PR2005

This study investigates numerically the occurrence and duration of higher relative humidities in a cold attic space, which are a consequence of excessive moisture supply from ventilating the attic and from air infiltration from inside the dwelling. Hygrothermal states of the attic air zone and the adjacent construction elements are calculated by a whole building heat, air and moisture simulation tool. Airflows to the attic are determined by taking into account the total distribution of pressure around and inside a building.

Building materials and furnishing used in contact with indoor air have some effect to moderate the variations of indoor humidity in occupied buildings. Very low humidity can be alleviated in winter, as well as can high indoor humidity in summer and during high occupancy loads. Thus, materials can possibly be used as a passive means of establishing indoor climatic conditions, which are comfortable for human occupancy. But so far there has been a lack of a standardized figure to characterize the moisture buffering ability of materials.

The paper gives an outline of existing modelling capabilities as well as an overview of current developments in integral modelling of hygrothermal conditions for whole buildings as presented within IEA Annex 41. Such models deal with the heat, air and moisture conditions of most relevant elements of buildings: The indoor air, the building envelope, inside constructions and furnishing. These building elements interact with each other and they are influenced by the use of the building, the building services, and the outside climate.

With the exception of a few analyses of the impacts of ASHRAE Standard 62-89 and energy use in specific buildings, the energy use in commercial building due to infiltration and ventilation flows has received little attention. However, as improvements have been made in insulation, windows, etc., the relative importance of these airflows has increased. Previous work at NIST described a research plan to quantify, and assess opportunities to reduce, the energy and indoor air quality impacts of building airtightness and ventilation system control in office buildings (Emmerich et al. 1995).

At the conceptual design stage, one needs to pay considerable attention to both the energy as well as indoor air quality (IAQ) requirements. Often, designers tend to overlook ventilation and IAQ issues and conceptualise the HVAC design more from energy considerations. An energy efficient design of airconditioning system in hot and humid climates is quite challenging in view of the high humidity levels prevailing all-year round. This paper outlines some of the key factors that could lead to inadequate or inefficient ventilation and, thereby, poor IAQ.

Application of ventilation techniques, as well as the use of any passive environmental solution in a rehabilitation, requires knowledge of the particularities of the climate and the specific characteristics of the building stock. In a theoretical approach, these two variables would be enough to predict indoor behaviour. Nevertheless, in practice, one third variable needs to be considered, as user habits can completely change the equation.

Natural night ventilation is an energy efficient way to improve thermal summer comfort. Coupled thermal and ventilation simulation tools predict the performances. Nevertheless, the reliability of the simulation results with regard to the assumptions in the input, is still unclear. Uncertainty analysis is chosen to determine the uncertainty on the predicted performances of natural night ventilation. In addition, sensitivity analysis defines the most important input parameters causing this uncertainty.

According to the R&D Project on Low Energy Housing with Validated Efficiency, the CO2 emissions due to operation of ventilation systems are estimated to be 7 to 12% of total CO2 emissions of a unit of multi-family buildings in mild climate regions of Japan. Using network model calculations, CO2 emissions of a hybrid ventilation system using Natural Ventilation Openings and other ventilation systems were estimated.

This project aims to demonstrate via a refurbishing operation, how a mechanical ventilation system can both provide a good indoor air quality and limit the energy consumption due to air renewal. The field of this operation concerns the improvement of indoor air quality for sensitive people as young children in classrooms, associated to a rational use of energy by the ventilation systems.

Industry-wide methods of assessing duct leakage are based on duct pressurization tests, and focus on highpressure ducts. Even though low pressure ducts can be a large fraction of the system and tend to be leaky, few guidelines or construction specifications require testing these ducts. We report here on the measured leakage flows from ten large commercial duct systems at operating conditions: three had low leakage (less than 5% of duct inlet flow), and seven had substantial leakage (9 to 26%).