Как выбрать гостиницу для кошек
14 декабря, 2021
J. Rodriguez1, W. Sparber1
1 EURAC Research, Institute of Renewable Energies, Viale Druso 1, 39100 Bolzano, Italy
2 Universita degli Studi di Bergamo, Viale Marconi 5, 24044 Dalmine (BG), Italy
Corresponding Author, francesco. besana@eurac. edu
In the present work the attention is focused on the heat rejection part of solar combi+ systems looking at the performance of two different technologies: air-cooled heat exchanger and wet cooling tower. A deck for dynamic simulations in TRNSYS of a small Solar combi+ system has been prepared, where a thermally driven chiller with both the technologies runs. The air-cooled heat exchanger is simulated by an EES based code. In this investigation the effects of three different climates, resulting in different available dry and wet bulb temperatures, on the performance of the heat rejection equipment and of the solar combi+ system are studied. In particular the specific primary energy consumption per unit of rejected heat and the specific costs of the heat rejection per unit of cooling energy produced by the chiller are calculated. For the geometries of the cooling tower and dry cooler here considered and without implementing any fan speed control strategy, the results show that the wet cooling tower has a lower primary energy consumption and specific cost compared to the dry cooler in all the three different locations.
Keywords: heat rejection, dry-cooler, wet cooling tower, solar combi+ systems, absorption chiller.
Since the beginning of the 1980s, the growth rate of the utilization of solar collectors for domestic hot water production has shown that solar heating systems are both mature and technically feasible. However for several years, solar thermal systems seemed to be restricted to this application. When the first systems for combined domestic hot water production and space heating, called solar combisystem, appeared on the market, complex and individually designed systems were the rule. Especially in the Mediterranean regions the design had to take into account the seasonal displacement between the solar energy availability peak and the heating demand peak of the building. This, in summertime, could lead to overheating phenomena (stagnation temperature) causing thermal stress for most of the components and driving down the overall efficiency of the system. For these reasons the typical size of systems for single-family houses doesn’t exceed 15 m2 of solar collector area [1].
An integration of a small thermally driven chiller in a solar combisystem is a suitable solution to manage in a better way the heat production by solar collectors [2]. The share of building loads met by
solar energy can be increased, thereby reducing conventional energy consumption and giving to this technology a better possibility to penetrate the market. A system of this kind, which provides space cooling as well as space heating and domestic hot water, is called Solar combi+ system.
Next to the installation of a thermally driven chiller, cooling towers are often used in this kind of applications to reject heat coming from the cooling circuit of the chiller. In southern region for part of the day, this requirement needs evaporative cooling processes to cool down the water below the ambient temperature. For this reason beside the fossil fuels saving, drinkable water consumption has to be reduced especially in the regions with low water availability [3]. Moreover in few European countries there are law restrictions for this technology due to the possible legionella disease proliferation.
An air-cooled heat exchanger can be a possible solution for replacing a cooling tower. With this technology a good compromise between the efficiency of the absorption chiller and the electricity consumption is achieved.
Many articles treating this theme can be found in literature and some of them were used as starting point for this paper. Although the investigation was conducted for big capacity and for industrial processes purposes, overviews on heat rejection technologies and useful approach to this theme are presented by Jaggi/Gtintner manufacturer and University of Stellenbosch in South Africa, [4,5]. A contribution to these overviews in the direction of residential purposes with small heat rejection capacities and a different approach with dynamic simulations is given below.