A semi-analytical model for serpentine horizontal ground heat exchangers
Résumé
This paper focuses on a particular type of horizontal ground heat exchangers (HGHE) which can be used as a heat source (or heat sink) for geothermal heat pumps. It consists of a long pipe buried about 1 m below the ground surface and arranged in parallel regularly-spaced sections so as to form a serpentine. In the first part of the paper, a model for such a heat exchanger is proposed. In this model, the serpentine is discretized axially and a three step calculation procedure is then performed on each node. First, the axial fluid temperature variation in the pipe is computed by using an implicit numerical resolution scheme. Then, heat transfer in the ground surrounding the pipe is obtained by using the analytical cylindrical heat source (CHS) solution. In the third step, used for mid- to long-term simulations, thermal interference between parallel pipe sections is taken into account using spatial superposition. Finally, these solutions are coupled iteratively to obtain the axial fluid and pipe temperatures at each time step. The model is then validated using a full-scale experimental facility located in Orléans, France. Following a brief description of the facility, validation results are reported. The main validation test consists of supplying the HGHE with a constant inlet fluid temperature (40°C [104°F]) for a 200 hour period in a soil at an initial temperature of 7.5°C (45.5°F). After an initial transient period, the recorded outlet fluid temperature matches the model prediction within 1°C (1.8°F).
Mots clés
Time step
Validation results
Validation test
Calculation procedure
Cylindrical heat source
Experimental facilities
Fluid temperatures
Ground heat exchangers
Ground surfaces
Heat sources
Long pipe
Long term simulation
Model prediction
Numerical resolution
Parallel pipes
Semi-analytical model
Thermal interferences