Energy saving potential integrating multi-stage evaporative technology in HVAC systems for Italian climate

Abstract

SYNOPSIS Evaporative cooling, extensively used in dry climates, can be justified in wetter areas by integration into HVAC systems; in this way the saving-energy technique will not always replace mechanical cooling, but has to be integrated with commonly employed equipment. In this paper Test Reference Year (TRY) data for Italy were processed to estimate using potential of multistage integrated evaporative HVAC systems. Specific humidity and wet-bulb temperature were computed to define five regions for external air, and then to evaluate hours per year and relative energy saving for each of these regions and Italian climatic areas. The systems subjected to comparison were a multi-stage evaporative—direct, indirect and mechanical—and a traditional mechanical one; both all air, single duct, single zone, constant volume systems with wet-bulb economizer. The method of analysis is based on a strongly simplified approach. It is not intended as a substitute for accurate modelling schemes to simulate building and system behaviour, but as a tool to estimate the energy saving potential related to the Italian climate. The following parameters have been assumed as constant throughout: sensible heat ratio of the conditioned space, adiabatic saturation and heat exchanger effectivenesses, indoor space and supply air temperatures and relative humidities. Outside air temperature and relative humidity are assumed to change hour by hour following the TRY profile. Energy savings are evaluated hourly, the mass flow rate of the supply air being kept constant. Seasonal energy savings for the majority of the climatic areas appears to be encouraging, ranging between 28% and 67% (space air temperature and relative humidity: 26°C −60%) or 36% and 74% (space air temperature and relative humidity: 26°C −70%). If it is assumed that the system operates always with 100% outside air (also for regions with outside wet-bulb air temperature greater than space wet-bulb air temperature) energy cooling requirements display different trends for different climatic areas.