Energetic and economic savings of free cooling in different Mediterranean climates

In a wide range of conditions heat recovery in mechanical ventilation systems can give, when a suitable air flow control system is set up, an important contribution to cooling and humidity indoor comfort with low energy supply. Free cooling is sometimes useful to face up not only ventilation load but cooling load as well, taking advantage, directly or indirectly, of the enthalpy difference between inside and outside air in summer. The paper reports on a summer analysis of the energetic advantage of direct and indirect evaporative cooling techniques in different Mediterranean climates, in which external air flow is established by outdoor, indoor and inlet air enthalpies comparison. Psychrometric diagram has been divided into seven zones as a function of external air conditions; for each zone outside air flow control logic and obtainable free cooling effect have been developed and evaluated. As a function of indoor conditions, outdoor conditions (expressed hourly by Typical Meteorological Year), inlet temperature, external ventilation air flow and building cooling load, energy savings with free cooling techniques have been calculated, considering water consumptions in the adiabatic saturators. Interaction of free cooling, sensible heat recovery and indirect evaporative cooling allows very interesting seasonal cooling load reductions, with the additional advantage of decreasing the chiller cooling capacity. All the energetic advantages have been evaluated by an economic point of view, in terms of Net Present Worth and Discounted Payback Period of the investment.