Print this page Refrigeration Chiller Systems - Principles, Applications & Acceptance Testing
A. Bhatia, B.E.
Course Outline
A chiller is a
refrigeration system that cools water. Once cooled, chilled water is used in
air-conditioning applications for cooling/dehumidification and thus creating
comfortable and productive environments. Chillers are also used in the manufacturing
environment to provide process cooling to equipment in an effort to maximize
productivity.
This 3-hr course material is based entirely on US Corps of Engineers Construction
Engineering Research Laboratory (USACERL) technical report 99:20, May 1999.
This course lists the Appendix C of the report.
The course includes a multiple-choice quiz at the end, which is designed to
enhance the understanding of the course materials.
At the conclusion of this course, the student will:
- Understand the basic vapor compression refrigeration cycle;
- Learn the different types of mechanical compressors including reciprocating, centrifugal, screw and scroll;
- Understand the vapor absorption refrigeration cycle, its components and applications;
- Describe the efficiency and coefficient of performance of refrigeration systems;
- Learn the function of essential components of chiller such as evaporator, compressors, condensers and expansion valves;
- Understand the concept of heat rejection through contact and non-contact type cooling towers;
- Learn about different type of refrigerants and their effects on environment;
- Learn the sizing, cost and method of selecting an appropriate chiller;
- Understand the operation and maintenance aspects including importance of water treatment in closed and open systems; and
- Learn basic
testing, adjusting and balancing (TAB) procedures as applicable to chillers.
Intended Audience
This course is aimed at beginners, novice engineers, building services design engineers, end users, service technicians, architects, maintenance supervisors, contractors, energy auditors, layout professionals and general audience.
Course Introduction
A chiller is a
refrigeration system that cools a process fluid typically water, which in turn
is used in commercial and industrial facilities for process cooling or air-conditioning.
Water can be cooled to temperatures as low as 5°C (~40°F) and pumped
through a hydraulic circuit to reach the process equipment or the air handling
units. For still lower temperatures glycol or brine solution may be used.
A chiller will use either a vapor compression or absorption cycle to cool. There
are four broad types of chillers (1) reciprocating, (2) centrifugal, (3) screw
driven (4) and absorption chillers. The first three types are mechanical chillers
which are powered by electric motors, steam, or gas turbines. Each of these
chillers is a complete package comprising of a compressor, condenser, evaporator,
expansion valve, refrigerant, internal piping and controls. The term Chiller
is also used when all these components are used with cooling tower.
An absorption chiller is powered by a heat source such as steam and uses no
moving parts.
Course Content
In this course, you are required to study the US Army Corps of Engineers Construction Engineering Research Laboratory (USACERL) technical report 99:20, May 1999 Appendix C.
You need to open or download above document to study this course.
There are two basic types of chillers -- mechanical compression chillers and absorption chillers.
The mechanical
compression cycle has four basic components through which the refrigerant passes:
(1) the evaporator, (2) the compressor, (3) the condenser, and (4) the expansion
valve. The evaporator operates at a low pressure (and low temperature) and the
condenser operates at high pressure (and temperature).
The cycle begins in the evaporator where the liquid refrigerant flows over the
evaporator tube bundle and evaporates, absorbing heat from the chilled water
circulating through the tube bundle. The refrigerant vapor, which is somewhat
cooler than the chilled water temperature, is drawn out of the evaporator by
the compressor. The compressor "pumps" the refrigerant vapor to the
condenser by raising the refrigerant pressure (and thus, the temperature). The
refrigerant condenses on the cooling water coils of the condenser giving up
its heat to the cooling water. The high-pressure liquid refrigerant from the
condenser then passes through the expansion device that reduces the refrigerant
pressure (and temperature) to that of the evaporator. The refrigerant again
flows over the chilled water coils absorbing more heat and completing the cycle.
Mechanical compression chillers are generally classified by compressor type:
reciprocating, centrifugal, and screw.
- Reciprocating - This is a positive displacement machine that maintains fairly constant volumetric flow over a wide range of pressure ratios. They are almost exclusively driven by fixed speed electric motors.
- Centrifugal - This type of compressor raises the refrigerant pressure by imparting momentum to the refrigerant with a spinning impeller, then stagnating the flow in a diffuser section around the impeller tip. They are noted for high capacity with compact design.
- Screw - The
screw or helical compressor is a positive displacement machine that has a
nearly constant flow performance characteristic. The machine essentially consists
of two matting helically grooved rotors, a male (lobes) and a female (gullies),
in a stationary housing. As the helical rotors rotate, the gas is compressed
by direct volume reduction between the two rotors.
The absorption
and the mechanical compression cycles have the evaporation and condensation
of a refrigerant in common. In both cycles, the refrigerant evaporates at low
pressure (and low temperature) to absorb heat and then condenses at higher pressure
(and higher temperature) to reject heat to the atmosphere. Both cycles require
energy to raise the temperature of the refrigerant for the heat rejection process.
In the mechanical compression cycle, the energy is supplied in the form of work
to the compressor whereas in the absorption cycle, heat is added (usually steam)
to raise the refrigerant temperature.
The absorption
cycle requires two working fluids: a refrigerant and an absorbent. Of the many
combinations of refrigerant and absorbent that have been tried, only lithium
bromide-water and ammonia-water cycles are commonly used today.
There are essentially
three types of maintenance performed on chillers; water chemistry, mechanical
maintenance and operational procedures. Water chemistry is maintained to keep
proper balance and minimize the effects of scale, corrosion and micro-biological
/ debris fouling. Mechanical maintenance includes proper lubrication, adequate
liquid refrigerant, oil levels and pump curve tests. Operational procedures
include eddy-current tests, oil analysis, calibration of gauges and meters and
other various tests.
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
