Submitted by Maria.Kapsalaki on Mon, 10/28/2013 - 12:03
The approval of the Technical Building Code has meant major changes in the construction of multi-storey buildings in Spain. One of the most important revisions, with respect to the buildings erected prior to the Technical Building Code, has been the obligation to ventilate each one of its rooms. Depending on the use and occupancy a minimum flow rate of ventilation is required in each room.
Submitted by Maria.Kapsalaki on Mon, 10/28/2013 - 10:33
For residential forced air heating and cooling systems conventional thinking is that air supply registers should be located under exterior windows. There were good reasons for this in the past (primarily to counteract the cold downdraught from the window) but new construction standards (well-insulated walls, better glazing and air tight wall/window interface) mean that there is now less downdraught. Positioning the supply air register away from a window could have a large impact for new construction as duct lengths could be shortened (saving materials and construction time).
Submitted by Maria.Kapsalaki on Fri, 10/25/2013 - 16:50
An experimental study of the phenomenon of buoyancy driven natural ventilation through single-sided horizontal openings was performed in a full-scale laboratory test rig. The measurements were made for opening ratios L/D ranging from 0.027 to 4.455, where L and D are the length of the opening and the diameter of the opening, respectively. The basic nature of airflow through single-sided openings, including airflow rate, air velocity, temperature difference between the rooms and the dimensions of the horizontal openings, were measured.
High local concentrations of a pollutant can be the result of high local emission rates of the pollutant orinsufficient ventilation. Using tracer gases to map the ventilation in multi-zone buildings combined withmeasurements of the local pollutant concentration provide the means to discriminate between thesecauses.
The development of a new device for the injection of tracer gas is discussed with the objective of practical application in the field of HVAC airflow measurements. The uniform tracer gas dispersion for very short distances, when measuring airflow by the constant emission method is of great interest. This new injection device has a compact tubular shape, with magnetic fixation to be easy to apply to duct walls. After a preliminary study with an initial prototype already tested, further detailed experiments had been carried out, culminating in a second prototype.
Carbon dioxide produced by occupants can be used as a natural tracer gas for analysing air change rates in dwellings. However, a high level of concentration uniformity is necessary for tracer gas measurements. Therefore, mixing fans are usually used. The use of such fans in occupied homes is not convenient, thus the uniformity requirement may not be fulfilled. Experiments in climate chambers were carried out to simulate the distribution of CO2 under different controlled conditions, without additional mixing. Sufficient concentration uniformity was observed in all measured cases.
Carbon dioxide exhaled by people can be used as a tracer gas for air change measurements in homes. Good mixing of tracer gas with room air is a necessary condition to obtain accurate results. However, the use of fans in dwellings to ensure mixing is inconvenient. The natural room distribution of metabolic CO2 was simulated in laboratory experiments and verified in a field study. The results of the field measurements presented in this paper support the findings of the laboratory study, i.e. that CO2 is well mixed into the room air even though fans were not used.
Today, tracer gas is used as a reliable means to examine various queries related to mechanical systems. Prerequisite is the safe and routine handling of the relevant analysis methods. Apart from some basic considerations, the present paper includes results of ventilation efficiency studies and a comparison of different systems on the basis of characteristic parameters.
Tracer gases are often used to assess airflow rates in air handling units. Published methods aremostly designed for units with recirculation ratios lower than those commonly found inSingapore and other tropical countries. Large recirculation ratio homogenize theconcentrations, so that concentrations in supply and extract ducts are close to each other. Inaddition, such units often present a large time constant, so the time needed to reachequilibrium is very large. A procedure for tracer gas dilution technique adapted to such airhandlingunits is presented.
Tracer gas sorption in and permeation through building materials influence tracer gas ventilationmeasurements. Therefore, it is important to have knowledge about these processes.The permeation of three commonly used tracers (SF6, N2O and the PFT C6F6) through untreatedgypsum board has been experimentally investigated. The result shows that all three tracers diffusereadily through this material (diffusion coefficients in the order of 1 10.-6 m2/s). Caution shouldtherefore be exercised when using tracer gas measurements in rooms with walls of gypsum boardor other porous materials.