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A new theoretical formulation of dew point temperatures applicable for comfort air-cooling systems
... providing insights for public safety, agricultural planning, and climate research [6]. Furthermore, DPT plays a crucial role in various engineering applications such as construction [7,8] and industry. Controlling humidity through dew point manipulation is essential for ensuring product quality and process efficiency in diverse sectors like food processing [9], electronics manufacturing [10], or water harvesting [2,11]. ...
... Current empirical models and some machine learning models fail to provide accurate estimates under extreme environmental conditions. Accurate DPT estimation under a wide range of conditions is critical for applications like water harvesting and energy efficiency [8,9,15,27,28]. • Lack of Specialized Tools: Currently, there is no tool specifically designed to address the combined results of temperature and humidity conditions beyond the simplistic rule of thumb, which is often inadequate. Developing dedicated tools that can handle these combined scenarios with precision and reliability is essential for advancing practical applications and enhancing model accuracy in diverse environmental contexts. ...
Accurate dew point estimation is crucial for measuring water condensation in various fields such as environmental studies, agronomy, or water harvesting, among others. Despite the numerous models and equations developed over time, including empirical and machine learning approaches, they often involve trade-offs between accuracy, simplicity, and computational cost. A major limitation of the current approaches is the lack of balance among these three factors, limiting their practical applications under diverse conditions. This research addresses these key challenges by developing a new, streamlined equation for dew point estimation. Using the Magnus–Tetens equation, deemed as the most reliable equation, as a benchmark, and by applying a process of non-linear regression fitting and parametric optimization, a new equation was derived. The results demonstrate high accuracy with a streamlined implementation, validated through extensive data and computational simulations. This study highlights the importance of accurate dew point modeling, especially under variable environmental conditions, provides a reliable solution to existing limitations, paving the way for enhanced efficiency in related processes and research endeavors, and offers researchers and practitioners a practical tool for more effective modeling of water condensation phenomena.
... Instead, it incorrectly referred to the equation as the Magnus formula. Unfortunately, the misattribution to Magnus (1844) spread from Holmboe et al. (1945) to several other publications (Parish and Putnam, 1977;Baldus et al., 2015;Sarkar, 2015;Sanger and Kirkpatrick, 2017;Frasca et al., 2018). ...
The Rankine‐Kirchhoff equation for the saturation vapor pressure has been derived independently many times, sometimes with the presumption of novelty. As a result, the equation is referred to in the literature by a bewildering number of different names and, often, by no name at all. Here, the history of the Rankine‐Kirchhoff equation is reviewed. The three approximations used to derive it (ideal gas, constant heat capacities, and zero‐volume condensates) can be used to derive a whole system of accurate and analytic expressions of relevance to the atmosphere. Consequently, it is proposed that this set of approximations be elevated to a named entity, e.g., the Rankine‐Kirchhoff approximations.
... Further in this paper will be focus only on situation when floor heat exchanger is set only for cooling of humid air under its dew point. There is direct link between a value of dew point and comfort perceived by people [2]. ...
The quality of environment, not only outside but
also inside buildings, is at the forefront of interest of experts as
it greatly affects the efficiency of work processes and the
perceived well-being. One of the most important factors for
perceived comfort is the amount of moisture contained in room
and circulation associated with it. This paper summarizes
results and methods used to determine and validate amount of
condensate created from humid air in floor heat exchanger.
Paper contains theoretical and practical knowledge connected
with perception of environment quality, determination of
humid air state variables, design elements of heat exchangers
and also summary of published scientific articles on humid air
condensation under normal atmospheric. Main vision is to
create one virtual model with corresponding settings and
boundary conditions which will precisely calculate amount of
condensate from flow created under defined conditions. For
validation purposes experiment was designed, created and run.
Results of both methods are presented, compared and
discussed with respect to their range of use for practical
purposes.
... In a study by Sarkar [12], a new theoretical formulation for dew point temperatures was developed with the use of modified Clausius-Clapeyron equation. The developed formulation was aimed for comfort aircooling systems. ...
Dew point is the temperature at which water vapor in the air condenses into liquid with the same rate it evaporates. Dew point study is important in arid lands with low rainfall, also in other regions with various hydrological and climatological conditions. In this study, the Grey theory is applied for the first time to propose a framework approach to identify the important parameters affecting the prediction of dew point temperature. The ability of Grey theory to estimate and rank the parameters of a problem with missing data and uncertain conditions means that it has a good potential for mentioned application. For this research, 8 parameters are selected using literature review including: global solar radiation on a horizontal surface (H), water vapor pressure (VP), atmospheric pressure (P), sunshine duration (n), minimum air temperature (T min), maximum air temperature (T max), average air temperature (T avg), and Relative Humidity (RH). The study is conducted for the city of Abadeh in Iran by using the data pertaining to a 10 year period between 2005 and 2015. The findings show that RH, T avg , P, T max , T min , H, n and V p with the grey possibility degrees of, respectively, 0.534, 0.551, 0.608, 0.622, 0.635, 0.695, 0.697 and 0.712, are the most important and effective parameters in prediction of dew point temperature. The proposed method also prioritizes the studied parameters in the order of their effectiveness on predicted dew point temperature.
... Theoretical parametric study of Wrap-Around Heat Pipe (WAHP) in air conditioning systems15 Considering the first case, when Cr = r, Eq. Expressing the evaporator to heat pipe NTU ratio as a function of the condenser to evaporator air mass flow ratio:Since the evaporator and condenser sections are assumed to have identical geometrical configuration: ...
Warp-around heat pipes (WAHP) belong to a special class of recuperative heat exchangers that transfer heat from inlet to outlet locations via thermal gradient, without using any energy. In the present work, effects of various mechanical parameters on the performance of a WAHP dehumidifier system that are based on the underlying principles of heat and mass conservation are presented primarily from a theoretical point of view. A simplified methodology pertaining to wet cooling coils is applied here for defining the case of moisture condensation during precooling process at WAHP evaporator. Inlet air temperature, inlet humidity ratio, air mass flow rate, dehumidifier outlet temperature and effectiveness are the main operational parameters considered in this study. On the other hand, comparative performance study of the WAHP system is done through an other set of thermodynamic parameters like the supply air temperature, supply humidity ratio, specific coil load and recovered enthalpy. The subtle variations in these factors against the operational parameters not only help in stipulating functional characteristics of the WAHP but also allow HVAC designers to make informed decisions for system design and performance without relying entirely on manufacturer's equipment data.
... In Eq.28, both the supply ADP and humidity ratio are unknown. The ADP (in Kelvin) can be expressed in terms of humidity ratio through a quadratic equation 27 The design dew point temperature of the space can be considered as the initial guess (Tadp0) for obtaining successive solutions. Dew point temperature can be determined in terms of humidity ratio 27 by Eq.32 as: ...
A framework for creating thermal zones in a building for effective and efficient Heating Ventilation and Air conditioning (HVAC) system design is introduced here. This method is based on simple “sort and eliminate” schemes and requires design cooling loads of conditioned spaces obtained from load calculation tools as primary input. The developed methodology is applied for creating thermal zones, determining corresponding supply conditions and ascertaining sizing of a dedicated outdoor air system (DOAS) with local recirculating units. A simulation study on a prototype-building model shows that a DOAS coupled with zoned recirculating systems that serve distinct thermal zones in a building (zoned model) perform comparatively better in controlling both space temperatures and humidity without significantly compromising HVAC energy and chiller loads than un-zoned HVAC systems serving the whole building as a single thermal block (un-zoned model). The consistency in the performance of zoned HVAC systems is verified by applying three different simulation weather files for New Delhi. Better performance along with logical and computational simplicity makes this design procedure a good alternative to traditional methodologies.
... This fact leads to two important conclusions. Firstly, increasing the heat gains, e.g. by appropriate orientation of windows, may contribute to a significant reduction of energy need for heating [21][22][23][24][25][26][27][28]. Maximization of gains can at the same time cause increase of energy need for cooling, which was confirmed in the article of Enshen [29]. ...
In this study a comparative energetic analysis is investigated of a single family house with different calculation procedures. One of the methods that were used is the Ministry without Portfolio Decree No. 7/2006 for energy certification and MSZ-140-04 for energy demand calculations (by using WinWatt computer software) that are a widely used in the Hungarian practice by HVAC designers and experts. Passive House Planning Package (PHPP) is also more and more common used PC software in Hungary due to the continuously tightening energy requirements. To see the differences and imperfections between these methods the heating, cooling and ventilation system was designed of a given single family house and the annual energy consumption was investigated with these methods. To perform the investigation in more detailed three different heating systems were designed. In the first case the heat source is a condensing boiler operated with floor heating. In the other two cases the thermal systems are heat pumps with floor and ceiling heating. One of the heat pumps is an air-to-water system, the other one is a geothermal heat pump. The advantages of the heat pumps are that heating, cooling and domestic hot water energy is produced by only one equipment and efficiency. However comparing investment and operating costs for the heat pumps with gas boiler the payback time is very long based on this study. The investment costs, payback periods are investigated for the three different systems evaluating the results also with PHPP and WinWatt computer software tools in this study.
... A simple methodology for determining the net sensible and latent load of an ideal cooling-dehumidification process in terms of discrete summations has been established in a previous work [24]. The mathematical model presented above discusses an actual cooling-dehumidification process in terms of key input variables. ...
... survival particularly in the arid areas with rare rainfall (Agam and Berliner, 2006). It may generally be stated that the dew point temperature is an element which either explicitly or implicitly contributes to the plants' productivity, crop harm during freezes, loss of human life during heat waves and levels of human comfort (Shank et al., 2008;Sarkar, 2015). ...
The dew point temperature is a significant element particularly required in various hydrological, climatological and agronomical related researches. This study proposes an extreme learning machine (ELM)-based model for prediction of daily dew point temperature. As case studies, daily averaged measured weather data collected for two Iranian stations of Bandar Abass and Tabass, which enjoy different climate conditions, were used. The merit of the ELM model is evaluated against support vector machine (SVM) and artificial neural network (ANN) techniques. The findings from this research work demonstrate that the proposed ELM model enjoys much greater prediction capability than the SVM and ANN models so that it is capable of predicting daily dew point temperature with very favourable accuracy. For Tabass station, the mean absolute bias error (MABE), root mean square error (RMSE) and correlation coefficient (R) achieved for the ELM model are 0.3240 °C, 0.5662 °C and 0.9933, respectively, while for the SVM model the values are 0.7561°C, 1.0086°C and 0.9784, respectively and for the ANN model are 1.0324°C, 1.2589°C and 0.9663, respectively. For Bandar Abass station, the MABE, RMSE and R for the ELM model are 0.5203 °C, 0.6709 °C and 0.9877, respectively whereas for the SVM model the values are 1.0413 °C, 1.2105 °C and 0.9733, and for the ANN model are 1.3205 °C, 1.5530 °C and 0.9617, respectively. The study results convincingly advocate that ELM can be employed as an efficient method to predict daily dew point temperature with much higher precision than the SVM and ANN techniques.
In heating, Wet-bulb temperature in HVAC (heating, ventilation, and air conditioning) applications is crucial for building the equipment. But radiation from the surrounding surfaces caused the errors during the thermodynamic wet-bulb temperature measurement. The wet-bulb temperature of moist air is measured in the current work utilising an aspiration psychrometer designed, developed, and built to reduce the error term caused by radiation and convection heat transfer. Wet-bulb temperature is calculated in the experiments using an aspiration psychrometer at various locations throughout the year, both with and without a shield. It has been found that the error term depends on several factors, including airspeed, the characteristics of wick fabric, the distance a person may breathe between thermometers, and the heat transfer coefficient owing to radiation and convection. A minimum of seven minutes must pass during the measurement of WBT to stabilise heat and mass transfer. It has been noted that the calculated term of error is higher in the afternoon than it is in the morning and evening because of the high solar radiation. The margin of error is approximately 15% in the morning and evening and at its highest in the afternoon. This investigation has led to the conclusion that direct sunlight should be avoided when measuring WBT. It has been discovered that greater heat transfer coefficient values provide the bigger term of error for fabrics with high textile emissivity.
While the Clausius-Clapeyron equation is very important as it determines the saturation vapour pressure, in practice it is replaced by empirical, typically Magnus type, equations which are more accurate. It is shown that the reduced accuracy reflects an inconsistent assumption that the latent heat of vaporization is constant. Not only is this assumption unnecessary and excessive, but it is also contradictory to entropy maximization. Removing this assumption and using a pure entropy maximization framework we obtain a simple closed solution, which is both theoretically consistent and accurate. Our discussion and derivation are relevant to students and specialists in statistical thermophysics and in geophysical sciences, and our results are ready for practical application in physics as well as in such disciplines as hydrology, meteorology and climatology.
Through a newly developed climate analysis tool, this paper examines the potential of improving thermal comfort under the climates of Vietnam thanks to passive strategies. A building climatic chart for Vietnamese was proposed based on Fanger's theory [1] and the comfort zone of this chart was then extended by calculating the effects of passive heating and cooling strategies. Typical Meteorological Year weather data are used for extracting and graphically printing of hourly environmental parameters on the psychrometric chart and for climate analysis, subsequently. The limitation and the scope of this method are also specified. The climates of three climatic regions in Vietnam have been used as case studies using all year, seasonal and monthly analysis. The results show that natural ventilation is an effective cooling solution as thermal comfort improvement varies with the climatic zones, increasing from 24.8% in Hanoi, 22.1% in Danang to 32.0% in Hochiminh city. Meanwhile, passive solar heating is only effective under the climate of Hanoi. Direct evaporative cooling also shows great cooling potential for comfort improvement but probable elevated humidity is not expected. Total possible comfort in a year of each location indicates that further climate modification methods are inevitable to achieve comfort during extreme weather conditions, especially in Hanoi.
In the current study, the relation between the psychrometry working upon the thermodynamic analysis of humid air and drying at a timber dryer was investigated. In order to bring the air to suitable drying conditions, an air conditioner unit was used and the mass change of the unit with energy was analyzed. In the psychrometric analysis of the timber dryer with a heat pump, the pine and poplar timber were used. The mass change in the timber was followed with a load cell. At the end of the analysis, the amounts of humidity vaporized and intensified at the timber after drying were compared. Depending on these values, 5.7 kg humidity was taken from the pine timber at the end of 50 h, and 12.5 kg from the poplar timber at the end of 70 h.
Blow-through (BT) and draw-through (DT) modes are the two common types of air handling unit (AHU) configurations that are prevalent in heating ventilation and air conditioning (HVAC) systems in existence. The arrangements of a supply fan and a cooling coil in these systems have advantages on each other in terms of cooling coil loads, moisture removal and noise levels. In the present work, a simple equipment load formulations for the two modes are shown, which may be used by designers for early diagnosis and decision making. From the comparison of derived loads for a cooling-dehumidifying chilled water coil, it is proved that DT type AHU shows higher cooling load than BT type, when supply air temperature from both these types of AHU is same. It is also seen that the difference between these coil-loads are actually affected by the AHU inlet condition and fan heat addition. An early choice between a DT and a BT system based on usage and requirement saves a lot of future hassles and untimely retrofits.
This study presents energy and exergy analyses and sustainability assessment of the novel evaporative air cooling system based on Maisotsenko cycle which allows the product fluid to be cooled in to a dew point temperature of the incoming air. In the energy analysis, Maisotsenko cycle’s wet-bulb and dew point effectiveness, COP and primary energy ratio rates are calculated. Exergy analysis of the system is then carried out for six reference temperatures ranging from 0°C to 23.88°C as the incoming air (surrounding) temperature. The specific flow exergy, exergy input, exergy output, exergy destruction, exergy loss, exergy efficiency, exergetic COP, primary exergy ratio and entropy generation rates are determined for various cases. Furthermore, sustainability assessment is obtained using sustainability index method. As a result, maximum exergy efficiency is found to be 19.14% for a reference temperature of 23.88°C where the optimum operation takes place.
A spreadsheet add-in for the psychrometric data at any barometric pressure and in the air-conditioning and drying temperatureranges was developed using appropriate correlations. It was then used to simulate and analyse air-conditioning and dryingprocesses in the Microsoft Excel environment by exploiting its spreadsheet and graphic potentials. The package allowsone to determine the properties of humid air at any desired state, and to simulate and analyse air-conditioning as well asdrying processes. This, as a teaching tool, evokes the intellectual curiosity of students and enhances their interest and abilityin the thermodynamics of humid-air processes.
This is a journal article [© American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org)]. Reprinted by permission from HVAC&R Research, Vol. 12, Part 3c. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE’s prior written permission. It is also available at: www.ashrae.org/hvacr-research This paper reports on the energy implications of HVAC system configuration by analyzing the energy balance and psychrometrics of typical and innovative systems. Three criteria were shown to be significant: (1) the ability to minimize outside air load, (2) the ability to eliminate simultaneous cooling and heating and use mixing effectively, and (3) the availability of interzonal airflow. Configurations that meet these criteria would be able to deliver the desired indoor air quality with reduced energy consumption. The performance of ten two-zone system configurations, including single-duct, dual-duct, fan-coil-based variations, and other specialized systems in the literature, were analyzed for a number of operational conditions. The results confirmed that fan-coil-based configurations with interzonal airflow paths perform better than other configurations. The conclusion of this study may be used as a guideline for multi-zone system designs.
This paper proposes the use of a cubic polynomial to evaluate the saturation vapor pressure (es) in order to transform the psychrometirc equation into a cubic equation in Tw (wet bulb temperature). This is done because it is not possible to write Tw as a direct function of dry bulb temperature (T), relative humidity (RH) and pressure (P). Statistical comparisons show that this polynomial is accurasier than other semi-empirical methods used to calculate es. Results of the third degree equation for Tw were compared with resultant values of an iterative method and they were satisfactory. -Author
Engineers use spreadsheet programs for calculations and graphing because of relatively easy-to-use embedded features. This paper describes a series of macros that use psychometric equations to compute moist air properties by entering the dry-bulb temperature, wet-bulb temperature (RH), and local elevation. The resulting spreadsheet is an electronic psychometric chart with the added benefit of being appropriate for any elevation.
Determination of the wet-bulb temperature at the surface of a material is the basis of one class of humidity measuring instruments, and is important in industrial applications such as dryer modelling and simulation. The psychrometer equation is a frequently used method of estimating wet-bulb temperature, and contains a psychrometer constant. Analysis shows that this is in fact a variable coefficient affected by temperature, pressure, radiation and conduction effects, and the identity of the gas and vapour. Radiation and conduction affect the difference between adiabatic saturation temperature and indicated wet-bulb temperature. Inconsistencies in currently recommended values for the psychrometer coefficient, including published international standards, are identified and explained. Particular problems arise when the enhancement factor is applied to vapour pressure to account for non-ideality of gases. Special considerations are also needed for wet-bulb temperatures approaching the boiling point, where the psychrometer coefficient tends to zero. Self-consistent recommendations recently published in the new British Standard BS1339 are given, which cover both the air-water system and a general vapour-gas system.
As part of a national program, NREL is currently characterizing the state-of-the-art in desiccant dehumidifiers, the key component of desiccant cooling systems. The experimental data will provide industry and end users with independent performance evaluation and assess the energy savings potential of the technology. Accurate determination of humidity ratio is critical to this work and an understanding of the capabilities of the available instrumentation is central to its proper application. This paper compares the minimum theoretical random error in humidity ratio calculation for three common measurement methods to give a sense of the relative maximum accuracy possible for each method assuming systematic errors can be made negligible. A series of experiments are also conducted to illustrate the capabilities of relative humidity sensors as compared to dewpoint sensors in measuring the grain depression of desiccant dehumidifiers. These tests support the results of the uncertainty analysis. At generally available instrument accuracies, uncertainty in calculated humidity ratio for dewpoint sensors is determined to be approximately constant at 2%, wet bulb sensors range between 2% and 6% above 10 g/kg (4%-15% below), and relative humidity sensors vary between 4% above 90% rh and 15% at 20% rh. Below 20% rh, uncertainty for rh sensors increases dramatically. Highest currently attainable accuracies bring dewpoint instruments down to 1% uncertainty, wet bulb to a range of 1%-3% above 10 g/kg (1.5%-8% below) and rh sensors between 1% and 5%.
In order to determine the efficiency and consumption of an evaporative cooler, which follows the Maisotsenko cycle, an experimental installation was constructed, able to provide multiple options of inlet conditions and supported by measurement systems. The degree to which it is possible to achieve the nominal efficiency levels as well as the effect of the ambient conditions on water consumption were examined, and it was discovered that under different conditions and in the optimization mode, the efficiency levels vary between 97% and 115%, while water consumption varies between 2.5 kgw kWhc−1 and 3.0 kgw kWhc−1. The experimental procedure and the measurement processing are analyzed in detail and finally, it is ascertained that Maisotsenko cycle based coolers can satisfy the cooling demand with high efficiency in the hot and arid Mediterranean climate.
With the change in the temperature scale of ITS-90, new temperature dependent equations were required which predict saturation vapor pressure over water and ice, enhancement factor over water and ice, frostpoint temperature, and dewpoint temperature. Internationally recognized formulas based on the previous temperature scale, viewed as self- consistent data sets for vapor pressures and enhancement factors, were chosen as initial defining equations. These formulas, coupled with those defining the temperature difference between the two scales, were used to compute new data sets consistent with the temperature scale of ITS-90. These new data sets were then fitted to equations of the original form, yielding new ITS-90 compatible coefficients to the familiar vapor pressure and enhancement factor equations. In addition, the resulting vapor pressure equations were used to produce a set of inverse approximating equations to yield frostpoint and dewpoint temperatures when the vapor pressure is known. The resulting coefficients, equations, and the conversion methods that produced them are presented.
As dehumidification is one of the most important tasks of environment control of the building, it is necessary to know the energy efficiency of dehumidification processes. The energy efficiency can give the energy cost of drawing moisture from indoor air to the outside environment. This paper presents analysis of the ideal cost of dehumidification process by a liquid desiccant cycle. Formulas to calculate ideal efficiency of dehumidification process are obtained, which is determined by indoor temperature, outdoor temperature, and the temperature of the intersection point of the iso-relative humidity line of indoor air and the iso-humidity ratio line of outdoor air. The ideal efficiency of the condensing dehumidification method is lower than the ideal dehumidification process, due to the fact that condensing dehumidification method must dehumidify the air at the temperature of dew point. Results from this paper can be used as theoretical foundation for the further analysis of various dehumidification methods and the development of new dehumidification processes.
Equations are presented which relate saturation vapor pressure to temperature for moist air. The equations are designed to be easily implemented on a calculator or computer and can be used to convert in either direction. They are more accurate than the commonly used Goff-Gratch equations for the meteorologically interesting region of 80 to +50°C. Equations also are given for the enhancement factor.
The paradigm shift in the design of building comfort control systems is in its early stages. This paper discusses the requirements of the new paradigm as well as the factors that will facilitate transition.
This report consists of world weather and climate extremes that have been extracted from various sources. The report contains discussions covering the measurement of various meteorological elements, measurement practices, and instrumentation. All extremes are presented in terms of their location and date and, where supportive information is available in the professional literature, detailed discussions of the extreme event are provided. The elements covered in this report include surface air temperature, precipitation (rainfall, snowfall and hail), wind, thunderstorms, air pressure, solar radiation, dew point temperature and fog. The report contains five maps. There is one each for the worldwide extremes of temperature, precipitation, and other elements. The remaining two maps show U.S. state extremes for monthly temperature (absolute maximum and absolute minimum) and precipitation (maximum monthly and maximum 24-hour).
a b s t r a c t In this paper, the most important energy and exergy characteristics of wind energy were examined. Atmospheric variables as air temperature, humidity and pressure and their effects on the wind turbine output were investigated toward wind energy exploitation. It was shown that these usually disregarded meteorological parameters while planning new WFs (Wind Farms), in fact, do play an important role in the farm's overall exergetic efficiency. The wind potential around a coastal mountainous area was studied based on field measurements. Understanding atmospheric parameters variation appears to be of great importance for estimating energy yield in rough terrain and in this paper special focus was given to that.
In textbooks of thermodynamics or air conditioning engineering we can find the psychrometric chart at atmospheric pressure. However, standard psychrometric charts cannot be used directly in those areas where urban elevations and barometric pressures are considerably different from those given on the charts. Based on the formulas suggested by ASHRAE, a generalized psychrometric chart for different pressures is constructed, using composite thermodynamic properties φ/p, pw/p, and vp. A nomograph is given to relate these composite thermodynamic properties to the psychrometric variables φ, pw, and v with p. Other commonly used psychrometric variables can be read directly from the generalized psychrometric chart. Three numerical examples illustrate the use of the generalized psychrometric chart. It will be of material help in both the design of air conditioning systems for different barometric pressures and the teaching of psychrometrics.
This research updates the modeling of moist air as a real gas mixture using the virial equation of state. It includes the Hyland and Wexler model (1983a, 1983b) and considers the Nelson-Sauer model (2002). All new National Institute of Standards and Technology reference equations and the latest International Association for the Properties of Water and Steam (IAPWS) standards, as well as the current values for the molar masses and gas constants, have been incorporated. The deviations of the proposed model to the Hyland-Wexler and Nelson-Sauer models are very low at ambient pressures but increase with increasing pressures and temperatures. The range of validity of the new model is in pressure from 0.01 kPa up to 10 MPa, in temperature from −143.15°C up to 350°C, and in humidity ratio from 0 kgw/kga up to 10 kgw/kga. This model was used to produce moist air and H2O saturation property tables for the psychrometric chapter in the 2009 ASHRAE Handbook—Fundamentals (ASHRAE 2009). The paper summarizes ASHRAE Research Project 1485 (RP-1485).
Simple and precise equations for calculation of saturation vapour pressure in three different temperature ranges are presented in the paper. Input parameters required for calculation of psychrometric properties are wet- and dry-bulb temperatures, dew point and dry-bulb temperatures and relative humidity and dry-bulb temperature. In this paper, the equations used for computing saturation vapour pressure may also be used for deter-mining dew point temperature for the entire pressure range. (C) 2002 Published by Elsevier Science Ltd.
Knowledge of the psychrometric properties is essential during the designing of air conditioning, cold storage, and drying processes where humid air is a working fluid. In this study detailed procedures for calculating psychrometric properties are given. Seven main properties of the psychrometrics, namely dry-bulb, wet-buld and dew-point temperatures, atmospheric pressure, humidity ratio, relative humidity and enthalpy can be calculated using the given procedures. According to the Gibbs Phase Rule, in the humid air case, any three intensive properties will be sufficient to evaluate the remaining properties. Therefore the combination of three out of seven properties gives a total of 35 different sets. Computer software has been developed and utilised to obtain the psychrometric properties of humid air. It was found that given three input parameters, the remaining four parameters could, except in three cases, can be calculated with negligible error.
Dew point evaporative cooling system is an alternative to vapor compression air conditioning system for sensible cooling of ventilation air. This paper presents the theoretical performance of a novel dew point evaporative cooling system operating under various inlet air conditions (covering dry, moderate and humid climate) and influence of major operating parameters (namely, velocity, system dimension and the ratio of working air to intake air). A model of the dew point evaporative cooling system has been developed to simulate the heat and mass transfer processes. The outlet air conditions and system effectiveness predicted by the model using numerical method for known inlet parameters have been validated with experimental findings and with recent literature. The model was used to optimize the system parameters and to investigate the system effectiveness operating under various inlet air conditions.
A solar-regenerated liquid desiccant ventilation pre-conditioning system has been proposed for use in hot and humid climates. The system aims to dehumidify the ventilation air which is the major source of latent load. A heat exchanger is used to cool the dehumidified air instead of typical evaporative cooling to maintain the dryness of the air. The use of solar energy at the regeneration process and cooling water from a cooling tower makes the system more passive. The simulation procedure for the proposed system has been presented. By inputting the climatic data and the physical parameters of all equipments, the operating parameters at each equipment and the performance parameters of the system can be evaluated. The simulation procedure is demonstrated by showing the daily profiles of the operating and performance parameters on a typical day as well as investigating the influence of the selected operating parameters on the system performance. The results suggest that the most influential parameters are solar radiation, ventilation rate, and desiccant solution concentration. The balance between the water removed at the dehumidifier and that evaporated at the regenerator needs to be considered to maintain uniform performance during continuous operation.
An effective prediction is proposed to estimate the optimal rotation speed and performance of a rotary adsorber, in which simultaneous enthalpy and humidity changes are dealt with separately by visualising changes of state of product or exhaust air on a psychrometric chart. Assuming that the adsorbent rotor is completely regenerated to equilibrium with the regeneration air during the corresponding period, the optimal rotation speed corresponds to the region of the short time adsorption in which penetration theory holds and enthalpy exchange between both streams through the adsorbent rotor follows the behaviour of a rotary sensible heat exchanger at lower revolution rates. The change of the product/exhaust air condition with increasing rotational speed is presented as a set of simple equations. Also, by considering the relative humidity of product air and that of regeneration air to be almost the same at a sufficiently high flow rates of regeneration air, an optimal rotation speed and the product air condition are easily found by simple calculation. In comparison with experiments, the proposed method gives a rotational speed near the “optimum” and the humidity and temperature of the product air are predicted almost exactly.
The building bioclimatic charts of Givoni are used to test whether passive downdraught evaporative cooling, in conjunction with night ventilation, might yield thermal comfort in an office building in Southern Europe. Dynamic thermal simulation indicated that the direct evaporative cooling boundary, proposed by Givoni, was an unreliable indicator of the climatic conditions for which comfort could be provided. New boundaries, defining the climatic limit of thermal comfort for direct evaporative cooling in offices, with differing levels of internal heat gain, are proposed. For each one, a band of climatic conditions, within which comfort is sometimes achieved and sometimes not, is also indicated.
Humidification dehumidification desalination process is viewed as a promising technique for small capacity production plants. The process has several attractive features, which includes operation at low temperature, ability to combine with sustainable energy sources, i.e., solar, geothermal, and requirements of low level of technical features. This paper evaluates the characteristics for several layouts for the humidification dehumidification desalination process. The common feature among these processes is the air humidification tower, where the humidity of the ambient air is increased to saturation at the desired design temperature. The main difference among various layouts is the dehumidification process. The most common scheme is to use a condenser to reduce the humidified air temperature and to condense the fresh water product. Other possible layouts includes vapor compression, desiccant air drying, and membrane air drying. The design equations are developed for the humidification/condenser and the humidification/desiccant systems. Discussion and performance evaluation of various layout shows the need to fully optimize these configurations. This is necessary to obtain the best design and operating conditions that give the minimum product cost.
Independent air dehumidification provides an attractive alternative to traditional coupled air dehumidification with reduced energy use, better humidity control and indoor air quality. According to this concept, latent load is treated by an independent system and the sensible load is treated by chilled-ceiling panels. In this work, four independent air dehumidification systems with energy recovery strategies are proposed. They are as follows: system 1, mechanical dehumidification with heat pump; system 2, mechanical dehumidification with sensible heat exchanger; system 3, mechanical dehumidification with membrane-based total heat exchanger; and system 4: a heat pump incorporating an active desiccant wheel and evaporative cooler. They are compared with a mechanical dehumidification system with no heat recovery. Hour-by-hour energy analysis is performed on the systems proposed. The results show that the system of mechanical dehumidification with membrane total heat recovery (system 3) consumes the least primary energy. However, since, the systems employ energy recovery measures, the energy savings for the four systems are in the same order, around 4.40×106 kJ per person.
A general expression based on the Claperon-Clausius differential equation that relates saturation vapor pressure, absolute temperature, and the latent heat of transformation was derived that expresses saturation vapor pressure as a function of absolute temperature. This expression was then used to derive general expressions for vapor pressure, absolute humidity, and relative humidity as functions of either dewpoint and ambient temperature or psychrometric parameters. Constants for all general expressions were then evaluated to give specific expressions in both the international system of units and U.S. customary units for temperatures above and below freezing.
Equations for the Determination of Humidity from Dew-point and Psychrometric Data, National Aeronautics and Space Administration
- O Parish
- T Puntam
O. Parish, T. Puntam, Equations for the Determination of Humidity from Dew-point and Psychrometric Data, National Aeronautics and Space Administration, Washington, DC, USA, 1977.
The Computation of Saturation Vapor Pressure, Environmental Prediction Research Facility (Navy)
- P Lowe
- J Ficke
P. Lowe, J. Ficke, The Computation of Saturation Vapor Pressure, Environmental
Prediction Research Facility (Navy), CA, USA, 1974.
Thermodynamic Properties of Dry Air, Moist Air and Water and SI Psychrometric Charts
- A Wexler
- R Hyland
A. Wexler, R. Hyland, Thermodynamic Properties of Dry Air, Moist Air and Water
and SI Psychrometric Charts, American Society of Heating, Refrigeration and Air
Conditioning Engineers, Inc., GA, USA, 1983.
Chapter 1-Psychrometrics, American Society of Heating, Refrigeration and Air Conditioning Engineers
- Ashrae Handbook-Fundamentals
ASHRAE Handbook-Fundamentals, Chapter 1-Psychrometrics, American
Society of Heating, Refrigeration and Air Conditioning Engineers, Inc., GA, USA,
2009.
Using the psychrometric chart in building measurements
- P Horan
- M Luther
P. Horan, M. Luther, Using the psychrometric chart in building measurements,
in: 44th Annual Conference of the Architectural Science Association (ANZAScA
2010), Unitec Institute of Technology, New Zealand, 2010.
Diurnal Cycle of High Absolute Humidity on Earth's Surface, Environmental Research Papers No. 416, Air Force Cambridge Research Laboratories
- H Samhela
- D Grantham
H. Samhela, D. Grantham, Diurnal Cycle of High Absolute Humidity on Earth's
Surface, Environmental Research Papers No. 416, Air Force Cambridge Research
Laboratories, Bedford, MA, USA, 1972.
Thermal Environmental Conditions for Human Occupancy, American Society of Heating, Refrigeration and Air Conditioning Engineers
- Ansi Ashrae
ANSI/ASHRAE Standard 55-2010, Thermal Environmental Conditions for
Human Occupancy, American Society of Heating, Refrigeration and Air Conditioning Engineers, Inc., GA, USA, 2010.
The ASHRAE Guide for Buildings in Hot and Humid Cli-mates American Society of Heating, Refrigeration and Air Conditioning Engineers
- L Harriman
- J Lstiburek
L. Harriman, J. Lstiburek, The ASHRAE Guide for Buildings in Hot and Humid Cli-mates, 2nd ed., American Society of Heating, Refrigeration and Air Conditioning Engineers, Inc., GA, USA, 2009.
Standard Method for Measurement of Moist Air Properties, American Society of Heating, Refrigeration and Air Conditioning Engineers
- Ansi Ashrae
- Standard
ANSI/ASHRAE Standard 41.6-1994, Standard Method for Measurement of Moist Air Properties, American Society of Heating, Refrigeration and Air Conditioning Engineers, Inc., GA, USA, 1994.
Method for Obtaining Wet-bulb Temperatures by Modifying the Psychrometric Formula, Center for Experiment Design and Data Analysis
- J Sullivan
- L Sanders
J. Sullivan, L. Sanders, Method for Obtaining Wet-bulb Temperatures by Modifying the Psychrometric Formula, Center for Experiment Design and Data
Analysis, Washington, DC, USA, 1974.
- W Wagner
- H Kretzschmar
W. Wagner, H. Kretzschmar, International Steam Tables, 2nd ed., Springer,
Berlin, Germany, 2008.
The ASHRAE Guide for Buildings in Hot and Humid Climates
- L Harriman
- J Lstiburek
L. Harriman, J. Lstiburek, The ASHRAE Guide for Buildings in Hot and Humid Climates, 2nd ed., American Society of Heating, Refrigeration and Air Conditioning
Engineers, Inc., GA, USA, 2009.