Exergoeconomic optimization of a district cooling network

Abstract

A district cooling system (DCS) is superior to conventional air conditioning as it helps to reduce energy consumption and protect the environment by reducing carbon dioxide emissions. The main disadvantages of a DCS are the high initial investment costs and the long payback period. The distribution network (DN) represents a large share of initial investment costs; therefore, it has a great impact on the decision to construct a DCS. In order to ensure the competitiveness of DCS, the DN has to be optimized. In this paper the exergoeconomic concept is applied to evaluate a DN in a DCS. The objective function in the analysis is defined as the exergy based cost of the final product-cold. The exergy-based cost of cold depends on the total annual cost of a DN, the input exergy to the DN, the exergy losses and the exergy destruction. The aim of this study is to find the exergetic optimal pipe diameter and the insulation thickness, as well as the exergoeconomic optimal pipe diameter and the insulation thickness. The analysis was made for different cooling capacities and for two types of pipes: pre-insulated steel pipes, where the insulation material is polyurethane, and polyethylene pipes, without any insulation.

Sustainable District Cooling Systems: Status, Challenges, and Future Opportunities, with Emphasis on Cooling-Dominated Regions

“…The DC system design and analysis studies in Table 1 have focused on energy analyses, except for Coz et al [39], who evaluated DC system performance based on exergy and exergoeconomic analyses. Although still limited in number, exergy-based analyses of combined district heating and cooling systems in heating-dominated regions have received more attention [39,111].…”

“…The DC system design and analysis studies in Table 1 have focused on energy analyses, except for Coz et al [39], who evaluated DC system performance based on exergy and exergoeconomic analyses. Although still limited in number, exergy-based analyses of combined district heating and cooling systems in heating-dominated regions have received more attention [39,111]. Energy-related DC operating and performance parameters typically include annual cooling energy supplied, maximum cooling load supplied over the operational life consumed, central chiller plant COP, annual energy consumption, chilled water supply temperature, design chilled water temperature difference, average chilled water temperature difference achieved, and distribution system makeup water rate (% of circulation) [10].…”

“…Rezaie et al [12] presented a generic district enviro-economic function to extend investment and operating costs to business environmental costs, including carbon tax and carbon benefits. The exergoeconomic cost of cooling was only evaluated in one study [39].…”

“…An overview of DC system optimizations [22,24,25,32,35,37,39,121,122], with emphasis on studies for cooling-dominated regions, is presented in Table 4. Most of these studies [22,24,25,32,122] have focused on the optimization of the DC distribution network infrastructure, which represents substantial investment, to investigate possible distribution pipeline designs and network configuration alternatives that would reduce piping capital and installation costs, and pumping energy cost.…”

“…Most of these studies [22,24,25,32,122] have focused on the optimization of the DC distribution network infrastructure, which represents substantial investment, to investigate possible distribution pipeline designs and network configuration alternatives that would reduce piping capital and installation costs, and pumping energy cost. Coz et al [39] extended these efforts to exergetic and exergoeconomic optimizations of a DC distribution pipeline network. Note: DCS-district cooling system; GA-genetic algorithm; GFA-gross floor area; MILP-mixed integer linear programing; MTR-mass-transit railway; (1) Algebraic sum of water flow of all branches connected to one nodal point is zero;…”