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With the growth of energy-efficient building sector, ventilation systems are becoming increasingly important not only of fresh air supply but also in terms of energy consumption. The aim of this paper is to describe and analyse the operation of an air handling unit (AHU) with a heat pump using energy and exergy analyses under the variable environmental temperature (from –30 °C to 10 °C). The application of selected methods is illustrated in a case study of an AHU using environmental temperatures of Vilnius city during heating season (from the beginning of October to the end of April). An analytical method for determining distribution of the environmental (outdoor air) temperature is used. Energy and exergy analyses showed periods when the highest amounts of energy and exergy were consumed and the greatest exergy losses occurred. This allowed to reveal the component of the system with the highest exergy losses – the heat pump evaporator. Therefore, further research is needed for its design and application. At the end of the article, the seasonal indicators of the AHU with heat pump operation were calculated: coefficient of performance and exergy efficiency. The presented research procedure could be applied to the analysis of other energy systems and processes in them. [ABSTRACT FROM AUTHOR]

Renewable energy sources (RES) and their transformation technologies become more attractive in building sector as energy demand and emissions to the environment increase. Along with renewable energy transformation technologies, the importance of energy storage also arises as these RES are characterized by volatility and energy mismatch over time. For this reason, engineering systems which use RES are becoming increasingly dynamic. This study examines ongoing processes in a vertical cylindrical storage tank designed to cover domestic hot water demand in a building. Simultaneous dynamic mode of operation when the energy is being charged and at the same time discharged from the storage tank is analysed. Experiments are performed and stratification number describing thermal stratification is calculated. The obtained data are used for the development and validation of the numerical model. Using Ansys Fluent software, the influence of different discharge rate on operation mode of the storage tank is investigated. Graphical and numerical interpretation of results is performed. [ABSTRACT FROM AUTHOR]

The application of heat pumps in the heating systems of buildings in the cold or transitional season is becoming an increasingly common practice not only in Lithuania but in other countries as well. Due to the growing popularity of air-to-air or air-to-water heat pumps in the building sector, the problem of the evaporator heat exchanger freezing is also becoming more and more relevant. As the outdoor temperature drops, so does the heat pump's coefficient of performance (COP) for heating. The freezing of the evaporator surface increases the energy consumption of the system, has a negative effect on heat exchange, distorts the normal operating cycle of the heat pump and the energy is wasted for defrosting processes. This article describes the experimental investigation of an air-to-water heat pump, presents the results obtained during the experiments and their interfaces. The experiments were carried out during the transitional/cold season. It was found that frost formation on the evaporator started when the outdoor temperature was <3.5 °C and the relative humidity reached 88%. The defrosting cycle took an average of 5 min. The impact of the evaporator freezing on the operation and COP of the heat pump was assessed. [ABSTRACT FROM AUTHOR]

In order to achieve ambitious goals for energy efficiency and requirements for near zero energy buildings, various technological solutions enabling the use of renewable energy are proposed and applied. One such rapidly spreading technology is heat pumps. However, the use of air-to-water heat pumps in countries where the cold season is cold and humid has unfavourable conditions for the operation of this equipment during the heating season. As a result, the performance efficiency of the equipment decreases. This article presents the simulation results of an air-to-water heat pump operation in Lithuania using the TRNSYS modelling tool; its nominal heating capacity is 6.55 kW. The model was calibrated using real data obtained at Vilnius Gediminas Technical University when measurements were performed under heat pump freezing conditions. The seasonal performance factor of the heat pump heating mode was determined during the calculation. Parametric analysis of the model was also performed, when sensitivity of the model to the initial climatic data was observed. Comparable results are obtained for Vilnius, Prague and London. [ABSTRACT FROM AUTHOR]

This paper analyzes an experimental heat pump used for heat recovery in a mechanical room ventilation system. The aim of the work is to examine the operation, control logic of the heat pump and evaluate the possibilities of its operation modes, cycle control by outdoor air temperature. A review of scientific literature and experimental tests of the heat pump were performed to achieve this goal. Tests were performed in three stages, after each stage, according to the results obtained the heat pump stand was improved and experimental modes were adjusted. During the experiment, the tendencies of the heat pump freon and air involved in the heat exchange parameters are analyzed with different combinations of expansion valve positions and compressor power. Knowing these experimental characteristics, the extent to which the combination of these two controls can be used to efficiently control of the heat pump according to the outside air temperature is assessed. Based on the results of the research the heat pump control algorithms (depending on the variable outdoor air temperature) are prepared. [ABSTRACT FROM AUTHOR]