C013 -- District Feasibility Assessment for Wastewater Heat Exchanger Integrated Ground Source Heat Pump System

Extracting heat from a sewage pipe through a horizontal ground heat exchanger has recently been introduced as a renewable energy alternative to reduce fossil fuel usage. A recent technology has been developed for extracting and injecting heat into a wastewater line called a wastewater heat exchanger (WWHX). A WWHX is a hollow concrete cylinder with a helical high-density polyethylene pipe embedded within the concrete pipe walls where heat is captured from effluent in sanitary and storm sewer pipes, and from the earth surrounding it. The main objective of this study was to evaluate the feasibility of utilizing a WWHX to heat and cool multiple buildings connected to a shared pipe. Additionally, the amount of auxiliary ground heat exchanger needed to supplement the system was investigated. To determine the feasibility of utilizing the WWHX, detailed hourly energy models of two residential homes were created and used to determine the peak and total monthly energy demand. Next, a thermal energy model was created to determine the amount of energy that could be extracted from and injected into the WWHX on an hourly basis. The amount of energy was then compared to the annual heating and cooling demand of the residential homes to determine if an auxiliary heating or cooling source was needed. Based on the results, to meet the incremental heating demand of the two homes, it was determined that seven additional slinky loops of 390 ft (118 m) connected to the WWHX are needed. The minimum annual temperature of the wastewater in the WWHX was 47.1°F (8.4°C) on February 8th. The maximum temperature was 62.1°F (16.7°C) on August 1st. The outcome of this study is a designed solution for replacing conventional fossil fuel consuming residential heating and cooling systems that can be implemented worldwide to assist in reaching CO2 emission targets and fight climate change.