ExRET-Opt: An automated exergy/exergoeconomic simulation framework for building energy retrofit analysis and design optimisation

doi:10.1016/j.apenergy.2017.02.006

Applied Energy

Volume 192, 15 April 2017, Pages 33-58

https://doi.org/10.1016/j.apenergy.2017.02.006 Get rights and content

Highlights

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Development of a building retrofit-oriented exergoeconomic-based optimisation tool.
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A new exergoeconomic cost-benefit indicator is developed for design comparison.
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Thermodynamic and thermal comfort variables used as constraints and/or objectives.
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Irreversibilities and exergetic cost for end-use processes are substantially reduced.
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Robust methodology that should be pursued in everyday building retrofit practice.

Abstract

Energy simulation tools have a major role in the assessment of building energy retrofit (BER) measures. Exergoeconomic analysis and optimisation is a common practice in sectors such as the power generation and chemical processes, aiding engineers to obtain more energy-efficient and cost-effective energy systems designs. ExRET-Opt, a retrofit-oriented modular-based dynamic simulation framework has been developed by embedding a comprehensive exergy/exergoeconomic calculation method into a typical open-source building energy simulation tool (EnergyPlus). The aim of this paper is to show the decomposition of ExRET-Opt by presenting modules, submodules and subroutines used for the framework’s development as well as verify the outputs with existing research data. In addition, the possibility to perform multi-objective optimisation analysis based on genetic-algorithms combined with multi-criteria decision making methods was included within the simulation framework. This addition could potentiate BER design teams to perform quick exergy/exergoeconomic optimisation, in order to find opportunities for thermodynamic improvements along the building’s active and passive energy systems. The enhanced simulation framework is tested using a primary school building as a case study. Results demonstrate that the proposed simulation framework provide users with thermodynamic efficient and cost-effective designs, even under tight thermodynamic and economic constraints, suggesting its use in everyday BER practice.

Introduction

Improving building energy efficiency through building energy retrofit (BER) is one of the most effective ways to reduce energy use and associated pollutant emissions. From an economic and environmental perspective, energy conservation and efficiency measures could hold greater potential than deployment of renewable energy technologies [1]. Computational modelling and simulation plays an important role in understanding complex interactions. Building performance modelling and simulation is a fast flourishing field, focusing on reliable reproduction of the physical phenomena of the built environment [2]. Several retrofit-oriented simulation tools have been developed in the last two decades, commonly using as the main energy calculation engine open source tools such as DOE 2.2® [3] and EnergyPlus® [4]. Among the most recent developments are ROBESim [5], CBES [6] and SLABE [7]. Rysanek and Choudhary [8] developed an exhaustive retrofit simulation tool by coupling the transient simulation tool TRNSYS® [9] with MatLab® [10], having the capability to simulate large set of strategies under economic uncertainty.

Additionally, building energy design optimisation, an inherently complex, multi-disciplinary technique, which involves many disciplines such as mathematics, engineering, environmental science, economics, and computer science [11], is being extensively used in building design paractice. Attia et al. [12] found that 93% of multi-objective optimisation (MOO) research is dedicated to early design; however, some studies have also demonstrated the strength of MOO for BER projects [13], [14], [15]. Improvement of the envelope, HVAC equipment, renewable generation, controls, etc., while optimising objectives, such as energy savings, occupant comfort, total investment, and life cycle cost have been investigated. Among the most notable contributions in applying MOO to BER design was Diakaki et al. [16]. The authors investigated the feasibility of applying MOO techniques to obtain energy-efficient and cost-effective solutions, with the objective of including the maximum possible number of measures and variations in order to facilitate the project decision making. To date, the most popular available MOO simulation tools are GenOpt, jEPlus, Tpgui, Opt-E-Plus, and BEOpt. Taking the advantages from these tools, retrofit-oriented optimisation studies have become more common in the last decade, considering different decision variables (retrofit measures), objective functions, and constraints, while also investigating a wide range of mathematical algorithms.

Section snippets

Exergy and buildings

Although widely accepted at scientific and practical levels in building energy design, typical energy analysis (First Law of Thermodynamics) can have its limitations for an in depth understanding of energy systems. Energy analysis cannot quantify real inefficiencies within adiabatic processes and considers energy transfers and heat rejection to the environment as a system thermodynamic inefficiency [17]. The main limitation of the First Law is that it does not account for energy quality, where

Calculation framework

The basic exergy and exergoeconomic formulae together with an abstraction of the building energy supply chain has been presented in previous publications [57], [58]. In this paper, the methodological calculation has finally been integrated into a software, where the modules details will be presented in the following sections.

ExRET-Opt simulation framework

ExRET-Opt, a simulation framework consisting of several software subroutines, was developed combining different modelling environments such as EnergyPlus, SimLab® [64], Python® [65], and the Java-based jEPlus® [66] and jEPlus + EA® [67]. This software was chosen for four main reasons:

a.
Open source software that can be modified and adapted according to the research necessities.
b.
EnergyPlus was selected for First Law analysis as it is the most widely used building performance simulation programme in

ExRET-Opt subroutines verification

To ensure that ExRET-Opt is reliable, a validation or verification process is necessary. Due to lack of empirical exergy data, both an ‘Inter-model Comparison’ using an existing tool and an ‘Analytical Verification’ using various case studies found in the literature, are performed.

Case study and baseline values

To demonstrate ExRET-Opt capabilities, this has been applied to recently retrofitted primary school building (1900 m²) located in London, UK. The simulation model consists of a fourteen-thermal zone building. The largest proportion of the floor area is occupied by classrooms, staff offices, laboratories, and the main hall. Other minor zones include corridors, bathrooms, and other common rooms. Heating is provided by means of conventional gas boiler and high temperature radiators (80 °C/60 °C) with

Conclusions

This paper presented ExRET-Opt, a retrofit-oriented simulation framework, which has become a part of EnergyPlus in performing exergy and exergoeconomic balances. The addition was done thanks to the development of external Python-based subroutines, and the support of the Java-based software jEPlus. ExRET-Opt, apart from providing the user with exergy data and pinpointing sources of inefficiencies along the energy supply chain, gives the possibility to perform a comprehensive exploration of a

Acknowledgments

The first author acknowledges support from The Mexican National Council for Science and Technology (CONACyT) through a scholarship to pursue doctoral studies with a CVU: 331698 and grant number: 217593.

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