principles of thermal design - weebly
TRANSCRIPT
Principles of
Thermal
Design
CHAPTER 3ANJANAA DEVI , LAKSHYA WADHWANI , HEENA MEVADA , KASHYAP MEWADA , SHIVANI BHANDHARI ,
DEVANSHI SARAYIA
Heat Flow
Heat energy tends to flow from high temperature
to lower temperature zones by the following
ways:-
Conduction
Convection
Radiation
Conduction
When two bodies are in direct contact,heat flows
through molecular movement.
The rate of the molecular movement in a body is
the thermal conductivity of the material.
Factors Of Resistance
Density of the material.
Surface conductance – In addition to the resistance of a body to the flow of heat , a resistance will be offered by its surface.
Air – to – Air resistance is the sum of the body’s resistance and the surface resistance.
Transmittance is the reciprocal of air – to – air resistance.
Cavity Resistance.
Sol-air Temperature
An imaginary temperature of a layer of air
adjacent to the surface of the material.
It is used to calculate cooling load of the building and determine the total heat gain through the
exterior surfaces.
Solar Gain Factor
It is the increase in temperature in a structure due
to solar radiation.
It is defined as the heat flow rate through the construction due to solar radiation expressed as a
fraction of the incident solar radiation.
Thermal Balance Equation
𝑄𝑖 + 𝑄𝑠 ± 𝑄𝑐 ± 𝑄𝑣 ± 𝑄𝑚 − 𝑄𝑒 = 0
If the sum of this equation is less than zero,the
building will be COOLING.
If it is more than zero,the TEMPERATURE IN THE
BUILDING WILL INCREASE.
Applications
Heat loss calculation
Heat gain calculation
Cooling by air
Heating by air
Transmittance
Thermal Gradient – Calculating the temperature
at any point within the wall.
Condensation
Thermal design
Assumption of steady
state
The equation and calculation methods are valid
only if both outdoor and indoor temperatures are
constant.
This does not occur in nature.
Hence periodic calculation is graphically
represented – Timelag and Decrement factor.