Comfort Zone
Content
Comfort Zone
GOAL:
To understand how air temperature, humidity, mean radiant temperature (MRT), wind and sunshine affect human comfort.
OBJECTIVE:
You will be able to:
1. Describe ways that the human body reacts while seeking its comfort zone. 2. Explain how air temperature, mean radiant temperature, humidity,
wind, and sun affect human comfort.
3. Use the comfort zone chart correctly.
LESSON/INFORMATION:
The weather is always changing. As winter approaches, the
rabbits shed old fur and grow a new heavier pelt, birds fly south,
and bears hibernate. When trying to maintain a body
temperature close to 98.6°F, humans have few natural controls
with which to adapt to these changes in climate.
The human body has three mechanisms to maintain this narrow
temperature range. The first is heat generated inside the body,
the second is by gaining heat from surroundings, and the third is
by losing heat to the surroundings. The body automatically
makes constant changes to control these three mechanisms and
regulate body temperature.
Body Heat
Heat is continuously produced by the body due to metabolism, or the processes of food conversion and tissue building. Additional heat is produced by muscular activity,
which varies from 70 watts while sleeping to 1100 watts for maximum heavy manual
work. Of all the heat produced, 20% is utilised, and 80% must be dissipated, in order to maintain deep body temperature at 37°C. Any heat gained from the environment
and from solar radiation must also be dissipated. The body can lose heat by
convection, radiation and evaporation, and to a lesser extent by conduction. Convection is produced when heat is transferred from the body to the air adjacent to
the skin or clothing, which rises and is replaced by cooler air. Radiant heat loss
depends on the temperature of the body surface and the temperature of opposing surfaces. Evaporative heat loss depends on the rate of evaporation which depends on
the humidity of the air.
The following are a few of the ways the body responds in order to stay within the comfort zone:
Increased muscle activity and a higher metabolic rate increases internal heat production.
Sweating -
Blood Flow -
Reduced flow to the hands, feet and skin surface in the winter to
reduce heat loss to surroundings and an increase in blood flow to
these areas in the summer to encourage heat loss.
Comfort
Human beings can tolerate a fairly wide range of climatic
conditions, but comfort in the climatic sense involves more than
just avoiding the extremes of freezing to death and dying of heat exhaustion. Comfort depends on more than temperature; air temperature, humidity, radiation and air movement all produce thermal effects. Most climatic comfort indicators are objective, i.e. they can be measured, and acceptable ranges established quantitatively.
Factors Affecting Human Comfort Include:
Air temperature is the most significant ambient factor which
affects our internal temperature and our level of comfort. But, it is not the only factor involved; air speed, humidity and mean radiant temperature must also be considered. Each of these four factors has a direct influence on the rate at which the body loses or gains heat to or from the surroundings.
Air Temperature -
This affects temperature difference between the body and the surroundings, consequently affecting the rate of heat loss or gain by convection. Air Speed This affects the rate at which the body loses heat by convection. The chill factor is one way to quantify the effects of air speed on heat loss. An air temperature of 35°F and a wind speed of 20 miles/hour combine to give a wind chill temperature of 11.2°F. This means that a body exposed to 35°F air and 20 mile/hour wind loses heat at the same rate as a body exposed to 11.2°F and no wind. Air speed is also very important during summer when the body is trying to lose heat to maintain comfort.
Mean Radiant Temperature (MRT) -
MRT is the average of the surface temperature of the surroundings
with which the body can exchange heat by radiant transfer. Radiant
heat transfer to and from the body is quite apparent when sitting
near a fireplace (high MRT) or large cold window area (low MRT).
Humidity -
Affects the rate at which the body loses heat by evaporation. During
hot weather, high humidity increases discomfort by making it more
difficult to evaporate perspiration into the air.
The diagram shows the
area of warmth and
humidity
human
which
body
the
would
classify as comfortable.
The higher the relative
humidity the lower the room temperature must be.
An easy way of describing the effect of air temperature, humidity, MRT, wind and sunshine is the
Bioclimatic Chart below.
The comfort zone can be pushed up by the presence of air movement, but lowered by higher levels of radiation. The results were obtained from a study of men in sedentary occupations, wearing clothing (suit, cotton underwear) in a warm climate.
The air temperature is plotted on the vertical axis and relative humidity
on the horizontal axis. The shaded area near the center of the graph shows the combination of temperature and humidity which most
humans would find comfortable during the summer if they are sitting in
the shade. The dotted area shows the comfort zone for the winter. It is interesting to see that the human body can actually adjust somewhat to different seasons.
The climatic elements around the comfort zone are shown by means of
curves which indicate the nature of corrective measures necessary to restore the feeling of comfort at any point outside the comfort zone. For any point of known dry-bulb temperature and relative humidity which
falls within the boundaries of the comfort zone, no corrective measures
are needed.
For example, at dry-bulb temperature, 73°F, relative humidity of 50%,
no corrective measures are needed because this point falls within the comfort zone.
At dry-bulb temperature, 78°F, relative humidity of 70%, it would
require a wind speed of about 250 FPM to provide comfort.
At dry-bulb temperature of 50°F, relative humidity of 55%, it would
require 250 Btu/hr of sunshine to provide comfort.
Building Skin Parameters Affecting Thermal Heat Gains
Introduction · The building skin is the external barrier which protects the
occupants from the undesirable climatic conditions; the need of suitable shelter was a motive that made man search for suitable strategies concerning the design of that barrier. Many architectural features of the building skin affect its thermal performance with respect to solar radiation, and taking advantage of theses features helps us to shift the internal conditions if the building towards the human comfort zone.
The building skin parameters affecting solar heat gains are: Building material. Building glazing. Shading strategies. Building compactness. Building color. Building orientation.
The amount of heat that flows through a building's skin due to temperature difference between the outside and the inside is a function of magnitude of that difference, in addition to the resistance to heat flow by the skin materials. · Since heat flows from hot to cold, if the inside of the building is warmer than the outside, heat will flow through the building skin outwards and vice versa. · Accordingly, the kind of material used in the external building's skin represents a vital factor in securing a suitable thermal environment inside the building. · This part will study the performance of skin materials with respect to solar radiation and temperature difference between the outside and the inside.
Definitions:
Thermal Resistance (R-value):
It is a property of the building's skin material giving the number of hours needed for one Btu to flow through one square foot of that skin, given a temperature difference of 1º F, it has the units of (ft, ºF, hr / Btu) or in metric units, ( m2 ºk/W ). Thermal Conductance (U-value):
Building Skin Performance with Respect to Heat Flow:
There are three methods of heat flow: · By Conduction. · By Convection. · By Radiation.
Temperature Difference and Modes of Heat Flow:
Architectural Examples Making Use of Building Materials
Building Material Efficiency with respect to Solar Radiation
The quantitative thermal performance of the building
materials depends upon its U-value, where table illustrates different U values for some masonry and manufactured building materials.
Thanks…
GOAL:
To understand how air temperature, humidity, mean radiant temperature (MRT), wind and sunshine affect human comfort.
OBJECTIVE:
You will be able to:
1. Describe ways that the human body reacts while seeking its comfort zone. 2. Explain how air temperature, mean radiant temperature, humidity,
wind, and sun affect human comfort.
3. Use the comfort zone chart correctly.
LESSON/INFORMATION:
The weather is always changing. As winter approaches, the
rabbits shed old fur and grow a new heavier pelt, birds fly south,
and bears hibernate. When trying to maintain a body
temperature close to 98.6°F, humans have few natural controls
with which to adapt to these changes in climate.
The human body has three mechanisms to maintain this narrow
temperature range. The first is heat generated inside the body,
the second is by gaining heat from surroundings, and the third is
by losing heat to the surroundings. The body automatically
makes constant changes to control these three mechanisms and
regulate body temperature.
Body Heat
Heat is continuously produced by the body due to metabolism, or the processes of food conversion and tissue building. Additional heat is produced by muscular activity,
which varies from 70 watts while sleeping to 1100 watts for maximum heavy manual
work. Of all the heat produced, 20% is utilised, and 80% must be dissipated, in order to maintain deep body temperature at 37°C. Any heat gained from the environment
and from solar radiation must also be dissipated. The body can lose heat by
convection, radiation and evaporation, and to a lesser extent by conduction. Convection is produced when heat is transferred from the body to the air adjacent to
the skin or clothing, which rises and is replaced by cooler air. Radiant heat loss
depends on the temperature of the body surface and the temperature of opposing surfaces. Evaporative heat loss depends on the rate of evaporation which depends on
the humidity of the air.
The following are a few of the ways the body responds in order to stay within the comfort zone:
Increased muscle activity and a higher metabolic rate increases internal heat production.
Sweating -
Blood Flow -
Reduced flow to the hands, feet and skin surface in the winter to
reduce heat loss to surroundings and an increase in blood flow to
these areas in the summer to encourage heat loss.
Comfort
Human beings can tolerate a fairly wide range of climatic
conditions, but comfort in the climatic sense involves more than
just avoiding the extremes of freezing to death and dying of heat exhaustion. Comfort depends on more than temperature; air temperature, humidity, radiation and air movement all produce thermal effects. Most climatic comfort indicators are objective, i.e. they can be measured, and acceptable ranges established quantitatively.
Factors Affecting Human Comfort Include:
Air temperature is the most significant ambient factor which
affects our internal temperature and our level of comfort. But, it is not the only factor involved; air speed, humidity and mean radiant temperature must also be considered. Each of these four factors has a direct influence on the rate at which the body loses or gains heat to or from the surroundings.
Air Temperature -
This affects temperature difference between the body and the surroundings, consequently affecting the rate of heat loss or gain by convection. Air Speed This affects the rate at which the body loses heat by convection. The chill factor is one way to quantify the effects of air speed on heat loss. An air temperature of 35°F and a wind speed of 20 miles/hour combine to give a wind chill temperature of 11.2°F. This means that a body exposed to 35°F air and 20 mile/hour wind loses heat at the same rate as a body exposed to 11.2°F and no wind. Air speed is also very important during summer when the body is trying to lose heat to maintain comfort.
Mean Radiant Temperature (MRT) -
MRT is the average of the surface temperature of the surroundings
with which the body can exchange heat by radiant transfer. Radiant
heat transfer to and from the body is quite apparent when sitting
near a fireplace (high MRT) or large cold window area (low MRT).
Humidity -
Affects the rate at which the body loses heat by evaporation. During
hot weather, high humidity increases discomfort by making it more
difficult to evaporate perspiration into the air.
The diagram shows the
area of warmth and
humidity
human
which
body
the
would
classify as comfortable.
The higher the relative
humidity the lower the room temperature must be.
An easy way of describing the effect of air temperature, humidity, MRT, wind and sunshine is the
Bioclimatic Chart below.
The comfort zone can be pushed up by the presence of air movement, but lowered by higher levels of radiation. The results were obtained from a study of men in sedentary occupations, wearing clothing (suit, cotton underwear) in a warm climate.
The air temperature is plotted on the vertical axis and relative humidity
on the horizontal axis. The shaded area near the center of the graph shows the combination of temperature and humidity which most
humans would find comfortable during the summer if they are sitting in
the shade. The dotted area shows the comfort zone for the winter. It is interesting to see that the human body can actually adjust somewhat to different seasons.
The climatic elements around the comfort zone are shown by means of
curves which indicate the nature of corrective measures necessary to restore the feeling of comfort at any point outside the comfort zone. For any point of known dry-bulb temperature and relative humidity which
falls within the boundaries of the comfort zone, no corrective measures
are needed.
For example, at dry-bulb temperature, 73°F, relative humidity of 50%,
no corrective measures are needed because this point falls within the comfort zone.
At dry-bulb temperature, 78°F, relative humidity of 70%, it would
require a wind speed of about 250 FPM to provide comfort.
At dry-bulb temperature of 50°F, relative humidity of 55%, it would
require 250 Btu/hr of sunshine to provide comfort.
Building Skin Parameters Affecting Thermal Heat Gains
Introduction · The building skin is the external barrier which protects the
occupants from the undesirable climatic conditions; the need of suitable shelter was a motive that made man search for suitable strategies concerning the design of that barrier. Many architectural features of the building skin affect its thermal performance with respect to solar radiation, and taking advantage of theses features helps us to shift the internal conditions if the building towards the human comfort zone.
The building skin parameters affecting solar heat gains are: Building material. Building glazing. Shading strategies. Building compactness. Building color. Building orientation.
The amount of heat that flows through a building's skin due to temperature difference between the outside and the inside is a function of magnitude of that difference, in addition to the resistance to heat flow by the skin materials. · Since heat flows from hot to cold, if the inside of the building is warmer than the outside, heat will flow through the building skin outwards and vice versa. · Accordingly, the kind of material used in the external building's skin represents a vital factor in securing a suitable thermal environment inside the building. · This part will study the performance of skin materials with respect to solar radiation and temperature difference between the outside and the inside.
Definitions:
Thermal Resistance (R-value):
It is a property of the building's skin material giving the number of hours needed for one Btu to flow through one square foot of that skin, given a temperature difference of 1º F, it has the units of (ft, ºF, hr / Btu) or in metric units, ( m2 ºk/W ). Thermal Conductance (U-value):
Building Skin Performance with Respect to Heat Flow:
There are three methods of heat flow: · By Conduction. · By Convection. · By Radiation.
Temperature Difference and Modes of Heat Flow:
Architectural Examples Making Use of Building Materials
Building Material Efficiency with respect to Solar Radiation
The quantitative thermal performance of the building
materials depends upon its U-value, where table illustrates different U values for some masonry and manufactured building materials.
Thanks…
