Characteristics of the compressor for a heat pump of an air handling unit

Abstract

Energy consumption in buildings is increasing every year. The main consumers in buildings are heating, ventilation, and air conditioning (HVAC) systems, which consume half of the energy consumed by the European Union (EU), of which a lot is lost due to inefficient use. It is HVAC systems that require new solutions that open opportunities for creating more efficient products that directly contribute to the achievement of the strategic goals of the EU and Lithuania to reduce energy consumption, use renewable energy sources, and improve energy efficiency. The use of heat pumps for heating systems in buildings is not new, but their use in ventilation systems is less common. Recently, the situation has begun to change, more and more manufacturers of ventilation units (e.g., FläktGroup, Mandik, Dantherm A/S, Komfovent, VENTS) offer air handling units with built-in heat pumps. The energy conversion modes of such devices are permanently changing in accordance with the constant change of the outdoor air state (temperature, humidity). Flexibility, the ability to rationally respond to permanently changing ambient air parameters is an important feature of the choice of operating mode of energy transformers and its control. The overall seasonal efficiency of the air handling unit depends on it. The main component dictating the operating mode of the heat pump is the compressor. The change in its operating characteristics should be defined by the functional purpose of the heat pump. At each outdoor temperature, the compressor must have a specific combination of pressure ratio and flow rate. Theoretical models and experimental studies of heat pump compressors are presented in the scientific literature, in which the issues of compressor operation efficiency are analyzed. However, these works are more focused on the operating parameters and efficiency of the compressor, little attention is paid to the thermodynamic cycle of the heat pump and its demand. No attempt is made to follow the specific needs of changing the cycle with a compressor. The issue is viewed from the perspective of design solutions, not from the optimal demand mode. This work is aimed at finding out what should be the characteristic of the compressor that effectively operates in the heat pump of the air handling unit, corresponding to the given operating character of the heat pump. More precisely, its specific evolution of the cycle with changes in the outside air temperature.