I.Application occasions

The first condition for selecting well water source heat pump cold and hot water unit as the cold and hot source of central air conditioning is to have available and reliable underground water source. Specifically, the applicable underground water source shall meet the following requirements.

• sufficient water. The first question to be answered is whether the groundwater quantity can meet the engineering demand. The underground water required in winter and summer is determined by the performance of well water source heat pump cold and hot water units, well water temperature, cold and heat loads of building air conditioners, etc. Therefore, the selected underground water wells should meet the needs of the project, and it is best to have extremely rich water inflow of single wells (the water inflow of single wells is more than 5000 m/d) or rich water inflow of single wells is 1000 ~ 5000 m/d).

• Moderate water temperature. As we all know, the higher the temperature of well water, the greater the heating capacity and performance coefficient of well water source heat pump cold and hot water units. Therefore, it is hoped that the well water temperature will not be too low. Requirements: under the condition of heat pump, the well water temperature is 12℃~22℃, preferably not lower than 10℃; The cooling condition is 18℃~30℃. If the well water temperature is too low, the mixed cooling water system can be selected.

• The water temperature of deep well water is generally about 1~2℃ higher than the local annual average temperature. The temperature of deep well water in the northern part of Northeast China is about 4℃, about 12℃ in the central part and about 12℃~14℃ in the southern part. The temperature of deep well water in North China is about 15℃~19℃, and that in East China is about 19℃~20℃. The water temperature of shallow wells in northwest China is about 16~18℃, and that of deep wells is about 18 ~ 20℃. The water temperature of shallow wells in central south China is about 20 ~ 21℃.

• Appropriate water quality. To prevent corrosion, wear, blockage, etc. on pipelines and equipment, it is very important to ensure the quality of water. The water quality meets the requirements of the current national standard “Technical Code for Ground Source Heat Pump System Engineering”. Stable water supply. Well-water source heat pump cold and hot water units need to run continuously for 24 hours every day in winter, and the running situation of wells is quite different from that of domestic water wells. Therefore, it is required that the water storage capacity of aquifer should be large, the water supply of wells should be continuous and stable, and the long-term stable operation of well water source heat pump air conditioning system should be ensured.

• Recharge smoothly. Hydrogeological conditions of the project site (groundwater aquifer type, permeability, permeability coefficient, cross-sectional area of seepage, effective porosity, etc.) meet the requirements of well water recharge, which can make all the well water after heat exchange by heat pump units Smooth recharge to underground aquifer.

II.In the project design, whether to decide to use the well water source heat pump cold and hot water unit as the cold and hot source of central air conditioning, before, we should first drill the experimental well in the project site.

Through the experimental wells, the data of water quantity, water temperature and water quality are measured as the design basis. Then, according to the cold and heat load of the project, the selected unit performance and the design temperature difference of the plate heat exchanger, the total water flow of the required water source is determined, and finally the number and location of underground wells are determined.

III.water supply system is generally divided into direct water supply system and indirect water supply system

Flow of direct water supply system: well water → deep well pump → well water source heat pump cold and hot water unit → recharge well. If the water quality meets the requirements and no treatment measures need to be taken, the direct water supply system can be adopted at this time because of its simplicity and low investment. Indirect water supply system refers to the heat exchange between well water and secondary water through plate heat exchanger, and the secondary water enters the heat pump unit to ensure that the unit is not affected by well water quality. After passing through the heat exchanger, the well water flows to the recharge well and returns to the same aquifer where underground water is taken.

IV. Design Points of Groundwater Heat Exchange System

1. The design procedure of groundwater heat exchange system is as follows:

● Determine the total amount of underground water required for this project;

● Selection and design of groundwater recharge methods;

● Determine the number and location of heat source wells (pumping wells and reinjection wells);

● Design of heat source wells;

Low well or well group pipeline design;

Selection and calculation of plate heat exchanger:

● Selection and arrangement of wells, pumps and other equipment.

2. Types and application scope of heat source wells.

Heat source well is the general name of pumping well and recharge well of groundwater heat pump air conditioning system, which is a groundwater heat exchange system

An important part of. Its function is to take out qualified groundwater from underground aquifer and send it to heat exchanger

Set or send directly to the water source heat pump for heat exchange; And then return to the aquifer through the recharge well.

3. Structure of tube well.

Tube wells are mainly composed of well chambers, casing pipes, filters, settling pipes, etc. The diameter of existing tube wells in China is 200mm,

300mm, 400mm, 450mm, 500mm, 550mm, 600mm, 650mm and other specifications.

● Well chamber. Its function is to install well pump motor, wellhead valve, pressure gauge, etc., to protect the wellhead from pollution and provide a place for operation, management and maintenance.

Low casing pipe. It is installed in rock and soil sections (such as clay sections, etc.) where water is not needed, and its function is to reinforce the shaft lining and isolate the aquifer with poor water quality.

Low filter (also known as flower tube). It is a pipe with holes or gaps which is directly connected with the casing pipe and installed in the aquifer. Its function is to draw groundwater and block sand grains from the aquifer from entering the well.

● sedimentation pipe. It is located at the bottom of the tube well, and is used for settling fine sediment particles into the well and sediment precipitated from groundwater. The length of the settling pipe depends on the depth of the well and the possibility of settling sand in the well water, generally 2~10m

4. Filter of heat source tube well.

There are many types of filters, which can be divided into gravel-filled and non-gravel-filled. Gravel layers of certain specifications are backfilled around the filters to form gravel-filled filters. Otherwise, the filter is directly lowered to the aquifer part of the well, that is, the gravel-free filter. Commonly used filter types are: steel skeleton wire wrapping, steel pipe seam wire wrapping, steel pipe perforation, steel pipe perforation wire wrapping, steel pipe perforation gravel sticking, double-layer gravel filling filter, etc. The selection principles are as follows:

1) gravel filter should be selected in all kinds of sand, gravel and pebble aquifers to prevent sand gushing and maintain the stability of aquifers;

2) Under the condition of ensuring the strength requirements, filters with larger porosity should be adopted as far as possible;

3) In areas with fine sand and high iron content, double-layer gravel filter should be adopted for heat source wells alternately used for pumping and recharging.