air change

Purpose of the work

Can the minimum air change in naturally window-ventilated units be covered only through leakages?

Content of the presentation

In general, the infiltration airflow rate is dependent on meteorological conditions, especially wind pressure on the building / unit, and with regard to thermal effects, the temperature differential between the interior and the exterior, i.e. the infiltration airflow varies strongly.

For that study, the constant concentration dosing method and the decay method were used to test air changes performances in an office equiped with a VAV mechanical ventilation system and in a domestic apartment with natural ventilation . The measurement results from those two tracer gas methods are compared.

In this study, serial environmental measurements in 12 large buildings in Taiwan have been made to control the air exchange efficiency on the indoor microbial contamination. High levels of airborne microbes seem to be more easily observed in buildings equipped with fan coil unit system than with air handling unit system.
Adequate filtration of fresh air intake should be imperative to control effectively microbial contaminations of outdoor origin.

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.

The air exchange in a room with different windows and window geometries is investigated. The aim is to get reliable data for the air change rate and the air exchange efficiency for natural ventilation. Before using a CFD program for the calculations experimental studies have been carried out. In order to meet different demands we distinguish between short time and continuous ventilation. The results are availabe as figures, graphs or approximate equations.

Tracer gas measurements are commonly used to estimate the fresh air exchange rate in a room or building. Published tracer decay methods account for fresh air supply, infiltration, and leaks in ductwork. However, the time delay associated with a ventilation system recirculating tracer back to the room also affects the decay rate. We present an analytical study of tracer gas decay in a well-mixed, mechanically-ventilated room with recirculation.

The aim of that study was to find out if heating is the alternative for crawl space moisture control with a reasonable low energy consumption. Using a ground cover without thermal insulation and heating of the crawl space proved to be a good alternative method to control mold growth.

The aims of that study were to find out how the thermal capacity, resistance, and the placement of insulation layers affect relative humidity in crawl spaces. The results show that there are two alternative ways to use ground covers in combination with air change to achieve acceptable conditions in crawl spaces.

The aims of that study were on the one hand to find out how relative humidity can be reduced by optimal selection of ground covers and air change rates, and on the other hand to evaluate the acceptability of achieved moisture conditions by means of mould growth analyses. Two buildings (one relatively warm and the other relatively cold) were studied with the resistance-capacity network model. Simulations of thermal and moisture buffering effects of air change rates and various ground covers were made.