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At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Sorption heat pump and control method

A method operates an absorption heat pump system, specifically the flow of hydronic cooling fluid through the condenser during system start-ups, or when the cooling fluid temperature is low. To minimize the time for an absorption heat pump to reach full cooling or heating capacity, it is desirable for the high side pressure to increase as fast as possible, and the low side pressure to decrease as fast as possible. Since the high side pressure is a function of the temperature of the refrigerant exiting the condenser, if the condenser cooling fluid temperature is low, the corresponding high side pressure will be low, which may not permit adequate working fluid flow rates from the high pressure side of the system to the low pressure side.

Garrabrant, Michael A.↗
DOE OSTI2021

Heat Based Power Augmentation for Modular Pumped Hydro Storage in Smart Buildings Operation

In the U.S., building sector is responsible for around 40% of total energy consumption and contributes about 40% of carbon emissions since 2012. Within the past several years, various optimization models and control strategies have been studied to improve buildings energy efficiency and reduce operational expenses under the constraints of satisfying occupants’ comfort requirements. However, the majority of these studies consider building electricity demand and thermal load being satisfied by unidirectional electricity flow from the power grid or on-site renewable energy generation to electrical and thermal home appliances. Opportunities for leveraging low grade heat for electricity have largely been overlooked due to impracticality at small scale. In 2016, a modular pumped hydro storage technology was invented in Oak Ridge National Laboratory, named Ground Level Integrated Diverse Energy Storage (GLIDES). In GLIDES, employing high efficiency hydraulic machinery instead of gas compressor/turbine, liquid is pumped to compress gas inside high-pressure vessel creating head on ground-level. This unique design eliminates the geographical limitation associated with existing state of the art energy storage technologies. It is easy to be scaled for building level, community level and grid level applications. Using this novel hydro-pneumatic storage technology, opportunities for leveraging low-grade heat in building can be economical. In this research, the potential of utilizing low-grade thermal energy to augment electricity generation of GLIDES is investigated. Since GLIDES relies on gas expansion in the discharge process and the gas temperature drops during this non-isothermal process, available thermal energy, e.g. from thermal storage, Combined Cooling, Heat and Power system (CCHP), can be utilized by GLIDES to counter the cooling effect of the expansion process and elevate the gas temperature and pressure and boost the roundtrip efficiency. Several groups of comparison experiments have been conducted and the experimental results show that a maximum 12.9% cost saving could be achieved with unlimited heat source for GLIDES, and a moderate 3.8% cost improvement can be expected when operated coordinately with CCHP and thermal energy storage in a smart building.

Chen, Yang↗
DOE OSTI2022

Model Predictive Control for a Grid-interactive Efficient Thermal Storage-integrated Heat Pump System

Building heating and cooling systems can be used to overcome the mismatch between the intermittent supply of renewable power and the fluctuating demand for electricity. A novel underground thermal energy storage integrated with a dual-source heat pump has been proposed to mitigate the mismatch while meeting the thermal demand of buildings efficiently. Conventional thermostat control with heuristic rules cannot provide intelligent decisions to maximize the thermal efficiency and flexibility of the proposed system. Advanced control strategies like model predictive control (MPC) have provided a new paradigm for grid-interactive efficient building operation with the advancement of computation and sensing. This study developed an MPC for the proposed system to provide grid service for Demand Side Management and minimize the operating cost of building owners. A control-oriented dynamic model of the proposed system has been developed. Given an objective function and proper constraints, an optimization problem is formulated to determine the optimal control strategy of the system. Dynamic Programming is adopted to solve the optimization problem. A rule-based control (RBC) is also developed to achieve similar goals. Short-term simulations are conducted to compare the system performance resulting from the two controls. The simulation results indicate that the MPC performs more intelligently than the RBC in charging thermal energy storage and selecting heat pump sources by taking advantage of the predicted cooling demands of the building and the performance of the integrated system. As a result, the MPC could save energy and reduce operating costs compared with the RBC. A case study shows that, for a 3-day operation, the MPC saves 36.9% energy and reduces 38.5% operating cost compared with the RBC.

Shi, Liang↗
DOE OSTI2022

Carnot Analysis of Heat Pump Drying: Ideal Efficiency and Dry Time

Drying processes are important in appliances and in industry, and clothes drying accounts for approximately 3% of residential primary energy consumption in the US. Globally, heat pump tumble dryers (HPD) are increasing their market share against the ubiquitous electric resistance tumble dryer (ERD). In this work, efficiency and dry time limits are defined for ideal HPDs, for both closed air cycle (unvented) and open air cycle (vented). These limits are compared with the limits for ERD. The traditional Carnot efficiency limit for an ideal heat pump, operating between a hot and a cold thermal reservoir, does not apply directly to clothes dryers. One reason dryers require a novel analysis is the presence of additional degrees of freedom, since the hot and cold temperatures are floating, unfixed by ambient conditions. Furthermore, dryers can operate in a closed or open air cycle, and each requires a different analysis. In the closed (unvented) case, the hot and cold temperatures are coupled to each other; while in the open (vented) case, the hot and cold temperatures are both independent free variables. This paper provides an analysis of the fundamental efficiency limits of ERDs and HPDs, which can inform the design and performance limits of evaporative drying technology.

Gluesenkamp, Kyle↗
DOE OSTI2022

A Numerical Modelling Study on Submerged Condensers for Heat Pump Water Heaters Using Low-GWP Refrigerants

Challenges to global warming require reduction of GHG emissions, and increased use of renewable energy. Heat pumps extract energy from renewable sources and convert them to more useable forms for space conditioning, space heating and for water heating. They can be powered by renewable sources of electricity and must be engineered to use low global warming potentials (GWP) refrigerants (e.g., propane, GWP = 3) for a sustainable economy. Therefore, an electric heat pump water heaters (HPWH) using propane as refrigerant are developed in Oak Ridge National Laboratory to replace water heaters using all electric resistance and natural gas. A submerged condenser directly contacting with water is employed in the HPWH, which eliminates heat transfer barrier of the tank wall, and also prevents heat loss from the condenser tubes to the surrounding air. In present work, a numerical model is developed to model the submerged condenser. A dynamic temperature distribution on the condenser tubes from experimental data is applied to the model to enhance the accuracy of the numerical model. The model is essential to guide the design of the submerged condenser to achieve the performance required by the HPWH.

Zhang, Mingkan↗
DOE OSTI2022

Solid particulate pump

A pump for transporting particulate material that includes a first conveyor and a second conveyor together defining a passage, wherein a working surface of each of the conveyors are canted with respect to each other. The pump includes an inlet for introducing the particulate material into the passage and an outlet for expelling the particulate material from the passage, wherein the outlet is positioned out of line with the inlet.

Saunders, Timothy W.↗
DOE OSTI2023

Cold Climate Integrated Heat Pump with Energy Storage for Grid-Responsive Control

An air-source integrated heat pump (ASIHP) is a multifunctional unit, capable of space cooling, space heating, and water heating. We developed a packaged cold climate ASIHP, using a multi-stage compressor, capable of working down to -25°C, and providing 100% rated capacity down to -15°C with a heating COP > 2.2. An innovative system configuration and related controls were developed to solve charge balance in the integrated heat pump, smooth charge migration, and mode transition among multiple working modes. Extensive laboratory investigations for individual modes were performed to verify the performance. Its integrated heating capability provides speedy water heating to meet domestic hot water use and store heating energy in a phase change material ceiling/panel. The heating energy storage can be used to shift the load when the electricity price is high. Based on the performance data and a calibrated model from the laboratory testing, we conducted building energy simulations driven by a model predictive control, using EnergyPlus in one U.S. cold climate zone to investigate the grid-responsive control strategy and estimate the utility cost reduction potential.

Shen, Bo↗
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 OSTI2023

Exploration of Heat-Driven Ejector High-Temperature Heat Pumps

Heat-driven ejector heat pumps use a supersonic ejector as a thermo-compressor to replace the mechanical compressor. Supersonic ejectors have many advantages in high-temperature heat pump (HTHP) applications, including high operating temperature tolerance, no need for lubrication, low maintenance, and low cost. The coefficient of performance of ejector HTHPs could be improved by selecting binary fluids with unique thermodynamic properties. Although supersonic ejectors have been widely used in refrigeration systems, their application in spaces and water heating is limited. This study explores the theoretical potential of ejector HTHPs with a sink temperature of 100°C–130°C and a lift temperature of 10°C–30°C. Ejector HTHPs were evaluated with single-fluid ejectors (SFEs) and binary-fluid ejectors (BFEs). A comprehensive, geometry-free theoretical model of BFEs was developed to predict the theoretical maximum entrainment ratios. HFE7500 and R718 (water) were selected as working fluids for SFEs and BFEs. SFEs operating with R718 provided a higher coefficient of performance of ejector HTHPs than SFEs operating with HFE7500 and BFEs. This study preliminarily demonstrates the technical potential of ejector HTHP applications in recovering moderate-temperature heat sources

Wang, Pengtao↗
DOE OSTI2023

Modelling and Simulation of a Thermoelectric Heat Pump with Micro-Channel Heat Transfer

Thermoelectric heat pumps (TEHPs) have advantages of modularity and simple design for heating and cooling in some applications. Models of thermoelectric (TE) heat pumps are widely studied. Nevertheless, most existing modeling work focuses on the TE material or air-sourced TE modules. TEHP modeling, especially the relationship between modules and heat exchangers, has not been comprehensively conducted. This work presents a water-to-water TEHP modeling framework that combines Goldsmid’s approach for TE material performance, Gnielinski’s correlation for convective heat transfer, and thermal balance theory for heat exchange networks. This combined framework provides an accurate theoretical analysis of the water-to-water TEHP system. Subsequently, the framework was used to empirically determine TE material properties (electric resistivity, thermal conductivity, and Seebeck coefficient) that minimize modeling errors versus experimentally observed values from the literature. Finally, an additional set of experimental TEHP data was used to validate the model, all with relative absolute deviations of approximately 10% when predicting heating capacity and 10%–20% when forecasting cooling capacity at a 30 K temperature lift. For future work, people can further develop models of TEHPs with an air-based heat sink on one side and water channels on the other side.

Wan, Hanlong↗
DOE OSTI2023

Carbon Mitigation Potential of Heat Pump Integrated with Thermal Storage for Grid-Interactive Residential Buildings

Residential buildings’ heating and cooling loads are associated with significant carbon emissions and peak electricity demand. Phase change material (PCM) based thermal energy storage (TES) can be used for space heating and cooling by embedding into the heat pump equipment. Past work on TES integrated with heat pumps (HP) has demonstrated significant load shifting and economic benefits. However, the potential for TES to reduce carbon emissions has not been widely explored. This study evaluates carbon mitigation potential of an ice-based TES coupled to HP (HP-TES) based on a simple rule-based control strategy accounting for electric grid emissions data. A vapor compression HP model using Engineering Equation Solver (EES). The modeled HP-TES system for single-family residential building demonstrates decreased carbon emissions with reduced peak utility cost.

Sultan, Sara↗
DOE OSTI2023

Direct Expansion Heat Pump Using High Glide Low GWP Refrigerant

Next generation of refrigerants require drastically lower global warming potential (GWP). The refrigerant mixtures, with a GWP < 150, e.g., R-457A, etc., tend to have significant temperature glide, which prefer multi-row, cross counter flow configuration. Typical heat pump operation reverses the refrigerant flow direction, compared to the air flow, from cooling mode to heating mode. It is difficult to configurate cross counter-flow heat exchangers in heat pumps. We invented an innovative configuration, having check valve assembly to maintain uniform cross counter flow configuration in both cooling and heat modes, which optimizes the performance of a high temperature slide refrigerant mixture, i.e. R-457A. Based on it, we developed a laboratory prototype, using a 2-stage compressor, achieved a cooling SEER (cooling seasonal energy efficiency rating) of 16.0 (cooling seasonal COP of 4.69) and a heating HSPF (heating seasonal performance factor) > 9.5 (heating seasonal COP of 2.78). The unit was tested in an extensive ambient condition, heating operation from 5˚F to 62˚F (-15˚C to 16.7˚C); cooling operation from 82˚F to 95˚F (27.8˚C to 35˚C). The paper will introduce the system configuration, heat exchanger dimensions and laboratory investigations.

Shen, Bo↗
DOE OSTI2023

Passively pumped, polycrystalline ceramic high and ultra-high vacuum chambers

A sealed, passively pumped, polycrystalline ceramic vacuum chamber and method for fabricating the chamber are disclosed. The body of the vacuum chamber is made from a polycrystalline ceramic, for example, alumina. The vacuum chamber includes one or more windows made from a transparent ceramic, for example, sapphire, to accommodate optical access, while remaining amorphous-glass free to minimize or eliminate helium permeation. The vacuum chamber components are joined via laser welding or furnace brazing and the completed chamber is bakeable at temperatures up to 400° C. The vacuum chamber can operate at high or ultra-high vacuum pressures for an extended period through the use of one or more getter-based pumps. The vacuum chamber may include one or more atomic sources depending upon the application.

Walker, Charles A.↗
DOE OSTI2023

Hybrid renewable pumped storage hydropower energy storage system

A pumped storage hydroelectric system may include a reservoir system including an upper reservoir system and a lower reservoir system. At least one of the upper reservoir system and the lower reservoir system may include a modular reservoir arrangement. A penstock may be coupled with the upper reservoir system. A pump/turbine may be coupled with the penstock and with the lower reservoir system. The pump/turbine may be configured to receive water flowing from the upper reservoir system to the lower reservoir system for generating electrical power, and to pump water from the lower reservoir system to the upper reservoir system for storing energy.

Medina, Hector Eduardo↗
DOE OSTI2024

Geomembranes for Pumped Storage Hydro

Energy storage is fundamental to ensuring the reliability, stability, and resilience of the grid, essential for meeting the energy demands now and in the future. Pumped storage stands out as a proven energy storage solution. There are 43 pumped-storage plants operating in the USA today, and they offer unparalleled scalability, rapid-response capabilities, and long-term reliability at a competitive cost. With a history of successful operation spanning decades, and approximately 60 sites proposed at various stages of permitting and development, this technology is a critical component for the US energy sector. However, its development involves some complex engineering and regulatory challenges.

13 HYDRO ENERGY↗
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 OSTI2024

Influence of Thermal Energy Storage Integration Strategy on System Performance and Refrigerant Charge for Small-Scale R290 Heat Pumps

As small-scale (2.5 – 5 kW) heat pumps across the US increase straining the grid during peak hours, integrated heat pump thermal energy storage (HP-TES) systems can assist by load shifting. However, challenges arise when assembling these systems, as direct refrigerant-phase change material (PCM) heat exchangers (HXs) increase refrigerant charge, and indirect secondary loops degrade HP-TES performance. In this work, direct and indirect HP-TES configurations were sized using commercially available HXs to compare the available load shift time and performance at similar refrigerant charges. For the same indirect 5 kW HP-TES refrigerant charge, directly HP-TES can operate up to 72 and 145 minutes in cooling and heating modes, respectively, using small diameter tubes. Using Modelica, COP increases for direct and indirect HP-TES were 22% and 9%, respectively, given the parasitic losses in the indirect HP-TES. Overall, small-scale direct HP-TES can have comparable refrigerant charges with indirect HP-TES maximizing COP improvements.

25 ENERGY STORAGE↗
DOE OSTI2025

Field Test and Thermal Performance Comparison of a Novel Underground Thermal Battery with a Single U-tube Borehole Heat Exchanger for Geothermal Heat Pump Application

Geothermal Heat Pumps (GHP) are a proven technology to electrify and decarbonize space heating and cooling by utilizing the thermally consistent underground as a heat sink or source. However, the high drilling costs of conventional borehole heat exchangers (BHEs) associated with GHP systems and subsurface heterogeneity have been two major challenges to their widespread adoption. In this paper, we present results from a field-scale pilot of an Underground Thermal Battery (UTB) as a potential alternative to a conventional BHE. To benchmark the UTB performance, a side-by-side field test was conducted to compare the UTB with a conventional BHE installed at the same site. The UTB was installed in a 7.01-meter-deep borehole having a diameter of 0.9 meter, whereas the conventional BHE (with single U-tube loop) is in a borehole with 36.6-meter depth and 0.15-meter diameter. Both are integrated into a GHP system to meet the thermal energy demands of office space at the Illinois Energy Farm on the University of Illinois Urbana-Champaign campus. The system’s performance is compared in terms of heat transfer rate, outlet temperatures, and contributions to the overall thermal power of the GHP system under varying thermal demands and in different heat pump operation modes: heating only, cooling only, and hybrid (alternative, diurnal heating and cooling). Results to date indicate that the UTB delivers a more consistent response under during a time period of varying thermal demands. Its operational performance is better during short-term with higher thermal demands, while the conventional BHE performs better under continuous, long-term thermal demands.

Pokhrel, Sajjan [ORNL] (ORCID:0000000228523749)↗