Benefit Analysis and Comparison of Electric Heating System for Municipal Central Heating

Electric heating can not only relieve the pressure of municipal central heating but also help to solve the problem of wind and light abandonment, which is an important direction for the future development of central heating. To maximize the comprehensive benefits, this paper constructs three kinds of electric heating systems. According to the comprehensive benefit evaluation of technical, economic, and environmental aspects, the comprehensive optimal scheme is selected. An office area in Beijing is taken as an example to determine the optimal scheme of electric heating and heating supplement. The results show that the comprehensive benefit of the heat pump + phase change accumulator system is the best, but the environmental benefit needs to be further improved. To promote the pace of electric heating and heating supplement, the government should increase the subsidies for electric boiler technology. At the same time, clean energy power supply enterprises should improve the trading mechanism of the electric heating market and reduce the price of clean energy heating.


Introduction
The demand for heat load in winter in northern China is large, and the heating mode is mainly urban central heating.However, the overall planning of coal, natural gas, electricity, renewable energy, and other energy forms of heating is insufficient, and the heating layout is not scientific, resulting in the imbalance of heat supply and demand.The heat source in some heating areas can not be adjusted to each other, and the heat source shortage is generally faced.Moreover, the heating transformation of active units lacks unified overall optimization.After the transformation, the peak regulation capacity of the power grid decreases, which aggravates the problems of wind and light abandonment in some areas.Due to the large peak-valley difference of the power grid and the strong complementary relationship between the peak section of the heating load and the valley section of the power load in winter [1] [2] , the electric heating of municipal heating has become an important direction for the future development of central heating.
In recent years, scholars at home and abroad have conducted extensive research on the application and comprehensive evaluation of electric heating systems.Wang Zhiqiang [3] and other comprehensive consideration of heating methods, the main interests, building type characteristics, user energy consumption habits, climatic conditions, and multi-party interests, constructed a decision-making method for the adaptive development mode of regional clean heating, so as to better meet the heat demand of users who need clean heating in winter and improve the matching between heating load and power grid.Diana Böttger et al. [4] analyzed the impact of electric boilers on the cost of power systems and carbon dioxide emissions in 2012 and 2025 based on the actual situation of German power systems and the establishment of related models.Research shows that the application of electric boilers promotes the use of renewable energy, and predicts that with the decline in the price of electric boilers and the increase in the use of renewable energy, the cost of electric boiler heating will be able to compensate for its initial investment fully.
Xie et al. [5] established an economic analysis model of electric heating technology, and took a certain area of Zhangjiakou as an example.The research shows that the economic performance of electric heating is significantly higher than that of coal-fired boilers.Yang Yongcheng [6] analyzed the economy of the electric boiler and heat pump heating system from two aspects of equipment initial investment and operation cost and took commercial and civil buildings as examples to study the cost estimation method and the simplified structure of the system.Wu [7] established a mathematical model of the electric heating-heating system based on the consumption of abandoned wind, constructed a mathematical model of energy-saving benefits and economy of the technical scheme, and analyzed the feasibility of the electric heating-heating scheme based on the consumption of abandoned wind.Huang Wei et al. [8] established an evaluation index system that comprehensively considers five aspects of reliability, economy, energy efficiency, environment, and residents' adaptability to evaluate the clean heating system of characteristic towns.
It can be seen from the above research that the existing electric heating technology rarely involves the comparative study of different electric heating schemes.In this paper, three schemes of the electric heating system are proposed, and the influencing factors of its efficiency and economy are analyzed in combination with practical cases, and the best scheme is selected by comparison.The comprehensive evaluation of the municipal heating electric heating system provides a reference and basis for the government, power grid enterprises, and thermal enterprises to improve the level of regional winter heating cleanliness jointly.

The basic structure of electric heating
Figure 1 is the basic structure of the electric heating system.The electric heating system is mainly composed of a heating device and a heat storage device.
At present, the heating devices used in China mainly include air source heat pumps, electric boilers, and water-source heat pumps.The efficiency of heating equipment reflects the efficiency of converting electricity into heat under the same working conditions of different heating equipment, and the calculation method is as follows: In the formula, COP is the efficiency of heating equipment; Q h is the heating capacity of the system, kW; Q 1 is the system power consumption, kW•h.
The heat storage capacity of the system is determined by the running time of the electric heating equipment and the heat load of the heat user: e ( 24) where Q is the storage tank capacity, kW•h; q is the heat load of heat users, kW; T e is the running hours of electric heating equipment, h; η x is the heat storage efficiency of the heat storage tank, %; η w is the heating pipe network efficiency, %;

Electric heating system scheme
Fully considering the actual application conditions, according to the location of the heating station and the available resources, three kinds of electric heating system schemes are designed: Scheme 1: electric boiler + phase change heat storage system; Scheme 2: solid electric heat storage integrated boiler system; Scheme 3: air source heat pump + phase change regenerator system.EBSILON is used for modeling calculation.The models of the three schemes are shown in Figure 2, Figure 3 and Figure 4 respectively.

Example analysis
Taking an office area in Beijing as an example, the electric heating system is designed [9] .

Comparison of technical, economic, and environmental benefits of different schemes
When calculating the economic benefits, the current power grid sales price in Beijing is taken.The benefit calculation results of each scheme are shown in Table 1.  1 that the heat pump has high operating efficiency, so the heating energy consumption is low.Because the heat storage system of Scheme 1 is the same as that of Scheme 3, the heat storage capacity is equal.The electric heating equipment and the heat storage equipment are selected according to the designed heat storage capacity, so the heat storage capacity of the three schemes is not much different.
In terms of economic benefits, the initial investment cost of electric heating with a heat pump is significantly higher than that of the electric boiler, mainly because the cost of heat pump equipment and auxiliary thermal facilities is higher.However, the operation cost of heat pump heating is low, which is mainly due to the high electrothermal conversion efficiency of the heat pump.Therefore, the static payback period of the heat pump system is not long.
In terms of environmental benefits, the emission reductions of CO 2 and NOx in the electric boiler heating system of the two schemes are higher than those in the heat pump system, indicating that the choice of the electric boiler for heating has good environmental benefits.Scheme 1 has the largest CO 2 and NOx emission reduction and the best environmental benefits.

Sensitivity analysis
In order to further analyze the economic influencing factors of the electric heating system and provide a theoretical basis for the implementation of the electric heating system, the four index factors of electricity price, heat price, heating equipment efficiency and government subsidy are selected for sensitivity analysis, and the influence of index factors on the static payback period is analyzed.The results are shown in Figure 5-8.From the diagram, it can be seen that the sensitivity analysis curve of electricity price, heat price, and heating equipment efficiency fluctuates greatly, while the sensitivity analysis curve of government subsidy changes more smoothly.It shows that the static payback period is sensitive to electricity price, heat price, and heating equipment efficiency.The sensitivity of Scheme 2 to the efficiency of heating equipment, electricity price, and heat price is not much different, and the sensitivity to policy subsidies is the weakest.Scheme 3 is less sensitive to the four factors than Schemes 1 and 2, especially in terms of electricity price and heating equipment efficiency.This is mainly because the heat pump itself has higher efficiency and can consume less electricity to produce more heat energy, and consumes less electricity.In general, the increase in electricity price has a negative impact on the static investment recovery period, and other factors have a positive impact.
Therefore, to improve the economy of the electric heating system, the government should give some electricity price subsidies or introduce some corresponding preferential policies for users who use the electric heating system for municipal heating and further increase the subsidies for electric heating equipment.It is also necessary to increase the technical support for the development and optimization of electric heating equipment and improve the efficiency of electric heating equipment.

Comprehensive evaluation result
According to the weight value of each index and the grey correlation coefficient matrix, the grey correlation degree between each scheme and the optimal scheme is obtained.The order of correlation degree is shown in Table 2. From Table 2, it can be seen that Scheme 3 has the highest correlation with the optimal scheme; that is, it is the closest to the optimal scheme and is the optimal scheme among the three schemes.Therefore, Scheme 3 should be selected when the office area carries out municipal heating and electric heating.

Conclusion
Taking an office area in Beijing as the research object, the electric heating scheme of municipal heating is designed.The index system is selected from the aspects of technology, economy, environment, and policy, and the electric heating system is comprehensively evaluated.The conclusions are as follows : 1) This paper compares the technical, economic, and social (environmental) indicators of different schemes to find the optimal system scheme of heating and heating in municipal heating power systems.Through the example verification, the comprehensive evaluation index system and evaluation method constructed in this paper are practical and effective, which can provide support and reference for the comprehensive evaluation of the electric heating system.
2) According to the calculation results, the efficiency of heating equipment, heat storage capacity, and operation cost account for a large weight.If we want to optimize the electric heating scheme, we should start from these three aspects.The heat storage capacity is determined by the operation time of electric heating equipment and the heat load of heat users, which is difficult to change.The operation efficiency is limited by equipment research and development, and it is feasible to reduce the operation cost.The relevant clean energy power supply enterprises should further improve the market-oriented trading mechanism of clean energy power generation and reduce the price of clean energy heating.
3) The heat pump technology has high operating efficiency and high government investment subsidy, so it has a low operating cost, low energy consumption, and a short static investment recovery period.It has good technical and economic benefits, but the initial investment is high.The government should vigorously develop heat pump technology to reduce the cost of the heat pump.The electric boiler technology has good environmental benefits but low operating efficiency.The government should increase subsidies for electric boiler technology and improve the operating efficiency of electric boilers.
4) The air source heat pump + phase change regenerator system has good technical and economic benefits, and the social (environmental) benefits are general.Through comprehensive evaluation and analysis, this scheme is determined to be the optimal scheme.

Figure 1 .
Figure 1.Structure diagram of electric heat supplementation.

Figure 4 .
Figure 4. Air source heat pump + phase change heat storage body system.

Figure 8 .
Figure 8. Sensitivity analysis based on efficiency changes in heating equipment.

Table 1 .
Comparison of Benefits of the Program

Table 2 .
Correlation Degree and Correlation Ranking of Each Scheme and the Optimal Solution.