Guia Hvac

Source: HVAC Systems Design Handbook

Chapter

1
HVAC Engineering Fundamentals:
Part 1

1.1

Introduction

This chapter is devoted to ‘‘fundamental’’ fundamentals—certain principles which lay the foundation for what is to come. Starting with the
original author’s suggested thought process for analyzing typical problems, the reader is then exposed to a buzzword of our time: valueengineering. Next follows a discussion of codes and regulations, political criteria which constrain potential design solutions to the bounds
of public health and welfare, and sometimes to special interest group
sponsored legislation. The final sections of the chapter offer a brief
review of the basic physics of heating, ventilating, and air conditioning
(HVAC) design in discussions of fluidmechanics, thermodynamics,
heat transfer, and psychrometrics. Numerous classroom and design
office experiences remind us of the value of continuous awareness of
the physics of HVAC processes in the conduct of design work.
1.2

Problem Solving

Every HVAC design involves, as a first step, a problem-solving process, usually with the objective of determining the most appropriate
type of HVAC systemfor a specific application. It is helpful to think
of the problem-solving process as a series of logical steps, each of
which must be performed in order to obtain the best results. Although
there are various ways of defining the process, the following sequence
has been found useful:
1. Define the objective. What is the end result desired? For HVAC
the objective usually is to provide an HVACsystem which will control
1

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HVAC Engineering Fundamentals: Part 1
2

Chapter One

the environment within required parameters, at a life-cycle cost compatible with theneed. Keep in mind that the cost will relate to the
needs of the process. More precise control of the environment almost
always means greater cost.
2. Define the problem. The problem, in this illustration, is to select
the proper HVAC systems and equipment to meet the objectives. The
problem must be clearly and completely defined so that the proposed
solutions can be shown to solve theproblem.
3. Define alternative solutions. Brainstorming is useful here.
There are always several different ways to solve any problem. If remodeling or renovation is involved, one alternative is to do nothing.
4. Evaluate the alternatives. Each alternative must be evaluated
for effectiveness and cost. Note that ‘‘doing nothing’’ always has a cost
equal to the opportunity, or energy, or efficiency‘‘lost’’ by not doing
something else.
5. Select an alternative. Many factors enter into the selection
process—effectiveness, cost, availability, practicality, and others.
There are intangible factors, too, such as an owner’s desire for a particular type of equipment.
6. Check. Does the selected alternative really solve the problem?
7. Implement the selected alternative. Design, construct, andoperate the system.
8. Evaluate. Have the problems been solved? The objectives met?
What improvements might be made in the next design?
Many undertakings fail, or are weak in the end result, due to failing
to satisfy one or more of these problem-solving increments. There is
an art in being able to identify the key issue, or the critical success
factors, or the truly beneficial alternative.Sometimes the evaluation
will be clouded by constraint of time, budget, or prejudice. Occasionally there is an error in assumption or calculation that goes unchecked. The best defense against disappointment is the presence of
good training and good experience in the responsible group.
1.3

Value Engineering

Value analysis or value engineering (VE) describes a now highly sophisticated...