RP-560 -- Evaluation of Water-Side Fouling Resistance in Flooded Evaporators of Water Chilling Machines PDF

This work was conducted under ASHRAE RP-560. The objective of the program was to determine the potential for fouling on the water-side of tubes used in flooded refrigerant evaporators. The program was conducted in two parts. Part 1 of the program involving field sampling and analysis to determine the water quality used in water chiller evaporators. Water samples were taken from 71 chillers located in 31 cities across the continental U.S. A questionnaire was filled out for each sampling site. It provided information regarding the chiller installation, chilled water system, operating profile and maintenance practices. The collected samples were analyzed by water treatment companies. The results were then entered into a computer database. The water quality data were analyzed to infer the fouling potential as a function of building use, winter heating, use of corrosion inhibitor, geographic location and water softening. Important statistical parameters of all the fouling indicators were tabulated. A statistical model was developed for the data interpretation. The model was applied to assess the potential of chilled water for various fouling mechanisms. Threshold values, which indicate the potential for fouling, were defined. The results of the Part 1 work were published in Webb, R. L., Haider, S. Imam, and Meitz, A., "A Survey of Water Quality and Its effect on Fouling in Water Chiller Evaporators," ASHRAE Transactions, Vol. 97, Pt. 1, pp. 55-67, 1991. Part 2 of the program involved an experimental study to measure the fouling thermal resistance in the tubes of water chiller flooded evaporators operating at approximately 45° E The fouling resistance measurements were made in a specially designed test evaporator 12.6 ft long containing 16 tubes that was connected in parallel with an existing 250 ton R-ll chiller evaporator. The test evaporator used the same water that flowed through the tubes of the 250 ton evaporator. Refrigerant from the 250 ton evaporator was boiled on the outer surface of the test evaporator tubes. Two sets of fouling data were taken, one for the 1990 cooling season (May through October) and one for the 1991 cooling season. The data were taken for one internally plain and three internally enhanced tube geometries. The fouling resistance of each tube was compared with that of an identical tube, which was manually brushed twice weekly. During the first year, the data were taken with normal water quality at 3.5 ft/sec water velocity. During the second year, the data were taken with dirty water quality at 3.5 and 7.0 ft/sec water velocities. The data were analyzed to determine the fouling resistance obtained in each of the two cooling seasons. The results for two cooling seasons show that negligible fouling will occur in the evaporator tubes. The results of the Part 2 work were published in S. Imam, and Webb, R.L., "An Experimental Study of Tube-side Fouling Resistance in Flooded Water Chiller Evaporators, "ASHRAE Transactions, Vol. 98, Pt. 1, 1992.