air change rate

Describes method of estimating ventilation rate using organic vapours as tracer gases and ultra-violet absorption to measure concentration. Gives table of absorption of different vapours. Suggests estimation using a test paper. This method is less precise but requires a minimum of apparatus.

Briefly reviews methods of estimating infiltration rates in dwellings. Describes tracer gas method using methane. Gives results of measurements of air change rate made in houses in Minneapolis, Kansas and Denver. Concludes that technique works well for measuring residential infiltration.

Reports 312 measurements of ventilation rate in 31 rooms in old and new blocks of flats, 3 villa residences and a modern university building, made using coal gas as a tracer. Describes buildings and gives main results. Examines effect on air change rate of sealing flues and gratings, opening windows and weather conditions. Finds outside wind speed has most influence on ventilation rate. Discusses recommended standards of air supply.

Gives formula for calculating air-change-rate from decay rate of a tracer gas. Discusses different tracer gases and detecting instruments. Describes portable meter used to measure the concentration of helium. Discusses its performance and describes the experimental procedure.

Examines dependence of measured infiltration rates on wind speed, indoor/ outdoor temperature difference and pressure difference. Gives results in form of graphs of measured values. Calculates air-change-rate from crack length and finds good agreement with measured air-change-rate. Suggests that this is as a result of over-estimating the effect of wind and neglecting stack effect. Finds that stack effect is more important than wind. Comparison of the two houses found that the house shielded by trees and houses had a considerably smaller infiltration rate than that on an open site.

Describes experimental studies of the natural ventilation of four similar houses with different ventilating systems. Describes houses and gives experimental procedure and results of measurements of air-change-rates using hydrogen as a tracer gas.Shows variation in air-change-rates are due mainly to changes in wind speed and that wind direction and temperature difference are secondary factors. Estimates rate of heat loss as a functionof wind speed. Discusses relationship between measured pressure differences and wind speed and direction.

Explains method for calculating time dependences and average values of gas and particle concentrations in ventilated rooms, which permits determination of air pollution propagation in a room by means of given target functions. Applies method forvarious ventilation rates. Provides calculated example of determination of gas concentration occurring in a room with a leaky gas container. Illustrates representative time functionfor different pollutants.

Describes investigation of air infiltration in a house using chlorothene as a tracer gas. Gives table of the data collected. Reports the unexpected result that infiltration rates could bereduced by increasing inside relative humidity. Suggests this is due to changes in hygroscopic building materials, especially wood. Concludes that increasing relative humidity from 20 to 40%could save from 5 to 15% on fuel costs. This analysis does not take into account the energy used to evaporate humidification water.

Describes a simple pressure method for measuring the air tightness of small buildings. It measures the leakage rate from all apertures in the external envelope simultaneously, from which total leakage area of openings could be inferred. Site measurements have shown that obvious sources of leakage like doors and windows account for only the minor part of total leakage area in the average dwelling. Results from 25 dwellings show no trend of leakage area per unit of gross floor area.

A supply of fresh air is necessary in any dwelling to ensure a comfortable, safe and hygienic environment, but the heat loss to this air, during the heating season, may represent a substantial proportion of the total heat loss. This points to the need forgreater control of domestic ventilation, either by using a mechanical system or by better design for natural ventilation. This paper touches upon both of these possibilities. Gives simple method for assessing approximately the possible reduction in heat loss achieved by the use of a mechanical ventilation system.