Exergy Analysis of Conventional and Low Exergy Systems for Heating and Cooling of Near Zero Energy Buildings

The purpose of the study is to compare two heating and cooling (H/C) systems regarding individual thermal comfort conditions and rational building energy use. Real test room is firstly equipped with low exergy (LowEx) system (i.e. heating-cooling ceiling radiative panels) and secondly with a conventional system (i.e. electric heaters, cooling split system with indoor unit). Additional case presents a thermally noninsulated room equipped with a conventional system. Individual thermal comfort conditionsare analyzed through the simulation of human body exergy balance (hbExB), human body exergy consumption (hbExC) rates and predicted mean votes (PMV) index. Measurements of energy use and control of temperature conditions are performed on an integrated control system (ICsIE) based on fuzzy logic. The results confirm that both systems create comfort conditions if the room is thermally well insulated. In case of non-insulated room there appears cool radiant exergy that often leads to discomfort conditions. More acceptable comfortable conditions (PMV closer to 0) do not always result in a lower hbExC rate. Individual characteristics with experimental conditions have a significant influence on separate parts of hbExB. LowEx system connected with ICsIE enables to set air temperature and mean radiant temperature and creates optimal thermal comfort conditions for individual user. The measured energy use for heating was by 11 to 27% lower for LowEx system than for the conventional system. The energy use for cooling was by 41 to 62% lower for LowEx system. The presented approach of reciprocal consideration of individual thermal comfort conditions and building energy use is important for the future design of H/C systems and for their application in near zero energy buildings.

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