Thermal Energy Storage

Systems and Applications

Ibrahim Dinçer, Marc A. Rosen

• Publisher: Wiley
• Year: 2011
• ISBN:
  9781119956624
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Thermodynamics

The ability of thermal energy storage (TES) systems to facilitate energy savings, renewable energy use and reduce environmental impact has led to a recent resurgence in their interest. The second edition of this book offers up-to-date coverage of recent energy efficient and sustainable technological methods and solutions, covering analysis, design and performance improvement as well as life-cycle costing and assessment. As well as having significantly revised the book for use as a graduate text, the authors address real-life technical and operational problems, enabling the reader to gain an understanding of the fundamental principles and practical applications of thermal energy storage technology.

Beginning with a general summary of thermodynamics, fluid mechanics and heat transfer, this book goes on to discuss practical applications with chapters that include TES systems, environmental impact, energy savings, energy and exergy analyses, numerical modeling and simulation, case studies and new techniques and performance assessment methods.

1

General Introductory Aspects for Thermal Engineering

1.1 Introduction

Thermal energy storage (TES) is one of the key technologies for energy conservation, and therefore, it is of great practical importance. One of its main advantages is that it is best suited for heating and cooling thermal applications. TES is perhaps as old as civilization itself. Since recorded time, people have harvested ice and stored it for later use. Large TES systems have been employed in more recent history for numerous applications, ranging from solar hot water storage to building air conditioning systems. The TES technology has only recently been developed to a point where it can have a significant impact on modern technology.

In general, a coordinated set of actions has to be taken in several sectors of the energy system for the maximum potential benefits of thermal storage to be realized. TES appears to be an important solution to correcting the mismatch between the supply and demand of energy. TES can contribute significantly to meeting society’s needs for more efficient, environmentally benign energy use. TES is a key component of many successful thermal systems, and a good TES should allow little thermal losses, leading to energy savings, while permitting the highest reasonable extraction efficiency of the stored thermal energy.

There are mainly two types of TES systems, that is, sensible (e.g., water and rock) and latent (e.g., water/ice and salt hydrates). For each storage medium, there is a wide variety of choices depending on the temperature range and application. TES via latent heat has received a great deal of interest. Perhaps, the most obvious example of latent TES is the conversion of water to ice. Cooling systems incorporating ice storage have a distinct size advantage over equivalent capacity chilled water units because of the ability to store large amount of energy as latent heat. TES deals with the storing of energy, usually by cooling, heating, melting, solidifying, or vaporizing a substance, and the energy becomes available as heat when the process is reversed. The selection of a TES is mainly dependent on the storage period required, that is, diurnal or seasonal, economic viability, operating conditions, and so on. In practice, many research and development activities related to energy have concentrated on efficient energy use and energy savings, leading to energy conservation. In this regard, TES appears to be an attractive thermal application. Furthermore, exergy analysis is an important tool for analyzing TES performance.

We begin this chapter with a summary of fundamental definitions, physical quantities, and their units, dimensions, and interrelations. We consider introductory aspects of thermodynamics, fluid flow, heat transfer, energy, entropy, and exergy.

1.2 Systems of Units

There are two main systems of units: the International System of Units (Le Systéme International d’Unités), which is normally referred to as SI units, and the English System of Units. SI units are used most widely throughout the world, although the English System is traditional in the United States. In this book, SI units are primarily employed. Note that the relevant unit conversions and relationships between the International and English unit systems concerning fundamental properties and quantities are listed in Appendix A.

1.3 Fundamental Properties and Quantities

In this section, we briefly cover several general aspects of thermodynamics to provide adequate preparation for the study of TES systems and applications.

1.3.1 Mass, Time, Length, and Force

Mass is defined as a quantity of matter forming a body of indefinite shape and size. The fundamental unit of mass is the kilogram (kg) in SI units and the pound mass (lb_m) in English units. The basic unit of time for both unit systems is the second.

In thermodynamics, the unit mole (mol) is commonly used and defined as a certain amount of a substance as follows:

(1.1)

where n is the number of moles, m is the mass, and M is the molecular weight. If m and M are given in units of gram and gram per mole, we obtain η in moles. For example, one mole of water, having a molecular weight of 18 (compared to 12 for carbon-12), has a mass of 0.018 kg.

The basic unit of length is the meter (m) in SI units and the foot (ft) in the English system.

A force is a kind of action that brings a body to rest or changes its speed or direction of motion (e.g., a push or a pull). The fundamental unit of force is the Newton (N).

The four aspects, for example, mass, time, length, and force, are related by the Newton’s second law of motion, which states that the force acting on ...