introduction to energy management. week/lesson 7 hvac system types
TRANSCRIPT
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Introduction to Energy Management
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Week/Lesson 7
HVAC System Types
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HVAC System Types
After completing this chapter, you will be able to: Recognize air conditioning system components List ASHRAE descriptions HVAC systems Identify components of the basic central system Distinguish between zones and rooms Understand the operation of an all-air system
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HVAC System Types
Understand the operation of an all-water system List advantages/disadvantages of all-water
systems Explain the operation of various terminal units Understand how an air-water system operates List advantages/disadvantages of air-water
systems
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HVAC System Types
Components of Air Conditioning Systems Heating device – adds heat Cooling device – removes heat Distribution system – ducts and/or pipes Equipment – Fans and/or pumps
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HVAC System Types
Heat transfer devices• Diffusion devices• Terminal units
Operational equipment – valves, dampers, etc. Specialty devices – humidification, filtration
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HVAC System Types
Classifying HVAC systems ASHRAE classifications – by cooling medium
• All-air systems• All-water systems• Air-water systems
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HVAC System Types
The basic central system (all-air) Primary system – source of hot/chilled water Secondary system – delivers heating/cooling
throughout the building Portion of return air is exhausted Outside air is introduced Mixed air is filtered and
conditioned
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HVAC System Types
Packaged and unitary HVAC systems Self-contained Window and through-the-wall Air-to-air and water source heat pumps Rooftop systems Predesigned configurations
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HVAC System Types
HVAC zones and rooms Zone
• Requires separate thermostatic control• Usually comprises several rooms
Room• Separate partitioned area• May require separate thermostatic control
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HVAC System Types
The all-air system Supplies cooling (heating) capacity to the zones Advantages
• Adaptable to multiple zoning needs• Adaptable to seasonal changeover• Easily accepts heat recovery equipment• Provides year-round
ventilation
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HVAC System Types
Disadvantages Larger distribution systems than all-water systems Operate longer than all-water systems to maintain
temperatures Air distribution and performance are difficult to
balance
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HVAC System Types
Introduction to single-path and dual-path all-air systems Single-path, all-air systems
• Supply air flows directly from one conditioning device into the next
• Single duct system
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HVAC System Types
Dual-path, all-air systems• Splits supply air into two streams• One stream is chilled, the other is heated• Dual duct layout• Heated and cooled air is mixed together • Air is brought to the zone via mixing boxes
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HVAC System Types
Variations of the single-path, all-air system Constant volume variable temperature Zone reheat systems Design options
• Single zone, constant volume• Multiple zone, constant volume, zone reheat• Multiple zone, variable
volume
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HVAC System Types
Single-duct, single-zone, constant volume Delivers constant volume of air Air is the same temperature in all zones
Single-duct, Single zone, constant volume, zone reheat Reheat coil located at supply to each zone Air is heated as it enters the zone
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HVAC System Types
Single-duct, multiple zone, variable volume The volume of the air supplied is varied The occupied space is used as a mixing box The thermostat controls the volume damper Variable air volume, VAV, system
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HVAC System Types
Variations of the dual-path all-air system Dual-path, multi-zone, constant volume Dual-path, multi-zone, variable volume Dual-path, dual duct, multiple zone, constant
volume Dual-path, dual duct, multiple zone, variable air
volume
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HVAC System Types
Multi-zone systems Air streams are mixed centrally The mixed air flows to the individual zones
Multiple zone systems Both hot and cold air streams are distributed
throughout the facility The streams are mixed at the
individual zones
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HVAC System Types
Dual path, multi-zone, constant volume Hot and cold air is mixed centrally Air is distributed to the zone via a single duct
Dual path, multi-zone, variable volume Hot and cold air is mixed centrally Each duct is equipped with a volume damper
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HVAC System Types
Dual path, dual-duct, multiple zone, constant volume Separate hot and cold air ducts Air is mixed at each zone, constant volume
Dual path, dual-duct, multiple zone, variable volume Separate hot and cold air ducts Air is mixed in variable
volume mixing boxes
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HVAC System Types
The 100% outdoor, all-air system 100% of the return air is exhausted System requires pre-heating equipment Air must be properly filtered
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HVAC System Types
The all-water system Steam, hot water or chilled water Hydronic systems Terminal units provide heat transfer All-water system advantages
• Smaller distribution systems• Less expensive distribution
systems
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HVAC System Types
All-water system disadvantages• Do not filter or ventilate effectively• Lack humidity control• Must be switched over for seasonal operation• Require a great deal of maintenance
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HVAC System Types
Variations of the all-water system Series loop One-pipe main Two-pipe direct return Two-pipe reverse return Three-pipe system Four-pipe system
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HVAC System Types
Series loop All water flows through all terminal units Individual temperature control is impossible Distant units are not as effective System must be shut down for service
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HVAC System Types
One-pipe Each unit can be valved off from the system Individual control and service is possible Distant terminal units are less effective In the heating mode, the water gets cooler as it
flows through the loop
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HVAC System Types
Two-pipe direct return Separate supply and return lines All units receive water at the same temperature Balancing valves are needed
Two-pipe reverse return Supply and return lines are the same length System balancing and
operation are easier
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HVAC System Types
Three-pipe system Hot and cold supply pipes plus a return Units are equipped with three-way valves
Four-pipe system Units have separate heating and cooling coils Each coil is independent of the other
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HVAC System Types
Terminal units Facilitate heat transfer between the conditioned
water and the occupied space Heating or heating/cooling Do not filter the air effectively Does not humidify the air effectively
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HVAC System Types
Radiators Heat primarily by convection Natural airflow pattern is created
Convectors Finned tube or cast iron heat exchanger Baseboard convectors – residential use Fin-tube convectors – commercial
applications
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HVAC System Types
Unit heaters Cabinet unit heaters
• Internal centrifugal fans• Able to filter the air
Propeller unit heaters• Physically large in size • Noisy operation
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HVAC System Types
Radiant panels Tubing grids installed within the structure Located in the floors, walls or ceiling Heat is transferred by radiation Tubes are imbedded in the concrete
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HVAC System Types
Unit ventilators Coil can carry hot or cold water Can introduce outside air to the space
Induction units Used in air-water systems Require high velocity primary air Do not use a fan or blower
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HVAC System Types
The air-water system Heat transfer rate of the all-water system Filtration capability of the all-air system Water system provides heating/cooling Air system provides ventilation Can provide heating/cooling to different zones
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HVAC System Types
Advantages of air-water systems Water distribution system is smaller Smaller air distribution system Lower energy costs Provides ventilation and humidity control Individual temperature control
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HVAC System Types
Disadvantages of air-water systems Require a trained and qualified staff Between-the-season operation is difficult to
manage Normally limited to exterior zones Do not satisfy high exhaust rate needs
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HVAC
HVAC – Heating, Ventilation, Air-conditioning
Temperature
Humidity
Pressure
Ventilation
68°F (20°C) and 75°F (25°C)
30% relative humidity
A slightly positive pressure to reduce outside air infiltration.
Rooms typically have several complete air changes per hour
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Graphics Described
Mechanical Room: chillers, pumps, heat exchangers…
Air Handling Units (AHUs): heat, cool, humidify, dehumidify, ventilate, filter and distribute the air.
Room Controls: thermostats and Variable Air Volume (VAV) boxes
Pictures from http://www.learnhvac.org/
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In the mechanical room
ChillerPictures from https://rfd-training.tac.com/docs/HVAC.pdf
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Production Room
Exhaust air treatment
Central air handling unit
Terminal air treatmentat production room level
Fresh air treatment (make-up air)
Main subsystems
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FilterSilencer
Terminal filter
Weather louvre Control damper
FanFlow rate controller
Humidifier
Heating coil (maybe no coil)
Cooling coil
Production Room
Overview components
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Prefilter
Exhaust Air Grille
Heater
Secondary Filter
Re-circulated air
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Weather louvre
Silencer
Flow rate controller
Control damper
•To prevent insects, leaves, dirt and rain from entering•To reduce noise caused by air circulation•Automated adjustment of volume of air (night and day, pressure control)•Fixed adjustment of volume of air
Components
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Heating unit Cooling unit /dehumidifier Humidifier
Filters
Ducts
•To heat the air to the proper temperature
•To cool the air to the required temperature or to remove moisture from the air
•To bring the air to the proper humidity, if too low
•To eliminate particles of pre-determined dimensions and/or micro-organisms
•To transport the air
Components (2)
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Flow rate controller
Control damper
Humidifier
Cooling battery
Filters
Ducts
•Blocked
•Poorly adjusted, bad pressure differential system
•Bad water/steam quality/poor drainage
•No elimination of condensed water/poor drainage
•Incorrect retention rate/damaged/badly installed
•Inappropriate material/internal insulator•leaking
Problems with components
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Production Room
Exhaust air
Return air(re-circulated)
Fresh air(make-up air)
Supply air
Air types