Talking About Exhaustors

Used always when forced ventilation is needed in order to change the air in a room.

DILUTING VENTILATION

Let us talk in the first place about diluting ventilation, that provides a gradual dilution of the air in the room. This kind of ventilation is not recommended for rooms with polluted air, because it would distribut the pollutors prior to withdrawing them.
To calculate which type will supply the needs of the room i is necessary

To know the dimensions of the room

• To be in possession of the ASHRA table
• To have the lay-out of the building

Let us imagine that an auditorium is 15 meters broad, 10 meters long and 5 meters high. A survey has been requested of what would be necessary to renew the air this room.

1. The ASHRA table demands that the air in an auditorium be changed 10 to 20 times an hour
2. The existing air volume in this auditorium is 15x10x5=750m30
3. Calculation

   750 x 20 = 15000m3 / hour, in wich formula 750 is the air volume of the auditorium and 20 the number of the necessary changes of air
   15.000 m3/h ÷ 60 = 250m3/min

   If the lay-out permits such installation, we indicate 4 equipments of the E40T4 type, an exhaustor with 40 cm of diameter and a three phase, 4 pole drive motor. It can be verified in the axial exhaustor catalogue that this equipment has an output of 75 m3/min. By installing 4 such equipments we obtain an output of 300 m3/min which perfectly meets the requirements.

4. Important notes:
   • If noise must be avoided we indicate another exhaustor with higher polarity and lower rotation, that consequently produces less noise. In this case we recommend the E40T6 type.We will have to install 5 equipments of this kind with an output of
     55 m3/min each x 5 = 275 m3/min.
   • If there is no three phase current on the site of installation, an equivalent single phase equipment can be installed.
   • If there are heat generating sources in the room, the number of changes per hour must be increased.
   • If the site does not permit the installation of wall exaustors, the alternative is the installation of roof exhaustors (Ventisilva FV line).
   • In our example the recommended solution is the installation of 2 equipments of the E60FV type. This exhaustor has an output of 140m3/min which multiplied by 2 results in 280 m3/min.
     
5. INSTALLATION

   Whenever possible the exhaustors/ventilators should be installed on opposed walls. In our example higher efficiency will be achieved if two equipments blow the air into the auditorium and two equipments expel it.

The figure below shows the best way of installing exhaustors in the mentioned auditorium.

io.

	2 exhaustors withdrawing air from the room 2 exhaustors blowing air into the room
	2 exhaustors soprando air

An exhaustor/fans should never be installed near an open window, for in this case the air will describe a 360 degree movement between the exhaustor and the window

As a general rule for any room submitted to air exhaustion, the installation should be calculated in order to provide a positive pressure in the room, i.e. there should be more air blown into the room than withdrawn from it. If the contrary occurs, the internal pressure will be negative and external polluters will enter the room.

As to the hight, the ideal solution is to install the succioning equipment on a higher level, having in mind that warm air tends upward, and the blowing equipment on a lower level.

VENTILAÇÃO LOCALIZADA EXAUSTORA

Used in case of heat source or polluter. The important thing is to withdraw this "air" from the room.

The main applications are: industrial ovens, polishing machines, volatile liquids, smoke, rubber ou plaster manufactures, painting cabinets, gases, etc.

For each case there is a specific exhaustion/ventilation system and each case should always be treated individually.

The pressure depends on the charge lost in the piping.

For low pressures up to 20 mmca an axial exhaustor is indicated and for higher pressures over 20 mmca a cetrifugal exhaustor should be used.

Axial exhaustors are usually installed on walls or pipings. Contrary to this, centrifugal exhaustors are installed only on pipings. The illustration below gives an idea of the installation of a centrifugal exhaustor.

Still talking about centrifugal exhaustors, they are supllied in a high speed version (3.600 rpm) and in a normal speed version (1.750 rpm) and can be driven by three phase or single-phase motors (execution).

It must be pointed out that there are situations where it is impossible to install an axial ou centrifugal exhaustor with the motor inside the piping, because the motor must not get in touch with the polluting agent present in the pipes.

Example: succion of corrosive or explosive gases, hot particles and heavy polluters. In such cases exhaustors with transmission Ventisilva type TR apply.

In this equipment the motor is coupled to the helix by a belt transmision avoiding that the pollutors pass through the motor.

Ventisilva also offers a line of coupled axial exhaustors made of carbon steel for installation in windows, where the windowpane ist substituted by a steel plate. This equipment is recommended in situations where installation on walls is impossible.

Ventisilva FV-Line

When the conditions do not permit that the air exhaustion be performed by installing exhaustors on the walls, it becomes necessary to place the exhaustor on the roof. The exhaustor is fixed by a special fiber glass tile with a reinforcement of ¼ x ¾ x 1800 flat iron that measures 1,84 x 0,90 meters. On top of the exhaustor a cone made of galvanized sheet is adapted in order to prevent the passage of rain water

Ventisilva FC-Line

In some cases the exhaustors must act directly on heat generating sources and have to be constantly moved from place to place. In such cases, the recommended equipment ist the Fan-Cooler, built on a special undercarriage to facilitate handling. This equipment is also largely used for drying or cooling duties in the industry.

Metalúrgica Ventisilva Ltda Rua Tobias Barreto, 615 - Mooca - CEP 03168-902 - São Paulo - SP Fone +55 11 2602-2400 - FAX +55 11 2602-2443