Application of Water Source Heat Pump in Air Defense Project

Abstract: In this paper, the technical obstacles of water source heat pump air conditioning system in cooling tower are analyzed emphatically, and the feasibility of application of ground water source heat pump air conditioning system in civil air defense project is demonstrated by engineering examples. Some problems that should be grasped are put forward for project management And designer's reference.

Keywords: air defense project air source groundwater source heat pump

At present, the air-conditioning system of cooling tower water source heat pump commonly used in civil air defense projects is that the quantitative circulating water of the cooling tower is used as an intermediate medium to exchange heat with the outdoor air, and the low energy in the outdoor air is converted to high energy by the heat pump technology, Moisture-proof and dehumidification for civil air defense projects are essentially air source heat pump (SHP) systems. The fatal weakness is restricted by the weather conditions. The cooling efficiency in summer decreases with the increase of outdoor atmospheric temperature. In winter, due to outdoor air temperature Low and can not achieve heating, the overall efficiency is low. The ground water heat pump (GWHP) system is adopted to cancel the cooling tower. The project directly exchanges heat with the groundwater by the heat pump to avoid the influence of the atmospheric temperature, so that it can be dual-use and energy-efficient. It can not only meet the requirements of summer civil air defense works Dehumidification problem, but also can be introduced into the ground engineering, to solve the problem of heating and cooling in winter and summer of ground engineering, has good application prospects.

1 technical demonstration

Cooling tower water source heat pump air conditioning system, essentially belongs to the air source heat pump air conditioning system. Air source heat pump air conditioning system, low energy comes from the outdoor air, in summer cooling conditions, the heat pump needs a cooler air medium cooling condenser, the heat passed to the outdoor air, to achieve the purpose of cooling, to meet the cooling. In the winter heating conditions, the heat pump needs a higher temperature air medium, take away the evaporator's cooling capacity, to achieve the purpose of heating, to meet the heating. However, the natural law of the seasonal variation of atmospheric temperature is just opposite to the seasonal expectation of the heat pump. In summer, the outdoor temperature is high, which is unfavorable to cooling the condenser and reduces the cooling efficiency. In winter, the outdoor atmospheric temperature is low, which is not conducive to taking away the evaporator's cooling capacity. Reduce the overall operating efficiency is low, this is the air source heat pump air conditioning system can not overcome the technical obstacles. Civil air defense project is a closed underground space, heat pump air conditioning system can not directly with the outdoor air heat exchanger, only to quantitative circulating water as a medium, through the ground cooling tower and outdoor air heat exchanger to achieve refrigeration, to meet the dehumidification. However, due to the high outdoor summer air temperature, the temperature of the circulating water of the cooling tower also increases, resulting in a decrease of the cooling efficiency of the heat pump. In winter, even if the water-water heat pump unit is used, the heating can not be realized and has great limitations. Therefore, the cooling tower water source heat pump system still can not overcome technical obstacles caused by the atmospheric temperature.

Earth is a huge body of constant temperature, groundwater contains endless energy. According to the test, the temperature of shallow groundwater below 30 meters is stable at about 18 ℃ for many years, which is much higher than that in winter and far below that in summer. If the civil air defense heat pump air-conditioning system uses groundwater as the low-level energy source, Overcoming the technical obstacles of air source heat pump greatly improves the overall efficiency of the system. In addition, in the summer, the low-level groundwater cooling capacity is converted to high cooling capacity by heat pump technology. At the same time, waste heat from the civil air defense works is transferred to the groundwater through the recharge technology. In winter, heat is also applied to convert low ground water heat into high heat. Through the recharge technology to transfer cold water to groundwater, so that the cold winter with summer, summer heat summer use, groundwater plays the role of accumulator to ensure the perennial use of air conditioning systems. Therefore, the underground water source heat pump system, low energy from groundwater, heat pump directly with the temperature perennial steady groundwater heat exchange, without the influence of atmospheric temperature to overcome the air source heat pump system technical obstacles to achieve a dual-use and save investment , Low overall operating costs, suitable for ground-water-resource-rich air defense civil engineering systems.

2 project examples

Kaifeng City, an attached civil air defense projects, the use of groundwater source heat pump air conditioning system, cancel the cooling tower, with abundant groundwater as a low energy, direct heat exchange with the heat pump units to achieve the summer cooling, heating in winter, and achieved satisfactory results. According to the geological prospecting report, the location of this project is 0-3 meters of sandy soil, 3-15 meters of sandy soil, 15-60 meters of sandy soil, 60-90 meters of silt, and 90 meters of sandy soil. Perennial water table negative 3 meters. Due to the influence of the subsurface flow of the Yellow River, groundwater flows from the northwest to the southeast, with abundant water resources and good water quality, which makes it easy to form wells and contains abundant geo-energy resources. Have the groundwater source heat pump air conditioning system with the basic conditions. The project groundwater source heat pump system by the heat pump host circulating water system and heat source system consists of three parts. According to the calculation of heat and moisture load of the project, the main pump of the heat pump adopts the screw water-heat pump unit and adopts the environmental protection refrigerant HFC-134a. The working pressure is low, the maximum cooling capacity in summer is 582KW and the maximum heating capacity in winter is 634KW. The vertical circulation pump with a head of 50 meters has a prepared one, the closed circulation flow of cold water is 77t / h and the closed circulation flow of hot water is 84t / h. The groundwater system is provided with a water well of 84 meters with a well diameter of 0.3m Two wells, well depth 76m, diameter of 0.3m, well spacing 20m, well depth and well depth of 1m, submersible pump lift 50m, flow 46t / h. Groundwater temperature 17.5 ℃. After testing, the cold water temperature in summer cooling conditions 7-12 ℃, winter heating conditions hot water temperature 47-56 ℃, the project temperature and relative humidity have reached the design requirements.

3 application advantages

Practice has proved that underground water source heat pump system and cooling tower water source heat pump system, compared with the following advantages: (1) cancel the cooling tower of the system is conducive to engineering protection to ensure the normal operation of air-conditioning system in time of war to improve the overall effectiveness of the project . (2) The average temperature difference of groundwater is more than 1-2 times higher than that of the cooling tower water source, and the heat transfer efficiency is high. (3) Groundwater temperature is basically constant in winter and summer, avoiding the impact of outdoor atmospheric temperature on the unit. (4) Compared with other air-conditioning systems, energy efficiency ratio (COP) is 1: 5 in summer and COP in winter is 1: 4, saving 30% -60% compared with other air-conditioning systems. Water as a heat transfer medium, heat capacity, high density, heat loss. (6) The low-level energy water is taken underground, and the same amount of recharge to the ground, no air pollution, with good environmental benefits. (7) The system can not only solve the summer dehumidification of civil air defense works, but also can introduce hot and cold water into the ground works to solve the problem of cooling and heating of the ground works so as to realize the dual use of one machine and save investment.

4 should grasp a few questions

4.1 emphasis on hydrogeological survey. Groundwater source heat pump technology, you must first hydrogeological survey, there should be abundant groundwater resources, the applicable principles are: adequate water, water temperature, water quality is good, stable water supply, reliable recharge, well costs well.

4.2 optimize system design. To strictly calculate the heat and moisture load, flow resistance, a reasonable determination of the host power and circulation pump head, the use of frequency conversion device to improve groundwater utilization, reduce the power consumption of conventional circulatory system.

4.3 emphasis on well design. (1) According to the hydrogeological conditions, it is reasonable to determine the well depth, well diameter and well spacing of the water supply well and the backwater well, so as to ensure that all the heat source water is fully recharged and not polluted. (2) The water supply well should be located above the groundwater flow direction, and the water return well should be located below the groundwater flow direction. For areas with slow groundwater velocities, the return well should be located within the flume curve of the feed well dewatering. (3) In order to prolong the life of the well, the feed and return wells can be used interchangeably.