Retro-commissioning and analysis of the entire chilled water system to identify operational problems particularly associated with low secondary supply-to-return water temperature differentials, short cycling of chillers, and excess on-line chiller capacity.

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• The supply air temperature setpoints for the air handling units were all found to be below their intended design values. G/BA recommended that the AHU discharge air setpoints be increased to 54F during the cooling season.
• G/BA discovered that the chilled water supply temperature was allowed to climb to 48F (6F above setpoint) before another chiller was started. G/BA recommended that the plant be operated to maintain a chilled water supply temperature of 42F.
• Analysis of the pump performance revealed that the secondary chilled water flow rate was allowed to be greater than the primary flow rate, increasing secondary supply water temperatures. G/BA recommended implementing changes to assure that the primary flow rate always remains greater than the secondary circuit in order to increase ΔTs.
• G/BA identified an incorrect calculation for determining cooling load and estimating flow rates that was used to sequence the chillers. G/BA recommended a corrected calculation.
• Some chilled water flow meters, temperature sensors, and chilled water control valves were found to be broken or not-calibrated. All were either fixed or replaced.
• All recommendations were implemented by in-house Sears's personnel. The material costs were minimal: less than $5,000.
• Prior to G/BA's recommended adjustments, the chilled water ΔTs were typically between 6 and 8F- approximately 50% of the design ΔT of 14F. After implementing recommendations outlined in the study, chilled water ΔTs are generally at or above the design value (e.g., ΔT as high as 18F have been realized).
• Chillers can now be loaded to 100% of available cooling capacity.
• Colder chilled water temperatures and increased chilled water ΔTs resulted in reduced fan and pump energy use, respectively. Year 2007 actual energy savings were 696,000 kWH and $64,000.