Krzysztof Hoinka

Choice of the Structure of the Energy System of Complex Buildings in the Course of Preliminary Design

Traditional methods for choosing the structure of the energy management of complex buildings are based on the heuristic knowledge of designers, and as such they are restricted only to analyses of a few variants. Nowadays, this is insufficient due to the permanently growing amount of technical and economic information about new techniques in the production of electricity, heat, and cooling agents. This is in so far important that errors in the choice of the structure may cause not only unjustifiably high expenditures of investment but also higher expenditures of exploitation.

Systems Approach to Energy-Ecological Analysis of Complex Buildings

The mathematical model of the balance of direct energy consumption of energy carriers in complex buildings is based on Leontief’s input–output analysis [7]. Energy carriers are divided into those produced inside complex buildings, and possibly supplemented from outside, and energy carriers entirely supplied from outside. Direct consumption of energy carriers does not, however, comprise all the energy required for the needs of complex buildings, because the fuels, materials, and energy carriers, supplied to them, are changed by energy consumption due to: the extraction of primary energy and raw materials; the processing of primary energy to final energy carriers; and the transport and consumption of devices for gaining and processing energy carriers.The balance of cumulative exergy consumption is also expressed by the “input–output analysis”, assuming that the connections between complex buildings and the entire economy of a country are weak. This means that in the balance of cumulative energy consumption in complex buildings the indices of cumulative energy consumption concerning the input data (e.g., fuels and water) are assumed to be quantities known a priori, equal to the average values for the whole country. The mathematical model of the balance of cumulative emissions of complex buildings may be formulated based on analogical assumptions. A complete thermo-ecological analysis should also include the depletion of non-renewable energy resources. This may be expressed by the so-called thermo-ecological cost, based on the balance of cumulative exergy consumption. The thermo-ecological cost expresses the cumulative exergy consumption of non-renewable natural resources, including their additional consumption due to the necessity of compensating the environmental losses caused by the release of harmful emissions connected with the existence of complex buildings. Balances of the thermo-ecological costs of complex buildings are also based on input–output analysis, taking into account the principle of weak connections. Systems approach, similarly based on input–output analysis may be applied for the assessment of the system effects of the rationalization of energy management in complex buildings. The input values in this analysis are the results of thermodynamic process analysis concerning the individual consumers of energy carriers or the process of producing energy carriers.

Mathematical Modeling and Optimization of Energy Systems

The mathematical model of an energy system denotes a set of interdependences (equations, inequalities, logical conditions, etc.) which provide an approximated image of the properties, the functioning, and development of an actual system. The most effective trend in mathematical modeling of energy systems is the application of the property resulting from its hierarchical structure. This is connected with the decomposition of the global optimization task, based on the division of the global problem of optimization into several subproblems, solved independently and then coordinated.

Introduction into Systems Analysis

Process analysis and systems analysis are two approaches to energy-ecological analysis. Process analysis is a mechanistic approach that dominated the last centuries, although the notion of system has been known since the time of Aristotle. Systems analysis was formally discovered again just before the Second World War by the biologist Ludwig von Bertalanffy, although the methods of systems analysis were already known (e.g., Leontief’s “input–output analysis”). System is defined as a set of elements mutually connected and also with the environment, in which the system is situated. A characteristic feature of organized systems is their hierarchical structure. Every system is also characterized by a given degree of coherence and independence. Generally, systems are divided into natural and artificial ones. The features differentiating both these systems are conformability and optimization. The general theory of systems comprises, first of all, the mathematical theory of the system, and secondly system engineering. This book deals with the latter. There are two fundamental methods of describing systems, viz., causal description (input–output analysis) and intentional description (optimization models). The system structure is usually presented either by technological diagrams or structural matrices.

Life Cycle Assessment of Energy Systems in Complex Buildings

Life cycle assessment (LCA) is a full cycle-of-life analysis concerning the evaluation of hazards menacing the environment, connected with products or services burdened by the consumption of energy and materials which leads to the depletion of natural resources and affects both the quality of ecosystems and human health. As far as complex buildings are concerned, their full life cycle comprises the extraction of mineral raw materials and primary energy, as well as the production of building materials, the construction of buildings, their exploitation, and demolition connected with the recycling of building materials. LCA contains the following stages: definition of the goal and scope, inventory analysis, impact assessment, and interpretation. The second stage, also called life cycle inventory (LCI) analysis, consists in completing a database concerning the supply of energy and raw and other materials, information about main and by-production, amounts of noxious emissions, and other environmental effects. In the case of complex systems (e.g. complex buildings), as an algorithm of setting up material-energy balances, input–output analysis ought to be applied. In the third stage, the respective environmental burdens are expressed as corresponding categories affecting the environment (e.g. acidification, eutrophication, greenhouse effect, and ozone depletion) in compliance with accepted international references.

Energy Management of Complex Buildings as a System

Energy management of complex buildings is a set of mutually connected energy branches (energy processes and installations) the aim of which is the production, transport, and distribution of energy carriers to consumers (e.g. office rooms and garages). Due to these connections, the energy management treated as a whole is characterized by features not displayed by particular energy branches considered separately [5]. Therefore, energy management of complex buildings can be considered as a system from the viewpoint of the oldest definition of system formulated by Aristotle [7].

Supply of Heat, Cogeneration, and Trigeneration

Complex buildings belong to the municipal sector of the domestic economy, whose share in the demand for final energy carriers is considerable. The demand for final energy carriers (electricity and heat) can be covered by centralized supplies or distributed energy systems and also by both of them jointly.

Large Energy Systems

Complex buildings belong to large energy systems, which are continuously developing artificial systems with a hierarchical structure. The chief system in the hierarchy is the domestic energy system divided into five subsystems, four of which (solid fuels, liquid fuels, gaseous, and electro-energy systems) comprise the whole country and the fifth one—the thermal energy system—is a set of municipal, industrial-municipal, and industrial systems of feeding heat carriers (hot water and steam). The subsystem of transporting and transmission of primary and final energy carriers is the next stage in the hierarchical structure. Lower stages are centers of the supply of final energy carriers. A still lower stage comprises the consumers of final energy, among them complex buildings.

Systems Analysis of the Exploitation of Energy Management in Complex Buildings: Examples of Applications

Chapter 7 is devoted to practical applications of the mathematical models described in the previous chapter. The analysis in this chapter concerns a typical office building situated in Warsaw. The subsystem of consumers comprises office rooms, auxiliary rooms, garages, and standard equipment of the building. Six kinds of energy carriers are produced in the energy subsystem, viz., the cooling agent, hot process water with a temperature of 85/55 and 60/45 °C, hot tap water, air from the air-conditioning unit, and ventilation air for the garages. Electricity, heat, natural gas, and drinking water are supplied entirely from outside. The annual energy balance has been set up according to the input–output model of direct energy consumption. The balance of cumulative energy consumption has been struck based on the values of the indices of cumulative energy consumption of supplies from outside. The share of office rooms in the total cumulative energy consumption of the office building under consideration amounts to about two thirds. Cumulative energy consumption is dominated by electricity, which exceeds 75 % of the total. The share of cumulative energy consumption which changes the heat from the heating plant amounts to about 20 %. The analysis of cumulative emissions concerns NOx and CO2. The input data are indices of cumulative emissions charging the supplies from outside. In the case of both NOx and CO2 emissions, office rooms dominate (accounting for more than 50 % of those emissions). The analysis of thermo-ecological costs, like the analyses of cumulative energy consumption and cumulative emissions, is based on the principle of weak connections and denotes that office rooms also account for more than 50 % of those costs, and electricity and heat supplied from outside amount to about 96 % of the thermo-ecological cost of the analysed office building (68.4 of electricity and 27.6 % of heat from the heating plant).