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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Numerical and experimental analysis of precooled desiccant system

This paper presents a numerical and experimental study of four novel, desiccant air-conditioning systems based on pre-cooling of the ambient air. The purpose of the study is to: 1) establish which configuration is most profitable for the future studies through numerical and experimental methods; 2) verify the concept of precooled system and confirm that it is working in experimental conditions (for this purpose two prototypes of evaporative cooling units were developed and compared for different operation arrangements with desiccant wheel); 3) Analyze practical aspects of the systems, which includes water consumption analysis, economic analysis and establishing operational modes during a cooling season in temperate climate conditions (the proposed solution has a significant advantage during operation in a temperate climate, since it can utilize its first evaporative cooler the only source of cooling energy when the humidity of outdoor air allows to to meet the latent cooling load). Four arrangements of the system with different dew point evaporative air cooler prototypes were selected and developed for comparative analysis. The system was simulated as a whole, also, each component was individually tested on measurement station. develop the optimal arrangement of the system through numerical and experimental analysis. Four different performance indicators were considered: thermal COP (Coefficient Of Performance), the ERR (Energy Efficiency Ratio), coefficient a describing the potential in compensating indoor cooling loads, water consumption ratio. Also costs of the systems were compared through economic analysis. It was established that arrangement which is characterized by best-averaged performance in terms of all considered factors is a unit combined with two different types of evaporative coolers (marked as System B)- this is caused by the favorable arrangement of two units, where one is better suited to the pre-cooler role, while the other is better suited as the post-cooler.

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NASA NTRS1975

Self-regenerating desiccant system

Compact system uses inherent diurnal cyclic airflow in system and energy of sun as drying heat. System requires no power for operation, has no moving parts to wear out, requires no blowers or manifolds, and is relatively inexpensive to produce.

Anthony, K. G.↗
DOE OSTI2022

Review of liquid desiccant air dehumidification systems coupled with heat pump: System configurations, component design, and performance

Vapor Compression Systems (VCS) are the most common air conditioning technology. VCS cool the air to its dew point temperature (overcooling) to remove water vapor in the air through condensation and then reheats the air back to the comfort temperature for direct use. The VCS process is inefficient due to overcooling and reheating. Liquid Desiccant Dehumidification (LDD) is a potentially energy-efficient air conditioning. LDD removes water vapor in the process air using liquid desiccant’s high-water affinity. It hybrids with sensible cooling to control temperature and humidity separately. The LD in the LDD becomes weak after dehumidification. The LDD needs additional heating to regenerate the weak Liquid Desiccant (LD) to a high concentration for dehumidification. Earlier versions of the LDD systems use highly concentrated liquid desiccant (large water removal capability) to dehumidify the air by only dealing with latent load. It leads to highly elevated temperatures above 60 °C of heat sources (combustion or electric resistance-based heating) for regeneration. The energy needed for the elevated temperature heat resource significantly reduces or demolishes the benefit of LDD systems. In the recent two decades, researchers have investigated a new configured LDD system that couples an LDD with a heat pump at both dehumidification and regeneration sides for better efficiency. The heat pump provides cooling (from the evaporator) for both dehumidification and sensible cooling and simultaneous heating from the condenser for regeneration. The highly integrated system (HP-LDD) with improved efficiency enables the LDD to operate at lower concentrations and temperatures in dehumidification and regeneration. This paper depicts the working principle behind HP-LDD and its heating and cooling requirements. It reviews the comparison between the HP-LDD systems and the conventional LDD systems regarding system configurations, component design, energy efficiency, and dehumidification performance characteristics. The main findings from the review include the preferred use of packed bed over membrane-based dehumidifiers, the use of internally cooled dehumidifiers enabled by the HP cooling capacity, the high dispersion of HP operation conditions, and the dependence of dehumidification performance on various dehumidifiers. Finally, an outlook for future research on HP-LDD strategies is presented based on the reviewed works and their limitations.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Review of Dew Point Evaporative Cooling Technology for Air Conditioning Applications

Indirect evaporative cooling has the potential to significantly improve the natural environment. It follows from a significant reduction in electricity consumption in the hot period, and hence lower operating costs for cooling systems. This paper presents the current state of knowledge and research directions on dew point indirect evaporative cooling. It was found that researchers focus on the development of dew point indirect evaporative coolers (DPIEC) by improving its design, geometry, water distribution, and new porous materials implementation. To evaluate the performance of new types of DPIEC, different methods are used by the scientists. Finally, optimized devices are studied in terms of their performance in different systems, like hybrid and desiccant systems, considering different climate conditions. Potential directions of development of evaporative technologies were indicated, such as increasing the coefficient of performance of solid desiccant evaporative cooling systems, developing novel geometry, and efficient water distribution, including development of porous materials.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Liquid desiccant based dehumidification and cooling system

A liquid desiccant system including a high desorber, a low desorber, and an absorber that are in fluid communication with a working solution, where the high desorber provides rejected water vapor from the working fluid for condensation in a condenser of the low desorber that provides heat for rejection of additional water from the working solution in the low desorber effectively multiplying the heat provided for desorption. The low desorber provided the concentrated working solution to the absorber where water from ambient air is condensed into the concentrated working solution to provide a dilute working solution within a working solution conduit of the absorber that is thermally coupled to an internal cooler of the absorber. In some embodiments, the working solution can be an aqueous solution of at least one ionic liquid.

Moghaddam, Saeed↗
DOE OSTI2021

Liquid desiccant based dehumidification and cooling system

A liquid desiccant system including a high desorber, a low desorber, and an absorber that are in fluid communication with a working solution, where the high desorber provides rejected water vapor from the working fluid for condensation in a condenser of the low desorber that provides heat for rejection of additional water from the working solution in the low desorber effectively multiplying the heat provided for desorption. The low desorber provided the concentrated working solution to the absorber where water from ambient air is condensed into the concentrated working solution to provide a dilute working solution within a working solution conduit of the absorber that is thermally coupled to an internal cooler of the absorber. In some embodiments, the working solution can be an aqueous solution of at least one ionic liquid.

Moghaddam, Saeed↗
DOE OSTI2025

Dehumidification energy storage using a stratified liquid desiccant tank

Liquid desiccants can play an important role in reducing dehumidification energy requirements in the built environment. Because they are in a liquid state, the desiccant can be easily stored and then used to dehumidify buildings during peak energy consumption periods. By maintaining stratification between concentrated and diluted desiccant solutions, a single tank can be used to store liquid desiccant for energy storage purposes. Using a stratified tank instead of separate tanks for dilute and concentrated solutions will reduce storage costs and increase energy storage densities for liquid desiccant systems. This paper describes the experimental validation and one-dimensional modeling of a stratified liquid desiccant tank. The stratified tank prototype developed achieved 80 % of the theoretical energy storage density based on an imposed desiccant concentration change. Here, the stratified tank model was able to reasonably reproduce the experimental results. Using this model, the impact of varying operational conditions on the energy density of the stratified liquid desiccant energy storage was evaluated. Depending on the operating conditions, stratified liquid desiccant energy storage using aqueous LiCl up to 40 wt% can achieve energy storage densities in excess of 330 kWh/m 3 .

25 ENERGY STORAGE↗
DOE OSTI2022

Design of a Proportional-Control-Based Advanced Control Strategy for Independent Temperature and Humidity Control of a Pre-Cooled Desiccant Air Cooling System

In this study, the control of a desiccant-wheel-based evaporative cooling system with a double-layer dew-point cooler system is emphasized. There are two dew-point evaporative coolers in the system and the air taken inside is subjected to pre- and post-cooling processes. The dehumidification process of the air taken in is carried out by the desiccant wheel after the pre-cooling process. A proportional-based control strategy has been developed to adjust the temperature and relative humidity of the room quickly and robustly with different operation modes for actuators to bring comfort with less energy consumption. In addition, an automatic Stop/Run mode has been added to the control strategy to save extra energy. With the developed control strategy, enabling the actuators to switch between the operation modes, more energy savings are achieved compared to both traditional ON/OFF and proportional controls. The accuracy and applicability of the developed control strategy were analyzed and it was observed that the room comfort reached the desired levels successfully under all disruptive effects. The control inputs and the energies consumed by all the actuators were investigated and it was determined that 21.19% more energy savings are provided by adding the automatic Stop/Run feature. With the multi-mode control strategy, a total of 40.90% less energy consumption is achieved compared to the classical ON/OFF control technique. Thus, it is seen that the controller developed for the desiccant-wheel-based evaporative cooler is a viable method to provide fast and robust comfort conditions with less energy.

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DOE OSTI2021

An experimental study on dehumidification and regeneration performance of a new nonporous membrane-based heat and mass exchanger using an ionic liquid desiccant

As a promising alternative to inefficient vapor-compression-based air conditioning, liquid desiccant dehumidification uses a liquid desiccant in contact with the humid air absorbing the moisture. However, it has not gained much market share due to the issues related to the carryover, corrosion, fouling, and crystallization of liquid desiccant. The research has developed a new membrane-based exchanger, which uses a non-corrosive ionic liquid desiccant and nonporous tubular membranes to address these issues. As the second generation of the prototype, the new exchanger was tested at various operating conditions. According to the experimental data, when it is used in the dehumidification loop, the new membrane-based exchanger achieves a specific vapor transportation rate of 778.6 g/(h–m 2 ) and an average water vapor flux of 0.316 g/(h-m 2 -Pa), which is a significant improvement compared with the previous designs using nonporous membranes. It also achieved a comparable or even better dehumidification performance compared with the dehumidifiers that use porous membrane and conventional liquid desiccants. However, the regeneration performance is not as good as its dehumidification. It is mainly caused by the high operating temperature required in the regeneration loop. The experimental data and findings provide first-hand experimental data and enhance the understanding of advanced membrane-based ionic liquid desiccant systems.

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DOE OSTI2021

Low-Cost Electrochemical Compressor (ECC) Utilizing Green Refrigerants for HVAC Applications [Slides]

HVAC systems account for approximately 14 Quads or primary energy annually, or nearly 30% of all energy used in the U.S. commercial and residential buildings. Electrochemical compression (ECC) is a transformative solid-state technology and ECC based HVAC systems could result in 40% less energy use. The goal of the project was to develop the most efficient, noiseless, and most environmentally friendly cooling system based on integrating 2 (two) technologies: a) electrochemical compressors (ECC) to replace mechanical compressors for use in building heating, ventilation, and air conditioning (HVAC) applications and b) Ionic Liquid Desiccant Systems. The overall objective was to develop and build a scalable ILD/ECC-based air conditioning system operating with a COP of 4.5, with a price premium of $70 installed per kBTU/hr.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Performance and Characterization of Membrane Liquid Desiccant Air Conditioning Systems

This document is intended to describe the work objectives and tasks for several projects between the National Renewable Energy Laboratory (NREL) and 7AC Technologies, with indirect support from 3M. The projects all revolve around the performance and characterization of membrane liquid desiccant air conditioning systems. Projects are listed in order of preference to 7AC's technical and business goals.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Modeling and Experiments on a Dedicated Outdoor Air System Using Liquid Desiccant Heat and Mass Exchangers

Liquid desiccants can provide efficient dehumidification but have yet to see widespread adoption. Most systems studied previously use natural gas-combustion to heat and regenerate the desiccant, and a central chiller plant or cooling tower for removing the heat of absorption. Here we present modeling and experimental results on a novel packaged air conditioner integrating liquid-desiccant heat and mass exchangers with a vapor compression cycle. The packaged system does not need cold or hot water from a central plant or cooling tower and is suitable for rooftop unit air conditioners. The system uses the evaporator to cool the liquid desiccant that is absorbing moisture from the air, and the condenser to heat the liquid desiccant to regenerate it. Efficiency is improved by reducing the load on the evaporator for a given supply-air dewpoint. This paper presents the measured dehumidification efficiency for a 10- ton packaged air conditioner, focusing on dehumidifying ventilation air. The paper also presents a numerical model to predict the outlet conditions and dehumidification efficiency, which we compare with the measured data.

air conditioning↗
DOE OSTI2022

Independent temperature and humidity control of a precooled desiccant air cooling system with proportional and fuzzy logic + proportional based controllers

Providing room comfort quickly by using less energy in cooling systems is important both in terms of efficiency and environment. In this study, independent temperature/humidity control strategies are designed for precooled desiccant based evaporative cooling system to provide room comfort quickly with less energy. Therefore, the speed controls of the system's actuators become important depending on the room, cooler and atmosphere conditions. The mathematical models are obtained to determine the relation between voltages of actuators and the variations in the room's temperature and humidity. After that, new control strategies are developed based on Proportional and Fuzzy+Proportional techniques and the control performance is increased by adding extra modes to the operation of the actuators. The effects of the control techniques on the cooling performance and energy consumption were investigated for different cases. It has been observed that the room temperature and relative humidity reach the set values in a short time for both techniques and are successfully kept at these values under the disturbances. By using Fuzzy+Proportional controller, the robustness of the cooler increases due to more precisely adjustment of controller's parameter depending the system conditions. Finally, both control strategies provide more than 20% energy savings compared to the traditional ON/OFF control.

42 ENGINEERING↗
NASA NTRS1973

Desiccant humidity control system

A regenerable sorbent system was investigated for controlling the humidity and carbon dioxide concentration of the space shuttle cabin atmosphere. The sorbents considered for water and carbon dioxide removal were silica gel and molecular sieves. Bed optimization and preliminary system design are discussed along with system optimization studies and weight penalites.

Amazeen, J.↗
NASA NTRS1975

Desiccant humidity control system

A water vapor and carbon dioxide sorbent material (designated HS-C) was developed for potential application to the space shuttle and tested at full scale. Capacities of two percent for carbon dioxide and four percent for water vapor were achieved using space shuttle cabin adsorption conditions and a space vacuum for desorption. Performance testing shows that water vapor can be controlled by varying the air process flow, while maintaining the ability to remove carbon dioxide. A 2000 hour life test was successfully completed, as were tests for sensitivity to cleaning solvent vapors, vibration resistance, and flammability. A system design for the space shuttle shows a 200 pound weight advantage over competitive systems and an even larger advantage for longer missions.

Lunde, P. J.↗
DOE OSTI2024

DEVAP-EDDR-TES (Simulation framework for a desiccant assisted air conditioning system with heat pump regeneration and energy storage) [SWR-24-66]

This software is a simulation framework that models a load flexible air conditioner system. The system consists of an evaporatively cooled liquid desiccant air conditioner (eLD-AC) subsystem, an electrically driven desiccant regenerator (EDDR) subsystem, and a stratified liquid desiccant storage (SLDS) subsystem. The software can be used to 1) predict the steady-state performance of the system given user-specified convergence criteria; 2) predict the dynamic performance of the entire system over a typical drive cycle operation subjected to user-specified building thermal loads and desired electrical load profile; 3) evaluate the synergy of all three subsystems operating altogether and improve the energy storage control strategy.

Huang, Ransisi↗
DOE OSTI2022

Effect of geometry and operational parameters on the dehumidification performance of a desiccant coated heat exchanger

Solid desiccant dehumidification systems are an alternative to vapor-compression-based air dehumidification systems. They use solid desiccant materials to adsorb air moisture in space cooling. DCHE can integrate the cooling component in the heat exchanger to achieve higher dehumidification capacity. Comprehensive numeric modeling would be necessary to assist in the design and operation of the DCHE under development to achieve maximum performance. Here, we provide the details of a heat and mass transfer model developed for this purpose. The model aims to cover a gap in existing models by independently modeling heat transfer on the solid desiccant, fin, and tube. The model results were compared with an experimental reference for validation. The air outlet humidity and temperature results for dehumidification and regeneration showed a deviation lower than 15% from the experiment. The validated model was used to perform a parametric study for a series of design and operating conditions. The parametric analysis showed that an increase of 25% in desiccant layer thickness and thermal contact resistance between solid elements reduces moisture removal by 9.1% and 1%, respectively. These results indicate the need to independently model the desiccant layer.

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