CHAPTER 6
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).
Figures 6.1&2 for vapor compression and 6.3 for absorption are useful tools for the instructor to
construct on the board, drawing each component in sequence and discussing its function.
Section 6.4 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 the COP of evaporative cooling
cannot be defined, since no energy is used to condense the refrigerant.
Sections 6.3 and 6.4 present two basic system options – direct expansion (including ground
source heat pumps) and chilled water. Section 6.4.1 is especially important, containing
information about selecting between the two options.
Section 6.5 covers heat rejection equipment. This section should be of high interest for
architectural students, since this equipment is by necessity outdoors and tends to be unfriendly
due to noise, moisture, and appearance. (See also Chapter 21)
Section 6.6 shares experience of practice in configuring central chilled water systems and details
of design. This material will be most interesting to practicing engineers, or facility management
staff contemplating a new facility.
CHAPTER 6
COOLING PRODUCTION EQUIPMENT AND SYSTEMS
QUESTIONS AND ANSWERS
6.1 How do the vapor compression and the absorption cycle differ in their methods of
condensing refrigerant?
6.2 A vapor compression refrigeration machine uses 30 kW of electric power to produce
50 tons of cooling. What is its COP?
6.3 An absorption refrigeration machine uses 30 kW and 1200 lbs. per hour of steam to
produce 100 tons of cooling. What is its COP (excluding electric used for operation of
auxiliaries)?
6.4 What is the difference between direct evaporative air cooling and indirect evaporative
air cooling? What are likely applications for these cooling methods?
6.5 Describe the basic difference between unitary and split DX systems?
6.6 What are the limitations of DX equipment that prevent its application to large
systems?
6.7 What types of compressors are typically installed on water chillers?
6.8 Which compressors are appropriate for smaller machines? Which for large
machines?
6.9 Give a ranking order of compressors in terms of their typical energy efficiency.
6.10 Under what circumstances would an absorption water chiller be an economical choice
with respect to the energy cost of its operation?
6.11 What is the most widely used type of cooling tower for small- and medium-capacity
applications and why?
6.12 What advantages are offered by air-cooled condensers in comparison with water-
cooled systems using cooling towers?
6.13 Electric demand charges are a large portion of the cooling bill for large buildings.
Since cooling typically contributes to peak demand, the cost per kWh used for cooling
is effectively higher than the average cost per kWh. (True/False)
6.14 What design options are available to reduce cooling demand charges?
6.15 Outline the progress and rationale that has taken the industry from early refrigerants
to refrigerants currently under development.
R-123 is the current substitute for low–pressure water chillers, which used R-11 before its
R-134A was devised as a replacement for R-12 or R-500, which are obsolete owing to
environmental concerns. R-134A was developed for its low ozone depletion potential;
6.16 If ammonia is a high-performance, environmentally friendly refrigerant, why is it not
used in most applications?
6.17 What are the pros and cons of low-pressure versus high-pressure refrigerants?
6.18 What would be the advantage of using electric chillers and gas-fired chillers in
combination? How would you sequence their operation?
6.19 What options are available for using natural gas rather than electricity as an energy
source for cooling?
6.20 What is the most widely used type of cooling tower for large-capacity applications, and
why?
6.21 How do primary and secondary chilled-water loop arrangements save energy in
comparison with unit loop arrangements?
6.22 What applications might favor selecting a modular chiller design?
6.23 What are the major advantages of ice as a thermal storage medium in comparison
with water?
6.24 Approximately how much chilled water storage would be required to reduce chiller
load by 250 tons for a period of 6 hours? How much ice storage would be requried?
6.25 Why would chillers of unequal size be installed in a chilled water plant?
6.26 What factors need to be considered in locating a cooling tower?
6.27 What factors need to be considered in mechanical plant layout for future removal
and replacement of components and equipment?
6.28 What non-mechanical support spaces should be provided near a major mechanical
plant?