When assessing whether it is effective to use evaporation cooling of air in a stable in a particular area, it is essential to have available long-term meteorological data. However, sometimes such data is for various reasons not available. This paper tests a method of generating an artificial series of daily maximum air temperatures from monthly averages. With standard deviation σ (ºC) determined from a statistical analysis of available data and a median expected temperature toc (ºC) obtained from fitting a sine curve through twelve and two monthly average maximum temperatures. The computed values are compared with measured values. The series generated from 12 monthly averages gave better results, although the series from 2 averages would do the job for assessing cooling efficiency. Results of a climatic development model show that around year 2050 the maximum air temperature in June, July and August will increase by 1.8 K, 2.3 K and 3.2 K, respectively, assuming a pessimistic scenario of the growth in greenhouse gas emissions, or by 0.7 K, 0.8 K and 1.2 K, respectively, assuming an optimistic scenario. Based on these values, a series of data was generated for the period around year 2050. It shows that the number of ...
The installation of an energy-saving facility must be preceded by analysisof its financial effectiveness. Among methods enabling such evaluation is thebasic net profit calculation method. For this, the annual consumption of electricityfor ventilation or of thermal energy for heating must be determined. The calculationformula uses the sum of energies for temperatures within the range fromthe calculation temperature for the area in question to the long-term average ofthe maximum temperature at the site, or to the temperature at which the heatingpower is zero. It is necessary to know the summary time of occurrence of a giventemperature during a year. The site data can only be assessed based on long-termmeteorological information. In fact, data used by current national standards todescribe climatic conditions in the Czech Republic are from the years 1901 to1950.The dependence of the average yearly temperature on altitude is shown inFig. 1 for the 1961 1990 and 1991 2000 periods. It is evident that the averagetemperatures for the latter period are nearly 0.6 K higher than those for the formerperiod, irrespective of the altitude.In this paper the climatic conditions are assessed based on daily datameasured throughout the period from 1 January 1991 to 31 December 2000.Weather stations were ...
In the contribution is submitted proposal of the vessel construction for water for industrial use. For heating is being used the secondary heat from the cooling system. More frequent utilization of this energy is limited of present by two facts: 1. The cooling devices contain toxic charge and therefore the pipeline for cooling medium passing through must not be in direct contact with the heated water for hygiene and safety reasons. 2. Sufficient thermal difference for effective heat sharing is possible only when the cool water is supplied to the place of heating.The suggested construction solves both these problems. The primary pipeline with ammonia is located on the container outer side into other heat-carrying protective medium. The inner arrangement provides the isothermal water stratification in container. In to the container is located the insert from non-conductive material with outer dimension smaller than the inner diameter of container. This enables formation of the slot filled by the heated water. Between the hot water in the slot and cold water inside the vessel creates the pressure difference, heated water rises into the upper part of the container and cold water is sucked into the slot from the bottom. Within the heating almost ...
This paper deals with the determination of several efficiency types of a cross-current recovery exchanger which is a part of the air venting system in the swimming pool hall on the premises of the Czech University of Life Sciences (CULS) in Prague. The product is a cross-current plate exchanger with a heat-exchanging surface of antirust aluminium. According to the manufacturer, the exchanger is fit for temperatures common in air ventilation systems. The air is forced in by fans at a flow quantity of 16,000 m3, maximum speed 2000 rpm, electric motor output 7.5 kW, filters for the air coming from the outside – grade G4, pressure loss from 42 to 200 Pa, filters for the air coming from the inside – grade G3, pressure loss from 46 to 200 Pa. The results presented are derived from in-process measurements taken on 31 January 2007 and 7 February 2007, from 9.15 to 11.30 on both days. Air temperature and air humidity were measured with 9636-51B-type sensors by Ahlborn, connected to the AHLBORN ALMEMO 5990-2 centre. These sensors were placed into each of the four input/output channels, very close to the exchanger itself (Fig. 2). The data measured were saved in the centre ...
The research is focused on energy sorrel as a fuel for local low-power heating systems with output up to 100 kW. Sorrel is perennial plant surviving in its location nearly 18 years which is very good from the point of crop expenses. It is a robust plant with height of about 2 m in second year of plantation. Dry phytomass is energetically rich fuel with total heating value 17.5 – 18.0 MJ*kg-1 at the average yield of 10 tons per hectare. An experimental combustion of pure sorrel and its blends were done with boiler VERNER A25 – a hot water boiler for pellets. 11 different sorrel fuels consisting of 5 primary kinds were tested during the experiment: sorrel (Rumex tianshanicus x Rumex patientia), Phalaroides arundinacea, Canabis sativa, pine-bark, sorrel (Rumex tianshanicus x Rumex patientia), brown coal. Based on collected data it is possible to obtain an overview of these fuels and their emission properties. Satisfactory values of CO concentration are possible to gain partly by choosing appropriate combustion device and its settings and partly by mixing with other types of fuel. In the case of sorrel the combination of both has been shown very useful. It is very hard to ...
In the technical field the energy balances are derived from the 1st thermodynamic law, which covers merely the instantaneous quantitative aspects of heat flows. In terms of energy conservation law these balances are expressed in the form of constant sums of exergy and anergy. And that is why they cannot, or can only to a very limited extent, be used to define the transformation of part of the energy (exergy) to the less valuable energy (anergy). Using the 2nd thermodynamic law we have a chance to trace the energy transformation through entropy, a quality indicator of every heat process and an accompanying symptom of process irreversibility. The plate air-to-air heat exchanger, whose exergy analysis is in the spotlight of our interest, operates, in terms of the laws above, in irreversible changes, while the change of entropy induced by the heat flows depends on the construction and surface of the heat exchange areas. The article analyses the influence of air inlet temperatures on the thermal exergy efficiencies of the heat exchanger and the heat loss exergy. Assessment is based on extensive measurements of the temperature, humidity and flow rate of the heated and cooled air in the plate heat exchanger. Both ...
