## 1 Introduction  
Buildings consume more than 40% of the total primary energy in developed countries, with approximately 70% of the buildings' energy demand being for space heating and domestic hot water [1]. Due to Canada's cold climate and its heavy reliance on fossil fuels for heating [2], cutting the greenhouse gas emissions (GHG) due to space and water heating is crucial to meet the country's national GHG emissions targets and international commitments under the Paris Climate Agreement [3]. The City of Surrey, in British Columbia, is one of the fastest-growing cities in Canada and has recently launched a district energy network (DEN) to supply hot water for more than 250,800 m\({}^{2}\)[4] of various residential and commercial buildings in the Surrey Centre area for space and domestic hot water heating. The network currently runs on natural gas boilers and geothermal exchange with highly insulated pipes to move hot water to various buildings, and exchanges energy using heat exchangers located at the customer side. Integrating renewable and low carbon energy sources in district heating and cooling is vital to meet rising urban energy needs [5]. Surrey aims to improve energy efficiency, reduce GHG emissions, increase resilience and provide competitive pricing by using the DEN as a key development in reaching its GHG reduction targets in the building sector [6]. Low carbon Surrey DEN will be a collective energy system that employs multiple renewable energy technologies, e.g., biomass boilers, solar thermal and waste heat recovery. Using renewables and low-energy sources in DENs is a strategy that many communities are following to decarbonize heat productions; for example, (i) Aarhus, Denmark: electric boiler and heat pump for district heating [7], (ii) London Olympic Park, Great Britain: biomass boilers [8], (iii) Ulm, Germany: replacement of fossil fuel plants with biomass plants [9]. Other examples of using low-carbon energy sources in district heating and cooling can be found in the IRENA case studies report [10].  
Utilizing waste heat from industrial sites is a potential technology that Surrey is considering as a possible low carbon energy source. In this paper, a techno-economic analysis (TEA) has been performed to determine the potential emission reduction of integrating industrial waste heat (IWH) into Surrey's DEN using a mobile thermal energy storage (M-TES), to capture, store and move excess heat from industrial locations to the Surrey district heating network. M-TES consists of a truck and thermal energy storage system.  
One way to connect IWH and DEN is the use of pipelines, e.g., one Chinese city, Anshan, aims to limit the use of heavily polluting coal by a projected 1.2 million tons per year through connecting its district energy networks to capture waste heat from a local steel plant [11]. However, the cost of pipelines and the complexity of the system significantly increases when waste heat sources are in multiple areas and away from the DEN. Pipeline connections require a huge upfront cost, which limits the collection of waste heat from multiple locations to multiple DENs. On the other hand, storing and moving thermal energy in a truck using M-TES is a flexible option with a lower upfront cost [12]. Moreover, due to the Fraser river in Surrey district energy network case study, the pipeline option is not possible.  
The TEA presented here examines scenarios for integrating industrial waste heat in terms of (i) locations (distance); (ii) transportation modes; and (iii) the energy storage densities of the targeted M-TES technologies. The goal is to assess the feasibility, cost-effectiveness, and overall environmental impact. The TEA also helps in estimating GHG emission savings in \(\text{tCO}_{\text{2e}}/\text{MWh}\), estimates the useful heat from M-TES [MWh/year], and establishes target prices [5/MWh, 5/\(\text{tCO}_{\text{2e}}\) avoided] that makes the proposed M-TES system economically viable.