Modelling the potential for multi-location in-sewer heat recovery at a city scale under different seasonal scenarios

Abstract

A computational network heat transfer model was utilised to model the potential of heat energy recovery at multiple locations from a city scale combined sewer network. The uniqueness of this network model lies in its whole system validation and implementation for seasonal scenarios in a large sewer network. The network model was developed, on the basis of a previous single pipe heat transfer model, to make it suitable for application in large sewer networks and its performance was validated in this study by predicting the wastewater temperature variation across the network. Since heat energy recovery in sewers may impact negatively on wastewater treatment processes, the viability of large scale heat recovery was assessed by examining the distribution of the wastewater temperatures throughout a 3000 pipe network, serving a population equivalent of 79500, and at the wastewater treatment plant inlet. Three scenarios; winter, spring and summer were modelled to reflect seasonal variations. The model was run on an hourly basis during dry weather. The modelling results indicated that potential heat energy recovery of around 116, 160 & 207 MWh/day may be obtained in January, March and May respectively, without causing wastewater temperature either in the network or at the inlet of the wastewater treatment plant to reach a level that was unacceptable to the water utility.

Energy Recovery from Wastewater: A Study on Heating and Cooling of a Multipurpose Building with Sewage-Reclaimed Heat Energy

“…If recovery is too high, wastewater temperature drop may be significant, and may have adverse consequences on the efficiency of treatment processes, reducing carbon and especially nitrogen removal rates, and inducing the need to upgrade the possible treatment units. All these situations require a preliminary facility assessment to determine the limits to which wastewater heat energy recovery can be carried out without impairment [19]; recently, modeling has been proposed as a solution to evaluate the amount of heat that can be recovered from wastewater without harming the biological processes in WRRFs [38][39][40].…”

Operation Algorithms and Computational Simulation of Physical Cooling and Heat Recovery for Indoor Space Conditioning. A Case Study for a Hydro Power Plant in Lugano, Switzerland

“…[18]. Another popular application is heat recovery from waste water (drain water) [19][20][21]. Finally, among the scientific literature an article proposing a novel heat recovery system for a variable refrigerant flow (VRF) system is also presented in [22].…”

“…The recovered heat surplus: q sur = q r − q Rth (21) from thermal zone 1 is disposed in the ambient. The mass flow rate from the circulation fan will beṁ Rmax .…”

In-building heat recovery mitigates adverse temperature effects on biological wastewater treatment: a network-scale analysis of thermal-hydraulics in sewers

“…In addition to expanding the temporal scope of thermal-hydraulic investigations, studying the impacts of in-building alterationsfor instance an energy efficiency measure or a heat recovery installationrequires an additional extension of their spatial scope. Some authors have led network-wide analyses in the context of sewer-level heat recovery (Abdel-Aal et al 2018, Abdel-Aal et al 2019. However, existing thermal-hydraulic models such as TEMPEST (Dürrenmatt and Wanner 2014) generally do not allow thorough system-level investigations due to their inability to simulate full sewer networks, from the household to the treatment plant.…”