Temperature and humidity in portable school classrooms, Halifax 1969-70

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Temperature and humidity in portable school classrooms, Halifax

1969-70

NA TIONAL RESEARCH COUNCIL OF CANADA DIVISION OF BUILDING RESEARCH

TEMPERATURE AND HUMIDITY IN PORTABLE SCHOOL CLASSROOMS HALIFAX 1969 - 7 0

by

D. R. Robson

ANALYZED

Internal Report No. 384 of the

Division of Building Research

OTTAWA February 1971

TEMPERATURE AND HUMIDITY IN PORTABLE SCHOOL CLASSROOMS HALIFAX 1969 -70

by

D. R. Robson

Records have been presented of temperature and humidity in class-rooms in six school buildings in Halifax, N. S., for the period October 1961

to June 1962 in Internal Report No. 265. Since that time the school

facili-ties have become extremely crowded owing to a rapidly expanding population

in the metropolitan area and a lag in school construction. As a temporary

solution portable classrooms have been located at existing school sites until a definite growth trend becomes evident and permanent facilities may be built.

With the use of portable classrooms questions have arisen as to temperature and humidity in this type of classroom in comparison with

temperature and humidity in conventional classrooms. Records of

tempera-ture and humidity for five portable classrooms and two conventional class-rooms for the period November 1969 to June 1970 are now presented.

Indoor records of temperature and humidity were obtained by means of a hygrothermograph ( Figure 1), a clock-driven 7 -day drum chart on

which are recorded continuous records of temperature and humidity. Changes in temperature are registered by a bimetal element and changes in relative

humidity by a hair element. Because the hair element cannot be relied uponfor

accuracy over a wide range of humidity the hygrothermographs were re-calibrated on a regular basis, using an electrically aspirated psychrometer. Outdoor weather records were obtained from the published data of the

Meteorological Branch, Department of Transport, for the Halifax area.

The location of each school in relation to the Atlantic Regional

Station is shown in Figure 2. The weather station from which the outdoor

weather records were obtained is

4i

miles east and

It

miles south of the

DBR/NRC Regional Station. A photograph of each school site is included

(Figure 3). Site 1, Halifax West, has two portable classrooms; Site 2,

B. C. Silver, has three portable classrooms. Details are shown in Figures

4,5 and 6.

The occupancy for each classroom varied from day to day and fr o m

hour to hour, but examination of the attendance records indicated that 15 pupils per class could be considered average.

The charts collected from each school were processed for daily average temperature and humidity, and from these weekly average values

were calculated. Both occupied and unoccupied periods were included in

the calculation of weekly averages because very little difference was

in-dicated when only occupied periods were considered. The humidity ratio

was calculated from weekly average temperature and relative humidity.

2

-Outdoor wea ch e r records were processed {l'O,O pub lis h ed daily

values to obtain weekly averages of temperature, relative hurnIditv and

hurrridity ratio.

PRESENTATION OF RESULTS

Temperature, Figure 7

Weekly average temperatures for all schools have been plotted

against weekly outdoor temperatures. As expected, variations in outdoor

temperature have practically no effect on indoor temperature because each classroom is automatically controlled.

At Site 1 any variation between the temperatures maintained in

the portables and the temperature in the classroom is negligible. The

records for the portables indicate better control of temperature than do

those for the classroom. Both portables are new and this would have

some effect, as would the fact that the thermostats were in better con-dition.

At Site 2 the portable classrooms showed poor control of

temper-ature. There were some problems with vandals and early in the year the

thermostats were not functioning at all.

It is clear that the portables at Site 2 did not take full advantage of natural ventilation, although the window design may have made this

impossible. The small high windows in the portables at Site 1 may

provide a better method of controlling ventilation without uncomfortable

drafts. It is also clear that the thermostats must be of a more rugged

construction for buildings of this type if they are to function properly.

Relative Humidity, Figure 8

The weekly average relative humidity for all classrooms has

been plotted on the same graph as the weekly average relative humidity for

out-door conditions. The curves are generally similar, indicating the effect

of outdoor relative humidity. This will be more evident on the humidity

ratio graph.

The weekly average relative humidity for each school has been shown, but because of the temperature variations a direct comparison

is not possible. It is, however, quite evident that extremely low relative

humidities are experienced in school classroorns fr orn January to March.

Humidity Ratio, Figure 9

The average weekly humidity ratio for all schools has been plaited

on the same graph as the average outdoor humidity ratio. The two curves

are quite close in the spring and fall, diverging slightly through the winter,

indicating reduced ventilation and a moisture contribution from the pupils. There is very little difference between portable classroom humidity

- 3

-portables are new and there is a better rrre th od of ventilation the hurn idity

ratio is slightly lower in the winter period than it is in the standard clas

s-rOOITl. At Site 2, there is very little differenc e between the standard and

portable c Ia s s r o orn.s . GENERAL REMARKS

Heat f r orn pupils and lighting supplies app r oxirria te ly 50 per cent

of the heat r equir ern erit of a portable cIas s r oorn at outside design t

errr-perature; thus the heating s y s te rn can rna irrta in a comfort level of 72 ° F

even with three to four air changes per hour. At outside terrip e r a tu r e s

of 40° F and above, no heat is required fr orn the heating systern to offset

heat loss. Consequently, a rne an s of adequate natural ventilation is

rn o st irnpo r tarrt in the design of a portable c Ia s s r o orn, but it rrru st be

achieved without dis c ornf o rt to the occupants. It appears fr orn the rec ords

that the s y sterri of natural ventilation in the newer portables results in

better ternp er a tur e control as well as better ventilation.

Daily Record, Figure 10

A graph of the daily record of ternpe r a tu r e and relative hurn idity

shows quite clearly the effect of the student load on both ternp e r a tur e

and air rno i stur e content. The rise in air rnoistur e content is perhaps

not as rrruc h as one would expect, but outdoor ternp e r a tu r e at the tirne

was about 30°F and the rOOITl was therefore well ventilated. CONCLUSIONS

It appears that indoor conditions in portable cIas s r oorn s are at

least as good as those in conventional cIas s r o orn s ; and that with the

venti-lation possible in newer designs better terripe r a tur e control is possible.

The relative hurrridity level, however, is still very low and SOITle rn e a n s

of adding rn ois tu r e to the air would be desirable.

ACKNOWLEDGEMENTS

The author wishes to thank the Halifax School Board, the

principals of each of the schools involved, and the individual teachers. The assistance of M. L. Fisher, who collected and processed the records is also gratefully acknowledged.

Figure 1 - Hygrothermograph with Guard Removed and Case Open.

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Site 1 Halifax West

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Site 2

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Portables North and West of Main School,

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7

(a)

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