This document provides an overview of HVAC system types. It begins by describing the components of air conditioning systems and classifications of HVAC systems according to cooling medium, including all-air, all-water, and air-water systems. It then discusses the basic central all-air system and variations of single-path and dual-path all-air systems. The document also covers all-water systems, terminal units, air-water systems, and HVAC zones and rooms.
3. 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
4. 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
5. 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
6. HVAC System Types
Heat transfer devices
• Diffusion devices
• Terminal units
Operational equipment – valves, dampers, etc.
Specialty devices – humidification, filtration
7. HVAC System Types
Classifying HVAC systems
ASHRAE classifications – by cooling medium
• All-air systems
• All-water systems
• Air-water systems
8. 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
9. 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
10. 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
11. 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
12. 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
13. 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
14. 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
15. 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
16. 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
17. 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
18. 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
19. 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
20. 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
21. 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
22. 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
23. 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
24. 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
25. 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
26. 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
27. 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
28. 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
29. 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
30. 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
31. 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
32. 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
33. 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
34. 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
35. 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
36. 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
37. 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
38. HVAC
38
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
39. Graphics Described
39
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/
40. In the mechanical room
40
Chiller
Pictures from https://rfd-training.tac.com/docs/HVAC.pdf
41. +
Production Room
Exhaust air treatment
Central air handling unit
Terminal air treatment
at production room level
Fresh air treatment
(make-up air)
Main subsystems
42. Filter
Silencer
Terminal filter
Weather louvre Control damper
Fan
Flow rate controller
Humidifier
Heating
coil
(maybe
no coil)
Cooling
coil
Production Room
Overview components
+
Prefilter
Exhaust Air Grille
Heater
Secondary Filter
Re-circulated air
43. 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
44. 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)
45. lFlow rate controller
lControl 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
To understand the air handling systems, it is necessary to know what their components are.
A conventional Air Handling System has 4 sub-systems:
1. Air handling of the incoming (fresh) air: elimination of coarse contaminants and protection from frost if necessary. In the case of air re-circulation, the fresh air is also called make-up air.
2. Central air handling unit (AHU), where the air will be conditioned (heated, cooled, humidified or de-humidified and filtered), and where fresh air and re-circulated air, if any, (indicated here by the dotted line) will be mixed.
3. Air handling in the rooms under consideration (pressure differential system, additional filtration, air distribution).
4. Air exhaust system (filtration).
Another way to look at an air handling system is to consider the different components and to know their function.
Some of the components, particularly the filters, are essential to ensure the quality of the air.
We will later consider individual components in detail.
Of course, a well-designed air handling system must not only be properly designed, but also properly installed, qualified and maintained (sealed ducts, tight filters).
(The trainer should make the audience aware that this slide is just an example, and that all components may not necessarily be present in each system.)
A typical HVAC unit consists of a small number of elements only.
It is important that these elements are compatible, properly installed, and fulfilling their goal.
Whereas a weather louvre and silencer are less critical elements, the components associated with the flow rate control are essential, as they allow adjustment of the air volumes supplied to the rooms, which in turn forms the base for a pressure differential concept: to have an automated or a fixed system is largely a financial matter, but a fixed system is more difficult to set up.
Silencer – check internal lining material of silencer as this can cause contamination.
Heating and cooling units (batteries), as well as humidifiers are used to adjust the climate in the room (temperature and humidity).
Special de-humidifiers, on a dessiccant base, will be addressed later.
Filters are one of the main components, as they determine the size of airborne particles that pass through them, and thus the hygiene class.
It is wise to protect the finer filters by pre-filters, thus extending their life cycles, and making them less prone to clogging.
Ducts transport the air from the air handling units to and from the rooms. Inspectors must verify that ducts do not have internal insulation as this is a great source of contamination.
Problems may arise with components, with the following consequences:
Flow rate controller Blocked No control of pressure differentials
Control damper Poorly adjusted Bad pressure differential systems
Humidifier Bad water/ Risks of microbial contamination
steam quality
Cooling Unit No elimination Risks of microbial contamination
of condensed water
Filters Incorrect retention Risks of contamination
rate (particles, micro-organisms)
Damaged Filter integrity fails
Badly installed Risks of contamination (particles, micro-organisms)
Ducts Inappropriate material Danger of corrosion
Leaking duct work Intake of unfiltered air
Internal insulation Inability to properly clean
There are different air types to be considered within the air handling system:
Fresh air (if the plant is of the re-circulation type, it is necessary to replace some of the re-circulating air with fresh air, which is then called make-up air).
A proportion of about 15% fresh air is normal, but this proportion can vary, depending on factors such as number of people, National Regulatory Authority requirements, the presence of certain substances in the air, leakage due to pressure control, etc.
Supply air to the rooms
Exhaust air from the rooms
Return air (about 85% is being re-circulated)