Giovanni Angrisani

Thermo-Economic Analysis of a Solar Heating and Cooling System With Desiccant-Based Air Handling Unit by Means of Dynamic Simulations

Solar Heating and Cooling systems are a virtuous alternative to conventional air conditioning plants, as a renewable energy source (solar energy) is exploited.In this paper the coupling of low temperature solar devices with an innovative desiccant-based air handling unit, which meets the sensible and latent loads of a simulated lecture room, is analyzed through TRNSYS dynamic simulation software. The components have been characterized by means of experimental tests carried out at the test facility of Universita degli Studi del Sannio. The desiccant-based air handling unit current set-up allows summer operation only. However, heating operation is also simulated, as comfort conditions can be maintained in the conditioned space exploiting solar thermal energy also in winter, with some modifications to the air handling unit. A parametric analysis is performed to compare different technical solutions (collector types, surface, tilt angle) and to identify the optimal one, taking into account energy, economic and environmental performance with respect to a reference system.The best case in terms of energy and environmental performance is represented by evacuated collectors, achieving a primary energy saving of 64% and a CO2 emissions reduction of 61%; flat-plate collectors are instead the best solution in terms of pay-back period (6 years).Copyright

Application of the TEWI Methodology to a Desiccant Cooling System Interacting with a Microcogenerator

Desiccant cooling systems, supplied by fossil or renewable fuels, represent a very interesting alternative to conventional electric units based on cooling dehumidification for air conditioning purposes, as they can achieve significant energy and emissions savings. The analysis of environmental impact of energy conversion devices, e.g. in terms of global warming effect, is usually limited to energy-related emissions (indirect contribution), neglecting direct greenhouse gas emissions related to working fluids, such as refrigerants. The Total Equivalent Warming Impact (TEWI) is a more comprehensive methodology, as it takes into account both direct and an indirect contributions to global warming. In this paper, this method is applied to a small scale trigeneration system, in which a microcogenerator, a chiller and a boiler interact with a hybrid desiccant-based cooling system, equipped with a silica-gel desiccant wheel. This trigeneration system is compared with other two systems, in order to assess its potentiality in terms of TEWI reduction. The different direct and indirect contributions of the several equipment are evaluated, and the share of the direct contribution is investigated, considering both the overall TEWI of the complete system, and that of the electric vapour compression device only. Finally, the effect of the greenhouse gas emissions of the electricity production mix and of different values of the Global Warming Potential (GWP) of the refrigerant fluid on the overall TEWI of the three compared systems is investigated.

Residential microcogenerators for multifamily houses

Miniaturization of energy conversion devices is an ongoing process which could also be extended to cogeneration systems. Many models of microcogenerators are being commercialized worldwide nowadays. With respect to energy performance, many benefits are expected by these systems, such as the reduction of cycling losses and of transmission and distribution losses due to distributed generation. Furthermore, the reduction of performance with the size of the device must be considered to evaluate the effective reduction of primary energy consumption, greenhouse gas emissions and operating costs. This paper reports the results of an energy, economic and environmental analysis performed on different microcogenerators used to meet energy requirements of a residential building located in Southern Italy. On the basis of thermal and electric load profile of a typical residential user, two configurations have been considered: central and autonomous heating system. Primary energy saving is satisfactory for microcogeneration systems considered, ranging between 16.6 % and 26.4%. A similar results is obtained by environmental parameter with avoided CO2 emission higher than 24%. The economic analysis does not produce positive results due to high specific investment cost of small size cogeneration units and low operating hours per year. Finally the solution based on centralized heating system provides the best results.

Dehumidification and Thermal Behavior of Desiccant Wheels: Correlations Based on Experimental and Manufacturer Data

ABSTRACT Desiccant cooling systems (DCS) represent a suitable alternative to conventional systems for air-conditioning purposes. Their benefits should be correctly assessed by means of dynamic simulations, taking into account both the operating context and the available control variables. Several models are available in literature to model solid DCS based on desiccant wheels (DW). Nevertheless, physical models are rather complex to be implemented in dynamic simulation tools of building-integrated energy systems, while constant effectiveness models have low performance. Regression models can represent a suitable alternative, as they can provide high accuracy but with a low modeling effort. In this paper, experimental data are used to develop correlations to predict the dehumidification and thermal performance of a DW, as a function of inlet air temperature and humidity ratio, regeneration temperature, air flow rates, and rotational speed. Statistical tools are used to investigate the effect of those independent operating variables. Furthermore, the selection software provided by another DW manufacturer is used to generate operational data of a further desiccant rotor and to derive the related correlations. At last, the proposed model is compared with the correlations found in the relevant literature. The results show that a very good agreement is found in the comparison between measured and predicted values, with maximum relative errors not higher than 5%. Furthermore, an excellent behavior of the proposed model is also found when it is used to simulate a generic desiccant wheel, without the need of a detailed physical model. Finally, a better agreement is found with respect to other models based on correlations developed in literature, even using a higher number of coefficients to be calibrated.

The Micro-cogeneration and Emission Control and Related Utilization Field

Micro-cogeneration is a developed technology aiming to produce electricity and heat close to the final users, with the potential, if designed and operated correctly, to reduce both the primary energy consumption as well as the associated greenhouse gas emissions when compared to traditional energy supply systems based on separate energy production. The distributed nature of this generation technology has the additional advantages of (i) reducing electrical transmission and distribution losses, (ii) alleviating the peak demands on the central power plants, and (iii) diversifying the electrical energy production, thus improving the security of energy supply. Micro-cogeneration devices are used to meet both electrical requirements and heat demands (for space heating and/or hot water production) of a building; they can be also combined with small-scale thermally fed or mechanically/electrically driven cooling systems. Many micro-cogeneration units are already commercialized in different countries (such as Japan, Germany, United Kingdom, etc.) and in recent years several researches have been carried out in order to advance the design, operation, and analysis of this technology. Currently the use of commercial micro-cogeneration units in applications such as hospitals, leisure facilities, hotels, or institutional buildings is well established. The residential cogeneration industry is in a rapid state of development; the market remains not fully mature, but interest in the technology from manufacturers, energy utilities, and government agencies remains strong.