Issue 5/2005

The article is devoted to the evaluation of sound attenuators evaluation. The article describes the basic theoretical relations of sound attenuation are indicated in connection with attenuator geometrical design and the absorption capacity of the used material. An example is given of sound attenuator design is indicated for a typical HVAC installation. The main topic concentrates on sound attenuator optimization in terms of actual attenuation and hydraulic resistance. The author introduces a coefficient of attenuator quality that should be utilized in attenuator design by designer. Tables of other values of attenuator quality coefficients are also given for different types of multiple frames attenuators in tables.

The article indicates outlines appropriate specific rules for the dimensioning of suspended radiant heating panels for meeting halls heating (including their placement). The rules are documented based on actual examples.

The article represents the first one in a series of the articles focusing on problems with the condensing cycle of the contribution series concentrated on problems of refrigeration systems condensation side that will be published subsequently in this journal. As the refrigerating system functioning is influenced by climatic conditions at the installed location, the first two articles deal with these conditions in more detail and consequently they have a more general character. This article is concentrates on localization and year choice that was the most taxing on the refrigerating system operation. In the article the reasons are given for the choice of Prague as reference location and the choice of 2003 as the referenceyear.

The article describes the conditions necessary for the utilization of water vapors condensation heat in combustion products of natural gas boilers. The low-temperature boilers operation is compared with that of condensation boilers operation.

A new way of evaluation of the nonuniformheat load on man in building interior, based on the measurement of the so called “stereotemperature” is proposed. The way recommended by EN ISO 7730 so far and by the Government Directive No. 178/2001Code. in valid version cannot be successfully applied in practice being based on the radiant temperature asymmetry which reflects only the impact of the difference of human body irradiation on opposite sides. Because its optimal value can be reached e.g. by irradiation increase on the opposite side (by which human body suffers even if the asymmetry decreases, maybe to zero) but not e.g. by air conditioning unit application streaming the cold air at irradiated surface – asymmetry doesn’t change. Stereotemperature, in contradiction to asymmetry, reflects the physiological response of human organism because a) responses the radiation from one side only, b) convection impact is included as well. And more, the stereotemperature average equals globe temperature and from stereotemperature difference, if necessary, asymmetry can be estimated.

An under floor ventilation system providing two different airflow patterns (short and long throw) was tested and compared with a mixing and displacement ventilation system in a mock-up of a typical office. The impact of the relation between the penetration height of under floor airflows and the stratification of exhaled air contaminants on the inhaled air quality is shown. No difference between the ventilation systems tested was found in regard to the floor contaminant. The main conclusion is that an under floor ventilation system providing a short throw can ensure both a high air quality (comparable to displacement ventilation), while providing a low risk of thermal discomfort for occupants.

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