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  • 8/12/2019 Service Ducts



    Prepared by Rajendrasingh Pardeshi

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  • 8/12/2019 Service Ducts


    INTRODUCTION Although the Electrical supply intakecan be terminated in a meter boxsituated within a dwelling, mostsupply companies prefer to use theexternal meter box to enable themeter to be read without the need toenter the premises.

    The local company is responsible

    for providing electricity up to andincluding meter, but the consumer isresponsible for safety and protectionof the companys equipment.

    The supplier will install the servicecable up to the meter position wheretheir termination equipment isinstalled

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    Rewire able systems housed in

    horizontal conduits can be castinto the structural floor slab orsited within the depth of the floorscreed.

    To ensure that such a system isrewire able, draw in boxes mustbe incorporated at regularintervals and not more than tworight angle boxes to be includedbetween draw-in points.

    Vertical conduit can be surfacemounted or housed in a chasecut in to a wall provides depth of

    the chase is not more than 1/3 rd of the wall thickness

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    Gas Service Pipes

    1. Whenever possible the servicepipe should enter the building onthe side nearest to the main.

    2. A service pipe must not passunder the foundation of a building.

    3. No service pipe must be runwithin a cavity but it may passthrough a cavity by the shortestroute.

    4. Service pipes passing through awall or solid floor must beenclosed by a sleeve or ductwhich is end sealed with mastic.

    5. No service pipe shall be housed

    in an unventilated void.6. Suitable material for service pipes

    are copper and steel.Polyethylene is normally usedunderground.

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    INTRODUCTIONFire Protection or Service Openings:Penetration of compartment walls and floorsby service pipes and conduits is very difficult

    to avoid. An exception is where purpose builtservice ducts can be accommodated.Wherever a pipe passes through acompartment interface, it must be providedwith a proprietary seal. Seals are collars ofintumescent material which expands rapidlywhen subjected to heat, to form acarbonaceous charring. Expansion issufficient to compress warm plastic andsuccessfully close a pipe void for up to 4hours.

    In some circumstances fire stopping aroundthe pipes will be acceptable, providing thegap around the pipe and hole through the

    structure are filled with non combustiblematerial. Various materials are acceptable,including reinforced mineral fibre, cement andplasters, asbestos rope and intumescentmastics.

    Pipes of low heat resistance, such as PVC,lead, aluminium alloys and fibre cement mayhave a protective sleeve of non combustiblematerial extending at least 1m either side of

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    INTRODUCTIONTelephone Installations: Unlikeother services such as water, gasand electricity, telephones cannot be

    connected to a common main supply.Each telephone requires a pair ofwires connecting it to the telephoneexchange.

    The external supply services andconnection to the lead-in socket iscarried out by telecommunicationengineers. Internal extensions canbe installed by the site electrician.

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    INTRODUCTIONElectronic Installations: In addition tostandard electrical andtelecommunication supplies in to a

    buildings, there is a growing demand forcable TV, security cabling andbroadband access to the internet.

    Previous construction practice has notforeseen the need to accommodatethese services from distributionnetworks into buildings, andretrospective installation throughunderground ducting is both costly anddisruptive to the structure andsurrounding area, particularly whenrepeated for each different service.Ideally there should be a commonfacility integral with new construction to

    permit simple installation of thesecommunication services at any time. Atypical installation will provideconnection from a common externalterminal chamber via undergroundducting to a terminal distribution boxwithin the building. Internal distributionis through service voids within thestructure or attached trunking.

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    INTRODUCTIONCOMMERCIAL, industrial, andresidential air duct system design must

    consider air diffusion3.noise levels,4.air distribution system (duct andequipment)5.duct heat gains and losses,6.balancing, and smoke control8.initial investment cost, and9.system operating cost.

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    INTRODUCTIONHVAC DESIGN Combining comfortwith efficiency

    When defining an HVAC installation,comfort is the most obvious primaryconsideration, as it is invariably themain reason for installing an HVACsystem in first place.

    The air duct distribution network is animportant component of HVACinstallations, helping to significantlyreduce energy costs and reduce noisenuisance generated by the systemsequipment.

    An HVAC installation is designed toensure the thermal and acoustic comfort

    of a buildings occupants, use energyefficiency and comply fully with safetyrequirements.

    The shape of ducts usually installed asrectangular, because dimensions caneasily be changed to maintain therequired area

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    INTRODUCTIONAdvantages of Installation HVACDuct work

    Installing an HVAC duct work systemduring a buildings construction oftenmeans reduced costs in the long run, asit avoids any future necessary structuralmodifications.

    Installation typically consists ofdesigning space for the distributionnetwork and the location of AHUs.

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    DESIGN CONSIDERATIONSSpace Pressure Relationship

    Space pressure is determined by fan location and duct system arrangement.

    For example, a supply fan that pumps air into a space increases space pressure; anexhaust fan reduces space pressure.

    If both supply and exhaust fans are used, space pressure depends on the relativecapacity of the fans. Space pressure is positive if supply exceeds exhaust andnegative if exhaust exceeds supply .

    System pressure variations caused by wind can be minimized or eliminated by carefulselection of intake air and exhaust vent locations

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    DESIGN CONSIDERATIONSFire and Smoke Management

    Because duct systems can convey smoke, hot gases, and fire from one area toanother and can accelerate a fire within the system, fire protection is an essential partof air-conditioning and ventilation system design. Generally, fire safety codes requirecompliance with the standards of national organizations. fire safety requirements for

    1.ducts, connectors, and appurtenances;2.plenums and corridors;3.air outlets, air inlets, and fresh air intakes;4.air;6.electric wiring and equipment;7.air-cooling and -heating equipment;8.Building construction, including protection of penetrations; and

    9.Controls , including smoke control.

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    In all new construction (except low-rise residential buildings), air-handling ducts andplenums that are part of an HVAC air distribution system should be thermallyinsulated in accordance with ASHRAE Standard 90.1. Duct insulation for new low-riseresidential buildings should comply with ASHRAE Standard 90.2. Existing buildingsshould meet requirements of ASHRAE Standard 100.

    In all cases, thermal insulation should meet local code requirements. Insulationthicknesses in these standards are minimum values; economic and thermalconsiderations may justify higher insulation levels. Additional insulation, vapourretarders, or both may be required to limit vapour transmission and condensation.Duct heat gains or losses must be known to calculate supply air quantities, supply airtemperatures, and coil loads.

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    It is recommended that all transverse joints, longitudinal seams, and ductworkpenetrations be sealed. Longitudinal seams are joints oriented in the direction ofairflow. Duct wall penetrations are openings made by screws, non-self-sealingfasteners, pipe, tubing, rods, and wire. All other connections are consideredtransverse joints , which are connections of two duct or fitting elements orientedperpendicular to flow. System (ductwork and equipment) leakage should be tested toverify the installing contractors workmanship and sealing practices.

    Leakage in all unsealed ducts varies considerably withthe fabricating machinery used,material thickness,assembly methods, andinstallation workmanship.

    For sealed ducts, a wide variety of sealing methods and products exists

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    DESIGN CONSIDERATIONSSystem and Duct Noise

    The major sources of noise from air-conditioning systems are diffusers, grilles, fans,ducts, fittings, and vibrations. Sound control for terminal devices consists of selectingdevices that meet the design goal under all operating conditions and installing themproperly so that no additional sound is generated.

    The sound power output of a fan is determined by the type of fan, airflow, andpressure. Sound control in the duct system requires proper duct layout