Branimir Pavković

A numerical and experimental investigation of the dynamic behavior of a heat pump

A dynamic numerical model of a compression vapor cycle heat pump is presented. The model is based on mass and energy balances, thermodynamic and thermal properties of the working fluid and constructive characteristics of heat pump components. The model enables the prediction of temporal and spatial distribution of refrigerant temperatures, pressures and mass flows, as well as water temperatures for variable boundary conditions that occur during the heat pump operation. Experimentation has been performed on a laboratory test rig. Refrigerant pressures and temperatures, compressor electric power consumption, as well as water temperatures and mass flows were measured. The measurement of dynamic operating conditions was successfully performed using the data acquisition system controlled by personal computer. The use of graphic interface enabled analyses of working conditions at operating limits of the heat pump. Results of the dynamic heat pump model were confirmed by comparison with experimental data.

Tehno-ekonomska opravdanost zamjene sustava odvojene proizvodnje toplinske/rashladne i električne energije CCHP sustavom s mikroturbinom i apsorpcijskim rashladnim uređajem

Original scientific paper The system of separate production of heat energy from a boiler and cooling energy from a compression refrigeration unit powered with electrical energy from an external network can be replaced with a CCHP system based on the operation of a gas turbine and absorption refrigeration unit. For this purpose, models of the system were derived through the use of the object-oriented programming language Modelica, on the basis of which steady-state simulations were carried out, as well as technical-economic and the sensitivity analysis of the system, in relation to the changes of influential parameters such as coefficient of performance, the boiler efficiency, the ratio of the electric load, costs of electrical energy, fuel prices and investment costs. Developed system model is intended to be used in further research for dynamic simulations with implemented dynamic boundary conditions.

Investigation on possibilities for biogas production from organic waste on the Croatian island of Krk

The subject of this paper is the analysis of the possibilities of using biodegradable municipal and agricultural waste in a biogas energy production facility on the island of Krk. The main characteristic of this type of waste is the variable composition. The total amount of municipal waste on the largest Croatian island of Krk is relatively small in comparison to cities. Particularly significant is the high variability of feedstock volumes depending on the period in the year. As a result, the biogas production is unstable and varies on a monthly basis. To overcome that situation a scenario with two cogeneration units was compared to a scenario when only one unit is used. The approach of two units, that operate based on the available biogas inflow, has shown to be more efficient than using a single unit. Net GHG emissions are negative.

Modelling, Simulation and Optimization of smalscalle CCHP energy systems

The article defines and discusses techno-economic models of CCHP system based on a power system with an internal combustion engine or a gas turbine with electric power of 0, 2–1 MW including an absorption or vapour-compression refrigeration unit. The thermodynamic, ecological and economical features of the CCHP system under different load situations are analysed in relation to the basic model of energy generation with boiler and vapour-compression refrigeration unit. Based on the data of the equipment manufacturer, functional dependency curves of individual components are created in dependency to the load, which enables the construction of a system model composed of a power system (internal combustion engine or a gas turbine), single-stage or two-stage absorption refrigeration unit and boiler. A program solution has been developed applying the object-oriented programming language Modelica that enables the insight into the behaviour and techno-economic validity of usage of the analysed systems in transformable operating conditions. The article examines various energetic models, defining for the influential parameters (electric energy and fuel prices, investment costs and the level of heat recovery) the value of total energy efficiency, the return period on investment costs and the environmental impact concerns.