Introduction to Energy Management

Week/Lesson 7

HVAC System Types

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

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

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

HVAC System Types

Heat transfer devices• Diffusion devices• Terminal units

Operational equipment – valves, dampers, etc. Specialty devices – humidification, filtration

HVAC System Types

Classifying HVAC systems ASHRAE classifications – by cooling medium

• All-air systems• All-water systems• Air-water systems

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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