Print this page Heat Rejection Options in HVAC Systems
A. Bhatia, B.E.
Course Outline
The range of air-conditioning and associated heat rejection equipment is wide ranging. There are two prominent types of heat rejection systems; 1) Air cooled and 2) water cooled. An air-cooled chiller uses the flow of outside air across the condenser to remove or reject heat from the chiller. A water-cooled chiller use water to remove the heat from the condenser and is typically more efficient than air-cooled chillers.
This 4-hour course provides a comprehensive description of the five prominent heat rejection methods as applicable to air conditioning systems.
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
Learning Objective
This course is intended to provide you with the following specific knowledge and skills:
- The concept of total heat of rejection (THR), its derivation and how it applies to the process of air conditioning;
- Five prominent methods of heat rejection;
- Importance of sub-cooling and super-heat in air-cooled condensers;
- Types, rating and selection of air cooled condensers;
- Operating principle of wet cooling towers;
- Types of cooling towers, cross-flow, counter-flow, induced draft and forced draft;
- Capacity control of air cooled and water cooled systems;
- Closed circuit fluid coolers v/s evaporative condensers;
- Energy performance of air-cooled chiller v/s water cooled systems;
- Effectiveness of adiabatic cooling technology;
- Benefits and limitations of various heat rejection methods; and
- The selection of appropriate method on capital costs and environment criteria.
Intended Audience
This course is applicable to architects, air-conditioning engineers, controls engineers, contractors, environmentalists, energy auditors and loss prevention professionals. It is assumed that all the readers know the basic functioning of the air-conditioning system.
Benefit to Attendees
This course will help design engineers gaining a basic understanding of heat rejection system and apply the best fit to their application.
Course Introduction
One of the basic requirements of the air conditioning and refrigeration system is to reject heat to the outdoors. Air conditioning chillers come in two different forms:
- An air-cooled chiller uses the flow of outside air across the condenser to remove or reject heat from the chiller. Air-cooled chillers typically have the condenser mounted on the roof or somewhere outside the facility while the evaporator can either be inside or outside the facility.
- Water-cooled chillers are typically 100 tons or greater and use water to remove the heat from the condenser. Water-cooled chillers are typically more efficient than air-cooled chillers. The condenser water is kept cool by a cooling tower, or water from the city main or well water is used. A water-cooled chiller will typically have the condenser and evaporator inside a facility while the cooling tower is located outside.
This 4-hour course will introduce you to the various heat rejection options.
Course Content
This course content is in the following PDF document:
Heat Rejection Options in HVAC Systems
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Course Summary
Water cooled condensers are typically specified when a supply of cooling water is readily available. Due to the cost of city water, water treatment, pumping costs and maintenance of a water delivery system, air cooled condensing is preferred in applications where service water is not required for other plant operations or where existing heat rejection capacity is insufficient. In general the following rules apply:
- For cooling loads below 100–125 tons, the initial capital and recurring maintenance costs for a water-cooled system are rarely justified and the chiller(s) shall be air-cooled.
- Above 200 tons capacity systems and with the use of rotary compressor chillers, the water-cooled condensing option becomes justifiable. Note that the centrifugal chillers are always water cooled due to lower compression ratio.
- Between 100 and 200 tons peak cooling load, it becomes a matter of the owner’s ability to deal with the maintenance requirements of a cooling tower system and the capital funds available.
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.
