Preface

The low-temperature market is growing and expanding. It plays an essential and growing role in the global economy. A wide range of low temperatures are required almost in all branches of everyday life and industries, including the food and beverage industries, air conditioning (comfort, technological, technical, IT equipment), water and "dry" ice, winter sports, chemical industries, freeze-drying (for food, pharmaceutical, biological applications, hair care industries, etc.); metallurgy, mechanical industries, machinery, civil engineering, liquefaction of natural gas, etc. The total number of low-temperature systems recently in operation over all the world is roughly 3 billion. Such a development must be sustainable, with limited impact on the environment and reasonable energy consumption (https://iifiir.org/en).

The scientific publications related to refrigeration cover the directions of new and/ or advanced technologies for application, thermodynamic cycles, working fluids (one-component and mixtures), heat and mass transfer processes, materials etc. The methods for the analysis and optimization are adjusted for in the refrigeration machines because of the processes below/crossing the temperature of the environment. The initial idea of this book was to provide the reader with a comprehensive overview of the latest developments and perspectives of research in the very wide spectrum of refrigeration: feasibility of new technologies and improvements in existing technologies; energetic, economic, and environmental effectiveness of machines and processes; different optimization methods; and many other aspects related to low temperatures.

This book, "Low-temperature Technologies", consists of 13 chapters. These chapters cover a wide range of low-temperature applications from the temperature slightly below the environment (air conditioning) down to cryogenics.

The energy consumption for industrial, commercial, and domestic heat, ventilation, and air conditioning has become a very important issue in the energy balance of many countries. Therefore, continuous updating to the latest developments helps the researchers and practical engineers in their work as well as the students for the education process. Chapter 1 discusses the central air condition systems and their applications: all-air, all-water, and air-water systems. The topic of a special air conditioning system and its new application is addressed in Chapter 2. The desiccant-based systems have been evaluated: standalone and assisted by the Mcycle. The recommendations for the optimal applications have been formulated. Desiccant-based air conditioning systems are also the focus of Chapter 3. A solarbased technology, i.e. solar pond driven air conditioning systems, have been investigated theoretically and experimentally. Chapter 4 reports the evaluation of the micro thermoelectric air conditioning system. The aim of this work is to validate the theoretical model using the experimental data. The results obtained from experimental study have been reported in Chapter 5 as well. The research interest of the authors is synthetics and natural refrigerants gases usually used for air conditioning systems in Brazil.

The research in the field of nanorefrigerants is one of new developments for improving the performance of refrigeration systems. Chapter 6 summarizes the information about behavior of different nanoparticles in vapor-compression refrigeration machines.

Within Chapter 7, the authors suggest an approach for modeling the total thermal energy needed for freezing the bound water in logs subjected to refrigeration. The approach maximally considers the physics of the freezing process of the bound water in wood.

Chapter 8 addresses the application of low-temperature technologies for medical application. Heat transfer aspects have been discussed for the technologies applied to whole-body cryotherapy.

"Cryogenics" is the key word for Chapter 9. The authors reported the evaluation of air separation units. An exergetic analysis has been applied in order to identify the thermodynamic inefficiencies and the processes that cause them. The economic characteristics of these systems have been also reported.

The remaining chapters discuss the performance of the equipment. Chapter 10 is dedicated to the evaluation of impacts of air-conditioning filters on microbial growth and indoor air pollution. The design of the spiral plate heat exchangers is the topic of Chapter 11. The authors focus on the thermal and hydraulic performance of such a heat exchanger. Computational fluid dynamics is performed to validate the thermal and hydraulic method. Particular attention is given to the maintenance of the spiral plate heat exchangers. Within Chapter 12, the influence of low temperatures on the performance of the vacuum pumps for steam power plants using air cooling is discussed.

Chapter 13 is dedicated to the overview of the energy and exergy analyses applied to the different types of refrigeration systems.

We hope that the readers will find this book to be interesting and useful for their professional activities.

> **Tatiana Morosuk (Editor)** Professor, Technische Universität Berlin, Germany

**Chapter 1**

**Abstract**

and Applications

Central Air Conditioning: Systems

It became evident nowadays that modernization influences domestic and commercial HVAC industry, and thus high technological and energy-efficient central air conditioning systems are demanded. Therefore, the selection of proper type of central air conditioning system is a crucial target in the construction industry as improper selection can maximize initial and/or running costs of the system and decreases the human comfort and indoor air quality levels. In fact, a pre-assessment of the construction type and budget available is required for selecting the proper type of central air conditioning system. Therefore, there is a continuous need for an updated material in the literature that reviews the central air conditioning systems and applications, which is the motivation of the present chapter. The present chapter reviews the central air conditioning systems and applications. Specifically, all-air systems, all-water systems, and air-water systems are discussed. In addition, all provided systems are further explored through several developed schematic diagrams enabling the identification of their various components and the understanding of their working principles. It is may be of interest to note that this chapter is suitable for undergraduate level students in the fields of

*Mohamed Elnaggar and Mohammed Alnahhal*

HVAC and R, mechanical, and construction engineering.

air-water systems, air handling unit

**1. Introduction**

**1**

cooling purposes.

for heating and/or cooling purposes.

fluids for producing heating and cooling purposes.

**Keywords:** central air conditioning, all-air systems, all-water systems,

In central air conditioning, air, water, or both are used as working fluids to produce the required heating and/or cooling, and therefore based on working fluids, central air conditioning systems can be classified into three groups [1–5], namely:

1.All-air systems: in these systems air is used as working fluid for heating and/or

2.All-water (hydronic) systems: in these systems water is used as working fluid

3.Air-water systems: in these systems both air and water are used as working

It is may be of interest to note that each type of the central air conditioning systems has several systems of sometimes different configurations, and the use of

**Muhammad Sultan (Co-editor)** Assistant Professor, Bahauddin Zakariya University, Pakistan
