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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Theoretical Analysis of a Single-Stage Gas-Fired Ejector Heat Pump Water Heater

Ejector driven systems have the ability to operate at high efficiencies, utilizing recycled thermal energy as a power source. For a typical ejector heat pump system, the increase of the condenser temperature reduces the coefficient of performance (COP). In addition, if the condenser temperature is higher than the critical temperature, the ejector may not function. In this situation, the condenser temperature must be reduced, and an additional heater will be utilized to heat the production water from the condenser temperature to the desired temperature. In this investigation, a single-stage gas-fired ejector heat pump (EHP) is investigated and thermodynamically modeled in order to optimize the system COP for the purpose of heating water by utilizing the thermal energy from the ambient air. The effects of the high-temperature evaporator (HTE) and low-temperature evaporator (LTE) temperatures on the ejector critical back pressure and the EHP system performance are examined for a HTE temperature range of 120–180 °C and LTE temperatures of 15.5, 17.5, and 19.5 °C. Results show that an optimized COP of the EHP system exists which depends on HTE and LTE temperatures, primary nozzle throat diameters. In addition, it is found that the EHP COP is independent of the ejector COP. From this investigation a maximum EHP COP of 1.31 is able to be achieved for a HTE temperature of 160 °C and a LTE temperature of 19.5 °C with a total heat capacity of 15.98 kW.

Spitzenberger, Jeremy↗
DOE OSTI2026

Case Study of Integrating High-Temperature Heat Pump with LiBr-H2O Absorption Chiller for Data Center Liquid Cooling

Data centers (DCs) are physical infrastructures that support artificial intelligence workloads. The rapid growth of artificial intelligence is putting substantial pressure on the US power grid. Most of electricity consumed by IT equipment, accounting for 50%-60% of total DC power, ultimately becomes waste heat. This heat is dissipated by DC’s cooling facilities, accounting for an additional 30%-40% of total DC power. Recovering and repurposing this waste heat offers a significant opportunity to enhance energy efficiency and reduce operating costs of DCs. One potential pathway is converting heat to cold using thermal-driven absorption chillers, therefore, reducing the power consumption in DC cooling facilities. Existing studies mainly demonstrate the technical and economic feasibility of repurposing DC’s waste heat for cooling applications but provide limited technical details on how to integrate the thermal-driven absorption chillers with DC cooling systems. In addition, the low-grade waste heat available from DCs must be upgraded to higher temperatures suitable for absorption chillers. This paper presents a case study on integrating high-temperature heat pumps with a LiBr-H2O absorption chiller to use DC waste heat for cooling. A thermodynamic model of single-effect, LiBr-H2O absorption chiller and an empirical model of high-temperature heat pumps were built. The case study considers ASHRAE W17 liquid-cooled DC, with facility service water supplied at 17.0℃ and returned at 25.3℃. The thermal behaviors of absorption chiller components were predicted for the generation temperature ranging from 75.0℃ to 115.0℃. Based on the available waste heat in the integrated system, two waste heat recovery strategies were evaluated: a facility service water-based strategy and cooling water-based strategy. Results indicated that the cooling water-based strategy achieves higher Coefficient of Performance (COPs) than the facility service water-based strategy. The relatively low cooling COPs of single-effect LiBr-H2O absorption chillers could be offset by high heating COP of high temperature heat pumps. The maximum cooling COP of absorption chiller and the overall COP of integrated systems occur at lower generation temperatures, but these conditions also yield lower cooling capacities. In practice, system operation should balance the trade-off between the COP and cooling capacity

Wang, Pengtao [ORNL] (ORCID:0000000214713429)↗
DOE OSTI2025

Heating performance of an air source heat pump with a portable thermoelectric subcooler

This study investigates the heating performance of an integrated air-source heat pump (ASHP) with a thermoelectric subcooler (TES) module, revealing significant performance enhancements, particularly in colder temperatures. Results show that adding the portable TES boosts the ASHP's heating capacity, making it feasible for residential applications. The coefficient of performance (COP) for the TE system, which is influenced by condensing temperatures and ambient conditions, ranges from 1.51 to 2.07. If condensing temperatures are consistently maintained above 35 °C, a TE COP of approximately 2.07 is achievable, supporting system downsizing and reducing supplemental heating. When coupled with an oversized indoor coil, the TES-ASHP system delivers comparable heating to a baseline unit while achieving a 10 % higher COP. Capacity increases by 8.7 %–24 % with TES in colder conditions, though COP declines by 9 %–18 %, diminishing as temperatures drop. Compared to systems with supplemental heating, this setup achieves a COP 10 %–17 % higher. Future work will involve extended field testing in various climates, exploration of advanced materials for thermal efficiency, and assessment of alternative refrigerants to improve performance and sustainability. This integrated ASHP-TES system holds promise for increased efficiency and reduced environmental impact in cold climates.

Air source heat pump↗
DOE OSTI2025

Experimental study of a tri-functional propane hydronic heat pump

This study investigates the performance of a propane hydronic heat pump system for space cooling, heating, and water heating applications, focusing on various operational conditions, with a total refrigerant charge below 1200 g. Cooling performance was evaluated at different outdoor temperatures, compressor stages (capacity levels), and water flow rates. The results showed that the coefficient of performance (COP) for cooling was higher at lower outdoor temperatures, with peak values exceeding 5.0 under low-stage operation and lower water flow rate. The cooling capacity increased with higher flow rates and compressor stages, reaching 12 kW. Space heating performance, evaluated at ambient temperatures ranging from −8.3 °C to 16.7 °C, revealed a decrease in COP with lower temperatures. However, high-stage operation maintained higher heating capacities even at low temperatures. The system demonstrated high Heating Seasonal Performance Factors (HSPF), exceeding 10.0. For water heating, the COP decreased with lower ambient temperatures and higher supply water temperatures. The system efficiently heated an 189-L water tank, outperforming conventional water heaters, with process COPs exceeding 4.0 under cooling-season conditions. Despite some efficiency loss due to defrosting at low temperatures, the propane heat pump consistently delivered strong performance. Seasonal energy efficiency ratios (SEER) and seasonal heating COP values indicated significant overall efficiency. The study concludes that propane is a promising refrigerant for heat pump systems, with future research needed to future reduce total system charge and optimize system performance through advanced controls and heat exchanger designs.

Hu, Yifeng [ORNL] (ORCID:0000000242875185)↗
DOE OSTI2020

Design screening and analysis of gas-fired ammonia-based chemisorption heat pumps for space heating in cold climate

Thermally-driven ammonia-based chemisorption heat pumps (CSHP) have the potential to provide high-efficiency space heating in cold climates. Using the reversible chemical bond between sorbent salt and ammonia, CSHP thermochemically pumps heat from the cold ambient to the end-uses of space heating at 50 °C. The heating coefficient of performance (COP) of a CSHP largely depends on the selection of the sorbent salts, cycle configuration, and the system operation. This study uses a thermodynamic model to investigate the performance of six CSHP system configurations, including four single-effect and two double-effect cycles. The feasibility and performance of 121 available NH 3 /salt reactions are studied for each configuration. The thermal COP of the cycles and the primary energy COP of the gas-fired CSHP systems are evaluated assuming 50 °C supply temperature for building space heating and the optimal system designs are identified. The highest thermal COP for single-effect and double-effect cycles under -25 °C ambient temperatures are predicted to be 1.22 and 1.57, respectively. The corresponding primary energy COPs are above 1.0 and 1.15, which are 30% higher than condensing furnaces and is sustained into the same cold temperatures.

42 ENGINEERING↗
DOE OSTI2021

Conditional Point Sampling: A Monte Carlo Method for Radiation Transport in Stochastic Media.

Current methods for stochastic media transport are either computationally expensive or, by nature, approximate. Moreover, none of the well-developed, benchmarked approximate methods can compute the variance caused by the stochastic mixing, a quantity especially important to safety calculations. Therefore, we derive and apply a new conditional probability function (CPF) for use in the recently developed stochastic media transport algorithm Conditional Point Sampling (CoPS), which 1) leverages the full intra-particle memory of CoPS to yield errorless computation of stochastic media outputs in 1D, binary, Markovian-mixed media, and 2) leverages the full inter-particle memory of CoPS and the recently developed Embedded Variance Deconvolution method to yield computation of the variance in transport outputs caused by stochastic material mixing. Numerical results demonstrate errorless stochastic media transport as compared to reference benchmark solutions with the new CPF for this class of stochastic mixing as well as the ability to compute the variance caused by the stochastic mixing via CoPS. Using previously derived, non-errorless CPFs, CoPS is further found to be more accurate than the atomic mix approximation, Chord Length Sampling (CLS), and most of memory-enhanced versions of CLS surveyed. In addition, we study the compounding behavior of CPF error as a function of cohort size (where a cohort is a group of histories that share intra-particle memory) and recommend that small cohorts be used when computing the variance in transport outputs caused by stochastic mixing.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2023

Thermodynamic analysis of a two-stage binary-fluid ejector heat pump water heater

Ejector heat pump water heaters (EHPWHs) could significantly increase the thermal efficiency of domestic water heating and reduce greenhouse gas emissions. This study addresses two major technical barriers to using EHPWHs in domestic water heating—low heating cycle coefficient of performance (COP) and low condensation temperatures—using binary fluid pairs as a working fluid in a two-stage ejector system. A comprehensive, geometry-free model of binary-fluid ejectors was built and validated to predict the entrainment ratios of binary-fluid ejectors. A thermodynamic model of a two-stage binary-fluid ejector EHPWH was built to predict the heating cycle COP of EHPWHs. The performance of the EHPWH was theoretically evaluated using HFE7000 and Novec649 as primary fluids and R600 and R1234ze(Z) as secondary fluids. HFE7000/R600 gave the highest heating cycle COP (i.e., 1.356) in producing domestic hot water at 60.0 °C. An optimum evaporation temperature of the primary fluid was identified for the maximum effective entrainment ratio and effective pressure lift ratio of two-stage ejectors. Here, the effective entrainment ratio of the two-stage ejector dominated the heating cycle COP of the EHPWH. Primary fluids with lower latent heats of evaporation and/or secondary fluids with higher latent heats of evaporation yielded higher heating cycle COPs of EHPWHs.

42 ENGINEERING↗
DOE OSTI2022

Off-design performance of an organic Rankine-vapor compression cooling cycle using R1234ze(E)

In this study, a 264 kW th organic Rankine-vapor compression cycle (ORVC) was experimentally tested over a range of conditions to quantify the individual impact of off-design external conditions. The ORVC was designed to recover waste heat at 91 °C, reject heat to a liquid condenser stream at 30 °C, and produce chilled water at 7 °C. Here, the condenser heat rejection temperature was varied from 16.6 °C to 32.6 °C, the chilled water delivery temperature was varied between 2.1 °C and 13.1 °C, and the heat input temperature was varied from 91 °C to 120 °C. As the condenser heat rejection temperature decreased, the coefficient of performance (COP) of the ORVC improved from 0.558 at 30 °C to 0.682 at 16.6 °C, despite a reduction in compressor isentropic efficiency. Although the chilled water temperature variation had almost no impact on the organic Rankine cycle performance, the compressor efficiency decreased when the delivery temperature was below 7 °C. At the highest chilled water temperature, 13.1 °C, the COP of the ORVC was 0.643. Compressor stall was noted when the condenser heat rejection temperature was greater than 32.6 °C and the chilled water delivery temperature was below 2.1 °C. Increasing the driving heat source inlet temperature improved the COP of the ORVC and the thermal efficiency of the organic Rankine power cycle, while decreasing the efficiency of the compressor and the COP of vapor compression cycle. In addition, the integrated part load value of the system was determined through experimentation to be 0.682, which provides a realistic estimate of real-world performance.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2025

Risk-Aware Reinforcement Learning Framework for User-Centric O-RAN

The evolution of Open Radio Access Networks (O-RAN) presents an opportunity to enhance network performance by enabling dynamic orchestration of configuration and optimization parameters (COPs) through online learning methods. However, leveraging this potential requires overcoming the limitations of traditional cell-centric RAN architectures, which lack the necessary flexibility. On the other hand, despite their recent popularity, the practical deployment of online learning frameworks, such as Deep Reinforcement Learning (DRL)-based COP optimization solutions, remains limited due to their risk of deteriorating network performance during the exploration phase. In this article, we propose and analyze a novel risk-aware DRL framework for user-centric RAN (UC-RAN), which offers both the architectural flexibility and COP optimization to exploit this flexibility. We investigate and identify UC-RAN COPs that can be optimized via a soft actor-critic algorithm implementable as an O-RAN application (rApp) to jointly maximize latency satisfaction, reliability satisfaction, area spectral efficiency, and energy efficiency. We use the offline learning on UC-RAN to reliably accelerate DRL training, thus minimizing the risk of DRL deteriorating cellular network performance. Results show that our proposed solution approaches near-optimal performance in just a few hundred iterations with a decrease in risk score by a factor of ten.

6G and beyond↗
DOE OSTI2020

Technology Development and Field Monitoring in nZEB - US Country report IEA HPT Annex 49 Task 3

The International Energy Agency (IEA) Heat Pumping Technologies (HPT) Annex 49, “Design and Integration of Heat Pumps for Nearly Zero Energy Buildings,” deals with the application of heat pumps (HPs) as a core component of the HVAC system for nearly or net-zero energy buildings. This report covers the Task 3 activities of the US team. Three institutions are involved on the US team and have worked on the following projects. 1) Oak Ridge National Laboratory (ORNL) summarized development activities since the conclusion of IEA HPT Annex 40 for several integrated HP (IHP) systems - electric ground-source IHP and air-source IHP versions and engine-driven AS-IHP version. 2) The University of Maryland partnered with ORNL and Blue Bear Management to develop a personal cooling device called RoCo that can provide personalized conditioned air to occupants in inadequately or unconditioned environments. With RoCo, building facility management can elevate the HVAC thermostat settings without compromising occupants’ thermal comfort. Researchers have found that a 4°F increase in thermostat settings can save 12–30% energy savings. Therefore, RoCo is a promising technology that can help reduce building energy consumption and facilitate achievement of net-zero energy building performance. 3) The National Institute of Standards and Technology (NIST) is working on a field study effort on the NIST Net-Zero Energy Residential Test Facility. Two air-source split-system HPs were installed in a residential, net-zero energy home that was constructed as a laboratory on the NIST campus in Gaithersburg, Maryland. The first HP was a two-stage, 7 kW (2 ton), 15.8 seasonal energy efficiency ratio (SEER), 9.05 heating seasonal performance factor (HSPF) conventionally ducted system; the second HP was a variable-speed, 10.6 kW (3 ton), 14 SEER, 8.35 HSPF, high-velocity ducted system. These two systems operated side by side, using separate supply ducts and a common return duct, on a weekly alternating schedule to condition the home that was operated with very consistent simulated thermal loads. The team wanted to determine whether the high-velocity system could provide comparable energy-use efficiency to the conventional system. The results of this study showed that it did meet the required loads and had slightly greater efficiency; the average cooling coefficient of performance (COP) was (0.40 ± 0.11) higher, and the average heating COP was statistically equal. A new firmware was provided at the end of the heating season that greatly improved the performance of the high-velocity system; its average heating COP went from (1.8 ± 0.9) to (2.5 ± 1.1) at a 95% confidence level. The new firmware heating COP averaged (1.05 ± 0.23) higher than the old firmware over the same outdoor temperatures. The defrost performance is very different for these two systems, yet they consumed equivalent energy per HDD. The conventional system uses a timed-initiate, temperature-terminate algorithm with auxiliary electric resistive heating, whereas the high-velocity system uses calculated evaporator parameters with a hot-gas bypass before a full reverse-cycle defrost with no supplementary resistive heat.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Searching for eco-friendly working fluids for an ejector-driven heat pump for domestic water heating

This study searches for refrigerants with low global warming potential (GWP) and zero ozone depletion potential (ODP) for an ejector heat pump water heater (EHPWH). Several criteria are set, and R1336mzz(Z), R601a, R1233zd(E), R1224yd(Z), R1234ze(Z), and R600a are shortlisted. A theoretical model is built to study the performance of EHPWH and the corresponding ejector design at different operating conditions. For the same ejector design, a refrigerant with a high specific heat ratio produces a high entrainment ratio and heating COP. This is because the expansion wave angle in the ejector is small for refrigerants with a high specific heat ratio, allowing more mass flow rate to be entrained. A higher entrainment ratio does not necessarily correlate to a high COP because the saturation curve of the tested refrigerants is not the same. Results show that the heating COP of R601a is the highest, but it is extremely flammable. R1224yd(Z) and R1234ze(Z) are the most candidates for EHPWH when the trade-off between the COP and safety criteria is considered. The results presented in this work could help building an EHPWH using eco-friendly refrigerants.

Mohammed, Ramy H.↗
DOE OSTI2023

Experimental study of steam-driven ejector heat pump

Ejector-driven systems have been shown to be promising for heating applications. Most of the research works have been devoted to cooling purposes, while little attention has been focused on heating applications. An experimental steam ejector heat pump system (EHP) was designed and constructed to assess its applicability to water heating applications. The effect of the primary nozzle exit position (NXP) on the performance of the steam ejector system was investigated for primary nozzle throat diameter of 1.5 mm and 2.0 mm. The ejector system was run for high-temperature evaporator (HTE) temperatures of 120, 130, and 140 °C and low-temperature evaporator (LTE) temperatures of 10, 15, and 20 °C. The target of this investigation was to attain the highest condensing temperature to be able to use the proposed system for water heating purposes. The ejector heat pump coefficient of performance (EHP COP) was used to determine the system efficiency. Larger LTE temperatures were found to result in higher EHP COPs and condensing temperatures. A maximum EHP COP of 2.02 was attained for a HTE and LTE temperatures of 120 °C and 20 °C, respectively; however only resulted in a condensing temperature of 22.88 °C. Higher HTE temperatures were found to result in higher condensing temperatures but at the cost of EHP COP.

Spitzenberger, Jeremy↗
DOE OSTI2024

Experimental Investigation on Heating Performance of a Cold Climate Thermoelectric-Assisted Heat Pump

To accelerate the electrification of air source heat pumps (ASHPs) in cold climates across the United States, various initiatives have been launched to enhance the effectiveness of ASHPs. One avenue of research involves incorporating thermoelectric (TE) technology into vapor compression refrigeration cycles. This study aims to assess the heating performance of a cold climate ASHP by employing TE modules as a liquid line subcooler. The tested system is a nominal 4.5-ton split heat pump utilizing R410A, equipped with a scroll compressor and an accumulator. An electronic expansion valve was employed for both cooling and heating modes. Two configurations of TE sub-coolers, one utilizing 2 TE bundles and the other 4 TE bundles, were integrated into the liquid line of the tested system. The heating performance of these configurations was evaluated. The results revealed that activating the TE subcooler led to a notable increase in total heat capacity, reaching 1318 W at -15.0 °C and 1164 W at -19.0 °C. The corresponding TE coefficients of performance (COPs) were 1.76 and 1.63, respectively. The activation of the TE sub-cooler resulted in a slight reduction in the overall system COP, with a decrease ranging from -2.6% to -4.2% for these two temperatures. The system COPs were measured at 2.10 and 1.86 for -15.0 °C and -19.0 °C, respectively. This prototype demonstrated a significant augmentation in heating capacity with a minimal sacrifice in COP.

Hu, Yifeng↗
DOE OSTI2025

Development and evaluation of a multi-functional heat pump with embedded thermal storage

We developed and tested a novel multi-functional packaged vertical heat pump designed for multi-family buildings, capable of providing space cooling, space heating, water heating, and energy storage integration. The system employs a 3-speed scroll compressor and supports energy-efficient cooling and heating across different ambient conditions, while utilizing both indoor and outdoor air sources for water heating. Key performance metrics include an integrated energy efficiency ratio of 18.0 for cooling, a heating seasonal performance factor of 10.0, and a coefficient of performance (COP) of 2.1 for heating in cold climates down to −15 ˚C. Additionally, the system delivers an annual water heating COP greater than 4.0, with outstanding performance in combined space cooling and water heating modes, achieving a total COP of 8.8 by recovering condenser waste heat. The heat pump also demonstrated thermal energy storage capabilities, integrating with phase change material systems to store heating and cooling energy. Furthermore, this versatile system offers a promising solution for improving energy efficiency and sustainability in multi-family buildings, providing high-performance heating, cooling, and water heating across a range of climates.

COP↗
DOE OSTI2022

Final Scientific/Technical Report-FREE-piston Zero Emissions Refrigerator (FREEZER)

The FREE-piston Zero Emissions Refrigerator (FREEZER™) is a natural refrigerant Stirling-cycle cooler developed by AMSC in partnership with Heatcraft, targeted as a replacement refrigeration system for walk-in coolers or freezers found commonly in restaurants, convenience stores, supermarkets, etc. The FREEZER™, combined with a closed-loop CO2 heat-transfer system, had the goal to provides an efficient (Target COP = 1.4), zero ODP (Ozone Depletion Potential) and near zero GWP (Global Warming Potential) refrigeration solution with no synthetic, flammable, or toxic refrigerants. Other near zero GWP refrigeration systems do not exist at the scale and performance level of FREEZER. ARPA-E Continuation Funding enabled the design and fabrication of one Advanced Development Unit (ADU) cooler and two Field Test Unit (FTU) coolers, and a new revised Field Test Unit (new FTU). Heatcraft was to extensively test the various coolers at their facilities, which closely simulate real-world conditions. The original plan was to install and operate FREEZER FTUs alongside a traditional cooling solution at one or more customer locations to obtain data on direct performance comparisons with existing commercial refrigeration systems. Success in this FREEZER refinement and field-test project will establish the basis for a new class of environmentally friendly refrigeration systems that will revolutionize the industry. The hardware developed under the program is shown below in Figure 1. Five Stirling-cycle machines were built within the program, with a sixth cooler still under construction. The original DU and the ADU coolers met the performance target with a coefficient of performance (COP) of 1.2. The FTU was underperforming during the initial tuning of the free-piston Stirling cycle dynamics when there was a catastrophic failure of the fasteners on pressure boundary. This caused a pause to the program while the failure mechanism was investigated. The root cause was an inadequate flange design that allowed an excessive cyclic loading on the fasteners, leading to a fatigue failure. It was determined that existing FTU design could not be reasonably salvaged in a safe manner, and that fact, combined with the lower-than-expected performance of the new experimental heat exchanger modules lead to the design of the “new FTU” with a more conventional shell-and-tube heat exchanger design which should get close to the design target COP of 1.4, but have a higher overall machine cost. The program ran out of time before the fabrication of the new FTU was completed, but AMSC is still working on the cooler, with the majority of the parts fabricated, and hopes to have the unit under test sometime in early 2022, after which it will be shipped to Heatcraft for additional testing.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2025

Structures of a synthetic antibody selected against and bound to the C‐terminal domain of Clostridium perfringens enterotoxin

Abstract Clostridium perfringensenterotoxin (CpE) causes cytotoxic gastrointestinal disease in mammalian epithelium by binding membrane protein receptors called claudins. Claudins direct the formation of cell/cell tight junctions through oligomerization and govern the transport of molecules between individual cells. CpE binds claudins through its C‐terminal domain (cCpE) and induces cytotoxicity through its N‐terminal domain. The non‐toxic cCpE is a useful tool to study claudins, tight junctions, and for translational applications, such as increasing the permeability of restrictive tissues like the blood–brain barrier or selective targeting of claudin overexpressing cancers. Conversely, there are no specialized molecular tools to study CpE or cCpE, or to modulate or inhibit their functions. We previously reported the development of synthetic antigen‐binding fragments (sFabs) that bind cCpE, and low‐resolution structures of them bound to claudin/cCpE complexes. Here, we determine high‐resolution structures of sFab COP‐2 bound to cCpE using X‐ray crystallography and cryogenic electron microscopy. The structures and biophysical findings provide the mechanism of COP‐2 binding to cCpE and the molecular determinants driving their interactions. These insights can advance the design of new antibody‐based tools from our COP‐2 scaffold to study or alter cCpE function and give rise to a “Trojan horse” strategy that exploits cCpE's tight junction barrier disrupting function to selectively deliver conjugated therapeutics through normally impermeable tissues.

Biochemistry & Molecular Biology↗
DOE OSTI2021

Experimental validation of an organic rankine-vapor compression cooling cycle using low GWP refrigerant R1234ze(E)

There is a significant global opportunity to capture and utilize low grade waste heat to reduce fossil fuel consumption, greenhouse gas emissions, and improve energy efficiency across a wide range of industries. In this work, an advanced type of thermally activated cooling system, an organic Rankine-vapor compression cycle (ORVC) with novel heat integration strategies, was designed and tested at a relevant scale for industrial waste heat recovery (300 kW th cooling capacity). The ORVC linked an organic Rankine power cycle and a vapor compression cooling cycle using a turbine and compressor that shared a single shaft. The ORVC test facility absorbed waste heat from a liquid stream at 91 °C to simulate engine coolant in diesel generator sets, rejected heat to a glycol stream at 30 °C, and generated chilled water at 7 °C. A cooling capacity of 264 kW ± 3.5 kW was experimentally validated with a COP of 0.56 ± 0.01 during steady-state operation at the design temperatures. The thermal efficiency, accounting for pump work, of the Rankine cycle was 7.7% ± 0.22% and the COP of the vapor compression cycle was 5.25 ± 0.09. The centrifugal turbo-compressor operated at 31.5 kRPM ± 0.3 kRPM, with a turbine and compressor isentropic efficiencies of 76.7% ± 0.90% and 84.8% ± 0.54%, respectively, with near-perfect power transmission between these components. The pressure drop in the piping and heat exchangers were significantly larger than expected which had a detrimental impact on the performance of the ORVC. In addition, the condenser on the cooling cycle could not deliver the subcooling as specified from the design point modeling. Furthermore, the results from the sensitivity analysis showed that the higher condenser glycol outlet temperature had the largest impact on performance, which is consistent with other analytical models in the literature. When the ORVC simulations were updated with experimental values for isentropic efficiencies of the turbomachinery, the thermal COP was 0.66 which represents an estimate of the predicted performance if test facility limitations are overcome.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Thermal performance of an absorption-assisted two-stage ejector air-to-water heat pump

In this work, a gas-fired air-to-water ejector heat pump (EHP) for domestic hot water production is proposed and analyzed thermodynamically. The COP of the EHP is improved by using binary fluids (HFE7500 and water), and the high backpressure in the primary ejector (first-stage) is actively controlled by either a second-stage ejector and/or a LiBr-H 2 O absorption subsystem. A thermodynamic model is established for analysis and performance evaluation. A case study shows the backpressure of the first-stage ejector is reduced by 53.5%, and the backpressure control using the second-stage ejector increases the system COP by 21.0% compared with that using LiBr-H 2 O absorption. Parametric studies are conducted to investigate the roles of the first-stage ejector, the second-stage ejector, and the LiBr-H 2 O absorption subsystem. The first-stage ejector plays a dominant role in the EHP system performance. The EHP’s heating COP can reach 2.0 with an entrainment ratio of 0.12 in the first-stage ejector. EHP performance can be improved with a high entrainment ratio and a low-temperature primary working fluid in the first-stage and second-stage ejectors, a low condensation temperature in the first-stage ejector, and a high generating temperature and a low concentration of the LiBr-H 2 O solution.

30 DIRECT ENERGY CONVERSION↗