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  • 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

Centralized ac system Centralized ac system Presentation Transcript

  • GROUP 4 AISWARYA AMALU ARJUN FEBIN SAMEER SANOOB VISHNU VIJAY CENTRALIZED AIR CONDITIONING SYSTEMS
  • Fan coil details CONTEN TS AHU Centralized AC systems Comparis on with noncentralize d systems
  • 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
  • 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
  • Sub systems of centralized AC Chilled water plant condenser water system (heat rejection system) air-delivery system
  • 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.
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  • 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).
  • 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.
  • 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.
  • Photo courtesy of ©iStockphoto/DonNichols.
  • AHU AIR HANDLING UNIT
  • WHAT IS AHU? • • • •
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  • WORKING • • • • • •
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  • TYPES OF AHU SYSTEMS • • • • • single-zone Multizone dual-duct Reheat variable air volume systems
  • 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
  • • • • • • 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
  • •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 -
  • • AHU classified on basis of installation VERTICAL AHU HORIZONTAL AHU CELING MOUNTED AHU
  • 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
  • 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
  • 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
  • • 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
  • •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
  • 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.
  • 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
  • • 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
  • FAN-COIL UNIT
  • 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.
  • 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.
  • 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
  • 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.
  • COMPARISON
  • configuration Decentralized Centralized
  • configuration CENTRALIZED SYSTEM 1. Source components – • Compressor (reciprocating , screw , centrifugal, scroll) • Condenser (water cooled shell & tube , air cooled finned) • Expansion valve • Evaporator (chilled water shell & tube , direct expansion) • Plant room Compre ssor types
  • 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
  • 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
  • types Decentralized Centralized
  • 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
  • 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
  • heat rejection options Decentralized Centralized
  • 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
  • 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
  • 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.
  • 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
  • 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)
  • 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
  • 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
  • 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.
  • SUMMARY CENTRALIZED FIELD ASSEMBLED DECENTRALIZED FACTORY ASSEMBLED EASILY NETWORKED MAINTENANCE IN EACH UNIT IN LARGE BUILDINGS IN MID RISE BUILDINGS HIGH AND CONSISTENT USAGE TIME HIGH FLEXIBILTY IN MEETING REQUIREMENTS MULTIPLE THERMAL ZONE APPLICATION SINGLE THERMAL ZONE APPLICATION
  • 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
  • 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
  • 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