Perspectives of a climate-neutral urban district : Evaluation of greenhouse gas emissions, exergy and energy balances

Abstract: A climate-neutral city can be viewed at in many different aspects. This report investigates the greenhouse gas, exergy and energy balance for both heat pumps and district heat supply at local, national and methane gas perspectives of the energy conversion processes. Through a numerical grey box model of a geographical information system based urban district. There seven different passive-, nearly zero-, and plus-energy residential buildings are implemented. That are developed and annually simulated in the IDA ICE software. There, thermal transmittance and building geometry are the most urgent parameters that impacts the space heating demand and energy performance. They are estimated by current and proposed primary energy weight factors where the geometry shape is undefined, while the altitude impact’s the building's energy, exergy, and greenhouse gas balance. Therefore high-rise building's energy performance are poorer than low-rise buildings, simultaneously as heat pump supply enables higher altitude than district heating. Other energy savings occur through additional energy-efficient technologies, energy generating technologies and soft tools that change residents’ behavior. The investigated urban district is placed in the Swedish city Gävle, which meets residents’ demand for approximately 6000 apartments without additional service. It is a plus energy district for heat pump supply and passive energy for district heating supply. Although the district heated urban district electricity-saving towards heat pump corresponds to 32 percent of the urban district's total facility and household electricity utilization. The energy analysis include the perspective of the facility’s energy utilization and generation, and the perspectives of residents’ energy utilization and recovery from their waste resource production. This makes the urban district exergy productive and carbon-negative during the operating phase, regardless of emission value and heat supply technology, since the facility perspective compensates for the residents’ electricity utilization and consumption of goods. Therefore, there are no need for tree plantation as compensation of greenhouse gas pollution since the carbon negativity corresponds to between 2 to 154 hectares of forest. The study is therefore relevant for other geographical locations in Sweden depending on geographical location, heat supply technology and emission value from the primary energy conversion processes.