Print this page HVAC Pumps Characteristics and Energy Efficiency
A. Bhatia, B.E.
Course Outline
In large commercial and industrial campuses, chilled water and cooling water system serves as means to transfer heat from building spaces to the refrigeration system and from refrigeration system to atmosphere. Water is heated or cooled in a central plant, then pumped to air handlers, where ventilation air is conditioned as needed. Centrifugal pumps are most widely used for transporting chilled water, hot water and condenser cooling water.
This 5- hour course provides an opportunity to refresh and enhance pump knowledge related to heating, ventilation and air conditioning (HVAC) applications and energy conservation.
This 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 reader will:
- Understand the basic types of pumps used in HVAC applications;
- Become familiar with key fluid properties such as viscosity, density, temperature, specific gravity, and vapor pressure and their effect on pump performance and selection;
- Understand the term “head” and why pump performance in typically rated feet of head and not pressure;
- Understand the various head terms such as suction lift, static head, discharge head, friction head, velocity head and pressure head;
- Become familiar with affinity laws and how to apply them correctly;
- Understand the influence of impeller diameter and specific speed on flow and head of pump;
- Understand the pump curve, system curve, operating point and the best efficiency point for the pump operation;
- Understand the flat, smooth and drooping characteristic curve for the centrifugal pump and the applications for which it is best suited;
- Understand the relationship of specific speed to the shape of impeller (radial, mixed or axial);
- Become familiar with NPSH and the effect suction conditions have on pump performance and cavitation;
- Understand the various techniques for flow control including throttling, impeller trimming and speed adjustment;
- Understand the multi-pump installation considerations in parallel or series arrangement;
- Understand the Bernoulli’s relationship and Darcy-Weisbach equation;
- Learn by example the method to compute the frictional head through the HVAC chilled water system; and
- Define the pumping system efficiency and learn the tips to optimize the same.
Intended Audience
This course is ideal for mechanical engineers, HVAC engineers, energy auditors, facility managers, architects, O & M personnel, technicians, construction or building management professionals wanting to further increase their knowledge of HVAC systems.
Benefit to Attendees
Attendees of this course will get better understanding of pump designs and application related differences between the pump types. The course will be extremely helpful to the amateur engineers who desire to build on their design experience and the skilled professionals who have learnt the trade informally on the job.
Course Introduction
The course describes how to select centrifugal pumps for your HVAC application. Topics covered include the performance curve, series operation, parallel operation, the affinity laws, friction, specific gravity & viscosity, suction lift, and NPSH.
Discussion will be in six modules which cover:
- Pumping system overview
- Pump system characteristics
- Pump selection considerations
- Flow control in centrifugal pumps
- Heat and capacity relationships
- Pumping system energy efficiency
Course Content
This course is in the following PDF document:
HVAC Pumps Characteristics and Energy Efficiency
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Course Summary
Pumps are an important part of any water distribution system. Within distribution systems, pumps discharge water under pressure to the pipe network and lift water where it cannot go by gravity, especially to water tower. Centrifugal pumps are the most common type used in water distribution. A typical centrifugal pump consists of an impeller rotating inside a spiral casing, a shaft, mechanical seals and bearings on both the ends of the shaft, suction inlet and discharge outlet.
Different types of applications require different types of pumps. Pumps are selected based on system requirements, discharge pressure required, flow capacity required, and availability of space. Water-distribution systems are either closed-loop (cooling- or heating-system water does not come in contact with outside air) or open-loop (condenser water is exposed to outside air, usually in the cooling tower).
HVAC pumps are generally designed for peak conditions and the output of these systems is controlled by mechanically constricting the flow with throttling valves. This wastes energy. By using a variable speed drives, chilled water flows can be matched to actual heating and cooling demands.
The impact of low efficiency on power consumption is significant. During the pump selection process, only pumps having high efficiencies (above 70%) for the design discharge should be considered for a system. It is common practice to select a pump capable of producing higher head and larger flow rate (approximately 10%) than the design parameters. This will assure that as the pump wears, its performance will remain adequate.
Total pump operating costs may justify the purchase of a more expensive pump that can operate with higher efficiency under needed conditions. Economics is often the primary criterion for pump selection. It is important to estimate the cost of pump operation and consider this cost together with the initial cost of the pumping equipment.
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.
