1,721,116 research outputs found
Valutazione delle prestazioni energetiche ed ambientali di impianti basati su pompe di calore operanti con diversi fluidi refrigeranti
No full textIn questo lavoro sono state valutate attraverso il software TRNSYS le prestazioni energetiche ed ambientali ottenibili da un impianto di tipo idronico, basato su una pompa di calore elettrica ed accoppiato ad un edificio mono-familiare di recente costruzione situato a Padova. In particolare, sono state considerate due tipologie di pompa di calore, una macchina aerotermica ed una geotermica, entrambe operanti con fluidi refrigeranti alternativi: R-410A e R-454B.
Le simulazioni numeriche effettuate hanno confermato come l’utilizzo di una pompa di calore geotermica permetta di incrementare le prestazioni energetiche complessive dell’impianto di circa il 10%, a parità di refrigerante. L’impatto ambientale delle configurazioni impiantistiche studiate è stato valutato per mezzo del TEWI (Total Warming Equivalent Impact). L’utilizzo del refrigerante R-454B comporta da un lato un lieve calo delle prestazioni energetiche complessive dell’impianto, pari al 2-3% su base annuale, mentre consente di ottenere una marcata diminuzione del TEWI. Considerando infatti l’attuale fattore di emissione italiano dell’energia elettrica prelevata da rete, le emissioni totali lungo l’intero ciclo di vita della pompa di calore calano di circa il 25% grazie all’utilizzo del fluido a basso GWP. Tuttavia, seguendo l’attuale trend di riduzione del fattore di emissione ed assumendolo nullo al 2050, tale riduzione può arrivare in prospettiva fino all’80%, azzerando così le emissioni indirette di CO2 dell’impianto
Design rules for the optimal sizing of a hybrid heat pump system coupled to a residential building
No full textNowadays the use of heat pumps is spread widely in new and refurbished high-efficient buildings. Heat
pumps can be very efficient but their energy performance is influenced by the temperature of their external
thermal reservoir which can be unstable during the heating season (i.e. outdoor air) and characterized by low
values. For this reason, the thermal capacity of the heat pump decreases in the colder days and in order to match
the maximum heating load of a building the unit must be slightly oversized. A suitable solution to avoid the energy
losses due to an excess of on-off cycles during the milder part of the season is the adoption of a hybrid system,
consisting of a heat pump, sized to partially cover the peak load of the building, coupled to a second heat
generator (back-up device). The aim of this paper is to assess the influence of the heat pump sizing, the unit
cycling losses and the typology of back-up system on the seasonal performance of a heating plant based on a
hybrid generator obtained by coupling a single-stage on-off air-to-water heat pump to a back-up device (electrical
heater or gas boiler). In this work, the dynamic model of the hybrid heat pump system is presented; several
simulations were performed to assess the seasonal energy performance of the system coupled to a single-family
house located in Bolzano (Italy) and to compare it with those of monovalent heating systems based on an air-towater
heat pump or a gas boiler only. The analysis enables to evaluate the energy savings achievable by
employing a hybrid system in which the generators can work in parallel or alternatively and to study the influence
of the cut-off temperature on the seasonal performance of the system. Results point out that hybrid systems can
be a suitable solution to achieve significant energy savings with respect to the classical monovalent systems.
More in detail, the largest seasonal efficiency was obtained by selecting a heat pump sized to cover the half of
the building peak load and by setting a control logic in which back-up and heat pump work in parallel: the
introduction of a cut-off temperature larger than the design external temperature is not beneficial. It is
demonstrated that an energy savings close to 16% can be achieved by adopting a hybrid system (air-to-water
heat pump + gas boiler) if compared to a traditional heating system based on a single gas boiler, even in
presence of an undersized heat pump
A strategy for the optimal control logic of heat pump systems: impact on the energy consumptions of a residential building
No full textThis paper presents a study on the effect of the modulation capacity of three different kinds of air-to-water heat pumps (i.e.
single stage, multi-stage and inverter-driven heat pumps) on the seasonal energy performance of the heating system coupled
to a typical single-family house located in Bolzano (Italy). The specific dynamic model of each heat pump and its control
logic has been developed by using TRNSYS 17. These models are able to take into account the energy penalty linked to the
on-off cycles by using experimental data obtained by the manufacturer of the selected heat pump units. A comparison of the
energy performance of the HVAC system as a function of the heat pump typology is presented. Results highlight the strong
influence of the control algorithm on the performance of the heat pump: it is shown that the multi-stage unit is unable to
fully exploit its energy saving potential since its typical control logic is not able to reduce the number of start-ups during the
warmer period of the heating season, when only one compressor is switched on. It has been demonstrated that dynamic
simulation can be a valid tool for the optimization of the control logic of the multi-stage and inverter-driven heat pumps, in
order to maximize the seasonal performance of the system and to minimize the number of on-off cycles
Dynamic simulation and energy performance analisys of a dual-source heat pump
No full textIn this paper the energy performance of a dual-source heat pump (DSHP) able to use both air and ground as
external thermal sources is analyzed by using TRNSYS17. The DSHP energy performance is compared with
those offered by a conventional ground-coupled heat pump (GCHP) and by an air-to-water heat pump (ASHP) in
order to evaluate the advantages obtainable with the use of a double external thermal source. Numerical
simulations are carried out by coupling three heat pumps (DSHP, GCHP and ASHP) having similar nominal
thermal power to the same residential building located at Bologna. By using dynamic simulations the seasonal
and annual energy consumptions of these three heat pumps are calculated and compared. The simulations have
been used in order to determine the best shifting strategy for DSHP between air and ground heat sources during
the season in order to maximize the energy performances of this kind of heat pumps. As expected, the results
show that the energy performances of DSHP are between the performance of GCHP and ASHP. It is
demonstrated that the use of the ground during the winter can eliminate the energy losses and the problems
linked to the cycle inversion due to the defrosting cycles and for this reason DSHP performs better than
conventional ASHP. However, DSHP can become more attractive of GCHP because the use of air as alternative
to ground allows a significant reduction of the boreholes size and, hence, a reduction of the investment costs. In
addition, DSHP can solve the problem of the undesired ground thermal drift in buildings characterized by
unbalanced winter and summer loads (with winter loads larger than the summer ones). A preliminary analysis
about the economic convenience of DSHP with respect to GCHP and ASHP is also presented. This study has
been conducted in the frame of the HEGOS (Heat pumps for EnerGy Harvesting Of Smart Buildings) project
Comparison between metallic-foam and finned-tube water-to-air heat exchangers
No full textThe thermal performance of two water-to-air heat exchanger prototypes, with the air-side conventional finned surface replaced by metal foams, is investigated. Two different metal-foam packaging techniques (S-type, K-type) are tested. The heat exchangers are inserted in the same fan-coil case, equipped with a 3-speed fan, to compare their performance under the same operative conditions. A 10 PPI aluminum foam with 96% porosity shows similar pressure drops and air flow rates with respect to the traditional finned fan-coil. Nonetheless, a strong penalty in terms of heat transfer rate is observed with respect to the conventional finned surface, due to the worse tubes-foam thermal contact and to the 60% lower surface-to-volume ratio of the metal-foam. Due to the presence of by-pass corridors for air, the performance of the K-type heat exchanger is worse than that of the S-type. Also the fin efficiency of the metal foam prototypes is lower than that of the traditional heat exchanger. The experimental data highlight that metal foams cannot compete with conventional fins if the tubes-foam thermal contact is not as good as that of finned surfaces
Influence of the hydronic loop configuration on the energy performance of a CO2 heat pump for domestic hot water production in a multi-family building
Full text linkIn this work, a numerical analysis of the influence of the hydronic loop on the energy performance of a CO2 heat pump dedicated to DHW production for an apartment
block located in Bologna (Italy) is presented. The energy model of the whole heating system, implemented in TRNSYS17, has been validated by means of a monitoring
campaign performed during the winter season of 2017- 2018. The experimental results highlighted a poor and unexpected energy performance of the heat pump. The comparison between experimental and numerical results showed a significant penalty of the heat pump performance due to an erroneous use of the hot stratified
thermal storage system. Outcomes of this paper confirm that CO2 heat pumps are very sensible to the temperature of the fresh water at the inlet of the gas cooler. This value can be strongly reduced thanks to the presence of the stratified tank in the hydronic loop
Experimental Study of A LTES Made By a Finned Heat Exchanger Immersed In a Paraffinic PCM
No full text–In this paper, a new Latent Thermal Energy Storage (LTES) system, made by a finned tube heat exchanger immersed in the commercial paraffinic Phase Change Material (PCM) RT44HC is studied experimentally. The storage capacity and the thermal performance of the LTES during both melting and solidification processes of the PCM was analysed for different test conditions using water as heat transfer fluid. In particular, experimental tests were performed by considering several values of hot and cold water temperature at the heat exchanger inlet, ranging from 55 to 70 °C and from 14 to 29 °C during charging and discharging processes, respectively. For each test, three different values of the water flow rate through the heat exchanger (25, 50, 100 kg/h) were considered. Results show how the thermal power increases considerably by charging (discharging) the LTES with higher (lower) inlet water
temperature and with a higher water mass flow rate. For a fixed inlet water temperature and for growing flow rates, an increase in thermal power up to 1.16 kW occurs. For fixed flow rates, a thermal power increase of 49.5% is registered going from 50 to 70°C of the inlet water temperature. The thermal performance of the LTES are also compared with those obtained using pure water as heat storage material, outlining that the storage capacity of the system using PCM instead of water is increased of about 300-400%
Dynamic modelling of a dual-source heat pump system through a Simulink tool
Full text linkIn this paper, the performance of a reversible Dual-Source Heat Pump (DSHP) system, able to exploit renewable energy from, alternatively, air and ground sources, is evaluated by using Matlab-Simulink. The actual source exploited depends on a simple control strategy on the basis of the current external air temperature. Yearly dynamic simulations have been carried out by coupling the DSHP to a detached residential building located in Bologna, in which heating and cooling loads are strongly unbalanced, and coupled to a borehole heat exchangers (BHEs) field. Different case studies have been analysed in which the length of the borefield has been modified. The obtained results show that an optimal switching temperature can be determined to maximise the Annual Performance Factor (APF) for a fixed BHE field length. Additionally, it has been demonstrated that DSHPs can be very useful in order to reduce the total required length of the borehole heat exchangers and, consequently, the associated costs, and to solve the problems linked to the ground temperature drift, which can be originated by the presence of an undersized borefield and/or by unbalanced building loads. As a consequence, DSHPs can be suggested for the retrofitting of traditional ground-coupled heat pump systems in presence of undersized BHEs
The benchmark of the SIMULINK open library ALMABuild for dynamic modelling of buildings
No full textNowadays, European Directives and National laws impose more and more strict limits on the primary
energy consumption of buildings, pushing towards a new generation of energy saving buildings named Near Zero
Energy Buildings (NZEB). In order to achieve an important reduction of the primary energy consumptions in
NZEB the use of renewable energy, which gives a discontinuous contribution during the day and the season, is
strongly encouraged; due to the typical unsteady behaviour of renewable energies, for an accurate analysis of
the behaviour of NZEB it becomes important to study the dynamic interactions between the building and the
adopted HVAC system. A dynamic analysis of the energy performances of NZEB can be obtained by using
specific dynamic simulation software (i.e. TRNSYS, ESP-r, Energy Plus, MODELICA, DesignBuilder) or by using
a customized approach based on the use of SIMULINK. In the past, some open block libraries made in
SIMULINK have been proposed for the dynamic analysis of HVAC system. However, a weak point of these
libraries is the creation of the building model. In fact, no fully satisfactory SIMULINK blocks for the accurate
modelling of a whole building have been presented up to now; in many cases, the user is called to add manually
all the envelope elements by setting the thermo-physical properties of each element and connecting each
element to the others. In this way, the modelling of a building becomes not only time consuming but it becomes
an activity characterized by a significant probability to make mistakes during the manual construction of the whole
model. For this reasons, in this paper a new SIMULINK library, named ALMABuild, for the dynamic modelling of
the energy behaviour of a building is presented. The strength point of ALMABuild is that the user is driven
towards the modelling of the building by means of a series of Graphical User Interfaces (GUI). In this paper the
main results obtained during the benchmark of this library, following the BESTEST procedure, are discussed and
the main advantages achieved by using GUIs for the creation of the dynamic building model are described
Numerical modelling and seasonal performance analysis of air-to-water heat pumps using low-GWP refrigerant R-454B as an alternative to R-410A
No full textIn this paper, a numerical model for air-to-water heat pumps is presented and validated with experimental data. The model is used with the aim to test the differences, in terms of seasonal energy performances, obtained by using the low-GWP refrigerant R-454B as alternative to R-410A. Each component of the heat pump (i.e. compressor, heat exchangers, fans, expansion valve) is modelled and its thermodynamic performance is evaluated following nested iterative cycles. Different configurations of the heat pump have been simulated. Results confirm that R-454B is a valid alternative to R-410A. An increase of the heat pump seasonal energy
efficiency ratio (SEER) up to 2.5% can be obtained with the low-GWP refrigerant
- …
