Juozas Bielskus

EXPRESSING THE BUILDING ENERGY SYSTEMS THERMODYNAMIC SEASONAL EFFICIENCY

In order to reduce impact to environment, a qualitative approach of energy saving is global aspect that is included in various forms of CO 2 emissions, primary energy limitations and benchmarks in EU and member countries policy. Exergy analysis allows expressing the quality of energy flows in comparison to ambient or other reference conditions. Despite of this valuable information, this concept is not widely used in engineering practice. The article suggests the calculation procedure for sessional or periodical thermodynamic (exergy) efficiency in relation to variable reference conditions. Knowledge about defined procedures unlocks the possibility to fill up the implementation gap for building system engineering practice where seasonal performance parameters are widely used to express efficiency. Prepared algorithm allows determining seasonal or periodic thermodynamic efficiency of individual elements and energy transfer chains in building energy systems. Defined calculation procedure workflow is suitable for integrated approach when coupled heat transfer and fluid flow processes are explored in short time steps with dynamic simulation software tools. Presented algorithm ensures result that fits in thermodynamically correct range 0-1 and helps to summarize separate time step results. By adding duration of specific conditions, this analysis enables to identify critical peak periods and base load conditions across operation period. The presented framework fills the gap in lack of systematic expression for seasonal thermodynamic efficiency and suggests the process for calculation procedures workflow. DOI: https://doi.org/10.3846/enviro.2017.271

Analysis of seasonal exergy efficiency of an air handling unit

Ventilation systems play an important role for providing suitable indoor climate in buildings. Improving these systems allows promoting energy efficiency in building sector, which is responsible for a large percentage of global energy consumption. Therefore, this work focuses on assessment of ventilation air handling unit (AHU) using thermodynamics. The exergy analysis is used to evaluate the performance of an AHU. Special attention is made about seasonally varying exergy flows of a system. As efficiency of a ventilation system is closely linked to local climate, especially to the varying reference temperature. The paper presents an approach for calculating the seasonal exergy efficiency and gives the results of the AHU analysis. The case study reveals that the highest exergy consumption is when the outdoor temperature is −2.5 °C. The AHU case with heat recovery and water heater is the most efficient comparing to other cases investigated. The use of this methodology may be extended for determining of the ...