# Multi-Objective Optimization of Hybrid Renewable Tri-Generation System Performance for Buildings
###### Abstract
Annex 54 took a close look at multi-source micro-cogeneration systems, poly-generation systems, renewable hybrid systems, and analysis of integrated and hybrid systems performance when serving single and multiple buildings [35]. Some researchers have studied hybrid systems employing MCHP, geothermal and other renewable sources. [PERSON] [11] reported experimental results of a residential tri-generation system using an internal combustion engine and ground source heat pump. [PERSON] [36] studied a trigeneration system for a sewage treatment plant under subtropical weather conditions and showed that the use of an absorption chiller provided the highest thermal efficiency and shortest payback period. Recently, advanced design concepts have been introduced in buildings, significantly reducing heating and cooling loads. In Europe, the passive house concept has established standards for low-energy buildings, such as airtightness \(\leq\)0.6 air change per hour (ACH) and a maximum residential dwelling heating load of less than 15 kWh/m\({}^{2}\)-yr [37]. [PERSON] et al. [38] investigated the thermal performance of an integrated air-air heat exchanger (AAHE) and Earth-Water Heat Exchanger (EWHE) in a multi-zone passive house. The main conclusion was that AAHE and EWHE systems reduced annual heating consumption by 72% with an energy intensity of 6.9 kWh/m\({}^{2}\)-yr. The effect of the earth tube heat exchanger on the energy savings for a single house, a row-house, and a small office were investigated [39] under three different climate conditions. The simulations showed that the energy-saving increased from 2.2 to 9.4 kWh/m\({}^{2}\) for the single house and from 1.3 to 4.1 kWh/m\({}^{2}\) for the row house. The geothermal system was able to save 43% and 37% of the primary energy consumption during the heating and cooling seasons [40]. [PERSON] et al. [41] studied a novel renewable trigeneration plant powered by solar, geothermal and biomass energy, producing simultaneously electricity, heating and cooling. Additionally, they implemented a dynamic simulation of a thermo-economic optimization of the polygonation plant. Furthermore, [PERSON] et al. [42] conducted a dynamic simulation of a trigeneration system integrating an absorption cooling system and photovoltaic thermal solar collectors. The total efficiency of the trigeneration system was 18%, with an annual solar fraction of 28%. In addition, [PERSON] et al. [43] developed a simulation model to investigate the integration of a concentrated solar Organic Rankine Cycle with an absorption chiller for residential applications. Furthermore, [PERSON] et al. [44] conducted a feasibility study for zero office buildings using integrated trigeneration and PVT systems. System optimization is an important part of technology design and operation. There are a variety of programming techniques that can be applied depending on problem complexity: linear programming [45; 46], mixed-integer linear programming [47; 48; 49; 50; 51; 52] and mixed-integer nonlinear programming [53; 54; 55; 56; 57]. [PERSON] et al. [47] used mixed-integer linear programming techniques (MILPT) to select, size and control the optimal parameters of building energy systems, whereas [48] used MILPT to select the optimal building's utility system. [PERSON] and [PERSON] [53] applied multi-objective optimization as an alternative to the combination of mixed-integer nonlinear programming and the evolutionary algorithms approach. The current study aims to fill a gap in the literature by estimating the optimum design parameters of the hybrid renewable tri-generation system of integrated AWHP, PVT and GAHX technologies using dynamic simulation based on a multi-objective optimization model to minimize both system cost and environmental impact. A multi-objective optimization model is developed using General Algebraic Modeling System (GAMS) techniques and is coupled with the TRNSYS model. The hybrid system performance, employing the optimum design parameters, is evaluated under a variety of conditions and operational strategies.