TY - JOUR
T1 - A method to determine stratification efficiency of thermal energy storage processes independently from storage heat losses
AU - Haller, M.Y.
AU - Yazdanshenas, Eshagh
AU - Andersen, Elsa
AU - Bales, C.
AU - Streicher, W.
AU - Furbo, Simon
PY - 2010
Y1 - 2010
N2 - A new method for the calculation of a stratification efficiency of thermal energy storages based on the second law of thermodynamics is presented. The biasing influence of heat losses is studied theoretically and experimentally. Theoretically, it does not make a difference if the stratification efficiency is calculated based on entropy balances or based on exergy balances. In practice, however, exergy balances are less affected by measurement uncertainties, whereas entropy balances can not be recommended if measurement uncertainties are not corrected in a way that the energy balance of the storage process is in agreement with the first law of thermodynamics. A comparison of the stratification efficiencies obtained from experimental results of charging, standby, and discharging processes gives meaningful insights into the different mixing behaviors of a storage tank that is charged and discharged directly, and a tank-in-tank system whose outer tank is charged and the inner tank is discharged thereafter. The new method has a great potential for the comparison of the stratification efficiencies of thermal energy storages and storage components such as stratifying devices.
AB - A new method for the calculation of a stratification efficiency of thermal energy storages based on the second law of thermodynamics is presented. The biasing influence of heat losses is studied theoretically and experimentally. Theoretically, it does not make a difference if the stratification efficiency is calculated based on entropy balances or based on exergy balances. In practice, however, exergy balances are less affected by measurement uncertainties, whereas entropy balances can not be recommended if measurement uncertainties are not corrected in a way that the energy balance of the storage process is in agreement with the first law of thermodynamics. A comparison of the stratification efficiencies obtained from experimental results of charging, standby, and discharging processes gives meaningful insights into the different mixing behaviors of a storage tank that is charged and discharged directly, and a tank-in-tank system whose outer tank is charged and the inner tank is discharged thereafter. The new method has a great potential for the comparison of the stratification efficiencies of thermal energy storages and storage components such as stratifying devices.
KW - Solar heating systems
KW - Thermocline
KW - Thermal stratification
KW - Thermal energy storage
U2 - 10.1016/j.solener.2010.03.009
DO - 10.1016/j.solener.2010.03.009
M3 - Journal article
SN - 0038-092X
VL - 84
SP - 997
EP - 1007
JO - Solar Energy
JF - Solar Energy
IS - 6
ER -