A Convenient Spreadsheet-Based Thermal Model for Heat Recovery and Effluent Cooling

The prime objective of this work was to identify the major sources of internal heat generation and locations within the water recovery facility that provide the most potential for heat dispersion to the atmosphere. A facility-wide thermal energy model applied to each unit process was developed, calibrated and validated at two water recovery facilities. The model was verified by applying it to three separate months representing cold, intermediate and warm influent temperatures at the two facilities. Differences between model predicted and facility recorded effluent temperatures were within 0.06% to 2.3%, with an average of 1.13%. With these results, the thermal model was deemed to be calibrated. Subsequent detailed temperature monitoring at each unit process within the plants confirmed the validity of the model predicted results. The overall net heat gain, without hot water discharges to the effluent from cogeneration cooling water, ranges from 2.63×106 Joule/m3 influent flow at cold (15.7°C) influent temperatures to 3.73×106 Joule/m3 at warm (21.6°C) influent temperatures.The model showed that in critical colder months, covers over unit processes are largely ineffective in cooling the effluent. With heat recovery in the influent interceptor system, temperature impacts on biological processes were verified using the model.