classified as Wet and Dry Tropical (Aw) Climate, according to Koppen- Geiger 21, with the wet period from about November to March, inclusive.
From this survey, and subsequent analysis of about 3,000 votes obtain- ed from 46 participants, it appears that an increase in mean night tem- perature above 76°F is accompanied by more disturbances of sleep, and a sharp increase (in percentage of sleep- ers disturbed) occurs around 80°F. even with enhanced ventilation. Above 80°F the degree of distur- bance due directly to thermal discom- fort is likely to rise sharply. Even a small rise in temperature above this level will produce a disproportionate increase in physical discomfort and disturbed sleep.
The range of mean night tempera- ture encountered during the survey period was from 72°F to 81°F, with over 95 per cent dry bulb tempera- tures greater than 75°F. The rela- tive humidity at these temperatures is always high, so that these data may be particularly relevant to Malaysia and other countries in the humid tropics.
The Batchelor survey was concern- ed with disturbed sleep among adults, in an acclimatised white population. Ellis(3), Peel(4) and Hindmarsh and MacPherson (5) have supported the growing view that racial differences in preferred temperature during the day- time are unlikely, whilst Webb(6) was unable to detect any differences in re- sponse to thermal discomfort by sub- jects from different races in Singa- pore. Thus, the Batchelor informa- tion could be generally valid for Ma- laysia and other tropical countries.
In both the Batchelor and Singa- pore surveys, the subjects probably enjoyed a relatively higher standard of living than many people in humid tropical regions, so these data may not necessarily apply to indigenous people generally in tropical countries. at the present time.
There will be differences due to diet, weight, and size of people, lightness of clothing. overcrowded conditions in
many large tropical cities, and the generally different ways of living—all of which could have some bearing upon the up- per limit of temperature for sleeping comfort. The need for confirmatory research and evidence is obvious.
Batchelor Survey
to
Now
The most important, yet tentative, inference is that the upper limit for non-disturbance of sleep due thermal discomfort is 75°F. this dry bulb temperature corres- ponds, approximately, with the lower limit of daytime thermal comfort in humid regions (i.e. below 75°F dry bulb temperature during the day, it is likely that people will feel cold*, see Table 1).
55
52
*These dry bulb temperatures have
been recorded at times when the humidity was high, thus humidity is partly taken into account in the as- sessment, and the comparisons are generally equivalent.
At 76°F, one per cent of the po- pulation were disturbed in their sleep by thermal discomfort. At 81°F, cor- responding approximately to the op- timal
day-time thermal comfort ranges given in Table 1, 81⁄2 per cent of people were thermally disturbed. This is no small number, and it should be remembered that other causes of disturbed sleep will swell this total. At Batchelor, a further 19 per cent were disturbed at 81°F by other causes. In a city of one mil- lion population, well over 4 million people might be disturbed.
These figures for disturbed sleep should give much cause for thought and reflection, and should demon- strate in no uncertain terms that the matter is well worthy of deep and searching investigation. as to the cause, effects, and possible remedies. A start could well be made by ex- amining metabolic rates during sleep. and human physiology at night.
The normal human body is at its lowest when asleep in the early hours of the morning, having a metabolic rate of about 250 B.t.U. per hour as against about 400 B.t.U. per hour for a sedentary task during the day- time(12). Other tasks involve greater exertion with metabolic rates up to a maximum in the range 3,000-4,800 B.t.U. per hour.
Now, one would perhaps expect that sleep with the lowest metabolic rate would be the most comfortable "activity", but the Batchelor evidence points to an upper limit for undisturb- ed sleep at 75°F, and not the day- time range shown in Table 1.
In colder climates, the sleeping body is regularly assisted in keeping warm by the use of blankets, hot water bottles, etc. but in warm and humid climates it may be necessary posite kind. to employ artificial means of an op-
We do not yet know the complete answer, but as Webb(6) has indicat- ed, "populations of the tropics are peculiarly subject to thermal discom- fort". This peculiarity when examin- ed in much greater detail should pro- vide some basic design information for buildings at night.
Environment at Night
It is well known that a good night's sleep is necessary to allow the human body to recuperate. As Fry and Drew (13) put it, "The pressures of climate enforce a rhythm of move- ment and relapse of energy given out and restored by sleep". Certainly, a restful and refreshing night's sleep, or a mid-day siesta in reasonable "sleep- ing" comfort, will enable a person to face the monotonous climatic condi- tions of the enervating tropical humid day with greater energy and vigour, thereby to negate the somewhat slight- ing, yet traditionally held, view that "the heat of the tropics lulls people into a passive complacency and saps their vitality" (14) ̧
In colder climates, the ability to sleep in a cold environment has been fully investigated. In a warm and
humid environment, the human being can only remove barriers such as blankets and clothing from the skin, to keep cool and comfortable. Once sweating begins, the human body is already beyond the tolerance limits for thermal comfort and is in fact ex- periencing thermal discomfort. May we hope that a cheap and effective way of providing radiant cooling, without condensation on the inner surfaces of rooms, can be found, to assist in night comfort. In Australia,
radiant prototype
cooling panels. which are not affected by natural ven- tilation or high humidities, have been found to be successful(15).
The problem in tropical climates is to provide desirable thermal condi- tions in order to prevent disturbance of sleep by excessive warmth and the heavy atmosphere. But sleep may al- so be disturbed by the chilling of a perspiring skin surface suddeny ex- posed to a cooling draft of air. It should be unnecessary for human be ings to be thermally forced, as fre- quently happens in warm humid clim- ates, to reject the comfort that a mat- tress, canvas bed, hammock, Indian charpoi or niwar bed, or bed of woven cane, can provide.
The thermal discomfort experienc- ed may be so severe that a comfor- table bed is rejected, in favour of a cool hard floor, in order to gain relief and obtain some sleep. This forced behaviour emphasises the degree of thermal discomfort sometimes felt. and calls for urgent attention. This example perhaps suggests a method of alleviating thermal discomfort at night,
The concrete floor, albeit a hard surface, provides true cold comfort to the weary body by encouraging heat loss by conduction, mainly, but also by radiation of heat from the skin to the cooler concrete. The thermal inertia, or time-lag effect of masonry materials enables the con- crete to store large quantities of heat without the occurrence of a major change of temperature within(16). Perhaps this is the basis upon which the bed may be re-designed. Has a cold water-filled mattress been con- sidered?
Radiation Climate at Night
Thin sheet materials cannot gain or lose large quantities of heat without changes in temperature, so that a light-weight timber building will fol low quite rapidly, (in about 30 minutes to 11⁄2 hours, depending on thickness and weight) any changes in external temperature. Inside a tim- ber house, the night-time temperature will only be a shade higher than that prevailing outside.
Concrete and brick buildings, on the other hand, with their thermal capacity, will follow the external daily
course
of temperature variation at some time much later (from 4 to 10 hours). Because of this slow response the temperatures reached inside the building during the day may not be so high, but at night a masonry build- ing will reflect the daytime conditions.
Far East Architect & Builder March, 1967