Power Engineering MCQ: Power Engineering Chapter 135

When complete control systems become very complex, which control signal medium is preferred?

a) Pneumatic
b) Electric
c) Electronic
d) Digital
e) Fibre optic

Answer: A

Dehumidification is achieved by

a) absorbing the moisture with a sponge filter
b) absorbing moisture with a chemical drying agent
c) cooling the air to a corresponding dew point temperature
d) heating air to a corresponding wet bulb temperature
e) saturating the air until the precipitation point at room temperature is reached

Answer: C

Air conditioning with respect to heating coils is achieved in which of the following ways?

a) A combination of tempering control functions
b) The selected mixing of warm return air and cooler outside air
c) Selective heating by passing air through the heating coils
d) Proportioning the amount of air flow through the face damper for heat addition, or through the bypass dampers for no heat addition.
e) All of the above

Answer: E

Which of the following is not a correct method of heat regulation?

a) Direct modulation of the control valve on the steam or hot water to the heating coil
b) Modulating the position of a 3-way mixing valve on the hot/cold water line into the coil
c) Modulating the relative positions of face and bypass dampers controlling air flow across the coils
d) Modulating the actuators or the steam or water supply in conjunction with the coil bypass damper
e) Modulating the valve and the face and the bypass damper 30 degrees out of phase.

Answer: E

When the outdoor air damper increases the flow of fresh air, which of the following is true?

a) The return air damper throttles up to reduce the volume of recirculated air.
b) The return air damper throttles up to increase the volume of returned air.
c) The return air damper is not affected.
d) The return air damper throttles down to reduce the volume of returned air.
e) The return air damper throttles up to increase the volume of returned air.

Answer: D

Why is the positioner for the outdoor air damper of an HVAC air handling unit interlocked with the supply fan?

a. So the damper will close when the fan starts
b. So the damper will open when the fan starts
c. So the fan starts when the damper opens
d. To ensure the fan stops when the damper is fully open
e. To ensure the fan starts when the damper is fully closed

Answer: B

A main advantage of steam grid humidifiers over steam pan humidifiers in HVAC systems is?

a. Steam grid humidifiers can use inexpensive 2-position controls
b. There is minimal response-time lag with steam grid humidifiers
c. Steam grids can achieve higher relative humidity
d. Steam grids do not require humidistats
e. Steam grids humidifiers require less space

Answer: B

HVAC control systems maintain minimum _______ air during periods of extreme high and low ambient temperature.

a. Return
b. Supply
c. Ventilation
d. Exhaust
e. Recycled

Answer: C

The outdoor air inlet damper of an HVAC air handling unit may be split into two parts to provide:

a. Extra outside air when extra ventilation is required
b. A means of controlling building static pressure
c. Minimum outside air during periods when maximum air is being exhausted
d. Maximum outside air during periods when minimum air is being exhausted
e. Minimum outside air required for ventilation, during times of maximum return air recirculation

Answer: E

When the outdoor air damper of an HVAC system opens to increase the flow of fresh air, the return air damper

a. opens to reduce the recirculated air
b. opens to increase the recirculated air
c. closes to increase the recirculated air
d. closes to reduce the recirculated air
e. modulates to maintain building static pressure

Answer: D

In an HVAC system, a differential pressure controller maintains supply air duct static pressure constant by

a. modulating the position of the relief air damper
b. decreasing air temperature
c. modulating the damper on the suction side of the fan
d. modulating the damper on the discharge side of the fan
e. increasing air temperature

Answer: C

In extremely cold climates, it may be necessary to _________________________ in an HVAC system.

a. Increase the temperature controller's throttling range
b. Close the outdoor air dampers
c. Install two separate pre-heater coils
d. Heat the dampers
e. Spray warm glycol on the hot water coils

Answer: C

In an HVAC system, to provide a two-position damper with manual proportional control, a/an _________ is required.

a. Gradual switch
b. Offset returned air duct
c. Air mixer
d. Variable air volume box
e. Variable frequency motor drive

Answer: A

A variable air volume HVAC system requires static pressure control on the _______ air duct system.

a. Return
b. Supply
c. Ventilation
d. Exhaust
e. Recycled

Answer: B

What should be done to prevent the compressor in a cooling system from starting and stopping too frequently?

a. Start and stop the compressor with a setpoint thermostat
b. Turn off the compressor when temperatures required for conditioning are reached
c. Run the compressor continuously and vent any excess cold air
d. Run the compressor continuously, and unload it when the temperature setpoint is reached
e. Run the main supply air fan continuously

Answer: D

In an HVAC air-handling unit, temperature control that uses face and bypass dampers:

a. Closes the bypass damper and opens the face damper to direct air through the coil
b. Closes both the bypass damper and the face damper to direct air through the coil
c. Opens the bypass damper and closes the face damper to direct air across the coil
d. Increases air flow through the bypass to increase air temperature
e. Modulates the hot and cold deck airflows to maintain a constant supply air temperature

Answer: A