This paper overviews Helmholtz energy equations of state for pure HFC and natural refrigerants. The equations of state consist of the ideal-gas part and the residual part. The ideal-gas part can be calculated from the ideal-gas isobaric heat capacity according to the ideal-gas law, and the residual part is determined empirically by fitting to experimental thermodynamic property data. Polynomial and exponential terms are used to represent the residual part. Some equations have more complex terms for accurate descriptions of critical behavior. Mixture models for applications of the pure-fluid equations of state to refrigerant mixtures are summarized. Until now, two mixture models have been developed for HFC refrigerant mixtures. This paper also discusses calculation methods for the pvT relation, vapor-liquid equilibrium, and critical point using Helmholtz energy equations of state. Few literature discusses the methods in detail, although such information is very precious to make a computer program for calculating thermodynamic properties.
In this study, a temporary space cooling system using ice was evaluated for the simple cooling of spaces, such as prefabricated buildings and tents used for events and at times of disaster, and analysis and experiments were conducted concerning the system. First, the concept of this system was established. Two types of cooling methods - natural and forced circulation - were adopted. Next, the cooling capacity was predicted by calculation. Measurement results were also presented concerning the cooling capacity of the forced circulation-type system in a temporary tent. Furthermore, this system was actually tested on a temporary tent and a prefabricated building and demonstration experiments were conducted. The operation results were indicated and the cooling capacity was evaluated.
In this paper, we investigated experimentally the growth of frost layer under natural convection to obtain effects of conditions related to air and cooling surface. We compared the results with numerical calculations, which are based on a non-homogeneous frost layer growth model used in the study of the forced convection. The comparison showed that the trend of the numerical results for the frost layer growth is in good agreement with the experimental results. The growth of the frost layer is markedly influenced by the thermal conductivity of the frost layer. The present numerical calculations suggest a thermal conductivity for the frost layer that is twice the value predicted by Yonko-Sepsy relationship. An accurate evaluation of the thermal conductivity of the frost layer is necessary to be able to match the frost layer thicknesses with those of the experiments. The present numerical model has the potential as a tool for the systematic investigation of influences of various factors affecting the frost phenomenon.
Frost deposition mechanism in low temperature environments need to be clarified when improvements to the coefficient of performance of heat exchangers is sought after. Some examples of heat exchangers being used under frosting conditions are: air conditioners in heating mode in winter and indoor units of showcases and unit coolers. Only a few studies have focused on the frost growth at low air temperatures although it is an important phenomenon, and therefore frost properties were measured at temperatures below 0°C. The results of experiments were compared with those of calculations based on reported models that predict transportation of water vapor in the frosting phenomena. Selected models were used to analyze the growth of frost in the two periods, crystal growth period and frost layer growth period. The analyzed growth results were compared with the experimental results obtained under chilled and frozen conditions.
Heat island effect changes the local weather pattern, increases energy costs to offset this effect, and increases demand for cooling. While considering urban heat island, local effects due to waste heat from vehicles, as well as from building and commercial energy consumption should be taken into consideration. In this research, state-of-the-art WRF model coupled with urban canopy model has been modified by including the gridded anthropogenic heat emission data of Osaka, Japan for meteorological modeling of Osaka region in order to assess the contribution of urban canopy effect and anthropogenic heat emission towards the formation of urban heat island. We developed and used a detailed urban land-use map to be used for urban canopy modeling, and a gridded emission map consisting of spatial and seasonal distribution of anthropogenic heat emission for better representation of urban heat emission. Using area-averaged and one-week averaged time series simulation results, we could understand the spatial and temporal behavior of urban heat island effect in more detail. The results showed an average increase of 0.8 K in near-surface air temperature in Osaka City when anthropogenic heat and urban canopy effect were taken into consideration.
The air temperatures have been measured in Sakai, Osaka, Higashi-Osaka and Hirakata located in Osaka plain in summer and winter seasons. The influence of the land use to the air temperature is clarified by measuring at the fixed points covered with the different land use, and the influence of the sea and land breeze is also discussed. Moreover, the comparison of these cities with different location and scale is performed. The air temperature distribution maps in Sakai and Hirakata are made based on the fixed point measurement data, and the current state of the thermal environment is clarified. The air temperature is high in Osaka and Higashi-Osaka regardless of day and night. The air temperature difference is actualized generally in winter compared with summer. The spatial difference in air temperature showed the tendency to become small generally excluding the coast part in summer when the sea breeze developed. There were strong correlations in air temperature and land use, and was a plain rise effect of air temperature on commerce and business use.
Simple expressions to predict actual performance of vapor compression air-conditioners such as room air-conditioners and multi-split type air-conditioners are proposed. Coefficient of performance is expressed in these simple expressions as a function of outdoor temperature, indoor temperature, air-conditioning load rate, air flow rate of indoor unit (in case of room air-conditioners) and difference in height between indoor unit and outdoor unit (in case of multi-split type air-conditioners). Those simple expressions are obtained by neural net work analysis (Rule extraction method from facts, RF5). Actual performance of air-conditioners which are used for training data and teaching data of net work are obtained by numerical simulations developed by the authors. Calculation results of these simple expressions usually agree with experimental values of other researchers. Furthermore, amount of exhaust heat from air-conditioners calculated with these expressions are 10% or lower than traditional approach: calculated with constant value of coefficient of performance.
This paper describes the numerical (CFD) analyses for thermal environment around the air-cooled outdoor units of air conditioning system installed on a roof of building to investigate the mechanism of Short-Circuit (SC) phenomenon. Especially, we focused on the effect of the condition of airflow around the air-cooled outdoor cooling units and the density of heat discharge. And then we developed the prediction formula to estimate the average or maximum rising inlet air temperature without CFD analyses and evaluated an effect of the decreasing inlet air temperature by applying various countermeasures. Based on these analyses, we proposed the method to estimate the required area for installing the air-cooled outdoor units and showed the possibility of decreasing the required area by applying various countermeasures.
A novel simple measuring method of actual performance of room air-conditioners by neural net work analysis (NNW) has been developed. The actual performance for a long term which is difficult to be measured by air enthalpy method is able to be measured easily by this method. In other words, actual performance of room air-conditioners can be measured by the proposed NNW method without measurement of air flow at indoor unit and outdoor unit which changes due to clogging of heat exchanger by dust. In order to gather data for training and testing the proposed NNW method, the room air-conditioner for experiment was set up. Inputs to NNW are outdoor temperature, indoor temperature, indoor wet-bulb temperature, inlet temperature of evaporator, outlet temperature of evaporator, condensation temperature and power consumption. The output from NNW is COP. The COP by NNW method has mean errors under 2.8% in quasi-steady operation condition and has mean errors under 4.6% in unsteady operation condition, compared to the COP of air enthalpy method. Results show that the COP of air conditioners can be measured easily for a long term using NNW within a high degree of accuracy.
Fine water mist sprays with average droplet diameters around 20 microns are being increasingly used as an energy-efficient means of cooling outdoor and semi-enclosed spaces such as rail platforms and shopping arcades. At high relative humidity there is a higher risk of wetting people and the ground beneath mist nozzles. Automated control systems are often set to run above a set dry bulb temperature and below a set relative humidity. Experiments show that mist evaporation rates before reaching the ground are closely related to the difference between the dry bulb and wet bulb temperatures, here labeled ΔTWB. Changing the operating parameters to include a minimum ΔTWB can allow use at higher relative humidity levels. If a common 28°C, 70% condition is sufficient to prevent floor-wetting, then a condition of 28°C with a ΔTWB > 4.3K should still prevent floor-wetting. This would allow operation at 75% relative humidity near 39°C.
There is increasing concern about the health effects of the severe thermal environment in urban area. Because of these situations, it is important to estimate the thermal comfort for environmental improvements and designs. Several studies have been performed dealing with the increasing problems of worsening thermal environment. However, only few studies have been performed that cover the theme of conditions in outdoor space. In the present study, a thermal comfort index for outdoor environment was newly proposed. The field experiments were conducted in the open space. Based on the heat balance in human body, the thermal load of human body is calculated from the mean skin temperature and the surrounding environmental factors such as air temperature, solar radiation and wind speed. A correlation between the measured thermal sensation of all subjects and the evaluated thermal load was recognized enough. The thermal sensation in outdoor space could be evaluated by the thermal load as a thermal comfort index. The new findings could provide fundamental data for the improvement of outdoor living environments.
The simple and noninvasive measuring methods of bioinstrumentation in humans is required for optimization of air conditioning and management of thermal environments, taking into consideration the individual specificity of the human body as well as the stress conditions affecting each. Changes in human blood circulation were induced with environmental factors such as heat, cold, exercise, mental stress, and so on. In this study, the physiological responses of human body to heat stress and exercise were investigated in the initial phase of the developmental research. We measured the body core and skin temperatures, skin blood flow, and pulse wave as the indices of the adaptation of the cardiovascular system. A laser Doppler skin blood flowmetry using an optical-sensor with a small portable data logger was employed for the measurement. These results reveal the heat-stress and exercise-induced circulatory responses, which are under the control of the sympathetic nerve system. Furthermore, it was suggested that the activity of the sympathetic nervous system could be evaluated from the signals of the pulse wave included in the signals derived from skin blood flow by means of heart rate variability assessments and detecting peak heights of velocity-plethysmogram.