Filippo de Rossi

Transient heat transfer through walls and thermal bridges. numerical modelling: methodology and validation

The current advanced numerical codes for the energy audits carry out 0-dimensional simulation (i.e., one computational node representing the thermal zone), underestimating the effects of thermal bridges on the seasonal heating demand of buildings. The paper suggests a numerical resolution model, implemented in Matlab, aimed to be transferred in numerical engines for the hourly energy simulation. The proposed methodology solves common thermal bridges in buildings, evaluating their effects on the energy demand. Typical thermal bridges have been studied and implemented, analyzing the reliability of the methodology, in terms of accuracy, computational time, required sources, comparing the solutions with those derived by computational fluid dynamic codes. The method reveals very satisfactory results, both as regards the computational time and CPU sources required, as well as with reference to the reliability. Moreover, the solution stability is commonly very high, regardless the chosen computational time-step.

Application of the TEWI Methodology to a Desiccant Cooling System Interacting with a Microcogenerator

Desiccant cooling systems, supplied by fossil or renewable fuels, represent a very interesting alternative to conventional electric units based on cooling dehumidification for air conditioning purposes, as they can achieve significant energy and emissions savings. The analysis of environmental impact of energy conversion devices, e.g. in terms of global warming effect, is usually limited to energy-related emissions (indirect contribution), neglecting direct greenhouse gas emissions related to working fluids, such as refrigerants. The Total Equivalent Warming Impact (TEWI) is a more comprehensive methodology, as it takes into account both direct and an indirect contributions to global warming. In this paper, this method is applied to a small scale trigeneration system, in which a microcogenerator, a chiller and a boiler interact with a hybrid desiccant-based cooling system, equipped with a silica-gel desiccant wheel. This trigeneration system is compared with other two systems, in order to assess its potentiality in terms of TEWI reduction. The different direct and indirect contributions of the several equipment are evaluated, and the share of the direct contribution is investigated, considering both the overall TEWI of the complete system, and that of the electric vapour compression device only. Finally, the effect of the greenhouse gas emissions of the electricity production mix and of different values of the Global Warming Potential (GWP) of the refrigerant fluid on the overall TEWI of the three compared systems is investigated.