Conventional Vapor Compression System Research Articles

Feasibility of air cycle systems for low-temperature refrigeration applications with heat recovery

In this paper the viability of an air cycle refrigeration system (Joule cycle) is investigated for a moderately low-temperature cooling system with heat recovery. The goal is to determine the best possible cycle configuration of heat exchangers and turbomachinery components for this particular application, and then to determine whether it can compete with a conventional vapour compression system. Simple models were developed for each cycle configuration, and the results were compared with each other on a consistent basis. The sensitivity of the system to heat exchanger effectiveness and expander and compressor efficiency was determined, and contours were plotted.

A Study of the Performance of a Hybrid Liquid Desiccant Cooling System Using Lithium Chloride

This paper presents field test of a hybrid solar liquid desiccant cooling system conducted at a test house at the University of Florida’s Energy Research and Education Park. These tests consisted of operating the air conditioning system at the test house in two configurations: the conventional vapor compression system and the hybrid desiccant system. Experiments were conducted to study the influence of the air mass flow rate, temperature of the inlet air, temperature of the desiccant, and desiccant mass flow rate on the performance of both system configurations. Based on the field test results, it was found that the hybrid desiccant system improves the air conditioning performance in the field test house by decreasing the outlet humidity and temperature of the air.

Experimental results for a hydraulic refrigeration system using n-butane

The hydraulic refrigeration system (HRS) is a vapor-compression system that accomplishes the compression and condensation of the refrigerant in a unique manner, by entraining refrigerant vapor in a down-flowing stream of water and utilizing the pressure head of the water to compress and condense the refrigerant. A multi-stage HRS was designed, fabricated, and tested using n-butane as the refrigerant. In general, both the refrigeration rate and the coefficient of performance ( COP) increased with a corresponding decrease in the compression fluid temperature of the third and final stage. The refrigeration rate and COP were also found to increase with a corresponding increase in evaporator temperature. The predictions of an enhanced model incorporating two-phase hydraulic losses show excellent agreement with the experimental data with a maximum error of ±20%. The results of the experimental investigation indicate that the HRS offers an attractive and feasible alternative to conventional vapor-compression systems, especially in applications where direct-contact heat exchange in the evaporator is desirable.

Experimental studies on the dehumidifier and regenerator of a liquid desiccant cooling system

Liquid desiccant cooling systems are being explored as an alternative to the conventional vapor compression systems. The dehumidifier and the regenerator form the heart of these systems. A falling film tubular absorber and a falling film plate regenerator have been studied experimentally. The experimental results have been compared with the predictions from theoretical models. Two wetness factors to account for the improper wetting of exchanger surfaces have been defined and estimated. After taking these factors into account, the theoretical models predict the experimental data within ±30%.

Is solar air conditioning feasible?

This paper examines the feasibility of desiccant cooling in UK climates, using gas-solar hybrid technology for regeneration. Desiccant cooling is a heat driven system. It has potential to reduce energy costs and environmental pollution, when compared with conventional vapour compression systems. The regeneration of the desiccant can be provided by any low temperature warm air or water source including waste heat, CHP, gas or solar. Heat recovery is also available. Gaia Research worked with Napier University to develop computer codes for the simulation of solar energy collection and hot water delivery to drive the desiccant cooling system, based on real meteorological data. A solar desiccant computer model was developed with the University of Leeds which analysed the energy consumption and costs associated with desiccant cooling using meteorological data for an inner London site in 1994. The study demonstrates that coupling the desiccant system to solar collectors produces significant savings in both running cost and CO2 emissions. The existing models of solar contribution and desiccant cooling will be refined. This will enable an assessment to be made of the UK opportunities for energy conservation and CO2 emission reduction in relation to latitude, internal design conditions, and real loads. Cet article traite des possibilités de réalisation de systèmes de refroidissement par déshydratation dans les conditions climatiques propres au Royaume-Uni, en faisant appel à la technologie hybride gaz-énergie solaire pour la régéneration. Comparés aux solutions classiques de compression de vapeur, de tels systèmes de refroidissement, basés sur la puissance thermique, permettent de réduire les coûts énergétiques et de diminuer la pollution environnementale. La régénération du déshydratant peut être assurée par toute source d'eau ou d'air chauffée faiblement: chaleur perdue, CHP, gaz ou énergie solaire. Le Groupe Gaia Research et l'Université Napier ont travaillé ensemble au calcul de codes informatiques pour simuler le captage de l'energie solaire ou la fourniture d'eau chaude pour alimenter le système de refroidissement par déshydratation en fonction de données météorologique brutes. Avec l'Université de Leeds, ils ont mis au point un modèle de déshydratant solaire qui analyse la consommation énergétique et les coûts du refroidissement par deshydratation; ce modele utilise des donnees meteorologiques recueillies a Londres en 1994. Cette etude demontre que l'association d'un systeme deshydratant a des capteurs solaires degage des economies non negligeables au niveau des couts d'exploitation et reduit sensiblement les emissions de CO2. Les modèles existants, basés sur la contribution de l'energie solaire et du refroidissement par déshydratation, seront améliores et serviront à évaluer les possibilités pour le Royaume-Uni de faire des économies d'énergie et de réduire les émissions de CO2 en fonction de la latitude, des paramètres de conception et des charges réelles.

Performance enhancement of a two-stage vapour compression heat pump with solution circuits by eliminating the rectifier

Performances of four versions of a two-stage vapour compression heat pump with solution circuits (VCHSC) are compared. The VCHSC represents a cascade system that requires only one compressor. Performance curves for the best cycle, the modified version with a bleed line and a desuperheater are obtained and studied in detail. The four cycles are compared for the same total UA value (product of overall heat transfer coefficient and area) including all heat exchangers while pumping heat from an average desorber temperature of −2.5°C to an average absorber temperature of 105°C. Simulation results show that the cycle with a bleed line and a desuperheater has 40 to 50% higher cooling COPs and 30 to 40% higher cooling loads as compared to the cycle with a rectifier. Both the rectifier and the bleed line cycles show an increase of up 20% in the cooling COP and capacity by adding a desuperheater. Performance curves are obtained by simulating the best cycle at various weak solution concentrations in the low temperature loop and different solution pump flow rates. The parameters studied are the cooling COP, the solution heat exchanger effectiveness, the pressure ratio, the solution temperature glides in the absorbers and desorbers, the low temperature desorber load and the distribution of the UA value. Cooling COPs up to 1.05 and pressure as low as 7.05 are obtained for the modified VCHSC. The cooling COPs are twice as much and the pressure ratios are two thirds less of what would be found in a conventional single-stage vapour compression system. Changing the weak solution concentration in the low temperature loop from 40 to 80 wt% ammonia increased the cooling load by four times. The results indicate that the two-stage VCHSC with a bleed line and a desuperheater can work at temperatures above 100°C and achieve temperature lifts of more than 100 K with well known and environmentally safe refrigerants.

Analysis and Comparison of Active Solar Desiccant and Absorption Cooling Systems: Part II—Annual Simulation Results

A comparative analysis has been performed to compare the cooling and dehumidification performance of future ventilation mode desiccant systems, proposed advanced absorption systems, and conventional vapor compression systems. A common framework has been developed for direct comparison of these different cooling technologies; this method is described in a companion paper. This paper presents the application of this method to annual simulations of cooling system performance in five cities.

Analysis and Comparison of Active Solar Desiccant and Absorption Cooling Systems: Part I—Model Description

A comparative analysis has been performed to compare the cooling and dehumidification performance of future ventilation-mode desiccant systems, proposed advanced absorption systems, and conventional vapor compression systems. A common framework has been developed for direct comparison of these different cooling technologies; this method is described in this paper. A companion paper presents the application of this method to specific cooling systems in five cities.

Open cycle absorption cooling—A review

This article presents a comprehensive review on open cycle absorption cooling. Basic physical processes, detailed literature survey and current state-of-the-art on open cycle absorption cooling are described. The authors have studied the feasibility of an open cycle absorption cooling system both theoretically and experimentally. Various investigations on heat and mass transfer processes in solar regenerators and thermodynamic modelling and thermal design aspects of open cycle absorption solar cooling systems are summarized. A comparative study of open cycle absorption cooling with closed cycle absorption cooling has also been presented, and it is found that the former is better in performance, less expensive and simpler in technology. A closed cycle vapour absorption cooling system is known to be a casual alternative of conventional vapour compression systems. However, a more promising open cycle absorption cooling system (OCACS) is proved to be a better alternative for solar cooling/air conditioning applications by various researchers from the U.S.S.R., U.S.A., Australia, India and Japan. This review also highlights the importance of open cycle absorption solar cooling system possible applications, and some innovative concepts relevant to open cycle absorption cooling are also mentioned. A detailed list of references on open cycle absorption cooling is given.

Full-Core Test Method for Experimental Determination of Convective Boiling Heat Transfer Coefficients in Tubes of Crossflow Compact Evaporators

An experimental methodology is proposed in which localized convective boiling heat transfer coefficients inside the tubes of compact evaporators are determined by testing of full evaporator cores. The proposed technique makes use of a special test system having two main flow circuits. One of these flow loops is a conventional vapor compression system, which provides a steady, low-quality, two-phase flow of refrigerant to the tube side of the evaporator. The second primary flow loop provides a steady flow of the vapor of a second working fluid, which condenses on the finned side of the evaporator. Measured data from this system are analyzed using an iterative scheme. Trends in the variation of the refrigerant-side heat transfer coefficient determined by this method throughout a typical evaporator core are described, and the differences and similarities relative to previously published results for single round tubes are discussed.

Desiccant integrated hybrid vapor-compression cooling: Performance sensitivity to outdoor conditions

The performance of a desiccant integrated, hybrid, vapor-compression cooling system is modeled numerically. The concept of hybrid cooling investigated in this paper utilizes the waste heat rejected from a vapor-compression cycle to directly activate a solid desiccant dehumidification cycle. The hybrid system consists of four major components; a compressor, an evaporator and two desiccant integrated condensers/dehumidifiers. The performance sensitivity of a first generation prototype hybrid, vapor-compression cooling system to variable outdoor conditions is reported and compared to the performance of conventional vapor-compression systems.

Conventional and solar cooling systems for Kuwait: An economic analysis

The economics of five cooling systems — two conventional vapour compression systems and three solar (absorption and photovoltaic) cooling systems — are discussed and compared for different occupancies and capacities on the basis of respective life-cycle costs per unit of refrigeration output. The absorption system and the water- and air-cooled photovoltaic systems are assumed to receive equal amounts of conventional electricity. The study concludes that occupancy is a major factor in determining costs per ton-hour and cost per ton of installed capacity for all the cooling systems. At present, no solar cooling system can be considered a viable substitute for the conventional systems. Among all the solar systems considered, the absorption system is the most promising and the cost difference between that system and the conventional systems declines steadily as occupancy increases.

Absorption cycle heat pumps

This paper considers the features of absorption cycles which are relevant to the development of a practical and viable design for applications which include waste heat recovery. These include the operating principles, performance assessment and practical difficulties. The absorption cycle is compared with the more conventional vapour compression systems and the market for both types is discussed.