HORIZONTAL GROUND-COUPLED HEAT EXCHANGER FOR GEOTHERMAL SYSTEMS

摘要

Horizontal ground-coupled heat exchanger for geothermal systems is proposed. The exchanger includes sub-surface formation of not expensive special structure heat conductive stratum around conduit loops. Analytical and finite element modeling allowed estimating the new structure efficiency. The proposed decision permits to increase by 2-3 times the transmitted heat power of the exchanger and correspondently to reduce the required pipe length and land area. The underground loop must be sized to meet the peak thermal power load. The proposed exchanger structure may fill simply this requirement, because at relatively short-term operation the efficiency of the proposed structure is even higher and reaches increasing by 2.5-4 times in dependence on climate zone.

主权项

1. Horizontal ground-coupled heat exchanger for geothermal system, which is underground part of the system for exchanging of Earth heat energy with upper part of the geothermal system, and the underground part contains one or more conduits with heat transfer liquid, and said conduits are located in Earth below frozen soil level, and the ground has temperature above 0° C.,
wherein, in order to increase transmitted Earth heating/cooling power especially in arid and semiarid climate zones and to make minimal power dependence on drought and seasonal variation of temperature and ground water level, said underground part includes an additional intermediate stratum between conduits and Earth, fully located at depth 1.2-3 meters and separated from surrounding soil by thin thermo-conductive waterproof material from all sides, bottom, walls and top, and this stratum has such dimensions that its section area exceeds the total cross-sectional area of conduits not less than 40 times, and this stratum contains heat conductive moist fill material with temperature above 0° C., and the filling inside the stratum is provided with additional water such that volumetric water content significantly exceeds volumetric water content of surrounding soil, and said waterproof material prevents penetration of water from said stratum to the soil disposed around, and said conduits with heat transfer liquid pass through filling in this stratum, and the additional stratum together with conduits form the new structure of ground-coupled heat exchanger with two operating parts (conduits and additional stratum), creating effective underground heat energy exchange between three mediums (conduits liquid, stratum moist filling and Earth) with enlarged thermal conductivity and high efficiency, and said stratum has size of minimal side (d1) per pipe dependent on stratum efficiency (Keff) by the following relation:Keff=PwithPwithout=2π+α0*d0*ln(1.35d1/d0)/λ22π+α0*d0*ln(d1/d0)/λ1+0.3α0*d0/λ2, where: d1—size of minimal side of the stratum per pipe, m, Pwith—power of heat exchanger containing stratum, kW, Pwithout—power of heat exchanger without stratum, kW, d0—diameter of the conduit with liquid, m, α0—heat transfer coefficient of conduit (pipe) with liquid, W/(m2*K), λ1, λ2—coefficients of thermo-conductivity of the stratum medium and ground, surrounding the stratum, W/(m*K), correspondently, and d1 rational dimensions are in borders 0.20-0.75 m, and the heat exchanger contains also means to compensate for unintended small leaks of water from the stratum.