The main objectives, not only for Slovakia but also internationally, are to limit energy consumption and to honour the commitments ratified under the Kyoto Protocol. The importance of protecting the environment and using energy resources economically has been confirmed by recent events connected with problematic fuel supplies from eastern countries. The European Community has drawn up a political plan to ensure that the objectives set in this area are met through joint efforts and resources within the Community.
In this context, the European Parliament and the Council of the European Union issued a special directive in 2002, which became an effective instrument at European Community level for ensuring that these objectives are applied throughout the Union. This is Directive 2002/91/EC, better known by the abbreviation "EPB", which stands for "Energy Performance of Buildings'.
As the name itself suggests, the central idea of this document is the heated building and, above all, the energy-related measures that can be carried out in it. The directive sets out which solutions can be chosen, and for which types of building, in order to have a truly significant impact on the energy situation in Europe. It therefore confirms and reinforces the principle of the close interdependence between a heated building and its heating system.
In Slovakia, the provisions of this directive are transposed by Act No. 555 / 2005 and implementing decree 625/2005.
We will not discuss the content of the decree in detail, because many of its points are still being worked out, but let us take a closer look at the directive. So far the directive has been the subject of purely technical and standards-related discussions, which will form the basis for the correct application of its mandatory part.
As the directive has a Europe-wide impact, the first step in applying it is the existence of the relevant legal standards:
• these must take into account the current state of the art in installations and construction,
• they must ensure the necessary unanimity on the theoretical basis of the calculation methodology at European Community level,
• they must make it possible, in the relevant annexes valid for individual countries, to introduce parameters defining the construction and climatic conditions that are specific to each country.
For these reasons, the European Commission mandated CEN to prepare a suitable technical basis for applying the EPB Directive.
It should first be made clear that the new technical and standards basis for energy saving must be far more extensive and more finely structured, because it has to cover a larger number of possible solutions and pay greater attention to alternative energy sources. This follows from new experience gained in the field of design. The CTI institute is currently cooperating very actively in the preparation of these documents and is making the expertise and experience of industry and specialists available to the European project.
Let us look at what this new legislative package will look like.
As already mentioned, the adoption of the new European directive has already been reflected in some standards, such as the forthcoming standard prEN 15316 - Heating systems in buildings. Unlike the existing regulations, the future standard will not be drawn up as a single document but will be divided into many parts. This will make it possible to determine in detail and in a targeted way - by means of calculations - the prescribed parameters of the individual subsystems of the heating system (generation, emission, storage and distribution) for different installation solutions, from traditional to condensing systems, district heating and solar collectors, while all the energy sources used must be taken into account.
It would not be right to analyse in detail standards that are still only in preparation, so we suggest instead forming a picture of the current state of European heating technology from a philosophical point of view.
The basic principle on which the new European legislation would be based when calculating the efficiency of a heating system could be a different concept of the heating system.
As can be sensed "between the lines" of the preceding paragraph, where control was not listed among the subsystems of the heating system, some European countries prefer an alternative strategy in which they favour analysing the "storage system". This choice was prompted by the need for a more thorough and integrated analysis of the operation of the heating system as such. The new approach brings the assessment of the heat demand for heating and for producing domestic hot water (DHW), which are often markedly different, into a single design procedure. From a thermodynamic point of view, this approach is definitely "more principled".
When a heating system is put together, the thermodynamic point of view takes precedence, that is, the actual heat transfer and consequently the heat losses are considered. From a purely physical point of view, however, it must be admitted that the control system really does influence the heat flow, even though the heat itself does not physically pass through the control system. In any case, as we shall see on the following pages, if the control subsystem is left out we obtain an incomplete picture of how the system works and therefore of its characteristics.
The practical consequence of this principle is that the management of heat, generated in proportion to the needs of the building, is an internal property of each of the subsystems, which run in heating mode almost continuously, with a very low number of ignitions and shutdowns. Technically, this type of heat generation subsystem is very simple and requires an equally simple method of control.
This concept, which is “academically” very sound, runs into some practical problems which, at least in our country, partly offset its advantages. As always, let us first divide installations into two kinds: those in new buildings and refurbishments in older buildings.
In new buildings there are, of course, fewer technical constraints on the choice of installation type, but there are economic ones.
Today an installation with a large storage volume can no longer be used in new buildings because, given the high prices, housing development favours medium-sized and small flats, which sell better.
Here both the designer and the installer have to tackle the question of saving space. It is then very important to design the connections correctly, to position the hot water cylinder suitably (which is not always easy) and to route the pipework in line with the customer's architectural requirements.
In addition, such storage installations have the disadvantage of high thermal "inertia', which often requires a supplementary source, for example solar energy or, much more often, electricity. Electric sources are used as supplementary ones in countries where, for certain reasons, electricity is relatively cheap. In these cases, high thermal inertia penalises the efficiency of the control.
Apart from these factors, choosing this type of installation would increase the overall cost of the heating in terms of both materials and labour. In view of this, large-capacity installations for central heating often give way to solutions with independent gas-fired water heating, combined with a heating system that uses other types of fuel (liquid or solid).
Italian heating technology, however, is focused on high-technology products that Italian industry is able to bring to market at acceptable prices.
Finally, as practical experience shows, it is conceptually impossible to assess the efficiency and performance of a heat generation system in general without taking into account the specific type of equipment used to manage the heat. The current state of technical development has made it possible to introduce a direct electronic link between the heat source and the temperature control system.
The heat source and temperature control system in effect forms the real "brain" of the heating system. The close link between the heat source and the control must also be reflected in the logical conceptual diagram.
Let us stress that it is precisely the temperature control system that must always be designed in line with the latest knowledge in this field. This aspect is specifically addressed by the standards of some EU member states, such as the Italian standard UNI l 0348 on the efficiency of heating systems.
The currently prescribed calculation procedure does not take the most modern and most advantageous temperature control systems into account.
At this point we consider it necessary to set out the parameters that could establish more credible tabulated values for calculating control efficiency (see table).
