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Transforming Residential Energy Systems Across Europe
No full textThe global demand for energy has
surged by 19% since 2010, with over half of
this increase attributed to the building sector.
Fossil fuels still account for 80% of energy
consumption, contributing significantly to
climate change. In response, the European
Union (EU) has set ambitious goals to reduce
CO2 equivalent emissions in an increasingly
drastic manner. Projects like ITS4ZEB are crucial
to achieving these targets by encouraging the
use of natural fluids, such as hydrocarbons, and
promoting renewable energy sources.
Buildings, particularly residential ones,
are some of the contributors to energy
consumption. Traditional heating and
cooling systems rely heavily on fossil
fuels and electric current drawn from the
grid, leading to high carbon footprints.
The ITS4ZEB project addresses this by
introducing cutting-edge technologies
designed to optimise energy use and reduce
dependency on non-renewable resources
Application of innovative refrigerants with low environmental impact for refrigeration and thermal control
Get PDFAfter a brief introduction on the global warming effect and on the measures that have been adopted to limit it, this thesis is focused on low GWP refrigerants and, above all, on HFOs, which have been studied during two phase flow in several operating test conditions. To cover a great portion of the existing devices, four heat exchangers have been investigated: a tube in tube heat exchanger, a Brazed Plate Heat Exchanger (BPHE), a roll-bond type heat exchanger, and a Finned Heat Pipe Heat Exchanger (HPFHE).
In Chapter 2 the four experimental test rigs used to collect experimental data are explained and the data reduction processes used to analyze the recorded data are shown.
In Chapter 3 all the experimental data points collected are presented, critically discussed, and compared against some existing correlations. In addition, new analytical procedures are proposed to evaluate the heat transfer coefficient and the pressure drop during vaporization and condensation inside BPHEs respectively. Furthermore a new computational procedure to calculate the heat capacity and the heat transfer coefficients of a HPFHE is presented.
In Chapter 4, the experimental data obtained with different fluids under the same working conditions are grouped and compared to highlight the refrigerant effect on the global performance of the heat exchangers.
Finally some performance evaluation criteria to discriminate the best refrigerants on the basis of thermophysical properties and to select the ones that perform better in terms of heat transfer and pressure drops are presented
A new computational procedure for refrigerant condensation inside herringbone-type Brazed Plate Heat Exchangers
No full textThis paper presents a new computational procedure for refrigerant condensation inside herringbone-type
Brazed Plate Heat Exchanger (BPHE). A transition point between gravity controlled and forced convection
condensation was found for an equivalent Reynolds number around 1600. At low equivalent Reynolds
number (<1600) the heat transfer coefficients are not dependent on mass flux and are well predicted
by a simple model based on the Nusselt (1916) equation for vertical surface. For higher equivalent
Reynolds number (>1600) the heat transfer coefficients depend on mass flux and condensate drainage
is controlled by the combined actions of gravity and vapour shear. A new model was developed for
predicting the heat transfer coefficients in the forced convection condensation region. This new model
was also applied to super-heated vapour condensation by using the equation of Webb (1998) to account
for super-heating effects. The new computational procedure was compared against data from the
literature: the mean absolute percentage deviation between experimental and calculated heat transfer
coefficients was lower than 16%
Comparative performance analysis of the low GWP refrigerants HFO1234yf, HFO1234ze(E) and HC600a inside a roll-bond evaporator
No full textThis paper presents the comparative performance analysis of the low GWP refrigerants HFO1234yf, HFO1234ze(E) and HC600a inside a commercial roll-bond evaporator for household refrigerators. The vaporisation performances were evaluated at two evaporation temperatures, -15 and -20 degrees C, and different refrigerant mass flow rates and compared with those of the traditional refrigerant for domestic refrigeration HFC134a. The performance analysis was carried out using both thermocouples installed on the rear side of the roll-bond evaporator and an IR thermo-camera. Each of the low GWP refrigerants tested can be considered a good substitute for HFC134a, provided that the compressor displacement is adjusted to deliver the proper refrigerant mass flow rate. Only HFO1234yf exhibits performance similar to HFC134a at the same mass flow rate, therefore it can be considered a direct drop-in substitute for HFC134a
Condensation of the low GWP refrigerant HFC152a inside a Brazed Plate Heat Exchanger
No full textThis paper presents the experimental heat transfer coefficients and pressure drop measured during refrigerant HFC152a condensation inside a commercial Brazed Plate Heat Exchanger (BPHE) and compares this data with similar measurements previously obtained for refrigerant HFC134a, HC290 and HFO1234ze(E) in order to assess the low GWP substitutes for HFC134a for large chiller application. The effects of saturation temperature, refrigerant mass flux and vapour super-heating are investigated. HFC152a exhibits heat transfer coefficients much higher than those of all the other refrigerants considered in the present comparison and frictional pressure drop similar to HC290 and slightly higher than HFC134a and HFO1234ze(E). Therefore, considering that HFC152a is the unique HFC refrigerant candidate with a GWP < 200, taking into account also its good thermodynamic properties, it seems to be a very promising low GWP refrigerant for large chiller application
Development of an innovative raw milk dispenser based on nanofluid technology
Get PDFThe comparative analysis of a traditional raw milk dispenser and an innovative prototype based on nanofluid technology is presented. The traditional dispenser consists of an off-the-shelf up-right air cooled refrigerator, whereas the innovative prototype presents a tank equipped with a serpentine tube jacket operated with Al2O3 - ethylene glycol aqueous solution nanofluid. The systems are experimentally analysed in the ambient temperature range 19 - 35 °C to evaluate the energy performance and the temperature control inside the milk tank. The innovative prototype is demonstrated to be superior both from the point of view of energy saving and of food safety. In fact, it exhibits a 63 - 70 % energy saving with respect to the traditional one.
Furthermore it is able to reach the “safe” temperature of 4 °C in about half of the time required by traditional system and it keeps the milk always in the “safe” temperature range
Experimental Analysis of R134a and R1234ze(E) Flow Boiling Inside a Roll Bond Evaporator
Get PDFThis paper presents an experimental study of R134a and R1234ze(E) inside an off the shelf roll bond evaporator, commonly used for small size domestic refrigerators. The evaporator was mounted inside a climate dark chamber where ambient temperature and humidity were maintained stable during the tests. To control the inlet conditions (evaporation
temperature, inlet quality, refrigerant mass flow rate) it was used a water cooled miniature scale vapor cycle system with R134a and R1234ze(E) as working fluids. By means of an IR-thermo-camera and thanks to 16 thermocouples collocated on the back of the evaporator, the whole roll bond temperature field was investigated under different working conditions. During the experimental tests the refrigerant mass flow rate as varied by regulating the compressor speed,
while ambient temperature and evaporation temperature were kept as constant. From the IR pictures it was possible to delineate the super heating region and to point out the areas of the evaporator in which heat transfer is less efficient depending on the fluid and on the working conditions. The data acquired from the vapor cycle system (i.e. condensation and evaporation pressure, evaporator inlet quality, vapour superheating, refrigerant mass flow rate) coupled with the IR
thermo-camera images allowed to evaluate the behavior and the efficiency of the roll bond. Since the data were collected maintaining the same operating conditions in term of ambient temperature and humidity, heat flow rate and evaporation temperature, it was possible to highlight differences among the two refrigerants in terms of mass flux.
Furthermore, on the basis of the IR images and of the thermocouples measurements, an average heat transfer coefficient was defined and determined both on the air and the refrigerant side. The average heat transfer coefficients of the two refrigerants are compared and outlined in the paper
Condensation of the low GWP refrigerant HFO1234ze(E) inside a Brazed Plate Heat Exchanger
No full textThis paper presents heat transfer coefficients and pressure drops measured during condensation of the low GWP refrigerant HFO1234ze(E) inside a BPHE. The condensation temperature ranges between 24.8 and 40.2 °C, the refrigerant mass flux from 10.7 to 39.9 kg m−2 s−1 and the heat flux from 5.3 to 26 kW m−2. The heat transfer coefficients show weak sensitivity to saturation temperature and great sensitivity to refrigerant mass flux and vapour super-heating. At low refrigerant mass fluxes (20 kg m−2 s−1) the heat transfer coefficients depend on mass flux and forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 32%–35% enhancement for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are from 8% to 11% higher than those of saturated vapour. HFO1234ze(E) exhibits lower (4%–6%) heat transfer coefficients and higher (10%) frictional pressure drops than those of HFC134a
Theoretical analysis of free convection in a partially foam-filled enclosure
No full textFree convection in a partially foam-filled enclosure is theoretically investigated. Two independent approaches are undertaken. Scale analysis has been conducted along with a thermal resistance network model to predict the performance of metal foams as heat sinks to remove heat from a horizontal heated plate. Results from scale analysis were used to predict the flow regime transition from that of the viscous drag-dominated to that of form-drag dominated flow. Predictions from the two approaches are then cross-validated and compared against available experimental data in the literature. A good degree of agreement was observed. Finally, using the theoretical models, a parametric study was conducted to investigate the effects of different parameters on the Nusselt number
R1233zd(E) flow boiling inside a 4.3 mm ID microfin tube
No full textThis paper explores the heat transfer and fluid flow characteristics of a new low-GWP refrigerant R1233zd(E) during flow boiling inside a mini microfin tube with internal diameter at the fin tip of 4.3 mm. The microfin tube is brazed inside a copper plate and electrically heated from the bottom. Several T-type thermocouples are inserted in the wall to measure the temperature distribution during the phase change process. In particular, the experimental measurements were carried out at constant mean saturation temperature of 30 °C, by varying the refrigerant mass velocity between 100 kg m-2 s-1 and 300 kg m-2 s-1, the vapor quality from 0.2 to 0.95, at four different heat fluxes: 15, 30, 60, and 90 kW m-2. The experimental results are presented in terms of the two-phase heat transfer coefficient, onset of dryout vapor quality, and frictional pressure drop as a function of the operating test conditions
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