Dynamic-type ice storage systems have been developed in the 1990's, and many kinds of system have been adopted as actual equipments in Japan. Many reports of research and development for making ice methods and ice making processes were published. However, reports for melting ice were few, although ice melting processes were important on design technology of ice storage systems and on ice slurry systems in future. In this paper, reviews of research and development for dynamic-type ice storage systems and for characteristics of melting ice in the dynamic-type ice thermal storage tank are presented. Moreover, prediction methods for ice melting processes in dynamic-type ice thermal storage tanks are introduced for design technologies of dynamic-type ice storage systems.
The annual performance factor (APF) of gas engine heat pumps (GHPs) is determined in accordance with Japanese industrial standards (JIS). The JIS-based performance rating method is easy and useful, but it does not take into account the intermittent driven mode of the compressor as well as the standards used for package air conditioners. From the results of the experiments conducted on packaged air conditioners, a substantial difference was found between the APF determined by the JIS-based method and the APF determined using the results of the experiment and by taking into account the intermittent driven mode. Because GHPs have the same mechanism as package air conditioners (GHPs are driven by gas engines, whereas package air conditioners are driven by motors), it was believed that the same issues affect the annual performances of both these systems. For both systems, it was found that the COP decreased with the load. Furthermore, various new rating methods were suggested. The use of the newly proposed methods will result in a more accurate APF as compared to the JIS-based method. Additionally, electricity consumption of GHPs was taken into account when calculating the APF.
The development of a gas clean technology may be one of the most expecting techniques in a wide field from global environment to living conditions. In this paper, the authors proposed the new concept of a gas clean technology by utilizing negative air ions and ozone gas with the formation of mist. A system is composed of the heat exchanger of staggered fins and a electrostatic precipitator. The negative air ions and ozone gas generated by corona discharge provide an electric charge and bactericidal effects. Formation of the mist in the field of super-saturation state by cooling of the system can make them high efficiency. Experimental data showed that the present system allowed air to be sanitized in high efficiency.
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 those in hot water demand and one of two operating conditions are estimated under daily constant ambient and the other operating conditions by multilayered neural network models. In addition, the former operating condition is determined based on the values of performance criteria estimated by the models. A numerical study is conducted using the values of performance criteria obtained by a numerical simulation for a simulated monthly hot water demand, and the validity and effectiveness of this
In the first and second reports, visualization experiments were performed using tracer particles and thermo-sensitive liquid crystals. Experiments were also carried out to find the unsteady temperature distribution in a tank when the positively or negatively buoyant jet was injected horizontally in the middle of the tank. One dimensional model for simulating temperature distribution was proposed. The model had applicability to a basic initially uniformed tank temperature. But, by considering an actual equipment, there is a temperature gradient around the jet nozzle, and mixing process is more complicated. In this report, the model was applied for the case of having a temperature gradient around the horizontal jet height. And a modified model, “non-uniformly mixing model" was proposed, which was considered with a vertically mixing process by applying a cubic function for a mixing region. The mixing region was determined by a buoyancy force and a vortex near the wall. The performance of the model was verified by comparing the results with the unsteady temperature distribution obtained experimentally. The model was also compared with the measurements obtained using a commercially available hot water storage system. Both results showed good agreements. Hence adequacy of the model was clarified.
In this study, an adhesive film method was newly applied to observe ice crystal morphology of frozen fish meat. A frozen fish meat was embedded with OCT compound and sectioned by use of a cryomicrotome. During the sectioning process, a cryo-adhesive film was used to collect the sections. Then, the section was fixed and stained on the cryo-adhesive film. These processes enabled facile and rapid observation of ice crystals by microscope. With measurement of ice crystal morphology, it was found that ice crystals observed with this applied method were about the same size and shape as those of the freeze-substitution method. Those results demonstrate that this applied method is useful to the observation of ice crystals. Moreover, by use of sequential sections obtained by this method, three-dimensional image of ice crystals in frozen fish meat was easily reconstructed.
The results of laboratory measurements on the performance of the HVAC system powered by solar air heater, solar cell and wind generator, are described. Experiments were performed in various weather conditions both in winter and summer. The experimental results show that 30-90% of thermal energy to regenerate the desiccant in this system and 20-65% of the energy to power the system were supplied by natural energy in summer, and 30-97% of the energy to power the system was supplied by natural energy in winter. The results of measurements on the performance of a desiccant dehumidifier unit with solar air collectors are also described. Room exhaust air is used to cool the 17% of the desiccant rotor area in this unit. Experimantal results show that the amount of dehumidification was increased by 6% and the amount of energy to cool the air was decreased by 8% by this rotor cooling process.
We built the advanced office building where Low Carbon Building with high workplace productivity. This building realizes large energy saving with Sensible/latent heat separated Air-conditioning system. In this system, I adopted Return-air Desiccant method. We report the most suitable ability adjustment in the Real load driving of the Return-air Desiccant air conditioner.
In the present flow system for a low dew point desiccant dehumidifier, multiple rotors have to be arranged in tandem. Because each rotor requires a regeneration heater, running costs of the system becomes large. In this work, from the viewpoint of energy saving, low-dew point dehumidifiers for how to achieve energy saving problems were studied. In the proposed energy-saving super-low dew point dehumidifiers system, the first rotor regeneration heater can be removed, and the second rotor regeneration outlet air without re-heating as the first rotor regeneration air to be used directly. Compared with the existing dehumidifier, new energy-saving super-low dew dehumidifier energy consumption can be reduced by about 46% or more.
Complex of hydroxyl-aluminum-silicate and low crystalline clay (HAS-Clay) and precursor of HAS-Clay were developed as adsorbents for desiccant air-conditioning system. The water vapor adsorption isotherms of HAS-Clay and precursor of HAS-Clay were linear shaped. Both HAS-Clay and precursor of HAS-Clay had micro-pores about 0.6 nm in diameter and meso-pores of two different sizes. Although the heatproof temperature of HAS-Clay was higher than 300°C, the heatproof temperature of precursor of HAS-Clay did not become clear because of amorphous material. The amount of water vapor of HAS-Clay were 33.7, 38.2 and 41.8 wt% in the dehydration temperature of 60, 80 and 100°C, respectively. And the amount of water vapor of precursor of HAS-Clay were 24.4, 28.5 and 29.9 wt% in the dehydration temperature of 60, 80 and 100°C, respectively. So HAS-Clay and precursor of HAS-Clay were adsorbents which were excellent in low-temperature dehydration (regeneration) and were suitable for desiccant air-conditioning system.
Adsorption / desorption behavior of water vapor in a desiccant honeycomb containing a silica-alumino-phosphate type zeolite AQSOA-Z02, which exhibited a S-shaped adsorption isotherm, was experimentally investigated for humidity swing. The pieces of ceramic paper impregnated with AQSOA-Z02 as a desiccant material and Silica gel as a binding material were prepared and tested to understand the influence of the composite material similar to a desiccant honeycomb. At first, their adsorption isotherms of water vapor were unable to be explained by the additivity of each material adsorption isotherm. The most significant finding was that the relationship between the adsorption / desorption rates in humidity swing and the driving force of adsorption changed at the specified amount of adsorption. This specific amount of adsorption probably corresponded to the amount at which the change of adsorption mechanism occurred.
An optimum operating and design concept for miniaturization of adsorbent desiccant wheel were presented by means of numerical analysis of simultaneous heat and mass transport in the desiccant wheel. First, the influence of the operating parameters, such as regeneration air temperature and air flow rate, and design parameters, such as the ratio of the adsorption area and length of the wheel, on the optimum rotation speed and amount of dehumidified water were investigated. Based on these results, the minimum volumes of the desiccant wheel achieving the certain dehumidification performance were calculated under various air conditions. As an example of the results, the minimum volume of the desiccant wheel, 0.019 m3, which was 30 % smaller than that of the conventional one, was obtained to achieve 8 g/kg of the amount of dehumidified water when regeneration air was 80 oC, 11.2 g/kg, and adsorption air was 35 oC, 20 g/kg. In order to satisfy this volume, the retention time, which could be calculated dividing the rotor length by air velocity, was calculated as 0.075 s, and ratio of the adsorption area was calculated as 0.55. Consequently, this study could conduct an optimum operating/design concept for the miniaturization of the desiccant wheel although the above mentioned reduction in volume, 30 %, is possible to range from 5 to 50 % due to the accuracy of the estimation.
In this paper, the desiccant rotor with double ventilation system is proposed in order to improve the sorption efficiency of the rotor. In this system, the processing air is dehumidified with the rotor. Next, the air becomes high relative humidity by cooling with an air cooler, and it is ventilated to the rotor again for dehumidification. This desiccant rotor with the organic sorbent has high adsorption ability at high relative humidity and can be recovered at low temperature. In this study, ventilation experiments of four types of air flow routes were investigated. In the experiment, temperature and absolute humidity of the air at the entrance and exit of each zone were measured. It is clarified that each route has own characteristics on dehumidification. As a result, it is found the most suitable route of the double ventilation dehumidification system.
In order to improve the sorption efficiency of the desiccant rotor, double ventilation rotor system has been proposed. In this system, at first the process air is dehumidified in the rotor. Next, the air becomes high relative humidity by cooling with an evaporator, and it is ventilated to the rotor again. In the first report, ventilation experiments of four types of air flow routes were investigated and it is clarified that each route has own characteristics on dehumidification. In this paper, the experiments of double ventilation rotor system of various flow routes were investigated with a refrigerator as a heat pump. Temperature and absolute humidity of the air at the entrance and exit of each zone were measured. Dehumidification amount of the rotor in single ventilation dehumidification system was equal to that in double ventilation dehumidification system. But recovered cold heat from evaporator in double ventilation dehumidification system was higher than that in single ventilation dehumidification system. With increasing the absolute humidity of inlet air, dehumidification amount of the rotor in each route and the absolute humidity of exit air increased. The COP of double ventilation dehumidification system was higher than that of single ventilation dehumidification system.
This paper presents the performance evaluation results of polymeric sorbent and inorganic adsorbent used for a direct cooling adsorption heat pump desiccant outdoor air handling unit. The results show that polymeric sorbent has a higher efficiency in humidification under the partial latent heat load and in dehumidification under any load factors. The difference between their efficiency under the maximum humidification load is negligible. An analysis based on the performance evaluation indicates that the polymeric sorbent's higher efficiency under the partial humidification load is due to its high regeneration rate in low temperature. Furthermore, the analysis suggests that its higher efficiency in dehumidification is due to the increase of saturated water content under the high relative humidity condition. An energy simulation model for a total air conditioning system is created based on the characteristic formulas for the desiccant outdoor air handling unit. The modeling results reveal that the total air-conditioning system using polymeric sorbent reduces the annual power consumption by 10.2% compared to the system using inorganic adsorbent. The analysis on each unit's power consumption shows that the improved efficiency of the outdoor air handling unit leads to the reduction.
The purpose of this study is to examine the dehumidification behavior of a block type desiccant unit of organic sorbent. This unit has simple rectangular parallelepiped shape, and initial cost can be lower than the desiccant rotor. This unit will be used in batch system that one unit is used for sorption and another is used for desorption at the same time. Experimental conditions are as follows, sorption air temperature is 18 °C, sorption air relative humidity is 90%, desorption air temperature is 40°C, and desorption air relative humidity is 36%. It was found that completed time of desorption is earlier than that of sorption. As a result, sorption and desorption characteristics of the block type sorbent unit and their overall-mass-transfer coefficients are clarified.
This article is the 3rd report of the series. The objective of this study is to evaluate the dehumidification amount of newly developed desiccant rotors by using paper containing Wakkanai siliceous shale (WSS) which is a natural mesoporous material in Hokkaido. The dehumidification amounts were evaluated at the following air conditions (OA: 30 ºC, 75 %RH, RA: 40 ºC, 27.3 %RH). The WSS rotor and a B type silica gel rotor (400 mm of the rotor diameter and 200 cpsi of the rotor cell numbers) showed same values of 3.1 and 3.2 g/kgDA at 1 rpm of rotation speed, even though the maximum water adsorption amount of the B-type silica gel is three times higher than that of the WSS. To enhance the dehumidification ability of the WSS rotor, an impregnation of NaCl and MgCl2 into the WSS paper was carried out, and it gave more than 3.8 g/kgDA. In addition, for the development of the compact desiccant system, dependency of the rotor rotation speed, the size of the rotor diameter, and a rotor cells number were examined. Finally, 4.7 g/kgDA was obtained at 500 mm diameter and 270 cpsi of the rotor cell numbers.
The objective of this study is to develop a desiccant system using Wakkanai siliceous shale (WSS). This article is the 4th report of the series. Two honeycombed desiccant rotors containing WSS powder with chlorides impregnated was made and evaluated. These rotors were applied into the test desiccant apparatus. It has an additional sensible heat exchange rotor (SHE). To regenerate the first rotor, hot water at 40 ℃ was supplied to HEX. In addition, cold water at 23 ℃ was provided to HEX for pre-cooling the second rotor. The amount of dehumidification was 5.7 g/kgDA at 1-1 rpm operation, and the condition of air temperature and humidity of the outside and room were 30 ℃, 75 %RH and 26 ℃ and 60 %RH respectively. (1-1 rpm: rotating speed of the first - second rotors) Though the amount of dehumidification didn't increase according to equipping a SHE rotor, we found that it was effective to reduce a used thermal energy for pre-cooling. As the result, the maximum dehumidification of 6.5 g/kgDA was obtained at 1-4rpm of first and second rotors with additional pre-cooling for outside air. This was 86 %RH of the latent cooling load between OA and RA.
The objective of this study is to develop a desiccant system using Wakkanai Siliceous Shale (WSS). This article is the 5th report of the series. In the first part of this paper, various parameters of the WSS rotor were estimated by the numerical calculation to find the higher dehumidification amount. An optimal rotor configuration was selected as 500 mmφ of the rotor diameter, 60 mm of the rotor thickness and 270 cpsi of the rotor cell number. In the second part, as a calculation model for the desiccant ventilation, an appropriate system, which consists of two rotors with two heat exchangers for pre-cooling and two heat exchangers for regeneration, was applied. To get over the target value of the dehumidification amount (7.6 g/kgDA), the numerical simulation was carried out based on the desiccant ventilation model. As a result, the maximum dehumidification amount of 8.6 g/kgDA was obtained at 0.5 rpm of each rotor rotating speed.
This study aims to develop and evaluate a desiccant ventilation system using desiccant rotors of the Wakkanai siliceous shale (WSS). The desiccant apparatus consists of two WSS rotors, two heat exchangers for regeneration and two heat exchangers for pre-cooling. The target for the system is to remove all of latent heat load from outside air (7.6 g/kgDA) without condensing. In the experiments, when 40 ℃ water supplied to one of the heat exchanger for regeneration, condensation was inevitable in heat exchangers for pre-cooling. The condition to dehumidify 7.6 g/kgDA without condensation was to run two rotors at 0.5 rpm and to supply 21.5 ℃ water to heat exchangers for pre-cooling and 45 ℃ water to another two for regeneration. Under the condition, enthalpy needed to dehumidify was reduced by 18 % compared to conventional dehumidification.
In air-conditioning field, a dehumidification has become increasingly important for human health and comfort especially in hot and humid climates. However, a conventional mechanical dehumidification with a vapor compression refrigerator has some problems. Therefore, much attention has been paid recently to a desiccant air-conditioning system as an alternative to the conventional system. In this paper, we focus on a desiccant air-conditioning system using a rotary desiccant wheel. The purpose of this study is to develop the simulation model of the desiccant wheel that can be applied to the various operating conditions. In this paper, the simulation model is validated under indoor air circulation condition by comparison with the detailed experimental results. In the model, the heat and mass transfer phenomenon in both air channel side and desiccant wall side are considered in detail. As a result, the simulation results of outlet humidity and temperature were in good agreement with the experimental results under indoor air circulation condition and then the simulation model was validated.
A simple mathematical model, in which the linear driving force (LDF) was adopted and local values of mass and heat transfer coefficients were considered, was applied to express or predict a dehumidification behavior of an adsorbent desiccant rotor. Penetration theory was also employed to correlate the mass transfer coefficient and the rotor rotation speed. Applicability of this simple model was discussed in terms of the dehumidification performance and the angular distribution of outlet air conditions (humidity and temperature). At first, this simple model gave a good agreement with the experimental results especially in a low regeneration temperature region, although the applicability of the simple model was limited to the region of the rotation speed at which the penetration theory was held. However, the differences of the angular distribution of the process / regeneration outlet air conditions between calculation and experiment tended to be large especially at the angular region of the rotor where the mass and heat transfer occurred drastically. This implied that changes of the process and regeneration air velocities along the air flow direction, which affected the mass and heat transfer coefficients, should be considered in the mathematical model at least.
A numerical simulation model of a desiccant rotor for the use in the low dew-point dry air production process was developed and tested. At first, the adsorption isotherm curve of the tested desiccant honeycomb was accurately measured in the low relative humidity region. Also, the numerical simulation model was modified in consideration of temperature and humidity gradients in the radial direction of honeycomb channel of the desiccant. The validity of the modified simulation model was discussed by comparison with an adsorption-desorption behavior of the desiccant honeycomb block. It was found that the simulated results almost agreed with the experimental results and correctly indicated the adsorption / desorption behavior. Also, simulated results implied that consideration of the radial humidity gradients into the numerical model became more important as the size of honeycomb pitch increased.
In air-conditioning field, a dehumidification has become increasingly important for human health and comfort especially in hot and humid climates. However, a conventional mechanical dehumidification using a vapor compression refrigerator has some problems. Therefore, much attention has been paid recently to a desiccant air-conditioning system as an alternative to the conventional system. In this paper, we focus on a liquid desiccant air-conditioning system using lithium chloride - water solution and experimentally investigate the heat and mass transfer of the packed bed absorber and regenerator that are the main components of the system. In the experiment, effects of the air superficial velocity and solution mass flux on the overall heat and mass transfer coefficients are examined. As a result of the study, we found that the heat and mass transfer coefficients increase with increase of the air superficial velocity, however, the heat transfer coefficient is approximately constant with increase of the solution mass flux.