N. Arcuri, R. Bruno, S. Ruffolo,

Department of Mechanical Engineering — University of Calabria
87036 Rende, Cosenza
e-mail:natale. arcuri@unical. it

01

Abstract

A procedure developed in a TRNSYS environment has allowed to estimate the thermic performances of a radiant floor system supplied by solar collectors, connected to a house. A suitable control strategy has been employed to use in the best way the incident solar energy. For three representative localities of Italian territory the curves of solar fraction have been obtained, as well as efficiency of the system and some economic indices in relation to the variation of collectors’ surface and tank’s storage volume.

1. INTRODUCTION

The increasing greenhouse gas concentration and the successive risk of climatic changes can be mostly attributed to the use of fossil sources in order to produce energy. Reducing their emissions implies turning to a system of energetic supplying based on the use of renewable energies, especially solar energy. To get a remarkable energetic saving, several ways can be used to reduce the building thermal requirements. This can be surely obtained by using active solar systems. Using solar energy to domestic hot water (DHW) has demostrated that solar technology is fully developed and it can be used for house heating too. The present work has considered a solar combisystem to produce hot water both for house heating and domestic hot water to satisfy a fraction of yearly energy requirement, that it is function of the system size. Among heating systems the radiant floor is the best to exploit solar energy since thermal power must be supplied by a flow rate at low temperature that may be produced by a solar system with satisfactory efficiency. A comparison between radiant floor heating system with fan coil system has evidenced energy requirement savings in the period of heating equal to 24% for Cosenza, 21% for Rome and 18% for Milan [1,2].

The present work develops an energy analysis about a house heated by radiant floor. The radiant floor is supplied by a secondary circuit powered by a storage tank that is ulteriorly supplied with thermic energy by a field of solar collectors. The tank acts as a thermic accumulator and regulates inlet temperature by a mixing valve. When heat level of tanking fluid is not enough to satisfy energy requirement, an independent system supplied by traditional fuel is actived. A heat exchanger in the storage tank provides domestic hot water with an auxiliary heating system to get wished temperature. Radiant floor has been designed by a stationary method, according to UNI EN 1264 standard. The building thermic design is suited to N°10/1991 italian Law. The system building-radiant floor has been studied by the simulation code TRNSYS [3] which has made possible to estimate the fraction of energy requirement from the solar source in relation to the collectors’ surface and of the tank’s storage volume variation. To simulate the climatic variability, an appropriate procedure has been used, generating hour values of solar radiation and outside air temperature starting from respective monthly average data.