As the thermal performance of buildings continues to improve, air exchange will eventually become the dominant mechanism for building heat loss. Although, therefore, an essential parameter of the energy equation, ventilation is nevertheless vital forthe dilution and removal of pollution generated within buildings. An inadequate supply of fresh air or poor air distribution will result in high levels of indoor contaminants, discomfort and a poor living environment, it could also result in more serious health related problems.
AC pressurisation is a method for measuring the airtightness of buildings. This technique, which is also called the infrasonic method, employs a reciprocating piston or bellows to impose a sinusoidal small change in volume inside the building
The Air Infiltration and Ventilation Centre is currently finalising the detailed work program for its Numerical Database. This is being developed in response to the need to establish a core of numerical data, suitable for model validation, themodelling of real buildings, assessment of standards, the effects of new building methods and the use of differing ventilation systems.
This investigation was performed to evaluate the effectiveness of detecting air leaks in typical constructions through the measurement of sound transmission. The sound transmission of various slits was measured. These were designed to simulate field constructions. Due to the fundamental difference between steady air-flow and sound propagation, it was concluded that the method fails, particularly in the case of foil-covered slits and slits coupled to damped cavities.
As part of its new operating programme, the Air Infiltration and Ventilation Centre is establishing a numerical database to be used both in support of design studies and for the verification of numerical models. In addition to being available as a computer database, it is intended to present selected source data and simple algorithms in loose leaf form as a new volume in the AIVC's series of Application Guides.
Wind pressure coefficients (Cp values) are among the basic data required for ventilation and air infiltration calculations and modelling. More than two years of systematic wind tunnel testing in ETI of some of the most frequent building shapes has resulted in a database that has been provided with a handling program. This package is available from ETI, for IBM XT/AT and compatible PC's.
Leakage area measurement by fan pressurisation becomes more difficult as the volume of a building is increased. The equipment becomes bulky, and measurements of air flow through the fan and the resulting pressure differential require more care. AC pressurisation offers an attractive alternative. However, in the case of large industrial buildings, the exterior envelope is often constructed of thin flexible sheet material, and also industrial leakage paths may have a much larger area than is found in, say, typical domestic construction.
This article briefly describes a new piece of apparatus, recently developed at UMIST, which can be used for the determination of ventilation rates in, and air movement rates between, four interconnected cells.
These problems can be overcome by compensating for the pressure drop over the flow meter in such a way that the pressure on the duct side of the grille remains the same before and after the positioning of the flow meter. This is a very well known technique. However in the field of air conditioning, devices using this principle are rare. The compensation of the pressure drop is performed by a fan and regulator which blows just enoughair through the flow meter to meet the pressure compensation before the grille.
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