Abstract: This paper introduces the comprehensive situation of Pilot Project of two projects of deep well geothermal heating demonstration project and geothermal cascade utilization technology of Beijing University of Technology. This paper introduces the geothermal heating (and cooling) Pilot Project System Overview of 2000 square meters office building in the School of Economics and Management of our school, taking into account the choice of heat pump in deep well geothermal and the COP value of heat pump, considerations in system design, dynamic experiments, geothermal utilization The total operating efficiency of the open system η, the relationship between geothermal utilization ξ and so on. Key words: deep well geothermal cascade use of water source heat pump building heating I. Overview Deep well geothermal water has a long history of widespread use in the world. In the deep well geothermal area of ​​the western United States, about 300-400 meters deep can be used to excavate geothermal water at 80-90 ℃. From the point of view of the underground environment protection, different states in the United States have different policies but they generally do not advocate the use of open System, if used, strictly require the same level of recharge. France's low-enthalpy aquifer hot water temperature is not warm above 50 ℃, well depth from a few hundred meters to 1000-2000 meters, the application of the cascade use, and the strict implementation of "well" system, that is, a production well , A recharge well. The groundwater level in the Paris basin has been a great accomplishment for 20 years, basically keeping the water level unchanged. The water temperature in Poland that holds aquifer thermal storage is between 30-130 ° C and several utilization techniques are used. The geothermal water heating in our country should have a long history in Tianjin and Tanggu area, but its tail water temperature is relatively high. In recent years, Tianjin has adopted advanced technology and strictly implemented the "right well" system so that the groundwater level gradually rises. Beijing is one of the few capitals in the world with deep-water geothermal water resources. Over the past 30 years, a total of about 200 deep-well geothermal water wells were drilled and more than 130 wells were used normally. As most of the geothermal well water temperature between 40-60 ℃, limited to the rational use of hot springs villas. Few cases are used for direct heating of geothermal heat. In 1999, geothermal water at a depth of 3800 meters at 88 ° C was found in the south of Beijing. Since the bid to host the 2008 Olympic Games, relevant departments in Beijing conducted a comprehensive geophysical survey and discovered three large geothermal fields with a water temperature of 70-80 ℃ and well depth of about 3,500 meters. Beijing's deep well geothermal water level drops by 2 meters per year. From the perspective of sustainable development, it is very important to consider the deep well geothermal water utilization technology and recharge technology. Second, the pilot project of the building and load characteristics 1, architectural features: The building is the original building. Office and laboratory part of 2000 square meters of five-story building, surrounded by a connected two-story classrooms a total of 10,000 square meters. The middle of a 20-meter glass vault hall, surrounded by eight outside the door for evacuation purposes. Due to the "smokestack effect", the cold wind in winter outdoor is poured into the room through the normally open Dongdaemun, causing the temperature of the hall to be around 6 ° C. The inner wall of the surrounding five-story room becomes a heat-dissipating external wall. In addition, the large single-storied glass windows in each office have the infiltration of cold air and are limited to the economic conditions during the construction. The external wall insulation is simplified and the room temperature in winter is about 13 ° C. 2, load characteristics: calculated by the winter heating design load of about 120W / m2. Due to the office building, daily working hours are 8: 00-20: 00. Night and weekend or holidays, room temperature just to maintain 10 ℃. Heat load than the heat load. Third, pilot project system design considerations 1, back to the water temperature and the amount of water back to consider: Our school geothermal recharge well depth of 2,000 meters, 400 meters deeper than the production wells. For the allowable amount of recharge, recharge temperature, the impact on thermal storage, it takes a long time experimentally determined. Therefore, on the one hand to try to use the heat of geothermal water, to maintain a certain temperature of the tail water, such as peak load below 20 ℃, you can try a short time to 10 ℃, observe its long-term effects. On the other hand, in non-peak load, but also to reduce the amount of underground hot water extraction, do not make a lot of hot water recharge at higher temperatures, such as: Try to avoid 25 ℃ water temperature above recharge. 2, consider the utilization of geothermal water ξ: Recharge temperature directly affects the utilization of geothermal energy. Because of the energy of geothermal energy, it is calculated on the basis that the geothermal water temperature drops to the local annual average outdoor temperature. The extraction of deep geothermal water consumes not only the energy of the submersible pump, but also the potential for contamination, as well as the working conditions of unknown recharging wells. 3, Considering the direct utilization of geothermal water: There are two geothermal production wells in our school. The water temperature in the production wells is about 52 ℃. The output of both wells is greater than or equal to 70m3 / hr. 52 ℃ geothermal water, after the plate heat exchanger, the circulating water up to about 50 ℃, the direct use of the fan coil unit is used, the power consumption, only the circulating pump power. 5, the use of heat pump considerations: Select the water source side can withstand the inlet water temperature (ESWT) 30-35 ℃ geothermal water heat pump, so that it has a high thermal cycling COP value. According to ARI-320 standard, water source heat pump water conditions, the water inlet temperature control is 21 ℃, according to ARI-325 standards for the 10 ℃ and 21 ℃. Therefore, the average manufacturer does not provide a heat pump that can withstand ESWT of 30-35 ° C. Select the United States ClimateMaster Inc GSW-120 water - water heat pump. Manufacturers recommend the use of ESWT does not exceed 35 ℃. Later run proved good performance curve provided by the study shown in Figure 1,2,3,4. Fourth, pilot projects using the system and instrumentation Based on the above considerations, the pilot system shown in Figure 5. Uncertainty of the instrument used for testing: See Table 1 Direct test parameters and calculation parameters of the uncertainty Table I Basic parameters Calculation parameters Water temperature Water temperature difference Air temperature Water flow Input electrical power Heating capacity Thermal cycling characteristics of the coefficient of total efficiency Fifth, the operating results and system evaluation 3 The total system efficiency η: The experimental results shown in Figure 6, hot water tail water temperature T02 (℃) lower, the lower the total system efficiency η. The COP of the heat pump is also lower. Figure 6 under different operating conditions, the total efficiency η and geothermal water recharge temperature T02 (℃) between the relationship Six conclusions 1, the total system efficiency η and geothermal water utilization rate ξ can be used as one of the geothermal heating system evaluation criteria. The value of the system up to 5 ~ 9. The corresponding ξ up to 0,9 ~ 0,7. 2, deep well geothermal water contains heat, ore, water three components, in addition to winter heating, the other three quarters can be used for domestic hot water and other comprehensive utilization. So there is no direct comparison with other source heat systems. PVC Sheet Extrusion,PVC Sheet Extrusion Line,PVC Sheet Production Line,PVC Foam Board Production Line WUXI HAOBANG MACHINERY MANUFACTURING CO.LTD , https://www.haobangmachinery.com
4, consider the peak load: As most buildings in Beijing, the cooling load is greater than the heating load, part of the heat pump can also serve as the peak heat load. Regional boiler room to provide heat, you can do peak heat source.
Figure 1 COP and heat source water side of the water temperature LSWT (℃)
Figure 2 COP and heat load side of the water temperature LSWT (℃)
Fig.3 Relationship between inlet water temperature and heating capacity of geothermal water in deep well (inlet water temperature at source side = 32,2 ℃ and flow rate at load side 1,69L / S)
Figure 4 heat pump water side of the relationship between water temperature and water down
T ΔT TWN Q COP η
(℃) (℃) (℃) (m3 / hr) (KW) (KW) 1 1
± 1% ± 2% ± 2% ± 2% ± 2% ± 3,8% ± 3,8% ± 3,8%
1-Production well; 2-Injection well; 3-Water treatment equipment; 4-plate heat exchanger; 5,6 Geothermal direct utilization pole; 7 Geothermal as indirect utilization level of auxiliary heat source; 8-Terminal heating and cooling Equipment; T1, T2, T3, T4, T5, T6, T7, T8, T9, T1, T11, T12, T13, T32, T39 - temperature sensor Figure 5 pilot project experimental systems and equipment
1, the operating results: Geothermal water after plate heat exchange, direct heating and heat pump indirect heating buildings, warm in winter and cool in summer. Hall about 16 ℃, the temperature gradient is reasonable. Room temperature controlled by the user, in part by the computer network Zhang control, generally about 22 ℃. Where there is a computer network control room, room temperature is more reasonable, not heating at night when the room temperature dropped to 12 ℃ -16 ℃ or so. Dynamic testing of a semi-winter, customer satisfaction.
2, system evaluation:
The main formula:
COP = Q1 / N1 (1)
η = ΣQ / ΣN (2)
ξ = (T01-T02) / (T01-Tave) (3)
Where:
ΣQ = Q1 + Q2 (4)
Q1 = W2 (T4-T5) (5)
Q2 = W2 (T1-T2) (6)
ΣN = N1 + N2 + N3 + N4 + N5 + N6 (7)
Type symbol:
COP - heat pump thermal cycling coefficient T01 - geothermal fluid supply temperature (℃)
N1 - heat pump input power (KW) T02 - geothermal fluid recharge water temperature (℃)
N2 - submersible pump input power (KW) T1 - heat pump water inlet side temperature (℃)
N3-- geothermal water pipeline pump input power (KW) T2 - heat pump water side outlet temperature (℃)
N4-- water side of the circulating pump input power (KW) T4 - load side backwater temperature (℃)
N5-- level load pump input power (KW) T5 - load side of the water temperature (℃)
N6-- level load pump input power (KW) Tave - average annual air dry bulb temperature (℃)
Q1 - heat pump heat (KW) W0 - geothermal fluid flow (Kg / S)
Q2 - direct use of the level of heat (KW) W1 - the water side of the water flow (Kg / S)
ΣQ - total system heat (KW) W2 - load side water flow (Kg / S)
ΣN - the sum of the system input electrical power (KW) ξ - thermal energy utilization of geothermal fluid η - total efficiency of geothermal heating system
The lower the load side water supply temperature, the lower the total system efficiency η and the heat pump total cycle COP of heat pump.
4 geothermal energy utilization rate ξ: The experimental results shown in Figure 7. Without using too large ξ, the total efficiency η will be increased.
Figure 7 Geothermal water utilization coefficient ξ and total system efficiency η under different conditions
April 06, 2021