District energy systems, especially those integrating renewables or low exergy sources, have multiple elements for generating heating and cooling. Some of these elements might be used for both purposes: heating and cooling, either simultaneously or alternatively. This makes it more complex to separate the assessment and have a clear picture on performance of cooling service on one side, and heating services on the other, in terms of energy, environmental, and economic results. However, a correct comparison between different district energy configurations or among district energy and conventional solutions requires split assessment of each service. The paper presents a methodology for calculating different district heating and cooling system key performance indicators (KPIs), distinguishing between heating and cooling ones. A total of eleven indicators are organized under four categories: energy, environment, economy and socio-economy. Each KPI is defined for heating service and for cooling service. According to this, the methodology proposes a demand-based and an investment-based share factors that facilitate the heating and cooling KPI calculation.

Two‐dimensional finite difference calculations are carried out to study laminar flow in longitudinal and transverse convection rolls for three different geometries: a single rectangular cavity with high aspect ratio; a double cavity with a thin separation sheet; and a double cavity with a separation sheet and a honeycomb structure. The equations for the convection‐diffusion in the fluid and conduction in the solid region are solved simultaneously. Good agreement with experimental data is achieved for Rayleigh numbers not too high above the critical value for the onset of secondary convection rolls (Ra < 8500 for vertical and Ra < 2700 for horizontal cavities filled with air). Simulation fails for inclined cavities, where the flow structure is essentially three‐dimensional.

The roofs of residential buildings represent a relevant potential for the construction of photovoltaic panels. Given that roof structures are passive, the construction of photovoltaic systems on residential buildings does not interfere with the functionality of the building, nor do they affect the environment in any other way. By installing photovoltaic systems on the roofs of residential buildings, the production and consumption of electricity are brought closer to the maximum possible extent, so such systems ensure a significant reduction of electricity losses in the distribution and transmission network. This paper presents the results of research aimed at establishing a framework for decentralized and decarbonized production of electricity from photovoltaic systems integrated into the roofs of residential buildings in Serbia, through the support of the prosumer approach. For each defined category of residential building in Serbia, the possible annual production of electricity per unit of average roof area was estimated. Summarizing all the results, assessments of the possible installed capacity of photovoltaic systems and annual electricity production at the national level were made.