Reducing CO2 emissions by optimization of cooling strategies in buildings - literature review

This paper presents a literature review about the exergetic analyses of cooling systems in buildings. The main focus is on temperate climate zones where mainly cooling systems like heat pumps, natural cooling, solar climatisation and PCM`s are used. In the past, exergy was only determined for steady state conditions. Consequently, significant errors arose from the non-consideration of the constantly changing reference environment. These errors are greater for cooling than for heating systems, since under summer conditions, indoor air temperature is almost identical to the external air temperature. This leads to strong fluctuations of the Carnot factor during the summer cooling period, and thus, the exergy flows. Dynamic fluctuations of the indoor and outdoor humidity strongly influence the chemical and physical exergy of the system. If the humidity is regarded in the analysis, dynamic calculations are necessary to allow a more precise determination of the exergy flows. Therefore, the most important question is the problem of the humidity treatment in context of cooling applications under dynamic conditions. In addition, an important issue is how the exergy concept can help in increasing the use of renewable energies or passive systems that are adjusted to the buildings and their utilization.