A Guide in Practical Psychrometrics for Students and Engineers

By Stephen Bird C Eng. MCIBSE MASHRAE

This publication has been conceived from the author’s active career in a demanding but rewarding working genre. The day to day situation where advice and clear guidance of other more experienced engineers sometimes becomes a limiting factor has been the catalyst for the production of this publication. It is trusted I will be found to guide in many of the areas of HVAC that can cause shortcomings and disappointment in successful delivery.
From initials stages of employment it was found that fundamental advice and directives were in “short supply” and given by default. Study and investigative enquiries were generally found to be most beneficial. Much learnt and proven can be valuably passed on to those who take up a career with the intentions of become an accomplished and asset to a major sector of the construction industry. It is honestly hoped this publication has or will go some way to aiding both individuals and the industry as a whole.

• Language: English
• Publisher: Balboa Press UK
• Release date: Mar 16, 2021
• ISBN: 9781982283025

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Copyright © 2021 Stephen Bird C Eng. MCIBSE MASHRAE.

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ISBN: 978-1-9822-8301-8 (sc)

ISBN: 978-1-9822-8302-5 (e)

Balboa Press rev. date: 02/12/2021

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A GUIDE IN

PRACTICAL

PSYCHROMETRICS

FOR

STUDENTS AND ENGINEERS

FOREWORD

Through the history of mankind the need has been for living space that provides protection from the outdoor environment and a degree of comfort.

Comfort needs were simple and basic. Shelter with warmth and light was that need. Both were produced initially by the use of a fire.

As time has progressed the whole subject of environmental needs have developed and become significantly more complex.

From the open fire through the Roman hypocaust to today, demands have developed for high degrees of environmental control in personal comfort to highly complex scientific processes.

Such has been the vast move over millenniums that building environmental conditioning enabling modern life styles has increased demands on engineering knowledge and skills.

Today’s life patterns have developed into considerably more and sophisticated buildings demanding what is today known as building engineering services.

The science of environmental control by means of engineering systems involves the understanding in systems definition, design, installation and operation of plant. The process known as PSYCHROMETRICS is the basic science used to function what has now become known as air conditioning.

The word is from Greek entomology:

Psychrometrics can be stated as the science of determining, measuring, assessing, modelling and calculating temperature and moisture modifications within samples of air.

In the building engineering services industry it has become essential to be able to identify both quantity and quality of air to achieve designated design targets that include:

A target environment to enable the provision of personal comfort or a process

Definition of ambient conditions all year round

A means of satisfactorily modifying and controlling air within given conditions

Between specific conditions to maintain or change conditions in a controlled manner

The determining, measuring, calculating, changing and applying the conditions of samples of air in a practical manner is the objective subject of this publication

Current need for air conditioning has increased in the need for treating and adjusting air for the control of human comfort and various processes where air quality is vital.

The subject matter presents in a practical and appropriate manner the science by definition, calculation, application of psychrometric systems and their components in building services air conditioning.

In concluding this foreword a statement recorded by an author in an internationally established industry journal is considered a most valuable, helpful and accurate quote;

Whilst under training my manager said it is always worthy of learning from our mistakes but much better to learn from other people’s mistakes. It is valuable if not imperative that an understanding is developed from basic principles as to why or how errors come about.

Students or engineers in training, need to possess a good understanding of psychrometrics and how it impacts the HVAC, drying systems design and operation, controls, or diagnosis for achieving client comfort and system shortcomings. Some students and young engineers may lack the motivation to learn psychrometric skills and some ideas that might provide the motivation to acquire these skills. This publication provides resources to help expand practical knowledge of psychrometrics basic and practical methodology.

Mistakes happen but by having a clear understanding and ability to apply fundamentals in any practice of science should avoid or at worst limit many mistakes. It is intended and truly hoped that this publication may serve industry to some valuable degree.

INTRODUCTION

PSYCHROMETRICS

Psychrometrics is the science involving the dynamic properties of moist air and effects of atmospheric moisture on materials and human comfort. Within the purposes of this publication definitions need to be broadened to include methods of modifying and controlling the thermal properties of moist air.

Psychrometrics is one of the four sciences in the scope of technical expertise, including refrigeration, heat and mass transfer, and fluid flow. Psychrometrics is a sub science of physics dealing with the properties and processes of moist air. Moist air is defined as a mixture of two gases: dry air and water vapour (the gas phase of H2O).

The water vapour content of air varies from as little as 0.2% by volume to as much as 3.5%, but that small percentage accounts for a significant part of the energy required operating air-conditioning systems and is associated with many system comfort complaints.

The starting point is to set out some basic terminology and definition that are regularly and fundamentally used within the psychometrics process

The building engineering services industry has made available to practicing engineers considerable amounts of literature on the subject matter of psychrometrics. Much is invaluable to the practicing engineer and benefits in system design and delivery.

There is, despite the volumes of Manuals and Guides available, an absence of basic and simplistic guidance on the subject. It is hoped that this publication may make good some of the deficiency and provide a possible short format practical guidance on the subject.

This publication has been produced with the objective of dual readership, comprising both student and industry practising engineer. An emphasis may be found that answers the needs of the student.

It is targeted that the content of the publication will assist those who are preparing to undertaken formal academic studies and further those applying for professional corporate membership of an associated institute.

The author has served extensively in the successful conceptual, detailed design and installation of wide ranging systems that have demanded application of the subjects on which this publication focuses.

The fundamental origins of psychometrics are based on much of the work completed and published by past scientists in the subject of thermodynamics. Much, if not all principles, rely on the detail of thermodynamic principles of gas temperatures, total and partial vapour / gas pressures.

Modern psychrometrics and the practical application of operating these laws was built and developed in the