VENTILATION

Ventilation : This guide is intended to help employers and employees assess the health risks associated with ventilation systems in their workplace. such assessments can be no more than an examination of what, in the course of work , could possibly cause harm to people . with the help of this guide . you may identify hazards, the degree of risk and the possible solutions.

VENTILATION

VENTILATION

Introduction

This guide is intended to help employers and employees assess the health risks associated with ventilation systems in their workplace. such assessments can be no more than an examination of what, in the course of work , could possibly cause harm to people . with the help of this guide . you may identify hazards, the degree of risk and the possible solutions.

Ventilation of a Building .

Ventilation is the process of supplying and removing air by natural or mechanical means to and from a building . the design of a building's ventilation system should meet the minimum requirements of the Building (Ventilation Systems) Regulations .

Natural Ventilation 

Covers uncontrolled inward air leakage through cracks , windows , doorways and vents ( infiltration) as well as air leaving room (ex filtration) through the same routes . Natural ventilation is strongly affected by weather conditions and is often unreliable.

Natural Ventilation

Mechanical Ventilation

Mechanical or forced ventilation is provided by air movers or fans in the wall, roof or air - conditioning system of a building . It promotes the supply or exhaust air flow in a controllable manner .

Mechanical Ventilation

Purposes of Ventilation 

Ventilation in building serves to provide fresh and clean air , to maintain a thermally comfortable work environment . and to remove or dilute airborne contaminants in order to prevent their accumulation in the air .

Air conditioning is a common type of ventilation system in modern office buildings. It draws in outside air and after filtration , heating or cooling and humidification, circulates it throughout the building .

A small portion of the return air is expelled to the outside environment to control the level of indoor air contaminants .

An air- conditioning system

The efficiency of a ventilation system can be evaluated through investigation of environmental factors such as the quality of supply air, the thermal comfort conditions of the occupied space and the level of airborne contaminants therein .

Natural ventilation 

Typical examples of natural ventilation 

• Infiltration - air permeates through leaking structural joints. window gaps, etc .
• Historically the most widely used ventilation in residential and small office buildings.
• Modern windows are light, so infiltration is too small to keep ventilation requirements 
• Interrupted ventilation - ventilation through openings.
• Suitable only for auxiliary increase of ventilation rate.

Typical examples of natural ventilation 

• Aeration-air supply and exhaust is caused through inlets with proper high difference 
• Industrial halls, stables .
• Regulation of inlets and outlets opening .

• Existing natural ventilation system .
• System features variety of ventilation towers, skylights, sunroofs, etc 

• Passive cooling .
• Heat gains-avoid of building overheating 
• Mechanical components like pumps and fans are not used .
• Suitable for mild climates with cool dry nights - can be done with simple ventilation .

Mechanical ventilation

• Mechanical ventilation 
• Dynamic pressure of a mechanical device-fan ,blower .

Basic purposes 

• Ventilation operable independent (less) on exterior conditions.
• High ventilation demand - high rate of pollutants production .
• Precise operation control.
• Temperature and humidity control .
• Categories Air pressure in a ventilated room .
• Pressure balanced system - into a ventilated room is being supplied the same amount of air as it is exhausted from it . No pressure difference to neighboring rooms.

Categories Air pressure in a ventilated room :

• Under pressure system- into a ventilated room is being supplied less amount of air than it is exhausted from it .Negative pressure difference to neighboring rooms - air permeates into room .

Categories Air pressure in a ventilated room :

• Over pressure system - into a ventilated room is being supplied more amount of air than it is exhausted from it . Positive pressure difference to neighboring rooms- air permeates from room .

Categories Purpose of a system 

• Ventilation - waste air exchange for fresh air , pollutants production.
• Warm air heating- air exchange controlling required indoor air temperature. Supply air temperature is higher than indoor air temperature .Coverage of entire or partial of a room heat loss. May be in combination with ventilation .
• Air condition - complex control of indoor air parameters through supplied air . Maintenance of temperature . moisture parameters and quality of supply air.

Local / decentralized systems .

Local / decentralized systems 

Advantages :

• Institution of local zone with different parameters ( even in one air volume of a hall) .
• Without duct work .
• Avoid degradation of fresh air in compare to central system (in case of poor maintenance) .
• Local control and automation of units .
• reuse of warmer air layers bellow roof .

Disadvantages:

• Higher number of smaller units (maintenance)
• More complicated connection to other system.

CFM/exh : Is the amount of air drawn from the place to be ventilated .

V: The volume of the place to be ventilated .(M^3)

ACH : Air change per hour . depended on the application . obtained to from code .

The most famous places : 

In bathroom we draw an amount of air through a Fan (exhaust fan) and compensate for this quantity with fresh air through the doors .

Ventilation of garages

Example : Assuming we have a garage area of the garage is 850 m3 and the height is 4 m 

CFM = 850 * 4 * 8 / 1.7  = 16000

• This quantity of CFM is pulled from the place by FAN and ducts and air terminators ( girls).

• But car exhausts are heavy . part of the quantity withdrawn is ( high level ) and the anther part is drawn from (low level) .

High level 2 / 3       ( 65% ) .

Low level  1 / 3       ( 35 %) .  ( 40 cm from F.F.L)

CFM exh,up = .65 * 16000 = 10400 CFM

CFM exh down = .35 * 16000 = 5600 CFM

CFM fresh = ( 85% - 90% ) from CFM exh

CFM fresh =  .85 * 16000 = 13600 cfm 

We will need tow fans 

• Fan is exhaust (16000 CFM )
• Fan is fresh air ( 13600 CFM )

Type of Fans : 

• Axial Fan . 
• Mixed Flow Fan .
• Centrifugal Fan .

Hours power of fan ( in tow way )

• From the fan catalog .
• From code 

Engine room ventilation

Thank you