power (HCHP) concept was recently demonstrated through a DOD innovative energy program. It included several high performance components for distributed energy systems and a unique drive-train design, which efficiently converts waste heat into useful energy in the form of cooling, heating and power depending upon the energy needs. Compared to a standard military environmental control unit (ECU) which puts an electric load on a diesel generator, the HCHP system uses engine exhaust heat as the primary energy input. Utilizing the exhaust heat can potentially provide 27% reduction on fuel consumption when operating in the cooling mode. When cooling is not needed, it is able to provide power output using engine waste heat — a potentially significant advantage over other heat activated cooling technologies.
Summary Rankine (steam) cycle traditionally has been the exclusive energy conversion system (the secondary side) for nuclear power plants based on light‐water reactors (the primary side). In an effort to improve the economics of nuclear as a clean, sustainable energy source, various small modular reactor designs have been developed and some have been scheduled to deploy at the end of this decade. In this work, technoeconomic analysis is conducted for three alternative power cycles for the light‐water small modular reactor by NuScale Power, which include a regenerative reheat Rankine cycle, a transcritical ethanol cycle and a recompression supercritical CO2 cycle. The results have shown the baseline regenerative Rankine cycle is a good fit for the current small modular reactor due to its attractive cycle efficiency (31.2%), low cost and relatively simple design. Using the selected first‐order cost models, the costs for the major power cycle components including turbines, compressors, pumps, and heat exchangers, as well as the levelized cost of electricity for each cycle are estimated. The results show both the regenerative reheat Rankine cycle and transcritical ethanol cycle would provide higher cycle efficiencies (33.1% and 33.9%) and a lower levelized cost of electricity (5.14% and 4.96% reduction from the baseline, respectively), while the recompression supercritical CO2 cycle has a lower thermal efficiency (29.8%) while a higher levelized cost of electricity (21.8% increase from the baseline). As the result, the recompression supercritical CO2 cycle is not suitable as the energy conversion system for light‐water small modular reactors. HIGHLIGHTS Technoeconomic analysis of three alternative power cycles for a small modular light‐water reactor is conducted. Cost models for major components are comparatively selected for calculating levelized cost of electricity for each alternative power cycle. Supercritical CO2 cycle is not suitable for light‐water SMRs based on the technoeconomic analysis. The transcritical ethanol cycle and regenerative reheat Rankine cycle have shown higher thermal efficiency and lower levelized cost of electricity than the baseline regenerative Rankine cycle.
A unique hybrid cooling, heating and power (HCHP) concept has been recently developed as an alternative to environmental control units. It combines a small-scale organic Rankine cycle (ORC) with a vapor compression cycle. The unique drive-train design flexibly and efficiently converts engine waste heat into useful energy in the form of cooling, heating and power depending upon the energy needs. Compared to a standard military environmental control unit which puts an electric load on a diesel generator, the HCHP system uses engine exhaust heat as the primary energy input. Utilizing the exhaust heat can potentially provide 27% reduction on fuel consumption when operating in the cooling mode. When cooling is not needed, it is able to provide power and/or heating output using engine waste heat – a significant advantage over other heat activated cooling technologies. The prototype unit based on the HCHP design has been developed to demonstrate the concept. It leveraged the microchannel heat exchanger and scroll expander technologies to achieve high-performance, small-size and low-cost design in order to meet the growing distributed energy applications.
As research continues into the generation IV advanced nuclear reactors, exploration of liquid sodium as a coolant, or Sodium Fast Reactors (SFRs), coupled to supercritical CO2 (sCO2) Brayton cycles are currently underway. Liquid sodium offers unique and beneficial fluid properties that can achieve higher efficiencies and longer equipment lifespans compared to conventional water cooled reactors. Coupling sodium with sCO2 matches well with sodium’s temperature profile and is less reactive with sodium when compared to water used in standard Rankine cycles. To achieve commercial viability, methods for developing diffusion-bonded Hybrid Compact Heat Exchangers (H-CHX) to couple SFRs with sCO2 Brayton cycles are being developed. This paper includes thermal-hydraulic analysis of these fluids to quantify thermal and pressure stresses within the H-CHX for use in determining a structurally sound design. Two models for predicting the temperature profiles within a practical H-CHX channel design are presented. The first is a 1-D heat transfer model employing heat transfer correlations to provide both bulk fluid and wall temperatures. The second is a 3-D computational fluid dynamics model (CFD) providing a three-dimensional temperature profile, but at a significantly increased simulation time. By comparing the results of the two models for specific design conditions, significant temperature deviation is shown between the models at a short channel length of 10 cm. However, for longer channel lengths, although the 1-D model neglected the strong axial conduction on the sodium side, it generally shows good agreement with the CFD model. Thus, for any practical H-CHX designs, the findings reveal both simulation methods can be used to extrapolate the temperature gradient along the channel length for use in designing a H-CHX, as well as predicting the overall size and mass of the heat exchanger for component costing.
City’s electricity power grid is under heavy load during on-peak hours throughout summer cooling season. As the result, many utility companies implemented the time-of-use rate of electricity leading to high electricity cost for customers with significant cooling needs. On the other hand, the need for electricity and/or cooling decreases greatly at night, creating excess electricity capacity for further utilization. An innovative ice energy storage system is being developed leveraging a unique supercooling-based ice production process. During off-peak hours the proposed system stores the low-cost electric energy in the form of ice; during on-peak hours the system releases the stored energy to meet extensive home cooling needs. Thus, it can not only reduce energy and cost of cooling, but also increase the penetration of renewable energies (especially wind energy). In this paper, the working principles of the system is presented along with the modeling details of the overall system and several key components. The Simulink model takes in hourly temperature and peak/off peak electricity cost data to dynamically simulate the amount of energy required and associated cost for cooling an average home. Both energy consumption and cost for homes using the cooling system with ice energy storage in two US cities have been compared with those using conventional HVAC cooling system. According to the model, huge reduction in energy cost (up to 3X) can be achieved over six months of cooling season in regions with high peak electricity rates. While only moderate reduction on energy consumption is predicted for the ice energy storage system, further energy reduction potentials have been identified for future study.
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