Maximizing Thermal Energy Recovery from Drinking Water for Cooling Purpose

• Main Authors: Jawairia Imtiaz Ahmad, Sara Giorgi, Ljiljana Zlatanovic, Gang Liu, Jan Peter van der Hoek
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: Energies
• Subjects: energy transition; cold recovery; cooling; carbon footprints reduction; drinking water distribution networks; greenhouse gas emissions
• Online Access: https://www.mdpi.com/1996-1073/14/9/2413

Drinking water distribution networks (DWDNs) have a huge potential for cold thermal energy recovery (TED). TED can provide cooling for buildings and spaces with high cooling requirements as an alternative for traditional cooling, reduce usage of electricity or fossil fuel, and thus TED helps reduce greenhouse gas (GHG) emissions. There is no research on the environmental assessment of TED systems, and no standards are available for the maximum temperature limit (T_max) after recovery of cold. During cold recovery, the water temperature increases, and water at the customer’s tap may be warmer as a result. Previous research showed that increasing T_max up to 30 °C is safe in terms of microbiological risks. The present research was carried out to determine what raising T_max would entail in terms of energy savings, GHG emission reduction and water temperature dynamics during transport. For this purpose, a full-scale TED system in Amsterdam was used as a benchmark, where T_max is currently set at 15 °C. T_max was theoretically set at 20, 25 and 30 °C to calculate energy savings and CO₂ emission reduction and for water temperature modeling during transport after cold recovery. Results showed that by raising T_max from the current 15 °C to 20, 25 and 30 °C, the retrievable cooling energy and GHG emission reduction could be increased by 250, 425 and 600%, respectively. The drinking water temperature model predicted that within a distance of 4 km after TED, water temperature resembles that of the surrounding subsurface soil. Hence, a higher T_max will substantially increase the TED potential of DWDN while keeping the same comfort level at the customer’s tap.