People spend nearly one-third of their life on sleeping. Several factors can affect bedroom air quality and comfort of sleep, such as temperature, relative humidity and air quality. The most common indicator of indoor air quality is the concentration of carbon dioxide, its presence in indoor environment being strictly related to respiration and human metabolism. Since 2002, when the European Parliament and Council approved the directive on energy performance of buildings, EU member countries launched various programs for refurbishment of buildings and HVAC (Heating, Ventilation and Air Conditioning) systems, in order to reduce the energy consumption. Unfortunately, the renovation operations, such as replacing old windows with new tight ones or thermal insulation of the facades, lead to tightly sealed interior spaces. Insufficient infiltration of fresh air and limited natural ventilation result into increased pollutant concentration and deterioration of the indoor microclimate. Permissible concentration of carbon dioxide in the closed spaces according to World Health Organization is 1000 ppm. When the level exceeds this threshold, occupants may complain of headaches, drowsiness, lack of concentration and fatigue. The present study shows the measurements of carbon dioxide concentrations conducted in several sleeping rooms located in refurbished buildings, with or without mechanical ventilation system for fresh air supply, as well as suggested measures.
Melting-freezing phenomena are largely studied due to their importance in many applications such as latent heat storage, ice build-up in different settings, solidification of moulded pieces, epitaxial growth of silicon bars used to produce semiconductor waffles, etc. The paper deals with studying the ice build-up process around a cylindrical pipe through which a coolant flows, extracting heat from the surrounding water. Such a situation can be encountered in ice rinks where pipes are immersed in a shallow water basin that freezes. The approach of the paper is to determine the required time necessary for the ice thickness of the layer that builds up around the pipe to freeze under specified conditions (coolant temperature, pipe radius, and total radius of the water domain). An implicit finite difference technique with constant space step is employed to perform this task and the results are plotted and discussed.
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