Part B Exam - Unit 10

In general, relative humidity should be kept between:

30% and 70%

Rooms on the _____ side should be kept warmer in winter.

North

Fixed outdoor air percentage systems do not respond well to:

Weather changes

On cold winter days, more air will be:

Recirculated

On hot summer days, more ___________ is drawn in.

Outdoor air

When a mixture hits dewpoint, the mixture is said to be:

Saturated

From a health standpoint, the relative humidity should be kept between:

35% to 50%

What does it mean if a slight condensation appears on the corners of the window panes?

The building has reached its maximum permissible value with relation to the outside temperature

How should plate units be maintained?

They should be soaked in a slightly acidic solution, then washed in soapy water

What is the most versatile industrial/commercial humidifer?

Air washers

Why should air washers be installed on the suction side?

So it can be maintained slightly below atmospheric pressure

When used for humidification, the air washer spray water must be:

Heated above the dew point

When used for both heating and humidification, the air washer spray water must be:

Heated above the dry-bulb temperature

The steam pressure in the steam grid humidifier must be around:

35 to 70 kPa

Why is it not recommended to use an on-off control for a steam grid humidifier?

Because fogging, overheating, and fluctuations in the RH may occur

What is the purpose of a baffle in the steam grid humidifier?

It knocks down any condensate formed in the supply line

In clean steam humidification, the connecting piping must be made of:

Stainless steel

How often should you flush the humidification system?

Weekly

Air pressure is normally:

Slightly above atmospheric

The static pressure can be read by connecting the manometer at a __________ to the ducts.

Right angle

Why is the conversion of pressure and velocity never 100% efficient?

Due to eddy currents

In centrifugal fans, air enters near:

The axis of the wheel

Where is the outlet located in centrifugal fans?

Tangentially to the fan wheel

The fan housing of centrifugal fans is of the _________ shape.

Scroll or volute

What are the types of centrifugal fans? (4)

Backward inclined

Forward curved

Backward inclined airfoil

Radial

What characteristics does an FC fan have compared to a BI fan?

Can operate at a much lower speed, but consumes much more power and is less efficient

Why is the BI fan also called a non-overloading fan?

It has relatively constant power requirements for a given speed

Why is the FC fan also called an overloading fan?

Power requirements will increase with changes to airflow, which causes the motor to overload

The difference between axial flow fan curves and the other two fan curves are the slopes of the:

Horsepower and static pressure

BI fans and FC fans are both logical choices when:

Large volumes of air must be moved at low pressures

Direct drives are normally used on:

Smaller air moving equipment

Which drive is used on most HVAC applications?

V-belt drives

To minimize vibration problems on the V-belt drive, use:

Balanced sheaves

It is customary for the manufacturer to supply a _______________ when the motor size is 5.6 kW or smaller.

Fixed pitch fan sheave

An _______________ is available for sizes 7.5 kW or larger.

Adjustable pitch motor sheave

Why do better quality belt guards have a facing of expanded wire mesh?

To allow inspection of belts while they are in motion

What permits measurement of the fan and motor speed without removal of the belt guard?

Tachometer holes

Which volume control is the most efficient?

Variable speed motor control

VFDs control speed and torque by controlling:

The input frequency and voltage

Which volume control is the least efficient?

Outlet damper control

The outlet damper control is used on fans with:

Constant speed

How does the variable inlet vane control reduce energy consumption?

By controlling the amount of air spin

In the natural air intake & mechanical exhaust, the pressure in the building is:

Slightly lower than atmospheric pressure

In the mechanical air intake & natural exhaust, the pressure in the building is:

Slightly higher than atmospheric pressure

While operating a mechanical air intake & mechanical exhaust, a concern for the operator is maintaining:

Positive building static pressure

If people are having trouble opening or closing doors using mechanical air intake & mechanical exhaust:

The building might have incorrect static pressure

Dry filters are efficient when screening:

Dust and lint

Bag type and wedge type dry filters have a very large filtering area and are made from:

A special modacrylic fibre

Rotating filters are less expensive, and thus are used to:

Capture larger particles that would plug up the more expensive filters

What is the most common filter type used?

Viscous impingement filters

An air velocity of _____ m/s is common for viscous impingement filters.

2.5

What material should you use for viscous impingement filters?

Fibreglass

Which filter must use multistage filtering?

HEPA filters

In electrostatic precipitators, alternate plates are _________ charged with _____ VDC.

Negatively, 6000

What is placed ahead of the electrostatic precipitator to filter any large particles?

Throwaway dry filters

Which air filter is the best filter for the removal of fine dust, smoke, and fumes?

Electrostatic precipitators

Charged members in charged-media electronic air cleaners are _____ VDC.

12000

What is an advantage of the charged-media electronic cleaner?

Even if the power supply fails, the filter media will still act as an impingement filter

What are some disadvantages of the charged-media electronic cleaner?

It offers resistance to airflow, and the medium needs replacing at regular intervals

Which filter has low efficiency in dust removal?

Air washers

Odour adsorbers contain _________ or _________ that adsorb odour-causing gases up to about _____%.

Carbon

Potassium permanganate

20

Sometimes, odour adsorbers may be reactivated by heating it to ____degC.

540

In areas required to be bacteria-free and mould-free, use:

Germicidal lamps

Duct systems are classified by:

Pressure and velocity

By increasing the size of the ducting, what will decrease?

Air friction and resistance airflow

What are the materials used in sheet metal duct?

Galvanized or black steel

What is the advantage of using galvanized steel?

It has corrosion resistance

What are black steel heavy gauge sheets used for? (3)

Kitchen exhaust ducts

Ducting protected with waterproofing mastic coatings

Drain pans

What are cement asbestos ducts used for?

Buried exhaust of corrosive material

How is the air handling unit connected to the duct work?

With a flexible connector to reduce vibration and sound transmission

Ducts of large dimensions must:

Be provided with stiffeners or be diagonally creased

The ratio of the slope should be:

1 in 7

What may be used in ductwork to increase velocity?

Mitre elbows

Short radius elbows should be provided with:

Turning vanes

Fire dampers with fusible links set for about ____degC must be installed in ducts.

70

Air leakages from ducts vary from __________%.

5 to 30

When the entire supply duct is outside the conditioned space, assume ____% leakage.

10

When the entire return air duct is outside the conditioned space, assume ____% seepage.

3

Seepage may increase the load on the air system in terms of:

Volume of air

Duct liners consist of flexible or semi-rigid fibreglass blankets to:

Help withstand erosive air velocities

Refer to NFPA _____________ on duct lining materials.

Standard 90A

When should acoustical liners not be used for thermal insulation?

If the duct wall temperature can fall below the dew point of the air flowing in the duct

What are the two different types of modulating dampers?

Mixing boxes, face and bypass dampers

Relief dampers can be compared to:

A check valve

The relief damper is also referred to as a:

Backdraft damper

Why are single blade dampers restricted to small sizes?

Because of the difficulty of securing proper operation with high velocity air

Parallel blade dampers are best suited for what kind of damper operation?

Two-position

Opposed blade dampers are superior when:

A modulation of airflow is required

It is important to locate air intake louvres away from:

Exhaust air streams

The diffuser ____________ and is the most common terminal air distribution device.

Reduces the velocity of air

Sound-absorbing material must be:

Porous

One of the most effective locations for sound-absorbing lining is in the:

Suction and discharge plenum of the fan

Short length steam coils are ____ m or less.

1.1

Most freeze-up problems occur in steam coils handling:

100% outside air

What should you do for a less chance of freeze-up in coils with long tubes?

Use a two-position control valve and preheat coil

The preheating coil should not be used to increase the temperature to more than ____degC.

18

Coils with long tubes are used when there is a __________% fresh air makeup.

35 to 100

The damper motor of the coil with long tubes must be of the ______ type.

Spring return

It is a good practice to select steam coils so that at least ____% of the coil capacity is used.

40

High-pressure drop across the valve is desirable, as long as the drop is ____% of its initial steam pressure.

50