Reconstruction project of heating and refrigeration equipment of a source heat pump in Changping District, Beijing
The project site is located in the south of Changping District, Beijing, with a total construction area of 1 1,000m2, of which the total construction area of offices, restaurants, guest rooms and other ancillary buildings is 8400m2, and the temporary dormitory area is about 1 1,600m2. The buildings are patchwork and multifunctional, with the highest three floors. Initially, oil-fired boilers were used for heating and split air conditioning refrigeration. Because the oil-fired boiler has reached its service life, it needs to be updated.
According to the preliminary hydrogeological investigation, the project is located at the lower part of a small alluvial fan formed by Dongsha River, a tributary of the upper reaches of Wenyu River. The stratum is mainly cohesive sand, and the lithology of the aquifer is mainly medium-coarse sand, the thickness of which is less than 15m, and the water yield is poor. The water output of a single well is about 500m3/d, and the recharge amount is generally only 30% of the pumping amount. Therefore, the local hydrogeological conditions are not suitable for using ground source heat pump technology. According to the large area of green space and public roads where the project is located, the geological prospecting department suggests adopting ground source heat pump technology to realize heating in winter and cooling in summer.
According to the engineering design drawings provided by China Building Technology Group Co., Ltd., the heat load of air conditioning system is 6 18kW, and the cooling load is 773kW.
The project started construction in August 2005 and was officially completed in June of the same year 165438+ 10, with a total investment of about 4.4 million yuan. See table 6- 1 for the main equipment of the project, and the statistical table of the main equipment of the project. It should be pointed out that the power consumption of the main engine and the circulating pump is measured separately, which lays the foundation for the economic analysis of the project.
Table 6- 1 Statistical Table of Main Equipment of the Project
Project * * * has been constructed 183 buried pipe hole, with the buried depth of100m. After placing a single U and pe pipe, the whole hole is backfilled with medium coarse sand, and the horizontal main pipe is φ50 and PE pipe, with the buried depth below1.5m. * * is connected to the diversity water tank in the machine room in 33 ways. All boreholes are arranged under the ground of the site green space and parking lot, as shown in Figure 6- 1 distribution map of buried boreholes in the site.
Figure 6- 1 Distribution Map of Buried Pipe Holes in the Site
2. Typical characteristics and representativeness of the selected project.
The typical characteristics of the project are also the reasons for the selection of the project. The project has the following five characteristics:
1) Independent heating and cooling project
This project is an independent heating and cooling project, without any auxiliary cold and heat sources (such as ice storage, electric heating and cooling tower). ), it is convenient to analyze the economy of ground source heat pump project.
2) Reconstruction project
This project is a reconstruction project. The original heating mode is oil-fired boiler heating, and the refrigeration mode is split air conditioning refrigeration. Therefore, after the project runs, the economic comparison of the schemes can be directly carried out.
3) The scheme selection is reasonable, the overall design is reasonable and the construction difficulty is moderate;
The ground source heat pump technology adopted in the project conforms to the local hydrogeological conditions; The overall design of the project was completed by China Building Technology Group Co., Ltd., and the design scheme was reasonable; Before the project started, Beijing Geological Engineering Survey Institute conducted preliminary survey and drilling test, and the construction difficulty was moderate.
4) After the project runs, all monitoring records are complete.
The internal management of the project owner is serious and responsible, and the important data are monitored completely and recorded in detail, which is conducive to technical and economic analysis.
5) The functions and uses of the project are moderate.
The buildings of this project are mainly offices, houses and hotels. , are ordinary buildings, different from stadiums, swimming pools, greenhouses and so on. The degree of use is 24 hours a day in the whole heating season, which is different from intermittent heating units such as schools.
Due to the above characteristics, this project is representative of many existing projects. Therefore, its economic analysis results will objectively reflect the economy of the built projects.
3. Economic evaluation of the project
The economic evaluation of the project shall be carried out in accordance with the Notice of the Ministry of Construction of the National Development and Reform Commission on Printing and Distributing the Methods and Parameters of Economic Evaluation of Construction Projects (Development and Reform Investment [2006] 1325). The evaluation content is implemented according to three annexes in the document: Several Provisions on Economic Evaluation of Construction Projects, Methods of Economic Evaluation of Construction Projects and Parameters of Economic Evaluation of Construction Projects.
To solve the problem of heating in winter, the owner has two options:
Scheme 1: update the oil-fired boiler and continue to use the oil-fired boiler for heating;
Scheme 2: Ground source heat pump with buried pipe is used for heating.
According to the characteristics of this project, the cost-effectiveness analysis method is proposed as the economic evaluation method. Cost-effectiveness analysis refers to judging the effectiveness or economic rationality of the project cost by comparing the expected effect of the project with the paid cost. When the effect is difficult or impossible to monetize, or the monetization effect is not the main body of the project goal, the cost-effect analysis method is adopted in the economic evaluation, and its conclusion is one of the bases for the project investment decision. Among them, the cost in cost-effectiveness analysis refers to the financial cost or economic cost paid to achieve the predetermined goal of the project, measured in currency. The cost-benefit analysis method follows the principle of multi-scheme comparison, and the analyzed projects shall meet the following conditions:
(1) There are at least two alternatives, which are mutually exclusive or can be converted into mutually exclusive schemes;
(2) The alternatives have the same goal;
(3) The cost of alternatives should be monetized;
(4) Substitutes should have comparable life cycles.
(5) The effect should be measured by the same non-monetary unit of measurement.
According to the above requirements, the adaptability of cost-benefit analysis method to this project is analyzed:
(1) There are two alternative schemes for this project, which are mutually exclusive, that is, only one of Scheme I and Scheme II can be adopted;
(2) The goal of the project is consistent: to achieve heating in winter. According to the existing HVAC technology, the effects of the two schemes can meet the requirements, and the effects are difficult to monetize.
(3) The expenses (i.e. costs) of the two schemes can be monetized, which is not only the initial investment, but also the operating cost.
(4) The service life of the oil-fired boiler in Scheme 1 is 8 years, and the boiler cost is increased by 500,000 yuan every 8 years; In the second scheme, the service life of the ground source heat pump host is 15 years, and the host cost increases by 600,000 yuan every 15 years. The service life of ground source heat pump is calculated as 50 years.
(5) Because the terminal building has not been rebuilt, it can be considered that the heat load of the two schemes is equal and the heating effect is the same. It should be pointed out that scheme 2 can also achieve cooling in summer and eliminate common split air conditioners, so the effect of scheme 2 is obviously greater than that of scheme 1, but for the convenience of evaluation, the effects of scheme 1 and scheme 2 are summarized as the same.
Through the above adaptability analysis, it can be determined that the cost-effectiveness analysis method is suitable for the economic evaluation of this project.
The cost of scheme I and scheme II consists of initial investment and operation cost. The initial investment and operating cost of the two schemes are compared as follows.
1) Scheme 1
Initial investment:
The initial investment of Scheme I includes the cost of purchasing oil-fired boilers, updating original auxiliary equipment and pipelines, and installation and debugging, with an investment of about 500,000 yuan, as shown in Table 6-2 (data provided by the owner).
Table 6-2 Initial Investment Schedule of Scheme I
Operating costs:
The operating cost in winter is provided by the owner according to the actual operating data for many years, which is mainly composed of diesel oil, circulating pump power consumption and labor cost, as shown in Table 6-3.
Table 6-3 Statistical Table of Operation Cost of Scheme I in Winter
2) Scheme II
Initial investment:
The owner's actual initial investment in Scheme II is 4.4 million yuan (including construction and design), which mainly includes the purchase and installation of main engine, the construction of buried pipe hole, the purchase and installation of fan coil unit and the construction of external pipeline. The project was completed by Beijing Geological Engineering Survey Institute from August 2005 to June 2005.
Operating costs:
Scheme 2 has actually run for two heating periods, namely 2005-2006 and 2006-2007. The operating cost is mainly the actual power consumption of the main engine, circulating pump and fan coil unit. See Table 6-4 for details.
Table 6-4 Statistics of Actual Electricity Consumption of Scheme II
See Figure 6-2 and Figure 6-3 for the comparison of initial investment and operating cost of the two schemes.
Figure 6-2 Comparison of Initial Investment between Scheme I and Scheme II
Figure 6-3 Comparison of Operating Costs between Scheme I and Scheme II
The initial investment of scheme 1 is small, but the operation cost is high, and the initial investment of scheme 2 is large, but the operation cost is low. In order to scientifically evaluate the two schemes, it is calculated according to the present value (PC) and annual value (AC) of the expenses, provided that:
Assume that diesel, electricity and artificial price will remain unchanged during the evaluation period;
Scheme 1: The service life of oil-fired boilers is 7-8 years, and the boiler cost is increased by 500,000 every 7-8 years; Option 2, the service life of the ground source heat pump host is 15 years, the cost of the host increases by 600,000 every 15 years, and the service life of the buried pipe is calculated as 50 years;
Assume that the bank discount rate remains unchanged during the calculation period;
(1) See Formula 6- 1 for the calculation of present value of project cost (PC).
Shallow geothermal energy resources in Beijing
In which: (co)t-t cash outflow;
N-calculation period;
I-discount rate, calculated at 4% per year;
(p/f, i, t)- present value coefficient.
After calculation, the present value of the expenses of Scheme I and Scheme II are shown in Table 6-5. It should be noted that in the calculation process, in the 7th year,15th year, 22nd year and 30th year of operation, due to the expiration of the service life of the oil-fired boiler, the boiler cost increased by 500,000 yuan each. Similarly, in 15 and 30 years of operation, the service life of the ground source heat pump host expires, and the cost of each host increases by 600 thousand.
Table 6-5 Present Value Table of Project Investment Scheme Cost Unit: 10,000 yuan
As can be seen from Table 6-5, under the assumption that the heating effects of the two schemes are the same (that is, regardless of the availability of Scheme II in summer and the environmental protection and safety benefits of Scheme II), the current cost of Scheme I is 458.3 10000 yuan in the fifth year after operation, while the current cost of Scheme II is 6.2983 yuan, which is higher than that of Scheme I.. The second scheme of 10 is 475,800 yuan lower than the first scheme, and the present value cost of the second scheme in 15, 20, 25 and 30 years is lower and lower than that of the first scheme, which gradually shows the superiority of the second scheme.
After calculation, the present cost values of the two schemes are equal in the 8th and 5th years after operation, as shown in Figure 6-4, which shows that both schemes are in a new working state in the 5th and 30th years, and the present cost value of the second scheme is still lower than that of the first scheme, showing the advantages of the second scheme.
Figure 6-4 Comparison of Current Cost between Scheme I and Scheme II
(2) See Formula 6-2 for the calculation formula of annual cost (AC).
Shallow geothermal energy resources in Beijing
Where: (a/p, i, t)- capital recovery coefficient; Other symbols are the same as before.
After calculation, the annual cost tables of the two schemes are shown in Table 6-6.
Table 6-6 Annual Output Value Table of Project Investment Scheme Expenses Unit: 10,000 yuan
As can also be seen from Table 6-6, the initial annual cost of Scheme II is higher than that of Scheme I, and the economic benefits of Scheme II gradually emerge as time goes by.
See Figure 6-5 for the annual cost comparison of the two schemes. As can be seen from the figure, the annual cost of scheme 1 in 15 is 1023700 yuan, while the annual cost of scheme 2 is 853300 yuan, saving 170400 yuan and saving 295600 yuan in the 30th year.
Figure 6-5 Comparison of Two-year Costs of Scheme I and Scheme II
Therefore, based on the above analysis, it can be concluded that the ground source heat pump scheme is better than the oil-fired boiler scheme after about 8.5 years of operation by using the cost-effectiveness analysis method, and the longer the time, the more obvious the economy. In fact, the effect of ground source heat pump scheme is better than that of oil-fired boiler scheme, because ground source heat pump scheme can also be used in summer, and compared with oil-fired boiler, it also has many indirect benefits such as environmental protection and safety.
The heating cost per unit area of the ground source heat pump in this project is relatively high (4 1 yuan /m2), but compared with the oil-fired boiler (88. 19 yuan /m2), it still saves half the operating cost. The reasons for the high operating cost of ground source heat pump are:
(1) The circulating pump consumes too much power.
According to the statistical results, the power consumption of circulating water pump accounts for 36% of the total power consumption in winter operation and 45% in summer operation, which is significantly higher than that in general projects.
The first reason is that the wharf buildings are scattered, which leads to a large design power (22kW) of the circulating pump. According to the actual investigation, most buildings in this project have only one floor, which is relatively scattered, with a distance of 320m from north to south and a distance of 120m from east to west, as shown in Figure 6-6.
The second reason is that the project * * * has 183 underground pipe holes. Due to the limitation of the site, the underground pipe holes are scattered and far away from the main engine room, resulting in a large power (22kW) of the underground circulating pump.
Figure 6-6 Schematic Diagram of Distribution of Buildings and Connecting Pipelines in this Project
The third reason is that the circulating pump is not equipped with frequency conversion device, which means that as long as the main engine is running, the circulating pump will consume 44kW·h of electricity, which is obviously uneconomical in the early and late heating period.
The fourth reason is that the heat exchange capacity of a single hole in this project is designed to be 22w/m, which is obviously lower than that of the general project, resulting in a large initial investment of the project and a large power of the circulating pump at the buried side.
(2) The heating period of the project is as long as 5 months.
Because the project is located in Changping District, the weather is colder than that in the urban area, and the heating time is as long as 5 months, one month longer than the normal heating time.
(3) The electricity price of the project is on the high side, and the peak-valley electricity price has not been realized.
The actual electricity bill paid by the project owner is 0.79 yuan/kW h. Since the operating cost of the ground source heat pump project is basically the power supply cost, the high electricity price directly leads to the increase of heating cost. Because of heating in winter, the electricity consumption of the main engine is mainly concentrated in the evening, but the project does not implement peak and valley electricity prices, and the advantages are not reflected.
(4) The project building is a lightweight building with poor thermal insulation performance, which leads to a large load and increases the power consumption of the main engine.
In view of the above problems and shortcomings, the optimization scheme and suggestions are put forward:
(1) adopts distributed computer room and automatic frequency conversion control.
In view of the fact that the buildings in this project are scattered and there are many underground pipes, it is suggested to adopt a distributed computer room to improve the COP value of the system, which is particularly important in projects with scattered buildings and large service area.
Automatic frequency conversion control is an effective method to reduce energy consumption, but attention should be paid to the heating effect of the farthest building after reducing the flow, or two circulating pumps with small flow (half of the original pump flow) should be adopted under the condition of constant head, and then the number of circulating pumps should be controlled according to the actual situation.
If the farthest building area is small, it is recommended to use other heating methods. The farthest end of this project is a gas station with a service area of only about 30㎡. But for heating, not only the pipe diameter is increased, but also the power of the circulating pump is increased. Economically, it is better to use dual-purpose air conditioning directly.
(2) Strengthen the management system.
The power consumption of the main engine is determined according to the terminal load, and reducing the load can directly reduce the operating cost. Therefore, adopting an effective management system to reduce the terminal load will save operating costs. For example, flexible measures such as controlling the office temperature at about 5℃ at night and appropriately lowering the dormitory temperature during the day when there is no one in the dormitory will effectively reduce operating costs.
The heating time of the project is as long as 5 months. It is also a very important measure to start and stop the main engine according to the weather conditions at the beginning and end of heating.
(3) It is suggested that the relevant government departments expand the scope of application of peak-valley electricity price. Using the peak-valley electricity price and the thermal storage device to store heat or cold energy when the electricity price is low at night and recycle it during the day will effectively save the operation cost.
(4) Strengthen research and monitoring, and properly adjust the power and model of the buried side circulating pump according to the temperature of the buried side supply and return water, which will have room for further energy saving. Moreover, the monitoring data will be used as an important design parameter (heat transfer capacity per linear meter) for other projects in the future.