Zhao Jiankang Zhang Yong Zou Dengliang Huang Changjun He Yuncheng Yang Junwei Shi Hanjing Li Weifang
(Beijing Geothermal Research Institute)
Abstract: The article introduces the Jinhan Green Harbor Home Community in Shunyi, Beijing Geothermal wells combine water source heat pump heating and geothermal resource comprehensive utilization technology to provide hot spring bathing. Based on this project, the author gives the relationship between geothermal well water volume, water temperature and heating area. This relationship has guiding significance for the early demonstration of geothermal heating projects. This article focuses on a detailed analysis of the operating costs of geothermal wells combined with water source heat pump heating technology. Research shows that the operating cost of heating by geothermal wells combined with heat pump technology is 18 yuan/m2, which is lower than Beijing’s central heating heating charge standard of 24 yuan/m2. At the same time, the cost of bathing in hot springs is much lower than bathing in heated tap water.
1 Introduction
In the past, medium and low temperature geothermal resources, especially geothermal water around 50℃, were usually only used for hot spring bathing and planting and breeding, and were rarely used for heating. This is mainly because the supply and return water temperature requirements for old-fashioned radiator heating are relatively high, generally 95℃/70℃. It is difficult for 50℃ geothermal water to reach room temperature requirements through radiator heating. At present, with the development of floor heating technology, fan coil technology and radiant ceiling technology, the heat source temperature required for heating has been greatly reduced. Generally, 40~45℃ can meet the heating needs. This provides a broad market space for geothermal direct heating and ground source heat pump technology heating.
Beijing Shunyi Jinhan Lvgang Home Community is a comprehensive geothermal utilization project undertaken by our hospital that uses medium and low-temperature geothermal resources for heating and hot spring bathing. The interior end of the project adopts floor radiant heating and uses heat pump technology to basically meet the heating and hot spring bathing needs of a 230,000 m2 residential area with three geothermal wells, making effective use of low-temperature geothermal resources. The use of clean geothermal energy for heating and hot springs in homes has greatly improved the quality of residences. It not only provides residents in the community with a good living environment and atmospheric quality, but also provides developers with generous returns.
2 Project Overview
Jinhan Greenport Home is a large-scale comprehensive residential community integrating residences, hotels, restaurants, and entertainment. The total construction area is 630,000 m2. The first phase construction area is 230,000 m2, and the public building area is 30,000 m2. The total heating load and cooling load of the public building part of Jinghan Green Harbor Home are as follows: Heating load: The heat index per unit area in winter is 41W/m2, totaling 9430kW; Public building part: The cooling index per unit area in summer is 80W/m2, totaling 2400kW .
Based on the above hot and cold technical indicators and the geological conditions of the area, our hospital proposes to use geothermal hot spring wells combined with water source heat pump technology to provide heating and hot spring bathing in winter, and use floor radiant heating at the end of the heating room; use water source heat pumps in summer The unit and cold water well provide cooling to the public building, and a fan coil unit is used at the end. This project is a comprehensive utilization project of deep geothermal energy and shallow geothermal energy.
3 Determination of the amount of water required for heating and cooling
3.1 Derivation of the relationship between heating and cooling area and water amount
According to the law of conservation of energy, we can deduce the relationship between the heating area and the required water amount. The relationship between the amount of water in the geothermal hot spring well is needed. From this, the amount of groundwater required can be determined based on the heating area; similarly, the area that can be heated can also be determined based on the water output and water temperature of the geothermal well.
a. Direct heating
Shallow geothermal energy: Proceedings of the National Geothermal (Shallow Geothermal Energy) Development and Utilization Field Experience Exchange Conference
Where: S is the heating area, m2; q is the heat load per unit area, W/m2; J is the thermal work equivalent coefficient, 4187 joules/kcal; ρ is the density of water, 1 T/m3; c is the specific heat capacity of water, 1×103kcal /T·℃; Q is the water output of the geothermal well, m3/h; t1 is the water outlet temperature of the geothermal well, ℃; t2 is the tail water temperature after heating, ℃.
b. Heating combined with heat pump technology
Shallow geothermal energy: Proceedings of the National Geothermal (Shallow Geothermal Energy) Development and Utilization Field Experience Exchange Conference
Formula :cop is the heating coefficient of the heat pump unit, generally 4; t3 is the temperature of the tail water after extracting heat through the heat pump, ℃.
It can be seen from the relationships (1) and (2) that the heating area of ??the geothermal well is directly proportional to the amount of geothermal water. When the amount of water is constant, it is proportional to the temperature difference utilized, that is, the greater the temperature difference utilized, the larger the heating area.
Geothermal wells combined with heat pump technology for heating can increase the temperature difference of geothermal water utilization, correspondingly reducing the demand for geothermal water, thereby achieving the purpose of intensive utilization of geothermal resources. For example, t2 in the relationship equations (1) and (2) is generally around 40°C, while t3 is around 10°C, which increases the utilization temperature difference by 30°C. For a geothermal well with an outlet water temperature of 70°C, heat pump technology can enable one geothermal well to exert the effectiveness of two geothermal wells, which not only saves investment, but also saves valuable geothermal resources.
3.2 Determination of the required amount of geothermal well water
It is known that the total heating load of the community is 9430kW; the temperature of the tail water after the heat pump unit extracts heat can be reduced to 7°C; according to reliable Analysis of geological data predicts that the water volume and water temperature of the geothermal well are predicted to be 55°C, 60m3/h, and 3000m deep. The target heat storage layer is the Wumishan Formation of the Jixian System.
Based on the above known data, it can be concluded that the required geothermal well water volume is: 126m3/h.
3.3 Determination of the required amount of cold water well water
Similarly, according to the law of conservation of energy, the relationship between the water amount and cooling area for cooling in public buildings can be obtained:
Shallow Geothermal Energy: Proceedings of the National Geothermal (Shallow Geothermal Energy) Development and Utilization Field Experience Exchange Conference
Where: EER is the energy efficiency ratio of the heat pump unit, the ratio of the obtained cooling capacity to the input electric energy Ratio, generally 5; t1 is the outlet water temperature of the cold water well, ℃; t3 is the water temperature during recharge, ℃.
The total cooling load is known to be 2400kW; the outlet temperature of the cold water well is 15°C, the water volume, and the well depth; the recharge temperature is 27°C. According to the above known data and substituted into the relationship (3), the water required for the 30,000 m2 public building part can be obtained as: 206m3/h.
4 Engineering technical scheme design
The heating requirement of this project is 55°C geothermal water flow rate of 126m3/h. According to the known hydrogeological data, two geothermal wells can meet the requirement. Water volume needs. The recharge situation of geothermal wells in this area is good, and one recharge well can meet the needs. Therefore, the heating project design uses three "geothermal well-heat pump units" (two pumping and one filling) to meet the heating requirements of the 230,000 m2 building area of ??the first phase of the building and the hot spring bathing of community residents.
The cooling water supply required by public buildings requires 206m3/h of cold water well water. However, the regional well depth is 100m and the water volume can reach 80m3/h. Therefore, three pumping wells can meet the needs. The recharge situation in this area is average, and the pumping-to-irrigation ratio is 1:2. Therefore, the total number of cold water wells is 9. The cold water well-heat pump unit is used to meet the cooling needs of public buildings in summer. Floor heating technology is used at the indoor end, and fan coil units are used at the end of the public building.
In order to meet the temperature requirements of the inlet and outlet water on the evaporator side of the water source heat pump unit, and because the geothermal well water cannot directly enter the unit for use, the geothermal well water is used for heat exchange through a plate heat exchanger. The water inlet flow rate on the primary side of the heater is 120 tons/hour, the temperature is 55°C, and the outlet water temperature is 9°C. The water flow rate on the secondary side (water source heat pump unit side) is about 750 tons/hour, the inlet water temperature is 7°C, and the outlet water temperature is 750 tons/hour. The temperature is 15℃. The secondary water volume can meet the total water volume requirements of the unit during all operations.
5 Operation cost analysis
5.1 Main equipment and power distribution in the computer room (Table 1)
Table 1 Main equipment and power distribution in the computer room
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The total number of other equipment is tentatively estimated to be 150kW. The total power distribution is tentatively estimated to be 2880.2kW. The maximum power consumption in winter is 2880.2kW and in summer is 300kW.
5.2 Analysis of operating costs and costs
Heating operating costs mainly include the following items: electricity costs, personnel wages and benefits, equipment depreciation, annual maintenance fees, various taxes, etc. .
Operation of 6 heat pump units can meet the maximum load. The maximum heat that 6 units can provide in winter is 9504kW. When the units are operated at full load in winter, the total power consumption of the unit itself and its related auxiliary equipment is 2880.2kW.
Calculate winter operating costs based on the above power (2880.2kW) load, assuming that the average full-load operating time per day is 12 hours. The annual operating electricity cost of the water source heat pump central air conditioning cold and heat source solution equipment is: 2.4056 million yuan (winter).
Since this project adopts automatic control technology, it only requires 6 people for maintenance during operation (three shifts). The personnel salary is:
6 people × 4 months × 1,600 yuan/( Person-month) = 38,400 yuan
The service life of all equipment is 15 years, and the water well is 15 years. The annual depreciation expenses are: equipment, 770,000 yuan/year; water well, 830,000 yuan/year ;Total 1.6 million yuan. The annual maintenance fee is 100,000 yuan. A total of 4.144 million yuan. The equivalent annual operating cost per square meter is 18 yuan/m2. The current price of central heating in Beijing is 24 yuan/m2 and natural gas heating is 30 yuan/m2. Therefore, using geothermal wells combined with water source heat pump technology for urban heating is not only technically feasible, but also has a price advantage.
The geothermal well in the community not only serves as a heat source for heating, but also provides hot spring bathing in the community. It costs 23 yuan to use an electric water heater to heat a ton of tap water, and 14 yuan to use a gas water heater. However, a mineral resource tax of 3.5 yuan per ton is only required for household geothermal hot spring water bathing. In extremely cold weather, when there is a conflict between heating and bathing water, cold water wells can be activated for peak shaving.
6 Conclusions and Enlightenments
It is technically feasible to use geothermal wells combined with water source heat pump technology for urban heating and hot spring bathing, and the operating cost is also advantageous compared to gas. What's more important is that geothermal resources are a nearly renewable, clean energy source that does not emit any waste gas or waste materials and is very helpful in improving the city's air quality.
Geothermal well combined with heat pump technology heating has the following advantages over ordinary water source heat pump heating:
(1) While heating, hot spring bathing can be provided at the same time;
(2) Due to the high water temperature, the requirement for water volume is correspondingly reduced, thereby reducing the number of wells and reducing the area occupied;
(3) The depth of geothermal wells is generally 3000m The hot water extracted is generally bedrock fissure water, which has almost no impact on land subsidence; cold water wells are generally about 80 meters long, and most of them extract confined water in the Quaternary aquifer, which has a slightly greater impact.
The main disadvantages are that the cost of geothermal wells is higher and the risks of drilling are also greater.
Geothermal wells combined with water source heat pump heating technology provide a new idea for low-temperature geothermal heating. Most cities in my country have this low-temperature geothermal resource. If it can be widely used, it will have very positive significance for solving urban air pollution, saving energy, and saving land space.
References
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[2] Zhou Nianhu. Geothermal Resource Development A complete book on the use of physical objects. Beijing: China Geological Science Press, 2005
[3] Lu Yaoqing. HVAC Design Guide. Beijing: Construction Industry Press, 1990
[4] He Manchao et al. China's medium and low enthalpy geothermal engineering technology. Beijing: Science Press, 2004
[5] Zhu Jialing et al. Geothermal energy development and application technology. Beijing: Chemical Industry Press, 2006