Submitted by Maria.Kapsalaki on Thu, 02/06/2020 - 17:03
Building airtightness is a critical aspect for energy-efficient buildings as energy performance of a building can be reduced significantly by poor airtightness. The Pulse technique has been regarded as a promising technology, which measures the building airtightness at a low pressure of 4Pa by rapidly releasing a 1.5-second pulse of air from a pressurised vessel into the test building and thereby creating an instant pressure rise that quickly reaches a “quasi-steady” condition. However, questions have often been asked on the test viability due to the nature of the test.
Submitted by Maria.Kapsalaki on Fri, 10/25/2013 - 16:21
Air supply volumes and velocities in cleanrooms are monitored by airflow measuring hoods and anemometers but these measuring methods can be inaccurate if used incorrectly. It is demonstrated in this article that measuring hoods are accurate if the air supply passes evenly out of the hood, as occurs when the air volume is measured from a four-way diffuser or no air supply diffuser. However, when a swirl diffuser was investigated, the measuring hood gave readings more than 50% greater than the true volume. The reasons for the inaccuracy, and methods to correct it were established.
Airflow measurements techniques are necessary to determine the most basic of inddoor air quality questions : "Is there enough fresh air to provide a healthy environment for the occupants of the building?" . This publication outlines airflow measurement techniques, but it does not make recommendations for techniques that should be used. The airflows that are discussed are those within a room or zone, those between or zones, such as through doorways (open or closed) or passive vents, those between the building and outdoors, and those through mechanical air distribution systems.
Two methods have been used for measurement of natural convection flows in a narrow vertical channel of which one wall is heated : a hot wire anemometer adapted to measurements in flows where temperature gradients exist (two hot wires with different overheat) and a method for attaining bulk flow information in boundary layer flows. Results from these two methods are compared.
Three methods : step-up velocity change, step-down velocity change, and the cut-off frequency method were tested for the dynamic response of two low velocity thermal anemometers.This paper had the objective to identify whether those methods recommended in the standards and guidelines always succeed in determining accurately the frequency response curves and the time constant of low velocities anemometers.
In order to identify the complex flow located at the breathing zone of a seated person exposed to the airflow coming form a PVS (personalized ventilation system) two techniques are used and compared : the PIV ( a two-dimensional particle image velocimeter) and the LDA (laser doppler anemometer) technique with a single point measurement, given by a cross section of laser beams.
The PIV technique appears a very interesting tool in studies aiming at identifying airflow in rooms or around objects.
The rotating vane anemometer is an instrument that is widely used in the field by maintenance engineers and inspectors. The anemometer consists of a vane that is held at right angles to an airflow. In modem instruments the speed of rotation of the vane is sensed and measured electronically and the air speed, which is a function of the speed of rotation of the vane, is indicated on a meter.
A study was made of the impact of well-documented random velocity fluctuations and periodic temperature fluctuations with different amplitudes and frequencies on the accuracy of the mean velocity and the standard deviation of the velocity measured by three low-velocity anemometers with omnidirectional probes. The anemometers were tested in an airflow at 225 combinations of mean velocity, amplitude of the velocity, and temperature fluctuations, as well as frequency of the temperature fluctuations, as identified during field measurements.