CHAPTER 4
COOLING PRODUCTION EQUIPMENT AND SYSTEMS
OVERVIEW
The chapter begins by describing the two processes used to make cooling—vapor
compression and absorption. To describe refrigeration in the classroom, the author uses
the analogy of boiling water on a stove. The water boils, absorbing heat from the gas
flame, i.e., cooling the gas. This familiar process is similar to refrigerant boiling to cool
water or air in an HVAC system. Materials, pressures, and temperatures are different, but
the process is identical. A thorough description of refrigeration relies on understanding
the relationship between pressure and boiling temperature (and condensing temperature).
Understanding the last paragraph of section 4.1.1 is essential for students.
Figures 4-1 for vapor compression and 4-2 for absorption are useful tools for the
instructor to construct on the board, drawing each component in sequence and discussing
its function.
Section 4.1.3 introduces the concept of Coefficient of Performance as a method of rating
the energy efficiency of refrigeration processes. The instructor is cautioned to explain
carefully that absorption is sometimes a good choice despite its poor COP in comparison
with vapor compression. Inclusion of evaporative cooling as a refrigeration process in
the same section along with vapor compression and absorption is appropriate, since it
involves evaporation for cooling—same as vapor compression and absorption. Note that
CHAPTER 4
COOLING PRODUCTION EQUIPMENT AND SYSTEMS
QUESTIONS AND ANSWERS
4.1 How do the vapor compression and the absorption cycle differ in their
methods of condensing refrigerant?
4.2 A vapor compression refrigeration machine uses 15 kW of electric power to
produce 25 tons of cooling. What is its COP?
4.3 An absorption refrigeration machine uses 15 kW and 600 lbs. per hour of steam
to produce 50 tons of cooling. What is its COP?
4.4 What is the difference between direct evaporative air cooling and indirect
evaporative air cooling?
4.5 Describe the basic difference between unitary and split DX systems?
4.6 What are the limitations of DX equipment that prevent its application to large
systems?
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4.7 What types of compressors are typically installed on water chillers?
4.8 Which compressors are appropriate for smaller machines? Which for large
machines?
4.9 Give a ranking order of compressors in terms of their typical energy efficiency.
4.10 Under what circumstances would an absorption water chiller be an economical
choice with respect to the energy cost of its operation?
4.11 What is the most widely used type of cooling tower for small- and medium-
capacity applications and why?
4.12 What advantages are offered by air-cooled condensers in comparison with
water-cooled systems using cooling towers?
4.13 Electric demand charges are a large portion of the cooling bill for large
buildings.
4.14 What design options are available to reduce cooling demand charges?
4.15 Why are refrigerants R-11 and R-12 no longer used in new installations?
4.16 What are the most commonly used replacement options for R-11 (low pressure
applications) and R-12 (high pressure applications)?
4.18 If ammonia is a high performance, environmentally-friendly refrigerant, why
is it not used in most applications?
4.19 What are the pros and cons of low pressure vs. high pressure refrigerants?
4.20 What would be the advantage of using electric chillers and gas fired chillers in
combination? How would you sequence their operation?
4.21 What options are available for using natural gas rather than electric as an
energy source for cooling?
4.22 What is the most widely used type of cooling tower for large-capacity
applications and why?
4.23 How do primary and secondary chilled-water loop arrangements save energy
in comparison with unit loop arrangements?
4.24 What are the major advantages of ice as a thermal storage medium in
comparison with water?
4.25 How are the vapor compression, absorption, and evaporative cooling processes
similar?
4.26 What advantage is offered by plate heat exchangers when used in a system to
generate chilled water by the operation of cooling towers?
4.27 Approximately how much chilled water storage would be required to reduce
chiller load by 100 tons for a period of five hours? How much ice storage?
4.28 Why would chillers of unequal size be installed in a chilled water plant?
4.29 What factors need to be considered in locating a cooling tower?
4.30 What factors need to be considered in mechanical plant layout for future
removal and replacement of components and equipment?
4.31 What non-mechanical support spaces should be provided near a major
mechanical plant?