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.

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.

Thermal Performance Model for Spacesuit Waste Heat Rejection Using Water Membrane Evaporators

2010 ◽  
Vol 2 (3) ◽  
Author(s):  
Y. Janeborvorn ◽  
T. P. Filburn ◽  
C. C. Yavuzturk ◽  
E. K. Ungar
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Waste Heat ◽  
Water Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Performance Model ◽  
Heat Transfer Analysis ◽  
Water Evaporation ◽  
Heat Rejection

Hydrophobic, micropore membrane evaporators are studied for use in waste heat rejection in new generation spacesuits developed by the U.S. National Aeronautics and Space Administration (NASA). The waste heat rejection is accomplished via evaporation of liquid water through membrane pores, whereby the hydrophobic membrane allows only water vapor to pass through and retains the liquid phase inside the membrane water channel, allowing the waste heat rejection through the proposed spacesuit water membrane evaporator (SWME) system to be significantly less sensitive to contamination while improving the overall contaminant and system control. Although SWME uses the same heat transport loop as used in current NASA sublimator systems, thus eliminating the need for a separate feedwater system, it permits the system configuration to be simpler and more compact while also eliminating corrosion problems and reducing system freeze-up potential. An improved thermal performance model based on membrane segment energy balances is presented, which is a spacesuit water membrane evaporator for a single circular annulus water channel bounded by two annular vapor channels. The model allows for the investigation of the local heat transfer characteristics along the annulus including temperature gradients in the membrane wall and the water channel using a steady-state approach. The model also accounts for the effects of thermal and hydraulic entry lengths, far field radiation, and energy carried away by the mass of water evaporation. The local heat transfer analysis enables the straightforward calculation of the overall magnitude of heat transfer from the SWME. A model validation is presented via the sum of the squares error analyses between the model predictions and the experimental results.

scholarly journals Waste Heat Recovery from Servers Using an Air to Water Heat Pump

2021 ◽  
Vol 24 (1) ◽  
Author(s):  
Seweryn Lipiński ◽  
Michał Duda ◽  
Dominik Górski
Keyword(s):  
Heat Pump ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Hot Water ◽  
Coefficient Of Performance ◽  
Domestic Hot Water ◽  
Cooling Unit ◽  
Pump Inlet ◽  
The Cost

The analysis of advisability and profitability of using an air to water heat pump for the purpose of waste heat recovery from servers being used as cryptocurrency mining rigs, was performed. To carry out such an analysis, the cooling unit of the computing server was connected to the heat pump, and the entire system was adequately equipped with devices measuring parameters of the process. Performed experiments proves that the heat pump coefficient of performance (COP) reaches satisfactory values (i.e., an average of 4.21), what is the result of stable and high-temperature source of heat at the pump inlet (i.e., in the range of 29.9-34.1). Economic analysis shows a significant reduction in the cost of heating domestic hot water (by nearly 59-61%). The main conclusion which can be drawn from the paper, is that in a case of having a waste heat source in a form of a server or similar, it is advisable to consider the purchase of air-to-water heat pump for the purpose of domestic hot water heating.

Oscillating Heat Pipes for Waste Heat Recovery in HVAC Systems

2015 ◽  
Author(s):  
Govinda Mahajan ◽  
Heejin Cho ◽  
Scott M. Thompson ◽  
Harrison Rupp ◽  
Kevin Muse
Keyword(s):  
Heat Transfer ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Heat Pipes ◽  
Hvac Systems ◽  
Operating Conditions ◽  
Working Fluid ◽  
Low Grade ◽  
Potential Cost

Oscillating heat pipes (OHPs) were experimentally assessed as a passive-type heat transfer device for air-to-air heat exchange in a typical Heating Ventilation & Air conditioning system (HVAC) with adjacent air streams at different temperatures. The objective is to utilize, otherwise wasted thermal energy to pre-heat or pre-cool air in order to reduce the payload on HVAC systems, thus reducing energy consumption. OHPs can achieve effective thermal conductivities on-the-order of 10,000 W/m-K via no internal wicking structure and hence can perform aforementioned heat transfer task while providing an aerodynamic form factor. A unique working fluid with limited research inside OHPs, but with properties desirable for low grade heat fluxes, i.e. n-pentane with 70 % fill ratio, was chosen as the working fluid to achieve maximum heat transfer. Aerodynamic performance, in terms of pressure drop, was evaluated and juxtaposed with heat transfer gain/loss. The OHP thermal performance and total heat transfer for hot-environment HVAC operation was benchmarked with an empty/evacuated OHP with same overall dimensions. Results indicate that the current, atypically-long OHP is fully-capable of operating in the air-to-air convection mode for waste heat recovery for typical HVAC operating conditions. Since the OHP is passive, cost effective, and relatively aerodynamic (no fins were used), the potential cost savings for its integration into HVAC systems can be significant.

Energy, Exergy and Economic Analysis of Absorption Chiller Systems: A Case Study for a Wood Pencil Factory

2021 ◽  
pp. 1469-1477
Keyword(s):  
Waste Heat ◽  
Double Effect ◽  
Wood Chips ◽  
Exergetic Efficiency ◽  
Industrial Facility ◽  
Absorption Chiller ◽  
Temperature Range ◽  
Single Effect ◽  
Economic Analyses

This study examines the use of absorption chiller systems in a designated industrial facility having waste heat by conducting energy, exergy and economic analyses. The absorption chiller systems namely single-effect, double-effect series, double-effect parallel and double-effect reverse parallel were analysed to determine the best alternative for the wood pencil factory. The results indicated that the COP of the single-effect absorption chiller systems is changed from 0.758 to 0.763 when the temperature of the generator was increased from 89 ºC to 125 ºC. However, the exergetic performance of the single-effect absorption chiller system decreased by 40% in the same generator temperature range. On the other hand, COP of all double-effect absorption chiller systems increased about 8 % when the generator temperature was changed from 116 ºC to 155 ºC while the exergetic performance of all double absorption chiller systems decreased by around 14% for the same generator temperature range. The COP and exergetic efficiency values of the double-effect parallel system were found to be higher than other absorption systems at all generator temperature values. Overall, this study recommends that the double-effect parallel absorption chiller systems can be preferred for the factories having waste heat source wood chips. The average payback period of the system was also found to be 1.4 years. Furthermore, this study shows that double-effect parallel absorption chiller systems can be proposed for the facilities having wood chips waste sources instead of double-effect reverse parallel absorption chiller systems since they are easy to operate and have lower maintenance costs.

scholarly journals Energetic and Exergetic Investigations of Hybrid Configurations in an Absorption Refrigeration Chiller by Aspen Plus

Processes ◽  
2019 ◽  
Vol 7 (9) ◽  
pp. 609 ◽  
Author(s):  
Xiao Zhang ◽  
Liang Cai ◽  
Tao Chen
Keyword(s):  
Heat Transfer ◽  
Waste Heat ◽  
Aspen Plus ◽  
Coefficient Of Performance ◽  
Heat Sources ◽  
Exergy Destruction ◽  
Absorption Refrigeration ◽  
Exergetic Efficiency ◽  
Complex Heat Transfer ◽  
Steady State Simulation

In the present study, a steady-state simulation model was built and validated by Aspen Plus to assess the performance of an absorption refrigeration chiller according to the open literature. Given the complex heat transfer happening in the absorbers and the generator, several assumptions were proposed to simplify the model, for which a new parameter ε l i q was introduced to describe the ratio of possible heat that could be recovered from the absorption and heat-transferring process in the solution cooling absorber. The energetic and the exergetic investigations of a basic cycle and hybrid cycles were conducted, in which the following parameters were analyzed: coefficient of performance (COP), exergetic efficiency, exergy destruction, and irreversibility. According to the results, the basic cycle exhibited major irreversibility in the absorbers and the generator. Subsequently, two proposed novel configurations were adopted to enhance its performance; the first (configuration 1) involved a compressor between a solution heat exchanger and a solution cooling absorber, and the second (configuration 2) involved a compressor between a rectifier and a condenser. The peak COP and the overall exergetic efficiency (η) of configuration 1 were found to be better, increasing by 15% and 5.5%, respectively, and those of configuration 2 were also upregulated by 5% and 4%, respectively. The rise in intermediate compressor ratio not only reduced the driving generator temperature of both configurations but also expanded the operating range of the system under configuration 1, thus proving their feasibility in waste heat sources and the superiority of configuration 1. Detailed information about the optimal state for hybrid cycles is also presented.

scholarly journals Thermodynamic Performance of a Double-Effect Absorption Refrigeration Cycle Based on a Ternary Working Pair: Lithium Bromide + Ionic Liquids + Water

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4200 ◽  
Author(s):  
Yiqun Li ◽  
Na Li ◽  
Chunhuan Luo ◽  
Qingquan Su
Keyword(s):  
Least Squares Method ◽  
Operating Temperature ◽  
Double Effect ◽  
Coefficient Of Performance ◽  
Specific Enthalpy ◽  
Refrigeration Cycle ◽  
Absorption Refrigeration ◽  
Temperature Range ◽  
Thermodynamic Performance ◽  
Operating Temperature Range

For an absorption cycle, a ternary working pair LiBr–[BMIM]Cl(2.5:1)/H2O was proposed as a new working pair to replace LiBr/H2O. The thermodynamic properties including specific heat capacity, specific enthalpy, density, and viscosity were systematically measured and fitted by the least-squares method. The thermodynamic performance of a double-effect absorption refrigeration cycle based on LiBr–[BMIM]Cl(2.5:1)/H2O was investigated under different refrigeration temperatures from 5 °C to 12 °C. Results showed that the ternary working pair LiBr–[BMIM]Cl(2.5:1)/H2O had advantages in the operating temperature range and corrosivity. Compared with LiBr/H2O, the operating temperature range was 20 °C larger, and the corrosion rates of carbon steel and copper were reduced by more than 50% at 453.15 K. However, the double-effect absorption refrigeration cycle with LiBr–[BMIM]Cl(2.5:1)/H2O achieved a coefficient of performance (COPc) from 1.09 to 1.46 and an exergetic coefficient of performance (ECOPc) from 0.244 to 0.238, which were smaller than those based on LiBr/H2O due to the higher generation temperature and larger flow ratio.

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