## 2 Literature Review  
Previous studies have demonstrated the economic and the environmental potential of micro-CHP for residential. [PERSON] [4] designed a CHP system which relies on specifications of all equipment, maps, dimensions and equipment layout to prove the feasibility of using CHP in the factories of a manufacturing company in the Tehran Special Economic Zone, Tehran. The company reduced the total cost by 39.07% in comparison with the generation of electricity and heat separately. [PERSON] et al. [5] took into the simulation that micro-CHP-based Canadian Hybrid Residential End-Use Energy and GHG Emissions Model (CHREM) retrofit yields 13% energy savings and the total GHG emissions of the CHS would be reduced by 35%. This study indicates that ICE-based CHP system retrofits may provide an economically feasible opportunity. The micro-CHP systems have an advantage of total costs. Meanwhile, the micro-CHP system allows for a reduction of the equivalent carbon dioxide emissions and a reduction of the primary energy consumption in comparison to the conventional system. [PERSON] [6] applied a genetic algorithm based on optimization strategy of high-temperature PEMFC micro-CHP systems to place emphasis on generating power. The thermal efficiency and total system efficiencies are about 50% and 91%, respectively. A micro-CHP system integrated with geothermal-assisted methanol reformed and incorporated a PEMFC stack [7] such that the annual total cost-saving ratio can reach 20.9% considering methanol price, hydrogen price and service life. It shows that the micro-CHP achieves thermodynamic and economic potential, and provides an alternative way for efficiently using clean energy resources. [8,9]made a technical and economic analysis on the micro-CHP system of PEMFC and solid oxide fuel cell (SOFC) for single-family residence. The results pointed out that the total efficiency of the SOFC system is 6% higher than that of the PEMFC system. However, from an economic point of view, the payback period of the SOFC system investment is longer than that of PEMFC system in economic terms because its investment cost is not competitive. Finally, it is concluded that the KW-level PEMFC micro-CHP system is suitable for residential that consumes more electricity and heat. The internal combustion-based micro-CHP application in residential buildings in Korea has an advantage in terms of energy-saving and CO2 reduction compared to the baseline model with grid power and a gas-fired boiler systems [10]. However, the price difference between electricity and gas is a hurdle to implement for economic feasibility of micro-CHP applied in residential. In China, gas prices have an advantage when electricity prices peak using power generated by micro-CHP systems to replace electricity bought from the grid [4]. [PERSON] et al. [11] provided sensitivity analysis of the internal combustion-based CCHP system with biomass and gas fuel. They show that compared with biomass prices, natural gas prices have a greater impact on the exergy cost per unit product. The configuration of micro-CHP is an area that needs to be considered in terms of the economy. It is necessary to find the optimal design of power generators and thermal storage to minimize daily management costs and environmental impact. [PERSON] and [PERSON] [12] proposed a thermal economy model for the effect of carbon tax, which is used to select the appropriate ICE for the CHP system. The economy of micro-CHP also needs to focus on the importance of correctly sizing and designing a micro-CHP residential installation including the TES system, engine power, and the demand for DHW accumulation [2]. Moreover, a reasonable solution has been complemented with the economic yield each micro-CHP provides. It avoids energy waste reduction and saves daily energy cost. Its economic value depends on the NPV and payback period [3]. [PERSON] [13] studied the impact of ICE capacity at different working hours on the payback period of the CCHP system.