Geothermal ground heat exchangers in Malta : thermal performance assessment of infill grouts

The aim of this paper was to assess the thermal conductivity of proprietary grout mixes versus local ones in Malta. Ground source heat pump (GSHP) systems consume 75% less electricity than conventional environmental control systems and have lower maintenance costs. On the other hand the installation costs of GSHPs are comparatively higher. Attention has therefore been focused to try to lower the costs of installing the borehole heat exchange system. The grout is one of the key factors that influence the efficiency of ground source heat pumps, being the principal conductive medium to the natural terrain. This paper explores the variations in the thermal conductivity of different sand-cement grouts. It compares and evaluates options for the suitability of these materials for backfilling vertical boreholes of ground heat exchangers. In this study sixteen different sand-cement grouts have been designed, evaluated and compared with materials, which have been conventionally used to fulfil this purpose. Imported silica sand and local sand mixes were formulated, tested and compared so that the potential use of local sands could be closely examined. Output results prove that local sand-cement grouts improve thermal conductivity values by 27% and are also 17% less expensive when compared to silica sand-cement and bentonite grouts. This win-win scenario points towards improvements in both in thermal conductivity and cost effectiveness when using local resources.peer-reviewe

Diagnostic and prognostic significance of exercise-induced premature ventricular complexes in men and women: A four year follow-up

Two hundred eighty patients (197 men and 83 women) with normal rest electrocardiograms and no history of prior myocardial infarction were referred for evaluation of chest pain. It was found that exercise-induced premature ventricular complexes had a lower sensitivity, specificity, positive predictive value and negative predictive value in predicting significant coronary artery disease than exercise-induced ST segment depression greater than or equal to 1 mm. The incidence of exercise-induced premature ventricular complexes was not significantly different in patients with no significant coronary artery disease, single vessel disease or multivessel disease. The site of origin of exercise-induced premature ventricular complexes was not helpful in predicting the presence or severity of coronary artery disease. At a mean follow-up period of 47.1 months, exercise-induced premature ventricular complexes did not predict coronary events (cardiac death or nonfatal myocardial infarction) in men or women