martedì 1 settembre 2009

KEEPING ON WRITING...

Here you can read an article I translated from Italian into English concerning a pretty technical issue: absorption chillers. The article will be published in the proceedings book of an international conference about Solar Cooling. If you have any comments as far as grammar or style are concerned, please do not hesitate to post your comment!

Bye


USING HOT WATER TO COOL: INDIRECT- FIRED ABSORPTION CHILLERS

1. INTRODUCTION

The demand for cooling during summer, especially for what the tertiary is concerned, is growing steadily, both because more comfort is required and because of the noticeable rise of temperature in recent years. At the same time, the good traditional methods to allow a good comfort within the buildings seem to have been forgotten in the most recent construction techniques.
The growing use of cooling systems with compression chiller powered by electrical energy is certainly the main cause of the increase in the demand of electricity in summer, which sometimes leads to failures in power supply. The greenhouse gases, among which CO2, increase with energy production or with the loss of refrigerant fluids. Needless to say, this damages the environment and, at the same time, contributes to the vicious circle related to climatic changes. All this has lead to the need for real energy savings (D.L. 192) and to take into consideration the opportunity to use cooling systems with low primary energy needs which use renewable energy, such as thermal solar, biomass and photovoltaic systems.
There is ample choice of technologies for the passive cooling to improve indoor comfort and to drastically reduce the summer energetic need, both for buildings still to plan, and for existing building structures, both domestic and commercial.
Besides this, solar radiation is largely available in nature. The solar technologies for cooling are efficient and generally reliable both for the short and long term. These technologies do not make use of harmful refrigerant fluids (as a matter of fact, they generally use mixtures of water and LiBr) and have minimal energy consumptions in comparison to the traditional systems and therefore operating costs are lower.
Although absorption refrigerators powered by hot water –steam-combustible gases have been available to the market for more than a century, these were available only for elevated powers. In recent years the technology of the absorption cooling has made amazing progress, using new materials and electronic components, raising the quality standards both in terms of efficiency and reliability. Today we are witnessing a rapid development of enbloc frigorific absorption chillers of low power, hot water direct- fired (to 85-90°C). It is recognised that this opens interesting perspectives for their combined use with solar collectors.
It is impossible to foresee the course of the fuel prices of the traditional sources over a long period which is another element that has to be valued. These systems have a smaller environmental impact in comparison to the conventional systems of conditioning.

2. SPECIAL QUALITIES OF SYSTEMA’S ABSORPTION CHILLERS COMBINED WITH SOLAR COLLECTORS

Systema S.p.A. developed a unique absorption system in 2 different versions. The first one is an enbloc absorption chiller complete with all accessories (cooling tower, pumps, hydraulic connections, pipelines between absorption chiller and tower, valves, filters, pressure switch, differential pressure switch, control devices for temperature etc.). Being compact and completely enclosed, transport and installation are easy and fast. In the second version the cooling tower is separated from the absorption chiller and does not include the above mentioned accessories.

The absorption group must be selected according to needs of the building to be cooled, and to the quantity of hot water required.
The main advantages of using an absorption chiller powered by under vacuum solar collectors are:
• Use of thermal energy otherwise dissipated
The use of thermal energy allows lower costs and high energy savings. For these reasons absorption chillers are compared to energy recuperators;
• Environmental- friendly thanks to the use of a natural solution.
No harmful fluids are used. Furthermore, the energy used to power the absorption chiller has a low impact on the environment (low CO2 emissions);
• Low consumption of electric energy which is used exclusively for operation of circulation pumps;
• Simple and compact system thanks to enbloc equipment complete with all the necessary accessories, as a consequence, the installer will only have to connect pipelines for the hot water and conditioning systems. A further connection for makeup water must be provided to compensate for losses by evaporation from the cooling tower;
• Outdoor installation: space-saving solution;
• Modulation according to the thermal load thanks to inverters for managing the pumps. Thanks to Systema-Broad enbloc systems, frigorific power can be modulated from 20 to 100%. This allows water-supply/ electrical energy/ cooling water reduction, according to the customer’s needs;
• High efficiency (COP= 0,74)
The absorption chillers mod. SYBCTDH and SYBYDH have higher performances (COP= 0,74) than other conditioning systems of the same power which use hot water indirect-fired absorption chillers with low temperature (90°C);
• Long life-cycle and reduced need for maintenance: the reliability of the absorption chiller is due to minimal moving mechanical components and compressors;
• No noise and no vibration;
• Low fixed costs: since no electric cabin and transformer room are needed, the final user will have less fixed costs.
In order to satisfy several ranges of power capacity Systema can supply outdoor enbloc absorption chillers of high power or a series of absorption chillers can be installed using the cascade principle since the cooling tower is already included in the system.
The available powers capacity with temperature water of 98°C are: 45 kWs; 70 kWs; 175 kWs; 437 kWs; 656 kWs; 744 kWs; 875 kWs; 1094 kWs etc…

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