A minicomputer monitoring and control system is part of the HVAC system of a 1.4 million square foot commercial facility. The chiller system at the central plant consists of four 1250 ton centrifugal chillers, a six-cell cooling tower, five 100,000 gallon chilled water storage tanks, and associated pumps and piping.

 Computer models of the chilled water system were developed to study the energy conservation potentia1 of control strategies intended for the minicomputer control system. Empirica1 curve fits were used for all of the components except the cooling tower. An effectiveness model based on manufacturer’s data was used for the cooling tower. Comparisons of modeled performance with measured data showed good agreement both at the component and system levels.

Optimal control strategies for the number of chillers, cooling tower fan speeds, and condenser pump flow rates were developed. These resulted in an estimated combined savings of $4,400 a year. Demand limiting using the chilled water storage reduced annual peak demand by 161 kW and saved an additional $5,500. Reset of the chilled water set point saved an additional $4,400 for a total combined savings of $14,300.