Book - School of Science and Technology

344 Ventilationnormal circumstance therefore, with reliance upon ventilation alone, the result may wellbe that the temperature within the space is higher than that prevailing outside. If such asituation were considered to be unacceptable then it would be necessary to consider theapplication of air-conditioning, as dealt with in later chapters.Unwanted moistureIn certain special circumstances, the need to combat condensation may be the criterionfor ventilation rate. One such instance is that of a swimming pool hall where, of therequirements to supply air to the occupants ± removal of the familiar `chemical' smelland action to combat condensation ± the latter is by far the more important. It has beenshown that, with double glazing, the outside air supply rate should not be less than15 litre/s per m 2 of the water and wetted surround surface, i.e. about 18 litre/s per m 2 ofwater surface.*In housing, it has been shown that a mean ventilation rate of one air change per hour(see later comment upon this quantity) is required to prevent condensation on singleglazed windows in a dwelling which is heated uniformly. y In domestic kitchens, theventilation requirement to avoid condensation is about 100 litre/s for electric cookingand half as much again for gas cooking. Packaged units of continental manufacturewhich provide for whole-dwelling supply and discharge ventilation, including energyrecovery, appear to provide for an outside air volume of 70 litre/s or about 1.5 airchanges per hour.ContaminantsUnder this heading, a whole range of industrial hazards arises in addition to the particularrequirements for medical buildings, laboratories, animal rooms, horticulture, etc., whichare too diverse and too specialised to be dealt with here. It is not possible to offer anygeneralised observations in this respect other than to refer to the equilibrium expressionwhich follows here. This may be used when details of the process and the permissible zconcentration of the contaminant are known in any set of consistent units: a brief list ofcommon contaminants is given in Table 13.4.Q ˆ P[(1 C 1 )/(C 1 C 2 )]whereQ ˆ rate of supply of outside airP ˆ rate of contaminant releaseC 1 ˆ permissible concentration in roomC 2 ˆ contaminant concentration in outside air* Doe, L. N., Gura, J. H., and Martin, P. L., `Building services for swimming pools', JIHVE, 1967, 35,261.y Loudon, A. G., and Hendry, I. W. L., Ventilation and Condensation Control, IHVE, RIBA. IOB.Conference 1972.z Health and Safety Executive. Occupational Exposure Limits. Guidance Note EH 40/1993, HMSO.