ESET 444 Qz 3 QUESTIONS WITH COMPLETE
SOLUTIONS
This system keeps supply air always at the same temperature, and delivers more or less
air as required to maintain or change the temperature in the space - answer ( )Constant
volume
(x)Variable air volume
( )Fan-based temperature control
( )Constant density
This system always delivers the same airflow but the air may be hotter or colder as
required to maintain or change the temperature in the space - answer (x)Constant
volume
( )Variable air volume
( )Thermostatic temperature control
( )Constant density
How can a single-duct system be divided into zones with different thermal
requirements? - answer ( )Reheat method - Cool the airflow to meet the needs of the
zone that needs most cooling, and then reheat it for the other zones using a heating
terminal at the point of entry to each space
( )VAV method - Cool the airflow to meet the needs of the zone that needs most cooling,
and then reduce the volume of air supplied to the other zones using a VAV box at the
point of entry to each space
( )Provide separate hot and cold air flows to each zone
(x)Either reheat method or VAV method could be used
An air-side economizer is used when: - answer ( )Most zones in the system require
cooling and only one or two require heating. The system makes cold air to satisfy the
majority of the zones and reheat is applied in the one or two zones that need heating
( )The return air from the space is relatively free from contaminants and CO2. The return
air is then recycled into the space, since it has already been conditioned and will require
less energy to treat.
( )The price of electricity from the grid is greater than the price of on-site generation. An
on-site generator is then used to produce electricity for air-conditioning at lower cost.
, (x)The enthalpy of outdoor air is lower than that of the return air. The outdoor air is then
used to provide free cooling, by bringing in more outdoor air than is required to meet
needs for fresh air ventilation.
Reheat systems have many advantages - they permit simple zone control for areas with
different loads, can provide heating or cooling to different areas at the same time,
maintains close control over humidity and offers flexibility when zones are selected at
design stage. What is the main disadvantage? - answer (x)The system uses energy to
cool air and then uses energy again to heat it back up. This is wasteful of energy and
uneconomical
( )The system can't be easily changed to provide more zones once it is installed.
( )The system can't be easily metered to determine which zones consumed the most
energy
( )The system can't be easily adapted to allow for heat recovery.
Which of the following is/are disadvantages of a zoned variable air volume system? -
answer ( )Poor energy efficiency since so much energy is used for fans
(x)Possibly poor ventilation if a zone does not require much air for cooling
( )Difficult to adapt to an air-side economizer
( )Difficult to control to achieve the desired effect in each zone
Which of the following approaches has the lowest energy consumption: - answer
(x)Single-duct zoned variable air volume
( )Single-duct zoned-reheat constant volume
( )Dual-duct
( )Multizone
Select the answer which best describes this system. Air is supplied to an undivided
conditioned space by a system capable of providing a warm or cool airflow as required.
- answer (x)Single-duct single-zone variable air volume
( )Single-duct single-zone constant volume
( )Dual-duct
( )Multizone
Select the answer which best describes this system. Air is supplied to a conditioned
space by a system capable of providing a warm airflow and a cool airflow which is then
mixed by a box at the point of entry to the space. - answer ( )Single-duct zoned variable
air volume
SOLUTIONS
This system keeps supply air always at the same temperature, and delivers more or less
air as required to maintain or change the temperature in the space - answer ( )Constant
volume
(x)Variable air volume
( )Fan-based temperature control
( )Constant density
This system always delivers the same airflow but the air may be hotter or colder as
required to maintain or change the temperature in the space - answer (x)Constant
volume
( )Variable air volume
( )Thermostatic temperature control
( )Constant density
How can a single-duct system be divided into zones with different thermal
requirements? - answer ( )Reheat method - Cool the airflow to meet the needs of the
zone that needs most cooling, and then reheat it for the other zones using a heating
terminal at the point of entry to each space
( )VAV method - Cool the airflow to meet the needs of the zone that needs most cooling,
and then reduce the volume of air supplied to the other zones using a VAV box at the
point of entry to each space
( )Provide separate hot and cold air flows to each zone
(x)Either reheat method or VAV method could be used
An air-side economizer is used when: - answer ( )Most zones in the system require
cooling and only one or two require heating. The system makes cold air to satisfy the
majority of the zones and reheat is applied in the one or two zones that need heating
( )The return air from the space is relatively free from contaminants and CO2. The return
air is then recycled into the space, since it has already been conditioned and will require
less energy to treat.
( )The price of electricity from the grid is greater than the price of on-site generation. An
on-site generator is then used to produce electricity for air-conditioning at lower cost.
, (x)The enthalpy of outdoor air is lower than that of the return air. The outdoor air is then
used to provide free cooling, by bringing in more outdoor air than is required to meet
needs for fresh air ventilation.
Reheat systems have many advantages - they permit simple zone control for areas with
different loads, can provide heating or cooling to different areas at the same time,
maintains close control over humidity and offers flexibility when zones are selected at
design stage. What is the main disadvantage? - answer (x)The system uses energy to
cool air and then uses energy again to heat it back up. This is wasteful of energy and
uneconomical
( )The system can't be easily changed to provide more zones once it is installed.
( )The system can't be easily metered to determine which zones consumed the most
energy
( )The system can't be easily adapted to allow for heat recovery.
Which of the following is/are disadvantages of a zoned variable air volume system? -
answer ( )Poor energy efficiency since so much energy is used for fans
(x)Possibly poor ventilation if a zone does not require much air for cooling
( )Difficult to adapt to an air-side economizer
( )Difficult to control to achieve the desired effect in each zone
Which of the following approaches has the lowest energy consumption: - answer
(x)Single-duct zoned variable air volume
( )Single-duct zoned-reheat constant volume
( )Dual-duct
( )Multizone
Select the answer which best describes this system. Air is supplied to an undivided
conditioned space by a system capable of providing a warm or cool airflow as required.
- answer (x)Single-duct single-zone variable air volume
( )Single-duct single-zone constant volume
( )Dual-duct
( )Multizone
Select the answer which best describes this system. Air is supplied to a conditioned
space by a system capable of providing a warm airflow and a cool airflow which is then
mixed by a box at the point of entry to the space. - answer ( )Single-duct zoned variable
air volume
