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CHAPTER 6
AIR-HANDLING EQUIPMENT AND SYSTEMS
OVERVIEW
Chapter 6 deals first with air-handling units, including options with respect to
configuration, materials, types of coils, fans, filters, and accessories. The material helps
the student understand the function of components and achieve a spatial sense of area
requirements. This is important in building planning because air-handling units use more
space than any other equipment in HVAC systems. Information on air filtration will also
be useful to facility managers in light of concerns for indoor air quality.
Section 6.5 contains a primer on fan applications, including engineering methods for
predicting power requirements.
CHAPTER 6
AIR-HANDLING EQUIPMENT AND SYSTEMS
QUESTIONS AND ANSWERS
6.1 What is the difference between an air-handling unit and a fan-coil?
6.2 Why are the casings of air-handling equipment insulated?
6.3 What materials of construction are appropriate for indoor air-handling unit
casings? Outdoor?
6.4 Why can heating coils be designed for higher face velocity than cooling coils
can?
6.5 What is the advantage of bag-type filters over flat filters?
6.6 What type of air filters would be appropriate for hazardous particulate
materials?
6.7 What is the chief consideration in designing air-handling unit sections for
mixing outside air and return air?
6.8 What are the advantages of blow-through air-handling units in comparison
with draw-through units?
6.9 When might a plug fan be considered instead of a conventional centrifugal
fan?
6.10 What is the advantage of belt-drive fans compared with direct-drive fans?
6.11 What is the limitation of low-velocity ductwork in large distribution system
applications?
6.12 When might aluminum or stainless steel be preferred over galvanized steel
duct construction?
6.13 Why is plastic film ductwork especially appropriate for greenhouses?
6.14 When is fabric ductwork an appropriate alternative to sheet metal ductwork?
6.15 What is the function of a diffuser in an HVAC distribution system?
6.16 Name several conditions that could cause uncomfortable dumping of cold air
from a diffuser.
6.17 Briefly compare the relative benefits of commonly used diffuser types.
Louvered face diffusers are economical and work well over a wide range of airflow.
6.18 What potential problems do variable air volume systems pose in the selection
of diffusers?
6.19 What parameter is important in the selection of a diffuser for good room
coverage?
6.20 What is the significance of NC levels listed in catalogues? Will NC levels be
higher or lower as the airflow increases for a given diffuser? Why?
6.21 What are the benefits of using light fixture slots for air return from the room
to the ceiling?
6.22 What special provisions should be made to prevent heating supply air from
stratifying at the ceiling?
6.23 A fan with curve shown in Figure 6-14 is required to deliver 15,000 cfm at a
static pressure of 2.2 inches w.c. What will be the required fan speed and
brake horsepower?
6.24 If the motor driving the fan in the previous problem is 96% efficient, what will
be the electrical power consumption for the fan?
0.746 BHP
Electrical power =
6.25 Name the three commonly used methods for varying fan output. Which is
most efficient?
6.26 Why is a return fan or a relief fan good practice in design of large air-handling
systems?
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6.27 Compare the air quality of conventional overhead air distribution with floor
distribution.
6.28 How might floor air distribution affect thermal loads compared with overhead
air distribution?
6.29 What applications might be appropriate for considering floor distribution?
Why?
6.30 Briefly discuss pros and cons of natural ventilation for your current residence.
Open windows interfere with controls of air conditioning systems and can result in
freezing pipes in the building if windows are left open in cold weather. Open
6.31 Briefly discuss pros and cons of natural ventilation for a high rise office
building.
Open windows interfere with controls of air conditioning systems and can result in
6.32 Briefly discuss pros and cons of natural ventilation for a low rise faculty office
wing.
Open windows interfere with controls of air conditioning systems, which can be