crack

Gives measurements of air infiltration made in ten houses in Indiana using helium as a tracer gas. Assumes linear dependence of infiltration rate on temperature difference and wind velocity and calculates infiltration rate per unit crack length. Change rates ranged from about 0.6 to 1.5 changes per hour.

Details the retrofits at Twin Rivers, grouped into packages A,B, C and D. A,B and D reduced heat flow through attic and basement. B limits the amount of air infiltration from crack openings, especially round windows and doors, by the addition of Vinyl foam weatherstrips, caulking of window and door frames and adjustment of ill-fitting casements.

Developes mathematical model of air infiltration based on crack flow equations. Describes measurements made on test house. Shows that actual pressure distributions in walls deviate considerably from values in guidebooks. Finds background leakage area of house by pressurizing house with electric fan and measuring pressures. Suggests two distributions for leakage areas. Measures infiltration rate using helium tracer gas, recording temperature and pressure differences. Concludes that comparison between prediction and experimental results is encouraging.

Assuming higher than probable cd values for crack length openings on calculation of infiltration rates results in excessive allowances for heating and cooling capacity. Using a given cd graph, proposes equation to determine infiltration rates and reduce internal pressurization requirements to offset wind impingement.

A number of cases of water and frost damage in masonry and non loadbearing walls have been examined. This damage could not have resulted from vapour diffusion or rain penetration and is primarily caused by condensation due to exfiltration of air. Air exfiltrates through the many cracks and joints and in this connection the result of chimney action and wind is explained in some detail, including the pattern and magnitude of building pressure differences that induce ex-filtration together with a discussion regarding the moisture that is transferred.

For simplicity's sake the determination method outlined in previous issues of this article did not include the air infiltration through cracks. The graphical method is again demonstrated when allowing for air infiltration as specified in German standard DIN 4701 and examples are given.

Reports a theoretical study of natural ventilation made jointly by HVRA (UK) and Institute for Public Health Engineering TNO (Netherlands). Uses analogue and digital computers, and results so derived were used to produce a design method suitable for rapid assessment of the natural ventilation of projected buildings. Shows this method to be quicker, cheaper, and more accurate than the crack method (measured leakage at windows and doors) or the air change method.

Derives mathematical relationships for the connection between pressure loss and volume flowrate using simple crack models and applying known laws of similarity for flow in pipes or gaps. Demonstrates how these relationships permit more exact determination of the permeability of cracks in normal building structural components than has been possible hitherto with the use of a few approximate average values for crack permeability coefficients and pressure exponents.

Describes a diagram from which heat losses due to infiltration according to German standard DIN 4701 can be obtained, as well as rate of air infiltration per unit length of crack. By considering several factors the method can be generalised for the case of several windows and doors of varying quality of fit. The method is therefore useful for both the approximate and the accurate calculation of infiltration heat losses.

Describes experimental method used and results obtained in a series of experiments to investigate characteristics of air flow through cracks in dwellings, including the straight-through, l-shaped and multi-cornered forms found in the construction of a dwelling. Aim is to supply accurate knowledge for computer simulation of ventilation effects in a room.