How does U-M use steam to cool buildings?

Steam Absorption Chillers Program

• Steam absorption chillers use steam to drive an absorption refrigeration cycle. Water is the refrigerant. In the cycle, refrigerant water is:
  1. Absorbed into solution,
  2. Boiled by steam,
  3. Evaporated to cool chilled water for cooling the building,
  4. Condensed by cooling tower water,
  5. And reabsorbed to repeat the cycle.
     
     Two-Shell Lithium Bromide Cycle Water Chiller
• U-M has operated a central-campus steam distribution network since the 1800's. As air conditioning systems were installed and/or expanded around central campus, steam-absorption chillers made sense because steam capacity was already available at the buildings
• As long as fuel costs were relatively low, absorption chiller operating costs would have been comparable to, or lower than, other methods, and installed costs generally would have been comparable to, or lower than, equivalent electric chillers.
• Absorption chillers make economic sense primarily when the cost of heat is low (as it was during much of the 80's and 90's), or if there is a ready source of waste heat (steel mills, paper mills, etc.).
• The fuel economics have changed over the last few years, and we continue to evaluate opportunities to reduce operating costs for our CHW systems.

Strategies used at U-M for Containing Costs and Conserving Energy for Cooling Systems

• Convert multiple building systems to a shared regional system (e.g. NCCP, Hatcher)
  
  North Campus Chiller Plant
• Replace existing steam-absorption chillers with electrical centrifugal chillers (e.g. Hatcher, Ross)
• Regular steam trap rebuilds/replacement for steam-absorption chillers
• Routine maintenance to manage efficiency and equipment condition (cleaning tubes, calibrating controls, etc.)
• Real-time monitoring of absorption chiller condensate flows and chiller efficiency (e.g. Chemistry, Dental, and EUCP).
  
• Variable-speed drives for cooling tower fans
  
• Variable-speed drives for pumps
  
• Variable-speed drives for new electric centrifugal chillers
• Free-cooling heat exchangers for winter cooling loads
  
• Right-size CHW control valves to match observed load range
• Monitor and trend chilled water system parameters by BAS and UPE to identify and correct equipment issues