1. Introduction
1.2.1 Background
1.2.2 Lowex system
1.2.3 Objectives and scope
1.2.4 Strategy
1.3 Energy, exergy and environment
1.5 Historical overview on exergy
This Guidebook is intended to be useful for architects and
engineers designing of heating and cooling systems of buildings. A database of low exergy
components is completed with the guidelines for selection of products (in Chapter 4).
Examples of system concepts for different buildings and climates are presented (in Chapter
5) as well as a set of tools for analysis (described in Chapter 3, included in the
CD-ROM). All this is expected to be helpful for engineering offices, consultants and
architects in their search for energy efficient heating and cooling systems that can
provide the occupants with comfortable, clean and healthy environment.
An analysis of case studies (in Chapter 5) together with rationale of exergy concept (in
Chapter 2) and recommendations concerning regulations in building sector and energy
tariffs (in Chapter 7) are expected to be helpful for real estate builders, building
maintenance managers, political decision makers and the public at large. The description
of the current market situation (in Chapter 6) offers the reader additional background
information about the situation in different countries.
The CD-ROM version of the Guidebook includes the same information as the printable
version, but it offers the user some additional opportunities in moving around in the
Guidebook. Through the “Annex 37 Countries” page the user has access to the
country specific information, like the national contact persons and case examples as well
as the climate and housing standards. The country specific pages also include information
about the companies that provide services in the LowEx field and are located in the
country in question. There is a link to the country’s Market Analysis and Strategies
and Policies chapters. From the summary tables of the LowEx technologies and the case
examples, the user can choose projects or technologies matching certain criteria. There is
a link from the technologies table to the case examples, where these technologies have
been used and vice versa. We have also collected some Additional Information to the
CD-ROM. This includes the Technical reports written for the ECBCS ExCo, the LowEx
Newsletters, an English Brochure, the publication called “Introduction to
Exergy”, published articles etc.
Future buildings should be planned to use or to be suited to use sustainable energy sources for heating and cooling. One characteristic of these energy sources is that only a relatively moderate temperature level can be reached, if reasonably efficient systems are desired. The development of low temperature heating and high temperature cooling systems is a necessary prerequisite for the usage of alternative energy sources. The basis for the needed energy supply is to provide occupants with a comfortable, clean and healthy environment.
In Annex 37, 'low exergy (or LowEx) systems' are defined as heating or cooling systems that allow the use of low valued energy as the energy source. In practice, this means systems that provide heating or cooling energy at a temperature close to room temperature.
The interest of the Annex 37 covers all types of buildings. Both new and retrofitted buildings are considered. Attention is paid to the impact of the building on the whole energy chain. The building is regarded as a system. Life cycle aspect and environmental impacts of systems are discussed. End users point of view and behaviour are taken into account.
Figure 3a and b. The scope of Annex 37 covers both environmental impacts of the systems and the end user’s point of view. Both new and retrofitted buildings are considered.
The growing concern of environmental problems, such as global warming, which have been linked to the extended use of energy, has increased both the importance of all kinds of so called "energy saving measures", and the necessity for an increased efficiency in all forms of energy utilisation. Despite the efforts made to improve energy efficiency in buildings, the issue of gaining an overall assessment, and comparing different energy sources still exists. Today’s analysis and optimisation methods do not distinguish between diffe-rent qualities of energy flows during the analysis. An assessment of energy flows from different sources is first done at the end of the analysis by weighting them with the primary energy factors. The primary energy factors necessary for the calculation are not based on analytical ground or thermodynamic process analyses, yet they have been derived from statistical material and political discussion (DIN 4701-10 2001).
In the theory of thermodynamics, the concept of exergy is stated to be the maxi-mum work that can be obtained from an energy flow or a change of a system. The exergy content expresses the quality of an energy source or flow. This concept can be used to combine and compare all flows of energy according to their quantity and quality. Exergy analysis is commonly used in, for example, the optimisation processes of power stations. This method can be applied to buildings, as well. Most of the energy is used to maintain room tempera-tures at around 20 °C. In this sense, because of the low temperature level, the exergy demand for applications in room conditioning is naturally low. In most cases, however, this demand is satisfied with high quality sources, such as fossil fuels or using electricity. Exergy analysis provides us with additional information on where and when the losses occur. It helps us to see in which part of the energy chain the biggest savings can be achieved. (Schmidt 2004)
The need for energy saving is based on the will to reduce the effects of our actions to the environment. The negative environ-mental effects of energy production are mainly due to the use of fossil fuels. When all energy will be produced with renewable energy sources, then it becomes less interesting to save exergy. This is why we also want to include solar energy to our sources, even if it is a high exergy source.
Why couldn’t we use the primary energy approach? If we
always took into account the primary energy needed to perform something, we would get far
better results in our energy-analyses; with that perspec-tive it would be clear that 1 kWh
doesn’t always mean the same thing as another
1 kWh. One reason for using the exergy approach and not just settling for the primary
energy approach is that it is physi-cally more correct to talk about exergy- than energy
consumption and production.
It is a fact that the term "exergy" is an unknown term even for scientists not to mention "people on the street". In order to make this term less "strange" we need to first of all start talking more about it and stop using the term energy when we actually mean exergy. The publication "Introduction to the Concept of Exergy- for a Better Understanding of Low Tempera-ture Heating and High Temperature Cooling Systems" that has been published by members of the Annex 37 group, gives the term exergy a clear explanation. By disseminating this publication widely we contribute to making the term more known. Most of the contents of this publication can be found in chapter 2 of this Guidebook.
Although exergy analysis is not being widely used, there is a growing concern about the second law of thermodynamics in reports and books, which promote the use of this named method. Yet, due to difficulties and the complexity of these concepts, there still seems to be a lack of acceptance amongst engineers (Ahern 1980). Intensive literature studies have been carried out, showing the advantages of the proposed method (Cornelissen 1997, Wall 1986 and Ahern 1980).
The method of exergy analyses has been primarily developed in Europe, especially in Germany, Poland and the former Soviet Union. The term "exergy", first used by Rant in 1956, has been connected to the capability to do work or the available work from a process, and the Carnot efficiency of thermal systems. Baehr used the met-hod for the analyses of power stations in 1965 and provided several examples of exergy calculations. He presented analyti-cal results by comparing flowcharts of exergy analyses with energy calculations based on the first law of thermodynamics. The results clearly show the significant differences obtained by these two methods of analysis (Ahern 1980).
The discussed references are just a small portion of the literature to be found on the second law of thermodynamics and although engineers and physicists have been studying this subject since Carnot’s days, it is still under controversial and ambitious discussion (Ahern 1980). The texts available (Wall 1986, Cornelissen 1997) indicate the strong belief of the authors that exergy analysis and the application of the second law of thermo-dynamics are important aspects in desig-ning and evaluating all energy systems. As the concern about questions and prob-lems regarding the efficient use of energy is growing, pioneering efforts made in the past should be extended and implemented to commonly used methods for engineer-ing system design and performance analy-sis. The simplicity of the exergy analysis method might help in reaching this goal (Ahern 1980).
In case of building applications, only a few papers, mainly from Japanese (Shukuya 1994, Asada and Shukuya 1999, Nishikawa and Shukuya 1999) and German (Baehr 1980, Gertis 1995, Steimle 2000, Klemp 1997, Jenni and Hawkins 2002) research teams, have been published. Annex 37 working group continued the development of the use of exergy concept in connection with buildings and making the exergy concept more understandable and familiar to the public.
From an article by Shmidt (2004)