The Technique And Economy Study Of The Central Heating System With Secondary Peak-shaving Plants

The energy efficiency of central heating systems in our country is only from 35% to 55% at present. The energy efficiency is far below that in advanced countries, which is 80% or so. Main causes are as follows: The efficiency of large-scale CHP(Combined Heat and Power) plants or district boiler rooms can reach 80% or more by design, while it can not reach in fact, because the heat sources need to be adjusted frequently according to the varieties of heat load. It is difficult to carry out timely adjustment in the large-scale district heat supply networks by current control means. The heat loss caused by the hydraulic disorder has already reached 20%-30% of the real heat consumption of buildings.A new type of central heating systems is proposed in this thesis, which is called the central heating system with secondary peak-shaving plants. The new system keeps the original large-scale CHP plants or district boiler rooms as the main heat source, and sets minitype gas boilers as peak-shaving heat sources in the secondary heat supply network. The main heat source provides the fundamental heat load, operating constantly through the whole heating period; while the gas peak-shaving heat sources start working to supply rest heat, only when the temperature outside reaches certain figure. This thesis only studies the central heating system with secondary peak-shaving plants, which adopts district water boiler rooms as its heat source. The central heating system with secondary peak-shaving plants has been analyzed in this paper with a real project of a university in Tianjin in the following three aspects, including heat supply adjustment, hydraulic conditions, energy consumption analysis and economy analysis.First, according to the heating period operating data of the real project in 2004 ~ 2005, the thesis analyzes the situation of central heating systems in our coutry; then it discusses the advantages of the central heating system with secondary peak-shaving plants, and recommends the values of peak-shaving coefficients. Heat supply adjustment formulas of the central heating system with secondary peak-shaving plants have been deduced.Because of adding peak-shaving heat sources, some changes of hydraulic conditions appear instatus the secondary heat supply network correspondingly. Thus, the thesis proposes three projects to eliminate the changes, which are peak-shaving pumps in series, peak-shaving pumps in parallel, and without peak-shaving pumps. Matlab 7.0.1 Software is applied to program to calculate the annual electricity consumption of all pumps in the central heating system. The program calculates and analyzes the annual electricity consumption of the three projects and the central heating system without secondary peak-shaving plants. The results indicates that the project of peak-shaving pumps in parallel is the best.At last, the thesis adopts BIN method to build the energy consumption mathematic model of the central heating system with secondary peak-shaving plants, and adopts LCC (Life Cycle Cost) method to build life cycle cost mathematic model of the central heating system with secondary peak-shaving plants, analyzes the rules of preliminary investment, annually operation expenses and life cycle cost by different peak-shaving coefficients.The research results of this thesis can contribute to improving the energy efficiency of central heating systems in our country, which is of benefit to the economy and the society.