Issue 4/2007

For many commercial and industrial plants, maintaining required ventilation rates can result in a significant operating cost. Fortunately, passive (i.e. enthalpy exchangers) and active (dehumidifying) desiccant systems can be used to reduce the load on the HVAC equipment and reduce its operating costs. Considering current scenarios of energy costs, certain applications of these dehumidifier technologies were found to be economical in some areas of the U.S. and the respective climates. In this paper, authors expanded the evaluation to cover the relatively moderate climate of Central Europe. As in the U.S. situation the potential cost savings and return on investments had to be assessed individually for each application and solved on an hourly basis.

The author summarizes the preliminary results of thermal comfort evaluation in five American buildings. The study included long-run measuring and evaluation of air temperature, relative humidity, draught, flow velocity, vertical temperature gradient and carbon dioxide concentrations. The measurement was carried out according to the ASHRAE Standard 55-04. The preliminary results indicate that in most cases the measurements results were consistent with the personal comfort sensation of individuals evaluated by questionnaires. At present, the study continues in additional five office buildings around the USA.

The paper deals with a possible utilization of ceiling heating systems for summer high-temperature cooling. Indoor climate parameters achievable with a primary heating ceiling panel used for summer cooling are discussed on an example of open-space office using mathematical simulation.

The author presents his opinions and experience acquired during years spent in design practice. He compares the basic Czech legislation related to HVAC design with the European Union regulations. After describing the basic requirements on the microclimate in different cultural buildings, the paper pays attention to air conditioning of theatres. A detailed requirements analysis is elaborated including recommended solutions.

Through a brief evaluation of energy demand for heating the author identifies the basic issues associated with the use of closed fuel appliances. He explains closed chimney systems installed with closed fuels appliances in low-energy houses.

There are numerous reasons for problems with noise to occur in heating and air-handling equipment. One of them is a high acoustic pressure level inside ducts or pipes caused by the sound power of ventilating fans or by the noise generated from gas combustion in burning equipment. The surface of ducts or pipes then becomes a source of noise for the ambient environment. The paper is focused on those cases, where pipes or ducts are made from relatively thin metal sheet.

The paper evaluates the function of another ten equipment types designed for increasing the air cleanliness and for improving the environment comfort in rooms. Under the same and mutually comparable experimental conditions, the antidusty effectivities of these air cleaners were determined. Their volumetric air-flows (air outputs), noise levels and production of air ions and ozone were also measured.

The surface temperature of radiation surfaces affects the thermal comfort of persons at indoor environment. The author evaluates the various situations of local discomfort that take place at heating or cooling owing to radiation asymmetry of ambient surfaces – trees, walls and floors. He proposes an optimal solution.

The article deals with the modelling of a solar energy seasonal accumulation into water and semi-infinite ground massif, intended for the heating of a family house with low energy consumption. The heating system is an extremely low-temperature one and the accumulator discharging is natural (exergetic), without use of a small heat pump that would decrease the accumulator volume and the solar collectors surface.

The article describes the differencies between the temperature efficiency and exergy efficiency of recuperative heat exchangers used in ventilating. Theoretical values of the exergy efficiency are verified by laboratoria measurements of two type of heat exchangers (plat plate and heat pipe ones) under different heat capacities of inlet and outlet air flows. Also results of the operational measurements on existing flat plate heat Exchange under equal heat capacities o fair flows are presented.

The author makes a presentation of the hardly solvable problem of humidity condensation at small and medium winter stadia. He clears up the main humidity sources and their unfavourable effects at condensation. At the same time he makes the reader acquainted with the possibility of ventilation air drying while using adsorption dehumidifiers. In conclusion he draws the attention to the possibility of suitable adsorption dehumidification use at further industrial branches.

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