Ch 02_Intro to HVAC Systems

8/17/2019 Ch 02_Intro to HVAC Systems

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MEC653HVAC SYSTEMS

CHAPTER 2OVERVIEW OF AC SYSTEM


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SYSTEM COMPONENTS OVERVIEW

HVAC system components may be grouped into three functional categories:source components, distribution components and delivery components.

Source components to provide cooling/remove heat and to add/remove

moisture (e.g. chiller, heating system etc…) Distribution components convey energy from a source location to buildingthat require conditioning (e.g. air- handling unit , fan coil unit etc…) Delivery components serve as an interface between the distribution systemand occupied space (e.g. diffuser, grille etc...)


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SOURCE COMPONENTS

(Up to 5 RT)

(beyond 20 RT)(Up to 20 RT)


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Central systems are defined as those in which the cooling is generated in a chillerand distributed to air handling unit (AHU) or fan coil unit (FCU) with a chilledwater distribution system.

The following are type of chillers and typical machine range:

Chillers


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Thermal Energy Storage


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Chilled water storage tank Ice cell


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Chilled water storage tank Ice cell

Ice ball storage tank


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DISTRIBUTION AND DELIVERYCOMPONENTS OVERVIEW

The essential elements of delivery side cooling equipment are:Air handling equipment: Controls temperature, humidity, and qualityof air.Supply network: Distributes conditioned air to different part of the

building. Ducts required.Return path: Carries air back to the delivery unit (AHU). Ducting isoptional.Exhaust: Required to get rid of odors and air contaminants.Fresh air inlet: Required to replace exhaust air and maintain an

acceptable level of air quality.


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Central system: Consists of more than one AHU served by the same sourceof heat and/or cooling. These are usually custom built for particular application.

Unitary equipment: Consists of a factory-assembled AHU and cooling

compressor contained within a compact enclosure. It is distinguished from a

room air conditioner by its capability of being connected to a ductwork. These

are further categorized as package terminal air conditioners, rooftop systems

and split systems.

Packaged Unit: The packaged unit is the primary equipment in a packaged

air-conditioning system and is always equipped with a DX coil for cooling,

unlike an AHU. The portion that handles air in a packaged unit is called an airhandler to distinguish it from an AHU.

Air Handling Unit (AHU)


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Mixingchamber Cooling

coil

return air(RA)

supply air(SA)

outside air(OA)


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FCU is a small-scale air handling unit with circulation fan, cooling/heating coil,

filter, and appropriate controls. It is essentially a terminal device because itserves only one room or a small group of rooms.

Cooling coil

Fan Coil Unit (FCU)


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Fan Coil Unit (FCU)


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Air conditioning system requires some form of duct work to channel or directthe air to places where the conditioned air is needed. The power that causesthe air to move through the supply ducts is supplied by the fan in the AHU unitand the motor that drives the fan.

Duct System


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Duct System


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Return grill

Supply grill

Air louver


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Damper

Reducer Elbow


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COOLING TOWER

[hot refrigerant gasfrom compressor]

[cold liquidrefrigerant toexpansionvalve]

Make-up water


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Mechanical draft CT Natural draft CT


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HVAC SYSTEMS INTEGRATION


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OTHER TERMINOLOGY

1. Direct expansion vs indirect expansion2. Single zone vs multi zone3. VAV vs CAV


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SYSTEM & DESIGN CONSIDERATION


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Details of architecture:Structure, orientation, geographical location, altitude, shape, modules- size& height.Purpose of the building, area classification, occupancy and usage pattern.Ratio of internal to external zones, glazing, plant room sitting, space forservice distribution.Climate and shading, thermal insulation, passive climate control,relationship with adjacent buildings.New or existing building, renovation or extension project, retrofitting or newequipment.Plant and system design to match the characteristic of the building and theneed to meet the needs (known and unknown) of the ultimate occupants.


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Details of Space allocation:Floor space and clear heights to accommodate HVAC plant, equipment,distribution and room elements.Shaft spaces available for routing ducts/pipes etc..Location and size of structural column and beam, clearance throughsteelwork, position of reinforcing rod etc… Ceiling height, clearance between suspended ceiling and beam.Foundation and supports requirement, permissible loading etc… Location of obstructions that may be in the route of air-conditioningservices, particularly ductwork and piping.


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Details of building construction:Materials and thickness of wall, roof, ceiling, floor and partition and theirrelative positions in the structure, thermal and vapor transmittancecoefficients, area and type of glazing , external building finishes and color,shading devices at windows (overhang).Sound and vibration control requirement, relation of air-conditioningequipment to critical area.Coordination with other services (e.g. electrical and plumbing work), use ofservice shaft, duct and equipment room.


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Building regulationsGovernment and local regulation on occupancy & safety classification.Regulations of public utilities on electrical wiring, power usage, watersupply and drainage.Health and safety regulations on indoor air quality, ventilation airquantities, noise control, electrical, fuel, insulation and other hazardousmaterials.Local fire authority regulations and smoke removal systems.Insurance company regulations.


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Miscellaneous Requirements Accessibility for installation of equipment, space for maintenance.Location of fresh air intakes and exhausts (to avoid short-circuiting andcontamination).Location of fire zones and fire walls (position of fire dampers).

Acceptable noise level: space available to house equipment and itslocation relative to the conditioned space.Indoor & outdoor equipment preferences.

Acceptability of components obtruding into the conditioned space.Plumbing arrangements, drains – location, capacity, restriction ondischarge.


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System considerations:Thermal influence – Solar gain, ambient conditions (dry bulb/wet bulbtemperatures), indoor condition (dry bulb/relative humidity) requirements,heat gain from people, artificial lighting, equipment and machinery,ventilation air load etc… System behavior – Thermal comfort, indoor air quality, peak loads, partialloads, average load conditions and pattern of variation, capacity of thesystem etc… Load behavior – Sensible and latent heat balance, load diversity andsystem response related to thermal capacity storage effects.Psychrometric processes – engineer prefer to carry out their calculationson a psychrometric chart of the aspects include actual vapor pressure,relative humidity, moisture content, specific enthalpy, specific volume anddewpoint temperature etc...Operation philosophy- hours of system operation.


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System considerations (cont.)Control systems- zone or individual control, system response and lags,

permissible tolerances and time system, direct digital controls, sequence ofoperations and control logic etc… Energy efficiency- energy availability, level & pattern of energy use, type ofsystem, peak load and part load energy performance, variable speed drive,energy efficient equipment, building management systems, economizercontrols, zoning requirements etc… Control and operational requirements – supervision, records, type ofadjustment and regulation, hours of operation, summer/winter changeover,day/night and weekend operation, high/low limit protection, frost protection,fire protection, special control areas (e.g. computer rooms, executiveoffices) etc… Redundancy- spare & standby requirements, equipment configurationetc… Technology features – humidification/dehumidification requirements, airpurity, special acoustic treatment, fire protection & smoke management,water service – capacity, pressure, maximum temperature, chemicalanalysis (choice of materials), water treatment etc…

Ch 02_Intro to HVAC Systems

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