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HVAC MADE EASY - Selection Tips for Chiller Compressors

A. Bhatia, B.E.


Course Outline

This two-hour course provides comprehensive information on the air-conditioning chillers. The chiller package comprising of refrigerant compressor is a heart of main cooling system. The chiller is a single most expensive item of the air-conditioning system that influences the life cycle economics. The course focuses on the key issues pertaining to chiller selection and their applications. The practical considerations and assessment criterion is addressed in brief and is a recommended reading reference. The course is intended for use primarily to the students, end users, consultants, architects, contractors and HVAC designers.

This 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:

Course Introduction

The chiller is a refrigeration machine used for cooling water or brine. The most common active air-conditioning approach for building air-conditioning and process cooling, involves the operation of vapor compression chillers. The chillers are usually referred to by the type of compressor used and is of 4 types:

The majority of installations operating worldwide are based on the vapor compression chillers, although a moderate amount of absorption chiller capacity also exists. The course shall focus on the vapor compression chillers and the vapor absorption chillers are dealt separately. The course is divided as follows:

Course Content

The the course content is in a PDF file (73 KB) Selection Tips For Air-Conditioning Cooling Systems. You need to open or download this document to study this course.

Course Summary

The refrigeration equipment used for air-conditioning is almost invariably supplied in the form of a packaged unit. The classification of the chiller packages is by the type of compressor. The most common commercial available chilled packages can be one of the following:

The primary application of reciprocating chillers is for small systems that require cooling loads less than 150 TR. Above 150 TR either the multiple reciprocating or the screw and centrifugal compressors may be evaluated subject to the wider framework of life cycle analysis, energy performance, health and safety.

Centrifugal chillers are best suited for the larger installations typically above 750 TR. The centrifugal machines offer high peak load efficiency and operate reliably for applications demanding a steady state operation. On acute load variations, the centrifugal machines are susceptible to surge conditions. The machines are only recommended with water-cooled condenser option.

The screw chillers are well suited for applications demanding up to 750 TR. Above these capacities, centrifugal chillers may be more cost effective.

More than the initial capital costs, the cost of operation must be evaluated. The most important thing to remember is that the air-conditioning hardly runs on peak load. Therefore part load efficiency is paramount.

Install sufficient capacity to meet the imposed cooling loads. It is normal for an installation to have several chiller packages, both to provide standby and to enable cooling load to be matched with the minimum consumption of power. It is important for economy of operation, that the optimum equipment selection is achieved.

For applications where chiller must operate at 50% or less of capacity for more than 50% of the time, staged reciprocating units, screw chillers or a centrifugal unit equipped with VFD offer the most energy efficient solution. If the chiller is to operate at higher loads for longer periods of time, centrifugal or rotary units may be the best.


Related Reading

Glossary and Acronyms

The course HVAC made easy - 'Glossary and Acronyms of HVAC systems' is a compilation of most common HVAC terminology and is a recommended reading. The abbreviations and terms that may be unfamiliar to someone exploring HVAC systems for the first time have been carefully selected and presented in alphabetical order.

Auxiliary Components Of Chiller Package

The chiller package comprising of refrigerant compressor is a heart of main cooling system. The other two main elements of chiller package are called an evaporator for cooling water and condenser for heat rejection. For air-cooling applications, the production of chilled water is not mandatory and the system could be designed for the direct expansion (DX) type where the air is cooled directly with refrigerant medium. Further the heat rejection through the condenser could be through the air-cooled or water-cooled configurations. These aspects have been discussed exclusively with illustrations, advantages and disadvantages in another course HVAC made easy - 'Selection tips for cooling systems'.

Refrigerants

The refrigerants are considered to be one of the major sources of Ozone layer depletion. The choice of refrigerant is interwoven with major environmental concerns of climate change and global warming. Refrigerant selection thus assumes a key importance in selection of HVAC system. A one-hour course HVAC made easy - 'Facts about Refrigerants' briefly explores the myth and realities about refrigerants.

Life Cycle Assessment

HVAC system is a significant proportion of the overall building cost. Life cycle assessment (LCA) is a decision making process that is applied to large scale building projects for evaluating the appropriate selection. The LCA takes into account all capital costs, recurring operation & maintenance (O&M) expenses, replacement costs, energy, environment and the code issues for the life cycle of equipment. The overview of life cycle assessment (LCA) is presented in a course titled HVAC made easy- 'Overview of Life cycle assessment'. This is a generic one-hour course recommended for engineering and financial planners.

Air-conditioning Sub-systems

The HVAC sub-systems play a key role in providing the controlled environment indoor particularly for multi-zone applications. Introducing reheat (energy inefficient) or use of variable volume control terminal boxes can achieve variable conditions in multi-zone applications. The various types of sub-systems, that provide heating and cooling to the occupied space via distribution of the conditioned air include:

These sub-systems have a little influence on the selection of main system and assume significant importance while detailing. These have been discussed separately in another HVAC made easy series.


Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDHonline.com 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 professional engineer. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.