Issue 3/2009

It was necessary to make a list of rules regarding the computational evaluations of buildings for references as to the construction and energy saving quality thereof, which is sufficiently accurate for such a category and limits uncertainties and possibilities of presentation of speculative results due to a generally increasing interest for energy efficient buildings (low-energy consumption and passive houses).

Authors describe in the article numerical analyses of thermal and fluxional fields in a heated room in relation to situating the heating radiator. Two designs of heating radiators in the form of four variants of the solution are discussed therein. Heating radiators, designed in the classic way, were situated below the window at the perimeter wall, the inside side wall and the opposite inside wall. The heating radiator, designed in the balance method, was situated under the window, only.

Author describes the potential of heat pump application in the system of district heating and the problems that might occur when combining the operation of a heating plant and a heat pump system. Further, balance equations of a system comprising several heat pumps operating in series are provided as a basis for creating a calculation software tool. The tool allows for carrying out both efficiency and economic effectiveness analyses.

The article includes fundamental information regarding the new method of cooling in rooms, in which people stay or work, by way of open cooling ceilings belonging in the group of radiant cooling systems. It describes the structure, refrigerating capacity and the system dimensioning (sizing) thereof. Examples of their installations are shown in numerous pictures. The significance of this cooling system consists in the fact that it works with higher temperature of cooling water and so it saves energy and operation costs in comparison with the classic cooling method.

Different methods of continuous control of fans at air-cooled heat exchangers are presented and advantages and disadvantages are discussed. Finally, a comparison of energy consumption and noise reduction based on measurement results is carried out. It can be presumed from presented measurements that the basic correction for reduction of sound pressure level of protected external building areas at night according the Czech Regulation No. 148/2006 Sb. (?L=–10 dB) is reached at speed reduction by approx. 30 %. However, the sound behavior is very individual at phase cut control, so this presumption needn’t be fulfilled at each motor. And the capacity control has also other benefits then just a noise reduction. This article is a free continuation of the article “Energy Consumption and Noise Level of Air-Cooled Heat Exchangers at Part Load” published in VVI No. 2/2009 by the same author and it completes the theme of capacity control of air cooled heat exchangers.

The article presents both natural and artificial ionization of the air. For artificial ionization there are used generators of negative ions – ionizers. These devices can be built-in as a part of an aircleaner. They can also be used independently for increasing sedimentation of particulates indoor air and improving indoor air quality. In the paper there is informed about both mobil and personal ionisers.

Author summarizes in the article results of a five-year collection of hourly readings of thermal and humidity values in the industrial area situated in the eastern part of Prague. The selection taken from more than 120 original statistical graphs that were created during the period of years 2004–2008 shows possibilities of such evaluation in examples after the classification thereof according to types. He shows also a contour map of average frequencies with basis t-x. Further, the contribution is engaged in the analysis of conditions for designing the air conditioning, which were created on the basis of cumulative frequencies. He introduces use of three limiting states regarding the design of the cooler; there are defined conditions for run of the reheater installed in the air conditioning unit and states use thereof for dimensioning outputs of air conditioning unit elements in the standard (sample) design. Next chapter shows directions of the method of how to evaluate humidification or dehumidification from the view of water quantity that has to be evaporated in or condensate from the air during the traced period of time. The comparison of the average annual energy intensity related to different thermal and humidity microclimatic requirements regarding the inside environment are based thereon.

The building of the Faculty of Mechanical Engineering, CTU in Prague – Dejvice, has been heated by a ceiling radiant heating system („Crittall“ system) since 1961. One building block has been equipped by means which enable to use the pipes of the radiant heating system for ceiling radiant cooling. As optimization of this system is desired, the first step to be performed is the identification. Because of a complicated physical description of the entire system and a set of measured data which is large enough to perform statistical identification, a decision was made to identify the system by subspace identification methods (4SID). Scilab’s special libraries were used that not only identify the system model, but also design a state observer. The resulting identified model shows maximal deviation of 1 °C on verification data set and even 0,5 °C around the linearization setpoints. Such model can be used in modernmultidimensional controllers, such as model-based predictive controllers.

Author describes the technology of air ducts cleaning, particularly of exhausting systems polluted with greasy adulterants. The technology described is available in the CR and can be applied in considerably unapproachable air duct lines. Polluted and greased air ducts make probable sources for fire and hygienic risks. Operators and owners of air handling equipment should pay adequate attention to the cleaning of air ducts and whole systems. It is supported with the draft of the European standard prEN 15780 Ventilation for buildings – Ductwork – Cleanliness of ventilation systems.