Exergy Optimized Wastewater Heat Recovery: Minimizing Losses and Maximizing Performance

I n this project a system to utilize the heat that would otherwise be destroyed in warm water going down the drain has been optimized. Both the quantity and quality of the energy flows are considered using exergy analysis. The system recovers the heat using a batch process with an insulated tank containing a heat exchanger. The analysis is based on statistical annual hot water usage profiles. The system shows that the exergy available in warm wastewater can be optimized with specific tank size and heat exchanger flow rate to the exergy the extraction. This gives an energy recovery of 3000 kWh or 10% of the U.S. single-family residential household demand or over 50% of annual hot water demand. A complete system would utilize this optimized exergy output to minimize the temperature lift required by a heat pump. This would create an integrated low exergy space and water heating system. The project theory is a part of the IEA ECBCS Annex 49, and also collaboration has been setup with Geberit AG to eventually bring a product to market