ONCE THROUGH COOLING OF CHILLERS USING MUNICIPAL RECLAIMED WATER – FEASIBILITY EVALUATION
Abstract:Industrial and commercial facilities often use chillers to meet process and building cooling needs. In these applications, heated refrigerant in the chillers is cooled by potable water returning from cooling towers. This project evaluated the concept of once-through cooling using reclaimed water as an alternative to cooling tower return water for industrial/commercial chillers. Upon heat exchange, the reclaimed water will be returned to the reclamation main for subsequent use by other users. Technical feasibility, economic viability and market potential for the proposed system were evaluated in Southern California Edison (SCE) service area.
Preliminary technical evaluation indicated several benefits for the use of reclaimed water for once-through cooling. The proposed use can significantly reduce energy consumption due to i) elimination of cooling tower fans, and ii) improvement in chiller performance due to lower temperature of reclaimed water. Also, the once-through cooling eliminates the need for cooling tower chemicals. Additional benefits include conservation of potable (make up) water and elimination of blowdown discharge. Finally, since the proposed system uses reclaimed water non-consumptively, the same water can be used for multiple applications. Limitations of the proposed system include possible corrosion of heat exchange pipes, slight increase in the water temperature, and dissipation of disinfection residuals in the reclaimed water.
A planning level estimate (+50% and −30%) indicated that a 200 ton chiller can reduce the annual O&M cost by about 10,000 and a 1,200 ton unit can reduce the annual O&M cost by about 75,000. The lower costs are mainly due to savings in energy and elimination of cooling tower chemicals. In these estimates, an electricity cost of 0.10/KWh and chemical cost of 2.35 per 1000 gallons of make up water were used. The pay back period for retrofitting an existing 200 and 1,200 ton chillers with the proposed system are about 2 and 1 years, respectively. As part of economic evaluation, sensitivity analyses were performed using electricity costs of 0.07 and 0.13KWh and chemical costs of 1.35 and 3.00/1000 gallons of make up water. At 0.07/KWh, the pay back periods for 200 and 1,200 ton unit retrofits are approximately 2.1 and 0.5 years, respectively. At 0.13/KWh, the pay back periods are 1.6 and 0.45 years, respectively. At a chemical cost of 1.35/1000 gallons, the pay back periods are 2.1 and 0.6 years for retrofitting the 200 and 1,200 ton systems. The pay back periods are 1.6 and 0.5 years if the chemical cost is 3.00/1000 gallons.
Industrial sectors such as plastic molding, food processing and wine chilling facilities that needs cooling, and large commercial buildings (60,000 to 400,000 square foot) are potential candidates for this system. However, the number of facilities that can be retrofitted with the proposed cooling system is restricted by several factors. First, due to high costs of installing pipelines from the reclaimed main to the chiller, only those facilities that are in the same street as the reclaimed main can be viable candidates for this application. Secondly, adequate flow must be available in the main to meet the cooling needs of the chiller. Also, several reclaimed water systems deliver water only during the night (for landscaping and irrigation uses), whereas chillers in industrial/ commercial facilities may need cooling during the day. Finally, the proposed use will slightly elevate the reclaimed water temperature during heat exchange. The total number of retrofits must be restricted so that the overall increase in the temperature does not impact other intended uses of reclaimed water.
Document Type: Research Article
Publication date: 2002-01-01
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