Indoor Air Quality and HVAC Systems

David W. Bearg

• Editorial: CRC Press
• Año: 2019
• ISBN:
  9781351438940
• Edición: 1
• Categoría: Biological Sciences
• Categoría: Environmental Conservation & Protection

Indoor Air Quality and HVAC Systems is a practical guide for understanding the relationship between the design, installation, operation, and maintenance of HVAC systems and achieving indoor air quality (IAQ). The book describes the individual components of HVAC systems and the role each plays in maintaining good indoor air quality. It also identifies the techniques available for evaluating the performance characteristics of ventilation systems (including the use of carbon dioxide monitors and sulfur hexafluoride tracer testing equipment).
Other topics discussed include the determination of pathways of air movement through buildings and understanding pressure relationships, ventilation effectiveness, and efficiency. The book concludes with an overview of sources of air contaminants to be concerned about when performing an IAQ evaluation.
Indoor Air Quality and HVAC Systems provides critical information for industrial hygienists, HVAC contractors and engineers, and building owners and managers.

CHAPTER 1

Introduction

FOREWORD

This book was written to provide a practical guide to those people responsible for the design, installation, operation, and maintenance or evaluation of heating, ventilating, and air conditioning (HVAC) systems. The purpose of this book is to help them understand how these systems are intended to perform with respect to providing and maintaining good indoor air quality (IAQ). The intended audience for this book includes industrial hygienists, HVAC contractors, building owners, managers, facility operators, and those individuals that perform IAQ evaluations. The information in this book is based on experience accumulated over 12 years in the evaluation of over several million square feet of both low- and high-rise commercial (i.e., nonindustrial) office spaces.

OVERVIEW OF BOOK

The organization of this book begins with a detailed description of HVAC systems in Chapters 2 and 3. In Chapter 2, the discussion focuses on the basic types of HVAC systems from a macro perspective; that is, as a collection of parts working together. In Chapter 3, the discussion is again on HVAC equipment, this time from the micro perspective, where the importance of each of the individual components of typical systems are discussed in terms of the role they play and their importance in terms of the achievement of good IAQ.

Chapter 4 proceeds with a discussion of evaluation criteria for ventilation systems. Discussed first are the specific terms and units that are used for expressing and quantifying ventilation rates. This is followed by a discussion of the standards, regulations, and guidelines that exist for the evaluation of IAQ.

Chapters 5 and 6 present specific discussions of the evaluation techniques available for assessing the performance of ventilation systems. Chapter 5 focuses on how to evaluate the quantity of outdoor air entering the HVAC system, while Chapter 6 discusses how to quantify the amount of outdoor air actually being delivered to the building occupants.

Chapter 7 discusses the characterization of the performance of the ventilation system by discussing the concepts of ventilation effectiveness and efficiency, which refer to the relative ability of the outdoor air being delivered to the occupied areas to dilute and remove air contaminants, as well as to how much of the outdoor air entering the HVAC system(s) actually gets delivered to the occupied areas of the building.

Chapter 8 discusses pressure relationships and the resulting air movement patterns that can exist in buildings. These pressure relationships involve both those between the building and the outdoors and those that exist within the building itself. Included in this discussion is the relationship between these air movement patterns and the achievement of good IAQ, as well as a discussion on how to evaluate these air movement patterns. Examples are given from specific case studies. This chapter also presents a discussion on natural ventilation in buildings.

Chapter 9 discusses the specific tools and techniques available for evaluating ventilation systems, and the information that can be obtained from them. This chapter discusses the investigator as an instrument of evaluation, as well as the use of specific types of equipment.

The concluding portion of the book, Chapter 10, presents a discussion of the potential sources of air contaminants other than those arising merely from the occupants. This last chapter is included to balance out the other side of the dynamic relationship that exists between the amount of ventilation being provided and the sources of air contaminants that are present. Also presented are details on the steps necessary to evaluate the performance of the ventilation systems.

Relationship Between IAQ and HVAC Systems

In order to explain the relationship between IAQ and HVAC systems, it is first necessary to understand how buildings operate and the role that the HVAC system plays in that process. The HVAC system is one of four key elements that interact in a building to yield the conditions of the indoor environment. These four elements are presented in Table 1.1. One primary purpose, or goal, of the building is to provide a healthy and comfortable environment for the occupants of that building. In addition to this concept of the building providing shelter from the elements, there is also the economic reason that buildings are created in order to bring people together “under one roof to perform functions that they would not be able to perform as efficiently if they were more dispersed. Buildings therefore are created to increase the productivity of workers. The economic relationship between worker productivity and IAQ is discussed later in this chapter.

Table 1.1. Building Elements Affecting the Indoor Environment

Building shell (its “skin” and partitions) HVAC system and its condition Outdoor environment Building occupants and their activities

The components of the building interact to accomplish these goals. The physical geometry of the space and the allocation of uses within this space bring the people together. The building shell, or envelope, limits the exchange of air and energy between the indoor environment and the outdoors, and the mechanical systems condition the interior air by providing heating and cooling plus making provisions for the exchange of air. The combination of the removal of stale air and the introduction of fresh air dilutes and removes air contaminants, this being accomplished by either mechanical and/or natural ventilation.

Causes of IAQ Problems

An analysis of how a particular building performs these tasks is often essential to understanding the quality of indoor air being provided. One basic unifying premise maintained throughout this book can be summarized in the following statement:

Indoor air quality problems arise in nonindustrial buldings when there is an inadequate quantity of ventilation air being provided for the amount of air contaminants present in that space.

The nature of this dynamic relationship is that, based on the amount of air contaminants present in a particular building, the ventilation rate considered as “adequate” can vary. IAQ problems can also be due to inadequate pollution controls despite otherwise normal or baseline rates of ventilation.

The experience of the National Institute for Occupational Safety and Health (NIOSH)¹ in their IAQ building evaluations provides an example of this dynamic relationship, as evidenced by the breakdown of the causes of IAQ problems as presented in Table 1.2, which summarizes their investigations. Just as the majority of the IAQ problems investigated by NIOSH were attributed to inadequate ventilation, the majority of the information in this book focuses on the requirements for the delivery of adequate ventilation to the occupants of a building. However, since good IAQ is based on both this delivery of adequate ventilation and minimizing or eliminating sources of air contaminants, this book also addresses the need to assess the presence of air contaminants.

Table 1.2. NIOSH Indoor Air Quality Investigations by Problem Type (through December 1988)

Problem Type	No. of Buildings	% Attributed
Ventilation inadequate	280	53
Inside contamination	80	15
Outside contamination	53	10
Microbiological contamination	27	5
Building materials contamination	21	4
Unknown	68	13
Totals:	529	100

Defining Adequate Ventilation

Some dictionary definitions for the word “adequate” include: (1) able to satisfy a requirement; suitable; and (2) barely satisfactory or sufficient. With respect to the issue of adequate ventilation, sections of this book include both information on what constitutes adequate amounts of ventilation, as well as how to evaluate whether or not these adequate quantities of ventilation air are being provided. “Ventilation air” is defined as clean, outdoor air delivered to occupied areas of the building which, in conjunction with the air exhausted from the space, dilutes and removes air contaminants present in that space.

Sources of Air Contaminants

In addition to the requirement for adequate ventilation, the other side of the equation for achieving good IAQ is the presence or absence of air contaminants. It is important to remember that: In assessing the presence of air contaminants, it must be recognized that they can arise from the people who are present in that space, from the ac...