Air-conditioning System Assignment

Air-conditioning System Assignment
1. Sketch the air-conditioning system schematic diagram for a small restaurant (about 85 m2),
the system consists of a cooling tower; a inline pump and an indoor water-cooled package
unit. All major components must be properly labelled.
2. Sketch a piping schematic of a sea-water cooled air-conditioning system for a hotel. The
system consists of a sea water pump house located adjacent to the hotel and a central airconditioning plant-room located in basement.
Sea-Water Cooled Air-Conditioning Piping Schematic for a Hotel
3. List the systems included in a central air-conditioning system and draw a schematic
diagram to show their arrangement. State the heat flow path between the systems if the
central air-conditioning system is providing cooling to the conditioned space.
An air-conditioning system basically consists of air-side system, water side system and the
central plant.
The function of air-side is to distribute conditioned air to spaces to absorb heat and then
dumps heat to the circulating chilled water.
The function of water side is to circulate chilled water to remove heat absorbed by air side
system and dumps the heat to the central plant.
The function of central plant is to remove heat absorbed by waters system and dumps the
heat to ambient
4. A 20-storey office building is to be constructed with a central air-conditioning system. The
chiller plant is located on the roof using air-cooled condenser. Sketch a schematic diagram
showing the chilled water distribution system using reverse-return design.
FEED&
EXPANSION
TANK
UPPER
ROOF
ROOF
100mmdia.
CH.W.PIPEC/W
PHENOLICFOAM
INSULATION
AIR-COOLED
CHILLER
CHILLEDWATERPUMP#1
DETAIL
A
CHILLEDWATERPUMP#2
20/F
Typical
Floor
AHU20-1
AHU20-1
AHU20-1
AHUT-1
AHUT-1
AHUT-1
AHUG-1
AHUG-1
AHUG-1
G/F
Piping Schematic for Air-cooled A/C System
5.
With the aid of diagrams, describe the direct-return and reverse-return system chilled
water distribution systems and also state their advantages and disadvantages.
Direct-return system is a simple type chilled water distribution system. Chilled water is
circulated to the terminal units via the supply and return pipes. The system is suitable for
small central air-conditioning systems.
Reverse-return system is a more complicated chilled water distribution system. Chilled water
is circulated to the terminal units via the supply, return and reverse-return pipes. More
chilled water pipes are required and the system ensures that the length of piping circuit for
all the equipment is approximately equal.
Direct-return System
Advantages
Disadvantages
Lower initial cost because of shorter Water balancing work is not
piping system.
effective.
Simple and shorter piping system as Expansive water balancing valves are
compared with a reverse-return
required.
system with the same capacity.
Lower pump power consumption due Only suitable for small airto shorter piping system as compared conditioning system.
with a reverse-return system with the
same capacity.
Suitable for small air-conditioning
system.
Reverse-return System
Advantages
Less balancing work.
Suitable for large air-conditioning
system
6.
Disadvantages
Higher initial cost.
Piping system is more complicated.
A factory building is located in Tsuen Wan, suggest the most suitable air-conditioning
supply system for their.
a) Offices;
b) Stores;
c) Workshop.
State your reasons for the selected system and also state the most suitable heat rejection
system for the chiller plant.
Type of system
Air-water system
(using fan coil units)
System heat reject
method
Type of system
All-air system ( using
single zone airhandling unit)
System heat reject
method
7.
Office
Reasons
Localized temperature control is possible.
Less noise nuisance.
Does not require deep ceiling void to accommodate
air duct.
Air-cooled system is selected because sea water is
not available and the cost of refilling evaporated
water in cooling towers is very expensive.
Store/ Workshop
Reasons
Low maintenance cost.
Simple system control.
Ceiling space can accommodate large air duct.
Air-cooled system is selected because sea water is
not available and the cost of refilling evaporated
water in cooling towers is very expensive.
Explain the following all-air system in terms of the temperature and volume flow rate of the
air stream and illustrate the system classifications.
a) Constant air volume system.
b) Variable air volume system.
Constant air volume system – the volume flow rate of supply air remains constant but the air
temperature varies to match the variations of space heatload.
Variable air volume system – both volume flow rate and temperature of supply air vary to
match the variations of space heatload.
System classifications
Constant air volume system
• Single zone system.
• Multi-zone system.
• Central system with terminal reheat.
•
•
•
Variable air volume system
Single zone system.
Multi-zone system.
Dual duct system
Constant air volume system (Single zone system)
Variable air volume system (Single zone system)
8.
Give a brief description of the operation principle, application and the advantages of a
variable air volume (VAV) system.
Variable air volume system varies the supply air volume to match the variations of space
cooling or heating load. The air-conditioning system is operating in part load condition most
of the times and saving of power consumption can be achieved The VAV systems are widely
employed in places such as the office complexes, department stores, supermarkets and
auditoriums
The advantages of VAV system are:
a) Lower fan power consumption;
b) Better environment control;
c)
d)
9.
Good humidity control even in low load conditions;
Less temperature deviation in a large area.
Name Two major water-side components equipped in a sea-water cooled central airconditioning system and briefly describe their functions.
1. Pumps – circulates water in the water circuits;
2. Water-cooled chiller – provides chilled water for cooling purpose and dissipates removed
from chilled water to condenser water.
3. Plate –type heat exchanger – serves as a heat exchanger to permit heat dissipation from
condenser water to sea water. There is no direct contact between sea water and the
condenser tubes of the chiller. It eliminates the corrosion problem.
4. Strainer – removes rubbish from the circulating sea water.
10. Sketch an annotated air-side schematic diagram showing how the conditioned air is
supplied to a room using a VAV system. Briefly describe how the room temperature is
controlled in the VAV system.
Variable air volume system (Single zone system)
VAV system can maintain the room temperature within a small deviation by adjusting both the
temperature and volume flow rate of the supply air.
11.
State five (5) purposes of providing ventilation in a building.
a) To prevent depletion of oxygen content of air.
b) To prevent undue concentration of CO2, body odour and other indoor contaminants.
c) To remove sensible and latent loads inside buildings.
d) To remove toxic substances.
e) To provide air movement to prevent stuffiness.
12.
With the aid of diagrams, describe the three (3) basic types of mechanical ventilation
systems and also state their field of application.
Supply Ventilation
a) Air delivered by a fan to treated space.
b) Exhaust through purposely provided openings or other leakage path.
c) Space slightly pressurized.
d) Ingress of extraneous material prevented.
Applications
Store room.
Supply system
Extract Ventilation
a) Air extract by a fan.
b) Replacement air enters through any available gaps or purposely provided openings.
c) Removal of polluted air.
d) Space partially vacuum to prevent escape of contaminated air to adjoining space.
Applications
Pantry.
Toilets.
Extract system
Balanced Ventilation
a) Combination of supply and extract fans.
b) Close control of environment possible.
c) Space can be positively or negatively pressurized by varying flow capacities of supply and
exhaust fan.
d) Return / exhaust fan be considered for high return / exhaust duct losses. (usually above
60Pa)
e) Degree of pressurization: <50Pa
f) First hand approximation: achieved by 10-15% difference in air flow rates.
Applications
Transformer room.
Kitchen for restaurant.
Balanced system
13.
What is stack effect?
Stack effect is due to temperature differences between indoor and outdoor temperature. The
temperature difference results in pressure difference due to he difference in density between
warm air and cold air. In winter, the warm air tends to rise to the top of a building creating a
greater pressure at the top and a negative pressure at the bottom. This causes air to ex-filtrate
through openings and cracks near the top of a tall building and air infiltrates at the bottom. The
stack effect is significant in winter for building above four storeys.
14.
Briefly discuss two (2) the purposes of providing air-conditioning in buildings and
provide examples to support your discussion.
The main purposes of providing air-conditioning for building are:
a) To provide people with a comfortable and healthy indoor environment for various
activities in residential, commercial and public buildings.
b) To provide a suitable enclosed environment for certain manufacturing processes and
product storage such as factory workshops, scientific laboratories, test chambers,
computer rooms, and cold rooms etc.
15.
Briefly describe the air-side and water-side systems.
Air-side of a central air-conditioning system refers to the air distribution equipment and their
associated ductwork that circulate the conditioned air to rooms to cater for space heatload.
Water-side of a central air-conditioning system refers to the chilled water distribution
equipment and their associated pipework that circulate the conditioned water to remove the
heat released in the air-conditioned spaces.
16.
Compare the following heat rejection methods adopted by central air-conditioning
systems:
a) air-cooled system;
b) water-cooled system;
c) evaporative system.
Heat rejection method
Air-cooled system
Ambient air is used to remove heat.
Water-cooled system
Evaporative system
Water is used to remove heat.
Both ambient air and water are used to remove heat.
Tutorial – Introduction to HVAC System
1.
What are the purposes of air-conditioning systems?
The purposes of air-conditioning systems are:
a) To maintain a comfortable and healthy indoor environment in residential, commercial; and
public buildings;
b) To provide a suitable enclosed environment for certain manufacturing processes and product
storage.
2.
The window type or split type room air conditioner is also one of the air-conditioning systems,
what is the name? Give the name of the thermodynamic cycle inside the air conditioner to
produce cooling.
The air-conditioning system for window type or split type room conditioners is called directexpansion air-conditioning system. The thermal cycle for the system is called Simple Vapour
Compression Cycle.
3.
List the major components of vapour compression refrigeration cycle and state their functions.
The major components of vapour compression refrigeration cycle are:
Heat Rejection
Expansion
valve.
Compressor
Condenser
Air Off Coil
Refrigeration
pipework
Evaporator
Air On
DX coil as
evaporator
REFRIGERATION CYCLE WITH DIRECT
EXPANSION COIL
Evaporator – refrigerant evaporates inside the evaporator at a lower temperature than its surroundings,
absorbing its latent heat of vaporization.
Compressor – refrigerant is compressed to a higher pressure and temperature by compressor
condensation.
Condenser – gaseous refrigerant is condensed into liquid form by transferring its latent heat of
condensation to a coolant inside the condenser.
Throttling and Expansion Valve – the higher pressure liquid refrigerant is throttled to the lower
evaporating pressure by the expansion valve and is ready for
evaporation.
4.
List the systems included in a central air-conditioning system and draw a schematic diagram
to show their arrangement. State the heat flow path between the systems if the central airconditioning system is providing cooling to the conditioned space.
An central air-conditioning system consists of air-side system, water side system and a central airconditioning plant.
The function of air-side is to distribute conditioned air to spaces to absorb heat and then dumps heat
to the circulating chilled water.
The function of water side is to circulate chilled water to remove heat absorbed by air side system
and dumps the heat to the central plant.
The function of central A/C plant is to dump the heat absorbed by chilled water from the internal
area of building to ambient.
5.
What are the names of major central air-conditioning systems which can be classified?
Central air-conditioning systems can be classified as:
a) Air-cooled system;
b) Water-cooled system;
c) Sea water-cooled system;
d) Direct-expansion system.
6.
Name six types of all-air systems.
The six-type of all-air systems are:
a) Single zone system;
b) Multi-zone system;
c) Central system with terminal reheat;
d) Single zone VAV system;
e) Multi-zone VAV system;
f) Dual duct system.
7.
What is a chiller?
Chiller is a large air-conditioning unit to produce chilled water with compressor(s), condenser and
evaporator mounted on the same chassis. Its capacities range from 200RT to thousands RT.
8.
Describe with the aid of sketch the three methods of rejecting heat for water-cooled chiller.
a) Cooling Tower;
b) Dry Tower;
c) Sea Water.
a) Cooling Tower
b) Dry Tower
c) Sea-water
9.
Discuss the advantages and disadvantages of using air-cooled condensers and water-cooled
condenser.
Air-cooled condenser
Advantages:
a) Required no water;
b) Lower installation cost;
c) Lower maintenance cost;
d) Less Piping required;
e) Occupied less space.
Disadvantages:
a) Required located outdoor;
b) Relatively lower efficiency;
c) Noise problem;
d) Higher peak power requirement per ton;
e) Start-up problem at low outdoor temperature.
Water-cooled condenser
Advantages:
a) Higher efficiency;
b) Suitable for area fresh water is readily available;
c) Relatively quite in running condition.
Disadvantages:
a) Required located outdoor;
b) Higher maintenance cost;
c) More pumps and pipework required;
d) Water treatment required for the condensing water.