3. CENTRALISED
AIR CONDITIONING
Central air conditioning systems serve
multiple spaces from one base location. These
typically use chilled water as a cooling
medium and use extensive ductwork for air
distribution
Continuing Education and Development, Inc.
9 Greyridge Farm Court Stony Point, NY 10980
4.
5.
6. Centralized systems are defined as those in which the cooling (chilled water) is generated in a chiller at one
base location and distributed to air-handling units or fan-coil units located through out the building spaces.
The air is cooled with secondary media
chiller
AHU
H2O (CHILLED)
(COLD AIR)
interior
7.
8.
9. Sub systems of centralized AC
Chilled water plant
condenser water system
(heat rejection system)
air-delivery system
10. The chilled water system supplies chilled water for the cooling needs
of all the building’s air-handling units (AHUs)
The system includes a chilled
water pump which circulates
the chilled water through the
chiller’s evaporator section
and through the cooling coils
of the AHUs.
20. System Types
The Central system category could be further
broken down into the following:
Central systems with CAV air-handling units
Central systems with VAV air-handling units
Central systems with fan-coil units (All- Water
systems).
21. CAV system is an all-air system which accomplish cooling and heating by varying
the supply air temperature and keeping the air volume constant.
The system works well and maintains comfortable conditions in spaces with uniform heating
and cooling requirements.
22. Variable Air Volume (VAV) system is an all air system which can satisfy the
individual cooling requirements of multiple thermal zones.
This is achieved by supplying air at a constant temperature from central
plant to one or more VAV terminal units in each zone and adjusting the
amount of supply air to meet required cooling loads.
The primary benefit of VAV over constant volume systems (CV) is its ability to
simultaneously provide the required level of cooling to any number of zones
within a building.
39. TYPES OF AHU SYSTEMS
•
•
•
•
•
single-zone
Multizone
dual-duct
Reheat
variable air volume systems
40. Single-zone systemsserve just one temperature zone the load must be
uniform all through the space controlled by
varying the quantity of chilled water or
refrigerant, adding reheat, adjusting dampers
Multi-zone systemsused to serve a small number of zones with just
one central air handling unit. made up of
heating and cooling coils in parallel to get a hot
zone and a cold zone .
Zone thermostats control mixing dampers to
give each zone the right supply temperature
41. •
•
•
•
•
Dual-duct systemsinstead of mixing the hot and cold air at the air
handling unit, the hot and cold air are both
brought by ducts to each zone where they are then
mixed to meet the needs of the zone.
Use high-pressure air distribution systems with the
pressure reduced in the mixing box at each zone
Used at:
Office Buildings. Institutional.
Reheat systems-
supply cool air from a central air handler to meet
the maximum cooling load in each zone.
Each zone has a heater in its duct that reheats the
supply air as needed to maintain space
temperatures.
constant volume systems
42. •change the volume of air in
response to a change in load,
rather than a change in the
supply air temperature.
•may change the volume of
the whole airflow and/or the
volume of each individual zone
Total system airflow may be
varied by the use of inlet vanes,
discharge dampers, speed
control, and variable pitch
blades.
•Zone airflow may be
modulated in coordination
with total system flow
modulation or it may be varied
by passing the excess flow right
to the return air system with no
variation in total system flow.
•Used at:
•larger office buildings.
Variable air volume systems -
43. • AHU classified on basis of
installation
VERTICAL AHU
HORIZONTAL AHU
CELING MOUNTED AHU
44. VERTICAL AIR HANDLING UNITS
•designed for vertical in room mounting
•VAHU comes with a fan and a cabinet that
can produce high profile static pressures
without occupying the larger footprint area
FEATURES
•high performance
•cost effective small air-handling
•Suitable for spaces with less area
APPLICATION
•
•
•
Classroom
Laboratories
Pharmaceutical labs
45. HORIZONTAL AHU
floor mounted air handler is usually a large metal box containing a
bowler, heating or cooling element
Features:
Low cost
Reliable
Easy to use
High durability
Application
homes
offices
institutions
factories
46. CEILING MOUNTED AHU
Features :
Cost efficient
High quality product
Easy to use
Perfect functionality
Applications :
Shopping Malls
Multiplexes
Small Offices
•Can be suspended from the ceiling and
hence require no floor space
•Noiseless units and can be placed above the
false ceiling in the conditioned area
•Units are unobtrusive giving flexibility to the
design of the interior
47. • TYPE OF AHU DEPENDING ON LOCATION OF FAN
• Draw through type:
fan located after cooling coil
• Blow through type:
fan located before cooling coil
Draw through type
Blow through type
Lower condensation of
water
Higher condensation
Less air leakage
More chances of air leaking
heat generated by fan
and motor added toair
downstream
of cooling coil, requiring
a colder leaving-coil
temperature to achieve
a desired supply-air
temperature
Heat generated by the fan
and motor is added to the
air upstream
of the cooling coil, allowing
for a warmer leaving-coil
temperature to achieve
a desired supply-air
temperature
48. •PACKAGED AHU
•common in smaller buildings and
commercial applications, particularly as
rooftop units.
•Packaged unit contain fans, coils, filters,
and dampers in a single casing
• casing include air conditioning
compressors, heaters such as gas burners,
electric heating coils, or heat pump coils.
•serve single temperature zones, VAV
serving multiple terminal boxes (zones) are
available.
•FEATURES
•Compact
•lower initial costs
•DISADVANTAGES
•inefficient
•maintenance intensive
49. ADVANTAGES
•
•
•
•
•
•
Modular construction and wide selection of air handling unit sizes
Wide application range
Low energy consumption
Low risk of condensation : air tight
Easy installation and adaptability to building condition
Easy maintenance: hygienically friendly
DISADVANTAGES
•
•
•
AHU is physically large and requires careful planning in terms of a suitable
location.
The space required for ducting and the corresponding holes through
building fabric require careful co-ordination with builders and other
mechanical services within the room.
Rooms with variable or moving sources of heat gain such solar gain
traversing around the room require sophisticated duct work and controls.
Zone heaters may have to be incorporated into duct branches.
50. INSTALLATION PROCESS
lifting or rigging the ahu to the site
locate the ahu in the ahu room
preparing unit for the installation
assembling the unit
cabinet installation
fan installation
electrical installation
coil and piping installation sheet
metal installation
final installation
controls installation
final sensor and actuator
calibration verification
51. • MARKET RATE
•
•
•
•
•
GEA Group, Germany
Carrier Corporation, New Jersey
Daikin Industries, Japan
Johnson Controls, U S
Rheem, U S
•
•
Trane, U S
ECE UK Ltd
• SOME INDIAN
BRANDS
•
Zeco, delhi
•
•
•
Blow-Tech Engineers, Mumbai
Axenic Systems, Mumbai
Poly extrusions (india) private limited
53. FAN COIL UNIT
• It part of an HVAC system found in residential, commercial, and
industrial buildings.
• A simple device consisting of a heating or cooling coil and fan.
• Used to control the temperature in the space where it is installed,
or serve multiple spaces.
• It is controlled either by a manual on/off switch or by thermostat.
• Fan coil units are more economical to install than ducted or central
heating systems with air handling units.
• They can be noisy because the fan is within the same space.
54. DESIGN
•
A fan coil unit may be concealed or exposed within the room or area that it
serves.
•
An exposed fan coil unit may be wall mounted, freestanding or ceiling
mounted.
•
It typically include an appropriate enclosure to protect and conceal the fan
coil unit itself.
•
Return air grille and supply air diffuser set into that enclosure to distribute the
air.
• A concealed fan coil unit will typically be installed within an accessible ceiling
void or services zone.
•
The return air grille and supply air diffuser will be ducted to and from the fan
coil unit.
55. OPERATION
• The coil receives hot or cold water from a central plant, and removes
heat from or adds heat to the air through heat transfer.
• Traditionally fan coil units can contain their own internal thermostat,
or can be wired to operate with a remote thermostat.
• In most modern buildings with a Building Energy Management
System (BEMS), the control of the fan coil unit will be by a local
digital controller. equipment for adding heat to the building's water.
•
•
•
Fan coil units circulate hot or cold
water through a coil in order to
condition a space.
The unit gets its hot or cold water
from a central plant, or mechanical
room containing equipment for
removing heat from the central
building's closed-loop.
The equipment used can consist of
machines used to remove
heat and
56. TYPES
• Fan coil units are divided into two
types:
* Two-pipe fan coil units
* Four-pipe fan coil units
• Two-pipe fan coil units
* Consist of one supply and one
return pipe
* The supply pipe supplies either
cold or hot water according to the
need.
• Four-pipe fan coil units
* Having two supply pipes and two
return pipes
* It allows either hot or cold water to
enter the unit at any given time.
* Four-pipe fan coil unit is most
commonly used.
60. 2. Distribution system–
• Chilled water & cool
• AHU ( in separate air handling rooms )
• Duct work
3. Terminal elements–
• Grills , diffuser , ventilation systems
&elements for-humidity treatment ,
thermostat and air filtering
• Heat rejection system on the outdoors
eg :cooling towers
61. configuration
DECENTRALIZED
• Window/split
• Package- cooling/heat source, distribution,
delivery and control
• Heat pump air conditioning unit
• Collection of multiple independent units
• Compressor, evaporator coil , fan, condensing
unit and filtration unit for each unit
• Maintenance may have to occur directly in
occupied spaces
63. types
CENTRALIZED SYSTEM
1. Direct expansion ( DX)–
• Air is cooled directly by refrigerant in the finned type
cooling coil of the AHU
2. Chilled water (CHW)
• A secondary cooling medium (chilled water) is
used to deliver cooling to one or more locations
needing it
• The ordinary water / brine solution is chilled to a
very low temperature of about 400 F and pumped
to various AHUs
64. types
DECENTRALIZED
1. Direct expansion ( DX)–
• Window AC
• Residential & light commercial split systems
• Package through the wall and window
• Self contained ( floor by floor )
• Commercial outdoor roof tops
Higher cooling efficiency but not feasible to carry
refrigerant piping to distances beyond 100 feet
66. heat rejection options
CENTRALIZED SYSTEM
1. Air cooled
• Uses finned tube coil condenser
• Refrigerant flows through the
refrigerant piping from evaporator to
condenser
• When refrigerant flows in the piping
its pressure drops
•
So the length of refrigeration tubing
and the distance between the
condenser and evaporator should be
kept minimum
67. 2. Water cooled
• Uses shell and tube type
• Cooling water is pumped from tubes of the cooling towers at
a high pressure
• So it is easy to carry long distances
• The losses in the pressure of water accommodated by the
sufficient capacity of the pump, which has low capital and
running cost
• Can be placed at any distance from the cooling equipment
• For cooling loads between 100-125 tons- air cooled is used
• Above 200 tons- water cooled is suitable
• Between 100-200 tons, depends on the owner
68. heat rejection options
DECENTRALIZED SYSTEM
1. Air cooled
• Air cooled condensers used to
expel heat
• Generally kept very close to the
evaporator units
• For smaller systems- length=3040 ft
• For large systems- upto 3 to 4
times of smaller ones.
69. applications
CENTRALIZED SYSTEM
1. Hotels
2. Theatres
3. Airports
4. Shopping malls
• The largest capacity of chiller available in market-2000 tons
• Multiple chillers are installed to cater for higher loads
• Often a “hybrid system”, which a combination of centralized and
decentralized package units is preferred.
E.g.: in a hotel- packaged unitary ACs for individual guest rooms
Roof top units for meeting rooms/restaurants
Central plant system for lobby, corridors and other common
spaces
70. applications
DECENTRALIZED SYSTEM
1.
More appropriate for low to mid rise buildings
2.
3.
In places where large number of spaces are unoccupied
4.
Can be matched up to separate interior spaces in a large
building (advantage)
5.
Offer high flexibility in meeting the requirements of different
working hours and special design conditions
Capacity range from .5 tons- 130 tons (for roof top package
units)
71. efficiencies
CENTRALIZED SYSTEM
1. Improved efficiency and lower first cost by sharing
load capacity across an entire building
2. Chiller efficiency is typically defined in terms of
kW/ton and its coefficient of performance(COP)
3. The COP= (output Btu)/ (Input Btu)
4. Reciprocating chillers have a peak load power
requirement of 1.02- 1.3 kW/ton
5. Screw chillers - 0 .5- 0.7 kW/ton
6. Centrifugal- most efficient at peak load and
consume least power -
0.53- 0.7 kW/ton
72. efficiencies
DECENTRALIZED SYSTEM
1.
High kW/ton compared to chiller systems
2.
Federal law mandates a minimum efficiency of
10 SEER for both split and packaged equipment
of less than 65000 Btu/hr capacities.
3.
ASHRAE recommended 10 EER fro equipment
between 65000-135000 Btu/hr capacities
73. efficiency terms
1. SEER- seasonal energy efficiency ratio is a
representation of the cooling season efficiency of a
heat pump or air conditioner in cooler climates
2. The higher the SEER rating the more efficient the
AC system operates
3. EER- A measure of the relative efficiency of an air
conditioner, that is equal to the unit's output in BTUs
per hour divided by its consumption of energy,
measured in watts.
4. BTU/hr is a rate of heating/cooing expressed in
terms of British thermal units per hour.
5.Ton- 1 ton of cooling is the energy required to melt 1
ton of ice in 1 hour. 1 ton=12000 btu/hr.
75. CENTRALIZED
FULL CONTROL OVER :TEMPERATURE, RELATIVE
HUMIDITY, INDOOR AIR QUALITY,
AIR DISTRIBUTION
PROVIDE EXCELLENT DUST AND
PARTICULATE AIR FILTERATION
INDVIDUAL CONTROL OPTIONS
NOT ALWAYS AVAILABLE
DECENTRALIZED
SUITABLE IN SITUATIONS
WHERE ABSOLUTE HIGHEST
LEVEL OF PERFORMANCE
NOT REQUIRED
CANNOT BE MODIFIED TO
INCLUDE HIGH LEVEL OF
FILTERAION DUE TO FAN STATIC
PRESSURE LIMITATONS
GREATER OCCUPANT COMFORT
THROUGH INDVIDUALIZED
CONTROLS
HIGH EFFICIENCY OF FANS
LOW EFFICIENCY OF FANS
76. CENTRALIZED
LONGER LIFE EXPECTANCY
RECIPROCATING- 15 YEARS
SCREW AND CENTRIFUGAL- 25 YEARS
MAINTENANCE DOESN’T AFFECT
BUILDING FUNCTION
MECHANICAL ROOM WITH CHILLER
PLANT ROOM OF HEIGHT 4.3-4.9 M
REQUIRED
NEED SPACE ABOVE FALSE CEILING FOR
DUCTS
DECENTRALIZED
GENERALLY HAVE A MUCH
SHORTER USEFUL LIFE:
8-10 YEARS
EVENTHOUGH SMALL UNITS, ITS
MAINTENANCE AFFECTS THE BUILDING
FUNCTION
DOESN’T REQUIRE ANY MECHANICAL
ROOM
ARRANGED WITHOUT FALSE CEILING
77. CENTRALIZED
MACHINE NOISE IS
REDUCED SINCE
MECH.ROOM IS AWAY
CAN BE USED TO
INCLUDE ACTIVE
SMOKE CONTROL
DESIGN , ENGINEERING
AND CONSTRUCTION TAKE
LONGER TIME
DECENTRALIZED
OPERATING SOUND
LEVELS ARE
NOTICABLE
CAN’T BE USED FOR
SMOKE CONTROL
COMPACT AND OFFER
MUCH SIMPLER AND LESS
EXPENSIVE INSTALLATION
Editor's Notes
Centralized systems are defined as those in which the cooling (chilled water) is generated in a chiller at one base location and distributed to air-handling units or fan-coil units located through out the building spaces. The air is cooled with secondary media
