1. FUNDAMENTAL OF BUILDING PHYSICS
SOURCE OF HEAT GAIN IN BUILDING

2. HEAT GAIN IN BUILDING
Heat; is a form of energy, appearing as molecular motion in substances or as radiation in space. Measured in Joule, J
Temperature; considered as presence of heat in a substance.
Thermodynamics; the science of the flow of heat.
The first law of thermodynamics/energy is the principle of conservation of energy. Energy cannot be created or destroyed, only changed from one form to another.
The second law of thermodynamics, (Clausius 1850) states that heat (or energy), transfer can take place in one direction only. i.e. from hotter to a cooler body.
Heat transferred from hot to cold in 3 basic ways:
Conduction
Convection
radiation
FUNDAMENTAL OF BUILDING PHYSICS

3. HEAT GAIN IN BUILDING 50° C 30° C Heat transfer by conduction 45° C
Heat transfer by convection
35° C
35° C
50° C
sun
20,000° C
Radiation through vacuum
Heat transfer by radiation
20° C
earth
FUNDAMENTAL OF BUILDING PHYSICS : Method of Heat Transfer

4. HEAT GAIN IN BUILDING
FUNDAMENTAL OF BUILDING PHYSICS: Sources of Heat Gain

5. HEAT GAIN IN BUILDING
Qi= internal heat gain, heat from human bodies, lamps, appliances
Qs=solar heat gain
Qc=conduction heat gain
Qv=ventilation heat gain
Qe=evaporative cooling
Qm=mechanical cooling
FUNDAMENTAL OF BUILDING PHYSICS: Sources of Heat Gain

6. HEAT GAIN IN BUILDING Why we study Heat? To achieve THERMAL COMFORT.
Thermal balance exists when the sum of all heat flow is zero i.e.;
When this sum is greater than 0(+), temperature indoor will heat up. When less than 0(-), temperature indoor will cooling down.
FUNDAMENTAL OF BUILDING PHYSICS: Sources of Heat Gain

7. HEAT GAIN IN BUILDING
Result of the differing properties of heat radiation when it is generated by bodies at different temperature.
High temperature (sun) emits radiation of short wavelength pass through glass.
Heat absorbed (inside building) by objects, which then re-radiate the heat.
Object inside the green house (lower temperature) radiated heat (longer wavelengths) not able to penetrate the glass.
Re-radiate heat trapped and rise up the indoor temperature.
e.g: entering the closed car that has been sitting under the sun.
FUNDAMENTAL OF BUILDING PHYSICS: The Greenhouse Effect

8. HEAT GAIN IN BUILDING
Building envelope/enclosure/shell is the part of the building which physically separates the exterior environment from the interior environment/s.
Prevents air, moisture, heat/cool from freely flow in/out from a building.
Three parts of building envelope: interior, exterior and the system.
FUNDAMENTAL OF BUILDING PHYSICS: Building Envelope

9. HEAT GAIN IN BUILDING
Building envelope-critical component of any building (protects building occupants and regulate indoor environment).
Controls the flow energy between interior and exterior.
High performance building; envelope must be able control the heat gain in summer and heat loss in winter.
Consists of:
Roof,
Floor slabs
Walls
Windows
Doors.
Optimal design of the building fabric provide significant reductions in heating and cooling loads-which in turn allowing downsizing of mechanical equipment
Good design; extra cost justified by savings (building operations)
FUNDAMENTAL OF BUILDING PHYSICS: Building Envelope

10. Art School, Nanyang Technological University, Singapore
The glass facade provides a high performance building envelope that reduces solar gain and heat load while allowing the benefits of natural views and daylight into creative spaces. The glass walls provide a visual exchange between indoors and the surrounding landscape or interior plaza as fluid spaces. The diffused natural daylight is abundant throughout studios and classrooms, thus making them productive spaces for young creators.
The curving green roofs distinguish the building from among the other structures on campus but the line between landscape and building is blurred. The roofs serve as informal gathering spaces. Besides that purpose, the roofs serve as open space, insulate the building, cool the surrounding air and harvest rainwater for the landscape irrigation.
This amazing design is surely going to be used more widely because it provides better and healthier surrounding. In this particular example it offers a brand new experience in many perspectives, fulfilling the intent that a school for art should inspire creativity, while solving the green surface deficiency.

11. HEAT GAIN IN BUILDING
To control the three (3) components of heat transmittance through building fabric:
Conduction of heat through building fabric
Convection via air movement
Radiant transmission, (through glasses and other building fabric).
Good insulator reduce heat flow.
Consideration in determining insulation solutions:
Effect on building design
Heavyweight and lightweight construction balance.
Performance in use and longevity
Buildability and the risk
Sustainability implications
FUNDAMENTAL OF BUILDING PHYSICS: Thermal Insulation

12. HEAT GAIN IN BUILDING Thermal Conductivity (λ value or k value)
the measure of the rate at which heat is conducted through a particular material under specified conditions
property of a material that indicates its ability to conduct heat.
Measured as the heat flow in watts across a thickness of 1 m of material for a temperature difference of 1 degree K and a surface area of 1 m²
Unit : W/m K
Thermal resistivity (r)= 1/λ m.K/W
r = thermal resistivity (moC/W, hr ft2 oF/Btu)
λ= thermal conductivity (W/moC, Btu in/hr ft2 oF)
FUNDAMENTAL OF BUILDING PHYSICS: Thermal Conductivity

13. HEAT GAIN IN BUILDING
Thermal conductivity for a material calculated using:
insulation
Measured heat flow
Heat supply
Sample material
insulation
- Coefficient of thermal conductivity from the sample material (W/m K)
- rate of heat flow between the faces (J/s=W)
- Cross sectional area of the sample (m2)
- Temperature difference between the faces (°C or °K)
- Distance between the faces (m)
FUNDAMENTAL OF BUILDING PHYSICS: Thermal Conductivity

14. FUNDAMENTAL OF BUILDING PHYSICS: Thermal Conductivity

15. HEAT GAIN IN BUILDING Happens if there exist a temperature gradient.
Conductive heat flow occurs in direction of the decreasing temperature (higher temperature=higher molecule energy)
Fourier’s Law stated that CHT as:
- Heat transferred per unit time (W, Btu/hr)
- Thermal conductivity of the material (W/m.K or W/m °C, Btu/(hr °F ft2/ft))
- Heat transfer area (m2, ft2)
- Temperature difference across the material (K or °C, °F)
- Material thickness (m,ft)
FUNDAMENTAL OF BUILDING PHYSICS: Conductive Heat Transfer

16. HEAT GAIN IN BUILDING Example;
A plane wall constructed of solid with thermal conductivity 70 W/m °C, thickness 50mm and with surface area 1m by 1m, temperature 150 °C on one side and 80 °C on the other.
Conductive heat transfer can be calculated as:
q = (70 W/m°C)(1m)(1m)((150°C)- (80°C))/(0.05)
= 98,000 W
= 98 kW
FUNDAMENTAL OF BUILDING PHYSICS: Conductive Heat Transfer

17. HEAT GAIN IN BUILDING
or is the relative power of material surface to emit heat by radiation.
Rough black surfaces absorb most heat and emit least heat.
Color of most building materials has an important effect on the heat absorbed by the building from the sun.
Surface coefficients for building materials
Surface Emissivity Absorptivity
Aluminum
Asphalt
Brick-dark
Brick-black
Paint
Slate
FUNDAMENTAL OF BUILDING PHYSICS: Emissivity and absorption

18. HEAT GAIN IN BUILDING
Thermal transmittance (U-value) and thermal resistance (R-value) indicate the design thermal performance of a building material or assembly.
R-value; resistance of heat flow through a building material (m2 K/W)
bigger the value, better insulation (greater resistance).
Material Resistance
Thermal resistance of each layer of material depends on the rate at which the material conduct heat and thickness of the material;
Alternatively;
-thermal resistance of that component (mK/W)
-thickness of the material (m)
-thermal conductivity of the material (W/mK)
-resistivity of material = (mK/W)
1/λ
FUNDAMENTAL OF BUILDING PHYSICS: Thermal Transmittance and Resistance

19. HEAT GAIN IN BUILDING Example
Find the thermal resistance of a 100mm thickness of lightweight concrete block.
Solution:
value for from table given = 0.19W/m K
for the block = 0.1m
Therefore;
FUNDAMENTAL OF BUILDING PHYSICS: Thermal Transmittance and Resistance

20. HEAT GAIN IN BUILDING Airspace Resistances Surface Resistances
Depends on conduction, convection and radiation of the surface.
Factors affect surface resistance are:
Direction of heat flow; upward and downward
Climatic affects; sheltered or exposed
Surface properties; high or low emmissivity
Airspace Resistances
Depends on the nature of any conduction, convection and radiation within the cavity.
Factors affect airspace resistances:
Thickness or airspace
Flow of air in airspace; ventilated or unventilated
Lining of airspace; normal surfaces of reflective surfaces of low emmissivity.
FUNDAMENTAL OF BUILDING PHYSICS: Thermal Transmittance and Resistance

21. HEAT GAIN IN BUILDING
Total thermal Resistance (RT) is the sum of thermal resistances of all the components of the structure elements RT
Example of brickwall resistances;
RT= Rsi +R1+R2+Rso
FUNDAMENTAL OF BUILDING PHYSICS: Thermal Transmittance and Resistance

22. HEAT GAIN IN BUILDING Thermal Mass
Materials that have the capacity to storage thermal energy for extended periods.
Absorb daytime heat gains (reducing cooling load) and release heat during night (reduce heat load).
Lower initial temperature than the surrounding air (act as heat sink).
Beneficial for country which had a big different between day and night outdoor temperature. (e.g. UAE).
FUNDAMENTAL OF BUILDING PHYSICS: Thermal Transmittance and Resistance

23. HEAT GAIN IN BUILDING
U-value of a construction is defined as the quantity of heat that flows through a unit area of a building section under steady-state conditions.
Unit: W/m2 K
-Total thermal resistance.
FUNDAMENTAL OF BUILDING PHYSICS: Thermal Transmittance and Resistance

24. HEAT GAIN IN BUILDING Average U-Values
When a wall is composed of different construction materials with different U-value.
Overall insulation of the wall depends upon the relative areas of constructions;
FUNDAMENTAL OF BUILDING PHYSICS: Thermal Transmittance and Resistance

28. HEAT GAIN IN BUILDING
EE means use less energy for heating, cooling, lighting and equipments.
The building envelope play an important roles
Typical Malaysian office building consume
250kWh/m2/year of energy.
Building Energy Index (BEI);
i) PTM GEO; 50
ii) Kettha LEO; 114
iii) Typical KL; 300
iv) MS1525:2001; 14
FUNDAMENTAL OF BUILDING PHYSICS: Energy Efficient in Buildings

29. HEAT GAIN IN BUILDING Typical house Office building
FUNDAMENTAL OF BUILDING PHYSICS: Building Energy Index

30. FUNDAMENTAL OF BUILDING PHYSICS: Energy Efficient in Buildings

31. FUNDAMENTAL OF BUILDING PHYSICS: Energy Efficient in Buildings