Recovery of Sewer Waste Heat vs. Heat Pumps Using Borehole Geothermal Energy Storage for a Small Community Water Heating System: Comparison and Feasibility Analysis

The consumption of hot water represents a significant portion of national energy consumption and contributes to concerns associated with global climate change. Utilizing heat recovered from the sewer, or the stored heat by utilizing heat pumps with a borehole geothermal energy storage system, are simple and effective ways of heating water for domestic purposes. Reclaiming heat from the waste warm water that is discharged to the sewer or stored heat in a borehole geothermal energy storage system can help reduce natural gas energy consumption as well as the associated energy costs and greenhouse gas emissions. In this paper, sewer waste heat recovery is compared with heat pumps using geothermal energy storage systems for a small community shared water heating system including commercial and institutional buildings. It is found that the sewer heat exchanger method is relatively economical as it has the smallest rate of return on investment for the selected community size. The findings also demonstrate a reduction occurs in natural gas consumption and fewer CO₂ gas emissions are emitted to the atmosphere. The results are intended to allow energy technology suppliers to work with communities while accounting appropriately for economic issues and CO₂ emissions associated with these energy technologies.