ABSTRACT
This paper presents the results of the analysis of thermal issues and energy efficiency of three types of accumulators; namely stone-bed; water and phase change. Research experiments were carried out during April-October 2013 in a standard commercial semi-cylindrical high plastic tunnel with tomato cultivation of 150 m2. A stone-bed accumulator; with an area of almost 75 m2 was installed in the tunnel below ground level; while a water accumulator with a volume of 4 m3 was installed outside the tunnel. A phase change material (PCM) accumulator, with a volume of 1 m3 containing paraffin, was located inside the tunnel. The heat storage capacity of the tested accumulators and the energy efficiency of the process were determined based on the analyses of the 392 stone-bed charging and discharging cycles, the 62 water accumulator charging cycles and close to 40 PCM accumulator charging and discharging cycles. Dependencies in the form of easily measurable parameters; have been established to determine the amount of stored heat; as well as the conditions for which the effectiveness of these processes reaches the highest value. The presented analysis falls under the pro-ecological scope of replacing fossil fuels with renewable energy. As a result of the analysis; it was found that; in the case of a stone-bed; such an accumulator shows higher efficiency at lower parameters; that is, temperature difference and solar radiation intensity. In turn; a higher temperature difference and a higher value of solar radiation intensity are required for the water accumulator. The energy storage efficiency of the PCM accumulator is emphatically smaller and not comparable with either the stone-bed or the water accumulator.
Subject(s)
Horticulture , Hot Temperature , Solar Energy , WaterABSTRACT
Cardiovascular autonomic function is measured as heart rate variability (HRV). The aim of the study was the HRV comparison between type 1 diabetic patients without (R0) and with diabetic retinopathy (R1). The group R0 was significantly younger (36.08 +/- 13.52 years) than group R1 (42.90 +/- 10.42 years). Diabetes duration was significantly longer in the group R1 as compared to group R0 (22.60 +/- 8.72 years vs 16.72 +/- 11.54 years, p < 0.04). Also HbA1c level in the group R1 was significantly higher as compared to the group R0 (p = 0.006). The data demonstrated that abnormal HR variability measured over a 24-h period provides information on the risk of sudden death. To assess HR variability twenty four hour EKG monitoring were performed in all examined patients. RR intervals were significantly longer between 2.00 a.m. and 5.00 a.m. In each hour of 24-h EKG Holter monitoring VLF and LF were significantly lower in the group R1. In the group R1 - HF was also significantly lower but only during sleeping time (between 11 p.m. and 7 a.m.). 24-h EKG monitoring is a useful and promising tool in diabetic patients with different microvascular complications.
