air flow

Describes a computer program used to calculate the air exchange in multi- storey buildings. An air network is drawn up for the building and arbitrary initial pressures are assigned. A system of equations is drawn up for all linearly independent loops andjunctions and the program solves this system of equations. States that comparison with the hydraulic analogy method gives a discrepancy, not greater than about 3%. NOTES translation available from B.S.R.I.A. price 1 pound

Outlines principles behind a program for calculating air flow in buildings. The generally accepted method for these calculations is Kirchoff's network equations, of which the "knot method" and the "loop method" are alternatives. The program uses a mixture of both, in an attempt to keep the intermingling of the equations to be solved on a low level. Presents results of calculations on a 50-room example, in which it was the purpose to demonstrate the possibility of using the program for discussion of ventilating system fluctuations.

Describes computer program used to calculate air flows and pressure differential in a building as a result of a combination of wind effect, stack action and the operation of air handling systems. Describes mathematical model of building and the assumptions and limitations of program. Gives listing of complete program.

The amount of air leakage through window gaps in buildings depends on the width and length of the gaps, the pressures across the buildings and the resistances in the air circuit. Reviews the ranges of these factors for Britain and gives results of measurements within these ranges for standard metal and wooden windows and for weather-stripped windows. Gives two methods of estimating the air flow through gaps in complete windows.

Wind tunnel test conducted on a scale model of a classroom show that, provided the test air speed is kept in excess of about 3mph, it is feasible to use models for predicting, with good accuracy, the air-flow conditions in and around full-scale buildings. In the case of low-pitch roofs the height of the stagnant zone set up as a result of flow separation occurring at the windward eaves of a building is influenced by wall height rather than by roof pitch.

States that current methods of estimating heat demand of buildings are very inaccurate, and so large safety margins are used which usually result in overestimating the necessary heating plant capacity. Describes computer program developed to improve the accuracy of heat demand calculations. Gives formulae used in the program for calculating heat demand, pressure conditions and air flow within the building. Gives example of the use of the program to calculate the effect of wind on an eight-storey residential building.

Discusses the mechanisms which govern natural ventilation. These are wind speed, flow, characteristics of openings in buildings and pressures generated at building surfaces by wind and temperature difference. Gives formulae for simple cases. Outlines ways of determining natural ventilation rates. Gives brief account of the effect of turbulence and openings in one wall only.

Reports measurements of air pressure differences to determine influence of wind on air flow directions through door and window gaps. Studies measures to prevent air transport between the 4 wings of the cross-shaped hospital and to ensure air flows from the corridors to the rooms on both sides. Pressure differences measured between facades agreed well with wind-tunnel results. Air flow directions measured agreed with results from an electrical analogue ventilation model.

States that to obtain accurate estimates of wind induced natural ventilation of buildings the pressure distribution over the building is required. Reviews the available information for isolated buildings and groups of buildings. Gives the results of wind tunnel measurements made on a cuboid when surrounded by buildings of the same shape. Results are presented statistically and indicate that the pressure distribution on a building can be fairly accurately determined provided the density of the built form and the roughness fetch are known.

Describes research to study movement of air through fully or partially open doorways with and without influence of temperature, and to ascertain amount of supply air required toprevent this movement. Studies door openings of 0.10 to 104 m. wide and temperature differential of 0 to 12 deg.C. States that from these results critical areas in hospitals may be designed more effectively to given requirements.