How to determine the number of wells required for a ground source heat pump refrigeration unit

Rooms where HVAC system products such as heat pumps and fan coils are installed
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  1. According to the general outdoor plan of the building and the experimental drilling conditions, DN32, U-shaped vertical buried pipe heat exchangers were used. Preliminary estimates were made during the design of the underground pipe plan: the number of drilling holes is 300, the spacing is 5 meters, and the burial depth is 65 meters. The total buried length is 39,000 meters. Therefore, after comparative analysis: the soil source (vertical buried pipe) heat pump system solution is feasible and more economical.
Rooms where HVAC system products such as heat pumps and fan coils are installed
  1. Installation of various pipelines outside the building
    In the general outdoor plan of the building, there are mainly drainage pipes and cable pipes with a depth of more than 2m underground. In the buried pipe area, the horizontal main pipes are buried below 2.5m underground. At the same time, the entrance and exit of heavy equipment and driveways are reserved.
  2. Selection of underground pipes and fittings
    The design uses plastic pipes and fittings with good chemical stability, corrosion resistance, large thermal conductivity, and low flow resistance, d32 3.0+0.5/PE80 1.25MPa.
  3. Selection of heat transfer medium
    Because the outdoor temperature is high in winter and the depth of frozen soil is shallow in winter, water is used as the heat transfer medium in the design of this project. No consideration was given to adding antifreeze to the circulating water in underground pipes. However, to prevent the circulating water in the cooling circulating water pipe from freezing under extreme temperatures, a temperature-sensing automatic control system is used to start the circulating pump. When the system’s return water temperature is lower than 4°C, the automatic control system starts the circulating pump to drive the circulating water and gives an alarm, which can effectively avoid the problem of water freezing in underground pipes.
  4. Measures to balance the total heat absorption and total release of the soil source heat pump system
    In the design of the soil source heat pump air conditioning system, measures to balance the total heat absorption and total release of the soil source heat pump system are very important to ensure the thermal stability of the earth’s rock and soil, the economy of the soil source heat pump system, and the actual operating effect of the air conditioner.
    form of peak regulation. The outdoor 530m3 fire fountain pool is used to assist heat dissipation to eliminate the peak load in the hottest month.
  5. Selection of drilling backfill materials
    The borehole backfill material for this project uses original soil backfill.
  6. Design of underground pipe water system for soil source heat pump system
    The design uses fourteen horizontal co-path loops to connect to the water collector and water distributor in the machine room. The underground pipe water system adopts a one-time pump fixed flow system.
  7. The operation mode of the soil source heat pump system
    (1) The cooling of the five small heat pump units in summer is achieved by outdoor fountain pools, and the heating source in winter comes from the underground pipe system.
    (2) The cooling of the two large heat pump units in summer is realized by underground pipes, and the heating source in winter comes from the underground pipe system.
    (3), 5 small units, the cooling and heating conversion in summer and winter is achieved by switching the flow direction of the refrigerant through the electric four-way reversing valve built into the unit. The two large units switch the refrigeration and cooling water through twelve manual valves set outside to realize the conversion of cooling and heating between summer and winter.
  8. Design calculation and adjusted main data of outdoor vertical buried tube heat exchanger
    Calculations were performed using the GLHEPRO software program developed by the University of Oklahoma, Oklahoma, USA.
    Material selection for outdoor vertical buried pipes: PE pipe U-shaped single row pipe d32 3.0+0.5/PE80 1.25MPa
    (1). Well spacing: 5*5 meters
    (2). Well diameter: D110
    (3). Well depth: 73 meters
    (4) Number of wells drilled: 14 groups (each group is about 26), a total of 370, pipe diameter D32
    (5). Total buried pipe length: 54,625 meters
    (6) Indicators: cooling 44w/meter, heating 30w/meter.
    (7) Drilling backfill material: original soil backfill.
    Note: Due to the abundant buried pipe area in the outdoor general plane, at the request of the owner, to ensure the air conditioning effect, the total buried pipe length and the number of wells were increased by 15% based on the design calculation.

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