NUMERICAL SIMULATION OF THERMAL ENERGY STORAGE WELLS AND COMPARISON WITH FIELD EXPERIMENTS (AQUIFER, TRANSPORT, AIR CONDITIONING)

Aquifer thermal energy storage (ATES) uses ground water as a means of storing energy. ATES allows the heat from industrial waste or solar collctors operated in the summer to be stored for use as winter space heating. Cold water from spray cooling ponds operated in the winter can also be stored for use as summer air conditioning. A cold water ATES system consisting of a spray cooling pond, gravity sand filter, and a pair of wells was constructed and operated for two years at College Station, Texas. Each year of operation consisted of winter injection, spring storage, summer recovery, and fall idle periods. A 3-dimensional numerical model (ENSTOWEL II) was used with the average injection temperatures, total injected water volumes, and estimates of the aquifer hydraulic and thermal properties to simulate the system at College Station and a heated water system of Mobile, Alabama.; During the first year of operation of the ATES at College Station 16 per cent of the injected energy was recovered compared to 17 percent simulated by the model. During the second year 21 percent was recovered compared to 18 percent simulated by the model. The Mobile field system yielded a recovery of 66 per cent compared to the simulated recovery of 62 percent. There was good agreement between the field and model for the recovery temperatures for both field systems. There was fair agreement between the temperatures measured in observation wells at College Station and those calculated by the model. The natural aquifer flow at College Station moved much of the injected water downstream of the storage well, where it could not be recovered.; Numerous simulations were performed with ENSTOWEL II with a range of aquifer thickness, overburden thickness, pumping-injection rates, thermal conductivities, and porosities to investigate the influence of these parameters on recovery. Changing the vertical permeability an order of magnitude had the most significant influence, decreasing the recovery by 6 percent. An overburden thickness of 4 meters was sufficient to limit vertical conduction. The thermal recovery generally increased with aquifer thickness and well flow rate.