Application of water source heat pump in civil air defense engineering

Abstract: This article focuses on analyzing the technical obstacles of the cooling tower water source heat pump air conditioning system, and through engineering examples, demonstrates the feasibility of the groundwater source heat pump air conditioning system in civil air defense projects, and puts forward several issues that should be grasped for project management And the designer’s reference.
Key words: civil air defense engineering air source groundwater source heat pump
At present, the cooling tower water source heat pump air conditioning system commonly used in civil air defense projects uses the quantitative circulating water of the cooling tower as an intermediate medium to exchange heat with outdoor air. Through heat pump technology, the low-level energy in the outdoor air is converted into high-level energy. The moisture-proof and dehumidification used in civil air defense projects is essentially an air source heat pump (ASHP) system. The fatal weakness is that it is restricted by climatic conditions. In summer, the cooling efficiency decreases with the increase of outdoor air temperature. In winter, due to outdoor air temperature Too low to achieve heating, the overall efficiency is low. The ground water heat pump (GWHP) system is adopted, the cooling tower is eliminated, and the project directly exchanges heat with groundwater through the heat pump, avoiding the influence of atmospheric temperature, and achieves dual-use, high-efficiency and energy-saving. It can not only meet the requirements of summer civil air defense projects. The problem of dehumidification can also be introduced into surface engineering to solve the heating and cooling problems of surface engineering in winter and summer, and it has good application prospects.

1 Technical demonstration
The cooling tower water source heat pump air conditioning system is essentially an air source heat pump air conditioning system. In the air-source heat pump air-conditioning system, the low-level energy comes from outdoor air. In summer cooling conditions, the heat pump needs to use a lower temperature air medium to cool the condenser and transfer heat to the outdoor air to achieve the purpose of cooling and meet the cooling requirements. In winter heating conditions, the heat pump requires a higher temperature air medium to take away the cold capacity of the evaporator to achieve the purpose of heating and meet the heating requirements. However, the natural law of seasonal changes in atmospheric temperature is exactly the opposite of the expected seasonal value of the heat pump. The high outdoor temperature in summer is not conducive to cooling the condenser and the cooling efficiency is reduced; the outdoor atmospheric temperature in winter is low, which is not conducive to taking away the cooling capacity and heating efficiency of the evaporator. Reduced, the overall operating efficiency is low, this is the technical obstacle that the air source heat pump air conditioning system cannot overcome. The civil air defense project is a closed underground space. The heat pump air-conditioning system cannot directly exchange heat with outdoor air. It only uses quantitative circulating water as the medium to exchange heat with outdoor air through ground cooling towers to achieve cooling and meet dehumidification. However, due to the high outdoor atmospheric temperature in summer, the temperature of the quantitative circulating water of the cooling tower also rises, resulting in a decrease in the cooling efficiency of the heat pump. In winter, even if the water-water heat pump unit is selected, heating cannot be achieved, and the limitation is very large. Therefore, the cooling tower water source heat pump system still cannot overcome the technical obstacles affected by atmospheric temperature.
The earth is a huge thermostat, and underground water contains endless energy. According to tests, the temperature of shallow groundwater below 30 meters is stable at around 18℃ all year round, which is much higher than the outdoor air temperature in winter and far lower than the outdoor air temperature in summer. If the heat pump air-conditioning system of the civil air defense project uses groundwater as a low-level energy source, it can be Overcoming the technical obstacles of air source heat pumps, greatly improving the overall efficiency of the system. In addition, in summer, heat pump technology is used to convert the low-level cold of groundwater into high-level cold, and at the same time, the waste heat of civil air defense projects is transferred to groundwater through recharging technology; in winter, the low-level heat of groundwater is converted into high-level heat through heat pump technology. The cold energy is transferred to the groundwater through the recharge technology, so that the cold energy is stored in the summer for use in the winter and the heat is stored in the summer for use in the winter, and the groundwater acts as an accumulator to ensure the perennial use of the air-conditioning system. Therefore, in the groundwater source heat pump system, the low-level energy is derived from the groundwater. The heat pump directly exchanges heat with the groundwater whose temperature is stable throughout the year, without being affected by the atmospheric temperature. It overcomes the technical obstacles of the air source heat pump system, realizes dual use of one machine, and saves investment. , The comprehensive operating cost is low, and it is suitable for the air-conditioning system of civil air defense projects in areas with abundant groundwater resources.

2 Project examples
An attached civil air defense project in Kaifeng City uses groundwater source heat pump air conditioning systems, eliminates cooling towers, uses abundant groundwater as low-level energy, and directly exchanges energy with heat pump units to achieve cooling in summer and heating in winter, achieving satisfactory results. According to the geological exploration report, the location of this project is sandy soil at 0-3 meters, sub-sandy soil at 3-15 meters, sandy soil at 15-60 meters, silt sand at 60-90 meters, and sandy soil at 90 meters below. The groundwater level is minus 3 meters throughout the year. Due to the influence of the underground underflow of the Yellow River, groundwater flows from northwest to southeast. The water source is abundant, the water quality is good, it is easy to form a well, and it contains abundant earth energy resources. Have the basic conditions for the use of groundwater source heat pump air-conditioning systems. The groundwater source heat pump system of this project consists of three parts: the circulating water system of the heat pump host and the heat source system. According to the calculation of the heat and humidity load of the project, the heat pump host uses a screw-type water-water heat pump unit, using the environmentally friendly refrigerant HFC-134a, with low working pressure, the maximum cooling capacity in summer is 582KW, and the maximum heating capacity in winter is 634KW; the circulating water system uses two A vertical circulation pump with a head of 50 meters is used. One is equipped with one. The closed-circuit flow of cold water is 77t/h and the closed-circuit flow of hot water is 84t/h. The groundwater system is equipped with a feed water well, with a depth of 84 meters and a diameter of 0.3m. There are two water wells, with a depth of 76m, a well diameter of 0.3m, a well spacing of 20m, a depth of 1m of well closure and burying, a submersible pump lift of 50m, and a flow rate of 46t/h. The groundwater temperature is 17.5℃. After testing, the cold water temperature in summer cooling conditions is 7-12℃, and the hot water temperature in winter heating conditions is 47-56℃. The temperature and relative humidity in the project meet the design requirements.

3 Application advantages
Practice has proved that, compared with the cooling tower water source heat pump system, the groundwater source heat pump system has the following application advantages: (1) This system eliminates the cooling tower, which is conducive to engineering protection, ensuring the normal operation of the air conditioning system in wartime, and improving the overall protection efficiency of the project . (2) The driving force of the average temperature difference of groundwater is 1-2 times higher than that of the cooling tower water source type, and the heat transfer efficiency is high. (3) The groundwater temperature is basically constant in winter and summer, avoiding the influence of outdoor atmospheric temperature on the unit. (4) The cooling energy efficiency ratio (COP value) in summer is 1:5, and the heating energy efficiency ratio (COP value) in winter is 1:4. Compared with other air-conditioning systems, the energy efficiency is 30%-60%. (5) The entire system is adopted. As the heat transfer medium, water has large heat capacity, high density and low heat loss. (6) Low-level energy water is taken from the ground, and the same amount is recharged underground, without air pollution, and has good environmental protection benefits. (7) This system can not only solve the summer dehumidification of civil air defense projects, but also can introduce cold and hot water into the ground engineering to solve the cooling and heating problems of the ground engineering, realize the dual use of one machine, and save investment.

4 Several issues to be grasped
4.1 Attach importance to hydrogeological surveys. When using groundwater source heat pump technology, it is necessary to conduct a survey of hydrogeological conditions and have abundant groundwater resources. The applicable principles are: sufficient water volume, appropriate water temperature, good water quality, stable water supply, reliable recharge, and moderate well cost.
4.2 Optimize system design. It is necessary to strictly calculate the heat and humidity load, flow resistance, reasonably determine the power of the main engine and the head of the circulating pump, and use the frequency conversion device to increase the utilization rate of groundwater and reduce the power consumption of the conventional circulating system.
4.3 Attach importance to well design. (1) According to the hydrogeological conditions, reasonably determine the depth, diameter, and spacing of the water supply wells and return wells, which can be given multiple times at one time to ensure that all the heat source water is recharged without pollution. (2) The water supply well should be located above the flow direction of the groundwater, and the return well should be located below the flow direction of the groundwater. For areas where the groundwater flow rate is slow, the backwater well should be set within the influence range of the dewatering funnel curve of the feedwater well. (3) In order to extend the life of the water well, the water supply well and the return water well can be used interchangeably.