Maximizing Thermal Energy Recovery from Drinking Water for Cooling Purpose

Jawairia Imtiaz Ahmad,Jan Peter Van Der Hoek,Sara Giorgi,Gang Liu,Ljiljana Zlatanovic

doi:10.3390/en14092413

Abstract

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 (Tmax) 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 Tmax up to 30 °C is safe in terms of microbiological risks. The present research was carried out to determine what raising Tmax 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 Tmax is currently set at 15 °C. Tmax 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 Tmax 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 Tmax will substantially increase the TED potential of DWDN while keeping the same comfort level at the customer’s tap.

Highlights

Resource recovery from the water cycle is gaining much attention
Thermal energy recovered from drinking water for cooling can be used to provide either free cooling or if drinking water is not cold enough to provide the full load and quality of cooling needed, can be used as a pre coolant or act as a condensing fluid in chillers to produce higher quality cold with a better chiller Coefficient of Performance (COP) [25]
This study examined thermal energy recovery from drinking water in a non-chlorinated drinking water distribution system with a focus on maximizing the recovered energy for cooling purposes

Summary

Introduction

Resource recovery from the water cycle is gaining much attention. The focus is much on materials from wastewater, such as nutrients, carbon, energy in the form of biogas and water itself [1,2,3]. The thermal energy from sewage water and wastewater treatment plant effluent has been pointed at as a valuable resource [5,6]. The potential of thermal energy recovery from the water cycle, including wastewater, surface water, groundwater and drinking water, has been estimated for Amsterdam and its surroundings, focusing on the possibilities to reduce carbon emissions [8,9,10,11]. A specific thermal energy source appeared to be the cold water in the drinking water distribution network [12]. Depending on the drinking water temperature in the network, it can be used for both heating and cooling purposes

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