Mechanisms by which Human Body Loses or Gains Heat from Environment
Q1. With diagrams describe the ways that the human body gains or loses heat to its environment. Explain how these mechanisms work. (20 marks)
Prior of highlighting the environmental impact on the body of human Considerations should be taken by individuals about the heat producing capacity of human body in the absence of influential factors like temperature or environment. The food that is been intake by human beings are been transferred to metabolism that is known as energy. For the whole digestion process the body of human releases heat. Research done by scientists has indicated that 80% of energy gained by eating food has been released as heat and the remaining 20 % of heat is been consider as providing benefit to human bodies.
The metabolic processes taking place within the human bodies can be classified into two processes:
- Muscular Metabolism- Total energy that is been distributed throughout the body when the body is in active environment is called Muscular metabolism. In this phase the body deconstructed the food that has been consumed and digestion through energy takes place. In an environment that is active the level of heat increases as they are been overworking for producing adequate amount of energy compared to inactive environment where the bodies are relaxed as well as still.
- Basal Metabolism: Total energy distributed the body when the body is in relaxing as well as resting condition and inactive condition prevails for digestive system.
The human body might gain and lose heat. The gain or lose of the heat depends on environment. The understated processes describes how bodies are been affected by environment.
- Evaporation: The level of heat from the body of human can be lost due to respiration as well as perspiration. The process of respiration can be defined as breathing where dispersion of hot air takes place and cool air tries to provide relaxation to the body. The process of perspiration takes place when the water is been released by the body, which is also known as Sweat. Sweat helps in releasing all the heats that is been trapped within the active body. Evaporation can be defined as change in state of water from the state of liquid to gas. When humidity exists in high level in environment it limits evaporation from cooling down of the body and releasing off heat. As the level of evaporation decreases absence of water vapour takes place through lungs as well as skin that have an impact on breathing and level of humidity.
- Conduction: Depending on the interaction with variety of surfaces as well as objects the body can gain or loss heat. The variation of heat level is due to the variation of level of conductivity in certain materials. Heat transfer is minimal in the process of conduction due to the covering of human body with cloths and shoes. Excellent example of heat losing is when individuals are walking in bare feet on the surface of concrete or tiles and those surface having lower level of conductivity does not absorb any heat.
- Convection: Air currents motion and movement that is subjected for our bodies for generating heat. The body of human is been also subjected for persisting the cool air that is present outside for helping the bodies to cool. When our bodies’ reaches to a threshold limit the energy is lost and it cannot be recovered. This lost energy turned out to be inaccessible to human bodies.
High temperatures are been replaced by cool air in our bodies. The replacement is been initiated with trigger movement of winds or mechanical fans. This increases the process of convection within the human bodies. When temperatures are high the cooling by process of convection does not exists within the bodies and there is as increase in temperature for excessive heat.
- Radiation: In convection as well as conduction it is seen that transfer of heat has been taken place with the help of contact of hot and cold bodies. In radiation transfer of heat takes place without the contact of bodies. Heat is been discontinued with the help of infrared radiation in case of the process of radiation. The heat can be radiated from or to the bodies for either cooling it down or heating the bodies up. Cooling or heating depends upon the surroundings as well as surface of environments.
The perfect examples are exposure to fire or sun that increases the level of temperatures within the human bodies. On the other hand snow and cold winds helps in cooling the bodies by the process of heat losing.
Research shows the amount of heat that can be expelled by the above processes:
Radiation- 45%
Convection- 30%
Evaportation-25%
Q2. For an uninsulated brick veneer house in Sydney in winter describe the main paths of heat loss to the outside air. (Hint: Use a diagram showing a section through the building) (20 marks)
The major purpose that a building has is allowing the cool temperatures during the time of summer and having warm temperatures at the time of winters for the people living there. In the time of winter high heat loss is been faced by brick veneer home from the external walls in the location of Sydney.
The paths of heat loss are been mentioned below:
Ceiling (25 to 35%)- It is found out that the roofs or the ceilings contributed about 25 to 35% for discharging the heat outside. It is also been identified that the portion of ceiling is the susceptible section in the house for discharging the heat. Ceiling is the most vulnerable section as the heat losses has a tendency to rise upward which begins the process of convection in winter. Convection helps the group of molecules to move within the hot fluid that causes the sinking of denser material within the house and relatively less dense material raise in cold environment due to gravity.
Brief Comparison- During the summer season the dwellings roof has the capacity of drawing extra amount of heat ranging from 25 to 35 percent as been compared to other seasons. When it is been compared on the ground of other houses ceiling is exposed mostly to sun that results for the generation of great amount of solar heat. For stabilising the gaining and losing of heat insulation is been applied in between the joists of ceiling.
Paths of Heat Loss for Uninsulated Brick Veneer House in Sydney during Winter
Walls (15 % to 25 %) – 15 to 25 percent of hot air is been discharged from the veneer home walls. Therefore, it is been suggested to all the residents that insulation of home should be done appropriately. The home safeguard could be done by insulating it from the outside freezing weather. Inappropriate insulation of walls led to experiencing of a cold weather as the outside bricks become too cold and all the heat from the home goes outside due to bad insulation.
Brief Comparison: A rating of 15-25% is apparently applicable amid the period of summer where the blocks utilized for the structure draw the warmth. Insulation is incorporated inside the structural wall, 15 to 25 percent heat decrease flowing of heat will occur because of the ingestion utilizing this material.
Air Leakage (15 to 25 percent)- It is been found air spillages release almost 15-25% of warmth to the outside. All through the winter, the icy air goes through the block work and at last discovers the way by windows/entryways and any kind of gaps or potentially crevices inside home that gives a pathway to heat to get away from the house. Rooms that don’t have any immediate daylight will likewise “drain” sun based warming from the structure. They should work out of lightweight materials and can be warmed inconsistently. The surrender impact will happen when tall walls inside shaded zone assimilate up warmth and at last release out of building.
Brief Comparison- Summer is been famous for extraordinary temperatures that influence building foundation. The walls arranged inside homes assimilate the gain of heat rating of around 5-25% as opposed to the winter period of roughly 15-25% loss of heat. Inside the burning summer seasons our homes become defenceless to solid sunlight that enters homes as well as are ingest inside walls. This ingestion builds the temperature while lessening air spillage inside our homes.
Windows (10 to 20 percent) – It is been found that windows inside a home releases about 15-25% of warmth to outside air. Gaining or lossing of heat is crucial all through windows as a result of low thermal resistance that the sun enters. Convection permits loss of heat through window. Warmed air still can come inside cooled glass from window’s top end, regardless of the possibility that a curtain to be introduced. Once air gets cooled it winds up plainly thicker as well as increases. Cooled air is then substituted with more sultry air near the rooftop/roof and convection becomes evident.
Brief Comparison: A rating of 10-20% is apparently applicable amid the period of summer. A gyprock shaped or pre-assembled pelmet is utilized to anticipate warmed air achieving the window’s top end. Windows that are been shadowed with the help of pelmets is not only successful in winter additionally very viable at the time of summer. Despite the fact that warmth can in any case get to the home, air will constrained to its travel way and wont ready to go behind the window ornament and all through whatever remains of the room. Another method for reflecting warmth far from a window utilization of light-hued backings those are profoundly valuable. All curtains around windows should be closed to limit heat leaving the home during nights of cold winter season as well as to limit entering in the hot summer days.
Quick Calculation of Thermal Conductance of Cavity Wall
Floor (10 to 20 percent)- The floor inside the house is recognized to discharge around 10-20 percent of warmth to outside air. Un-protected floors are helpless to losing heat in winter, unequivocally when warm capacity is required.
Brief Comparison: A rating of 10-20% is apparently applicable in the period of summer where the floor utilized the heat to attract. Insulation should be applied in the floor structure. The warmth inflow increases inside the floor, shielding the floor from getting cold. Many deck frameworks incorporate conduction that aids safeguard the heat of the floor.
Q3. Do a quick calculation of the thermal conductance (U value) across a cavity wall consisting of:
- Outer skin 110mm brickwork (South facing, exposed aspect)
- 30mm cavity
- Inner skin of 90mm studwork
The necessary data can found in module 5. Compare this with the worked example of an insulated brick veneer wall in the worked example. Show your working.
Discuss whether or not cavity brickwork is a thermally efficient wall for housing in Australia. (20 marks)
- Brickwork’s thermal conductivity= 1.22 W/m.oC
- 10 mm plasterboard has thermal resistance= 0.06 m2.oC/W
U = 1/Rt
Brickwork
Thermal Conductivity = 1.22 W/m.oC(given in notes)
Resistivity – Kb = 1/1.22
= 0.09 m2.oC/W
According to Table 2: external conductance fo = 81.20 W/m2.oC;
internal conductance fi = 8.12 W/m2.oC
Ro = 1/fo
= 1/81.20
= 0.0123m2.oC/W
Internal Resistance
Ri = 1/fi
= 1/8.12
= 0.123m2.oC/W
Cavity Resistance
30mm Cavity (not provided on table 3)
30mm = 0.152m2.oC/W (Based on interpolate)
example of Worked interpolate;
20mm = 0.151
30mm = x
40mm = 0.153
0.153 – 0.151 = 0.002
0.153 – x
= 0.153 – x / 0.002
= 10/20
x = 0.153 – (0.002 x ½)
x = 0.153 – 0.001
x = 0.152.
10mm Plasterboard having Thermal Resistance of = 0.06 m2.oC/W
(Thermal Resistance provided within the notes)
Rp = 0.06 m2.oC/W
Insulation Resistance obtained from Diagram of Worked Example.
Rinsul = 2.5 m2.oC/W
Rt = 0.09 + 0.0123 + 0.123 + 0.152 + 0.06 + 2.5
=2.9373m2.oC/W
Therefore:
U = 1/Rtotal
U = 1/ 2.9373
U = 0.34m2.oC/W
Q4. Describe some strategies for passive solar cooling in hot dry climates. (Hint: Use diagrams) (20 marks)
- Concrete Flooring: Structure of the lab of a concrete floor should have a high level of reflectance (i.e. light-shaded) if heavyweight dividers as well as a low reflectance (i.e. dull shaded) if the dividers are lightweight. Having splendid shaded floors will divert sun based warmth towards high mass dividers where dividers will capture that warmth. On the chance that the pieces aren’t protected effectively the warmth will escape through the edge particularly amid winter. At whatever point warm should be put away the entire piece should be effectively protected around its limit.
- Masonry Walls: Any room that has the capacity for pulling in a considerable measure of direct daylight must have a huge wall surface region. The room should likewise comprise of large or high windows to build the infiltration of daylight into the room. Every high window are prescribed to have protected window shades to limit warm misfortune which happen during the evening. Rooms where absence of immediate daylight will deplete out the sun powered warming of the structure. Rooms having no daylight ought to fuse lightweight development highlights and ought to be warmed now and again.
- Earth Berming: Structures may be situated against earth bank. The dike lightens temperatures inside the building since ground temperature don’t vary much for yearly seasons
- Ground Coupled Plenums: Air plenum may be introduced below the structure to cool the building. Air goes inside plenum, then it is been cooled by collaboration with earth that is present underneath the structure. As the gathered air goes within building, building is get heated up. The warmth will then ascent and release through the windows present at highest point of structure.
Q5. Describe how a solar pergola can be designed to manage the entry of direct sunlight into a building in a location like Sydney. (20 marks)
It is noticed that the establishment of pergolas has been the best approach to manage courses of sunray coming into the home. The safe house/shading provided by the pergola help with enhancing interior temperature of building. Introducing a pergola on north side of the home in summer limits the daylight entry through the windows as well as walls. For the most part the tallness of pergolas are expanded amid the winter to give access to the daylight from underneath the pergola since in winter, sun is position much lower in the sky.
Introducing extra pergola frill, for example, angle blades helps in diminishing the height of summer daylight while as yet giving the low winter daylight to enter the sharp edges as well as on the building. Prior to introducing any blade angles they should have specially craft to guarantee the width and thicknesses are made accurately to give the proper shading impact. The angle blades should cover roughly 25% for working accurately.
There is an assortment of pergolas frameworks that can be utilized to help with giving climate assurance and splendid shading, one of them is sunlight based fueled pergolas. Despite the fact that, it must be noticed that in spite the sun oriented controlled pergolas are successful in decreasing daylight and vitality inside the home, the pergolas are not translucent and in this way shut out the daylight from entering inside the pergola even in winter season. This is unproductive in permitting daylight within the house.
References
- https://www.yourhome.gov.au/passive-design/thermal-mass.
- aprbuildingservices.com.au
- https://www.yourhome.gov.au/passive-design/insulation
- insulation.com.au
- https://renew.org.au.
- environmentdesignguide.com.au
- energyrating.gov.au
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