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DESIGN AND STUDY OF VENTILATION SYSTEMS FOR NATURAL AND PRIVATE BUILDINGS

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 03, March 2019, pp. 691-712 Article ID: IJCIET_10_03_067
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=03
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
Scopus Indexed
DESIGN AND STUDY OF VENTILATION
SYSTEMS FOR NATURAL AND PRIVATE
BUILDINGS
Nehayat H. Amin
Ministry of Agriculture and Water Resources. Erbil, Iraq
ABSTRACT
Ventilation moves outdoor air into a building or a room and distributes the air
within the building or room. The general purpose of ventilation in buildings is to
provide healthy air for breathing by both diluting the pollutants originating in the
building and removing the pollutants from it. The research summarized the following:
1)
Ventilation is two types (natural and private). The private ventilation
differs from the natural ventilation by adding filters and the work of blocking the air
going out from the space and then putting it out by private ducts. Private ventilation
also requires air rates and required ventilation models. The air is withdrawn from the
zones according to the intensity of air pollution in the space.
2)
This research showed the methods of air supplying which are through the
air ducts, which are three methods (velocity reduction method, equal friction method,
and static regain method)
3)
Fans were identified as Centrifugal fans, Vaneaxial Fan, Tubeaxial Fan,
and Propeller Fan. Vaneaxial fans were selected in the building model. It was
identified the types of filters in the ventilation, including Input Filters, Pre-Filters,
Primary, Final Filters, and High-efficiency particulate air (HEPA) filters used in the
most polluted areas.
Keywords: Study of Ventilation Systems.
Cite this Article: Nehayat H. Amin, Design and Study of Ventilation Systems for
Natural and Private Buildings, International Journal of Civil Engineering and
Technology, 10(3), 2019, pp. 691-712.
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Design and Study of Ventilation Systems for Natural and Private Buildings
1. FIRST CHAPTER
1.1. Introduction
Ventilation is defined as the process of providing or removing the air by nature or mechanical
methods, from and to space. This air may either pre-treated or not pre-treated [1]. The
quantities of required air for ventilation were a research field and controversy for many years
and still exist [2, 3]. Various principles and ideas have led to the emergence of different
ventilation standards. From these ideas and considerations of the adoption of quantities of
exhalation air mainly to determine the requirements of ventilation, and remove moisture from
internal air another basis and control the concentration of carbon dioxide, third basis [4]. The
rates of ventilation currently accepted in home applications, commercial buildings, and others
are based on the results of a number of scientific research began in the twenties and thirties of
this century and some processes and immunological activities are characterized by the
production of substances that may crumble or volatilize in the air, leading to producing air
pollutants, Some of these pollutants may be harmful, toxic, or may be non-toxic, but are
contaminated for air, flammable or explosive materials, or help them [5]. It is necessary for
these industrial applications to know the characteristics of pollutants in some detail and the
requirements of air purification and purifiers in the simple sense of the requirements of
ventilation in air conditioning systems for comfort, the climatic factors (temperature,
humidity, air movement, solar radiation) have a significant impact on the physiological
comfort for humans. So ventilation is very necessary for the buildings, it is one of the main
elements in the design of buildings, Natural conditioning and ventilation are important and
have a great role in reducing heat stress and high temperatures [6]. They are the main solution
for energy consumption crisis because the energy consumption crisis is due to mechanical
adjustment, require interacting with these climate variables to remove the thermal
accumulation and compensate it with a stream of refreshing moving air.
The question that arises is why ventilation?
The need to ventilate the spaces or provide them with fresh air is due to the following
reasons:
A. Oxygen is very necessary for human life and its continuity.
B. Air acts as an energizer, and the level of air required depends on the size of the room
to be conditioning because there are a lot of substances that release carbon dioxide
(CO2) and other odors which emanate from human bodies or radiate from other
substances present in the space.
C. Ventilation allows the air movement through the spaces and this, in turn, affects the
environment, here, Ventilation is considered a key to psychological comfort.
D. Control of the air combustions in factories.
2. VENTILATION METHODS
It is divided into two methods:
1. Natural ventilation.
2. Mechanical ventilation.
In natural ventilation, there are two reasons that make the air move through space.
 The wind.
 The density difference between the outside air and the air inside.
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2.1. The wind effect
wind is the result of different the pressure in the atmosphere, can determine the path of the
wind through the trees and plants high and the velocity of the pressure transform to static and
normal pressure, additional pressure will be generated (about 0.5 - 0.8 from the wind velocity
ventilation) while low pressure is produced when (0.3 - 0.4 from the wind velocity
ventilation), The difference between the two pressures will be generated through the building
and lead to the entry of air to the space through the openings of windows or other openings
[7].
2.2. Stack Effect
Hot air in the room tries to rise to the top because of its low density and take the place of cold
air. Since pressure outside or inside is affected by wind, the process of stacking effect is
partly controlled by wind pressure and partly by the design of the openings [8, 9].
2.3. Natural ventilation and infiltration in industrial applications
Natural ventilation is considered one of the cheapest ways to get moving air inside buildings,
especially factories with small areas, which do not need large ventilation rates because they
do not need capacity requirements such as air movement, there is also no noise, But there is a
problem in the winter is caused by changes in the weather where cold air enters from the
openings and it can be controlled through the roof or walls [1,10].
2.4. Chimneys effect
It depends on the power of producing natural ventilation in the buildings, which in turn
results from changing the air due to differences in temperature. Due to the difference in
pressure, the internal warm air is replaced by the external cold air while slow-moving air
generated by thermal forces can be sufficient for both of the supply with fresh air and cooling
with convection. These forces are very few and not enough to create the movement of air that
can be obtained and necessary for some warm areas to provide thermal comfort [11].
Figure showing the chimneys effect on the velocity and movement of air.
We can rely on the power of nature to display the dynamic impact of wind and to make
the necessary efforts to catch a large amount of wind, thus we conclude the inevitable and
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Design and Study of Ventilation Systems for Natural and Private Buildings
essential importance of ventilation, which can be obtained in several ways, the most
important of which are:
* Stack effect as a result of changing temperatures
* Mechanical methods
* Pressure wind and air currents
3. MECHANICAL VENTILATION
In mechanical ventilation systems, Fans are used to control air movement. In this case, the
control is much more than natural ventilation. Mechanical ventilation is used in which the
fan, the filter to clean the air, the batteries and the heater, where the air circulates through the
air openings and goes to the rooms through the convection [12, 13]. Mechanical ventilation is
a process of Disruptive in atmospheric pressure, where it is scientifically known that the air is
moving from Positive pressure (+) to negative pressure (-), In other words, ventilation is:
"Renewal, change, passage, replacement" for air in the space with pure air. This means that
ventilation does not deal with the characteristics of the air, and this is done through Fans [13].
3.1. Ventilation requirements
3.1.1. Air Requirements for Adequate Ventilation
The Ventilation Rule of Thumb is an example of this (air change per hour, temperature rise
between the inside and outside air in the system and the size for each square area) is
meaningless to the effect of the thermal barrier unless the specific rate is constant for the
successful exit of the systems similar to the suggestion of this standard that it is useful to give
true change and confirmation of ventilation designs. Changing air flow rates at the upper
level of the building is not necessary to secure equipped at the lower work areas [14]. Such
ventilation should turn the roof air and turn it into the ground, making working conditions
worse. Thermal barriers are reduced by a high temperature between the outside and supplied
air, and the temperature rise of (50-60 °F) can easily carry the air about (30-25 °C), especially
in areas with high roofs. A slight rise in temperature from (3 to 6 °C) is not suitable to
provide comfort or discharge in hot weather and as low as the high temperature required by
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large air volume and good design. For ventilation systems, maintain the working area within
(2 ℃) for the temperature of the applied air with less air and higher temperature [14].
We can calculate the temperature rise in the following equation:
H=1,08
Tq . q (H = 1.2
T .q)
T: Temperature rise of the air (F°) (C°)
H: The removed Heat (tu/h) (w)
q: Air supply (CFM) (latter /sec)
The amount of removed heat (H) shall include the internal heat for the equipment,
processes, lighting, Solar cells and gain due to the transition through the roofs. Ventilation
usually expresses about the size per square unit area and this relationship fails to calculate the
true thermal discharge of the provided system. But it gives a relationship that not depending
on the height of the building. It is the most logical approach to air changes per hour. For the
appropriate design, the desired heat will be equipped that independent from the height of the
roof for the spaces with few exceptions [15]. If the ventilation rate is equal to (10 L/SM2), it
will give acceptable and good results for many factories that have an internal shop ranging
from (400-300 W/m2) / (125-100 ft2). When the outlet ventilation center requires contaminant
control, the output rates are constantly increasing than the natural ventilation required to
control the comfort under these conditions, and the outlet rate will determine the air rates of
the simple extruder system with the minimum distribution (and the designer or manufacturer
to equip the compensation air) without disturbances when booking the hood and desired
processes. To ensure the effective power of the outlet system center, we need a wellorganized distribution for air [14,15].
3.1.2. The need for air compensating
In most industrial enterprises, the need for air compensating by replacing the large volume of
air that should come out and to give personal comfort conditions and industrial safety more in
the operational processes. It cannot use the windows and other entrances in the stormy
atmosphere because they represent obstacles. In particular, the need is more important for the
equivalent air and can be summed up by the following points [16, 17]:
1. To prove the amount required to remove from the processes, combustion and the
removed heat of buildings [17].
2. To delete the cross-currents by the proper regulation for the air and avoid leakage of
doors and windows and small openings, that is, the coverings are unsafe and
ineffective by eliminating the dominant effects such as mobile dust affecting cooling
or disturbances [17].
3. To get the air from a pure source, the applied Air, we can be filtering it or not filtering
4. Allow control of the pressure of the building and the flow of air from one area to
another, This control is necessary for three reasons:
A. To avoid positive pressure and negative pressure, when opening the doors at the same
time, we will encounter difficulty and gravity and avoid the conditions in paragraphs
(1, 2, 3) above.
B. To allow the identification or capture of contaminants and the positive control of air,
humidity and air movement.
C. Allow the removed heat which will be removed by the air of ventilation.
The heat will be contaminated unless it is properly identified and removed otherwise will
be spread to work areas or interfere with the applied air for conditioning [17].
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4. FANS
Fans are naturally used the device to drive and circulate air or other gases in air duct systems,
including air conditioning applications. Fans are divided into four types depending on how
they operate and place them [18].
4.1. Type 1: Centrifugal fans
Which are the most widely used in air conditioning applications. This fan is compatible with
most uses and can pump large amounts of air with good pressure. The fan is operated by an
electric motor, either with a single shaft for the engine and fan together or with pulleys and
belts. There are three possible types of fan wheels: Frontward curved blade fans, Backward
curved blade fans or Axial Blades. The fan characteristics vary depending on the type of
blades. This type of fan extends to include most fields, the fan chamber cover with Gases and
vapors that causing the corrosion, the fan chamber cover and blades are painted with Anticorrosion pigment and pitch, it is sometimes made of stainless steel [18, 19].
4.2. Type II: Vaneaxial Fan
It pumps the air by a pivotal current, and the blades are similar to the turbine blades. In some
fans, the angle of the curvature of the blades can be changed to give different pumping rates.
The blades are based on a large base similar to the Aircraft fan base, using with these types of
fans an air flow control panels either in front or behind the fan [20].
4.3. Type III: Tubeaxial Fan
The blades are normal and larger than their predecessors. The center on which the blades are
based is smaller and the direction of the blade cannot be changed, but they are fixed [21].
4.4. Type IV: Propeller Fan
It is characterized by the fact that it cannot provide great pressure and is often used to insert
and remove the air from a particular place without pressure, such as applications fans vent air
from kitchens and toilet room and placed in the walls with or without air ducts very short
[22].
4.5. Fan power and air power
The flow of air in the air ducts system is due to supplying the power to the system by a fan,
the fan receives power from its operating engine. The goal of calculating the loss of energy
(pressure) through the air ducts is to obtain sufficient information to determine the engine
power and the velocity at which the fan should rotate, The selection of the fan for a specific
system to pump a known air flow rate against computed pressure loss is the total loss of
pressure in the system. Each fan has a net input power is a Fan Power [23]. There is
dissipation in the fan's ability to overcome friction in the wheel bearings and dissipate in the
friction form and disturbance through blades of fan chamber cover. The remaining is called
Air Power, it is the net power that reaches the air current to overcome on the pressure drop in
the air duct system, parts of the air conditioning unit, distribution slots and other parts of the
whole system and accelerate the air to drive it quickly required, that is, it provides the static
pressure and required Dynamic pressure [23].
PA = mg Ht = Q Pt
Pt : total pressure
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Q: M3 /see
The percentage between fan power and air power =
The fan power Pf, which is the net power reaching to the fan axis, is calculated from the
multiply the power that the engine used by its efficiency when negligible the loss in the
process of movement transfer between them [23].
4.6. Types of ventilation
Ventilation is divided into two types:
1. natural ventilation
2. private ventilation
4.6.1. Natural ventilation
Natural ventilation refers to the removal or supplying of the air supplied for comfort or
replacement of The air coming out (Achieving ventilation refers to pollution control), the
used systems can equip the air equation with the external system which is in the process of air
conditioning to replace the outside air and represented by areas of comfort for people or
remove the air that leaks out of the structure of the building as a whole [1, 15].
4.6.2. Ventilation for the Storage Room, toilet room and showrooms
This ventilation is important in the modern industrial facilities to remove the unacceptable
smell and high humidity, in some industries, appropriate control of pollution in the workplace
requires to avoid inhalation, as well as the appropriate health facilities with the appropriate
ventilation needed for storage rooms, dining rooms, and rest rooms and showrooms. The
entering air through doors or through walls In some cases factory air is polluted, Therefore air
is filtered by preferred mechanical methods for ventilation, when we control the components
in the work rooms is not appropriate or useless, the total exposure of workers and users
certainly reduces the level of contamination of storage rooms and dining rooms and Break
room is low by reducing the area with excessive of the supplied air. When using mechanical
ventilation, the applied system can regulate the distribution of diffusers from ceilings and
walls, or by supplying air from plenums to suit the distribution through the producing areas.
In the storage rooms, the Air discharge must begin from the sanitary facilities and showrooms
and the remaining draws from the roofs and storage rooms. These assumptions for the
conditioning areas, which are produced from the edges of the doors and the most important
different distributions, which allow the moving air in the storage area to the sanitary facilities
and then to the showrooms [24].
4.7. Private ventilation and their requirements
4.7.1. Ventilation and filtration for private buildings
The system of ventilation and filtration for any factory working on radioactive decay
materials is an integral part of us natural arrangements for the handling or transportation of
these materials. There are two inherent risks are radiation and pollution [25]. The main
function of the ventilation system is personal protection from the transferred pollution in the
air. This function is common practice and isolating an effective building into zones and
classifying each of these zones depends on the safety factors associated with the operations
performed [1, 6]. There are four types of areas that are usually similar, each with a distinct
trait in the required ventilation. The relationship between the types of areas is an important
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factor. The require to transport material through the boundaries of the designated area is one
of the central problems to give a convincing system design. As well as, it is the basic
principle of air duct between areas must be cleaning for most areas full pollution. While the
reverse flow has not an important risk and is not desirable at the same time the relationship of
size between zones represented by the limits of the process of air velocity and the need for a
system that eliminates safety in the dangerous latent parts of the experimental project, which
makes the design of the system very complex [26, 27]. It is for the modern methods that have
been completed and are changing from a project and there are no standard and acceptable
designs. The growth curve of the effective projects is the same in terms of figures for these
projects [26, 27]. The invention of Radioactive Decay involves use that leads to a broad
discussion with the admission laws which should in the future highlight the protection of
workers in radiological institutions. This confirms and emphasizes the need to review
experimental information and operational experience which are clustered in projects over the
past two decades with the purpose of authorizing common problems and developing broad
lines and convincing solutions for them in the future. In some projects, where the conditions
are variable and where the original design is necessary to consider the suitability of existing
ventilation systems [26, 27].
4.8. Building Zones
There are four zones within the building that are naturally numbered (1-4), which were
developed by the International Organization for Standard item (ISO). The higher number
indicates the high radiation risk in Ref 10. The number zones, unlike AEA, represent a
natural similarity of these zones with the building by color laws. (ISO) does not make a
specific reference to the outside of the building, but the AEA refers to these white areas as
well as the changing areas that need to safely transport materials to and from the building.
4.8.1. Red Zone (ISO No4)
The red zones include the indoor areas of the cell which are closed from normal working
conditions and which are contaminated from operating load outside the area and reduce the
level of pollution too (10-3 .cm-2) which can be exceeded in the continuity of red rays.
Opening the port to allow it to turn Amber color under control conditions and there is no
direct outlet to reach the Green Zone (Radiation Workspace).
4.8.2. Amber Zone (ISO Zone3)
Services and maintenance zones for work equipment, cells and related to this zone, become
contaminated when the doors of the cell are open and the cell surface is shut off from the
transmission of materials, maintenance and for similar purposes. The connection between the
amber and green zones must be under control conditions using the necessary interconnections
and zones.
4.8.3. Green Amber (ISO Zone3)
Which are within the radiation work area, which includes the natural works and the zone
facing the cell working with the treatment of the decay of radioactive materials in the
building, but should not become contaminated under normal conditions [27].
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4.8.4. White Zone (ISO Amber)
The offices and control rooms, where ventilation rates are determined by traditional
measurements, they are located in the private contaminated building, classified as a green
area under the AEA color system [27].
4.9. The outside Zones for Active Building
The pollution of Beta-radiation in green zones with active buildings should not exceed (10-3
μ.cm-2) with a radiographic design that does not exceed (2.5 Millirems Per Hour) 5 rems per
year - and airborne radioactive gaseous material exceeding (1Mcp and 40 hour -week),
Active spaces presence outside active buildings are defined as Active, which has the same
limits as radiation and airborne pollution as green zones. The nuclear isolates are regulated so
that the highest permissible dose to which people are exposed is (1/10) and by means of the
indication of conformity to the minimum permitted airborne concentration. These zones are
classified as white zones and within the active zones there are data designed as green zones,
(Offices) where airborne considerations and airborne effectiveness are similar to (0.1 Mcp)
but should not exceed (1 Mcp). Here ventilation only needs to equip the comfort conditions to
work. Green zones shall be in contact with the red or amber zones within the building and
shall contain a gradual pressure for the gradation and maintenance within the boundaries of
the area and the deletion of the impact of the wind [26, 27].
4.10. Pressure difference
The direction of runoff should be maintained from the less polluted areas to those areas with
high pollution. This is achieved by maintaining on the least air pressure in the most polluted
zones and with the direction of the air duct. Acceptable measurements of how pressure varies
between zones to ensure that there is no opposite flow of contaminants, but we maintain the
double differences (local doors and openings for ventilation) in the formation of the changing
zones needed at the boundary of the zone for the transfer of material and character [28, 27].
4.11. Air Changes
The number of air changes per hour within the zone depends on the maintenance of the
acceptable process to people in the zone and in the case of the implementation of operations
in the red zone and the qualitative values are classified as follows [29]:
1. Ventilation of the red zone: The rate of air change as a minimum limit is (6 times/
hour)
2. Maintenance of Amber zone: Naturally, the acceptable level of air change is (20
times/ hour)
3. Work zones of Green Radiation: The rate of air change (12 times/ hour) [27].
4.12. Ventilation Models
Ventilation system designs are used to achieve operating conditions and are affected by the
interaction degree of the booking zone. There are two types of ventilation models [1]:
A. The appropriate design of the new system or project in which the interaction is good
for the reservation zones;
B. Suitable designs for existing projects where good interaction is not impossible for
these designs which are considered the systems of (Fresh Input) as shown in figures
(1, 2, 3) where:
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Figure 1: illustrates a good interaction model for ventilation is shown where all
extraction fans are attached to extraction filters and the extraction is 100% until it reaches the
main extraction fan.
Figure 2: illustrates the basis of simplified ventilation models where extraction is from
the most polluted zone.
Figure (3): illustrates a model for ventilation where extraction of this model from two
different zones in the intensity of the pollution [27].
Figure 1 illustrates a good interaction model for ventilation is shown where all extraction fans are
attached to extraction filters and the extraction is 100% until it reaches the main extraction fan.
Figure 2 illustrates the basis of simplified ventilation models where extraction is from the most
polluted zone.
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Figure 3 illustrates a model for ventilation where extraction of this model from two different zones in
the intensity of the pollution [27].
4.13. Filters
The principle of dividing the building into booking zones and maintaining air movement in
these areas to prevent the spread of radioactive elements within the chosen building. Collect
the resulting efficiency within the building and avoid the spread of activity outside the
building, it is achieved by using different types of filters, including [30]:
4.14. Input Filters
The input filters are used to stabilize the amount of air dust inside the building as low as
possible. If the entering air is not filtered, the external filters need to be changed continuously
because they will be exposed to the materials generated in the project and using good quality
for internal filtration [30].
4.15. Pre-Filters
When the high amount of transmitted radiation from the worktable uses filters with a good
filter for the working zone. The dust carries to the most hazardous zone and the Highefficiency particulate air (HEPA) extractors remove the dust until it remains at a
concentration of (1 mg.m-3). The used isolators for high dust levels are re-filtered before the
first HEPA filter is used. Ventilation Extraction is done by removing a large number of
particles. The degree of re-filtration depends on the materials carried out and the cost of
changing the filters [31].
4.16. Primary and Final Filters
In order to prevent the leakage of air containing radioactive materials to the ocean and reduce
the proportion of these substances to prevent their access to the air and the first filter (HEPA)
in the extraction area is designed to prevent the departure of pollutants to the outside area.
The filters must be constantly changed. In the case of high radiation of the filters must be
removed by the treatments of the cell (Manipulators) and filling for the purpose of disposal of
radioactive materials and put the insulators in the first stage of extraction filters before
helping extraction of air ducts to keep the ducts from becoming contaminated, in addition to
the first stage of the nomination we add two High efficiency particulate air filters (HEPA) for
the necessary considerations [31, 32]. To avoid leakage of dust from air ducts and building
filters, place a final filter before the extraction fan as shown in figure (4).
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5. SECOND CHAPTER
5.1. Building specifications
The building consists of five workshops which are as follows:
5.1.1. Plumbing workshop:
It consists of the melting furnace, the casting section, the sand section, the finished products
section. The number of persons for this workshop is 10 person. The administrative section
consists of the preparation of models and store management and the number of persons for
this workshop is 7 person.
5.1.2. Turning workshop
It consists of 6 lathes, 4 grinders, 4 drills; the number of persons for this workshop is 14
person. The administrative section consists of a rest room, store and administration.
5.1.3. Carpentry workshop
It consists of 4 woodworking drills, 4 woodworking lathe, and 4 saws with 4 grinders. The
administrative section consists of a rest room, store and administration.
5.1.4. Electricity workshop
It contains a motor winding section and a department of maintenance of electrical equipment,
contains a battery room in addition to the room management and rest room.
5.1.5. Welding and Blacksmithing of Workshop
It consists of five welding machines, five welding (Tungsten Arc Welding) with a
blacksmith. The administrative section contains a management room and a rest for workers
The length of the building is 75 m
The wide of the building is 17 m
The height of the workshop Roof is 5.5 m
The height of administrative sections is 3.5 m
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6. THIRD CHAPTER
6.1. Design of air ducts
The air distribution system can be high, medium or low in air ducts. This depends on the
spaces of the air ducts, the cost, the type of used windows and when there is a wider area for
air ducts, It is recommended to use the system of low velocity because the construction of air
ducts for this system is not critical and the cost of operating the fans of pumping the air is less
If you use a high-velocity air system. When the need for the use of the central system or highvelocity with high pressures resulting from the use of this system, must considering the
durability, sound and air leakage. In this case, circular air ducts and accessories are usually
ideal for medium or high-velocity systems. As for the points to be considered in the design of
ducts can be identified as follows [12]:
* Placing the air equipped unit in terms of placement in the appropriate place for the
average of air ducts
* Areas of the building that are ventilated
* placing the exits and entrances in terms of obtaining an integrated air distribution
* Suitable sizes for air inlets and outlets
* The sizes of Air ducts and their distribution
* placing air regulator valves in natural areas
The fresh air drawn into the heating and cooling air machines is an important factor in
increasing the capacity of the cooling machines in summer and winter, and this is more
obvious in our country in summer where the temperature of the air is relatively high. The air
flow through the ducts is accompanied by pressure loss due to friction. The larger the air
volume, the greater the friction loss. Similarly, the smaller the area of the duct, the greater the
friction loss. The initial cost of the air ducts depends on its size. The small air ducts are
initially cost-effective but the capacity required to pumping the air through these ducts is high
and therefore the operating costs are high. Therefore, air duct designs depend on the balance
between initial costs and operating costs
6.2. Methods of air duct design
1. velocity reduction method
2. equal friction method
3. static regain method
6.2.1. Velocity reduction method
In this method, the Velocity is chosen for each section of the duct network, So that the speed
is high at the outlet of the air intake fan, decreases at the branches, and it is the lowest
possible at the end of the duct. The Velocity is selected according to the used air conditioning
systems and their applications and by using the friction curve for the specified air size, the
size of the duct and loss in friction is determined at each section, The process of collecting
losses is then used by friction in each section and this method is usually used in simple air
ducts systems such as rooms and small shops [33].
6.2.2. The equal friction method
In this method, the friction factor (friction loss per meter of equivalent length) remains
constant during the air ducts system. The total loss of friction is calculated by multiplying the
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friction factor by the equivalent length of the duct network. The friction factor is determined
at the primary velocity in the main duct and air volume [34].
6.2.3. Static regain method
The basic principle for this method is determining the size of the duct so that the increase in
static pressure due to the decrease in velocity at each branch to overcome on the loss by
friction at the successive sections for the duct or in other meaning, The pressure of the
velocity decreases and the static pressure increases, so that there is a conversion from the
velocity pressure to the static pressure called the re-dormancy from this method as in the
equal friction method. The friction factor is calculated from the size and velocity of the air
and the loss is in friction calculated by multiplying the friction factor in the equivalent length,
From the beginning of the air-conditioning fan to the beginning of the first sub-duct and the
design of the air ducts to the length of the air duct for the longest duct in the air duct system,
so that the loss of friction at each start of the sub-duct is equal. This method is used in highspeed air-conditioning systems and air ducts designed in this method are smaller in size
compared to the equal friction method but the friction loss is high [12, 23].
6.3. Calculating the rates of Ventilation for persons
Zone
Number of persons Ventilation rate / sec
Plumbing Workshop
10
75
Preparation of models
4
30
Administration
3
22.5
Turning workshop
14
105
Restroom for Worker
16
240
Administration
3
22.5
Carpentry workshop
16
120
Restroom for Worker
16
240
Administration
3
22.5
Electricity workshop
10
75
Restroom for Worker
10
150
Administration
3
22.5
Welding and Blacksmithing of Workshop
13
97.5
Restroom for Worker
13
195
Administration
3
22.5
The ventilation rate for each person in the workshops =
The ventilation rate for each person in the restroom =
The ventilation rate for each person in the Administration office =
(3)
6.4. A model of calculating
1. We find the velocity and diameter of the air by knowing the air flow and from the
Ashre design for the air ducts, considering (P = 1.0 pa / m) [12].
2. The dimensions of the duct (w * b) for the knowing the area (A) where
A=b w
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(1)
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Nehayat H. Amin
A = d2/4 = 225 / (4
106) = 0.0397 m2
⇒ 4b = w
=
(2)
Sub the equation (2) in the (1)
b = 100 mm
w = 400 mm
Calculating the dimensions of takeoff (b1 and w1 from the first table)
b2 = b1
b2 = 100 *
= 20.75 mm
As well as for (w2)
considering (R = 1.5 m)
= 0.25 R
=
b and w from the table
=
= 3.76
From scheme (2) we use the equation
n = - 2.13 ( ) 0.126
= - 2.13 ( 0.25 ) 0.126 = -1.787
From scheme (2) we use the equation
L/W = ( 0.33
)-1.787 = 0.68
= ( 0.33
The equivalent length L = 0.331 m
Calculate fan power
Total length equivalent = 0.525 + 0.525 + 0.53 + 0.54
Length of bend = 0.27
Total length of duet = 30
T . P . L (Total Pressure Loss) = 1.0 Pa/m
Power of the fan = T . P . L
= 32.39
(30 + 0.27 + 2.12) = 32.39 Pa
( volumetric flow rate )
0.180
= 5.83 Kw
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6.5. Design of air ducts for workshops and offices
We use the equal friction loss method,
Considering the difference in pressure per meter is P (1.0 Pa / m), which is the average of
maximum limit (1.5 Pa / m) and the minimum limit (0.5 Pa / m)
Fan (A, c) for workshops, fan (B, D) for offices and rooms
Section
A – R1
R1 – R2
R2 – R3
R3 – R4
B – R5
R5 – R6
R6 –R7
R7 – R8
R8 – R9
D – R10
R10 – R11
R11 – R12
R12 – R13
R13 – R14
R14 – R15
R15 – R16
C – R17
R17 –R18
R18 – R19
R19 – R20
R20 – R21
R21 – R22
Q/sec P Pa/m Length M
180
142.5
105
52.5
315
292.5
172.5
52.3
30
652.5
630
435
412.5
262.5
240
120
292.5
232.5
172.5
135
97.5
48.75
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
12
6
6
6
5
3
4
7
5
6
4.5
5
4.5
10
3.5
3
12.5
6.5
6.5
6.5
4
4
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Velocity
m/sec
4
3.75
3.5
3
5
4.75
4
3
2.75
5.75
5.5
5
4.5
4.25
4
3.75
4.75
4.5
4
3.75
3
2.5
706
Diam
Area M2
(mm)
225
0.0397
200
0.0314
175
0.024
150
0.071
300
0.070
275
0.059
225
0.039
150
0.017
125
0.0138
400
0.125
350
0.096
300
0.070
275
0.059
250
0.049
225
0.0397
200
0.0314
275
0.059
250
0.049
225
0.039
200
0.031
175
0.024
150
0.0176
Dimension W * b
(mm*mm)
488 * 100
400 * 79
400 * 60
400 * 44
531 * 133
447 * 133
300 * 133
133 * 133
104 * 133
709 * 177
543 * 177
399 * 177
353 * 177
277 * 177
224 * 177
177 * 177
488 * 122
488 * 101
488 * 82
488 * 64
488 * 49
488 * 36
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Nehayat H. Amin
6.6. Calculations of Bends
Take off
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R19
R/W
2.50
2.50
2.50
2.50
1.88
2.23
3.34
7.52
9.62
1.41
1.84
2.50
2.98
3.6
4.45
5.64
2.05
2.05
2.05
2.05
2.05
2.05
n
-1.46
-1.46
-1.53
-1.61
-1.78
-1.82
-1.92
-2.13
-2.19
-1.78
-1.84
-1.92
1.96
-2.01
-2.06
-2.13
-1.46
-1.42
-1.40
-1.40
-1.49
-1.53
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L/W
1.31
1.31
1.33
1.35
2.34
1.75
0.82
0.14
0.07
3.92
2.49
1.44
1.05
0.91
0.45
0.26
1.770
1.776
1.728
1.73
1.79
1.82
707
b/w
0.052
0.052
0.075
0.111
0.250
0.297
0.444
1.000
1.279
0.250
0.326
0.444
0.528
0.639
0.79
1.000
0.051
0.053
0.036
0.037
0.061
0.074
L(m)
0.525
0.525
0.530
0.540
1.243
0.782
0.247
0.0195
0.008
2.779
1.35
0.577
0.353
0.254
0.100
0.047
0.862
0.86
0.84
0.84
0.87
0.88
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6.7. Fan power calculation
Total length
equivalent(m)
2.120
2.290
5.176
5.469
Length of
Bend(m)
0.27
1.8
0.33
4.02
Fan
A
B
C
D
Total length
duct (m)
30
24
40
36.5
Total pressure Power of fan
T.P.L (Pa)
(kW)
32.39
5.83
28
8.85
45.4
13.29
45.98
30
6.8. Fan power calculation
We calculate fan power on welding and Blacksmithing of Workshop, the drag rate of each
welding machine is 7.5 L / sec
From the right side of the workshop [25]
6.8.1. Inlet losses
K ( U2 / 2g )
Head loss = 0.061
K = 0.43
U = 3 m/sec
Head loss = 0.062
0.43
(9/2
9.81 ) = 0.012 m
6.8.2. Calculations of Bends
=
= 0.5
=
n = - 2.13 (
= ( 0.33
= 2.5
)0.126 = - 2.13 ( 0.5 ) 0.126 = - 1.95 m
) n = ( 0.33
2.5 ) -1.95 = 1.455
L = 0.873 m
Total length = 2 + 2
0.873 + 0.012 = 3.758
We take the amount of pressure losses (1.0 Pa / m)
T.P.L = 1.0
3.758 = 3.758 Pa
Power of each fan = flow rate
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T.P.L
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Nehayat H. Amin
= 3.758
0.075 = 0.281 Kw
The left side is similar to the right side but added to the losses is the length of the duct
amounted of (8 m)
Total length = 3.758 + 8 = 11.758
T.P.L = 11.758
Power of each fan = 11.758
0.075 = 0.881 Kw
A section of the duct at the rectangle inlet (0.3 0.6) (b
workshops a fans to outside, the power of each fan (1 Kw)
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Design and Study of Ventilation Systems for Natural and Private Buildings
7. CONCLUSIONS
Ventilation is two types (natural and private). The private ventilation differs from the natural
ventilation by adding filters and the work of reserving the air outside the space and then
putting it out by private ducts. The private ventilation also requires air rates and required
ventilation models. The air is withdrawn from the zones according to the intensity of air
pollution in the space. Air is withdrawn from areas according to the intensity of air pollution
in the space
From this research we know the methods of air supplying which are through the air ducts,
which are three methods
1. velocity reduction method
2. equal friction method
3. static regain method
Fans were identified as Centrifugal fans, Vaneaxial Fan, Tubeaxial Fan and Propeller
Fan. Vaneaxial fans were selected in the building model. Through this research we identified
the types of filters in the ventilation, including Input Filters, Pre-Filters, Primary, Final Filters
and High efficiency particulate air (HEPA) filters used in the most polluted areas
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