CHAPTER 8
AIR HANDLING EQUIPMENT AND SYSTEMS
OVERVIEW
Chapter 8 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 functions 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. Guidelines for proper applications are contained in this section.
• Primer on fan applications including engineering methods for predicting power requirements.
• Ductwork including guidelines for selection of materials based on application and provisions
for sound control. Figures in this section are valuable for architects to understand the bulk of
ductwork, which must fit above ceilings along with other components of
mechanical/electrical systems.
• Air devices, which are the only part of the HVAC system that most building occupants
actually see, and the material presented will be very useful for architects and interior
designers to coordinate visual elements of the HVAC system with their design. In addition,
poorly applied air devices are a major source of occupant discomfort and complaint.
CHAPTER 8
AIR HANDLING EQUIPMENT AND SYSTEMS
QUESTIONS AND ANSWERS
8.1 What is the difference between an air-handling unit and a fan-coil?
8.2 Why are the casings of air-handling equipment insulated?
8.3 Why can heating coils be designed for higher face velocity than cooling coils can?
8.4 What materials of construction are appropriate for indoor air-handling unit casings?
Outdoor?
8.5 What is the advantage of bag-type filters over flat filters?
8.6 What type of air filters would be appropriate for hazardous particulate materials?
8.7 What are the advantages of blow-through air-handling units in comparison with
draw-through units?
8.8 What is the chief consideration in designing air-handling unit sections for mixing
outside air and return air?
8.9 Why is plastic film ductwork especially appropriate for greenhouses?
8.10 What is the advantage of belt-drive fans compared with direct-drive fans?
8.11 What is the limitation of low-velocity ductwork in large distribution system
applications?
8.12 When might aluminum or stainless steel be preferred over galvanized steel duct
construction?
8.13 When might a plug fan be considered instead of a conventional centrifugal fan?
8.14 When is fabric ductwork an appropriate alternative to sheet metal ductwork?
8.15 What is the function of a diffuser in an HVAC distribution system?
8.16 Name several conditions that could cause uncomfortable dumping of cold air from a
8.17 Briefly compare the relative benefits of commonly used diffuser types.
Louvered face diffusers are economical and work well over a wide range of airflow.
8.18 What potential problems do variable air volume systems pose in the selection of
diffusers?
8.19 What special provisions should be made to prevent heating supply air from
stratifying at the ceiling?
8.20 What are the benefits of using light fixture slots for air return from the room to the
ceiling?
8.21 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?
8.22 A fan with curve shown in Figure 9-15 is required to deliver 10,000 cfm at a static
pressure of 2.2 inches w.c. What will be the required fan speed and brake
horsepower?
8.23 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
8.24 How might floor air distribution affect thermal loads compared with overhead air
distribution?
8.25 Why is a return fan or a relief fan good practice in design of large air handling
systems?
8.26 Compare the air quality of conventional overhead air distribution with floor
distribution.
8.27 Name the three commonly used methods for varying fan output. Which is most
efficient?
8.28 What applications might be appropriate for considering floor distribution? Why?
8.29 What is the most significant advantage of rotary exhaust energy recovery devices with
desiccant coating compared with other energy recovery devices?
8.30 Your laboratory building has outside air intakes and air handling units in a basement
mechanical room. The fume exhaust fans are on the roof. What type of exhaust
energy recover system would be appropriate? Why?
8.31 Your classroom building has rooftop air-handling units, and the ventilation rate is
high due to dense occupancy in the classrooms. A significant amount of exhaust must
be relieved. What exhaust energy recovery systems would you consider? Why
8.32 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 problematic
if multiple offices are controlled from a single thermostat. Operable windows can also result
8.33 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
8.34 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
freezing pipes in the building if windows are left open in cold weather. Open windows