HVAC Chilled Water Distribution - a PDH Online Course for Engineers, Architects and Surveyors

HVAC Chilled Water Distribution

Course Outline

In large commercial and industrial systems, chilled water system serves as means to transfer heat from building spaces to the refrigeration system. Initially, when energy costs were low, constant volume and primary-secondary systems provided a stable and simple operation of the chillers and distribution systems. However, as energy costs increased, particularly in the late 1970s, the efficiency of the chillers and the costs associated with operating the distribution system became more important. As a result, the need for new schemes to improve chiller performance and reduce energy costs drove the HVAC industry to advance chilled water technology, particularly in the manner that chilled water is delivered.

This 5 - hour course discusses the history of chilled water distribution systems and the development of “variable primary flow system” to answer the today’s approach to chilled water pumping. Problems such as low delta-T syndrome associated with the chilled water pumping schemes are defined and discussed and finally, this course compares the advantages and disadvantages of primary-secondary and direct-primary pumping schemes.

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 reader will understand:

The basic hydronic principles i.e. relationship of chilled water flow rate v/s cooling load and the energy savings due to adjustable speed pumps;
The fundamental affinity laws governing centrifugal water pumps and how does the variable speed pumping impacts the operating cost?
How do constant volume chilled water systems different from primary/secondary arrangement?
What is low delta-T syndrome and how it affects the chiller loading?
What are the causes and mitigation measures to prevent low delta-T syndrome?
Why distributed pumping arrangement is better than headered arrangement for constant flow systems?
How do primary/secondary chilled water systems create hydraulically independent loops?
How to size the de-coupler bridge?
The importance of chiller sequencing and staging on the overall performance of a primary-secondary pumping systems;
The characteristics and selection of control valves;
Why 2-way valve is better than 3-way valve in variable flow systems?
The comparison of variable primary flow system to the primary/secondary system;
The advantages and design challenges in the design of variable primary chilled water distribution scheme;
The importance of design tube velocity and rate of chilled water flow variations in variable primary flow systems; and
The cost comparison of variable primary flow with primary/secondary pumping schemes.

Intended Audience

This course is intended for people who plan, design, install, and operate HVAC systems for buildings. This course is ideal for experienced 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 to know more about identifying the most suitable type of chilled water scheme for their applications. 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

A chilled water system is a cooling system in which chilled water is circulated throughout the building or through cooling coils in an HVAC system in order to provide space cooling. The principal objectives of chilled water pumping system selection and design are to provide the required cooling capacity to each load, to promote the efficient use of refrigeration capacity in the plant, and to minimize pump energy consumption subject to whatever budgetary constraints may apply. In the typical design process, such decisions are made on the basis of economic calculations.
The course describes how to select appropriate chilled water scheme for your application and how to integrate various components as a working system. Discussion will be in three modules which cover:

Constant flow chilled water system
Primary/secondary chilled water flow scheme
Variable primary chilled water flow scheme (VPF)

Course Content

This course is in the following PDF document:

HVAC Chilled Water Distribution

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Course Summary

Three common chilled water distribution schemes used in modern buildings are:

Constant flow chilled water system
Primary/secondary chilled water flow
Variable primary chilled water flow (VPF)

Primary/secondary chilled water flow scheme is most commonly employed but in recent years the VPF system is gaining popularity due to advantages such as lower first cost, reduced peak demand, reduced energy sue, less mechanical room space and ability to cope with lower than design “delta-T” syndrome. However, the design of VPF scheme involves much greater skill to handle the challenges of control sequence. It is important to maintain a minimum flow rate through the evaporator to ensure proper heat transfer. The control must prevent rapid changes in flow, as a sudden drop in flow would result in a rapid drop in leaving chilled water temperature, and could trigger a low-temperature safety alarm.
The selection of a determined scheme should be based on a careful analysis of such factors in order to reach the best balance between equipment cost and system performance. In the context of HVAC design, decisions made to save money often involve a tradeoff between acquisition expense and operating cost. If you can realize savings on both fronts, so much the better.

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.