Study on Air-to-Water Heat Pumps Seasonal Performances for Heating in Greece

Air-to-water heat pumps (AWHPs) is a very good option for efficient heating in the residential and commercial building sectors. Their performance and therefore the use of primary energy and CO2 gas emissions are affected by various factors. The aim of this paper is to present a study on the seasonal coefficient of performance in heating (SCOP) of AWHPs, which are available in the Greek market. The sample consists of 100 models in total, offered by 12 manufacturers, in a range of heat pump’s thermal capacity up to 50 kW. The calculation of SCOP values was performed according to the methodology proposed by the EN14825 standard. The results indicate how the heating capacity, the local climate, the supply water temperature, the compressor’s technology, and the control system affect the seasonal performance of the various AWHP models examined. Setting the SCOP ≥ 3 value as a criterion, the analysis that was carried out in four climatic zones A, B, C, and D of Greece, shows that there are many models that meet this criterion, and, in fact, their number increases from the coldest to warmer climates, in combination with lower water supply temperatures to the heating system and a control system with weather compensation.

Influence of boundary conditions on the optimization of a geothermal heat pump studied using a thermodynamic model

This paper is the logical follow-up to a work [1] whose results were presented at the 28th French Thermal Congress which was to be held in Belfort in 2020. The model developed at that time is completed in this proposal to consider the specificity of the geothermal heat pump. This is a machine operating upon a mechanical vapor compression cycle, the limit of which is an inverse Carnot cycle. Its specificity consists of a cold loop at the source with the geothermal exchanger and the evaporator, then a hot loop at the sink with the condenser and a floor heat exchanger in the application considered here. We are particularly concerned with the optimal sizing of these heat exchangers through their effectiveness. The parametric sensitivity of this distribution to various boundary conditions is studied, especially by focusing on different conditions at the source: (1) imposed soil temperature, corresponding to a Dirichlet condition, (2) imposed heat flux (including adiabatic case), corresponding to a Neumann condition, (3) imposed mechanical power consumed by the heat pump, and (4) imposed coefficient of performance COP, to all cases being associated a finite thermal capacity in thermal contact with the geothermal exchanger operating in steady-state conditions.

SiGe/Si Multi-Quantum-Well Micro-Bolometer Array Design and Fabrication with Heterogeneous Integration

The micro-bolometer is important in the field of infrared imaging, although improvements in its performance have been limited by traditional materials. SiGe/Si multi-quantum-well materials (SiGe/Si MQWs) are novelty thermal-sensitive materials with a significantly high TCR and a comparably low 1/f noise. The application of such high-performance monocrystalline films in a micro-bolometer has been limited by film integration technology. This paper reports a SiGe/Si MQWs micro-bolometer fabrication with heterogeneous integration. The integration with the SiGe/Si MQWs handle wafer and dummy read-out circuit wafer was achieved based on adhesive wafer bonding. The SiGe/Si MQWs infrared-absorption structure and thermal bridge were calculated and designed. The SiGe/Si MQWs wafer and a 320 × 240 micro-bolometer array of 40 µm pitch L-type pixels were fabricated. The test results for the average absorption efficiency were more than 90% at the wavelength of 8–14 µm. The test pixel was measured to have a thermal capacity of 1.043 × 10−9 J/K, a thermal conductivity of 1.645 × 10−7 W/K, and a thermal time constant of 7.25 ms. Furthermore, the total TCR value of the text pixel was measured as 2.91%/K with a bias voltage of 0.3 V. The SiGe/Si MQWs micro-bolometer can be widely applied in commercial fields, especially in early medical diagnosis and biological detection.

Enhanced Solar Air Heaters For Crop Drying

Solar air heaters are placed on farms to provide heat for the drying of grain and crop harvesting and harvesting. The results of the thermal study showed that solar air heaters are capable of providing a sufficient increase in air temperature under the majority of crop drying circumstances studied. The restricted thermal capacity of air, as well as the low heat transfer coefficient between the absorber plate and the air flow via the ducting system, both contribute to the overall thermal efficiency of solar air heaters. Solar air heaters must be more efficient in order to be more affordable. This may be accomplished by increasing the heat transfer coefficient between the absorber plate and the air flow passing through the duct. More heat transfer coefficients can be increased by using either active or passive approaches. In most situations, it may be cost-effective to use solar air heaters and incorporate artificial roughness on the absorber plate. The rate of heat transmission from the solar air heater’s duct to the fluid flow may be increased by creating artificial roughness on the surface of the duct. The study focused on several roughness element geometries for solar air heater ducts, and the results indicated that there is a link between the two. This paper attempts to find ways to artificially increase the heat transfer capacity of solar air heaters’ ducts by using element geometries which have been utilised in solar air heaters’ heat transfer devices.

Enhanced Solar Air Heaters for Crop Drying

Solar air heaters are placed on farms to provide heat for the drying of grain and crop harvesting and harvesting. The results of the thermal study showed that solar air heaters are capable of providing a sufficient increase in air temperature under the majority of crop drying circumstances studied. The restricted thermal capacity of air, as well as the low heat transfer coefficient between the absorber plate and the air flow via the ducting system, both contribute to the overall thermal efficiency of solar air heaters. Solar air heaters must be more efficient in order to be more affordable. This may be accomplished by increasing the heat transfer coefficient between the absorber plate and the air flow passing through the duct. More heat transfer coefficients can be increased by using either active or passive approaches. In most situations, it may be cost-effective to use solar air heaters and incorporate artificial roughness on the absorber plate. The rate of heat transmission from the solar air heater's duct to the fluid flow may be increased by creating artificial roughness on the surface of the duct. The study focused on several roughness element geometries for solar air heater ducts, and the results indicated that there is a link between the two. This paper attempts to find ways to artificially increase the heat transfer capacity of solar air heaters' ducts by using element geometries which have been utilised in solar air heaters' heat transfer devices.

A Method for Determining the Impact of Ambient Temperature on an Electrical Cable during a Fire

Evaluating environmental conditions that trigger fire-fighting equipment is one of the primary design tasks that have to be taken into account when engineering electrical systems supplying such devices. All of the solutions are aimed at, among others, preserving environmental parameters in a building being on fire for an assumed time and at a level enabling safe evacuation. These parameters include temperature, thermal radiation, visibility range, oxygen concentration, and environmental toxicity. This article presents a new mathematical model for heat exchange between the environment and an electric cable under thermal conditions exceeding permissible values for commonly used non-flammable installation cables. The method of analogy between thermal and electrical systems was adopted for modelling heat flow. Determining how the thermal conductivity of the cable and the thermal capacity of a conductor-insulation system can be applied to calculate the wire temperature depending on the heating time t and distance x from the heat source is discussed. Thermal conductivity and capacity were determined based on experimental tests for halogen-free flame-retardant (HFFR) cables with wire cross-sections of 2.5, 4.0, and 6.0 mm2. The conducted experimental tests enable verifying the results calculated by the mathematical model.

Synthesis and Property Characterization of Ternary Laminar Zr2SB Ceramic

In this paper, Zr2SB ceramics with high relative density (99.03%) and high purity of 82.95 wt% (containing 8.96 wt% ZrB2 and 8.09 wt% zirconium) were successfully synthesized from ZrH2, sublimated sulfur and boron powder by spark plasma sintering at 1300 ℃. The reaction mechanism, microstructures, physical properties and mechanical properties of Zr2SB ceramic were systematically studied. The results show that Zr2SB was obtained by the reaction of zirconium sulfide, zirconium and boron, and ZrB2 coexisted in the sample as a symbiotic impurity phase. The average grain size of Zr2SB was 12.46 μm in length and 5.12 μm in width, and the mean grain sizes of ZrB2 and zirconium impurities were about 300 nm. In terms of physical properties, the measured thermal expansion coefficient was 7.64 × 10-6 K-1 from room temperature to 1200 ℃, and the thermal capacity and thermal conductivity at room temperature were 0.39 J·g−1·K−1 and 12.01 W∙m−1∙K−1, respectively. The room temperature electrical conductivity of Zr2SB ceramic was measured to be 1.74 × 106 Ω−1∙m−1. In terms of mechanical properties, Vickers hardness was 9.86 ± 0.63 GPa under 200 N load, and the measured flexural strength, fracture toughness and compressive strength were 269 ± 12.7 MPa, 3.94 ± 0.63 MPa·m1/2, and 2166.74 ± 291.34 MPa, respectively.