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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 HVAC HVAC – Heating, Ventilation, Air-conditioning Temperature 68°F (20°C) and 75°F (25°C) Humidity 30% relative humidity Pressure A slightly positive pressure to reduce outside air infiltration. Ventilation Rooms typically have several complete air changes per hour 38 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/ 39 In the mechanical room Pictures from https://rfd-training.tac.com/docs/HVAC.pdf Chiller 40 Main subsystems Exhaust air treatment Fresh air treatment (make-up air) + Terminal air treatment at production room level Production Room Central air handling unit Overview components Exhaust Air Grille SilencerFlow rate controller Weather louvre Fan Filter Control damper Heater + Humidifier Prefilter Secondary Filter Heating coil (maybe no coil) Cooling coil Re-circulated air Terminal filter Production Room Components Weather louvre •To prevent insects, leaves, dirt and rain from entering Silencer •To reduce noise caused by air circulation Flow rate controller •Automated adjustment of volume of air (night and day, pressure control) Control damper •Fixed adjustment of volume of air Components (2) Heating unit •To heat the air to the proper temperature Cooling unit /dehumidifier •To cool the air to the required temperature or to remove moisture from the air Humidifier •To bring the air to the proper humidity, if too low Filters Ducts •To eliminate particles of pre-determined dimensions and/or micro-organisms •To transport the air Problems with components lFlow rate controller •Blocked lControl damper •Poorly adjusted, bad pressure differential system Humidifier •Bad water/steam quality/poor drainage Cooling battery •No elimination of condensed water/poor drainage Filters •Incorrect retention rate/damaged/badly installed Ducts •Inappropriate material/internal insulator •leaking Air types Fresh air (make-up air) Supply air + Production Room Return air (re-circulated) Exhaust air
