Ventilation

Question 1

Purpose of ventilation

Answer 1

Control odors, temperature and humidity, contaminant concentration

Question 2

Local exhaust ventilation

Answer 2

Capture contaminant at source and remove from work environment

Question 3

Dilution ventilation

Answer 3

Dilute concentration by adding clean air

Question 4

General ventilation

Answer 4

Climate control, comfort of building occupants

Question 5

Dilution vs LEV

Answer 5

Dilution: moderate to low tox, disperse source, intermittent exposure

LEV: high tox, single source, direct exposure

Question 6

What affects the density of air?

Answer 6

Temperature, elevation, humidity

Question 7

Density correction factor

Answer 7

Accounts for non-standard conditions which affect air density

Question 8

Major assumptions about movement of air

Answer 8

1. Incompressible

2. Constant density

Question 9

Flow profile difference between laminar and turbulent flows

Answer 9

Turbulent: flatter
Laminar: parabolic, center line has higher velocity than sides

Question 10

How does air move through a duct?

Answer 10

Difference in pressure

Question 11

Static Pressure

Answer 11

Pressure against the sides of a duct, acts equally in all directions, differences in SP cause air to move, is like potential energy

Question 12

Velocity Pressure

Answer 12

Pressure of air motion, always positive and represents the pressure required to move air, is like kinetic energy

Question 13

Total Pressure

Answer 13

SP + VP

Question 14

Losses

Answer 14

SP in = SP out + losses

Losses are due to friciton and turbulence

Question 15

Volume flow rate

Answer 15

Q = VA

Question 16

3 types of hoods

Answer 16

Enclosing, capture, receiving

Question 17

Static hood pressure

Answer 17

SP[hood] = VP [duct] * (1 + K)

K values can be found in tables

Question 18

Coefficient of entry

Answer 18

Q[actual]/Q[ideal]

Question 19

Hood entry loss

Answer 19

he = F[h] x VP, where F[h] = loss factor (found in tables)

Question 20

How does SP losses occur in ducts?

Answer 20

Due to friction, affected by VP. Factors include smoothness of duct interior and presence of settled dust.

Question 21

Purpose of a fan?

Answer 21

To create SP

Question 22

Axial flow fans

Answer 22

• Flow moves along axis of rotation
• General/dilution ventilation
• Not good for LEV, insufficient SP

Question 23

Centrifugal fans

Answer 23

Used for LEV, can run backwards with correct airflow direction and reduced efficiency

Question 24

Centrifugal radial fans

Answer 24

Blades look like paddle wheel, self cleaning, work horse

Question 25

Centrifugal backward-curved fans

Answer 25

Wing shaped blades, higher performance, can’t be used in dusty environments, noisy

Question 26

Centrifugal forward-curved fans

Answer 26

Not good in dusty environments, moves large Q with little SP reqs, quiet

Question 27

Fan static pressure

Answer 27

Fan[SP] = SP[out] - SP[in] - VP[in]

Question 28

Six in three out

Answer 28

Allow 6D of duct into fan, allow 3D out of fan

Question 29

Air hp

Answer 29

min power needed to move air

Question 30

Brake hp

Answer 30

actual power needed to operate fan

Question 31

Motor hp

Answer 31

Bhp plus power for drive losses

Question 32

Fan Laws

Answer 32

Q ∝ RPM
SP ∝ RPM^2
HP ∝ RPM^3

Question 33

Volume of air needed to dilute

Answer 33

Q = (403 x 10^6 x SG x ER x k)
__________________
(MW x C)

k = safety factor (0-10)
SG = specific gravity
ER = Evaporation rate
MW = Molecular weight
C = Concentration

Question 34

What are non-equilibrium conditions?

Answer 34

Build up and decay