Francesco Minichiello

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.

A simple evaluator of building envelope moisture condensation according to an European Standard

Abstract The object of this work is the thermal and moisture performance analysis of building exterior walls, by means of a software code developed by the authors, according to the European Standard ISO 13788:2001. In particular, the European Standard focuses on two of the main reasons that cause moisture degradation in building envelopes: critical surface humidity and interstitial condensation. The approach is based on the steady-state diffusion theory and calculations are carried out on monthly basis, taking into account internal moisture production rates and outdoor climatic conditions. A user-friendly software tool (TMCE, i.e. thermal and moisture control for envelopes), developed in order to quickly and easily assess moisture and thermal behaviour of building components, is presented. The software, with graphical user interface, allows: (i) to determine the minimum thermal resistance of a building component in order to avoid critical surface humidity, and (ii) to check if interstitial condensation occurs in a multi-layer wall. In case of condensation occurrence during the winter months, the rate of condensed vapour is calculated, and the possibility that the moisture is completely removed during the warmer periods is evaluated. TMCE has been then used to analyse moisture and thermal characteristics of building components on varying input parameters such as outdoor climatic conditions and indoor moisture production; some relevant results and a case study are also presented.

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

Cost-optimal methodology and passive strategies for building energy efficiency: a case-study

ABSTRACT A passive strategy to reduce the energy consumption of existing buildings is to improve the thermal insulation of the opaque building envelope and insert windows with low thermal transmittance U. But what is the best compromise between cost of intervention and reduction of primary energy? The aim of this paper is to answer this question using the innovative cost-optimal methodology and a dynamic energy simulation software. The case study refers to an existing school in central Italy. Eight passive strategies are analysed, combining different insulation thicknesses and types of windows. Furthermore, a comparison between cost-optimal methodology and discounted payback analysis is reported. Finally, a sensitivity analysis on parameters influencing the cost-optimal method is conducted. The lowest primary energy is obtained considering an insulation thickness of 12 cm and windows with U of 1.10 W/m2 K, while the best case using the cost-optimal methodology refers to a low increase in insulation thickness.