Design analysis of a hybrid jet-pump CO2 compression system

Transport refrigeration contributes to anthropogenic global warming directly because of leakage of refrigerant, usually using high global warming potential (GWP) refrigerants, and indirectly because of the greenhouse gases emitted in driving the vehicle and the refrigeration system. A hybrid jet-pump CO2 compression system is being designed for transport refrigeration so that the GWP of the system is reduced and its performance improved. The jet-pump utilises waste heat from the exhaust gases of the engine to subcool the refrigerant and so enhance performance, reduce energy required from the engine and minimise GWP of the system. The hybrid jet-pump CO2 compression system has been simulated and its performance determined for different operating conditions and optimised using entropy generation minimisation. At an evaporator temperature of -18°C, an ambient temperature of 35°C and a generator temperature of 120°C, the COP increases from about 1.0 to 2.27 as the degree of subcooling increases from 0K to 20K. Similarly, compressor work is reduced by 24% at 20K subcooling. The optimum degree of subcooling was approximately 10K for the operating conditions described above. An improved COP is achieved whilst the size of heat exchangers required to operate the jet-pump are minimised with respect to the overall weight of the system and thus its impact on indirect emissions

A smart building material for low/zero carbon applications: heat insulation solar glass—characteristic results from laboratory andin situtests

Heat insulation solar glass (HISG) is a recently developed smart building material to minimize energy consumption of building sector. HISG might be presumed to be a conventional photovoltaic glazing product; however, it is completely unique by having some characteristic features such as superior thermal insulation, which is competitive with triple-glazed windows using argon as inert gas, acoustic and thermal comfort, self-cleaning ability owing to TiO2 nano-coating on module surface and extraordinary energy saving potential in both summer and winter. In our previous works, comprehensive experimental and numerical works have been carried out for power generation and thermal insulation performance of HISG under various climatic conditions. Within the scope of this research, optical- and lighting-related performance parameters of this smart building material are evaluated through extensive laboratory and in situ tests. Shading coefficient, visible light intensity, and UV and IR penetration are investigated via the tests conducted in real operating conditions. It is achieved from the results that the shading coefficient of HISG is only 0.136, which yields almost 80% reduction in solar heat gain compared with ordinary glazing. It is also observed from the in situ tests that HISG has a %100 UV and 99% IR blocking rate, which is of vital importance in terms of human health and thermal comfort conditions. Glaring effects are totally resolved via HISG, which is still a challenge for the buildings with conventional glazing products, especially in summer

Vacuum insulated panels for sustainable buildings: a review of research and applications

New research has identified vacuum insulation panels (VIPs) as highly efficient insulators for use in building construction. They are reported to be several times more effective than conventional materials of a similar thickness in terms of thermal conductivity. Because of their smaller space requirement, VIPs maximize the internal usage area of buildings and so reduce the cost of construction. There are however some obstacles that have hindered the application of VIPs, notably their high cost, susceptibility to perforation and the long-term water and gas effects that worsen their performance. This paper reviews the contemporary research on VIP as a state-of-the-art material for building insulation. The main components and physical principles of VIP performance are discussed. Finally, the review of VIPs available on the market and their performance is provided

An innovative psychometric solar-powered water desalination system

Important advances have been made in solar water desalination technology but their wide application is restricted by relatively high capital and running costs. Until recently, solar concentrator collectors had usually been employed to distill water in compact desalination systems. Currently, it is possible to replace these collectors by the more efficient evacuated tube collectors, which are now widely available on the market at lower prices. This paper describes the results of experimental and theoretical investigations of the operation of a novel small-scale solar water desalination technology using the psychometric humidification and dehumidification process coupled with a heat pipe evacuated tube solar collector with an aperture area of ~1.73 m2. Solar radiation during spring in the Middle East was simulated by an array of halogen floodlights. A synthetic brackish water solution was used for the tests and its total dissolved solids (TDSs) and electrical conductivity were measured. A mathematical model was developed to describe the system's operation. A computer program was written to solve the system of governing equations to perform the theoretical calculations of the humidification and dehumidification processes. The experimental and theoretical values for the total daily distillate output were found to be closely correlated. The test results demonstrate that, at temperatures of 55-60°C, the system produces ~5-6 kg/h of clean water with a high desalination efficiency. Following the experimental calibration of the mathematical model, it was demonstrated that the performance of the system could be improved to produce a considerably higher amount of fresh water

Experimental investigation of evacuated heat pipe solar collector efficiency using phase-change fluid

Performance of a microencapsulated phase-change material (PCM) as a heat-transport medium in an evacuated heat pipe solar collector was evaluated and the results compared with those using water. Collector efficiency was experimentally determined according to the method based on European Standard EN 12975–2:2006. This method proved unsuitable when using an encapsulated PCM suspension. A modified test method was proposed, which was appropriate for predicting solar collector efficiency when using a phase-change fluid. Average solar collection efficiency when using a PCM suspension was higher than that using water

A novel high capacity space efficient heat storage system for domestic applications

Energy consumption in domestic buildings is dominated by space heating 60 percent followed by hot water 14 percent in the UK. Space heating and water heating confers a disparate set of industrial challenges to the manufacture and this is a very demanding objective, which necessitates novelty. Space heating and water heating functions will become more significant as the trend towards low energy homes rises for a fully integrated system. The most common practical heat storage's are water and latent heat of fusion storage media. The new Thermochemical reaction materials regarded as most promising materials for the ability of store sufficient heat for practical domestic requirements. The volume capacities of materials play a key role for choosing storage system and this have a direct bearing on the performance of the heat storage system for domestic heating and heating water. Innovative thermal energy storage was conducted in a new concept for domestic applications at the Laboratory University of Nottingham, UK. An initial result has been investigated experimentally

A Solar-Driven Ejector Refrigeration System for Mediterranean Climate: Experience Improvement and New Results Performed

AbstractThe need for air-conditioning in the Mediterranean countries is higher and higher due to the effects of global warming. This paper deals with an investigation of a high performance, solar-driven air-conditioning system, the project entitled “Mediterranean AIRCOND”, is funded by the European Community under the „Community Activities in the Field of the specific program for RTD and demonstration on “Energy, Environment and Sustainable Development”. “AIRCOND” aims to study and investigate performances of advanced solar driven air conditioning system; the field system is composed of three sub systems: the heating loop, the ejector cycle and the cold storage-air handling units: The heating loop is composed of a solar array of 60 square meters evacuated tube solar collectors; installed at a tilt angle of 45o and facing to south, a 3000 L tank which is used as hot water storage in order to cover the required energy by the ejector cycle. The cold water produced by the ejector cycle will be then transferred in a 900L cold storage tank filled with 800L micro-encapsulated phase change material (MEPCM) for cold storage. It is designed to meet the dynamic cooling load. The ejector was tested at the School of the Built Environment in the University of Nottingham in UK and then transferred to Tunisia for field evaluation. Many previous theory studies have been fulfilled on this technology but never been performed experimentally at this level. This paper presents the research effort made and the experience gained during the implementation of the whole system: Different operation strategies were followed during more than one year to make the ejector cycle functional. The whole procedure has turned out to be very difficult; it was particularly difficult to obtain a deep vacuum and to ensure a good vacuum quality; this is a necessary working condition for the ejector cycle. Successful ejector tests were obtained during 8min, 15min and 40min, after many investigations; later experiments led to 3hours of continuous working. Results are very promising; the installation is still under tests in order to obtain a whole day permanent working of the ejector cycle and so of all the solar installation

Desiccant cooling systems: a review

Desiccant cooling systems have been considered as an efficient method of controlling moisture content in supply air. They do not use any ozone-depleting coolants and consume less energy as compared with the vapour compression systems. This communication provides an extensive review of liquid desiccant systems (LDSs). All the components of an LDS such as dehumidifier, regenerator, packing material and liquid desiccant properties along with its energy storage capabilities have been discussed in detail. In addition, hybrid of LDSs with sensible cooling technologies has been studied. Various types of mathematical models to predict the outlet parameters of the desiccant system and current issues in liquid desiccants have been reviewed in detail. Moreover, solid and other advanced desiccants have also been discussed briefly. Finally, a summary of some successful case studies and economic evaluation of desiccant systems have been given

Recent research developments in polymer heat exchangers: a review

Due to their low cost, light weight and corrosive resistant features, polymer heat exchangers have been intensively studied by researchers with the aim to replace metallic heat exchangers in a wide range of applications. This paper reviews the development of polymer heat exchangers in the last decade, including cutting edge materials characteristics, heat transfer enhancement methods of polymer materials and a wide range of polymer heat exchanger applications. Theoretical modelling and experimental testing results have been reviewed and compared with literature. A recent development, the polymer micro-hollow fibre heat exchanger, is introduced and described. It is shown that polymer materials do hold promise for use in the construction of heat exchangers in many applications, but that a considerable amount of research is still required into material properties, thermal performance and life-time behaviour