Andrea Gasparella

Chemical dehumidification by liquid desiccants: theory and experiment

Chemical dehumidification of air by a liquid desiccant in a packed tower has been investigated both theoretically and experimentally for air conditioning and industrial applications. A computer model of a packed tower, able to determine heat and mass transfer between air and desiccant, has been developed and a parametrical study was carried out considering the solutions H2O/LiBr and H2O/CaCl2 to determine the optimum operative conditions. An experimental apparatus including a packed tower and a desiccant regenerator has been described together with experimental results: a set of 70 experimental runs with H2O/LiBr. Data have been reported and compared against the results of the computer code simulations.

Technical and economical analysis of heat recovery in building ventilation systems

Abstract Heat recovery in ventilation systems can be obtained from both the sensible fraction and the latent fraction. The possible sensible and total heat recovery depends on the climate and on the operating period. Total heat recovery is limited in winter by the humidity of the supply air; this lowers the exchange capacity in the heating period. Three different climates are considered (Milan, Rome, Palermo), evaluating the recovery for unitary air ventilation flow rate and the economic savings, also taking into account the reduction in the heating or cooling capacity. Heat recovery in a ventilating system must always be evaluated, since the investment is often profitable.

Ammonia-water absorption machines for refrigeration: theoretical and real performances

Abstract In principle, absorption chillers of the ammonia-water type could work at temperatures well below the usual air-conditioning temperatures, arriving at the range 250–260 K, which can be useful for refrigeration applications. This possibility is studied for an air-cooled machine, comparing the results with the experimental data supplied by a manufacturer that recently commercialized such a refrigerator. The prediction is fair, and the study allows an insight into the internal parameters and into the possible behaviour for more severe conditions than those studied.

Unsteady state analysis of the compression cycle of a hermetic reciprocating compressor

In this work, an unsteady state analysis of the compression cycle of a small hermetic reciprocating compressor for domestic refrigeration was carried out. A specific one-dimensional model of the valves was developed and the mass and energy balances were applied to the refrigerant inside the cylinder to determine the mass, pressure and temperature behaviour and the heat and work transfer through the compression process. This analysis was inserted into a traditional steady state model of the compressor to evaluate the efficiency of the compression cycle and the performance of the compressor unit. The whole simulation code was validated against the experimental measurements carried out on a R134a commercial unit in a wide range of operative conditions: a fair agreement was found between predicted and measured performances. The simulation code can be a useful tool for the analysis, the design and the development of small hermetic reciprocating compressors for domestic refrigeration.

Analysis and improvement of the representativeness of EN ISO 15927-4 reference years for building energy simulation

Representativeness of weather inputs is crucial to limit the global uncertainty of building energy simulation results. The length of the multi-year weather data series and the methodology used for the typical month selection largely influence the results of the reference year development process. In this work, we investigate two possible modifications to the EN ISO 15927-4:2005 procedure aimed at improving the representativeness of reference year heating and cooling needs. The first modification maintains the reference years independent of their final use while the second one leads to the development of specific weather files for heating or cooling analyses by introducing weighting coefficients for the different weather parameters. The study is performed for five North Italy localities with 10 or less years in the data-set and for a sample of 48 simplified buildings. Both proposed modifications brought improvements to the representativeness of the reference year results.

Experimental Analysis on Chemical Dehumidification of Air by Liquid Desiccant and Desiccant Regeneration in a Packed Tower

This paper presents the experimental tests on the chemical dehumidification of air by a liquid desiccant and desiccant regeneration carried out in an absorption/desorption tower with random packing. The experimental set-up is fully described together with measurements, procedures, data reduction, and accuracy. The experimental tests include 46 dehumidification runs and 38 desiccant regeneration runs carried out with the traditional hygroscopic solution H 2 O/LiBr and the new solution H 2 O/KCOOH in the typical operative ranges of air conditioning applications. The experimental results are reported in terms of humidity reduction, desiccant concentration change, and tower efficiency. The experimental tests show that chemical dehumidification of air by liquid desiccants ensures consistent reduction in humidity ratio, which is suitable for the application to air conditioning or drying processes. The experimental results are also compared to a one-dimensional simulation code of a packed tower: a fair agreement was found between experimental and calculated performance.

Theoretical analysis of an open-cycle absorption heating and cooling system

Abstract In warm countries, such as Italy and Spain, the increasing demand for space conditioning cannot be met by the current capacity of installed electric power. This has led to a growing interest in cooling with natural gas. An interesting thermal cooling system uses open-cycle absorption. It treats the air directly without heat exchangers and with very low temperature drops. With absorption dehumidification it is possible not only to obtain a cooling system similar in performance to conventional thermal cooling systems, but also, with few modifications, a high-performance heating system fed by a natural gas burner, which combines simplicity with PER typical of a gas driven heat pump. The proposed new system described in the paper is studied both in winter and summer mode, evaluating the influence of the different parameters.

Common reeds (Phragmites australis) as sustainable energy source: experimental and modelling analysis of torrefaction and pyrolysis processes.

The aim of this study is to apply advanced analytical techniques and kinetic modelling to common reeds (Phragmites australis) to characterize its pyrolysis and torrefaction as possible environmental friendly and sustainable pathways of fuel upgrading. Simultaneous thermogravimetric and differential scanning calorimetry analysis have been carried out on common reeds. The evolved gases during the decomposition process have been analysed by a coupled infrared gas analyser and gas chromatograph/mass spectrometer. Different reed origins (China and Italy) and plant parts (stem and leaves) have been compared. The results have been used to calibrate a torrefaction kinetic model. The model has also been tested simulating a reed torrefaction run occurring in a bench‐scale apparatus, supplementing the chemical analysis with a thermal simulation of the reactor carried out through a finite elements approach. The results show that the proposed modelling approach allows the prediction of the reaction products with a satisfying degree of accuracy. Besides its phytodepuration potential, P. australis has proven to be an interesting natural biomass resource for thermochemical conversion processes and energy production both for its suitability and availability.

New ideas for energy utilisation in combined heat and power with cooling: II. Applications

Chemical dehumidification can be beneficial in a HVAC plant, both in terms of capital and operating costs. The sorption system can be integrated into a traditional plant, usually satisfying the latent heat load, but it can satisfy even the whole load with particular cycles which also use evaporative cooling. A number of applications are examined here, both integrated and self-sufficient systems, driven by natural gas or waste heat, working with liquid or solid sorption. Different lay-outs, performance and savings suggest new ideas for better energy utilisation in HVAC combined heat and power plants.

Extensive comparative analysis of building energy simulation codes: Heating and cooling energy needs and peak loads calculation in TRNSYS and EnergyPlus for southern Europe climates

The simulation codes are diffusing widely in building design and energy performance evaluation. They also allow to refine the steady-state methods, particularly the estimations of the utilization factors, according to the technical standard EN ISO 13790:2008. The necessary validation steps used for diagnostic purposes are not aimed to evaluate the agreement of the results over the spectrum of configurations and conditions in real applications. Moreover, the relative impact of a single parameter on the global performance can be investigated only with an appropriate choice of the set of configurations analyzed. In this work, a method to evaluate the relative inaccuracy arising from the choice of a specific simulation code has been applied to compare two well-known dynamic simulation software applications: TRNSYS 16.1 and EnergyPlus 7. The main envelope variables investigated are dispersing surface amount, wall insulation and heat capacity, glazings insulation and solar transmittance, glazing dimensions and orientation, and internal gains. More than 1600 configurations were obtained through a full factorial plan for two Italian climatic conditions. Monthly heating and cooling needs, heating and cooling peak loads, and peaks occurrence time have been considered. Inferential statistics allowed weighting of the different variables impact on the found deviations.