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Volume 58, 1928
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The Kata-Thermometer Applied to the Investigation of the Physical Conditions of Schoolroom Atmosphere.

[Read before the Philosophical Institute of Canterbury, 1st December, 1926; received by Editor, 5th February, 1927; issued separately 8th November, 1927.]

Modern ideas concerning the suitability of atmospheric environment depend on the physical condition of the atmosphere, and it is interesting then to determine how the ventilation schemes in our schools conform with the standards set down by the modern authorities. In this paper are set forth the results of a series of observations of the physical conditions of the atmosphere in two types of schoolroom, the open-air type and the modern departmental type. The object of the investigation was to determine whether any appreciable difference exists between the atmospheric conditions prevailing in the two types of room due to the difference in the ventilating schemes. The observations were made over an interval of roughly one month in the period November—December 1925. The results set forth herein are to be considered only as prelimi-nary, and by no means as final, since they require substantiation by further observations extending over a complete year at least. Nevertheless the author considers that they are indicative of the more general results to be obtained later. It is regrettable that circumstances which could not be controlled interrupted the investigation and prevented its continuance during the present year. However it is hoped to continue the work on a wider scale in 1927. The author believes that this is the first investigation carried on with the kata-thermometer in New Zealand.

Since the instrument used in this investigation is probably not well known, it has seemed advisable to preface the discussion of the observations by a brief outline of the physical principles of the kata-thermometer, together with a few remarks on the significance of the conditions measured with it from the standpoint of hygienic physiology. Most of that portion is really a restatement of the works of Hill, Griffith, Flack, Lefevre, and others, with the exception of the reduction of the observations to a standard condi-tion of temperature, barometric pressure, and humidity, of which the author has seen no mention elsewhere.

Physical Principles of the Kata-thermometer.

The kata-thermometer is an alcohol thermometer having a bulb of cylindrical form about 4 cm. long and 2 cm. diameter. The stem is about 18 cm. long, graduated by two marks the mean temperature

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between which is 36°.5 C. (body temperature), and has a small reservoir at the top to prevent bursting through overheating. Both dry and wet readings are taken, a wet stall covering the bulb in the case of the wet readings. The kata is heated until the alcohol enters the top reservoir. The time in seconds for the alcohol column to fall between the graduations is measured with a stop watch, and this divided into the factor for the instrument gives the rate of cooling of the atmosphere at the body temperature in milligrammecalories per square centimetre per second.

The rate of cooling of the dry kata clearly depends on radia-tion and convention, while that of the wet kata depends on these plus evaporation, so that by simple subtraction we can find the rate of cooling due to evaporation alone. Further it has been found that the rate of heat loss due to radiation Hr is equal to that due to con-vection (He) i. e., for the dry kata, if H is the rate of cooling,

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H = Hr + Hc = 2Hr = 2Hc

If V is the wind velocity in metres per second, and T the temperature in degrees centigrade of the medium in which the kata is placed, then it has been found by Hill and others that

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v = {(H/(36.5-T))-0.27/0.49}2

which expression has been fully verified by observations made in wind tunnels and tubes of various dimensions.

If H1 is the cooling power at a temperature T1 and H2 that at temperature T2, then the relation:—

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H2 = H1 {36.5-T2/36.5-T1

has been amply verified by experimental evidence.

If H1 is the cooling power when the barometric pressure is p1 and H2 is the cooling power when the pressure is p2, it has been shown and amply demonstrated by experiment that the following relation holds true:

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H2 = H1/2 (1+ √p2/p1

In the case of the wet kata, we have to consider also the influence of humidity. If W is the rate of cooling of the wet kata, F the vapour tension in millimetres of mercury of air saturated at 36°.5 C, f the tension of aqueous vapour in the air, and V the wind velocity in metres per second, the following equation has been shown to fit the facts adequately:—

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W = (0.27+0.49 √V) (36.5-(T)+(0.085+0.102 V0.3) (F-f)4/3

Hence by simple subtraction, we have that He the rate of cooling due to evaporation is given by:—

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He = (0.085 + 0.102 V0 8) (F-f)4/3

It is at once seen that by the use of these equations, readings taken with the kata-thermometer under one set of conditions can be reduced to their equivalents at a set of standard conditions. This reduction to standard conditions is very necessary if we wish to make a fair comparison between the efficiency of the ventilating systems in use at places some distance apart.

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Physiological Considerations.

There is an enormous collection of evidence which leads us to the conclusion that lack of fresh air has a marked deteriorating effect on the mental and physical powers of the human being. This effect has been ascribed to poisoning due to excess of CO2 or to exhaled organic matter of human origin or to both of these causes. Singly and collectively these ideas have proved inadequate. Three per cent. of CO2 can be endured without ill effect, and we know that the air sacs of the lungs contain from 5% to 6% of CO2, The oxygen-content of the worst ventilated and most over crowded room is higher than that of the air at the Alpine health resorts. The idea of a subtle organic poison has been shown by exhaustive scientific tests to be wholly without foundation. the cause of the “stuffiness” of crowded rooms has however been traced albuminous decomposition-products from buccal, nasal, and cutaneous surfaces, and clothing. The net result of the research performed of late years on this question, is that the evil effects of foul air are not due to chemical impurities acting through the lungs, but to physical changes acting through the skin. If the physical conditions of the air are such that equilibrium between the heat-production and loss is upset, heat-retention sets in which in its turn sets in operation chemical changes in the tissues which result in toxins producing fatigue, etc. This causes a further increase in temperature which increases oxidation processes leading in their turn to further heat-production. Evaporation from the skin enables us to cope with excessive heat-production from within and excessive heat-reception from without. Hence in order to determine the suitability of an atmospheric environment, we must determine the rate of cooling and the evaporative power of the air at the temperature of the body.

It was suggested to me that measurement of the standard meta-bolic rates of the children from the rooms under investigation would give an indication of the results of the two types of ventilation. This would have been very impracticable, and besides could hardly have led to any definite result, since the differences in the atmos-pheres of the two rooms turned out to be very small, and further it is customary to allow a 10% departure from the mean as a normal rate. In this connection we should remember, too, that in the examination of 1642 patients suffering from diseases other than thyroid disorders, Boothby & Sandiford found that the basal meta-bolic rate of 74% of these fell within the normal 10% range.

Various standards of suitability have been proposed from time to time by various investigators.

Wet Bulb Temperature as a Standard.

Haldane who studied the influence of wet and dry bulb readings on body temperatures, considered the wet bulb tempera-ture to be a measure of the suitability of conditions. The wet bulb temperature should be low enough to ensure evaporation; and he stated maximum wet bulb temperatures for various types of factories, e. g., spinning mills, etc.

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Dew Point as a Standard.

Bruce showed that any attempt to judge conditions by the wet bulb temperature alone is certain to be misleading, a wet bulb temperature of 28° C., being under certain conditions much more agreeable than one of 24° C. He found that when the dew point is between 21° C. and 24° C., the conditions became very trying, but that in the neighbourhood of 17° C., hard work can be carried on without inconvenience. He therefore fixed this as the maximum dew point for factories.

Wet Kata Reading as a Standard.

The rate of evaporation in the air is dependent upon:—

(1)

The tension of aqueous vapour in the air,

(2)

The tension of aqueous vapour in air saturated at 36°5C.,

(3)

The velocity of the air current.

It is now considered that the kata succeeds where the wet bulb and dew point criteria fail as a standard of comfort. The evaporative power has a great effect on human energy, as has been proved by world-wide observation, and so from kata observations one may be able to judge whether a certain place is suitable for work of a certain type.

As minimum cooling powers Leonard Hill lays down the follow-ing:—

Dry kata   not less than  6 millicalories/second

Wet kata  not less than  18 millicalories/second

but it is argued that in the case of schoolrooms they should be:—

Dry kata  not less than  7 millicalories/second

Wet kata  not less than  20 millicalories/second

However these values were calculated for England where the mean annual temperature is about 11° C., so that, if we reduce these to the condition of 15° C. (which is somewhere near the mean temperature for New Zealand) we have for the minimum for a schoolroom,

Dry kata  not less than  6 millicalories/second

Wet kata  not less than  16 millicalories/second

as a suitable standard for New Zealand.

Discussion of Results of Observations.

The observations were made in the Open-air classroom at the Fendalton School, and in the Form 5 Room at the New West–Christchurch School. The open-air room is built with the sliding doors facing north-west, since, in spite of a popular superstition. the north-west wind is not a frequent one in Christchurch, the wind direction-frequency records of the Magnetic Observatory showing a total of only 315 days for north-west winds over a period of twelve years. The north-east side has five large windows swinging into a horizontal position about a central pivot, and above these five smaller similar windows. On the south-east side at the same level as these latter are five similar small windows, and on the south-west side are three similar small windows also at the same level. In the south

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corner there is a fireplace for use in the cold weather. The sliding front consists of four slides which can be adjusted at will. The room measures 26 ft. × 24 ft. × 10 ft., and is designed to accommodate 60 children. The light entering the room through the open side does not have the ultra-violet rays filtered off by passage through glass. However, the windows were usually nearly all closed at the times when observations were made.

The room investigated at West-Christchurch is an upstairs one which would easily accommodate 60 pupils. The height is somewhat greater than that of the Fendalton room. The room faces approxi-mately north north-west, and has a large window-area on this side. These windows can be opened to an angle of about 30 degrees about horizontal axis, and this condition prevails over almost the whole side of the room. On the opposite side is another set of windows: some large ones each opening to 90 degrees about a vertical axis and some hopper windows below these. On the other side of this wall is a corridor which again has a very full set of windows opening out-side; but all the light passes through glass and so has the ultra-violet rays filtered off before it gets into the room. The heating is by means of steam radiators. It should be noted here that since the room is an upstairs one, the wind velocity affecting it is higher than that for a ground-floor room. The outside readings were taken standing on the ground, so that the outside wind velocities affecting this room were in reality a little higher than those given in the following results.

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Table 1. Circumstances of the Observations.
A.—Fendalton.
No. of Obsn. Date 1925 Time Wind Cloud C/A Remarks
h. m.
1 18 Nov. 14 15 N. E. cum. str. 3 50/60 3 small windows open 0 large windows open side open
2 23 Nov. 13 55 N. E. cum. 7 50/60 3 small windows open 0 large windows open side open
3 24 Nov. 10 25 E. N. E. cum. str. 3 50/60 0 windows open side open
4 30 Nov. 14 20 N. N. E. cum. 9 50/60 3 small windows open 0 large windows open side open
5 2 Dec. 9 35 S. W. cum. 6 50/60 0 windows open side open
6 9 Dec. 13 40 E. N. E. cum. str 6 50/60 6 small and 1 large windows open; side open
B.—West Christchurch.
1 24 Nov. 9 40 E. N. E. cum. str. 3 43/60 All possible ventilation
2 2 Dec. 13 50 S. W. cum. 6 25/60 All possible ventilation
3 3 Dec. 10 15 E. cum. 10 35/60 All possible ventilation
4 7 Dec 14 5 E cir. cum. 4 40/60 All possible ventilation
5 8 Dec 10 00 S. W. cum. 9 40/60 All possible ventilation
6 10 Dec. 13 50 E. N. E. cum. str. 6 14/60 All possible ventilation
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In the above table, C = number of children in the room, and A = the accommdation of the room.

However, much more complete meteorological data were taken both inside and out for the purpose of reducing the results to a standard condition, namely, temperature = 15° C., barometric pressure = 760 millimetres of mercury, and humidity = 70% (and therefore F - f0 = 36 mm, 76). The 70% humidity standard was chosen because the average humidity of Christchurch is in the neighbourhood of 70%.

The meteorological data collected in connection with the kata observations are set forth in the following table, in which the numbers of the observations correspond; with those of the previous table.

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Table 2.
Meteorological Data.
A.—Fendalton.
No. 1 2 3 4 5 6 Means
P1 764. 748.8 751.8 750.5 755.1 754.2 754.1
T1 18.0 17.2 19.0 20.2 18.0 23.9 19.4
T2 13.0 13.9 13.8 14.8 13.2 17.8 14.4
inside R 56 67 55 53 57 52 57
T3 8.8 9.8 9.7 10.5 9.2 13.4 10.2
F—f 36.8 35.7 36.5 36.0 36.8 34.0 36.0
T11 16 2 17.8 18.0 19.6 15.4 23.8 18.5
T21 12.6 14.4 13.6 14.2 11.8 18 1 14.1
outside R1 64 68 59 53 63 55 60
T31 9.3 11.7 10.0 9.9 8.6 14.3 10.6
(F—f1 36 6 35.3 36.3 36.4 37.1 33 4 35.9
(T1—T11 1 8 - 0 6 1.6 0.6 2.6 0.1 0.9
(T2—T21 0.4 - 0.5 0 2 0.6 1.4 - 0.3 0.3
(R—R1 8 1 4 0 6 3 4
(T3—T21 0.5 1.9 0.3 - 0.6 - 0.6 0 9 0.4
(F—f)—(F—f1 0.2 0.4 0.2 - 0 4 - 0.3 0.6 0.1
B.—West Christchurch.
P1 751.8 757 8 756.6 757.4 756.3 749.8 755.0
T1 17.9 16.1 14.8 19.5 17.5 26.0 18.6
T2 12.8 10.5 12 2 14.9 14.8 16.1 13.6
inside R 55 50 73 59 72 35 57
T3 7.9 5.2 9 9 11.2 12.4 9.2 9.3
F—f 37.5 38.9 36.3 37.4 34.7 36.8 36.9
T11 18.1 17.6 13.9 17.0 15.2 25.6 17.9
T21 13 0 12.1 12.3 13.8 13.4 15.8 13.4
outside R1 55 53 81 68 81 35 62
T31 8.2 7.5 12.3 11.0 12.3 9.3 10.1
(F—f1 37.4 37.7 34.8 35.7 35.2 36.8 36 3
(T1—T11 - 0.2 - 1.5 0 9 2.5 2. 0.4 0.7
(T2—T21 - 0.2 - 1.6 - 0.1 1.1 1.4 0.3 0.2
(R—R1 0 3 8 9 9 0 5
(T3—T21 0.3 2.3 2 4 0.2 - 0.1 0.1 0.8
(F—f)—(F—f1 0.1 1.2 1.5 1.7 - 0.5 0.0 0.7
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In the above table p1 is the barometric pressure, T1 the dry bulb temperature, T2 the wet bulb temperature, T3 the dew point, R the humidity. The same symbols dashed are the corresponding outside values.

The meteorological data show that the mean inside temperature was 0.8 higher at Fendalton, and the outside temperature 0.6 higher. The inside wet bulb was 0.8 higher and outside wet bulb 0.7 higher at Fendalton. The mean dew point was also higher at Fendalton by 0.9 inside and 0.5 outside. The differences between the humidities was of the same order as the probable error of observation, for it is very difficult to observe humidities to an accuracy of 1%. Further, the differences between the inside and outside mean dry bulb temperatures was 0.2 greater at Fendalton, and in the case of the wet bulb temperatures, 0.1 greater at Fen-dalton.

The following table gives the kata observations, both the observed values and the reduced values being recorded. They are in milligrammecalories per square centimetre per second correct to one place of decimals.

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Table 3.
Kata Observations.
A.—Fendalton.
No. of Obsn. Inside Outside
Observed Reduced Observed Reduced
D1 W1 D0 W0 D11 W11 D01 W01
1 10.4 17.0 11.5 18.7 17.0 24.2 17.1 24.3
2 8.0 14.7 8 9 16.8 8.4 14.9 9.7 17.7
3 6.7 13.9 8.2 17.2 9 0 16 4 10 5 19.3
4 8.1 14.1 10.7 18.9 9.8 18.7 12.4 24.0
5 7.5 15 8 8.7 17.3 16.3 20.7 16.4 21.1
6 6.2 15.2 10.5 27 7 8.5 20.9 14.3 38.4
Sums 46 9 90.7 58.5 116.6 69.0 115.8 80.4 144.6
Means 7.8 14.5 9.8 19.4 11.5 19.3 13.4 24.1
B.—West Christchurch.
1 7.5 13.9 8.7 16.0 13.4 21.9 15.7 25.5
2 7.2 14.3 7.6 14.5 17.0 20.7 19 4 23.5
3 8.1 13 9 8.0 13.8 11.5 17.7 10 9 17.3
4 7.6 14.2 9.6 16.8 16.7 27.1 18 4 30.3
5 8.0 13.2 9.1 15.4 16.2 22.8 16.4 23.4
6 5.1 14.8 10.6 30.5 7.3 16.7 14.4 33.7
Sums 43.5 84.3 53.6 107.0 82 1 126.9 95.2 153.7
Means 7.3 14.1 8.9 17.8 13.7 21.2 15.9 25.6
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From this table, considering the means of the reduced values, we have the following result:—

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Fendalton West Christchurch
Evaporative power inside 9.6 8.9
Evaporative power outside 10.7 9.7
Diff. of cooling powers (out - inside) dry 3.6 7.0
Diff. of cooling powers (out - inside) wet 4.7 7.8

It is immediately obvious from these results that the conditions in the open-air room are slightly better than those in the other room, as well as approximating more closely to the conditions prevail-ing outside.

Computing the wind velocity outside and the velocity of venti-lation inside from the mean reduced dry kata readings, by means of the formula

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V = {H/36.5 - T -0.27/0.49}2

mentioned above, we have the following:—

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School Inside Velocity (Metres per second) Outside Velocity (Metres per second)
Fendalton 0.1 0.5
WestCh ristchurch 0.1 0.9

Thus for the same wind velocity, the velocity of ventilation is higher in the open-air room than in the other in the approximate ratio of 2 : 1 when the ventilating system is fully open. If we group the observations made in the open-air room, taking those when all the windows were closed and those when only three small windows were open we find that the ventilation velocity in the first case was 0.1 metre per second, and in the second case 0.2 metre per second, which is the type of result one would expect according to the dictates of common sense.

The departures of these results from the minimum conditions as set down by Professor Leonard Hill, namely dry kata = 6, wet kata = 16 for the standard conditions of temperature, humidity and barometric pressure which we have adopted here are on the good side in the case of both rooms investigated. They are as follows:—

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Excess above minimum requirement
School Inside Outside
Dry Wet Dry Wet
Fendalton 3.6 3.4 7.4 8.1
West Christchurch 2.9 1.8 9.9 9.6

This shows clearly to what extent the conditions in the open-air room were superior to those in the other room. However, the difference is very small, even when we allow for the fact that the outside conditions were a little worse at Fendalton than at West Christchurch.

In considering the results, it is necessary to keep in mind the following facts:—

(1)

An upstairs room was observed at the West Christ-church School, which must therefore be effected by a wind velocity a little greater than that at the ground—where the outside observations were taken—and hence have a venti-lation velocity slightly greater than would otherwise be the case.

(2)

The room at West Christchurch always had all the windows open to the fullest extent, which was by no means the case at the Fendalton room.

(3)

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The average ratio of the number of pupils to the available accommodation was 33/60 in the case of the West Christchurch room and 50/60 in the case of the Fendalton room.

General Conclusions.

To summarize these results, we have:—

(1)

Higher cooling power of the atmosphere under the same conditions of temperature, humidity and barometric pressure in the open-air room than in the other.

(2)

The ventilation velocity was greater in the open-air room than in the other with the same external wind velocity, and without irritating draughts, which is an important feature.

(3)

The conditions in the open-air room were a closer approach to the outside conditions than were those in the other room.

(4)

Both rooms conformed to the standard set down by Prof. Hill.

However it will be noticed that the difference between the cooling powers was so small that any advantages which might be represented could easily be vitiated by conditions of clothing, diet, and muscular activity; in fact one could more than compensate for the difference by shaving the heads of the children in the room

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at West Christchurch, or by sending them to school without stockings. The greatest advantage of the open-air room would seem to be that due to the as yet not properly understood physiological qualities of the sun's rays, which qualities are apparently concen-trated in the ultra violet or high frequency part of the spectrum. These ultra violet rays are filtered out by passage through ordinary window glass, but can be effective in their action in the open-air room from which they are not screened. The question of the effect of the open-air room on the basal metabolic rate, or as Krogh more aptly terms it standard metabolism, has already been disposed of. Increasing this is not desirable, since high metabolic rates are found mainly in diseased conditions such as exophthalmic goitre. In any case the difference of the metabolic rate due to the difference of atmos-pheric conditions could not possibly be detected with any certainty, since it is usual to consider variations of plus or minus 10% as normal in the measurement of basal metabolic rates.

These results are only of a preliminary nature, and it is the author's intention to carry on the investigation continuously throughout the year 1927, in order either to verify or to disprove the results set forth in this present paper.

In conclusion, the author desires to thank Dr. R. B. Phillipps, Dr. R. R. D. Milligan and H. F. Skey, Esq. M. Sc., for much valuable albeit at times harsh criticism during the preparation of this paper.

Liberatum Referred to.

Hill, Prof. Leonard, 1919. The Science of Ventilation and Open Air Treat-ment, Part 1. H. M. Stationery Office, London.

Hill Prof. Leonard, 1920. Ibid., Part 2.

Hill, L., Griffith, O. W., and Flack, M., 1916. Phil. Trans. Roy. Soc., 207B' 183.