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52
Ventilation, occupation and illumination in relation to the hygienic conditions of classrooms.
Arising out of complaints of "dry throat" and other unsatisfactory physical conditions at certain
mechanically ventilated schools, an inquiry has been carried out during the past four years by Mr. E.
T. Swinsor, one of the Council's Inspectors, at Berner-street, Christian-street, Commercial-street and
South Hackney Central Schools.
Classrooms for comparison were selected as nearly alike as possible in respect to size, aspect,
occupation, general circumstances and surroundings. Double control tests were frequently used, and
the temperature and humidity of the external air were ascertained at the same time as the aerial state
of the classrooms. The factors investigated comprised (1) heat, (2) humidity, (3) odours, and (4)
air-movement The carbonic acid pollution was not taken into account, the view being accepted
that none of the symptoms produced as a result of poor ventilation, are due to its presence.
The observations made in regard to these factors under varying conditions of ventilation and artificial
illumination are detailed below, reference being made to diagram C where necessary.
Temperature
results under
natural
lightmgwith
(a) natural
and (b) mechanical
ventilation.
Fig. 1 shows the heat increment during the day under summer conditions, in which the increase
in temperature inside the classrooms, as compared with the external temperature or entering air, is solely
due to body heat given off by the occupants. Under natural ventilation the maximum excess of room
temperature is 7.5 deg. F., but with mechanical ventilation the maximum excess is only 3.5 deg. F. The
result for the naturally ventilated classroom is more favourable than generally obtained, because the
means of ventilation were fully utilised.
In the case of the mechanically ventilated room, the comparison made is that between the
entering air at the inlet and the room temperature itself. As the entering air was cooled by the process
of washing to a point 5 deg. below the outside air, the room temperature, in spite of occupation, never
exceeded that of the external air.
Under winter conditions (Fig. 2), the room temperature is affected by artificial heating, as well
as by heat emitted by the occupants. The naturally ventilated room shows an excess at the end of the
day over the external temperature of 16 deg., but in this total the whole of the effect of the artificial
heating is included; the rise of room temperature during the day is 6 deg. In the mechanically ventilated
room, where the air is already heated before it arrives at the inlet, the rise of room temperature
is only 1 deg., but while the room temperature is at the outset 1 deg. below the inlet temperature, it is
at the end of the day 2 deg. above.
The influence
of gas
and electric
lighting
upon temperature
u n d e r (a)
natural ventilation
and
(b) mechanical
ventilation.
Fig. 3 contrasts the conditions in two naturally ventilated classrooms one empty and the other
occupied—under winter conditions, with direct heating in all cases, but with varying conditions of
artificial lighting. Curve A gives the results in a room occupied and gas lighted; B gives a room
unoccupied and gas lighted; while C gives a classroom occupied without gas light. The large
amount of heat increment due to gas lighting is seen at a glance.
Fig. 4 shows the same thing in relation to mechanically ventilated rooms. When this diagram
is compared with Fig. 2, the excessive room heating produced by gas lighting is at once manifest. The
room B, which was unoccupied during the afternoon, but in which the gas was lighted, had an air
supply of 72,000 cubic feet an hour; yet there was an increase in temperature due to gas lighting of
6 deg. The influence of electric lighting is shown in Fig. 5.
An increase of absolute humidity was found under all conditions of lighting and ventilation—
an increase arising solely within the room from the occupants and illuminant. With natural ventilation
the relative humidity decreased under winter conditions to the mean extent of 14 per cent.
(occupation and natural lighting); 12.5 per cent. (occupation plus gas lighting); and 15 per cent. (gas
lighted unoccupied rooms). In summer there was a mean increase of 6.3 per cent. under occupation
with natural lighting. The winter results disclose an excessive drop in the humidity, and the summer
an undesirable increment. With mechanical ventilation the conditions were reversed, for the winter
conditions indicated increases up to 7.2 per cent., while in summer there was a definite mean decrease
of 10.8 per cent.—conditions tending towards the maintenance of a suitable atmosphere.
A large supply of air is needed to carry off the heat evolved within the room from the occupants
and from gas-lighting. Moreover, the state of the initial air-supply and the condition of the room
content as regards temperature and moisture markedly regulate the loss of heat and moisture by the
occupants, causing sensations of comfort or discomfort.
Under mechanical ventilation, with natural or electric lighting, odours were conspicuously absent
below a temperature of 67 deg. F., whereas with natural ventilation they were frequently noticed with
a temperature of 60 deg. F.; a result attributable to inadequate air-changes. The range of 9 a.m.
temperatures, January to April, is shown in Fig. 6,
In general, the enquiry leads to the following conclusions:—
Proper limitation of the maximum temperature, the elimination of dust, the regulation of the
humidity and freedom from odours, can only be obtained by a plentiful supply of clean and otherwise
suitable air. In crowded areas it may be desirable to provide mechanical ventilation coupled with
regulated warming and means for washing and cooling. Failing this the difficulties in producing and
maintaining proper ventilation by artificial or natural means under town conditions should lead to the
adoption of open air methods of education wherever practicable. If mechanical ventilation is employed
the provision should be based upon a minimum air supply per child per hour with heating surfaces
capable of warming such supply to a minimum standard. If the winter minimum supply were put at
1,750 to 2,000 cubic feet, with an initial temperature of 55 deg., the maximum could easily be kept
under 62 deg. F. If gas is used for illumination, even with a minimum supply of 2,500 cubic feet
of air the total temperature increment would be at least 10 deg. Heating provision should be based
on warming the hourly air supply to a minimum of 55 deg. F., when the external temperature stands
at 30 deg. below this, and this provision should be made both with mechanical and natural
ventilation.