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.

Learning Objective

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

US Army Corps of Engineers Construction Engineering Research Laboratory (USACERL) technical report 99:20 Appendix C

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.