101,225 research outputs found
Self-adapting double and triple-lift absorption cycles for low-grade heat driven cooling
No full textMultiple-lift absorption cycles are an interesting option for cooling and refrigeration driven by waste or renewable heat. Compared with single effect cycles, they allow higher thermal lift or lower thrust, but they often require the use of controlled valves, which can cause stability and control issues. The self-adapting concept, firstly introduced in the two-pump series-flow double-lift cycle, replaces the valve with a phase separator, overcoming this drawback. In this work, five new cycle layouts, incorporating the self-adapting concept, are presented: the one-pump series-flow double-lift cycle and four triple-lift cycles. The cycles are compared in terms of COP and heat duties under various conditions, using NH3–H2O and NH3–LiNO3 as working pairs. It is found that the double-lift cycles have a COP in the range 0.35–0.20, about 0.1 higher than the triple-lift cycles. However, triple-lift cycles accept cooling water temperature up to 8 °C higher. Cycles with multiple pumps have higher efficiency than single-pump cycles, especially at high lift conditions. The use of NH3–H2O as working pair guarantees higher COP at low thermal lift, while NH3–LiNO3 has wider operating range and better performances at high thermal lift
Innovative small capacity gas driven ammonia-water absorption heat pump prototype for space heating and domestic hot water production
No full textTesting of a Falling-Film Evaporator for Adsorption Chillers
No full textIn this work, the performance of an innovative evaporator based on water falling film was investigated. The studied evaporator has been equipped with a recirculation system to maximise the wetted surface. Tests have been carried out in a lab-scale adsorption unit connected to a test bench recently realised at Politecnico di Milano labs for evaluating heat transfer performances under realistic operating conditions. Several ad/desorption cooling cycles were performed, setting different liquid refrigerant initial contents (0.9–1.5 kg), different chilled water inlet temperatures (7–20◦ C) and flow rates (200–1000 L/h) and different adsorbent bed temperatures (25–30◦ C). Evaporation performance has been determined in delivered cooling capacity. Moreover, the experimental data were used to calculate the overall evaporator heat transfer conductance (UA). Experiments showed how the heat duty peaks are mainly due to the thermal level of the chilled water that enters the evaporator, not the water content inside it because this value only affects the duration of the process. Instead, the UA value does not depend on the evaporator inlet chilled water temperature and initial mass content inside the evaporator. UA is 540–570 W/K for temperatures of chilled water entering the evaporator, equal to 10–20◦ C, and mass of refrigerant of 0.9–1.5 kg
Environmental life cycle assessment of industrial high-temperature to residential small-size heat pumps: A critical review
No full textThe decarbonization process of the industry and the heating sector, underway in Europe, directly involves
heating, cooling, ventilation, and air conditioning systems. In this context, heat pump technologies play a key
role in having the ability to be powered by decarbonized energy carriers (i.e., electricity from renewables for
vapor compression cycle, hydrogen for absorption cycle, etc.), as well as harnessing renewable or waste heat, in
different applications (i.e., industry, district heating networks, and civil sector). The European Commission
considers the life cycle assessment method one of the leading methodologies for environmental metrics. Many
scientific studies related to analyzing the environmental profile of heat pumps have been written using this
method. With the aim to investigate the outcomes achieved and modeling approaches applied, this study reviews
existing environmental life cycle assessment studies of (i) high-temperature, (ii) large-size (over 300 kWth), and
(iii) medium and small-size heat pumps. In total, 19 articles containing 637 scenarios were found in the literature
to be relevant to the research aim. The study analyzes different heat pump technologies (i.e., vapor compression,
absorption, and indirect Stirling cycles). The analysis shows that the use phase is the main contributor: (i)
average value of 94.6% for the global warming potential, (ii) 69.9% for abiotic depletion potential indicator
(metals and minerals). The analysis reveals that life cycle assessment studies apply a rather narrow approach and
lack variability in modeling. For future research, it is recommended that the thermodynamic behavior of the heat
pumps be properly simulated or monitored. In addition, a stochastic evaluation shall be included in the analysis
to reduce and highlight the uncertainty of the results, especially the global sensitivity analysis. Finally, high temperature heat pumps shall also be investigated using the consequential approach to understand better the
environmental consequences of installation in an industrial production process
Letter, [Author unclear] to Paulina T. Merritt
No full textHandwritten letter to Paulina Merritt from an unknown author, October 1, 1876.
Development of a gas absorption heat pump for residential applications
No full textThermally Driven Heat Pumps represent an option to reduce the energy consumption for space heating and
domestic hot water in hard-to-decarbonize buildings without impacting the electrical grid and utilizing the
current and future gaseous energy vectors with high efficiency. Ariston Group and Politecnico di Milano
developed a gas absorption heat pump for the residential market, exploiting design and manufacturing solutions to enable large-scale production and introducing technical features to assure high performance over the entire working range.
In particular, the use of a variable restrictor setup coupled with a patented solution, called “booster”, can reduce the temperature of the generator at high load and high lift conditions, enabling the heat pump to provide the nominal capacity from -22 °C to +40 °C of outdoor air temperature, with supply temperature up to 70 °C.
Moreover, coupled with a specifically designed combustion system, the heat pump can modulate at 1:6 ratio
of its nominal capacity. This feature makes it possible to maintain high efficiency also at part load conditions,
avoiding the on-off operation and making redundant the installation of inertial buffer.
Additionally, an innovative strategy to perform the defrosting of the air-sourced heat exchanger without the
need of acting on the thermodynamic cycle has been developed. This allows defrosting operations extremely
fast, while offering an almost negligible effect on the heat pump performance and substantially no interruption to the heating service and contributing to the elimination of the need to install an inertial buffer.
The thermodynamic core of the appliance was built targeting large scale production. It allows for high specific
capacity (kg/kW) and a small footprint (m2/kW) with the ability to serve nominal capacities ranging from 8 to
15 kW based on the configurations. Laboratory test to assess the performances based on the European Standard
EN 12309 returned a seasonal gas utilization efficiency on the net calorific of 1.50, a seasonal primary energy
ratio of 1.27, and extremely low electrical consumption for the auxiliaries
A comparative environmental life cycle assessment between a condensing boiler and a gas driven absorption heat pump
No full textGas absorption heat pumps represent an alternative to condensing boilers for space heating and domestic hot water production in existing buildings. In particular, they enable fuel saving and the exploitation of renewable energy even in heating systems based on radiators, which require high supply temperature. However, in order to provide useful indications to policymakers, manufacturers, and system designers, a fair comparison of two technologies has to be based, besides the energy consumption and the direct CO2 eq emissions, also the environmental impact over the entire life cycle. Thus, in this paper, the environmental profiles of a condensing boiler and a gas driven absorption heat pump are compared as competing technologies to provide space heating and domestic hot water in old (constructed before 1980) and not refurbished buildings. The assessment was carried out for three buildings located in three representative European climates, using 1 kWh of thermal energy produced by the two systems as the functional unit. The Ecoinvent 3.6 was used as background database and the EF 3.0 normalization as weighting set method. Uncertainty and sensitivity analysis were also included. The results show that the use phase contributes for more than 97% of the total impact for both the energy systems in the three climate zones. Despite the higher electricity consumption, the gas driven absorption heat pump offered a lower environmental profile compared with the condensing boiler, mainly because of the lower amount of natural gas needed in the use phase. In particular, an average reduction of 27% was found for CO2 eq, 25% for fossil resource consumption, and 22% for weighting results
Rettificatore per un generatore di vapore refrigerante per macchine termiche ad assorbimento, e generatore comprendente un tale rettificatore
No full textRettificatore (100) per un generatore (200) di vapore refrigerante, detto
rettificatore essendo atto a modificare la percentuale di una sostanza
refrigerante presente in flussi di vapore (V) generati per ebollizione di
una soluzione liquida (L) comprendente almeno una sostanza
assorbente ed una sostanza refrigerante assorbita e caratterizzato dal
fatto di comprendere almeno:
- un involucro (101) che si sviluppa lungo un asse di riferimento
sostanzialmente verticale (X) e comprende almeno un primo condotto
trasversale (102) atto a permettere l'immissione di flussi di detta
soluzione liquida (L) da bollire;
- almeno un primo corpo (105) costituito da una schiuma ceramica a
celle aperte che è alloggiato in detto involucro (101) al di sotto di detto
primo condotto (102) in modo da essere attraversato da flussi della
soluzione liquida (L) da bollire che scendendo verso il basso bagnano
le sue superfici, e da flussi di vapore (V) generati per ebollizione che
risalendo verso l'alto scambiano calore con la soluzione stessa che
bagna le superfici del primo corpo 105, causando una contemporanea
evaporazione di refrigerante dalla soluzione (L) liquida e la
condensazione di almeno una parte della sostanza assorbente
contenuta in detti flussi di vapore (V) in risalita
DIRECT FLAME BOILER, IN PARTICULAR FOR A GENERATOR OF COOLANT VAPOR FOR ABSORPTION THERMAL MACHINES, AND GENERATOR INCLUDING SUCH A BOILER
No full textDirect flame boiler (100), characterized in that it comprises at least: - a first body (1) which extends along a substantially vertical reference axis (X) and at least partially encloses a first internal cavity (2) suitable for receiving a liquid solution; - a second body (10) which, with reference to said substantially vertical axis (X), is arranged below said first body (2) and at least partially encloses a second internal cavity (12) in which there is placed a burner ( 11) capable of generating heat to keep the liquid solution in the first internal cavity (2) boiling; - a third body (10B) which is arranged for at least a part thereof around the second body (10), said second and third bodies (10, 10B) delimiting between them a third internal cavity (13) which is arranged, for at least a part thereof, laterally around said second cavity (12); and - a fourth body (20) which is interposed between said first body (1) and said second body (10) and is at least integrally connected to them, said fourth body (20) being configured so that hot fumes (Fc) produced by the burner (11 ) flows through it flowing from said second internal cavity (12) towards the outer surface (6) of the first body (1) and flows of said liquid solution flow through it flowing from said first internal cavity (2) into said third internal cavity (13), wherein said fourth body (20) comprises one or more first through holes (21) which extend in a direction transverse to said substantially vertical reference axis (X) and are configured to put said first internal cavity (2) in communication with said third internal cavity (13)
Arsenic accumulation and thiol status in lichens exposed to As(V) in controlled conditions
No full textThalli of epiphytic lichen Hypogymnia
physodes (L.) Nyl. and terricolous Cladonia furcata
(Huds.) Schrad., collected from an area with background
arsenic concentrations, were exposed to 0, 0.1,
1 and 10 lg mL-1 arsenate (As(V)) solutions for 24 h.
After exposure they were kept in the metabolically
active state for 0, 24 and 48 h in a growth chamber. In
the freeze dried samples glutathione (GSH), glutathione
disulphide (GSSG), cysteine (Cys) and cystine
were analysed and induction of phytochelatin (PC)
synthesis measured by reversed-phase high-performance
liquid chromatography in combination with
fluorescence detection or UV spectrometry. Total
arsenic content in thalli was measured by instrumental
neutron activation analysis (INAA). In H. physodes,
which contained higher amounts of arsenic compared
to C. furcata, total glutathione content significantly
decreased in samples exposed to 10 lg mL-1 As(V),
whereas in C. furcata a significant increase was
observed. In both species PC synthesis was induced
in thalli exposed to 10 lg mL-1
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