Causal Model for Peak and Off Peak Waste Heat Recovery for Chilled Water Production

The objective of this study is to develop a causal model for estimating the amount of chilled water that can be produced from generated waste heat during off peak period of a district cooling plant. The methodology adopted is to calculate the amount of waste heat generated by the gas turbines of the plant during peak and off peak operations. Ten months of 2009 historical data of waste heat generated during peak and off peak periods were analyzed. The chilled water produced by absorption cooling for the ten months during peak period was also analyzed. Mathematical models using the causal relationship of the waste heat generated with the chilled water produced during the peak period for the ten months were formulated. Three models were formulated using the data namely linear, quadratic and exponential. The R2 values obtained are 0.5034, 0.784 and 0.5128 for the linear, quadratic and exponential respectively. Since the R2 value for the quadratic model is the highest, the quadratic model is used to evaluate the amount of chilled water that could be generated from the off peak waste heat. From the calculation, it is estimated that an average of 520,310 RTh of chilled water could be produced monthly from the off peak waste heat. This is 79.7% of the chilled water produced during peak period. Based on these findings the waste heat during off peak if converted to chilled water using absorption process will lead to economic benefits as well as reduced emission to atmosphere. Further detail study will be undertaken to enhance the model and to establish the design configuration of the system to recover the off peak waste heat for chilled water production by absorption process.