Page 8 - Low Temperature Energy Systems with Applications of Renewable Energy

xviii Preface

Chapter 1 focuses on this technology. We begin with a snapshot of world energy
usage, with an eye to renewable energy sources. A brief summary is given of pertinent
energy policies around the world, along with procedures needed to create and assess
energy efficient systems. We then trace the history of heat pumps and refrigerators
and describe these machines both qualitatively and quantitatively. Thermodynamically
ideal machines that set the standard for real-world systems are analyzed. Practical heat
pump and refrigeration systems are described in technical detail and analyzed using the
principles of thermodynamics. Both vapor-compression and absorption refrigeration
systems are discussed. The process of selecting appropriate working fluids is described
with special emphasis on the environmental impacts and international protocols. The
chapter concludes with a discussion of modes of operation of heat pumps and cold
storage systems.
In Chapter 2 we review the main systems using heat pumps in heat supply systems
for residences and public buildings using various low-grade heat sources. Heat supply
sources include: ambient air, water, and soil. Limitations on the use of these sources
are discussed. Heat pump performance is derived and presented as functions of tech-
nical parameters. This is done by means of analytical and practical methods, together
with numerical examples of typical calculations. The results show optimum operating
points where energy losses are minimized. Finally, we summarize the status of world-
wide heat pump usage.
Next, in Chapter 3, comes a wide range of heat pump heating applications from
individual private residences to modern skyscrapers to airports and other public facil-
ities. Although mainly technical topics are presented, the economics of various sys-
tems is covered in the last section where equivalent coal consumption is used as the
basis for comparison. Heat pumps are shown to be very effective in controlling the
conditions in pools, particularly indoor units where humidity can pose challenges
for designers. Water-loop systems are becoming popular in many places owing to their
inherent flexibility to allow heating and cooling simultaneously in large buildings with
variable thermal loads. In the case of hot-water heating systems, detailed assessments
are carried out and the results presented for a conventional water boiler and heat pumps
with three different means of powering the heat pump compressor, namely, electric,
diesel, or gas turbine. A heat pump with a gas turbine compressor drive is shown to
be the most efficient based on several thermodynamic and practical measures.
As we have discussed in the first three chapters, heat pumps have become well
known for providing cost-effective heating and cooling in domestic and commercial
buildings. Moreover, for countries with a large agricultural sector, a large share of en-
ergy is consumed in crop drying. Chapter 4 explains in detail how heat pumps can be
used in the drying industry. One section is dedicated to presenting a compendium of
general arrangements that have applications in various aspects of drying. We cover
eight different cases in a survey of applications, followed by sections covering two
particular applications, namely, grain and wood drying. The first one is important in
preparing foodstuffs for humans and animals, while the second one plays a vital
role in the construction and furniture industries. The thermodynamic advantages of
heat pumps over conventional drying methods are developed. The main obstacles
limiting the use of heat pumps in industry are high initial capital cost which might