Air-conditioning in residential buildings through absorption systems powered by solar collectors

Over the past years, the scientific community has been exploring alternative solutions to the fossil fuels used for indoor air-conditioning. The solution here suggested is formed by absorption machines powered by solar panels used to air-condition small residential buildings. The study examined a small residential building and evaluated energy savings, reduction of CO2 and the return on investment compared to a traditional solution. The results obtained might be considered as valid since the heat used was provided by a free energy source with a low environmental impact, devoid of CO2 emission

A Natural Wind Defrosting, Nano-coated Antibacterial Self-cleaning Energy-saving Health Air-cooled Refrigerator

The air-cooled frost-free household refrigerator is popular in the market because of its large size and frost-free size. However, the evaporator defrost process consumes a large amount of electrical energy to limit the wide spread of this refrigerator, at the same time because of its structural problems, resulting in its evaporator, air duct can not be artificially cleaned, leading to the growth of bacteria, pollution of food storage. This research has developed a self-cleaning energy-saving health refrigerator that uses indoor natural wind defrosting, ultra-hydrophilic nano-titanium dioxide coating photocatalytic sterilization and sterilization. After experimental comparison, under the same operating time of the same operating conditions, the refrigeration mode saves 1.5%, the defrost process saves 95%, reduces the amount of frosting by 23%, the temperature changes of the freezer is less than 7 ℃ , and the desterilization rate of nano-coated reaches 80%

Development of a dual purpose refrigeration system for domestic use

Refrigeration and air conditioning are very important in the daily activities of man, particularly in the tropical regions of the world; used in the preservation of perishable items, storage of pharmaceutical drugs, controlling of an atmospheric environment either for human/animal thermal comfort or effective performance of a scientific process. This paper is aimed at the design and construction of a dual purpose domestic refrigeration system, that can simultaneously function as a refrigerator and as well as an air conditioner henceforth known as REFACON. The refrigeration system employed was a vapour compression system. The machine was a split configuration with an Indoor and an outdoor unit (condensing unit). The machine used a singular 1,119 W single phase hermetically sealed reciprocating compressor, a fabricated condenser and split evaporator operated by temperature controlled solenoid valve. The system used 0.620 kg of R 22 refrigerant, with a discharge pressure of 1,355 kPa and suction pressure of 360 kPa. The input power was 1,350 W with an output cooling effect of 5,280 W. The combined cooling load/cooling capacity of the machine was 4,500 W. The results of tests conducted showed a total heat rejected of 6,680 W and a total evaporator heat absorption of 5,179 W. The Energy Efficiency Ratio was 3.91 while the Coefficient of Performance was 4.72. This research has shown that the design employed for the heat exchangers was appropriate and Thermal contact resistance cannot be neglected. http://dx.doi.org/10.4314/njt.v35i4.1

Design and fabrication of a long-life Stirling cycle cooler for space application. Phase 3: Prototype model

A second-generation, Stirling-cycle cryocooler (cryogenic refrigerator) for space applications, with a cooling capacity of 5 watts at 65 K, was recently completed. The refrigerator, called the Prototype Model, was designed with a goal of 5 year life with no degradation in cooling performance. The free displacer and free piston of the refrigerator are driven directly by moving-magnet linear motors with the moving elements supported by active magnetic bearings. The use of clearance seals and the absence of outgassing material in the working volume of the refrigerator enable long-life operation with no deterioration in performance. Fiber-optic sensors detect the radial position of the shafts and provide a control signal for the magnetic bearings. The frequency, phase, stroke, and offset of the compressor and expander are controlled by signals from precision linear position sensors (LVDTs). The vibration generated by the compressor and expander is cancelled by an active counter balance which also uses a moving-magnet linear motor and magnetic bearings. The driving signal for the counter balance is derived from the compressor and expander position sensors which have wide bandwidth for suppression of harmonic vibrations. The efficiency of the three active members, which operate in a resonant mode, is enhanced by a magnetic spring in the expander and by gas springs in the compressor and counterbalance. The cooling was achieved with a total motor input power of 139 watts. The magnetic-bearing stiffness was significantly increased from the first-generation cooler to accommodate shuttle launch vibrations

Design, Construction and Characterization of a Sliding- Plate- Evaporator Freezer (Spef)

This work embodied the design, construction and characterization of a sliding plate evaporator freezer, a modified version of the conventional freezer. The presence of a sliding plate evaporator reduces the freezing area, to increase the freezing rate and with a reduced freezing time. The freezer is intended to freeze agro and allied products in a record time. This is achieved by incorporating sliding plate evaporators to a conventional freezer to have two or more freezing sources, thereby, also giving the freezer with the option of a deferring freezing area to increase freezing rate. The results obtained are not exactly matched with the designed objectives because of construction flaws; and modifications can be made to improve the Coefficient of performance. The Coefficient of performance of the SPFE is obtained   to be 7.26. The SPEF is recommended for use in household and agro based industries for faster and effective freezing. Keyword: Freezer, Sliding Plate, Evaporator, and Refrigerator, Freezer chamber, Compressor power, Condenser power and Co-efficient of performance

Age-related efficiency loss of household refrigeration appliances: Development of an approach to measure the degradation of insulation properties

Despite the omnipresence of household refrigeration appliances, there is still a lack of knowledge about their age-related efficiency loss over time. Past studies provide basic evidence for increasing electricity consumption of cooling appliances with ageing but fail to investigate the associated technical wear. Concentrating on the degradation of the thermal insulation, we first determined the ageing process of sealed samples of polyurethane rigid foam by investigating changes in cell gas composition and thermal conductivity over time. Simultaneously, the main challenge was to develop an approach that investigates the age-related efficiency loss of the insulation without its destruction. This testing procedure is referred to as the Bonn method. The non-destructive Bonn method was applied to varying refrigerator models in a series of successive experiments to evaluate the insulation degradation over time. Subsequently, the physical relationship between the test value of the Bonn method and the heat transfer through the multi-layered compartment walls of domestic refrigeration appliances was established, ultimately characterising the degrading insulation in terms of increasing heat transfer. Our results give substantiated evidence that the efficiency loss of cooling appliances is greatly influenced by insulation degradation over time. The ageing of sealed samples of polyurethane rigid foam indicates a large initial increase of thermal conductivity by 15% within the first year, corresponding to a change in cell gas composition. These results are in line with those of the Bonn method, emphasising an increasing heat flow through the multi-layered compartment walls of domestic refrigerators with ageing. Therewith, the present study is of significance to a wide range of stakeholders and forms the basis for future research.BMWi, 03ET1544, ALGE: Alterungsmechanismen von Haushaltskältegeräte

THERMODYNAMIC AND THERMOPHYSICAL ASSESSMENT OF HYDROCARBONS APPLICATION IN HOUSEHOULD REFRIGERATOR

The research efforts and development in the refrigeration and air conditioning sector applied to the use of natural refrigeration fluids is not associated only with the need to preserve the environment alone, but has great importance with regard to the latent need for energy efficient equipment. With this perspective, the present study deals with the thermodynamic evaluation of the use of hydrocarbons refrigerants in household refrigeration systems that utilize HFC134a as a working fluid. A theoretical-computational analysis was developed for R134a, propane (R290) and the selected mixtures (R290/R600a 60%/40%, R290/R600a/R134a 40%/30%/30% and R600a/R290 50%/50%) in the standard refrigeration cycle ASHRAE, using the thermodynamic and thermophysical properties provided by the REFPROP 6.0 software. The results of computational simulations between the fluids were compared to find the evidence of the best alternative to HFC134a. In this sense, it was observed that the hydrocarbons reduced the levels of pressure on the condenser and evaporator, along with smaller compression tasks necessary in the system, owing to the thermo-physical properties privileged in these fluids. The use of these fluids is also proportionate to lower temperatures of compressor discharge, increasing the life of this highly valuable component of the system

Cooling systems for satellite remote sensing instrumentation

The characteristics of a cryogenic cooling system for the Pollution Monitoring Satellite (PMS) are discussed. Studies were conducted to make the following determinations: (1) the characteristics and use of proven and state-of-the-art cryogenic cooling systems for six specified ranges of performance, (2) the system most applicable for each of the six cooling categories, and (3) conceptual designs for candidate system for each of the six representative cooling categories. The six cooling categories of electrical loads are defined. The desired mission life for the cooling system is two years with both continuous and intermittent operating conditions

Causes, Consequences and Prevention of Fires in Domestic Refrigeration Systems

This study was proposed to investigate and examine the causes, consequences and prevention of fires occurring in domestic refrigeration appliances. The aims were to analyse such incidents, examine their characteristics and understand the underlying ignition and fire spread mechanisms that have led to their occurrence and how they might be prevented. The reasons for the cause and spread of domestic refrigeration fires have been examined, using information obtained from the analysis of fire data sets available in Great Britain and on the basis of fire investigations carried out in London. Visits to refrigerator disposal sites and local authority amenity centres also provided information on changes to appliance construction techniques and component use over several decades. Analysis of the available data suggests that once ignition occurs, fires caused by fridge/freezers are more likely to exhibit a higher degree of fire spread and produce greater levels of damage than other types of white goods appliance (washing machine, dishwasher or tumble dryer). Nearly 80% of fires with fridge/freezers as the source of ignition, spread beyond the first item involved, whilst almost 40% spread beyond the room of origin. Fires involving fridge/freezers also displayed a far higher casualty rate per fire than was found for the other types of appliance. Based upon evidence obtained from fire investigations a number of common failure modes leading to ignition in domestic refrigeration fires have been identified: (i) starter relay failures; (ii) PTC switch failures; (iii) mechanical defrost switch failures; (iv) capacitor failures; (v) solenoid valve failures; (vi) cut-out switch failures in integrated appliances, and (vii) rodents. Specific fire escalation and spread mechanisms have also been identified: plastic drip trays, “twin-wall” backing materials and polyurethane foam insulation panels. There is also evidence to suggest that the severity of refrigeration fires in Great Britain is significantly higher than in the USA. Based upon information obtained from LFB fridge and freezer fire investigations, and a comparison between the design and construction of refrigeration appliances used in Great Britain and USA, a number of recommendations have been made which could be used to significantly reduce the risk of a serious fire e.g. avoiding the usage of plastics in appliance housings and in particular employing a metal/non-combustible covering at the back of fridge and freezer appliances and ensuring that insulating foam is separated from the spread of fire by fire resisting material