air change rate

Assesses the role of natural ventilation in modern hospitals. Considers optimum standards of air change rates for winter and summer conditions and reviews factors within the hospital context that are likely to affect the achievement of natural ventilation. Notes an air change rate of 1.5/hr. is usually assumed for heat loss calculation. Finds cross ventilation is unlikely to be achieved and designs should be based on single sided ventilation. Reports tracer gas measurements of natural ventilation in Southland Hospital, Shoreham by Sea.

Radon, an inert radioactive gas, and its products of decomposition, will attack the lungs when present in high enough concentrations. Notes high concentrations of radon in mines and other underground spaces and even in well water. Radioactivity of building materials is a problem in Sweden. States concentration of radon in air is highly dependent on ventilation. Radioactivity in a dwelling is highest in the morning and drops in the daytime when doors and windows are open. Normally an air change rate of 0.5 per hour keeps radon content of indoor air at an acceptable level.

Reports results of a project to assess energy conservation measures in a group of typical three-storey, naturally ventilated, blocks of flats, built in 1940 in Stockholm. The measures were:< 1) Improvement of boiler efficiency< 2) Weatherproofing of windows and doors< 3) Adjustment of the heating system and reduction of indoor temperature< 4) Additional insulation of attic floor<5) Additional insulation of external walls< Discusses the energy conservation effect and profitability of each measure.

Reports methods used to measure the concentrations of Rn, Tn, and their decay products indoors and outdoors. Radon and Thoron concentrations are detected continuously by collecting the positively charged RaA and ThA atoms on a surface-barrier detector using electric field precipitation.< The concentrations of Radon and Thoron decay products were determined by collecting them on a membrane filter and simultaneously counting the activities by means of a collimated surface-barrier detector.Indoor and outdoor concentrations are measured simultaneously under different ventilation rates.

Reports measurements of Radon-222 concentrations, carried out in the living rooms of 81 dwellings in Great Britain in 1976. Measurements of the activity concentration of RaA both within the room, and of the ventilation rate for the room were made. From this an estimate of the "radon output" of the room was calculated. Gives histogram of the radon outputs in picocuries of radon 222 per litre of room air per hour. Disregarding a very high measurement in a granite dwelling, the mean was 0.54 pCi/l/h.

Fresh air requirements in individual rooms of an occupied house vary between 0.5 and 2 air changes per hour depending on the number and activity of the occupants. The most common method of ventilation control is by opening windows but measurements show that even quite moderate window opening results in air change rates greater than 2 air changes per hour throughout a house.< Reports measurement of the energy cost of window opening in a test house with a heat loss coefficient of 5 kWh/K day. Finds in a low energy house,controlled ventilation is essential.

The daughter products of radon are chemically active materials which, when inhaled are very likely to deposit in the respiratory tract. Defines a special unit, the working level, to indicate the radiation burden from radon daughters. Reports study of exhalation rates from various building materials made by enclosing samples in containers and analysing air samples from the containers. Gives table of results. Discusses control of airborne radiation by increasing the ventilation rate, sealing room surfaces, mechanical circulation and filtration of the air.

The ventilation rate and energy consumption of one of the ECRC test houses was monitored continuously during one heating season, with one bedroom window open by various amounts. Results show that a very small window opening is sufficient to satisfy ventilation requirements most of the time. 

Reports measurements of air change rates carried out in the living rooms of 39 flats built during the last 20 years using Freon 12 as a tracer gas. Ventilation rates ranged from 0.3 to 2.9 changes per, hour, the average being 1.3 changes per hour. Air temperature, humidity and wind speed were recorded and the ventilation rates corrected for wind speed and temperature. Notes large ranges in ventilation rates for similar flats.

Discusses the two methods for calculating air infiltration given in the ASHRAE handbook. These are the air change method, a gross estimate based on the number of windows and doors in each room, and the crack method based on measurements of flow through the cracks around windows and doors. Presents comparisons of tracer gas measurements with calculations by both air change and crack methods for test houses in California and Minnesota. Find agreement is adequate for sizing equipment but that the crack method underestimates infiltration at low wind velocity.