Miami University
IN-27: Innovation D

A 1.6 million gallon thermal energy storage (TES) tank located on South Campus (nearly completed) will operate with an innovative operating sequence unique to Miami’s campus due to our configuration.  When fully charged to 41°F chilled water temperature the capacity is rated @ 15,500 ton-hours.  There will be three different operating modes for charging and discharging the tank. 
The TESs will save on electric cost and the need for installing a transformer to satisfy Miami’s peak demand. It will save on water being lost to evaporation and blowdown in the cooling tower along with avoiding the use of chemicals for balancing the PH and controlling bacteria

The first mode(PLC) is during a hot summer day when the electrical grid is anticipated to see a top 5 peak electric demand, the TES tank will be charged the night before at 41°F and then during a 4-1/2 hour span from 1:30 pm to 6 pm the tank will fully discharge it's stored cooling capacity.  During this 4 1/2 hour span all electrical chillers will be turned off and the cooling loads served from the South Chiller Plant will be entirely served from the stored chilled water in the TES tank. This is anticipated to reduce Miami's peak electric load by 1.7 Megawatts. Thereby avoiding the cost to install a transformer to satisfy Miami's peak demand and reducing the need for more generation on the grid.

The second mode (Peak Shaving) will occur during normal summer days, during these days the TES tank will be charged the night before at 44°F and then during the local utilities On-Peak demand window 11:00 am to 8:00 pm the TES tank will be discharged at a 1500 ton-hr rate displacing the need for one chiller to run during this time. This avoids the cost to install a 1500 ton chiller and cooling tower.

The third mode (Shoulder Season) will occur when the campus is anticipated to go from a cooling dominant mode during the day and a heating dominant mode during the night.  The University is converting 19 buildings served from the South Chiller Plant in their South Quad area over from Steam to Heating Hot Water.  The University has installed 3 Heat Pump Chillers at the South Chiller Plant with a total capacity of 7 MMBtu's for heating, the heating loads during the summer months will be served by the rejected heat from these HP Chillers. During the Spring and Fall in mild weather the cooling load exceeds the heating load during the day and at night the heating load exceeds the cooling load during the night.  The TES tank will be utilized to level off these swings. It will be used as a cooling load during the night thereby charging the tank and then when the cooling load is dominant during the day it will discharge and avoid having to stage on cooling only electric centrifugal chiller. 

This will save on electric cost and also save on water being lost to evaporation and blowdown in the cooling tower along with avoiding the use of chemicals for balancing the PH and controlling bacteria.