Managing Temperature for Interior Design

Climate conditions our living. We find ways  to survive and conduct tasks in a manner that is easier than ever before. We adopt the climate through instincts, learning, and also have the built in resilience for occasional variations. We get acclimatized to the normal climate of the area. It is through the design of the built-form, exploration of materials and setting of a lifestyle that we achieve a greater degree of adaptability for climate. Through a continuous process of selection and elimination we develop a comprehensive system that is natural for the geographic region. Climate adoption also involves some physiological changes in the short and very long terms.

During early periods attempts to understand the climate were limited to determine the level of its predictability.  For these seasonal changes, rain fall, and temperature variations, were locally recorded and interpreted. The collated data of various regions gave an understanding of the macro climate. This helped in agriculture, migration, and seasonal comfort. Today we have a greater perception of the climate is much broader, with components such: as air currents, pressures, humidity level, solar heat, sea currents etc. We also have better knowledge about how other beings and plants respond to the climate. Study of human endurance in very acute conditions like space shuttles, arctic conditions, deep water diving, undersea explorations, supersonic jet travel, high altitude mountaineering, provide us with a lot of feedback on how to deal with climatic variations.

Climate profile parameters mainly include:

    TEMPERATURE

    HUMIDITY

    AIR MOVEMENT

An effective climate profile of a place and time emerges through comprehensive mix of all these parameters. However, temperature related comfort derives through fine tuning of siting, size, shape, form (openings and other architectural features)  of the building,  time-space scheduling of tasks, lifestyle setting, food and clothing.


TEMPERATURE: Temperature is the major determinant of comfort level. Air temperature determines the rate at which our body will exchange heat with the atmosphere. Rate of heat exchange also affects the metabolic activity of the body and as a result its work capacity, fatigue and recovery schedule. In a temperature range that is acutely different from the acclimatized one, our body has to work harder to adopt to the situation.

Direct solar radiation is the key factor for heat gain. It heats up various objects, depending on their thermal capacity, conductivity, colour, texture etc. Heated objects radiate this heat, as long wave radiation, back into atmosphere, often after the main source has ceased its input. Such delayed heat releases, create very complex patterns of heat gain or loss. A temperature profile of any space is rarely consistent and this causes different gradients and convective air movements. Such air movements affect the quality of air, rate of ventilation, density of air, rate of evaporation and the level of humidity in a space.

A building is affected by the type and level of energy transfer that takes place with its environment. Energy flows in and out of a building. For a building, the shell (shape. size, materials etc.),  siting, the amenities etc., are more or less constant factors, but the variables are: climatic parameters, inhabitants and tasks. When constants and variables are appropriately matched, we get an environment that is always in a flux, only partly predicable, and often with surprises.

A      Conduction of heat may occur from various types of surfaces, inward or outward,  depending on the temperature gradient. Conduction of heat is affected by the `transmittance factor' of the building materials. It is also affected by the area, colour, opacity and texture of the surface.

B      Solar gain through transparent surfaces is governed by the area, angles of the incidence, quality of the materials.

C      Convective heat exchange takes place with the movement of air (ventilation). This may be due to unintentional infiltration (leakages) or deliberate ventilation. The rate of convection depends on the rate of ventilation (air change), velocity of the convective medium (air), temperature difference and specific heat of the convective medium (air).

D      Internal heat gain in space occurs from the output of human bodies, lamps, gadgets and appliances.

E    Heat removal due to evaporation that occurs in the vicinity, outside and inside the building.

F    Deliberate addition or subtraction of heat by passive and mechanical devices.

The net thermal balance in a building shell is a result of all these factors. From a climate point of view, a building behaves like a biological entity, that is in a continuous process of achieving equilibrium. But the process, towards the equilibrium, is not always favourable to the inhabitants or their activities. We need to hasten, delay, curtail or terminate some of the climate processes. For the purpose primarily we use passive devices. Such devices include shading devices, insulation systems, heat absorption or dissemination systems. However, in a particular time and space frame when it is often not feasible or adequate to control the climatic processes, and we use non-passive (electro-mechanical or chemical) devices.

Designers primarily rely on materials and form of the building to achieve a favourable exchange of energy. Designers also utilize features of the surroundings to modulate the energy exchange. These tools are the site features like slopes, hills, mounds, gorges, valleys; or  landscaping features like pools, plants, shrubs, hedges, groves, etc.

Designers facilitate various activities at specific space sections by locating amenities and facilities. Designers promote and indirectly regulate the time schedules for various activities, making amenities and facilities to be either fixed or relocatable.

• For macro level perception and comfort planning several temperature zoning methods are used. Some depend on geo-spatial definitions through latitudes, and others depend on regional demarcations. A more practical method is the combined system.

• Humid tropical zone surrounds the equator 10 N to 10 S. Here mean daily temperatures are 25-27  C, and the diurnal variation exceeds the modest annual variation. Rainfall varies but is generally above 2000 mm per annum. There are no marked `seasons'.

• Semi arid tropical zone follows the humid tropical zone. Here the seasons are distinctive. Temperature and rainfall reach their maximum in summer months. A dry and slightly milder (colder) season prevails as soon as Sun moves to the other hemisphere.

• Arid tropical zone is next to the semi tropical zone, around 30 N and 30 S. This is a zone of subsiding air, with limited cloud cover and with sporadic rainfall. There is a high diurnal temperature range, due to high solar gain during day time and high loss during night time with clear skies. Evapotranspiration exceeds the normal precipitation, resulting in a net water deficit.

• Semi arid sub tropical zone has marked seasonal contrasts. Some variations occur in coastal regions such as in Mediterranean region. Here the subsiding dry air of the tropics predominates in summer, while in winter low pressure brings rain and lowers the temperatures.

• Temperate humid zone, at 50 N and 50 S are marked by the westerly-easterly winds. Here low pressure cells and polar fronts dominate. The winters are moderately cold, and summers are comparatively cool and rainfall year round. In regions away from the sea, there is snow in winter, and thunderstorm activity in summer. In deep set areas the temperature may reach 40 to 50 C , and are called semi arid temperate zones. In some areas the precipitation is so low that arid steppe climate develops.

• Boreal zone is closer to the pole regions, where winters are extremely cold and summer or non winter period is strikingly different short, but cool. Day lengths or daylight time zones are very varied. Land is mostly frozen (permafrost) year-round.

HUMIDITY: Level of Humidity level affects our sense of well being or comfort through the affective range of temperature (actual feel). Perspiration and sweating, the prime mechanisms to dissipate the body heat, depend to an extent on the rate of evaporation. Air with high percentage of humidity is also comparatively deficient in oxygen and may cause problems to people with TB or asthma. Low level of humidity removes the moisture from the nostril, reducing its filtering capacity to keep out the air borne pollutants.

Level of humidity is the amount of vapour held by air at a particular temperature. When there is a rise in temperature, the air expands to accommodate more vapour and inversely with a drop in the temperature, the air density increases can hold a lesser amount of vapour. A reduced level of humidity encourages higher rate of evaporation, which is accompanied by a drop in temperature. Nominally with reduction in temperature the capacity of air to hold the vapour decreases, and beyond certain temperature range the excess vapour  condenses as water droplets.

• Four distinct humidity-climate zones are recognised.  These are: 1  Hot-Dry (arid), 2 Cold-Dry (polar or glacial), 3 Hot-Wet (dense tropical forests -selva), 4 Moderate-warm to cool-humid (temperate).

In hot and humid climate high level of humidity does not allow adequate heat dissipation through evaporation of the perspiration. As a result body temperature increases and it has to resort to other methods of heat dissipation. In hot arid climates the low level of humidity causes rapid evaporation. Body cannot cope up with such rapid rates of moisture removal as it has limited amounts of water available within it. In cold arid climates the body has no excessive amounts of heat requiring dissipation through high perspiration. However, the low level of humidity removes even the moisture that helps the skin to remain soft and supple. In cold humid climates even minute perspiration does not evaporate readily, and in excessively cold climates it may cause a frost bite.


AIR MOVEMENT: Direction, Velocity and Movement patterns of air, are the three factors that govern the 1. Temperature profile (of human body, surrounding objects and atmosphere), 2. Quality of air (through dilution or change in contents of air) and 3. Rate of evaporation (humidity management).

Air movements occur in consonance with global patterns of air. The air velocity is caused by differential temperatures and pressures. At micro level air movements occur due to the macro changes in the surroundings, movements of people, objects (doors, vehicles etc.), opportunistic shapes and sizes (cones, wages), and air movement devices.

• High velocity air movements are known as Winds and affect large regions. Winds cause rapid change in level of humidity. It often causes discomfort  due to high pressure sensation over the skin.  Winds raise particulate matter in the air.

• Low to medium velocity air movements are known as Breeze and generally affect only local areas. Breeze causes immediate and very perceptible sensation of change. This can be avoided by appropriate screening and deflection of the breeze. The breeze does not raise the particulate matter, but also not allow the already air-borne-particulate matter to settle down.

• Very low level, almost imperceptible air movements are called Draught. Draught occur in enclosed spaces due to the temperature and air pressure thresholds near cracks and other leakage points. Draughts do not cause any sensation of pressure on the skin, however, cause convective heat exchange, evaporation and dilution of pollutants in the air. Draughts cause localized cooling or heating of sensitive organs of our body. Such sensation on feet is a common experience in trains, buses, sofas, undersides of office tables, etc. Children and aged people with deficient blood circulation and body temperature regulatory mechanisms are readily affected by such currents.

Air can become mobile due to fans or such air circulating devices. Below 0.15 m/s air velocities, even if all other parameters of comfort are satisfactory, most people complain of stuffiness. Above 1.5 m/s air velocities, the air movement becomes annoying, such as papers being blown out or dust stirred up. However, under very hot and humid conditions people may tolerate such a situation for the sake of some thermal relief. A turbulent air velocity is less comfortable than a laminar air velocity. Turbulent air movement achieves a better mix of air, whereas laminar helps in greater displacement of air mass. This is the reason why in hot arid climates small size opening is used to create turbulence or a viscous flow, and in hot humid climates body level stripe-opening generates a laminar flow to displace the humidity.  In hot and cold both types of climates people often close all the openings to reduce the air movements, and thereby control the convective heat gain or loss.


In next Blog-post I will discuss “Temperature related comfort parameters” such as siting, size, shape and form (openings and other architectural features)  of the building, time-space scheduling of tasks, lifestyle setting, food and clothing.
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