The daily performance of a water heating system composed of a CO2 heat pump and a hot water storage tank is affected by the history of ambient conditions, hot water demand, and operating conditions as well as the resultant history of temperature distribution of the storage tank. To operate the system optimally under daily changes in these items, it is important to accurately estimate daily changes in the values of performance criteria such as COP, storage and system efficiencies, and volumes of stored and unused hot water. In this paper, the daily changes in the values of performance criteria corresponding to that in hot water demand are estimated under daily constant ambient and operating conditions by multilayered neural network models, and the values of model parameters are identified by a global optimization method to heighten the estimation accuracy. A numerical study is conducted using the values of performance criteria obtained by a numerical simulation for simulated monthly hot water demands, and the validity and effectiveness of this approach are ascertained.
Microwave irradiation has a feature of direct and rapid heating of a material. Based on the advantages of microwave heating, we have proposed the combined microwave and hot-air heating for regeneration of desiccant unit. Combined heating is expected to improve regeneration efficiency of conventional desiccant air conditioning system. In this study, experiments for regeneration of silica gel desiccant unit were performed under various microwave powers (200-800 W) and hot-air temperatures (40-100 oC). As a result, combined heating improved regeneration ratio in the equilibrium state and initial regeneration rate of desiccant unit, because it leveled non-uniform temperature distribution in the desiccant unit caused by microwave irradiation. It was also found that microwave irradiation was effective for regeneration of unit in the initial period. In addition, microwave and combined heating had a potential to reduce energy consumption for regeneration compared to conventional electric hot-air heating.
There are many combinations of the piston stroke and the cylinder bore that yield a given suction volume in the reciprocating compressors. This study presents a fundamental optimal design concept to determine the combination of the piston stroke and the cylinder bore, which maximizes the mechanical efficiency of a compact single-cylinder reciprocating refrigerant compressor with a given ratio of the crank arm rotating radius to the connecting rod length. First, theoretical development of the equation of motion of the rotating crankshaft is briefly presented. Secondly, computer calculations are carried out to identify the mechanical efficiency for a variety of combinations of the major parameters, thereby permitting identification of the optimal combination for maximum mechanical efficiency. Finally, the identified optimal combination is subjected to a parametric study with a variety of friction coefficients, thus resulting in no effect of the values of friction coefficients upon the optimal combination.
The primary objective of this paper is to evaluate a magnetic refrigerator operated with an active magnetic regeneration (AMR) cycle. The magnetic refrigerator, which is a cooling technology based on the magnetocaloric effect, has an advantage of F-gases free over conventional vapor compression type refrigerators as well as high efficiency. In this study, we have developed a prototype rotational magnetic refrigerator having a disk geometry material bed and compact component arrangement. The refrigeration characteristics and cooling power of this system are obtained under a variety of conditions. In addition, a numerical simulation based on the AMR cycle of the prototype system is conducted for the estimation of the performance of the magnetic refrigerator with the AMR cycle. As results of this study, it is found that the cooling capacity of the magnetic refrigerator is dependent on a utilization factor which is the heat capacities ratio between the heat transfer fluid and packed magnetocaloric materials.
In this study, the condensation characteristics of R1234ze(E) and R134a were investigated experimentally ina horizontal multi-port extruded tube. The test tube has 17 rectangular mini-channels of 0.85 mm in hydraulicdiameter. Experiments were carried out in the mass velocity range of 100 to 500 kg･m-2･s-1 at saturationtemperature of 40 and 60 oC. The pressure drops were measured between both ends of the test tube. The localheat transfer coefficients were also measured in eight subsections, each of which is 75 mm in effective heattransfer length. The measured pressure drop of R1234ze(E) is larger than that of R134a at the sameexperimental condition. The measured heat transfer coefficient of R1234ze(E) almost equals to that of R134a.
A simulation method for design of solar air conditioning system that is composed of solar collectors and an absorption chiller was developed. For the optimized design of the system, it is necessary to make an integrated simulation of the collector and the chiller based on the customer's air conditioning demand and the weather data, but for the simulation of the chiller, the refrigerant cycle simulation has to include the design data of the chiller such as the heat transmission coefficient, the heat-transfer area and the solution flow rate that designers cannot obtain easily. The developed method is based of the specification data of collector and chiller that can be obtained from their technical manuals and designers can make the optimized design for each customer.
This research evaluated the energy -saving rate of a solar air conditioning system with an absorption chiller for commercial use by annual energy simulation including absorption cycle calculation and collecting solar heat calculation. The energy-saving rate of cooling is improved by higher temperature heat collection, but the rate changes sensitively against the radiation. The energy-saving rate of heating is saturated to area of solar panel when the heating load is small. The energy-saving rates of cooling and heating are improved by heat collection on wall, but the effect is not so high.
This paper presents the results of heat transfer performance of pool boiling type and falling film type heat exchangers and operation test about newly developed solar absorption chiller using the two types of new heat exchangers. It is well known that solar thermal energy has two advantages: largest volume of energy in renewable energy resources and high energy conversion efficiency. Solar cooling system utilizing solar thermal energy as energy sources is attracting attention as saving energy because industrial and commercial air conditioning occupies high energy consumption compared to other energy application. In order to utilize solar thermal energy for industrial and commercial air conditioning application effectively, we Kawasaki Thermal Engineering produced prototypes of two types of new heat exchangers: pool boiling type and falling film type, and evaluated the heat transfer performance for the two types. As a result, the utilization of about 75 degrees C hot water, which was hard to achieve in conventional absorption chillers for its relatively low temperature, succeeded using the newly developed falling film type heat exchanger.
Non-chlorinated and fluorinated refrigeration system is desired from both viewpoints of global warming and ozone depletion problems as well as providing a system for utilizing renewable energy resource would be an important issue. Ejector cooling cycle is not a new original idea, while the cycle is possible to work without consuming fossil-energy resource and CO2 emission when it works under solar energy. The major drawback of the cycle would be believed as its low energy conversion efficiency. It would not be academically true because the thermal efficiency of ejector cooling cycle is given for heat input, while the COP of conventional heat-pump system is not based on heat input but on electricity input. This research will provide the useful information for developing a realistic ejector cooling cycle from the analytical and experimental approaches. The results include the information on the best working fluid for the actual system and on an analytical method of performance as well as results of actual performance using an indoor testing apparatus.
The study proposed a solar chimney driven evaporative cooling system that can be integrated into the ceiling of a building. The aims of the study are to analyze the boundary conditions, such as a radiative cooling load and the inlet air conditions, on the cooling performance of the system, as well as to predict the energy saving potential of the system. The simulation results revealed that the system could cope with the radiative cooling load of 40W/m2 when the solar radiation on vertical surfaces was above 200W/m2.The cooling load of the existing air conditioner would be reduced by 11% on a summer representative day, if the system was attached to the perimeter zone of a south-facing office room.
Combined solar hot water driven with air-cooled equipments could be realized by two-stage ammonia-water absorption refrigeration systems for small scale residential uses. In this paper, both thermal and electrical performances are evaluated by system mathematical models. The analysis showed that cooling air should cool condenser firstly and absorber secondly to reach an optimum performance. Thermal COP about 0.34 and electric COP above 25 could be obtained in hot summer working condition. The researches show that both thermal and electrical COP increase with the increase of driven hot water and evaporation temperature, and with the decrease of cooling air temperature. Rectifier is not required in the system because the basic concentration of ammonia vapour has already reached the purity standard. Low-grade solar energy could be utilized efficiently due to large inlet and outlet temperature difference of the driven hot water. Absorption heat recovery of low pressure cycle could be realized to increase thermal COP for ceiling radiation cooling conditions.
The study was undertaken to evaluate refrigerating and air-conditioning technologies in cases of introducing both co-generation systems and energy networks at a food industrial park. Energy data of 12 factories obtained from interviews were classified into those of steam, hot water, heating, cooling, refrigerating, freezing, and electric power. The author developed a smart energy network model based on linear programming to minimize the total system cost. The industrial park was divided into 2,500 square meter meshes to incorporate analyses of steam transport. This study investigated four cases. The ratio of energy saving to demand reached 18 % compare with the reference system. It was introduced only slightly into the refrigerating supply though a heat driven chiller introduced into the air-conditioning supply in the smart energy network system. The inter-factory steam network became more advanced than the inter-factory electric power network. Results of these simulations underscore the useful role of a smart energy network in communities of the future.
This article presents the performance analysis of the pressurized adsorption chiller, which consists mainly of an evaporator, a condenser and two sorption beds. A total of two specimens of adsorbent/adsorbate pairs, namely Maxsorb III/R134a and Maxsorb III/R410a have been investigated. The evaporator temperature is operated between 5 to 12 °C and the condenser temperature is at ambient temperature, i. e. 30 °C. However, these refrigerants enable sub-zero evaporating temperatures. The R134a adsorbate cooling system is operated at lower pressure ranging from 0.35 to 0.77 MPa, and for R410a adsorbate cooling system, the operating pressure is ranging from 1.45 to 1.89 MPa. This shows R134a is more favorable to use due to its lower operating pressures. In current studies, parametric analysis has been carried out to study the effects of adsorption/desorption time and switching time on the system performance in term of cooling capacity and coefficient of performance.
The demand for a refrigerant as a cold packing material at lower temperatures is growing in the field of food transportation. However, because of the existence of supercooling, refrigerant cannot freeze at melting point. It must be cooled at a lower temperature than the melting point. It needs a high electrical load on the refrigerator. Therefore, in order to reduce the high electrical load, a method of freezing supercooled solution using a membrane is introduced. A capsule having a solution with a low concentration or tap water is installed in a package having a refrigerant inside. One part of the capsule wall is made of membrane and only water can pass through the membrane. Since the melting point inside the capsule is higher than the outside, water or low concentrated solution in the capsule freezes first, and it propagates through the membrane and becomes a trigger for the refrigerant to freeze. This study is a fundamental research, and so a sheet of membrane is put between refrigerant having a high concentration of solution and water or low concentrated solution, and they are cooled together. Parameters for the experiments were selected to be a difference of melting points, the location of initial ice appearance, the cooling rate and the membrane thickness. The results were compared and the effect and phenomena of these differences were investigated.