scholarly journals Computational Modeling of the Thermal Behavior of a Greenhouse

2021 ◽  
Vol 11 (24) ◽  
pp. 11816
Author(s):  
Bruno Lebre ◽  
Pedro D. Silva ◽  
Luís C. Pires ◽  
Pedro D. Gaspar
Keyword(s):  
Thermal Behavior ◽  
Air Temperature ◽  
Agricultural Sector ◽  
Computational Simulation ◽  
Double Cover ◽  
Operating Conditions ◽  
Weather Data ◽  
Thermal Mass ◽  
Airflow Rate ◽  
The North

The need for production of all kinds of crops in high quantities and over the entire year makes the agricultural sector one of the major energy consumers. The optimization of this consumption is essential to guarantee its sustainability. The implementation of greenhouses is a strategy that allows assurance of production needs and possesses large optimization potential for the process. This article studies different greenhouse structures by computational simulation using EnergyPlus and DesignBuilder. First, a comparison was performed between the computational results and the measured values from a greenhouse prototype at different operating conditions. Overall, the comparison shows that the computational tool can provide a reasonable prediction of the greenhouse thermal behavior, depending on the differences between the weather data modeled and observed. An outdoor air temperature difference of 16 °C can cause a difference of about 10 °C between the air temperature predicted and measured inside the greenhouse. Subsequently, a selected set of case studies was developed in order to quantify their influence on the thermal performance of the greenhouse, namely: the greenhouse configuration and orientation; the variation of indoor air renewal; changes to the characteristics of the roof; the effect of the thermal mass of the walls; and location of the greenhouse. The results show that a correct greenhouse orientation, together with a polyethylene double cover with a 13 mm air layer, a granite wall of 40 cm thickness on the north wall, and variable airflow rate, may lead to a reduction of the greenhouse energy consumption by 57%, if the greenhouse is located in Lisbon, or by 43%, if it is located in Ostersund, during the hottest months of the heating season.

A Gray-Box Based Virtual SCFM Meter in Rooftop Air-Conditioning Units

2011 ◽  
Vol 3 (1) ◽  
Author(s):  
Daihong Yu ◽  
Haorong Li ◽  
Yuebin Yu
Keyword(s):  
Real Time ◽  
Air Temperature ◽  
First Principles ◽  
Air Conditioning ◽  
Low Cost ◽  
Fault Detection And Diagnosis ◽  
Operating Conditions ◽  
Airflow Rate ◽  
Fault Diagnostics ◽  
True Value

Knowledge of supply airflow rate (SCFM) measurement in packaged rooftop air-conditioning units (RTUs) is vital for improving energy management and indoor air quality and facilitating real-time automated control and fault detection and diagnosis. Despite the importance of SCFM measurement in RTUs, the conventional SCFM metering devices are very vulnerable. The credibility of SCFM measurement would be compromised dramatically after a long-term use in adverse duct work surroundings. Moreover, application of conventional SCFM meters in RTUs is very costly in regard to procurement, installation, and periodic maintenance. A cost-effective and accurate nonconventional first principles based SCFM meter in RTUs was proposed previously to virtually monitor SCFM measurement. In order to overcome the deficiencies of the first principles based virtual SCFM meter in model implementation and fault diagnostics, experiments with a wider combination and coverage are investigated in this study. It is found that a gray-box based virtual SCFM meter can be obtained with available system information (outside air damper status) and low-cost temperature measurements (direct measurement of a manufacturer-installed supply air temperature sensor (SATmfr,meas) and outside air temperature). Further experiment evaluations demonstrate that the gray-box based virtual SCFM meter could predict the true value of SCFM very accurately (the uncertainty is ±5.9%) with significantly enhanced applicability in model implementation and capability in fault diagnostics. Additionally, the gray-box based virtual SCFM meter also inherits good characteristics of the first principles based virtual SCFM meter, such as high cost-effectiveness, good robustness against variations in multivariable operating conditions, and applicability to similar RTUs. This innovative virtual meter could serve as a permanent monitoring tool to indicate real-time SCFM measurement and/or to automatically detect and diagnose an improper quantity of SCFM for RTUs.

The Effect of Thermal Mass on Thermal Transmission Loads

2007 ◽  
Author(s):  
Robert B. Gilbert ◽  
Kelly Kissock
Keyword(s):  
Air Temperature ◽  
Thermal Load ◽  
Weather Conditions ◽  
Weather Data ◽  
Thermal Mass ◽  
Load Reduction ◽  
Difference Model ◽  
Data Files ◽  
The Mean ◽  
Sinusoidal Function

A finite-difference model is used to simulate the effects of thermal mass on thermal load. A sinusoidal function is used to simulate the exterior air temperature. The interior air temperature set point remains constant. The mechanism by which thermal mass affects thermal load is described. Equations are given to calculate thermal load as a function of the exterior air temperature amplitude, the temperature above and below the mean temperature. Equations are given to calculate the minimum thermal load resulting from thermal mass and therefore the maximum thermal load reduction with thermal mass. Equations and methods are given to calculate the minimum thermal load resulting from thermal mass from weather data files, TMY or TMY2 files. A design equation is given as a guideline to determine the amount of thermal mass required to reduce the thermal load with given weather conditions.

Effects of Air Temperature on Combustion Characteristics of LPG Diffusion Flame

2020 ◽  
Vol 1008 ◽  
pp. 128-138
Author(s):  
Ahmed M. Salman ◽  
Ibrahim A. Ibrahim ◽  
Hamada M. Gad ◽  
Tharwat M. Farag
Keyword(s):  
Air Temperature ◽  
Diffusion Flame ◽  
Nitrogen Addition ◽  
Flame Length ◽  
Combustion Characteristics ◽  
Operating Conditions ◽  
Low Oxygen ◽  
Air Temperatures ◽  
Air Stream ◽  
Wide Range

In the present study, the combustion characteristics of LPG gaseous fuel diffusion flame at elevated air temperatures were experimentally investigated. An experimental test rig was manufactured to examine a wide range of operating conditions. The investigated parameters are the air temperatures of 300, 350, 400, 450, and 500 K with constant percentage of nitrogen addition in combustion air stream of 5 % to give low oxygen concentration of 18.3 % by mass at constant air swirl number, air to fuel mass ratio, and thermal load of 1.5, 30, and 23 kW, respectively. The gaseous combustion characteristics were represented as axial and radial temperatures distributions, temperatures gradient, visible flame length and species concentrations. The results indicated that as the air temperature increased, the chemical reaction rate increased and flame volume decreased, the combustion time reduced leading to a reduction in flame length. The NO concentration reaches its maximum values near the location of the maximum centerline axial temperature. Increasing the combustion air temperature by 200 K, the NO consequently O2 concentrations are increased by about % 355 and 20 % respectively, while CO2 and CO concentrations are decreased by about % 21 and 99 % respectively, at the combustor end.

The Strength Analysis of Francis Turbine Runner Based on the Fluid-Solid Coupling

2014 ◽  
Vol 709 ◽  
pp. 41-45
Author(s):  
Kan Kan ◽  
Yuan Zheng ◽  
Xin Zhang ◽  
Bin Sun ◽  
Hui Wen Liu
Keyword(s):  
Water Pressure ◽  
Eastern China ◽  
Static Stress ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Strength Analysis ◽  
Maximum Deformation ◽  
The North ◽  
North Eastern ◽  
Turbine Runner

This paper does unidirectional fluid-solid coupling calculation on the runner strength under three designed head loading conditions of a certain Francis turbine in the north-eastern China. The water pressure on the blade in the flow fields of different operating conditions is calculated by means of CFD software CFX. With the help of ansys workbench, the water pressure is loaded to the blade as structural load to conclude the static stress distribution and deformation of the runner under different operating conditions. The results show that the maximum static stress increases with the rise of the flow and appears near the influent side of the blade connected to the runner crown; the maximum deformation increases with the rise of the flow and appears on the band. The results provides effective basis for the structural design and safe operation of the Francis turbine.

scholarly journals Air Temperature Model Evaluation in the North Mediterranean Belt Area

2002 ◽  
Vol 41 (8) ◽  
pp. 872-884 ◽  
Author(s):  
Julia Bilbao ◽  
Argimiro H. de Miguel ◽  
Harry D. Kambezidis
Keyword(s):  
Air Temperature ◽  
Model Evaluation ◽  
Temperature Model ◽  
The North

scholarly journals Dewpoint Temperature Prediction Using Artificial Neural Networks

2008 ◽  
Vol 47 (6) ◽  
pp. 1757-1769 ◽  
Author(s):  
D. B. Shank ◽  
G. Hoogenboom ◽  
R. W. McClendon
Keyword(s):  
Neural Networks ◽  
Artificial Neural Networks ◽  
Air Temperature ◽  
Heat Waves ◽  
Weather Data ◽  
Temperature Prediction ◽  
Related Data ◽  
Dewpoint Temperature ◽  
Artificial Neural ◽  
Selection Of

Abstract Dewpoint temperature, the temperature at which water vapor in the air will condense into liquid, can be useful in estimating frost, fog, snow, dew, evapotranspiration, and other meteorological variables. The goal of this study was to use artificial neural networks (ANNs) to predict dewpoint temperature from 1 to 12 h ahead using prior weather data as inputs. This study explores using three-layer backpropagation ANNs and weather data combined for three years from 20 locations in Georgia, United States, to develop general models for dewpoint temperature prediction anywhere within Georgia. Specific objectives included the selection of the important weather-related inputs, the setting of ANN parameters, and the selection of the duration of prior input data. An iterative search found that, in addition to dewpoint temperature, important weather-related ANN inputs included relative humidity, solar radiation, air temperature, wind speed, and vapor pressure. Experiments also showed that the best models included 60 nodes in the ANN hidden layer, a ±0.15 initial range for the ANN weights, a 0.35 ANN learning rate, and a duration of prior weather-related data used as inputs ranging from 6 to 30 h based on the lead time. The evaluation of the final models with weather data from 20 separate locations and for a different year showed that the 1-, 4-, 8-, and 12-h predictions had mean absolute errors (MAEs) of 0.550°, 1.234°, 1.799°, and 2.280°C, respectively. These final models predicted dewpoint temperature adequately using previously unseen weather data, including difficult freeze and heat stress extremes. These predictions are useful for decisions in agriculture because dewpoint temperature along with air temperature affects the intensity of freezes and heat waves, which can damage crops, equipment, and structures and can cause injury or death to animals and humans.

scholarly journals Potential of Thermal Energy Storage Using Coconut Oil for Air Temperature Control

Buildings ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 95 ◽  
Author(s):  
Surjamanto Wonorahardjo ◽  
Inge Sutjahja ◽  
Daniel Kurnia ◽  
Zulfikar Fahmi ◽  
Widya Putri
Keyword(s):  
Energy Storage ◽  
Air Temperature ◽  
Temperature Control ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Coconut Oil ◽  
Control Agent ◽  
Thermal Mass ◽  
Air Cooling ◽  
Thermal Chamber

The role of thermal mass in indoor air-cooling during the day is a common area of study, which is particularly relevant for an era characterized by energy crises. Thermal energy storage (TES) technologies for application in rooms and buildings are not well developed. This study focuses on the use of coconut oil (co_oil) as a temperature control agent for room air conditioning systems in tropical countries such as Indonesia, given its capability to store large amounts of heat at temperatures around its melting point. Heat exchange studies between co_oil and the air environment were performed by considering three factors: Temperature difference between co_oil and the air environment, the heat absorption behavior and the release of co_oil, and the mass of co_oil required to have a significant effect. The co_oil cell sizes were formulated as responses to natural day and night air temperature profiles, while the performance of the co_oil mass for decreasing room air temperature was predicted using a thermal chamber.

scholarly journals A review of airflow rate estimation techniques for natural ventilation in buildings

2021 ◽  
Author(s):  
Miguel Chen Austin ◽  
Dafni Mora ◽  
Denis Bruneau ◽  
Alain Sempey
Keyword(s):  
Thermal Behavior ◽  
Pressure Difference ◽  
Natural Ventilation ◽  
Airflow Rate ◽  
Empirical Equations ◽  
Friction Characteristics ◽  
Estimation Techniques ◽  
Thermal Buoyancy ◽  
Modeling Techniques

As natural ventilation involves local and global interactions, the estimation of these interactions can be performed by many approaches. Such approaches, rather more experimental and numerical than analytical, often require a great deal of instrumentation and equipment, which results in higher demands on project budget and funding.  The present work is devoted to comprehending the natural ventilation concept, and to assess the existing experimental techniques already implemented for past researchers in the estimation of the ventilation airflow rate due to the wind and thermal buoyancy effects. A brief review of modeling techniques is also presented. This will provide a strong theoretical grasp of the natural ventilation process as part of the main elements in the thermal behavior of buildings. Ultimately, these bases are intended to help choose the most suitable techniques to estimate the natural ventilation airflow rate. The adequate benefit-to-budget technique appears to be the airtightness tests (blower door tests), since empirical Equations relating the airflow directly to the pressure difference in the building for both cases: infiltrations (openings closed) and openings opened, can be obtained.  Also, the location of the leakages can be identified without complications, and this technique has the potential to estimate in situ the airflow capacity and friction characteristics of the openings.

scholarly journals Thermal behavior of premises equipped with different alveolar structures

2015 ◽  
Vol 19 (3) ◽  
pp. 929-938
Author(s):  
Nour Lajimi ◽  
Noureddine Boukadida
Keyword(s):  
Heat Transfer ◽  
Thermal Behavior ◽  
Air Temperature ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Point Temperature ◽  
Set Point ◽  
Alveolar Structure ◽  
Vertical Walls

This paper presents a numerical study of local thermal behavior. Vertical walls are equipped with alveolar structure and/or simple glazing in East, South and West frontages. Local temperature is assumed to be variable with time or imposed at set point temperature. Results principally show that the simple glazing number has a sensitive effect on convection heat transfer and interior air temperature. They also show that the diode effect is more sensitive in winter. The effect of alveolar structure and simple glazing on the power heating in case with set point temperature is also brought out.

scholarly journals 2D Numerical Simulation Study of Airfoil Performance

2021 ◽  
Author(s):  
Nasser Shelil
Keyword(s):  
Experimental Data ◽  
Wind Tunnel ◽  
Air Temperature ◽  
Wind Turbines ◽  
Aerodynamic Force ◽  
Angle Of Attack ◽  
Turbulence Models ◽  
Aerodynamic Characteristics ◽  
Operating Conditions ◽  
Ansys Fluent

Abstract. The aerodynamic characteristics of DTU-LN221 airfoil is studied. ANSYS Fluent is used to simulate the airfoil performance with seven different turbulence models. The simulation results for the airfoil with different turbulence models are compared with the wind tunnel experimental data performed under the same operating conditions. It is found that there is a good agreement between the computational fluid dynamics (CFD) predicted aerodynamic force coefficients with wind tunnel experimental data especially with angle of attack between −5° to 10°. RSM is chosen to investigate the flow field structure and the surface pressure coefficients under different angle of attack between −5° to 10°. Also the effect of changing air temperature, velocity and turbulence intensity on lift and drag coefficients/forces are examined. The results show that it is recommended to operate the wind turbines airfoil at low air temperature and high velocity to enhance the performance of the wind turbines.

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