Industrial Workshop – Mexico
In a few words:
Our EOLIOS engineers, experts in modelling and fluid mechanics, had as an objective the study of the optimization of the comfort of the operators all along a production line by taking into account the surrounding constraints (temperature and speed of ambient air, evacuation of smoke) and in particular at the level of the arches.
The challenge of such a project is the control of the particular thermoaerulic phenomena induced by the different manufacturing steps at very high temperature in the area.
Within this framework our EOLIOS engineers studied by CFD thermo-aerodynamic study the various aeraulic and thermal principles governing the air movement in the plant according to the configuration of the selected systems.
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Sizing the natural ventilation of an industrial workshop
Our EOLIOS engineers have encountered many constraints due to the characteristics of the site and the construction:
- the radiant temperatures of the walls strongly influencing the thermal comfort
- thermal draught from manufacturing processes
- wind pressure and internal resistance to vertical airflow
- location and flow resistance characteristics of envelope openings
- the local terrain and the immediate protection of the building structure from the wind
- the presence of mechanical systems that move air around the production elements, making traditional design complex
As the building is not air-conditioned, the only source of cooling is the supply of fresh air by natural draught to the static ventilators in the roof, or by forced ventilation. Improving thermal comfort therefore requires precise sizing of natural ventilation openings.
Our engineers have responded to various problems such as
- Evacuate the smoke and gases produced by the arches (especially by the internal burners)
- Dimension the natural or mechanical ventilation in relation to the new extension of the palletizer building.
- Propose solutions to optimize thermal comfort and air quality.
- Limit dust and mosquito infiltration.
Air pollution problems specific to the workshop
The production workshop has specific constraints related to the natural ventilation process.
The use of ventilation is diverse:
- Fight against overheating in order to maintain acceptable working conditions and ensure proper operation without human and material risk
- Air supply to the various fans and blowing systems of the machines
In this context, 3 sources of outdoor air pollution lead to difficulties in ventilation management:
- Area with flies, mosquitoes, and other insects with a diameter close to the mm.
- Residues of sugar cane combustion (ashes) of the order of mm, which originate from the exploitation of fields in the region. These are the most common residues identified in sand barrier systems with double screens.
A fine dust from the surrounding land. The dry climate combined with the very fine sediment of the land leads to the natural blowing of dust in the presence of wind. This phenomenon is accentuated by the presence of activity on these dry grounds (passage of trucks, trampling…) and quarries in the area. The fine dust from the site, once blown away, does not fall back and can be transported over several hundred meters.
The objective is to carry out an assessment of the systems in place, to measure the interior temperature conditions and to characterize the main thermo aeraulic conditions of the space in order to establish an assessment of the installations in place. In industry, we can carry out smoke audits in order to calibrate the numerical simulations with respect to real phenomena.
Videos of the smoke audit
Among other things, the audit consists of taking air temperature and air speed measurements , analyzing the movement of smoke bombs, producing a video support and an audit report allowing feedback of experience for all the actors. Additional recommendations (use of louvers, cellar access doors, etc.) will be made based on the various observations on site.
This page broadly details the conduct of the audit in order to explain our mission protocol.
Air movement with other rooms in contact with the production workshop
The production workshop is an area where the climate is managed by natural ventilation. As such, it is not equipped with a mechanical system and the air circulation is supposed to be ensured by a natural transfer between the air inlets in the lower part and a natural extractor in the roof.
The site teams alerted our experts to the presence of dust and residue from the static aerator on the floor in the clean process area.
Our analysis allowed us to highlight the fact that an important air transfer is carried out in the direction of the decoration zone and then towards the packaging zone. In fact, these areas are equipped with mechanical roof ventilators that contribute to the depression in relation to the naturally ventilated area.
Natural industrial ventilation
The natural ventilation (for small temperature differences) is carried out via thermo aeraulic motors with very low pressure delta. The presence of sand barriers, which increase the pressure drop of the air inlets, leaves the static aerator as the preferred transfer zone (single external orifice).
In this context, air intake via the roof is favoured as soon as a Fenwick passes by in the direction of the annex room. When the Fenwick doors are opened, air is drawn in via the roof ventilator: air speed in the doorway 1.7 m/s (i.e. approximately 100,000 m3/h of transfer).
In this context (building connected in natural ventilation to buildings under mechanical extractions by adding important losses of load to the natural entries). Our engineers have concluded that it will not be possible to operate this static aerator satisfactorily in natural extraction.
Increasing the number of air inlets would limit this phenomenon slightly, but the pressure drop across the sand seems too great to prevent the building from being mechanically depressurized via air transfer.
Conclusion of the site audit
The production workshop suffers from problems related to its exposure to the sun and the presence of systems that release very large amounts of calories. The air velocities are slightly higher than for the adjacent building due to the ratio of openings to the size of the building.
The systems also contribute to overheating the space by releasing a plume of overheated air at the entrance and exit which dissipates into the atmosphere. They are the main driver of air movement in the area.
Optimization of thermal ventilation comfort
CFD modeling of industrial processes
The thermal characteristics of the walls and the process are taken into account. The values integrated in the CFD calculation are the simulated values of the project.
In a numerical model, the elements are as described, and only as described. In terms of the envelope, this often leads to surreal perfection: the materials are perfectly homogeneous and perfectly implemented. The only thermal bridges are those described, and it is at best very complicated, if not impossible, to anticipate all thermal bridges (structural thermal bridges and those related to the attachment system are generally taken into account; thermal bridges due to holes or network passages are generally not).
The main issue of this tab will therefore be to distinguish the target value, resulting from the performance of materials, and the simulated value, taking into account the inevitable imperfections of implementation.
CFD modeling of natural ventilation systems
Sand guards equip most of the air transfer vents from the outside.
The sand screens are equipped with mosquito nets on their inner sides.
In the CFD study the sand pare modeled in such a way as to obtain an equivalent air flow without constraining the numerical model.
3D CFD model
The aim of this chapter extract is to outline the 3D model produced for the basic CFD study. The specific features of CFD models, linked to the robustness of their solver and the quality of the 3D model, mean that the geometry model has been entirely remodeled. Simplifications, related to curves, edges, points and small elements have been made.
The external CAD model produced shows the geometry of the site without its environment. It was made from the section plans and the revit model of the project.
The model is designed to take into account the air and heat transfers in the hall.
Our EOLIOS engineers have paid particular attention to the modeling of industrial systems to ensure maximum accuracy. Indeed, the furnaces being one of the main sources of heat release, they have the greatest impact on the surrounding thermo-aerodynamic phenomena.
The consideration of air masks is important in order to describe the different air movements in the area.
How to qualify thermal comfort in hot spaces?
Thermal comfort is the satisfaction of an individual with the thermal conditions of his environment. We speak of thermal comfort when the person does not want to be hotter or colder.
It is subjective and therefore depends on individual perceptions. It is influenced by physical activity, clothing and the levels and fluctuations of the characteristics of the thermal environment (air temperature, radiation, contacts, humidity and air speed).
In orange are represented the thermal comfort zones adapted according to the air speeds
Study of the air velocity distribution
The first figure below shows the volume mixing effects.
The general aeraulic movements of the room can be described in two stages induced by the air supply zones constituted by the sand barriers and then by the recovery zones.
Put simply, pressure differences are the driving forces of air currents. In other words, air flows from a high pressure space to a low pressure space, when these forces are greater than the pressure drops (friction).
In HVAC, air circulation is induced by two driving forces:
- Thermal draught occurs when a difference in temperature causes a difference in density between two air masses. This effect is accentuated by a greater height in the volume. “Hot air tends to rise”.
- The distribution of pressures and depressions induced by the HVAC systems in the volume.
Here, the return air systems have very little influence on the air velocities inside the building, the air movements are governed by the temperature rise of the oven zones.
Study of the air velocity distribution
The air velocities are not consistent with the comfort objectives for this type of activity in summer. The displacement air velocities are below the target values for thermal comfort in warm environments.
The highest air speeds are found in the continuity of the sandy parts. In fact, these areas are the main air inlets in the hall.
On the other hand, the simulation highlights the presence of a low velocity zone between the arches that can lead to a temperature increase.
Study of the air temperature distribution
In the absence of movement, or when the movements are slow and regular, the air forms layers with homogeneous temperatures that overlap, the warmest air being in contact with the ceiling.
These sections highlight the stratification phenomenon explained earlier.
The air temperature in the building is globally overheated, even in the lower part where the temperature is clearly higher than 35°C
Study of superheated thermal plumes
The vision of thermal plumes in iso surface allows to identify the different sources of strong heat and their impact in the model.
The low air circulation in the furnaces combined with their high temperatures results in high temperature zones. The simulation shows that the air between the furnaces rises in temperature and tends to flow under the ceiling. However, once under the false ceiling, the warm air struggles to be evacuated to the outside.
Moreover, the results of the study show that the hoods at the entrance of the ovens do not allow the suction of all the air loaded with calories. This phenomenon is mainly due to an undersizing of the suction flow.
The air coming out of the oven, not being sucked in by a hood, tends to go towards the ceiling. This phenomenon contributes to the rise in temperature of the room.
Another phenomenon not taken into account, but which can have an impact on the aeraulics of the room, is the thermal inertia of the products which can emit calories at the exit of the furnace in the zone.
The rear exhaust chimney of the oven working in natural ventilation does not appear to be efficient enough to recover all the calories. Indeed, as highlighted above, the air leaving the oven, loaded with calories, tends to go towards the ceiling, thus contributing to the rise in temperature.
However, we note an operation in extraction (no internal reflux which could have been caused by the depression of the room).
CFD simulation for industry
Numerical simulation offers new perspectives for manufacturers. This makes it possible to foresee a multitude of scenarios, and therefore to control all the unforeseen consequences of poor design. In the case of production plants, multiphysics modeling allows to take into account the totality of the phenomena at the origin of the thermo-aerodynamic flows which occur along the chain, from overheating to the comfort of the employees.
Thanks to its calculation servers, EOLIOS models can be simulated in their entirety with great accuracy in a short period of time. Moreover, the experience of EOLIOS in general aeraulics allows our team to propose innovative and relevant solutions in the case of overheating problems. Nevertheless, implementing CFD simulations in your design process means calling on experts in fluid mechanics, thermal and numerical simulations to ensure that no problems occur in the future.
Our EOLIOS engineers benefit from a strong experience in the audit by bringing directly their expertise in order to optimize the resolution of the various problems. Their state-of-the-art equipment allows for direct and distinct measurements guaranteeing an evaluation of the site, equipment, material and, if necessary, a thermal expertise including the systems, losses and climate control by the systems.