1,720,990 research outputs found
Gypsum based composite materials with micro-encapsulated PCM: Experimental correlations for thermal properties estimation on the basis of the composition
No full textComposite materials containing phase change materials (PCMs) are obtained by mixing PCM microcapsules with traditional construction materials. The composite materials thermal properties, which depend on the composition, are required when dynamic simulations of building structures containing composite material with PCM are performed. In order to avoid the need of measuring density, thermal conductivity and specific heat capacity for each possible composition, in this work correlations for the estimation of these thermal properties for gypsum based composite materials with micro-encapsulated PCM are derived. The correlations, obtained on the basis of experimental measures, give the composite material thermal properties as function of gypsum, water and PCM mass and volume fractions; it is verified that the correlations for density and thermal conductivity can be applied in the whole temperature range, including both the PCM liquid and solid phases, while a correction based on the temperature is applied for the correlation for specific heat capacity to extend its validity to the phase change temperature range. The correlations fit the experimental data with an error comparable with the measurement uncertainty and, when tested on a commercial product, they are able to predict its thermal properties with good accuracy
Simplified method for modification of weather data file for energy simulations within urban areas
No full textEnergy simulations for the estimation of building energy demand are in almost all cases carried out for
each site with a TRY (i.e. Test Reference Year), based on data collected at airports, thus out of urban
areas. Nevertheless, within urban areas, climatic and more generally environmental conditions – the
aspect mostly studied, though not the only one, is the Urban Heat Island – are different from the ones
in non urban zones, thus using the data collected at airports may introduce sometimes relevant errors
in the final result of the energy demand estimation. Nonetheless, climate data collected within urban
areas are rarely available over a long period of time necessary for building historical series (the World
Meteorological Organisation recommends 30 years).
In this paper the case of Milan is studied and a simplified method is proposed for estimating the
intensity of the Urban Heat Island, namely the increase in urban temperatures, which is an unsteady
phenomenon, over one year. The proposed method is based on the modification of weather data file (in
this case the IWEC for Milano Linate airport) with corrections linked to circulation types. Thus the
energy demand for an office building type in Milano is investigated, carrying out simulations both
with corrected climatic data and with the ones from airport measurements, results are then analysed
and discussed
Analysis of gas-fired NH3-H2O generator with cross flow gas burner
No full textThis paper presents a model to simulate the combined heat and mass transfer processes that occur in a gas-fired generator of an ammonia water absorption heat pump. The model comprises three interconnected components: the gas furnace, the distillation column and the rectifier. The furnace is modeled like a well-stirred single volume. The distillation column and the rectifier are discretized along their axial dimension. Several heat transfer mechanisms are simultaneously solved: radiative and convective heat transfer between combustion products and generator finned surface, flow boiling and pool boiling in the two-phase ammonia water mixture inside the distillation column. The model is applied to operating conditions of interest in real applications. The generated outputs provide insight on the internal gradients, the quantification of gas furnace efficiency, and effectiveness of solution boiling and internal heat recovery. The model can be used for the simulation of absorption heat pumps with modulating gas burners. © 2015 Elsevier Ltd. All rights reserved
Experimental characterization of a newly developed air-source waterammonia gas absorption heat pumpfor residential applications
No full textModelling and experimental analysis of a GAX NH3-H2O gas-driven absorption heat pump
Full text linkThe experimental analysis of a gas-driven NH3-H2O heat pump whose cycle approaches the GAX concept is carried out. Full load operation is investigated by varying hot water temperatures and partial load operation is investigated by decreasing gas input down to 50% of the full load value. Numerical simulations bolster measurements accuracy and provide insight on the variation of cycle COP and Gas Utilization Efficiency (GUE), based on gross calorific value. A nearly constant GUE of about 1.5 is found for hot water temperatures lower than 50°C. The GUE steadily decreases above 50°C, reaching about 1.33 at 60°C. The COP varies more smoothly, from 1.73 at 45°C to 1.60 at 60°C. The GUE and COP reduction at 50% of the nominal gas input is 6.8% and 6.4%, respectively. Simulations suggest that performances at partial loads can improve if active control of solution mass flow rate is implemented. © 2016 Elsevier Ltd. and International Institute of Refrigeration. All rights reserved
Development and economic/environmental benefits of a gas-fired absorption heat pump for domestic heating
No full textCurrently, the shift towards completely renewable and electrified space heating appears to be a necessary step in effectively mitigating climate change. However, this will require a long transition period to upgrade electricity generation and distribution capacity, as well as to renovate building envelopes and systems. Gas Heat Pumps (GHP) represent the most suitable option to reduce fuel consumption and CO2 emissions in building heated by gas boilers, thanks to their ability to efficiently deliver high supply water temperatures without reducing the heating capacity.
In this work, a single effect ammonia-water GHP for space heating and domestic hot water production is described. The GHP development was driven by three main goals:
1. Wide use of commercially available components, as stainless-steel plate heat exchangers, to boost the GHP industrialization.
2. Performance improvement in the whole wide range of operating conditions, thanks to the control of the flow rate of liquid solution.
3. Reduction of dimensions and cost by introducing a new design for some components of the GHP’s generator.
The GHP's ability to deliver high-temperature water without reducing the available heat output (in this case, 10 kW, but easily scalable) makes it suitable for replacing boilers in existing buildings with high-temperature heat distribution (radiators), reducing energy consumption by at least 30% with respect of a gas boiler. The achievable reduction in consumption and emissions is demonstrated through the calculation of yearly fuel consumption in specific case studies Chinese and international potential applications. These calculations relay on laboratory data measured in an accredited laboratory and are based on the BIN method, which includes specific climate data and customized heating curves
Numerical investigation on semi-GAX NH3-H2O absorption cycles
No full textDouble-lift absorption cycles represent a suitable solution for air-cooled thermally driven cooling applications. Among the several existing double-lift configurations, semi-GAX cycles are known as the most promising in terms of efficiency. These cycles incorporate the GAX effect in a pressure staged cycle, by means of a split on the solution leaving the low pressure absorber. Two configurations of the semi-GAX cycle have been proposed in the past, the semi-GAX 1 and the semi-GAX 2. The former achieves the GAX effect between the intermediate and the high pressure levels, the latter between the low and the intermediate. Within this paper, the semi-GAX cycles are numerically investigated at operating conditions suitable for a low temperature driven (e.g., by flat plate solar collectors) air conditioning application. The peculiarities of the two cycles are described and the factors affecting their performances are underlined. The COP resulted to be strongly influenced by the split ratio, which determines the intermediate pressure and the possibility to achieve the GAX effect. If the split ratio is optimized to achieve the maximum COP, the COP is higher for semi-GAX 2 for air temperatures below 27 °C and for semi-GAX 1 above. In both cases, the maximum air temperature which allows a circulation ratio below 15 is 40 °C, with chilled water at 7/12 °C and driving temperature of 90 °C. © 2016 Elsevier Ltd and International Institute of Refrigeration. All rights reserved
Combining high-end architecture and low energy: energy analysis to support the design of a large office building within the GreenBuildingplus project
No full textThe paper presents the analysis made to support an Architect Studio (Richard Meier, NY) in the process of designing a large office and laboratory building (6 400 m2 above ground and 10 600 m2 under ground) that will be constructed in 2008 in the new technology area near Bergamo. The building, following the design style of Meier (see for example the Dives in Misericordia Church in Rome) aims at constant visual contact of the occupants with the outdoor and the sky through use of transparent surfaces. Based on analysis made by eERG, the resulting challenge from the energy and comfort point of view has been addressed via a number of refinements and additions to the original design. The owner aims at achieving the GreenBuilding partner status
Macchina termica
No full textMacchina termica (1) comprendente:
- una miscela refrigerante comprendente almeno un fluido ed un cofluido avente
volatilità inferiore alla volatilità del fluido;
- un condensatore (2);
- un compressore (3) che comprime ed invia al condensatore, mediante una linea
di alimentazione (4), flussi di vapore (V) della miscela refrigerante in cui il fluido è
presente in una concentrazione prevalente rispetto al cofluido, il condensatore
condensando almeno parzialmente i flussi di vapore (V) mediante cessione di calore
ad un primo fluido di scambio termico (F1);
- mezzi regolatori di flusso (10, 12, 14, 15) atti a immettere lungo la linea di
alimentazione (4), per essere miscelati con i flussi di vapore
nel condensatore, flussi liquidi (L) della miscela di refrigeranti in cui il cofluido è
presente in una concentrazione prevalente rispetto al fluido;
- un evaporatore (5) che riceve in ingresso flussi di miscela refrigerante usciti dal
condensatore, evapora in parte i flussi ricevuti mediante assorbimento di calore da
un secondo fluido di scambio termico (F2), ed emette flussi di miscela refrigerante
aventi una parte in fase di vapore arricchita di fluido ed una parte in fase liquida
arricchita di cofluido;
- un separatore di fasi (7) che riceve e separa tra loro, i flussi di miscela
refrigerante aventi una parte in fase di vapore ed una parte in fase liquida, la parte
di miscela in fase di vapore essendo destinata al compressore, la parte di miscela
in fase liquida essendo accumulata in un accumulatore (8) compreso nel o associato
al separatore di fasi. Il controllore (50) pilota anche uno o più tra i mezzi regolatori
di flusso in modo da variare la quantità di miscela in fase liquida arricchita di cofluido per
immettere flussi liquidi (L) lungo la linea di alimentazione (4)
- …
