This paper presents the results of a thermo-economic and primary-energy-factor assessment based on the field-test results for a residential air-to-water heat pump (AWHP). The AWHP experimental setup consisted of a supervisory control and data-acquisition system, which was connected to a heat meter, an electricity meter, humidity and temperature sensors, a HP control system and a computer. Based on the experimental data, the 4-year-average seasonal performance factor was determined. This information was then applied in a thermo-economic and primary-energy-factor (PEF) analysis. The results served for a comparison of the AWHP with eight different heating systems (HSs). The results reveal that the considered AWHP represents the most thermo-economically efficient system in terms of the average final costs for heat production. The results of the PEF analysis reveal that the HS with the AWHP under investigation can be characterized as the most efficient system.
COBISS.SI-ID: 15291163
The article presents how to increase electrical efficiency and power output of photovoltaic (PV) panel with the use of a phase change material (PCM). The focus of the work is in experimental setup and simulation heat extraction from the PV panel with the use of TRNSYS software. A modification of PV panel Canadian Solar CS6P-M was made with a phase change material RT28HC. The actual data of cell temperature of a PV panel with and without PCM were given and compared. A simulation of both PV panels in TRNSYS software was performed, followed by the comparison of results with the simulation and experimental actual data. The experimental results show that the maximum temperature difference on the surface of PV panel without PCM was 35.6 °C higher than on a panel with PCM in a period of one day. Referring to experimental results the calculation of the maximum and average increase of electrical efficiency was made for PV-PCM panel with TRNSYS software. Final results of simulation shows that the electricity production of PV-PCM panel for a city of Ljubljana was higher for 7.3% in a period of one year.
COBISS.SI-ID: 14692891
Free cooling with enhanced night-time ventilation can significantly contribute to reducing energy demand for the cooling of buildings. Such systems are competitive regarding energy efficiency with other active natural or even mechanical cooling systems, if advanced weather-predicted control is implemented. In this article, the developing of a generalized model predictive weather control (G-MPWC) for controlling of free-cooling system by night time ventilation is presented. The result of the G-MWPC is a set of control matrixes that includes data on the forecast required night-time air exchange rate and forecast daily coefficient of the performance of the free cooling system regarding the forecast daily average ambient air temperature and amplitude and the pre-set free cooling system on/off temperature difference. An additional matrix that includes data on forecast maximum indoor air temperature is developed for the case of the free cooling system being unable to fulfil pre-set thermal comfort requirements. Despite the fact that the developed control algorithm is rather static and based on a control matrix, which must be developed for specific building, it was shown that such algorithm can be reasonably accurate and simple to integrate into the control unit of the mechanical ventilation system. Presented case study showed that that the coefficient of performance is 120–240% higher if the G-MPWC algorithm is implemented instead of conventional controlled free-cooling system.
COBISS.SI-ID: 14543131
This study deals with an uncertainty analysis of gas flow measurements using a piston prover primary standard. A detailed methodology for the uncertainty analysis, covering the components due to the gas density, dimensional and time measurements, the leakage flow, the density correction factor and the repeatability, is presented. At the upper end of the measuring range, using the adiabatic density correction model, as well as averaging multiple readings, proves important. Taking that into account the estimated expanded measurement uncertainty is less than 0.15 % in the flow range above 0.012 g/min. The results prove that our measurement capabilities are comparable with the capabilities of national laboratories in Europe, which is important for quality research work in the lab and for fulfilling the demands of customers for ensuring traceability to lower metrological levels.
COBISS.SI-ID: 14705435
Microstructured uniformly and non-uniformly wettable surfaces were created on 25-micro-meter-thin stainless steel foils by laser texturing using a marking nanosecond Nd:YAG laser (wavelength = 1064 nm) and utilizing various laser fluences and scan line separations. High-speed photography and high-speed IR thermography were used to investigate nucleate boiling heat transfer on the microstructured surfaces. The most pronounced results were obtained on a surface with non-uniform microstructure and non-uniform wettability. The obtained results show up to a 110 % higher heat transfer coefficients and 20-40 times higher nucleation site densities compared to the untextured surface. We show that the number of active nucleation sites is significantly increased in the vicinity of microcavities that appeared in areas with the smallest (10 micro-meter) scan line separation. Furthermore, this confirms the predictions of nucleation criteria and proves that straightforward, cost-effective nanosecond laser texturing allows the production of cavities with diameters of up to a few micrometers and surfaces with non-uniform wettability. Additionally, this opens up important possibilities for a more deterministic control over the complex boiling process.
COBISS.SI-ID: 15158043