System safety of the performance of mechanical ventilation systems can of course be analysed by means of general methods for system safety analysis. Such methods are used a lot in industrial practice, especially in manufacturing industry. However applications on ventilation systems are more or less non-existing today. This paper summarises today's methods for system safety analysis and shows possible future ways of applying the methods on performance analyses of mechanical ventilation systems.
Since 1985 more than 170 very low energy houses, all of the same type and structure, were built in the Flemish Region, Belgium. Because conduction losses are very low, mean Urn-value 0.30-0.35 W/(m².K), ventilation losses become very important, up to 45% of the heat losses if no heat recovery is utilised. Three of the houses were monitored in detail for energy consumption, energy and ventilation efficiency. All houses are equipped with the same ventilation system: balanced mechanical ventilation with heat recovery.
The work presented in this paper is aimed at the definition of tracer gas experimental procedures for measuring the air change rate, the age of air and the air change efficiency in real buildings under mechanical ventilation conditions. The measurement procedures, based on the decay method, were validated in a special experimental chamber and implemented in two rooms of a building under real operating conditions. Measurements of volumetric flow rate through the air ducts of two buildings, performed by means of the constant emission rate method, will be shown and commented.
The homogeneous emission passive tracer gas technique is described. This technique relies on an even distribution of constant tracer gas emission rate within the object to be measured, so that the emission rate per volume unit is constant. The local steady state concentration of the tracer gas is directly proportional to the local mean age of air and the emission rate per volume unit.
The performance of mechanical ventilation systems has been checked in several innovative residential houses in the frame of Swiss research as well as pilot and demonstration projects. This paper gives a list of performance criteria for the ongoing comparison and evaluation of these mechanical ventilation systems. For some criteria, target values are proposed. In the second part, this paper shortly describes four residential buildings with mechanical ventilation systems where such evaluations were performed and highlights interesting design features and results from the measurements.
The aim of this study was to compare the radon levels at workplaces and in homes located nearby. Homes (number of 57) and partly or fully underground workrooms (number of 55) have been studied at the four workplaces in southern Finland and one workplace in northern Finland. Radon concentrations both at workplaces and in homes seemed to be at the same level in the same district. The mean radon concentration in workrooms was 406 Bq.m³, and in homes concentration was 398 Bq.m³.
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