P. Mazzei

Desiccant HVAC systems for commercial buildings

Abstract HVAC systems with desiccant wheel (DW) are energy efficient, with a low ambient impact, and can be profitable if compared to traditional systems. They also allow a better indoor air quality. In this paper the summer operating costs of both the desiccant and traditional systems are obtained using three software codes. Two are based on DOE calculation engine (PowerDOE and DesiCalc™), one (DTPE) is an autonomously developed code, based on a subdivision of the psychrometric chart in zones, each one corresponding to a different air handling. DOE and DTPE take into account the most recent DW performance values. Calculation assumes hourly weather data extracted from the European file named “Test Reference Year” (TRY) and appropriately processed. With reference to operating costs of the desiccant systems in summer Italian conditions, for a retail store application, interesting savings (up to 35%) are obtained, as well as reduction in thermal cooling power (up to 52%). Starting costs of the desiccant system are generally greater with respect to the traditional system; considering the present costs of the Italian market, a simple payback of about 5–7 years is obtained. If slightly de-rated DWs are considered, the payback attains lower values, near to 3–4 years.

Weather data for building energy cost-benefit analysis

This paper deals with European TRY weather data processing for climatic indexes generation, useful for HVAC energy and cost simplified evaluation. For nine Italian locations are presented: 99 and 2.5% dry bulb temperatures, 2.5% wet bulb temperatures, heating and cooling degree days, latent enthalpy days, unitary sensible and latent loads. TRY psychrometric data were processed according to a bin method that preserves the correlation between dry bulb temperature and moisture content, and then reduced by an averaging technique. An example is worked out in order to present an engineering shorthand for energy and cost evaluation of HVAC system.

Exergetic and thermodynamic comparison of R12 and R134a as vapour compression refrigeration working fluids

Abstract A software package for both the computation of thermodynamic properties and the analysis of the usual vapour compression plant schemes is a useful tool for air conditioning and refrigeration researchers and manufacturers. At present, it could make an important contribution to the search for CFC substitutes; in fact, comparisons between two or more working fluids could be accomplished more easily. A program code carried out by the authors is presented by means of some demonstrative diagrams referring to a comparison between the ‘ozone killer’ R12 and its substitute R134a. An R134a exergy-enthalpy chart is also provided.

Outdoor-air design conditions relating to the capacity of air-conditioning systems

In this paper we present work involving the processing of climatic data relating to some Italian cities, taken from a set of data known as European ‘test reference year’ (TRY). We aim to make a critical comparison of the thermohygrometric conditions of outdoor air in the summer season thus obtained with those design conditions as laid down by Italian regulations (UNI 10339) and with those recently suggested by ASHRAE. Subsequently, and with reference to some traditional and recent applications in the field of air-conditioning, we report on how performance differs according to outdoor summer thermohygrometric design conditions, such as those indicated by UNI 10339, by ASHRAE and by the processing of TRY data. Finally, we discuss the optimal choice of design conditions according to the type of application. Copyright