scholarly journals Application of Semi-Empirical Ventilation Models in A Mediterranean Greenhouse with Opposing Thermal and Wind Effects. Use of Non-Constant Cd (Pressure Drop Coefficient Through the Vents) and Cw (Wind Effect Coefficient)

Agronomy ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 736 ◽  
Author(s):  
López-Martínez ◽  
Molina-Aiz ◽  
Valera-Martínez ◽  
López-Martínez ◽  
Peña-Fernández ◽  
...  
Keyword(s):  
Thermal Effects ◽  
Natural Ventilation ◽  
Discharge Coefficient ◽  
Ventilation Rate ◽  
Wind Effect ◽  
Wind Effects ◽  
Bernoulli’S Equation ◽  
Pressure Fields ◽  
Order Polynomial ◽  
Semi Empirical

The present work analyses the natural ventilation of a multi-span greenhouse with one roof vent and two side vents by means of sonic anemometry. Opening the roof vent to windward, one side vent to leeward, and the other side vents to windward (this last vent obstructed by another greenhouse), causes opposing thermal GT (m3 s−1) and wind effects Gw (m3 s−1), as outside air entering the greenhouse through the roof vent circulates downward, contrary to natural convection due to the thermal effect. In our case, the ventilation rate RM (h−1) in a naturally ventilated greenhouse fits a second order polynomial with wind velocity uo (RM = 0.37 uo2 + 0.03 uo + 0.75; R2 = 0.99). The opposing wind and thermal effects mean that ventilation models based on Bernoulli’s equation must be modified in order to add or subtract their effects accordingly—Model 1, in which the flow is driven by the sum of two independent pressure fields GM1=GT2±Gw2, or Model 2, in which the flow is driven by the sum of two independent fluxes GM2=GT±Gw. A linear relationship has been obtained, which allows us to estimate the discharge coefficient of the side vents (CdVS) and roof vent (CdWR) as a function of uo [CdVS = 0.028 uo + 0.028 (R2 = 0.92); CdWR = 0.036 uo + 0.040 (R2 = 0.96)]. The wind effect coefficient Cw was determined by applying models M1 and M2 proved not to remain constant for the different experiments, but varied according to the ratio uo/∆Tio0.5 or δ [CwM1 = exp(-2.693 + 1.160/δ) (R2 = 0.94); CwM2 = exp(−2.128 + 1.264/δ) (R2 = 0.98)].

scholarly journals A Grey Box Modeling Method for Fast Predicting Buoyancy-Driven Natural Ventilation Rates through Multi-Opening Atriums

2019 ◽  
Vol 11 (12) ◽  
pp. 3239 ◽  
Author(s):  
Peng Xue ◽  
Zhengtao Ai ◽  
Dongjin Cui ◽  
Wei Wang
Keyword(s):  
Natural Ventilation ◽  
Simulated Data ◽  
Ventilation Rate ◽  
Modeling Method ◽  
Predictive Equation ◽  
Evaluation Time ◽  
Ventilation Performance ◽  
Ventilation Rates ◽  
Semi Empirical ◽  
Key Parameter

The utilization of buoyancy-driven natural ventilation in atrium buildings during transitional seasons helps create a healthy and comfortable indoor environment by bringing fresh air indoors. Among other factors, the air flow rate is a key parameter determining the ventilation performance of an atrium. In this study, a grey box modeling method is proposed and a prediction model is built for calculating the buoyancy-driven ventilation rate using three openings. This model developed from Bruce’s neutral height-based formulation and conservation laws is supported with a theoretical structure and determined with 7 independent variables and 4 integrated parameters. The integrated parameters could be estimated from a set of simulated data and in the results, the error of the semi-empirical predictive equation derived from CFD (computational fluid dynamics) simulated data is controlled within 10%, which indicates that a reliable predictive equation could be established with a rather small dataset. This modeling method has been validated with CFD simulated data, and it can be applied extensively to similar buildings for designing an expected ventilation rate. The simplicity of this grey box modeling should save the evaluation time for new cases and help designers to estimate the ventilation performance and choose building optimal opening designs.

scholarly journals Alternative Method to the Replication of Wind Effects into the Buildings Thermal Simulation

Buildings ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 237
Author(s):  
Aiman Albatayneh ◽  
Dariusz Alterman ◽  
Adrian Page ◽  
Behdad Moghtaderi
Keyword(s):  
Air Temperature ◽  
High Performance ◽  
Real Data ◽  
Wind Effect ◽  
Wind Effects ◽  
Energy Assessment ◽  
Wind Simulation ◽  
Brick Veneer ◽  
Equal Capacity ◽  
Simulation Time

To design energy-efficient buildings, energy assessment programs need to be developed for determining the inside air temperature, so that thermal comfort of the occupant can be sustained. The internal temperatures could be calculated through computational fluid dynamics (CFD) analysis; however, miniscule time steps (seconds and milliseconds) are used by a long-term simulation (i.e., weeks, months) that require excessive time for computing wind effects results even for high-performance personal computers. This paper examines a new method, wherein the wind effect surrounding the buildings is integrated with the external air temperature to facilitate wind simulation in building analysis over long periods. This was done with the help of an equivalent temperature (known as Tnatural), where the convection heat loss is produced in an equal capacity by this air temperature and by the built-in wind effects. Subsequently, this new external air temperature Tnatural can be used to calculate the internal air temperature. Upon inclusion of wind effects, above 90% of the results were found to be within 0–3 °C of the perceived temperatures compared to the real data (99% for insulated cavity brick (InsCB), 91% for cavity brick (CB), 93% for insulated reverse brick veneer (InsRBV) and 94% for insulated brick veneer (InsBV) modules). However, a decline of 83–88% was observed in the results after ignoring the wind effects. Hence, the presence of wind effects holds greater importance in correct simulation of the thermal performance of the modules. Moreover, the simulation time will expectedly reduce to below 1% of the original simulation time.

scholarly journals Proposing Alternative Solutions to Enhance Natural Ventilation Rates in Residential Buildings in the Cfa Climate Zone of Rasht

2021 ◽  
Vol 13 (2) ◽  
pp. 679
Author(s):  
Roya Aeinehvand ◽  
Amiraslan Darvish ◽  
Abdollah Baghaei Daemei ◽  
Shima Barati ◽  
Asma Jamali ◽  
...  
Keyword(s):  
Natural Ventilation ◽  
Residential Buildings ◽  
Residential Building ◽  
Ventilation Rate ◽  
Humid Climate ◽  
The Sustainable Development ◽  
Passive Strategies ◽  
Development Goals ◽  
Ventilation Rates ◽  
Ventilation Systems

Today, renewable resources and the crucial role of passive strategies in energy efficiency in the building sector toward the sustainable development goals are more indispensable than ever. Natural ventilation has traditionally been considered as one of the most fundamental techniques to decrease energy usage by building dwellers and designers. The main purpose of the present study is to enhance the natural ventilation rates in an existing six-story residential building situated in the humid climate of Rasht during the summertime. On this basis, two types of ventilation systems, the Double-Skin Facade Twin Face System (DSF-TFS) and Single-Sided Wind Tower (SSWT), were simulated through DesignBuilder version 4.5. Then, two types of additional ventilation systems were proposed in order to accelerate the airflow, including four-sided as well as multi-opening wind towers. The wind foldable directions were at about 45 degrees (northwest to southeast). The simulation results show that SSWT could have a better performance than the aforementioned systems by about 38%. Therefore, the multi-opening system was able to enhance the ventilation rate by approximately 10% during the summertime.

Natural-Ventilation Flow in a 3-D Room Fitted With Solar Chimney

2012 ◽  
Author(s):  
B. P. Huynh
Keyword(s):  
Heat Flux ◽  
Flow Pattern ◽  
Natural Ventilation ◽  
Air Flow ◽  
Ventilation Rate ◽  
High Heat Flux ◽  
Solar Chimney ◽  
Solar Heat ◽  
Solar Heat Flux ◽  
Inlet Opening

Natural-ventilation flow induced in a real-sized rectangular-box room fitted with a solar chimney on its roof is investigated numerically, using a commercial CFD (Computational Fluid Dynamics) software package. The chimney in turn is in the form of a parallel channel with one plate being subjected to uniform solar heat flux. Ventilation rate and air-flow pattern through the room are considered in terms of the heat flux for two different locations of the room’s inlet opening. Chien’s turbulence model of low-Reynolds-number K-ε is used in a Reynolds-Averaged Navier-Stokes (RANS) formulation. It is found that ventilation flow rate increases quickly with solar heat flux when this flux is low, but more gradually at higher flux. At low heat flux, ventilation rate is not significantly affected by location of the inlet opening to the room. On the other hand, at high heat flux, ventilation rate varies substantially with the opening’s location. Location of the inlet opening to the room also affects strongly the air-flow pattern. In any case, ample ventilation rate is readily induced by the chimney.

Determination of Discharge Coefficient for Ball Valves With Calibrated Inserts

2004 ◽  
Author(s):  
Gino James Rouss ◽  
William S. Janna
Keyword(s):  
Discharge Coefficient ◽  
Polynomial Equation ◽  
The Body ◽  
Orifice Diameter ◽  
Flow Parameters ◽  
Dimensionless Groups ◽  
Order Polynomial ◽  
Experimental Process ◽  
Power Law Equation

The valve coefficient was measured for 1, 1-1/4, 1-1/2 and 2 nominal ball valves. A recently designed orifice insert was used with these valves to obtain smaller valve coefficients. Orifice inserts were threaded into the body of a ball valve just upstream of the ball itself. The valve coefficient was measured for every insert used with these valves, and an expression was determined to relate the orifice diameter to other pertinent flow parameters. Two dimensionless groups were chosen to correlate the collected data, and expressions were developed that can be used as aids in sizing the orifice insert needed to obtain the desired valve coefficient. The study has shown that a 2nd order polynomial equation as well as a power law equation can both be used to predict the desired results. Knowing pipe size and schedule, the diameter of the orifice insert needed to obtain the required valve coefficient can be approximated with minimum error. An error analysis performed on the collected data shows that the results are highly accurate, and that the experimental process is repeatable.

scholarly journals The Role of Ab-Anbars in the Vernacular Architecture of Iran with Emphasis on the Performance of Wind-Catchers in Hot and Dry Climates

Heritage ◽  
2021 ◽  
Vol 4 (4) ◽  
pp. 3987-4000
Author(s):  
Fazeleh Yousefi ◽  
Francesco Nocera
Keyword(s):  
Natural Ventilation ◽  
Vernacular Architecture ◽  
Ventilation Rate ◽  
The People ◽  
Desert Areas ◽  
Dry Climates ◽  
Yazd City ◽  
Cooling Loads ◽  
Contemporary Architecture

Vernacular and traditional Iranian architecture has always acted rationally, harmoniously, and climate-friendly to meet the needs of the people in dealing with the environment. In addition, without harming the environment, they have achieved the best initiatives with the least facilities. For example, we can mention that the Ab-Anbars in arid and desert areas of Iran, which are used to store water in seasons with precipitation for use in the rest of the year, has been an optimal way to use natural resources and provide climate comfort. The Ab-Anbars are realized with ventilated cisterns through openings on their roof or wind-catchers to keep the water cool and provide comfortable conditions for the occupants. In order to study the essential role of natural ventilation and cooling in the Ab-Anbars, thermal analysis with CFD software was carried out to assess the effectiveness of a typical wind-catcher according to different wind directions in Yazd city. The results showed that Ab-Anbars have played an important role in reducing cooling loads and supply the necessary ventilation rate of buildings and can be used in the future for application in contemporary architecture and urban planning.

On the thermal buffering of naturally ventilated buildings through internal thermal mass

2007 ◽  
Vol 580 ◽  
pp. 3-29 ◽  
Author(s):  
J. M. HOLFORD ◽  
A. W. WOODS
Keyword(s):  
Heat Exchange ◽  
Air Temperature ◽  
Natural Ventilation ◽  
Ventilation Rate ◽  
Temperature Cycle ◽  
Thermal Mass ◽  
Thermal Equilibration ◽  
Environment Temperature ◽  
Naturally Ventilated Buildings ◽  
Diurnal Fluctuations

In this paper we examine the role of thermal mass in buffering the interior temperature of a naturally ventilated building from the diurnal fluctuations in the environment. First, we show that the effective thermal mass which is in good thermal contact with the air is limited by the diffusion distance into the thermal mass over one diurnal temperature cycle. We also show that this effective thermal mass may be modelled as an isothermal mass. Temperature fluctuations in the effective thermal mass are attenuated and phase-shifted from those of the interior air, and therefore heat is exchanged with the interior air. The evolution of the interior air temperature is then controlled by the relative magnitudes of (i) the time for the heat exchange between the effective thermal mass and the air; (ii) the time for the natural ventilation to replace the air in the space with air from the environment; and (iii) the period of the diurnal oscillations of the environment. Through analysis and numerical solution of the governing equations, we characterize a number of different limiting cases. If the ventilation rate is very small, then the thermal mass buffers the interior air temperature from fluctuations in the environment, creating a near-isothermal interior. If the ventilation rate increases, so that there are many air changes over the course of a day, but if there is little heat exchange between the thermal mass and interior air, then the interior air temperature locks on to the environment temperature. If there is rapid thermal equilibration of the thermal mass and interior air, and a high ventilation rate, then both the thermal mass and the interior air temperatures lock on to the environment temperature. However, in many buildings, the more usual case is that in which the time for thermal equilibration is comparable to the period of diurnal fluctuations, and in which ventilation rates are moderate. In this case, the fluctuations of the temperature of the thermal mass lag those of the interior air, which in turn lag those of the environment. We consider the implications of these results for the use of thermal mass in naturally ventilated buildings.

Measurement of Natural Ventilation Rate in a Japanese Residential Building

2008 ◽  
Vol 7 (1) ◽  
pp. 37-47 ◽  
Author(s):  
Shigeki Nishizawa ◽  
Takao Sawachi ◽  
Hiromi Habara ◽  
Hironao Seto
Keyword(s):  
Natural Ventilation ◽  
Residential Building ◽  
Ventilation Rate

Wind Tunnel Study on the Pressure Coefficient Performance of Different Venturi Shaped Roof Configurations for Wind Induced Natural Ventilation

2014 ◽  
Vol 564 ◽  
pp. 287-291
Author(s):  
M.M. Boroojerdian ◽  
Nor Maria Adam ◽  
Azmin Shakrine Mohd Rafie
Keyword(s):  
Wind Tunnel ◽  
Negative Pressure ◽  
Natural Ventilation ◽  
Pressure Coefficient ◽  
Ventilation Rate ◽  
Wind Tunnel Study

Wind catchers are structures used for natural ventilation using wind induced into buildings. Recently this has attracted attention for green buolding features There is limited studies on the different venturi shapes and their effects on inducing wind into buildingss.. This study considered three configurations ie. the shallow ellipse, the ellipse and the hemisphere in a wind tunnel with different speeds ranging from 8 m/s to 20 m/s. The negative pressure coefficient at the lower center of the roof is considered as the criteria for higher ventilation rate. The shallow ellipse performed the best but due to construction limitations other alternatives are recommended.

scholarly journals CONVECTION IN MINERAL WOOL USED AS INSULATION FOR BUILDINGS

2013 ◽  
Vol 19 (2) ◽  
pp. 296-304 ◽  
Author(s):  
Vytautas Stankevičius ◽  
Valdas Paukštys ◽  
Raimondas Bliužius ◽  
Jolanta Šadauskienė ◽  
Zenonas Turskis ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Effects ◽  
Mineral Wool ◽  
Heat Fluxes ◽  
Conductive Heat ◽  
Climatic Chamber ◽  
Air Gaps ◽  
Pressure Fields ◽  
Air Movement ◽  
Modelling Methods

The paper considers the velocities of air movement in the ventilated air gaps of walls and focuses on pressure fields in both wall models arranged in a climatic chamber and exploited houses. The article investigates the influence of air movement on heat transfer through walls applying numerical modelling methods and conducting experiments in the climatic chamber. The thermal effects of air flows have been described with reference to the Nusselt number defined as the ratio of average convective and conductive heat fluxes and heat flux through still air

Sign in / Sign up

Export Citation Format

Share Document