Submitted by Maria.Kapsalaki on Wed, 04/17/2019 - 15:24
The different methods for air flow rate measurement at air terminal devices are presented in this overview, such as van anemometer with a cone, small velocity probe (thermal probe or small vane anemometer), compensation method, etc. Several measurement methods are available on the market at highly variable cost. However some of these methods are suspected to lack reliability.
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.
A cross-sectional questionnaire and field study of 160 Swedish office buildings and 260-2649 respondents (with case controls and prevalence comparisons) was made to assess the possible links between ventilation types, outdoor air flow rates and symptoms of Sick Building Syndrome. The ventilation rates proved to be higher than those required by most building codes and consisted of outdoor air inflow of 17 14L/p and 2.0 1.3 air changes/h.
In France, the regulation on residential building ventilation is based, since 1969, on a generaland continuous air renewal ; the fresh air comes into habitable rooms by air inlets and thestale air is drawn out to exhaust vents in the service rooms. So the air inters the habitablerooms crosses through the dwelling, is extracted in the service rooms.The Research and Development Division of Gaz de France and the CSTB have studied theneeds in each room of a dwelling (depending on the size and the occupancy) to perform newventilation system(s).
Indoor air quality ventilation airflow rates and HV AC capital and operating costs usually are closely related. Auxiliary energy loads for supply air heating or cooling sometimes can substantially reduce the need for dehumidifying or humidifying by using air-to-air heat or energy exchangers. The most important factors in reducing HVAC capital and operating costs are ventilation airflow requirements, climatic parameters, exchanger recovery system performance factors and duration of operation.
The paper presents the results of a study into the effects of unsteady wind pressures on the mean flow rates in certain types of purpose-designed naturally ventilated buildings. The study used non dimensional parameters and the results should therefore cover a wide range of conditions and should be of general application. It is concluded that unsteady) effects are restricted to a relatively narrow band of conditions. These conditions have been quantified in terms of non dimensional parameters.
Air handling units do not always function as planned: airflow rates are often larger than required, the recirculation rate is not at its set-point value and parasitic shortcuts sometimes decrease dramatically the ventilation efficiency. A dedicated diagnosis, based on the tracer gas dilution technique can easily detect such dysfunction, and help to cure the defects.
The use of tracer gas is of great help in measuring airflow rates and detecting shortcuts in air handling units, and is essential for ventilation efficiency measurement. However, the planning of experiments, that is choosing tracer gas injection locations and air sampling locations, is not straightforward. Moreover, the mathematics used for interpretation are quite complex, and require elaborate calculations. Therefore, a measurement protocol and the corresponding interpretation algorithms are being developed and implemented in a user-friendly computer program.
Displacement ventilation is acknowledged to be an efficient system for the removal of contaminants and excess heat from occupied zones of rooms, this system is aiming at supplying clean undiluted supply-air directly to the zone of occupation. Air flow rate, temperature and the design of the supply device strongly influence the parameters that determine thermal comfort. In the paper, one kind of displacement ventilation systems - ohair air supplying system is investigated.