Psychrometric Chart Research Articles

Simulation of unsteady ice accretion on horizontal axis wind turbine blade sections in turbulent wind shear condition

This study presents a comprehensive simulation approach to quantify power losses in horizontal axis wind turbines under environmental icing conditions. It investigates how wind shear and turbulence affect a 2.5 MW wind turbine's performance, particularly under ice accretion. Turbulence intensity, ranging from 1% to 20%, impacts the relative flow fluctuations and angle of attack on the blade sections, influencing the aerodynamic penalty ratio. The incoming wind speed and the flow angle at various blade sections were determined using the unsteady blade element momentum method, considering vortex induction effects and Prandtl and Glauert corrections. For ice accretion analysis, a fully unsteady simulation of computational grid motion due to ice accretion was performed, along with the solution of the multiphase flow of water dispersed particles in cold air, derived from the psychrometric chart. The findings highlight the significant impact of the incoming turbulent wind fluctuations on the dispersion of the ice shape formed at sections corresponding to their radial position on the blade according to the momentary angle of attack fluctuations. The formation of ice profiles along the blade has led to a subsequent degradation in the aerodynamic efficiency of the blade sections, which is directly proportional to the escalation in turbulence intensity. This phenomenon leads to a continual reduction in the power output of the wind turbine. This research provides valuable insights into the performance of wind turbines under icing conditions in real wind fluctuations.

Primary return air or all fresh air? A novel method for air source designing of heat pump desiccant wheel systems

Hybrid desiccant wheel systems are widely adopted for low humidity control in industrial field. The clarification of process and regeneration air management is required to achieve energy saving. The all-fresh air dehumidification and primary return air dehumidification are compared for a high-polymer desiccant wheel and heat pump system. The system simulation model was established and validated by field test results of a low humidity industrial workshop. Firstly, the fresh air flowrate and air stream pattern are analyzed and optimized, for achieving low annual energy consumption. Secondly, the system power of the optimized fresh air mode and primary return air mode were compared for different outdoor air temperature, outdoor air humidity and indoor humidity requirement. At last, energy saving rate of all fresh air dehumidification mode was analyzed for five typical climate zones in China. It was found that the optimized fresh air flowrate numerically equals to the summation of regeneration air flowrate and the positive pressure required air flowrate. With the optimized fresh air flowrate, 20.4% of the annual energy can be saved compared with primary return air system. Outdoor air conditions were divided into three zones on psychrometric chart, and the boundaries are related to indoor temperature and humidity ratio. Fresh air is energy efficient for high temperature high humidity and low temperature low humidity conditions. By using fresh air dehumidification mode, the energy saving rate can reach 69.6% for severe cold region. Primary return air dehumidification mode is suitable for HSCW and HSWW region for indoor relative humidity of 40%, and 41.8% of the energy can be saved.

Only the Greenhouse Gas, Water Vapor, Measurably Warms the Earth

Data is available for the 61 greenhouse gases (GHGs) in Table 2.14 of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) to calculate their contribution to global warming in degrees Celsius. The procedure is described in the recently published study Reliable Physics Demand Revision of the IPCC Global Warming Potentials. In the current study, the contribution was calculated for each 61 GHG. The sum of the contributions of the 61 GHGs was 0.00833oC out of 26oC, which, for this example, is the difference in temperature between Pond Inlet and Amsterdam. This amount of temperature is too small to measure. Thus, with all other GHGs except water vapor eliminated as warming gases, water vapor is the only GHG that causes measurable warming of the Earth’s atmosphere. This is the exact result of the mathematical model of the Earth’s atmosphere developed in 1904 by Willis Carrier, i.e., the psychrometric chart, which is now a computer program, i.e., Humidair. Thus, the two methods used 120 years apart are robust and give the same result, confirming the unique role of water vapor in the temperature of Earth’s atmosphere and the virtually non-temperature role of the 61 GHGs.

Research on Relative Humidity and Energy Savings for Air-Conditioned Spaces without Humidity Control When Adopting Air-to-Air Total Heat Exchangers in Winter

In view of the problem that the exchange effectiveness is calculated according to a fixed value or only considering the influence of outdoor air parameters when analyzing the suitability of total heat recovery for plate heat recovery equipment in air-conditioned spaces without humidity control, the indoor humidity calculation model and moisture balance equation were established in this research to predict relative indoor humidity. Moreover, the relationship between total heat recovery, effective heat recovery, and the reduction in outdoor air heating load was analyzed using a psychrometric chart of the outdoor air treatment process. Referring to the standard for weather data of building energy efficiency in the Ningbo region, 6 typical days were taken as the calculation conditions. The moisture balance differential equation was solved using MATLAB software to obtain numerical solutions for the hourly indoor air humidity ratio, relative humidity, exchange effectiveness, and effective heat recovery when adopting an air-to-air total heat exchanger in an air-conditioned room of an office, classroom, or commercial building in the winter. The results indicate that, under the calculation conditions, the relative indoor humidity of commercial buildings is relatively high, making it unsuitable for a total heat exchanger. The relative humidity of indoor air in offices and classrooms can be maintained above 30%, and the total exchange effectiveness of a total heat exchanger is between 45% and 100%. The effective total heat recovery was calculated as sensible heat recovery under most calculation conditions.

Ventilation and air conditioning design approach based on ASHRAE psychrometric chart and Mollier diagram

Society needs long-term sustainability and healthy building projects, and indoor air quality assurance engineering systems play a pivotal role in the energy performance of buildings. Therefore, when designing heating, ventilation, and air conditioning systems, it is crucial to make the most technically sound decisions in terms of energy consumption and assess their impact on the building’s energy performance. This article delves into the design of ventilation and air conditioning systems, presenting a method for evaluating their performance. The foundation of project development is an agreement on the design criteria, which are developed based on a preliminary analysis of the building concept. This agreement ensures cohesive collaboration among all stakeholders: the client, the architect, the system designer, the contractor, and ultimately the personnel responsible for commissioning, operating, and maintaining the systems post-construction. We suggest conducting a comprehensive analysis of the processes occurring within the space without initially linking them to room air exchange. From this analysis, we derive the angular coefficient for the direction of the air condition change on both a psychrometric chart and a Mollier diagram. The process line on the psychrometric chart provides insights into how the performance factor of the air distribution system will influence the desired supply air parameters. We can then evaluate how significantly the gap between the supply air and the exhaust air parameters expands if the room’s air exchange volume is reduced for budgetary reasons. The article showcases this design methodology using a simplified case study.

A holistic approach for solar-driven HVAC evaporative cooling system: Comparative study of dry and wet channel

In HVAC, indirect evaporative cooling powered by renewable energy sources is the key factor for effectiveness with respect to thermal comfort, sustainability, exergy utilization, leading to a cooler and greener environment. In the cross-flow heat exchanger, the tubular wet channel is the main objective for analysis of 3E (exergy, economic, environmental) and sustainability, for dry and novel channels separately. In this research, both channels have been developed to evaluate exergy variations, sustainability, and specific total cost based on the influence of dead-state temperature, working air ratio, wet bulb depression, and the inlet flow parameters of working air. The results show that the wet channel's exergy efficiency is 18.8 % lower than that of the dry channel, and the exergy destruction of both channels is 0.08406 kW and 0.1311 kW, respectively. Moreover, the tubular wet channel demonstrates a significant economic advantage for cross-flow IEC device. The STC of the wet channel found to be 85.35 % higher, and value of sustainability was 25% lower than that of the dry channel. The values of annual emissions were found to be 4.09 kg/year for CO2, 0.304 kg/year for NOx, and 0.189 kg/year for SO2 for solar-drive device. A psychrometric chart has been drawn for thermal comfort assessment. The findings of the novel tubular channels have been presented in terms of sustainability, thermal comfort, and green energy solutions and the results of exergy variations have been compared with previous work in the literatures.

Capacity evaluation of mechanical dehumidification systems: A theoretical framework

Vapor compression cycle-based mechanical dehumidification systems are common and have undergone extensive research to augment their dehumidification capacity. Traditional methodologies typically validate these enhancements via experimentation or simulation. In contrast, this study leverages an analytical perspective, developing a theoretical framework to evaluate system capacity. This is achieved through the analysis of the dehumidifying heat exchanger's performance or the impact of the air state entering the heat exchanger. Analytical solutions specific to the finned-tube heat exchanger are derived, establishing evaluation criteria for two distinct cases. These cases are visually represented as dividing lines on the psychrometric chart, fostering a more direct understanding of how system capacity changes with the incoming air state. The soundness of this theoretical framework is confirmed through numerical simulations and experiments and is subsequently applied to analyze various modifications to the traditional mechanical dehumidification system. These include the Cromer cycle, heat pipe, air-to-air heat exchanger, and evaporative cooling. The feasibility of these modifications is explained, and their relative strengths and weaknesses in theory are compared. The proposed framework provides insights into existing technologies and has the potential to stimulate the conception of innovative designs.

Engaging in covariational reasoning when modelling a real phenomenon: the case of the psychrometric chart

AbstractThe mathematical modelling of a real-life phenomenon is an elaborated activity, and it often requires complex forms of covariational reasoning, such as second-order covariation. This study aims to characterize how students use several forms of covariational reasoning when modelling a real-life phenomenon. To achieve this research goal, it is proposed the analysis of a teaching experiment conducted in an 11th-grade classroom and focused on the mathematical modelling of the relationship between three quantities, temperature, absolute humidity, and relative humidity, which is mathematically represented in the psychrometric chart. The qualitative analysis was focused on covariational reasoning and the students’ processes of mathematical modelling of the real-life phenomenon under investigation. Findings from five representative episodes showed an interlacing of several forms of covariational reasoning, the emergence of qualitative, quantitative, and global characterizations of covariational reasoning, and three different roles of covariation throughout the various steps of the modelling activities. From an educational point of view, the modelling activities described here offer practical insights for the design of activities aimed at promoting the modelling of real-life phenomena through a covariational approach.

Performance analyses and optimization studies of desiccant wheel assisted atmospheric water harvesting system under global ambient conditions

A heat pump driven atmospheric water harvesting system, which can be operated under direct cooling mode and desiccant wheels assisted cooling mode, was proposed in this paper. Investigations were carried out to find out the optimal operation mode and operation parameters under different ambient conditions and daily water harvesting requirements. Optimization studies were firstly carried out on each operation mode to find the recommended operation parameters, namely evaporation temperature and daily operation hours, for different ambient conditions, daily water harvesting rate and maximum operating hours. Then, the optimal operation modes, which has lower daily power consumption under their own recommended operation parameters, were suggested on the psychrometric chart. The results showed that, for different combinations of daily water harvesting rate and maximum operating hours, there exist a critical humidity ratio and a critical relative humidity ratio for each case. When ambient air relative humidity and humidity are both higher than the critical values, it is recommended to use the direct cooling mode. Otherwise, the desiccant wheels assisted cooling mode should be used. Lastly, performances of the system in different climate zones were analyzed. Under the optimal operation mode, the annual average water harvesting efficiency was from 1.08 to 1.22 kg/kWh in Urumqi, from 1.50 to 1.78 kg/kWh in Beijing, and from 2.22 to 3.72 kg/kWh in Haikou, respectively, when daily water harvesting rate is from 50 to 200 kg/day and maximum operating hours is from 6 to 10 h.

Theoretical investigation of combining cooling tower and cooling coil with direct evaporative cooler

A theoretical study is developed to examine the feasibility of using the cooling tower and the cooling coil with the direct evaporative cooler in the highest summer temperature in Karbala/Iraq. This is due to the inability of the direct evaporative cooler in reducing the outside air temperature and efficiency reduction in the mechanical vapor compression systems despite its high electrical energy consumption at high temperatures. The water in the cooling tower is cooled to a temperature higher than the outdoor wet-bulb temperature by (3.9 ^circ C). The water then passes through the cooling coil where the outdoor air is pre-cooled through it, and the outdoor air temperature decreases by (17 ^circ C) without an increase in humidity. Then the pre-cooled air passes through the direct evaporative cooler where its temperature decreases by (10 ^circ C) and humidity increases. The temperature of the air leaving this combining system is reduced by (27 ^circ C). The results showed that the temperature of the air leaving this combining system is adequate and passes through the comfort zone in the psychrometric chart. The results presented that the cooling tower and the cooling coil alone were unable to reduce the air temperature to reach the comfort zone. A similar observation is noted with the direct evaporative cooler. Therefore, the combining system is considered a more effective alternative to the direct evaporative cooler, and its effectiveness reaches more than 100%. Additionally, it is clean, environmentally friendly, energy efficient, and does not add heat to the surrounding environment in comparison with mechanical vapor compression systems.

Multi-objective optimization of desiccant wheel via analytical model and genetic algorithm

The dehumidification performance and energy consumption of desiccant wheel are affected by many design parameters and operating variables. However, there are few researches concerning multi-objective optimization. Therefore, an optimal design framework combining analytical model, multi-objective optimization and decision-making is proposed. The model was based on the overall heat and mass balances, so the objective functions of the desiccant wheel were derived, and the constraints for the equilibrium of the adsorption and desorption were obtained. Then, the non-dominated sorting genetic algorithm II (NSGA-II) was employed to calculate the Pareto optimal front of the two-objective optimization, and the results were analyzed with psychrometric chart. This solution set includes not only the optimum one with the design method of psychrometric charts, but also includes other better solutions. From the Pareto solutions, the final optimal solution was obtained with the technique for order preference by similarity to ideal solution (TOPSIS) based on four criteria. With the final optimal parameters applied to existing example, the further improvements on the outlet process air humidity ratio and the dehumidification coefficient of performance were found.

Highway to the Comfort Zone: History of the Psychrometric Chart

The psychrometric chart is the most common data visualization technique for the designers of thermal comfort systems worldwide. From its humble roots as means of expressing the characteristics of air in building systems design, the use of the chart has grown to include the representation of the zones of human thermal comfort according to both conventional and adaptive models. In this paper, we present an extensive history of this development and the fallacies with representing comfort simply as a box that sometimes moves on the chart. The origins of the link between refrigeration control and comfort control are examined through archival reviews, examining the works of Carrier, Yagoglou, and their contemporaries in the context of modern comfort mischaracterizations. A clearer understanding of the mapping of comfort, control, and climate metrics with psychrometrics is reported, and a critique of the conflation is reported to increase awareness of the limitations of such treatment of these three critical domains.

Performance comparison and suitable climatic zones of three water-mediated evaporative cooling technologies

Evaporative cooling is an alternative cooling technology to conventional vapor-compression systems with lower energy use and pollution emissions. This paper presents theoretical performance comparison for three water-mediated evaporative coolers and provides a design guideline for choosing evaporative coolers under specific climates and operating boundary conditions. Theoretical solutions of counter-flow evaporative cooling are given and verified with maximum absolute and relative errors of 0.26 K and 1.23% respectively. The heat transfer coefficient of the combined heat and mass transfer is 2.72–4.95 times than the pure heat transfer process if there were no mass transfer. Climatic dividing lines of various technologies are affected by the design parameters of the system, dropping the psychrometric chart into different applicable climatic areas. The simulation results show that the climatic areas in psychometrics where indirect outperforms direct evaporative cooling will expand when increasing the air–water ratio and heat transfer coefficient, and climatic area of series indirect evaporative cooling shrinks when increasing temperature difference. The simplified selection method using such difference in merits is verified by case study, which can serve as a useful guideline for choosing the proper evaporative cooling technology for a wide range of geographical locations.

Experimental evaluation of a variable-stage open absorption heat pump system utilizing aqueous KCOOH solution as absorbent

Open absorption technology is a potential alternative for the heat recovery of flue gas, which is one of the main carriers for the low-grade waste heat. A variable-stage open absorption heat pump was proposed to work on wide working condition ranges by adjusting its equivalent stage through a low-pressure generator-absorber assembly. We have demonstrated that with LiBr/H2O as absorbent, the system could achieve COP of 1.2–2, corresponding to an equivalent stage of 1–4.6. In this paper, an experimental prototype was established, including a solution distribution regulation, which aimed to optimize the solution distribution ratio between the spraying solution in the absorber and circulation solution in the cycle and further to enhance the system performance. KCOOH/H2O was selected as the absorbent to overcome the challenges of crystallization and corrosion. Experimental results showed a COP of 1.17–1.85 and heat recovery rate of 48.7–89% with heat source temperature varied from 86 to110 °C and hot water delivery temperature varied from 55 to 70 °C. A simulation model based on the thermophysical properties of KCOOH/H2O had also been established to supplement experimental results with a wider range of external sources. Results showed that compared to LiBr/H2O system, KCOOH/H2O system had a larger working temperature range and higher heat recovery rate at the expense of a lower COP, i.e., 6–11% and 12–15% lower than that of LiBr/H2O system under SDR of 0.2 and 0.5 respectively. A wider concentration working range of KCOOH/H2O (56.4%-79.8%), temperature range of 50–95 °C, and relative humidity range of 10–100% had been simulated to obtain performance maps of VS-OAHP system in the form of psychrometric chart. This work provided guidance for the practical operation and efficiency improvement for low-grade waste heat recovery.

Study of the thermal comfort and the energy required to achieve it for housing modules in the environment of a high Andean rural area in Peru

This study mainly evaluates and analyzes the thermal comfort of the young inhabitants of Imata, a high Andean rural village located at 4500 m of altitude in southern Peru. Acceptable thermal comfort ranges are defined for the villagers, from face-to-face surveys and with a device implemented for this study, which allows recording the temperature, relative humidity, clothing, and the thermal sensation vote TSV (considering a five-point thermal sensation scale). The comfort ranges are determined from the mean and standard deviation of each set of TSV values. Four thermal comfort zones are proposed, which are plotted on the psychrometric chart. Further, two experimental housing modules (M1 and M2) are analyzed, which were built in Imata with passive solar heating strategies. The simulation of both modules with m2m software allows determining the indoor temperatures for the year 2019 and the comfort schedules inside the modules by considering the comfort ranges established in this study. Finally, the energy required to achieve thermal comfort inside M1 and M2 is estimated using the simplified method of the ISO 13790 Standard.

Performance analysis and operation strategy of a dual-evaporation temperature heat pump system for electric vehicles in winter

With increasingly serious environmental and energy issues, efficient and environmentally friendly electric vehicles have received more attention. However, the high heating and dehumidification energy consumption of their air conditioning system reduces their driving range in winter, giving passengers and drivers range anxiety. In this study, a dual-evaporation temperature heat pump system is proposed to reduce the energy consumption of electric vehicle air conditioning systems in winter, and a simulation model of the proposed system is developed. First, the volume ratio of the dual-cylinder compressor is optimized. Subsequently, the performance of the proposed system in various operation modes under different ambient conditions is compared. The results indicate an optimized volume ratio of 2.85, which is taken as the system’s design condition. The dual-evaporation temperature heating dehumidification mode shows superior performance compared with the conventional mode under typical winter conditions in three different climatic zones. Moreover, energy consumption can be reduced by reasonably controlling the operation mode based on ambient conditions. An operation strategy for the dual-evaporation temperature heat pump system in winter is proposed through the regional division of the psychrometric chart, and the energy-saving operation mode of the system is analyzed for different climate zones in China.

Experimental study of vacuum-based membrane dehumidifier for HVAC system: Parametric analysis and dehumidification performance

Vacuum-based membrane dehumidifiers (VMDs), an emerging air dehumidification technology, use selective membranes to remove moisture from humid air; these dehumidifiers have the potential to save energy and enhance thermodynamic efficiency through decoupled latent and sensible cooling. In this study, a prototype of a vacuum-based membrane dehumidifier at the scale of an air-conditioning system was developed, and its dehumidification characteristics were experimentally evaluated under various test conditions (i.e., air temperature, air humidity, air velocity, and pressure on the permeate side). Four indices were selected to examine the dehumidification performance of the system: the humidity ratio difference, moisture removal rate, dehumidification efficacy, and performance coefficient. The results revealed that the humidity ratio difference ranged 3.38–14.76 g/kg, moisture removal rate 0.16–1.09 kg/h, dehumidification effectiveness 35.4 %–82.7 %, and COP 0.16–0.86. In the parametric analysis of the prototype, the airflow rate and humidity ratio are identified as essential parameters for the dehumidification performance. Moreover, the thermodynamic perspective in the Psychrometric chart and transient operation were utilized to evaluate the operational characteristics of the prototype unit. All experimental results showed that the difference in temperature between the inlet and outlet air was less than 1.5 °C, and the saturation time is shown to be within 5 min.

Bioclimatic Design of Low-Cost Rural Dwellings

Bioclimatic design is a crucial strategy to achieving the eco-friendliness, human-friendliness, and energy-friendliness of the built environment. The building patterns, materials, innovation, and use depend on the inhabitant’s choices, lifestyle, and economic viability. The study focused on examining bioclimatic components of low-cost dwellings in rural coastal environments in eastern India. A survey questionnaire administered to about 1,300 respondents from 15 villages (classified as remote rural, rural, and semi-urban) yielded their perception of different dwelling environment issues. The statistical analysis of bioclimatic dimensions indicated a significant difference among the dwellings. The low-cost mud houses of the remote rural and rural areas in coastal regions often follow local practices. Besides, different dimensions covered in the survey provided insights for the comparative evaluation of different categories of dwelling units. Principal component analysis (PCA) identified the clusters and component structures of the built environment characteristics provided from the response of the villagers as their perception of the dwellings. PCA yielded three components—1) interior design (PC1, building form, partitioning of rooms, type and materials of the wall, roof and window), 2) innovation of the built environment (PC2, building envelope, insulation, and sanitation facilities), and 3) natural ventilation priority (PC3, window design, window opening, and glaze material), which together explained 69% of the total variance. The psychrometric chart provided in identifies passive design strategies in constructing dwellings to improve residents’ yearly total thermal comfort hours in hot and humid regions. The relative contributions to thermal comfort hours are sun shading of windows (25.5%), a passive solar direct gain high mass (6.2%), a passive solar direct gain low mass (0.4%), and a high thermal mass, including night flush (4.3%), direct and two-stage evaporative cooling (4.3%), and natural ventilation and fan-forced ventilation cooling (2.2%).

Anti-frosting operation and regulation technology of air-water dual-source heat pump evaporator

In this study, a dual-source heat pump evaporator was designed using hot water and air as the heat sources. The hot water coil and the refrigerant coil in the evaporator were arranged in sequence along the air flow direction. The air temperature, relative humidity and velocity at the evaporator inlet, and evaporator hot water temperature were taken as the input parameters. The heat and mass transfer model of the dual-source evaporator was established. Based on the 90% relative humidity(RH) line of the psychrometric chart, the relationship between the refrigerant evaporation temperature and the air absolute humidity ratio under the critical frosting condition of the evaporator was fitted. In the cold season, the evaporator anti-frosting performance under the dual-source condition was tested experimentally and simulated. The results showed that the experimentally determined evaporator temperature was in good agreement with the simulated values. Besides, increasing the evaporator hot water temperature or inlet air velocity enabled one to improve the evaporator fin surface temperature. In particular, when the evaporator working temperature rose above the critical frosting temperature, the anti-frosting operation of the evaporator in winter could be achieved. If the ambient temperature was below 0 °C, the anti-frosting was provided by adjusting the refrigerant evaporation temperature.

A graphical method for assessing the effectiveness of evaporative cooling in naturally ventilated dairy barns

Preventing and alleviating heat stress remain an enormous challenge in dairy farming. Although enhanced air distribution techniques have been developed and deployed in many barns, ventilation alone is no longer sufficient even in regions with historically mild climates. There is an increasing need for cooling of the intake fresh air. Evaporative cooling is a cost-effective sustainable technique used in many applications, including livestock farming. This paper presents a graphical method for preliminary evaluation of evaporative cooling as a viable and effective solution. Thermodynamic principles are combined with models for heat transfer in dairy cattle to develop a set of criteria on the psychrometric chart. The proposed method is demonstrated for a naturally ventilated dairy barn located in the continental central European climate and in two locations with hot climates, a semi-arid/Mediterranean and a humid subtropical climate. • Thermoregulation models combined with thermodynamic principles. • Limits for effectiveness of evaporative cooling derived. • Developed criteria mapped onto psychrometric chart. • A graphical method to assess effectiveness of evaporative cooling proposed. • Proposed method demonstrated for sample barn in Europe.