AIVC - Air Infiltration and Ventilation Centre

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mathematical modelling

Ventilation strategies for crawl-spaces, attics.

In this paper ventilation of attics and crawl-spaces is investigated theoretically. Ventilation rates and temperatures of the spaces are calculated by means of flow balance procedures. Flow characteristics of ventilators and openings for attics and crawl-spaces are far from well known, so a laboratory investigation on pressure drops across such devices was undertaken and reported in the paper. As convective flows from the heated part of a houseinto a colder, ventilated space can create moisture problems this situation has been investigated extensively.

Use of a single tracer gas for measurement of ventilation rates in a large enclosure.

This paper describes a preliminary investigation of the validity of a means of calculating the ventilation rate of a large enclosure from experimental data. It was assumed that the air in the enclosure is not perfectly mixed. The measurement method selected was tracer gas concentration decay. Thecalculation of ventilation rate was performed by "least squares" fitting of a model to the observed tracer gas concentrations. Simulations of tracer gas concentration decay measurements were performed with varying initial distribution of tracer gas.

Multizone modeling and air leakage analysis.

Reviews the papers on air infiltration and ventilation research presented at the ASHRAE annual meeting held in Honolulu, Hawaii, in June 1985. The twelve most significant papers on multizone infiltration and air leakage are discussed at length and other infiltration-related papers mentioned. Authors' abstracts for the twelve symposium papers plus seven technical papers are presented.

Development of a simplified multizone infiltration model.

Several infiltration models treat the complexity of air flows in multizone buildings, but most of them are written as research tools and are not generally available or user-friendly. Professional engineers and architects are in need of a simplified multizone infiltration model. This paper describes the first step in Lawrence Berkeley Laboratory's development of a multizone infiltration model for calculating the air flow distribution of a building without using any iteration procedure.

Design for ventilation.

Ventilation can be advantageous as opposed to adventitious and, with careful building design, can eliminate the need for air conditioning in summer. This paper discusses the general principles of design for ventilation, inparticular the removal of excess heat, and presents two examples of buildings designed to eliminate air conditioning. One is a deep plan office block, the other an exhibition hall. In both cases ventilation models featured strongly in the design.

Determination of air infiltration in single family dwellings. Zur bestimmung des infiltrationsaustausches in einfamilienhausern.

Describes a procedure for the approximate determination of air infiltration for a single family house for given weather conditions. To carry out the calculation it is only necessary to measure the permeability of the building envelope using a blower door. The calculation procedure is so straightforward that it can be carried out on a programmable pocket calculator. Refers to a comparative study by the Air Infiltration Centre, which found that the calculation model described gave the best results of any single cell model for all the houses investigated.

A simplified model of thermal comfort.

The principal environmental factors that affect human comfort are air temperature, mean radiant temperature, humidity and air speed. Presents asimplified model of thermal comfort based on the original work of Fanger, whorelated thermal comfort to total thermal stress on the body. The simplified solutions allow the calculations of predicted mean vote (PMV) and effective temperature which (in the comfort zone) are linear in the air temperature and mean radiant temperature, and quadratic in the dew point, and which can be calculated without any iteration.

Errors resulting from the use of single zone ventilation models on multi-zone buildings: implications for energy conservation and indoor air quality studies.

Errors resulting from treating a house as an enclosure surrounding a single, well-mixed volume of air are explored in detail for a ranch house with abasement. A fairly typical ventilation pattern is assumed and three quantities, the air exchange rate, the indoor pollutant concentration from a given emission, and the energy required to heat infiltrating air, are calculated and compared using both the one and two zone models for this house.In general, the errors were around 10-20% if the basement was included in the one zone models and 30-40% if the basement was neglected.

Condensation prevention: loft ventilation - a discussion paper.

This is the third item in a series on methods for predicting condensation risks within structures. It answers criticisms made of the method described in NO 1729, on the basis that the method does not give the same answers, nor does it take account of the effect of the occurrence of condensation on the vapour pressure gradient within the structure, as does the graphical method described in NO 1728.

Condensation: prevention better than cure.

Describes in detail a computer-based technique for predicting the risk of condensation occurring in building structures. The technique not only indicates the position at which condensation is likely to occur, but also puts a figure on the risk of decay in timber within the structure. In the case of ventilated roofs or walls it gives the minimum sizes for ventilation openings.