Heat Transfer Analysis of Stratified Chilled Water Storage Tank for District Cooling Systems

The cooling demand is rising exponentially across the globe due to adverse environmental conditions,  us,  needs  more  energy-efficient  solutions  for  commercial  and  residential applications.  District  Cooling  System  (DCS)  is  a  cost-effective  method  for  providing comfort to consumers from a central plant through a distribution network improving the efficiency for reliable solutions in densely populated areas. The research work included designing, developing, and fabricating a DCS system for a 0.5 TR refrigeration system for learning  thermal  stratification  in  terms  of  thermocline  thickness,  figure  of  merit, and equivalent lost tank height for different volume flow rates of water. The system can perform  experiments  for  charging  and  discharging  operations  to  study  district  cooling systems. The system consists of three sections such as chiller, heating, and stratification. The  stratification  tank  has  centrally  located  ten  temperature  sensors  to  measure  the temperature drop between the cold and warm water to measure the mixing intensity. It is found that the thermocline thickness is 0.175 m, the figure of merit for half-cycle is 0.9, and the equivalent lost tank height is 0.07 for a water flow rate of 100 LPH. Thus, with the DCS system, energy is saved over the conventional cooling methods with less impact on the atmosphere in terms of CO2 and GWP for sustainable growth. The CFD simulations of the  thermal  stratification  phenomenon  are  performed  with  ANSYS  to  predict  the performance during charging and discharging operations. CFD results are validated with the  actual  experimental  observations  for  different  flow  rates.  The  relationship  between mixing  intensity  and  incoming  flow  is  established  to  study  thermal  energy  storage  by stratification.  It  is  found  that  a  stratified  chilled  water  storage  system  eliminates shortcomings of conventional ice bank storage systems due to higher power consumption for lower evaporating temperatures. Indian industry has now started using the concept of DCS  system  over  other  conventional  methods  as  an  energy  conservation  approach  for residential  and  commercial  heating,  ventilation,  air  conditioning  and  refrigeration applications.