Design and Testing of an Augmented Generator for Solar Fired Absorption Chillers

Solar Energy ◽  
2003 ◽  
Author(s):  
James Bergquam ◽  
Joseph Brezner ◽  
Andrew Jensen
Keyword(s):  
Heat Transfer ◽  
Temperature Difference ◽  
Lithium Bromide ◽  
Double Effect ◽  
Coefficient Of Performance ◽  
Solar Collectors ◽  
Absorption Chiller ◽  
Pressurized Water ◽  
Absorption Chillers ◽  
Design And Testing

This paper presents results from a project sponsored by the California Energy Commission that involved the design and testing of an augmented generator for a solar fired, double effect absorption chiller. Solar powered absorption chillers use water heated by an array of solar collectors to boil a solution of lithium bromide and water. The energy transfer process between pressurized water heated by the solar collectors and the LiBr/H2O solution is the focus of this study. A method of augmenting the heat transfer in the generator was developed, bench tested and implemented in an operating 70kW solar HVAC system. The augmented design involved installing twisted stainless steel inserts in the tubes where the LiBr/H2O solution boils and refrigerant vapor is generated. The inserts increased the overall heat transfer coefficient between the heat medium in the shell side of the generator and the LiBr/H2O solution in the tubes. A solar-fired, double effect absorption chiller requires the collector array and storage tank to operate at temperatures in excess of 150°C. At these temperatures, the heating water must be at a pressure of about 700kPa to prevent it from boiling. This combination of high temperature and high pressure requires that the collectors, storage tanks, pumps, valves and piping be designed according to pressure vessel codes. This increases the initial cost of the system and also requires significant maintenance. The main objective of this work is to develop a method of lowering the requirements for a 150°C heating medium. The ultimate goal is to operate at about 120°C while maintaining the Coefficient of Performance and cooling capacity of the absorption chiller. The results presented in this paper show that the generator with twisted inserts can operate with an average log mean temperature difference of 10°C. The average COP of the chiller is about 1.0 and the chiller provided all of the cooling required by a 743 m2 building. Without the twisted inserts, the generator operated with a temperature difference of 22 to 28°C. The inserts provide significant reduction in the operating temperature of the solar collectors and do not adversely affect the performance of the double effect absorption chiller.

Solar Fired, Compressor Assisted Absorption Chillers

Solar Energy ◽  
2002 ◽  
Author(s):  
James B. Bergquam ◽  
Joseph M. Brezner
Keyword(s):  
Heat Transfer ◽  
Waste Heat ◽  
Operating Temperature ◽  
Double Effect ◽  
Hvac Systems ◽  
Coefficient Of Performance ◽  
Heat Transfer Analysis ◽  
Absorption Chillers ◽  
Single Effect ◽  
The Cost

This paper presents the results of a thermodynamic and heat transfer analysis of solar fired, compressor assisted absorption chillers. The objectives are to determine and evaluate the feasibility of using vapor compressors to lower the operating temperature of the primary generator, simplify the maintenance and reduce the cost of solar/waste heat powered absorption HVAC systems. The nominal generator temperature in a single effect absorption chiller is 88°C and the coefficient of performance is approximately 0.8. A standard double effect chiller requires the high temperature generator to operate at about 150°C. The nominal COP of a double effect cycle is 1.2 to 1.4. Various modifications have been proposed to lower the operating temperature of the primary generator. One such modification is to add a vapor compressor to the basic cycle. Computer models that simulate the effect of vapor compressors at selected locations in single and double effect LiBr/H2O absorption chillers have been developed. Two locations were modeled for single effect chillers and three locations for double effect chillers. The best results were obtained for a double effect chiller with the compressor located between the high and low temperature generators.

Efficient Replacement of Centrifugal With Absorption Chillers Upgrading the Heat Transfer of the Cooling Tower

2001 ◽  
Author(s):  
E. D. Rogdakis ◽  
V. D. Papaefthimiou
Keyword(s):  
Flow Rate ◽  
Cooling Tower ◽  
Water Flow Rate ◽  
Cooling Water ◽  
Double Effect ◽  
Operating Conditions ◽  
Cooling Power ◽  
Absorption Chiller ◽  
Absorption Chillers ◽  
Cooling Water Flow Rate

Abstract It is a general trend today, the old centrifugal machines to be replaced by new absorption machines. The mass flow rate of the cooling water in the centrifugal machines is normally 30% less than that in the two-stage absorption chiller for the same refrigerating capacity. Some absorption chillers manufacturers have updated and improved the double-effect technology increasing the cooling water temperature difference from the typical value of 5.5°C to 7.4°C and reducing the cooling water flow rate by about 30%. Using such a modern double effect absorption unit to replace a centrifugal chiller the same cooling water circuit can be used and the total cost of the retrofit is minimized. In this case a new flow pattern of the cooling tower is developed, and in this paper the design of a new tower fill is predicted taking into account the new factors characterizing the operating conditions and the required performance of the tower. As an example, the operational curves of a modified cooling tower (1500 KW cooling power) used by a 240 RT double-effect absorption chiller are presented.

VRA Enhancement of Two Stage LiBr Chiller Performance Improves Sustainability

2007 ◽  
Author(s):  
Daniele Ludovisi ◽  
William M. Worek ◽  
Milton Meckler
Keyword(s):  
Transmission Loss ◽  
Double Effect ◽  
Elevated Pressure ◽  
Electric Utility ◽  
Efficiency Gain ◽  
Simulation Studies ◽  
Absorption Chiller ◽  
Market Pricing ◽  
Absorption Chillers ◽  
Upper Stage

Multi-effect LiBr absorption chiller must take advantage of higher temperature heat sources to achieve higher COP so as to be competitive with lower first cost comparable commercially available, efficient electric chillers under current market pricing conditions. Yet a nominal conventional double-effect absorption chiller operating at a COP of 1.0 versus a comparable efficient motor driven centrifugal chiller operating at a COP of 7.0 will consume slightly less than twice the amount of prime natural gas (NG) source energy assuming a local 28% NG fired electric utility plant’s annual average efficiency and a 10% gas distribution leakage and 10% electric transmission loss to user’s meter. However if the COP of the above referenced double-effect LiBr absorption chiller were doubled, it would consume approximately the same amount of prime NG source energy and equally sustainable from an environmental impact standpoint. Consequently research to further improve double-effect LiBr absorption chillers beyond the VRA benefits reported to date was investigated in this study. Former simulation studies of a low differential pressure-vapor recompression absorber (VRA) reported in 2001 indicated a 7% COP efficiency gain, while additional simulation studies reported in 2006 indicated a 38% COP efficiency gain with the VRA operating at elevated differential pressures at the same upper stage concentrator temperature previously considered. Double-effect LiBr absorption chillers are limited by corrosion effects, which have been shown to accelerate significantly above 160 °C. In this paper, a reverse series flow, double-effect LiBr absorption chiller employing a VRA is investigated over a wider range of upper stage concentrator and absorber cooling temperatures but operating at the same low and elevated pressure differential levels reported earlier showed significant improvement in COP efficiency, capacity performance and projected hybrid operational cost.

The Modeling of Air-Cooled Absorption Chiller Integration in CHP System

2004 ◽  
Author(s):  
Xiaohong Liao ◽  
Patricia Garland ◽  
Reinhard Radermacher
Keyword(s):  
Control Strategies ◽  
Lithium Bromide ◽  
Absorption Chiller ◽  
Absorption Chillers ◽  
Operation Conditions ◽  
Bromide Solution ◽  
Exhaust Heat ◽  
Lithium Bromide Solution ◽  
Prime Movers ◽  
Chp System

Absorption chillers are well suited for the use of exhaust heat from prime movers, and they improve the heat utilization of Cooling, Heating, and Power (CHP) systems. An air-cooled absorption chiller eliminates the cooling tower and brings considerable advantages as compared to water-cooled chillers. However, the expensive capital cost and crystallization of LiBr (Lithium Bromide) solution in certain operation conditions restrict the commercialization of air-cooled LiBr absorption machines. This paper discusses the feasibility of air-cooled absorption in CHP systems, where the control strategies based on the application can avoid the occurrence of crystallization. By using the fundamental thermodynamic principle, steady-state thermodynamic modeling and simulation have been done in Engineer Equation Solver (EES) to predict the operation of air-cooled absorption chiller integration in CHP systems with special consideration of the crystallization limits. The data of field operation acquired from a CHP system at UMD are used for validation.

Transient Modeling of a Lithium Bromide – Water Absorption Chiller

2013 ◽  
Vol 388 ◽  
pp. 83-90 ◽  
Author(s):  
Ang Li ◽  
Wai Soong Loh ◽  
Kim Choon Ng
Keyword(s):  
Water Absorption ◽  
Cooling Tower ◽  
Lithium Bromide ◽  
Cooling Water ◽  
Coefficient Of Performance ◽  
Absorption Chiller ◽  
Transient Model ◽  
Operation Conditions ◽  
Operation Process ◽  
Main Components

This article presents a thermodynamic framework for a lithium bromide – water absorption chiller, in which a transient model is developed to simulate the operation process. Local energy and mass balance within the main components like absorber, regenerator, condenser, evaporator and solution heat exchanger is respected to investigate the behavior of the chiller. Experimental correlations are used to predict heat transfer of the related working fluids. The cooling water is set to typical cooling tower conditions of tropical countries such as Singapore. The coefficient of performance (COP) is evaluated against a range of heat source temperatures from 75oC to 100oC. The results indicate the operation conditions of the chiller at its maximum COP is 95oC to 100oC.

Simulation of a Double-Effect Solar Absorption System for Traditional House in Yemen

2014 ◽  
Vol 695 ◽  
pp. 797-800 ◽  
Author(s):  
Osamah Zaid Ahmed ◽  
Farid Nasir Ani
Keyword(s):  
High Pressure ◽  
Lithium Bromide ◽  
Double Effect ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Absorption System ◽  
Alternative Source ◽  
Solar Absorption ◽  
Lithium Bromide Solution ◽  
Pressure Generator

During the last few years, the awareness of the pollution and the global warming has dramatically increased which encourage the researchers around the world to find an alternative source of energy. One of the most efficient sources of energy is the solar energy especially for cooling and heating applications. This paper, described the simulation of a double-effect solar absorption system in Yemen using water lithium bromide solution as a working fluid. The system will be applied to a typical traditional house in Yemen. The performance of the system will be analyzed based on different high pressure generator temperature for the yearly solar radiation data. At higher pressure generator temperature, the results show a higher coefficient of performance of the system. This simulation also estimate high pressure generator heat transfer required to operate the system. As a result, the size of solar collector area and the cost of such system will be calculated.

Modeling an Integral Dual Solar/Gas Fired Generator for a Water-Lithium Bromide Absorption Chiller

1999 ◽  
Author(s):  
Jiming Cao ◽  
Richard N. Christensen
Keyword(s):  
Heat Transfer ◽  
Natural Gas ◽  
Solar Energy ◽  
Current Flow ◽  
Lithium Bromide ◽  
Absorption Chiller ◽  
Transfer Resistance ◽  
Subcooled Liquid ◽  
Bromide Solution ◽  
Lithium Bromide Solution

Abstract This paper presents a design process for a dual solar/gas fired generator. A generator fired by solar energy and/or natural gas for a water-lithium bromide absorption chiller of 25 refrigeration tons (RT) was modeled. The natural gas is considered as the backup heat when the solar energy is unavailable or insufficient. The flue gas and the water-lithium bromide solution are in co-current flow, while the solar fluid and the water-lithium bromide solution are in counter-current flow. Fifty fluted tubes were installed vertically between two concentric cylindrical tubes. A solid ceramic insert was used to enhance heat transfer on the gas side that is considered as having the dominant heat transfer resistance. The burner is installed inside the smaller cylindrical tube. The solar fluid from the solar collector enters the generator through the fluted tubes while the water-lithium bromide mixture flows in the annular channel around the fluted tubes as a subcooled liquid. The generator is divided into two regions according to the heat transfer mechanism: subcooled liquid region and desorption region. In this model, a simultaneous solar and gas fired desorption process was investigated. The amount of makeup heat needed from natural gas was determined as a function of the solar fluid flow rate. Local temperature profiles were predicted by the model.

Comparison of Heat Transfer in Solar Collectors With Heat-Pipe Versus Flow-Through Absorbers

1987 ◽  
Vol 109 (4) ◽  
pp. 253-258 ◽  
Author(s):  
J. R. Hull
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Solar Collector ◽  
Hot Water ◽  
Solar Collectors ◽  
Heat Transfer Characteristics ◽  
Absorption Chiller ◽  
Transfer Characteristics ◽  
Proper Design ◽  
Flow Through

Analysis of heat transfer in solar collectors with heat-pipe absorbers is compared to that for collectors with flow-through absorbers for systems that produce hot water or other heated fluids. In these applications the heat-pipe absorber suffers a heat transfer penalty compared with the flow-through absorber, but in many cases the penalty can be minimized by proper design at the heat-pipe condenser and system manifold. When the solar collector is used to drive an absorption chiller, the heat-pipe absorber has better heat transfer characteristics than the flow-through absorber.

Performance Evaluation of a 4.5 kW (1.3 Refrigeration Tons) Air-Cooled Lithium Bromide/Water Hot-Water-Fired Absorption Unit

2007 ◽  
Author(s):  
Abdolreza Zaltash ◽  
Andrei Petrov ◽  
Randall Linkous ◽  
Edward Vineyard ◽  
David Goodnack ◽  
...  
Keyword(s):  
Heat Exchangers ◽  
Air Conditioning ◽  
Cooling Tower ◽  
Lithium Bromide ◽  
Cooling Capacity ◽  
Hot Water ◽  
Next Generation ◽  
Absorption Chiller ◽  
Flow Rates ◽  
Absorption Chillers

During the summer months, air-conditioning (cooling) is the single largest use of electricity in both residential and commercial buildings with the major impact on peak electric demand. Improved air-conditioning technology has by far the greatest potential impact on the electric industry compared to any other technology that uses electricity. Thermally activated absorption air-conditioning (absorption chillers) can provide overall peak load reduction and electric grid relief for summer peak demand. This paper describes an innovative absorption technology based on integrated rotating heat exchangers to enhance heat and mass transfer resulting in a potential reduction of size, cost, and weight of the “next generation” absorption units. This absorption chiller (RAC) is a 4.5 kW (1.3 refrigeration tons or RT) air-cooled lithium bromide (LiBr)/water unit powered by hot water generated using the solar energy and/or waste heat. Typically LiBr/water absorption chillers are water-cooled units which use a cooling tower to reject heat. Cooling towers require a large amount of space and increase start-up and maintenance costs. However, RAC is an air-cooled absorption chiller which requires no cooling tower. The purpose of this evaluation is to verify RAC performance by comparing the Coefficient of Performance (COP or ratio of cooling capacity to thermal energy input) and the cooling capacity results with those of the manufacturer. The performance of the RAC was tested at Oak Ridge National Laboratory (ORNL) in a controlled environment at various hot and chilled water flow rates, air handler flow rates, and ambient temperatures. Temperature probes, mass flow meters, rotational speed measuring device, pressure transducers, and a web camera mounted inside the unit were used to monitor the RAC via a web control-based data acquisition system using Automated Logic Controller (ALC). Results showed a COP and cooling capacity of approximately 0.58 and 3.7 kW respectively at 35°C (95°F) design condition for ambient temperature with 40°C (104°F) cooling water temperature. This is in close agreement with the manufacturer data of 0.60 for COP and 3.9 kW for cooling capacity. Future work will use these performance results to evaluate the potential benefits of rotating heat exchangers in making the “next-generation” absorption chillers more compact and cost effective without any significant degradation in the performance. Future studies will also evaluate the feasibility of using rotating heat exchangers in other applications.

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