Subsidies required for installing renewable energy supply systems considering variations in future climate conditions

 

1. Introduction

Sweden passed legislation to attain 100% renewable electricity production along with net zero greenhouse gas emissions targets by 2040 and 2045, respectively. The targets were set as a response to international agreements about mitigating environmental impacts. To fulfil these targets, drastic action should be taken in the form of adoption and mitigation policies in several sectors. The building sector is expected to play a fundamental role in achieving the national targets, as buildings make up about 24% of the final energy consumption and 8.5% of the total carbon dioxide emissions 40% of which comes from detached houses. The majority of detached houses in Sweden were built between 1960 and 1980; accordingly, they demonstrate poor energy performance due to technical deteriorations in heating, ventilation, and air conditioning systems as they approach the end of their expected lifetimes. Furthermore, they were built before strict energy codes came into play in Sweden; therefore, they are in need of energy renovations to conform to current Swedish energy codes. Thus, energy renovations of detached houses are essential in order to achieve national targets. The implementation of energy renovations should follow two main considerations. The first revolves around the energy consumption of detached houses after renovation to satisfy national energy codes. Former studies analysed and compared the implications of different renovation packages on primary and total energy use under several uncertainties. 

2. Materials and methods

The detached house used in the study was located in climate zone III in Växjö Municipality, Sweden. The National board of housing building and planning specified four climate zones in Sweden, with climate zone I representing the coldest, northernmost zone, while climate zone IV represents the warmest, southernmost zone. The detached house was a pre-fabricated timber-frame house of 140 m2, built in 1979. This detached house was selected since the majority of detached houses in Sweden were built between 1960 and 1980. According to Statistics Sweden about 1.2 million detached houses were built between 1960 and 2010, from which 60% were constructed from 1960 until 1980. The pre-fabricated timber-frame house have mainly poor energy consumption than concrete or site-built timber-frame houses, built before 1980. Because, air leakages of the pre-fabricated timber-frame house are generally higher . Information, required for evaluating the energy performance of the detached house was provided by house owners. These information comprise the thermal transmittance of the building envelopes, occupancy schedule, heating and ventilation systems, energy efficient renovations, which were previously implemented by house owner. The average total energy consumption of the detached houses (built between 1960 and 1980) was about 110 kWh/m2 

2.1. Energy supply systems

Three different energy supply systems were considered and their performances regarding reducing the total energy use of the detached house were analysed. The first energy supply system was an air-to-water heat pump (AWHP) with a coefficient of performance (COP) of 3 and a heating capacity of 11.7 kW. The lifetime of the AWHP was assumed to be 15 years. The second supply system included a ground-source heat pump (GSHP) with a COP of 3, a heating capacity of 12.5 kW, and a lifetime of 15 years. The third energy supply system comprised an integrated GSHP with photovoltaic solar panels (GSHP-PV). The GSHP used for the integrated supply system was identical to the first energy supply system. In total, 23 photovoltaic (PV) panels with a total area of 38 m2 and an output power of 6.6 kW were installed on the south-sloping roof with a 45° tilt towards the south. The output power of each panel was 285 W